Iron oxide-based multifunctional nanoparticulate systems for biomedical applications: a patent review (2008 - present).

Expert Opin. Ther. Patents Downloaded from informahealthcare.com by University of Ulster at Jordanstown on 03/31/15 For personal use only.

Review

Iron oxide-based multifunctional nanoparticulate systems for biomedical applications: a patent review (2008 -- present)

1.

Introduction

2.

Properties

3.

Synthesis methodologies

Mazen M El-Hammadi & Jose L Arias†

4.

Stabilization/surface coating

†

5.

Biomedical applications

6.

Conclusion

7.

Expert opinion

University of Granada, Department of Pharmacy and Pharmaceutical Technology, Faculty of Pharmacy, Granada, Spain

Introduction: Iron oxide nanoparticles (IO NPs) exhibit remarkable properties, including inherent magnetism, biocompatibility, high surface to volume ratio, and versatility of engineering, making them ideal candidates for a variety of clinical applications. Areas covered: The review provides an in-depth discussion on recent patents and developments related to IO NPs in Biomedicine from the last 7 years. It covers innovations in the chemical synthesis, surface coating and functionalization, and biomedical applications, including MRI and multimodal imaging, molecular imaging, cell labeling, drug delivery, hyperthermia, hyperphosphatemia, and antibacterial activity. A brief outline of the important properties of IO NPs is also presented. Expert opinion: The main focus of current research is the development of new approaches to generate high-quality IO NPs with optimal properties in terms of particle geometry, crystal structure, surface functionalities, stability, and magnetization. Among chemical synthesis methods, thermal decomposition and hydrothermal synthetics processes allow fine control of the particle properties. Plenty of coating materials have been successfully used as shells for these NPs to provide colloidal stability, even enabling the formulation of nanotheranostics for simultaneous disease diagnosis and therapy. However, long-term toxicity and pharmacokinetic studies are necessary before magnetic nanosystems can be approved for clinical use. Keywords: drug delivery, hyperthermia, iron oxide nanoparticles, magnetic properties, MRI, multifunctional nanoparticles, multimodal imaging, surface coating, theranosis Expert Opin. Ther. Patents [Early Online]

1.

Introduction

Iron oxide nanoparticles (IO NPs) have recently emerged as one of the top candidates for the engineering of diagnostic and therapeutic nanoplatforms. Because of their low toxicity, biocompatibility, magnetic properties, and ease of synthesis, IO NPs offer attractive opportunities in the biomedical field. IO-based NPs, mostly magnetite (Fe3O4) and maghemite (g-Fe2O3), can serve as drug carriers, enable drug targeting using an external magnetic field, facilitate non-invasive MRI by functioning as contrast agents, and provide antitumor activity through inducing magnetic fluid hyperthermia (MFH) [1-4]. Thanks to recent advances in nanotechnology, engineering of multifunctional magnetic IO NPs that exhibit several features simultaneously is currently achievable. In addition to their intrinsic ability for MRI contrast enhancement, IO particles can be equipped with imaging agents (contrast agents, dyes, probes, labels) that enable disease diagnosis as well as real-time monitoring of therapeutic response in 10.1517/13543776.2015.1028358 © 2015 Informa UK, Ltd. ISSN 1354-3776, e-ISSN 1744-7674 All rights reserved: reproduction in whole or in part not permitted

1

M. M. El-Hammadi & J. L. Arias

A total of 37 patents granted world-wide were considered in this review and are listed in Table 1.

Article highlights. .

.


.

.

Preclinical and clinical reports have demonstrated the potential use of iron oxide (IO) nanoplatforms in biomedicine. Recent patents and developments related to IO nanoparticle (NPs) in the biomedical field relies on advanced synthesis methodologies that can guarantee the fine control of the biocompatibility, pharmacokinetics, biodistribution, in vivo therapeutic activity, and toxicity. Efficient functionalization of IO NPs including biocompatible organic/non-organic shells, specific ligands, and/or stimuli-sensitive materials can bring about colloidal stability and a controlled/optimized behavior in vitro and in vivo. Next step in biomedicine is clearly related to the complete introduction of IO nanoplatforms in theranosis.

This box summarizes key points contained in the article.

theranostic systems, which combine imaging agents and therapeutic compounds (i.e., drugs and/or genes), using a wide range of imaging modalities, such as optical and fluorescence imaging [2-5]. Furthermore, the incorporation of a specific drug release mechanism (e.g., pH responsive drug release) and surface functionalization with a targeting ligand can highly enhance the specificity of the particles and facilitate their specific uptake by target cells, thus minimizing the total needed drug dose and associated adverse effects [3,4,6,7]. Despite high biocompatibility and relatively low toxicity of IO NPs, naked IO nanocrystals can stimulate reactive oxygen species (ROS) generation thus resulting in increased cytotoxicity [3,5,6,8,9]. Consequently, biocompatible organic or inorganic materials are used to form a protecting shell that coat the IO nanocrystal core. Chemical composition of the coating layers can determine the fate of coated particles in the body and it is selected based on the core type and the intended application(s). In addition to the nature of the surface coating, biological fate and in vivo functions of the particles are influenced by their magnetization, diameter and particle size distribution. In general, high magnetization values, a small particle size (preferably < 100 nm), and a monodisperse particle size are desirable. In this review, we describe recent patents published between 2008 and present in relation to fabrication, surface modification, and biomedical applications of IO NPs. We also summarize the main properties of the magnetic NPs. The websites of the World Intellectual Property Organization (WIPO), the European Patent Office (EPO), and Google patent search were used to carry out the search of patents published since 2008 on the subject. The search term was ‘IO NP’. Duplicates found in the search were removed and only patents relevant to the biomedical field were considered. 2

2.

Properties

Iron is one of the most abundant metals in living organisms and an essential element for a variety of biological processes, for example, hemoglobin-mediated oxygen transport and cellular respiration. IO NPs, however, are nanocrystals with a diameter ranging between 1 and 100 nm that exist in nature in a number of forms, among which Fe3O4 and its oxidized form g-Fe2O3 are the most common [5]. Being non-toxic, biologically well-tolerated nanostructures, IO NPs are among the few nanomaterials that can be injected safely into the body and are normally metabolized and eliminated from the human body through the natural iron metabolic pathways [10,11]. In both Fe3O4 and g-Fe2O3, the oxygen ions form a cubic close-packed crystal system. Fe3O4 has an inverse spinel structure with Fe3+ ions distributed randomly between octahedral and tetrahedral sites, and Fe2+ ions occupying octahedral sites [3,12]. g-Fe2O3 has a similar structure but differs from Fe3O4 by the presence of cation vacancies in the octahedral sites and in that all or most of the iron is in the trivalent state (Fe3+); two-thirds of the sites are occupied by Fe3+ ions arranged regularly, with two occupied sites being followed by one vacant site [3,12]. Iron atoms on the surface of IO have the ability to coordinate with molecules that donate a lone pair of electrons, thus functioning as Lewis acids. In aqueous media and owing to coordination with water, IO is in the form of hydroxyl groups [3]. Because the isoelectric point for IO NPs is around pH 6.8, the surface of the NPs will be positive or negative depending on the pH of the solution. Thus, whereas protonation of the particle surface occurs below the isoelectric point leading to the formation of Fe--OH2+ moieties, deprotonation takes place above the isoelectric point and gives rise to Fe--O- surface moieties [3]. Consequently, the pH-dependant surface charge can influence the attachment of coating materials on the surface of the particle. IO NPs with a diameter of < 100 nm exhibit superparamagnetic characteristics, and therefore they are known as superparamagnetic IO NPs [2-4]. Due to these properties, the particles become easily magnetized up to their saturation magnetization upon exposure to an external magnetic field and un-magnetized once the field is removed. Using this phenomenon, IO NPs attain the ability to travel to the site of interest in the body under the externally applied magnetic field and are inactivated when the field is turned off. Another interesting characteristic of IO NPs is their significant ability to produce heat when subjected to an alternating magnetic field (AMF). During the demagnetization process, energy is dissipated in the environment as thermal energy. The heating power (specific loss power) is used in the treatment of cancer, through MFH [2,3].

Expert Opin. Ther. Patents (2015) 25(6)

IO-based multifunctional nanoparticulate systems for biomedical applications

Table 1. Patents involving the synthesis and use of IO NPs for biomedical applications.


Disclosed innovation

Preparation method

Advantages

Preparation method of IO hollow nanocapsules

Wrap-bake-peel process

--

Drug delivery

[39]

Preparation of magnetic particles coated by a thermoresponsive positively charged polymeric matrix

Chemical coprecipitation

[13]

Hydrothermal synthesis

PEI and polyoxyethylene (POE)-poly(propylene oxide)-POE amphiphilic block copolymer (Pluronic) --

Drug delivery

Synthesis method of magnetic IO NPs using the ultrasonic-assisted hydrothermal process Synthesis of magnetic ironsalen complex

Good water dispersibility and biocompatibility. Uniform size distribution. Physiologically active materials can be loaded in the hollow space of the nanocapsule The nanosystem can be used to load DNA or RNA and negatively charged drugs (polyethyleneimine [PEI] effect). Temperature-controlled drug loading and release (Pluronic effect) Simple, low-cost process. Small and uniform particle size

General biomedical applications

[37]

--

Drug delivery

[41]

Synthesis of surface-modified IO NPs for cell labeling

--

The complex possesses magnetism, which can be exploited for magnetically directed drug delivery. Complex can be conjugated to a nucleic acid or a drug molecule Small particle size and polydispersity. It can be used for labeling stem cells to monitor their movement, localization, survival, and differentiation

Cell labeling using MRI

[45]

A method for fabricating monodisperse Fe3O4 NPs

Thermal decomposition

Mono-, di-, or poly-saccharides, amino acids, poly (amino acid)s, or synthetic polymers based on methacrylic acid Oleic acid


[29]

Conjugation of targeting ligands with specificity for a cell receptor, for example, luteinizing hormone (LH)/ chorionic gonadotropin and LH-releasing hormone for human breast cancer cell targeting, to IO NPs, either directly or through a spacer molecule Synthesis method of a coreshell nanocomposite with a single-crystalline thin magnetic IO shell surrounding a drugcontaining core


Only ligand molecules

Drug delivery and MRI

[14]

--

Drug delivery

[57]

Preparation of IO NP surface decorated with cyclodextrin (CD)


Arabic gum

Drug delivery

[15,16]

--

--

Small size, narrow size distribution, high saturation magnetization intensity, and superparamagnetism Specific accumulation in targeted cells improves imaging resolution, therapy, or both. The ligand precludes the need for a separate coating layer. Using the same method, drug molecules can also be covalently bound to the magnetic NPs Protection of sensitive drugs and biomolecules entrapped in the core by the outer IO shell. Controlled drug release characteristics via a magnetically rupturing mechanism Hydrophobic therapeutic agents can be accommodated within the cavity structure of CD, which acts as a host--guest complex

Coating

Main Application

Ref.

Patents are ordered chronologically. IO: Iron oxide; MFH: Magnetic fluid hyperthermia; NPs: Nanoparticles.


3


Table 1. Patents involving the synthesis and use of IO NPs for biomedical applications (continued).



Preparation method

Advantages

Coating

Main Application

Ref.

Preparation of thermosensitive liposomes encapsulating paramagnetic IO NPs. These NPs generate heat under alternating magnetic field leading to leakage of the therapeutic agent loaded Method for synthesis of magnetic ferroferric oxide NPs in non-nitrogen atmosphere Synthesis of hollow-type gold nanocage particles comprising IO NPs


Thermosensitive controlled drug release

Oleic acid and PEG

Drug delivery

[30]

Hydrothermal synthesis

Oleic acid


[38]

Gold embedded with silver

Drug delivery, MRI, and MFH

[31]

Preparation of a MRI contrast IO NP using a pH-sensitive polymer micelle [PEG-poly (amino acid) block copolymer]

--

Oleate

MRI

[58]

Encapsulation of superparamagnetic IO in the cytosol of viable erythrocytes using dialysis with a hypotonic buffer Synthesis of IO NPs surface modified with different biocompatible polymers and loaded with bovine serum albumin (as a model protein) Synthesis of biocompatible magnetic nanoclusters containing NPs of IO/IOboron

--

Improved product purity. Ultrafine particle size. Synthesis under non-nitrogen environment Integrating the magnetic property of IO NPs and the optical property of gold (strong light absorption or scattering in the near-infrared [NIR] region) Disease diagnosis based on pH concentration, such as cancer and cardiovascular diseases. Micelle surface can be conjugated with an optical dye, such as sulforhodamine 101, for dual-modality imaging Long blood circulation time

Dextran

MRI and drug delivery

[51]


Good colloidal stability. It can be used to load proteins

PEG, poly(ethyl methacrylate), and glutamic acid

Drug delivery

[17]


Phosphodextran, carboxydextran, aminodextran, or albumin

Drug delivery

[36]

Preparation of hollow mesoporous silica NPs which can be loaded with IO NPs

--

Combines magnetic drug targeting and boron neutron capture therapy. The nanoclusters can also be loaded with therapeutic agents, such as anticancer drugs Improved drug loading capability thanks to the hollow structure. In addition to IO NPs, hollow mesoporous silica NPs can also be loaded with other contrast agents, such as gold NPs and quantum dots (QDs)

--

Drug delivery

[54]



4






Preparation method

Advantages

Coating

Main Application

Ref.

Preparation of a thermochemoembolization formulation: IO NPs, a liquid tumorphilic drug carrier (such as ethiodized oil) that enhances tumor retention of the formulation, and a chemotherapeutic or radiotherapeutic agent Synthesis of multimodal, multifunctional IO NPs loaded with a lipophilic drug and a lipophilic fluorescent dye

--

Improved therapeutic outcomes as a result of combining MFH with either chemo- or radio-therapies. Image-guided monitoring of treatment

A biocompatible polymer (starch, dextran, and PEG) and a biocompatible surfactant (citric acid, phospholipid, and polysorbate)

MFH and MRI

[42]


A matrix of poly (acrylic acid)

Drug delivery

[18]

Synthesis of water dispersible glyceryl monooleate-coated IO NPs A production method of a core-shell structured IO hollow nanosphere Preparation of epirubicinsuperparamagnetic IO nanoparticulate transdermal drug delivery system with primary amine surface groups Method for synthesizing a drug carrier based on a magnetic carbon QD/ chitosan composite microsphere A drug-loaded IO magnetofluid complex NP with nuclide imaging, fluorescence imaging, and MRI functions


Efficient loading of hydrophobic drugs in hydrophobic pockets formed by the polymeric coat. Carboxylic surface groups enable further functionalization. Imageguided monitoring of treatment Good aqueous dispersibility. Good colloidal stability

Glyceryl monooleate

Drug delivery

[19]


Increased drug-loading efficiency

Ethylene glycol

Drug delivery

[20]


Magnetic nanovehicle for transdermal chemotherapy of skin tumors

Silica

Transdermal drug delivery

[21]


Simple, rapid, and low-cost method. The system combines magnetic targeting and fluorescence imaging

Thioglycolic acid and PEI

Drug delivery

[22]

Co-precipitation, hydrothermal, or thermal decomposition

Multimode imaging: nuclide imaging, fluorescence imaging, and MRI functions

Drug delivery

[44]

Synthesis of an amphiphilic polymer for the coating of IO NPs



[32]

Therapeutic agent-IO NP covalent conjugate


High drug entrapment efficiency, high biocompatibility, low cytotoxicity, and high capability for MRI A therapeutic magnetic drug delivery nanosystem designed to reduce the problem of payload leakage, that is, premature drug release

Coated with citric acid, polyvinyl alcohol, PEG or polyvinylpyrrolidone and wrapped in macromer (chitosan, gelatin, cellulose, or casein) and acrylic copolymer PEG-block- poly("caprolactone)-poly (acrylic acid)

Drug delivery

[23]

Silica, gold



5





Preparation method

A ‘nanobubble’ drug vehicle to carry hydrophobic drugs

--

Preparation of magnetic NPs with high specific absorption rate (SAR)


Preparation of a hydrosol of ferroferric oxide NPs


Preparation of a drug delivery system via entrapment of unmodified cargo molecules (therapeutics and other types of molecules) into the exterior coating of IO NPs

--

Use of ultrasmall superparamagnetic IO NPs for macrophage targeting

--

Preparation of IO NPs for use as oral phosphate adsorbent


Synthesis of superparamagnetic IO NPs with polymeric gaps and metallic rings. The metallic coating forms a ring-like structure on the outer surface of the superparamagnetic IO NP


Advantages Ultrasound-triggered drug release. Monitoring drug delivery by MRI or optical imaging Due to high SAR, the dose of NPs required for MFH treatment is minimized, and lower values of the product of magnetic field strength and frequency are used Ferroferric oxide NPs with uniform particle size, good stability, and good dispersibility Quantification and visualization of drug loading and release by MRI

Detection of macrophageassociated diseases, for example, inflammatory diseases and cancer. The ultrasmall superparamagnetic IO NPs can also be used as a drug carrier Efficient, easy to manufacture, and well-tolerated oral phosphate binder. Primary coating materials are selected to be easily displaced by inorganic phosphate

The NP has the ability to stop the growth of bacterial biofilms. Bacteria death can be enhanced by MFH. NPs with an intermediate gold coating can be engineered for theranosis


6


Coating

Main Application

Ref.

Amphiphilic chitosan to form ‘nanobubbles’

Drug delivery

[63]

Organic molecules, for example, carbohydrates

MFH

[24]

Oleic acid


[35]

Poly(acrylic acid), carboxymethyl dextran, polyglucose sorbitol carboxymethylether, and an aminefunctionalized molecule Biocompatible polymers (e.g., PEG)

Drug delivery

[43]

Drug delivery, MRI, and MFH

[61]

Primary coating (colloidal stability): mono- or disaccharides of aliphatic and/or aromatic hexoses or pentoses. Secondary coating (optimal dispersion in the gastrointestinal tract): polymeric carbohydrates, for example, dextran, gum arabic, and inulin Polymeric gap: carboxylateddextran compound, ethanediyl bis (isonicotinate) compound, bis 2-((4-pyridinyl carbonyl)oxy)ethyl disulfide compound, and poly-Lhistidine. Metallic ring: silver and gold

Hyperphosphatemia treatment

[25]

Antibacterial

[33]





Preparation method

Advantages

Coating

Main Application

Ref.

Preparation of plasmonic stable fluorescence IO-based nanosystem comprised of a superparamagnetic IO nanocore, a gold shell, and a fluorescent polymer dye (6-arm anthracene terminated) arranged in a gap between the core and the shell Preparation of a polysaccharide-based biodegradable gel containing IO NPs for MFH therapy of cancer


Permanent fluorescence capability due to entrapment of the dye in the gold-caged polymer matrix shell. Multimodal imaging: fluorescence, NIR, and MRI

Polymeric doublelayer gap: carboxyldextran and poly (ethylene oxide)/ gold shell

Multimodal imaging and theranosis

[34]

--

Starch

MFH

[46]

Synthesis method of IO NPs using high gravity controlled precipitation


The gel has sufficient deformability to spread over tumor interstitium and adhere directly to tissues, and exhibits sufficient mechanical characteristics to remain in place during MFH therapy. NPs draining from the tumor bed to the lymph nodes can be used to track the path of cancer through the body and ablate cancer cells within the lymph High heating capability

Surfactant, for example, citric acid

MFH

[26]


3.

Synthesis methodologies

Numerous physical and chemical approaches have been developed for the synthesis of IO NPs (Figure 1) [3,5,12]. Although methods of physical nature can be used to produce highpurity nanomaterials and their scale-up is relatively easy, the geometry of the synthesized particles is difficult to control. To address these limitations, a variety of chemical methods have been used to synthesize high-quality NPs. These methods have enabled the control of NP properties, that is, size, shape, morphology, and magnetic properties, which have significant impact on the different applications of IO NPs. However, owing to the colloidal nature of IO NPs their chemical synthesis is a complex process. Defining experimental conditions, that result in monodisperse particles of adequate size, and selection of an appropriate approach, that is simple, reproducible, scalable to industrial applications, and do not involve complex and expensive purification procedure, for example, size-exclusion chromatography and ultracentrifugation, are among the main chemical challenges for potential clinical applications in the future. It is equally important for the synthesis of NPs appropriate for the intended biomedical applications to avoid the use of toxic chemicals. Chemical approaches used to prepare IO NPs have been reported in the literature [3,5,12].

In this section, however, we briefly define methods that are most used in recently published patents concerned with IO NP preparation. Co-precipitation Co-precipitation is the simplest and most efficient and common chemical technique to synthesize IO particles [13-26]. Particles are prepared by reacting ferrous (Fe2+) and ferric (Fe3+) salts in an aqueous medium with a stoichiometric ratio of 1:2. Precipitation is induced by the addition of a base, such as ammonium hydroxide, to the medium. To obtain Fe3O4, it is essential to work under oxygen-free environment. However, because Fe3O4 is sensitive to oxidation, it can be further oxidized into g-Fe2O3 in the presence of oxygen in the reaction medium. The size and morphology of IO NPs could be controlled by modulation of the acidity, ionic strength, temperature, and nature of the salts and Fe2+/Fe3+ molar ratio, and controlling the crystal growth step in the co-precipitation process [5,12,27,28]. 3.1

Thermal decomposition IO NPs with a high level of monodispersity and size control can be produced by high-temperature decomposition of iron organic precursors in organic solvents containing stabilizing surfactants, such as oleic acid [29-34] and oleylamine [31]. 3.2


7


Aerosol production

Gas phase deposition

Ball milling

Physical procedures Laser-induced pyrolisis

Pulsed laser ablation

Electrodeposition


Co-precipitation Hydrothermal synthesis


Chemical procedures Flow injection

Sol-gel synthesis Microemulsions

Sonochemical reactions

Figure 1. Methods of physical nature and chemical approaches largely used to prepare iron oxide nanoparticles.

IO NPs synthesized by organic phase thermal decomposition demonstrate high crystallinity and uniform size distribution enabling fine control of the particle size from a few nanometers up to ~ 20 nm [35]. Reaction times and temperature, concentration and ratios of the reactants, nature of the solvent, and nature of precursors are among parameters that can be modulated for proper controlling of the geometry of the NPs. However, one significant challenge is the adaptability of this approach for industrial preparation, in particular in terms of safety of the organic reagents involved and the high temperature needed. Recently, a thermal decomposition method using high-boiling alcohols, in place of organic solvents, has been disclosed [35]. The method can be successfully used to synthesize Fe3O4 NPs with good stability, good dispersibility, and a uniform particle size ranging from 8 to 16 nm via thermal decomposition of iron organic precursors, for example, iron acetylacetone and iron pentacarbonyl, in high-boiling alcohols having a boiling point of 200 -- 300 C, for example, benzyl alcohol, PEG, diethylene glycol, and triethylene glycol, and consequent mixing with an aqueous solution of a carboxylic acid salt, for example, sodium citrate and/or sodium tartrate. A similar concept was suggested for the synthesis of IO nanoclusters by heating FeCl2 in non-toxic polyol propylene glycol under nitrogen gas flow and controlled pH at 110 C for typically 48 h [36]. The method enables the preparation of magnetic nanoclusters with tunable size distributions and a large magnetic moment per nanocluster. Hydrothermal synthesis process The hydrothermal approach involves the heating of iron precursors in the aqueous medium at high temperature and elevated autogenous pressure [3,12]. This type of synthesis is 3.3

8

carried out in reactors or autoclaves where the pressure can be > 2000 psi and the temperature can be > 200 C. The produced IO has very low solubility in water at these conditions leading to supersaturation and generation of nanocrystals [12]. The rates of nucleation and grain growth processes determine the particle size and can be controlled by tuning the reaction parameters, such as temperature, pressure, time, and the precursor product system [37,38]. IO NPs prepared by the hydrothermal approach are usually formed through two main pathways: hydrolysis and oxidation of ferrous salts or neutralization of mixed metal hydroxides [3]. In one invention the use of hydrothermal synthesis with the assistance of ultrasonic cavitation nuclei to promote the formation of Fe3O4 was disclosed [37]. Working under oxygenprotected nitrogen atmosphere, FeCl3·6H2O and FeCl2·4H2O (molar ratio of 1.75:1) dissolved in water are mixed with alkaline ammonia and the mixture is subjected to ultrasonic oscillation to obtain the precursor of Fe3O4. Next, hydrothermal synthesis is performed at 140 -- 160 C for 3 -- 5 h resulting in magnetic IO NPs. In a more recent invention, the formation of Fe(OH)3 gel, without nitrogen, was proposed as a precursor for the preparation of IO NPs by hydrothermal synthesis [38]. To prepare the Fe(OH)3 gel, FeCl3·6H2O is dissolved in water and concentrated aqueous ammonia is added to generate the Fe (OH)3 colloid. The gel is formed by mixing the mixture with water or an organic medium (hexane + ethanol + oleic acid) followed by the addition of iron powder (the molar ratio of Fe (OH)3:iron is 2:1). The obtained precursor is then transferred to the autoclave and the reaction is performed at 120 -- 180 C for 4 h. This approach allows simple, low-cost synthesis in a non-nitrogen atmosphere of IO NPs with controllable size. The hydrothermal synthesis method provides several advantages including production of high-quality magnetic NPs and avoidance of organic solvents and post-treatments, such as calcinations, making it an environmentally benign and versatile approach. Nonetheless, this method is relatively little explored. 4.

Stabilization/surface coating

Because of their hydrophobic surfaces, surface charge, and large surface area to volume ratio, IO NPs tend to aggregate in suspension and in biological media, leading to heterogeneous size distribution patterns, which can hamper the usability of these particles. In addition, naked IO NPs can be subjected to oxidation, resulting in increased cytotoxicity due to ROS generation, and non-specific interactions, which may cause rapid opsonization and elimination through the reticuloendothelial system (RES) uptake. For these reasons, there is a need to coat the surface of magnetic particles with a suitable biocompatible shell to tune the particle surface properties. The coating acts to stabilize the core IO NPs, improve diffusion in the aqueous medium and prevent aggregation, protect against the surrounding environment, and




increase plasma half-life. It can also be exploited for drug delivery by accommodating therapeutic molecules and for drug targeting intracellular uptake enhancement by surface functionalization with specific chemical moieties and targeting ligands. In addition, such modifications can be advantageously used for disease imaging and/or simultaneous diagnosis of the therapeutic response in theranostic systems (Figure 2). The coating material of the IO core should be biocompatible and biodegradable, and is selected based on the core type and the intended application. It is believed that the chemical composition of the coat can significantly influence the particle fate in the body. Surface coating of IO particles can be performed during their synthesis or in a separate process following core synthesis. A wide variety of monomers, polymers, and inorganic materials have been utilized for this purpose, some of which are listed below (Figure 3). Silica Silica coating of IO NPs is a common strategy due to its favorable characteristics including biocompatibility, ease of synthesis, and controllable coating density [21,23]. Silica is hydrophilic in nature and when used as a coating material it results in well-dispersed particles in aqueous suspensions. Silica-coated particles are negatively charged above the isoelectric point of silica (pH 2) and can therefore be used for separation of biomolecules via electrostatic interactions. Furthermore, the terminal silanol (Si--OH) groups present on the silica surface can be exploited for further functionalization via covalent bonding [21]. The most common approaches for forming silica coat are the St€ober method or the reverse microemulsion method. Interestingly, a method for synthesizing IO hollow nanocapsules involving silica coating as an intermediate stage was disclosed [39]. Using a wrap-bake-peel process iron oxyhydroxide (b-FeOOH) is first dispersed in an aqueous solution and coated with a silica-coating layer. The formed nanostructure undergoes heat treatment to form an IO layer around the internal hollow space of the silica-coating layer followed by silica removal to obtain the hollow nanocapsule [39,40]. The IO hollow nanocapsules fabricated by this method show several advantages including good water dispersibility, biocompatibility, a uniform size distribution, and can also be used to carry therapeutic agents by accommodating them within the hollow space. In another invention, a magnetic IO-salen complex was developed as a targeted drug carrier [41]. The complex can be conjugated to a nucleic acid or a drug molecule and using its magnetic properties the complex can be guided to the site of disease. 4.1

Polymers Surface coating with polymers enhances the biocompatibility and pharmacokinetic profile of particles as well as enables the tuning of drug loading and release behavior. In addition, terminal functional groups of polymers residing at the surface 4.2

of the coat allow the attachment of active agents, diagnostics, and/or targeting ligands. Polymer coatings can be performed during particle synthesis, but also by post-synthesis adsorption or grafting. In the last strategy the polymer terminal groups are attached to the surface of the particle forming brush-like extensions [4]. A broad range of natural and synthetic polymers such as dextran and its derivatives [30,36,42,43], PEG [17,22,42,44], polyethyleneimine (PEI) [13,22], poly(acrylic acid) [18,43], poly(ethyl methacrylate) (PEMA) [17], derivatives of poly(methacrylamide) [45], polyvinyl alcohol [44], polyvinylpyrrolidone (PVP) [44], poly(amino acid)s [45], PEG-block-poly("-caprolactone)-poly(acrylic acid) [32], polyoxyethylene (POE)-poly (propylene oxide) (PPO)-POE amphiphilic block copolymer (Pluronic) [13], arabic gum [15,16], and starch [42,46] have been extensively used for coating IO NPs. Using polymeric coatings the surface hydrophilic character can be controlled, but also the surface charge. For example, whereas PEG coating imparts a non-ionic surface, which is desirable for increased plasma half-life [17,22,42,44], the addition of PEI to the particle surface results in a positively charged surface [13,22], which can be exploited for gene delivery, by condensing genetic material having groups of negative electricity via electrostatic interaction, and to enhance the interaction with the negatively charged cellular membranes. Further, more than one polymer can be combined together to enhance the properties of the nanosystem. For example, a combination of PEI, to enable the delivery of DNA/RNA and other negatively charged drugs, and Pluronic, to facilitate temperature-responsive drug release, has been proposed for coating IO NPs [13]. Small organic molecules Small organic molecules that can strongly adsorb on the metal surface, via van der Waals forces, electrostatic attraction, salt formation, or complex formation, are frequently utilized for coating of IO NPs. Examples of these molecules include carboxylic acids [26,35,42,44], for example, citric acid, amino acids, such as aspartic and glutamic acid [17,45], long-chain acids, for example, oleic acid and its salt [26,42], mono- and di-saccharides, for example, D-glucose, D-galactose, and lactose [45], and surfactants, for example, polysorbates [42] and glyceryl monooleate [19]. In addition, organic molecules, such as carbohydrates, alcohols, and glycols, can be implanted or embedded in the particle structure to facilitate anchoring and attachment of polymers on the surface of the magnetic particle [24]. In a recently disclosed invention, a two-layer coat system has been developed to fabricate an IO-based nanosystem for the treatment of hyperphosphatemia [25]. The primary coating is preferably selected from mono- or di-saccharides of aliphatic and/or aromatic hexoses or pentoses. These coating materials have the ability to prevent IO NP agglomeration and undesired interactions with components of physiological fluids and food in the gastrointestinal tract (GIT) whereas at the same time they can be easily displaced by inorganic 4.3


9



PEG chain

Dye/contrast agent

Biocompatible shell

Iron oxide core

Targeting ligand

Therapeutic agent

Figure 2. Magnetic theranostic nanoplatform based on an iron oxide (IO) core embedded into a biocompatible shell further containing therapeutic molecules (i.e., drugs and/or genes) and signal emitters or contrast agents, for example, MRI probes, luminophores, and radionuclides. Long-circulating functionalities can be obtained by surface decoration with hydrophilic polymer chains, for example, PEG. Surface design with targeting moieties can assure ligand--receptor interactions with targeted cells, whereas the IO core can contribute to the selective (magnetic) accumulation into the non-healthy site.

Silica

Coating engineering

Reverse microemulsion

Enhanced stability in aqueous media

Polymers

Coating engineering

During NP synthesis Post-synthesis adsorption or grafting

Controllable stability in aqueous media

Small organic molecules

Coating engineering

Van der Waals forces Electrostatic attraction Salt formation Complex formation

Controversy on the provided stability Biomolecules (proteins)

Gold

Coating engineering

Surface deposition of dopamine prior to surface adsorption

Increased plasma half-lives

Coating engineering: nanocage method

Coating engineering: dialysis Increased plasma half-lives

Figure 3. Representative materials utilized as surface coatings of iron oxide nanoparticles.

phosphate. A secondary coating is added to obtain optimal dispersion in physiological fluids of the digestive tract. This coating is formed from a polymeric carbohydrate, for example, dextran, gum arabic, and inulin. A combination of inulin and gum arabic has been found to achieve particularly high phosphate adsorption. Unfortunately, coating of magnetic particles with small molecules may not provide adequate colloidal stability due to the breakup of interactions with the particle surface and removal of the coating molecules as a result of physiological pH, temperature, or displacement by competing molecules/ ions in the medium. 10

Gold Gold can form biocompatible and rigid coatings, on magnetic NPs, that are able to inhibit the generation of hydroxyl radicals and ROS and enhance their stability in aqueous dispersions. In the form of NPs, gold is non-cytotoxic, minimizes the formation of reactive oxygen and nitrite species, and does not induce the secretion of pro-inflammatory cytokines. IO gold nanocages have been described recently [31]. Magnetic particles are coated with gold followed by coating with a layer of silver, and finally gold ions (HAuCl4) are incorporated into the silver-coated magnetic NPs. The invented gold nanocages are multifunctional metal NPs that exhibit the optical property of absorbing near-infrared (NIR) light and magnetic property of the magnetic NPs and can be used for diagnosis, targeted drug delivery, and MFH. More recently, plasmonic fluorescent superparamagnetic IO NPs have been developed [34]. The nanosystem comprises an IO core coated with a polymer double layer made up of carboxyl-dextran layer followed by a layer of poly(ethylene oxide) containing 6-arm anthracene terminated, to form a dielectric fluorescent polymer layer, and an outermost gold shell. 4.5

Enhanced stability in aqueous media

Erythrocytes

Biological molecules The use of biological molecules in particular proteins, such as human serum albumin (HSA) [36,47], have been suggested for the stabilization of magnetic particles. HAS, the most abundant protein in the body with dysopsonic activity, has been demonstrated to inhibit association of serum proteins, thus reducing the affinity of NPs to macrophages, increasing their plasma half-life, and minimizing their non-specific disposition [48,49]. Furthermore, it has been reported that HSA can bind to cell membrane receptors, such as glycoprotein 60 (gp60) receptor, thus facilitating cell uptake [50]. However, this strategy is not common for coating of IO NPs. 4.4

Stöber method



4.6

Erythrocytes

The encapsulation of superparamagnetic IO NPs into human erythrocytes has been reported. IO NPs is taken up by erythrocytes through exposing the cells to dialysis with a hypotonic buffer [51]. Red blood cells offer increased plasma half-lives of the encapsulated IO NPs and can be used as MRI contrast agents and also as drug delivery vehicles [52].


5.

Biomedical applications

Due to their unique and adjustable physicochemical properties (e.g., size, surface charge, morphology, shell thickness, etc.), flexible fabrication methods, and functional versatility, IO NPs have received remarkable attention for their biomedical applications mainly as imaging contrast agents, as targeted drug and gene delivery vectors, as agents for MFH therapy, or all these functions simultaneously. Size and surface properties of the IO NP can be tailored precisely to produce particles with high colloidal stability at physiological pH conditions and exhibit desirable pharmacokinetics and biodistribution for their intended application. In addition to the intrinsic magnetism for MRI, IO nanosystems can be equipped with other dyes or contrast agents, such as quantum dots (QDs), which enable multimodal imaging. These particles can be exploited for disease diagnosis, such as cancer lesions, but also for real-time monitoring of therapeutic response when theranostic systems are utilized [2,3,53]. IO-based nanosystems loaded with drugs, proteins, or genetic materials and with the assistance of an external magnetic field are capable of reaching the site of interest where their therapeutic cargo is released. Enhanced targeted delivery can be achieved by surface functionalization with a targeting ligand and/or controlled drug release using stimuli-responsive engineered particles. This localized drug delivery offers a number of advantages including reduced drug dose and minimized adverse toxic effects. This section is devoted to provide a detailed discussion of biomedical applications of the newly developed IO NPs (Figure 4). MRI and multimodal imaging MRI is a powerful non-invasive tool for disease diagnosis, such as tumors and tissue lesions, and visualizing the internal structures of the body. Superparamagnetic (50 -- 100 nm in size) and ultrasmall superparamagnetic (< 50 nm-sized) IO NPs can be used as MRI contrast agents for molecular and cell imaging. In general, IO NPs are utilized as T2-agents (also known as negative control agents as they reduce signal intensity) although very small particles (diameter < 10 nm) function as T1 contrast agents (also known as positive agents that induce increased signal intensity) [35,54]. MRI contrast agents based on polysaccharide-coated IO particles, such as Feridex and Resovist, are currently approved for clinical use [3]. In comparison with small contrast agents, IO particles 5.1

provide several benefits including enhanced plasma half-lives, higher selectivity and specificity, and possible surface functionalization with specific cell targeting ligands making them particularly efficient for the detection of cancer cells and angiography. The use of multimodal IO NPs, by combining these particles with one or more imaging modalities, can further enhance the imaging properties of magnetic particles [55]. Thus, a variety of recent inventions have focused on fabricating multimodal particles using a combination of IO NPs with fluorescent dyes [18,34,44], nuclides [44], radio-contrast agents [42], gold coating [31], or semiconducting QDs [22]. In one invention, a thermo-chemoembolization formulation containing magnetic IO NPs and a radiotherapy agent, such as 90Y, 125I, and 131I, has been developed with the aim to provide magnetic resonance and X-ray visibility and serve as a dual-imaging probe for image-guided tumor targeting [42]. The said formulation was examined in the liver cancer [56]. In another invention, IO NPs coated with a matrix of poly (acrylic acid) have been suggested for the co-encapsulation of a lipophilic NIR dye and an anticancer drug within the hydrophobic pockets in the polymer matrix [18]. The multimodal NPs that combine optical imaging and MRI detection can be surface decorated by folate moieties for targeting folate-expressing cancer cells [57]. In addition, a dual-modality imaging nanosystem with pH-responsive properties has been developed [58]. The nanosystem comprises Fe3O4 particles (100 nm in size) encapsulated into a pH-responsive polymer micelle, conjugated with a red fluorescent dye sulforhodamine 101, for MRI and optical imaging. The sulforhodamine 101-labeled polymeric micelles demonstrated a red-fluorescent emission at 612 nm. Cellular uptake of the polymeric micelle conjugated with sulforhodamine 101 by breast cancer cells has been observed under confocal laser scanning microscopy [59]. Hollow-type gold nanocage particles containing IO nanocores (i.e., gold-coated IO NPs) with a controllable shell thickness and a smooth surface, and combined NIR absorption, photon scattering properties, as well as magnetic properties have also been suggested as a multimodal imaging tool [31]. Gold-coated superparamagnetic IO NPs with a polymeric gap (carboxyl-dextran and PEG) containing 6-arm anthracene terminated are another example of multimodal gold-based IO NPs [34]. Because surface-bound fluorescent dyes decay significantly after a short period of time due to quick dilution by the cells leading to limited biological tracking ability, this invention can ensure permanent fluorescence capability of the magnetic particles as a result of dye entrapment in the gold-caged polymer matrix shell [55]. The development of particles with three imaging modalities, nuclide imaging, fluorescence imaging, and MRI, has also been reported [44]. The IO NP is first wrapped in a macromer, such as chitosan, gelatin, cellulose, casein, and acrylic copolymers, NIR fluorochrome and nuclide (polyethylene terephthalate) molecules are marked on the surface, and the coating materials are cross-linked to produce particles with a


11


Vascular endothelium Drug delivery

MRI


Tumor Hyperthermia

MR imaging Iron oxide nanoparticle

PO4 PO4

3-

PO4

3-

PO4

3-

PO4

3-

3-

Hyperphosphatemia Molecular imaging, and cell labeling

Anti-bacterial activity (bacterial biofilm)

Figure 4. Biomedical applications of iron oxide nanoparticles claimed in recently published patents.

diameter of 80 -- 250 nm. A drug can then be loaded onto the multimodal magnetic particles. Although IO NPs are relatively safe, the toxicity of combined multimodal nanosystems requires more investigation in vitro and in vivo. Besides imaging agents, coating shell thickness, chemical nature and surface charge are also among features to be assessed for their effect on particle toxicity. In this context, it is noteworthy to indicate that carboxydextran-coated superparamagnetic IO NPs and ultrasmall superparamagnetic IO NPs have recently been shown to be toxic to human macrophages, although this cytotoxicity can be functionally antagonized by the ROS scavengers [60]. Molecular imaging Molecular imaging refers to the non-invasive imaging of targeted macromolecules and biological processes in living organisms. Successful molecular imaging requires selective accumulation of the contrast agent at the target site (at cellular or molecular levels) and at effective quantity to produce different signal intensity from the surrounding environment. IO NPs are promising candidates for molecular imaging not only due to the high T2 effect they produce at micromolar concentrations of iron, but also because their surface coating enables the attachment of targeting ligands, with the ability to recognize specific markers or receptors. Among important applications of molecular imaging using IO NPs are cancer, inflammation, and cardiovascular imaging and diagnosis [7]. A wide range of targeting ligands types, such as antibodies, proteins, and small targeting moieties, has 5.2

12

allowed active targeting of IO NPs to tumor lesions [14]. Furthermore, passive accumulation of IO NPs in tumors is also achievable through the enhanced permeability and retention (EPR) effect, internalization by macrophages in the RES organs (liver, spleen, lymph node, and bone marrow), as well as phagocytosis by tumor-associated macrophages [2]. Macrophage targeting is also an important strategy for diagnosis of cardiovascular disease and inflammation-associated diseases such as renal inflammation, inflammatory bowel disease, and chronic obstructive pulmonary disease [61]. Drug delivery Drug delivery research using IO NPs has mainly focused on cancer therapy. Theranostic nanosystems based on magnetic IO NPs have great promise in the delivery of chemotherapeutics, proteins, radionuclides, and genetic materials [2,3]. Conventional treatment of solid and malignant tumors by chemo- and radio-therapy is often challenged by low tumor localization, increased drug resistances, reduced cellular internalization, and poor selectivity of the antitumor agents. The utilization of IO NPs to target these agents into tumor lesions leads to improved antitumor efficacy and reduced toxicity and adverse effects due to unspecific distribution to normal tissues. Whereas the EPR effect can be exploited for passive accumulation of drug-loaded nanosystems in tumors, characterized by their leaky vasculature and poor lymphatic drainage, drug-loaded IO NPs transported by blood can be localized in the tumor region by applying an external magnetic field on the desired targeted site. Furthermore, the 5.3




magnetic properties of IO particles can also be used to visualize drug accumulation using MRI [2,3,53]. In general, molecules of the therapeutic agent are either covalently bound to the particle surface or non-covalently contained in the shell segment or in the pores of the hollow particle. As an example of covalent drug linking, magnetic fine particles based on IO-salen-therapeutic agent complex have been fabricated for magnetically directed drug/nucleic acid delivery [41]. Alternatively, unaltered cargo molecules can be incorporated into the exterior coating of IO NPs by physical entrapment [19,43]. IO NPs can be coated with biocompatible polymers, such as PEG and PEMA, for protein delivery [17]. Bovine serum albumin, as a model protein, was successfully physisorbed onto the coating of these nanocomposites [62]. Drug loading onto the magnetic NPs can also be possible by hydrophobic interactions between the drug and hydrophobic groups of the coating material. For this purpose, lipophilic superparamagnetic IO NP-containing ‘nanobubbles’ were fabricated using amphiphilic chitosan as a carrier for hydrophobic anticancer drugs [63]. The hydrophobic drug is entrapped by hydrophobic interaction with the hydrophobic segment of amphiphilic chitosan. Similarly, IO NPs coated with a matrix of poly(acrylic acid) have been proposed for the encapsulation of hydrophobic drugs in the hydrophobic ‘pockets’ formed by the polymeric coating [18]. The carboxylic groups along the outer periphery of the polymer coating can also be exploited for conjugation with a ligand for active drug targeting. Further, CDs can also be used to facilitate loading of hydrophobic therapeutics. For instance, CD was covalently conjugated to gum arabic-modified IO NPs via a diisocyanate linker [15,16]. The CD-magnetic nanocomposites can carry hydrophobic anticancer drugs, which form inclusion complexes with the CD moiety [64]. Another strategy for remarkable enhancement of drug encapsulation is the use of hollow nanostructures, such as IO-mesoporous silica NPs [54]. In this context, a core-shell nanocomposite with a single-crystalline thin magnetic IO shell surrounding a drug-containing core was fabricated [57]. To synthesize this nanocomposite, the IO precursor is added to a PVP-modified silica core on which iron ions will deposit to form a self-assembled thin shell, as a result of structuredirecting effect of PVP. Subsequently, the formed shell is reduced via a redox reaction to create an IO shell. One advantage of this nanosystem is that the outer IO shell can provide powerful protection for sensitive drugs and biomolecules entrapped in the core. In addition, the synthesized nanospheres demonstrate controlled drug release characteristics via a magnetically rupturing mechanism triggered by the application of an external high-frequency magnetic field [65]. In another invention, IO hollow nanocapsules synthesized using a wrap-bake-peel technique demonstrated improved water dispersibility, a large surface area of > 100 m2/g, and a narrow mesopore size distribution allowing the carrying of physiologically active materials [39,40].

The intrinsic properties of IO NPs can be exploited for drug targeting. Ultrasmall superparamagnetic IO NPs have been designed to target macrophages [61]. These NPs can be used for drug targeting to macrophages and investigate the extent of macrophage-dependent diseases. In addition, surface functionalization with certain ligands can improve the intracellular uptake of drug-loaded NPs via receptor-mediated endocytosis. NPs surface decorated by covalently bound luteinizing hormone (LH), chorionic gonadotropin, and LH-releasing hormone (LHRH) have been prepared [14]. LHRH-conjugated magnetic IO NPs targeting human breast cancer cells expressing LHRH receptors have been investigated for both cancer detection and specific drug therapy [66]. Another strategy used for magnetic drug targeting and controlled release is to use thermosensitive systems. The ability of IO NPs to function as a source of heat, under AMF, has been exploited in the engineering of thermosensitive liposomes. Using this approach MFH-induced controlled drug release can be achieved [30]. The surface of the IO NP can be modified either by a hydrophilic functional group, for encapsulation in the aqueous core of the thermosensitive liposomes, or by a hydrophobic functional group, for entrapment in the lipid bilayer of the vesicle [67]. However, such a heatingbased strategy may not be appropriate for application in tissues that are susceptible to environmental temperature change, for example, brain tissue. Another temperatureresponsive IO-based nanovehicle was synthesized by coating the magnetic core with PEI and POE-PPO-POE amphiphilic block copolymer (Pluronic) [13]. Although the thermosensitive Pluronic imparts the nanosystem with the advantage of temperature-controlled drug loading and release, the positively charged PEI enables the loading of negatively charged drugs and DNA/RNA [68]. An additional promising strategy is to use pH-triggered drug delivery systems. For example, pH-sensitivity IO NPpolymeric micelles have been developed. The micelles prepared by self-assembly of methoxy(polyethylene glycol)-poly (b-amino ester) (PAE) block copolymers [58]. The PAE backbone comprises tertiary amine groups, which are ionized in response to acidic pH environment leading to micelle dissociation and drug release. This approach can be of particular interest in the treatment of some solid tumors known to have a relatively acidic pH environment as a consequence of lactic acid accumulation associated with the high rate of glycolysis in these tumors [59]. Although drug-loaded IO NPs are majorly designed for administration by an intravenous route, other routes of administration, such as the transdermal route, can also be used. In this context, epirubicin-conjugated superparamagnetic IO NPs were synthesized as potential magnetic nanovehicles for targeted transdermal chemotherapy of skin tumors [21,69]. Magnetic fluid hyperthermia MFH is another application of IO NPs that involves the treatment of cancer by localized heating of tumor tissues from 5.4


13



inside. Upon exposure to an oscillating magnetic field, superparamagnetic IO NPs can absorb the energy provided by the field and convert it into heat. Administrated magnetic particles can be directed by an externally applied magnetic field to the site of interest where they are subsequently exposed to an AMF to heat tumor cells up to 41 -- 47 C. This temperature induces apoptosis in cancer cell (with abnormal blood supplies) and results in irreversible damage in the tumor tissue, whereas normal cells can tolerate this heat and remain undamaged owing to the increased blood flow involved in the cellular cooling response [70]. Energy absorption and heating-generation ability of magnetic particles is dependent on several characteristics, such as geometry and composition [26,36,61]. Recently, IO NPs with high specific absorption rate (SAR) values have been developed [24]. The increased SAR offers the advantages of reduced dose of NPs and lower values of magnetic field strength and frequency that are required for MFH treatment. Further, magnetic particles with ability to convert NIR light into thermal energy for MFH therapy of cancer have also been synthesized by gold coating of IO NPs [31]. With the aim to enhance the efficiency of anticancer treatment, a thermo-chemoembolization formulation has been introduced in which IO NPs and a chemotherapeutic or radiotherapeutic agent are combined in ethiodized oil, an iodinated derivative of poppy seed oil and a tumorphilic drug carrier that selectively accumulates in cancer cells [42]. The formulation is injected directly into the tumor or the blood artery feeding the malignant tissue to achieve targeted therapy. More recently, a gel infused with starch-coated IO NPs was formulated based on pullulan, a biodegradable water-soluble, film-forming starch polymer, for improved MFH efficiency [46]. The polysaccharide gel is sufficiently deformable to adhere directly to tissues and exhibits sufficient mechanical characteristics to remain in place during MFH therapy. IO NPs released from the gel are taken up by cancer cells at the tumor site. When an external AMF between 30 and 300 kHz is applied, IO NPs aggregated in the malignant cells will generate temperatures in the MFH range. Additionally, NPs draining from the tumor bed to the lymph nodes follow the route of cancer metastasis. This effect can be used to track the path of cancer through the body and ablate cancer cells within the lymph nodes via heat produced by IO NPs metastasized to the lymph nodes [71]. Cell labeling Superparamagnetic IO nanoparticulate probes loaded into cultured cells provide a useful tool for labeling and tracking cells in vivo by MRI [45]. Among other imaging methodologies used for cell-labeling, MRI presents several benefits including high spatial resolution (around 100 µm), long effective imaging window, high speed imaging acquisition in vivo, as well as the advantage of no exposure to ionizing radiation [72]. IO NPs-labeled stem cells are of particular interest in the growing area of stem cell research. Using this strategy, MRI contrast 5.5

14

agents-labeled stem cells can be monitored for their movement, localization/migration, survival/proliferation, and differentiation. In addition to a wide range of applications in cell-based therapies, such as ischemic [73], immune [74], and neurodegeneration [75] diseases, stem cells have demonstrated outstanding promise in tissue engineering and regenerative medicine, for example, in the regeneration of injured heart [76], cartilage [77], and bone tissue [78]. For these purposes, IO NPs surface modified with D-mannose [79], poly(L-lysine) [80], poly(N,N-dimethylacrylamide) [81], and oligoperoxide have been prepared and investigated as probes for stem cell labeling [82]. Another important application of MRI cell labeling is the use of MRI-labeled immune cells. This technique has been successfully developed and used to investigate and track in vivo fate of immune cells and generate significant insight into immune cell homing and engraftment, inflammation, and gene expression [83]. Hyperphosphatemia Hyperphosphatemia is a phosphate metabolism disorder that is developed in patients with reduced renal function. As a result of calcium imbalance, hyperphosphatemia increases the risk of cardiovascular disease in patients with chronic kidney disease [80]. A recent invention has disclosed the synthesis of an oral formulation based on IO NPs for the prevention and treatment of this disorder [25]. The IO core of the nanocomposite, preferably g-Fe2O3 because it exhibits higher phosphatebinding capacity than Fe3O4 owing to the surface area available for adsorption, is coated with suitable materials, such as monoor di-saccharides of aliphatic and/or aromatic hexoses or pentoses, that can be displaced by phosphate, but also provide long enough stability in the GIT. 5.6

Antibacterial applications Although silver NPs have remarkable antimicrobial activity, their use as antibacterial agents is challenged by their high toxicity to healthy cells and inability to penetrate and eradicate bacterial biofilms. To address these shortcomings, a multimodal NP comprising a superparamagnetic IO core and a silver ring with a plurality of polymeric gaps has been synthesized and shown to have significant antibacterial effects [33]. These effects are due to the ability of the silver ringengineered magnetic NPs to deeply penetrate in the bacterial biofilms when an external magnetic field is applied. Furthermore, these NPs have the ability to induce MFH, which can be used as additional means to escalate bacterial death [33,84]. In addition, the NPs can also be fabricated with a gold ring as an intermediate coating, followed by the silver coating, to produce NPs that can be exploited for theranosis applications [33,84]. 5.7

6.

Conclusion

In this review, we shed the light on recently patented work related to the development of biomedical IO NPs. IO NPs




exhibit outstanding characteristics, such as biocompatibility, low toxicity, and magnetic properties, making them exceptionally suited for biomedical use, such as in MRI and multimodal imaging, molecular imaging, cell labeling, drug delivery, MFH in addition to other suggested applications, namely hyperphosphatemia and bacteria killing. Several patents have been devoted to the generation of high-quality magnetic NPs with precisely controlled size, size distribution, shape, and crystal structure. These characteristics have a major influence on the particle magnetic properties and in return on their intended application. Strategies for designing biocompatible, efficient surface coatings have also been the focus of a large number of patents. Invented coatings do not only enhance colloidal stability in biological environments but also serve as a reservoir for biologically active materials and imaging agents as well as be exploited for further surface functionalization giving rise to highly promising multifunctional magnetic NPs. Drug loading strategies vary between covalent bonding, incorporation in the coating by physical entrapment, hydrocarbon interactions, and electrostatic interactions, and encapsulation in the hollow structure of the magnetic nanosystem. Although drug delivery can be efficiently controlled by an external magnetic field and a targeting ligand, further control over drug release is also achieved using environment-sensitive systems. In addition, incorporation of IO NPs into another system, such as erythrocytes, ‘nanobubbles’, and liposomes, have also been reported. Although IO NPs have been in the clinic as MRI contrast agents for many years, structure and chemical modifications involved in the newly developed IO-based nanosystems necessitate further in vivo exploration to assess their activity, toxicity, and biodistribution. 7.

Expert opinion

IO NPs have been receiving much attention for application in the biomedical field owing to their outstanding characteristics including superparamagnetism, high surface/volume ratios, low toxicity, and flexibility of preparation and surface engineering. Magnetic NPs are currently approved for clinical use as MRI contrast agents in a diverse range of indications. Furthermore, they are potential candidates for use in magnetically driven drug delivery, MFH, stem cell tracking as well as in the treatment of some diseases, such as infections and hyperphosphatemia. Current research focuses majorly on developing new strategies to synthesize IO NPs with optimal properties in terms of particle geometry, size distribution, surface morphology and charge, crystal structure, stability, and magnetization. Tuning of these important properties enables the fine control of pharmacokinetics, biodistribution, in vivo fate, biocompatibility, and toxicity of IO NPs. Although chemical co-precipitation is still considered the most common chemical synthetic technique for fabricating IO NPs, it is likely that the newly developed methods, that is, thermal decomposition and hydrothermal synthetic processes, will prevail as they

offer higher phase purity and enable more control over the properties of the magnetic particle. Achieving this goal will require the overcome of scale-up challenges ensuring reproducibility and cost-effectiveness, and a comprehensive safety assessment of the industrial production processes. A major challenge for producing stable IO NPs is to furnish the particle with an efficient coating that brings about colloidal stability on the shelf, ascertain optimal performance in biological environment as well as ensure avoidance of cytotoxicity, resulted from oxidative stress or non-specific interactions of the naked magnetic NP. Although there is a wide range of small and large organic and non-organic materials to pick from, the selection process of the ideal coating should take into account biocompatibility, stability, its effect on the biological behavior and magnetic properties of the particles, simplicity of the coating method, terminal groups for further functionalization, and drug loading, retaining, and release abilities when used in drug delivery. In addition to the colloidal stability, the properties and composition of the surface coating are crucial in determining particle size, pharmacokinetics, biodistribution properties, and biological fate of the coated particle. It is highly important to ensure the safety not only of the coating material but also of its degradation products, for example, biocompatible poly(methyl methacrylate) can form toxic products on degradation. Furthermore, although protective coatings can compromise the magnetic properties of the particle leading to limited targeting ability, investigating the mechanism underlying surface anchoring of the coating can reveal important information on the nature and the force of the surface binding to predict the effect of the coating layer on the magnetization of IO NPs and the efficiency of the provided colloidal stability. Tuning the balance between protective coating and magnetization ability, developing IO NPs with boosted saturation magnetization intensity [29], and the use of superconducting magnets [85] are among techniques that can be suggested not only to enhance the magnetic targeting ability but also to compensate to the low magnetization caused by the large distance between magnet and the targeted site as well as reduce the needed dosage of the NPs and, thus, potential toxicity, due to improved efficiency. One of the great advantages of the IO NP coating is its use to produce multifunctional NPs through the loading of biologically active agents and imaging probes, whereas the possible surface decoration with specific ligands enables targeting of specific cell types, for example, cancer cells. When it comes to drug delivery, the shell material should be compatible with the therapeutic agent and have the ability to retain the drug and prevent leakage while circulating in the body, but releases its cargo in a controlled manner at the site of interest. To avoid the drug burst effect researchers may consider the use of cross-linkable polymer coatings or drug conjugation with covalent bonds that are specifically cleaved at the target site. In addition, special attention should be paid to potential coating variations and biological fate when IO NPs are heated up by external magnetic field, as in MFH.


15



To sum up, a wide range of approaches to produce IO NPs for biomedical application with optimized properties are available. In particular, surface engineered multifunctional theranostic IO NPs hold great promise for the future of (combined) disease diagnosis and therapy. The materialization of clinical application for these nanosystems is pending the investigation of long-term toxicity and pharmacokinetic profiles in animals and humans. In fact, whereas coating techniques can efficiently prevent a direct interaction between the encapsulated IO nanocrystals and the biological system components thus avoiding acute toxicity, long-term toxicity is still a concern because particles that are not eliminated intact will accumulate and consequently are metabolized in the body. It is well established that any chemical/physical modification to the surface of the NP brought in by a coating material or a functional moiety is expected to influence the in vivo behavior and consequently its stability, kinetics, and fate [86]. In this context, protein adsorption [87] and particle aggregation [88] inside the organism are two key processes that are closely related to the particle surface properties and profoundly impact the biological fate of the NP. Interestingly, it has recently been demonstrated that superparamagnetic g-Fe2O3 NPs injected to mice are degraded, over the 3 months of the experiment, into poorly-magnetic iron species, which is likely Bibliography Papers of special note have been highlighted as either of interest () or of considerable interest () to readers. 1.

2.

3.

..

4.

.

16

Wang YX. Superparamagnetic iron oxide based MRI contrast agents: current status of clinical application. Quant Imaging Med Surg 2011;1:35-40 Arias JL. Advanced methodologies to formulate nanotheragnostic agents for combined drug delivery and imaging. Expert Opin Drug Deliv 2011;8:1589-608 Reddy LH, Arias JL, Nicolas J, Couvreur P. Magnetic nanoparticles: design and characterization, toxicity and biocompatibility, pharmaceutical and biomedical applications. Chem Rev 2012;112:5818-78 A comprehensive revision on iron oxide (IO) nanoparticles: from lab to clinics. Laurent S, Saei AA, Behzadi S, et al. Superparamagnetic iron oxide nanoparticles for delivery of therapeutic agents: opportunities and challenges. Expert Opin Drug Deliv 2014;11:1449-70 An interesting update on the use of IO-based nanostructures in the delivery of therapeutic agents.

5.

6.

7.

to be resulting from the incorporation of the particles in the biosynthesis of ferritin proteins [89]. Furthermore, in situ monitoring of IO NP transformation at the nanoscale has revealed that they degrade by the stochastic corrosion mechanism in which the nature and the distribution of particle coating determine sites of corrosion onset. The work also showed that particle aggregation was associated with reduced degradation [90]. These studies will generate valuable information on the behavior of developed IO NPs in the biological systems, which can add to the existing knowledge and facilitate the optimization of these particles. Exploring new potential biomedical applications, such as mitochondria targeting and blood--brain barrier crossing, is also among tasks to be challenged in the future.

Declaration of interest The authors were supported by project FIS 11/02571 (Instituto de Salud Carlos III, Spain). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Ling D, Hyeon T. Chemical design of biocompatible iron oxide nanoparticles for medical applications. Small 2013;9:1450-66 Gao J, Gu H, Xu B. Multifunctional magnetic nanoparticles: design, synthesis, and biomedical applications. Acc Chem Res 2009;42:1097-107 Jin R, Lin B, Li D, Ai H. Superparamagnetic iron oxide nanoparticles for MR imaging and therapy: design considerations and clinical applications. Curr Opin Pharmacol 2014;18:18-27

8.

Murray AR, Kisin E, Inman A, et al. Oxidative stress and dermal toxicity of iron oxide nanoparticles in vitro. Cell Biochem Biophys 2013;67:461-76

9.

Soenen SJ, De Cuyper M, De Smedt SC, Braeckmans K. Investigating the toxic effects of iron oxide nanoparticles. Methods Enzymol 2012;509:195-224

10.

Gu L, Fang RH, Sailor MJ, Park JH. In vivo clearance and toxicity of monodisperse iron oxide nanocrystals. ACS Nano 2012;6:4947-54

11.

Petters C, Irrsack E, Koch M, Dringen R. Uptake and metabolism of


iron oxide nanoparticles in brain cells. Neurochem Res 2014;39:1648-60 12.

Teja AS, Koh PY. Synthesis, properties, and applications of magnetic iron oxide nanoparticles. Prog Cryst Growth Ch 2009;55:22-45

13.

Institute of Process Engineering, Chinese Academy of Science. Chen G, Shu C, Huizhou L. Temperature sensing parents block polymer/iron oxide magnetic nanocarrier, preparation method and application thereof. CN101219218; 2008

14.

Board of Supervisors of Louisiana State University. Leuschner C, Kumar C, Hansel W, Hormes J. In vivo imaging and therapy with magnetic nanoparticle conjugates. US2009169478; 2009

15.

National Cheng Kung University. Chen DH, Banerjee SS. Magnetic nanoparticles for targeted hydrophobic drug delivery and their production method and application. TW200946131; 2009

16.

National Cheng Kung University. Chen DH, Banerjee SS. Cyclodextrin-coated magnetic nanoparticle and its production method and application. TW200946128; 2009

17.

Yathindranath V, Hegmann T, Van Leirop J, Moore DF. Enhancing



non-N2 atomosphere. CN101885512; 2010

physicochemical characterizations, and biological applications. Chem Rev 2008;108:2064-110

39.

29.

ChangChun Institute of Applied Chemistry. Jilin Z, Guangyan H, Jiazuan N, Dehui S. Method for preparing monodisperse Fe3O4 magnetic nanoparticles. CN101538068; 2009

Seoul National University Ind. Foundation. Hyeon T, Piao Y, Kim J. Metal oxide hollow nanocapsule and a method for preparing the same. WO2008069561; 2008

40.

30.

National Health Research Institutes. Yang CS, Lo LW, Tai LA. Drug release from thermosensitive liposomes by applying an alternative magnetic field. US20090004258; 2009

Piao Y, Kim J, Na HB, et al. Wrap-bake-peel process for nanostructural transformation from betaFeOOH nanorods to biocompatible iron oxide nanocapsules. Nat Mater 2008;7:242-7

31.

Korea Research Institute of Bioscience and Biotechnology. Chung BH, Lim YT, Kim JK. Gold nanocages containing magnetic nanoparticles. US2010228237; 2010

41.

IHI Corp. Eguchi H, Ishikawa Y. Medicine having magnetism, guiding system for medicine and magnetismdetecting system. JP2009196913; 2009

42.

Zhejiang University. Lu X, Rao Y, Hong D. Application of superparamagnetic iron oxide nanoparticle applied in transdermal drug delivery system. CN103182086; 2013

32.

Kaohsiung Medical University. Wang LF, Chen GJ. Preparation of poly (ethylene glycol)-b-poly-("-caprolactone)poly(acrylic acid) and its applications. TW201422240; 2014

The Johns Hopkins University. Ivkov R, Liapi E. Formulation and methods for enhanced interventional image-guided therapy of cancer. US2012277517; 2012

43.

Shanghai Jiao Tong University. Wan A, Gui R, Li H, Jin H. Method for preparing drug carrier based on magnetic carbon quantum dot/chitosan composite microsphere. CN102973948; 2013

33.

Memorial Sloan-Kettering Cancer Center. Kaittanis C, Grimm J. Delivery of therapeutic compounds with iron oxide nanoparticles. WO2014047318; 2014

44.

23.

University of Louisville Research Foundation, Inc. Knipp RJ, Nantz MH. Nanoparticles for drug delivery. WO2014124329; 2014

34.

Nanjing University. Ding Y, Chen H, Xu J. Drug-loaded nanoparticle with nuclide imaging, fluorescence imaging and MRI functions, and preparation method and application thereof. CN102921022; 2013

24.

The Trustees of Dartmouth College. Baker I, Kekalo K. Magnetic nanoparticles, composites, suspensions and colloids with high specific absorption rate (SAR). WO2014089464; 2014

45.

Hora´k D, Sykova´ E, Babicˇ M, et al. Superparamagnetic nanoparticles based on iron oxides with modified surface, method of their preparation and application. US2009309597; 2009

46.

The Trustees of Dartmouth College. Cunkelman BP, Tate JA, Petryk AA, et al. Biodegradable iron oxide nanoparticle gel for tumor bed therapy. WO2014121224; 2014

47.

Xie J, Wang J, Niu G, et al. Human serum albumin coated iron oxide nanoparticles for efficient cell labeling. Chem Commun (Camb) 2010;46:433-5 Remarkable research contribution on the benefits coming from a proper surface functionalization of IO nanoconjugates to label various types of cell lines.

clot busting medication in stroke with directed drug convection using magnetic nano-particles. US2010055042; 2010 18.

University of Central Florida Research Foundation, Inc. Perez JM, Santra S. Multimodal, multifunctional polymer coated nanoparticles. US8236284; 2012

19.

Institute of Life Sciences. Sahoo SK, Dilnawaz F, Singh AS. Water dispersible glyceryl monooleate magnetic nanoparticle formulation. US2013302508; 2013

20.

21.

22.

25.

26.

27.

28.

Knu-Industry Cooperation Foundation. Kim KS, Lee YS, Nguyen TD. Preparation method of iron oxide nano particle having core-shell structure using one-pot process and the hollow sphere using thereof. KR20130093392; 2013

Charite-Universitatsmedizin Berlin. Wagner S, Taupitz M, Schellenberger E, et al. Nanoparticulate phosphate adsorbent on the basis of maghemite or maghemite/magnetite, production and uses thereof. US2014248363; 2014 The Johns Hopkins University, Nanomaterials Technology Pte Ltd. Ivkov R, Goh YW, Ng MT, et al. A process for making iron oxide nanoparticle preparations for cancer hyperthermia. WO2014085651; 2014 Qiao R, Yanga C, Mingyuan Gao M. Superparamagnetic iron oxide nanoparticles: from preparations to in vivo MRI applications. J Mater Chem 2009;19:6274-93 Laurent S, Forge D, Port M, et al. Magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization,

35.

36.

Mahmoudi M, Shokrgozar MA. Super paramagnetic iron oxide nanoparticles with metallic coatings and a method of synthesizing the same. US2014234429; 2014 Mahmoudi M, Shokrgozar MA. Plasmonic stable fluorescence superparamagnetic iron oxide nanoparticles and a method of synthesizing the same. US2014234226; 2014 The National Center for Nanoscience and Technology -- China. Ge GL, Tang Y, Chu LY. Hydrosol of ferroferric oxide nanoparticles and preparation method and application thereof. CN103723773; 2014 Ciobanu N. Biocompatible magnetic nano-clusters containing iron oxide respectively iron oxide - boron with primary use in magnetic drug targeting and boron neutron capture therapy. EP2277544; 2011

37.

Civil Aviation University of China. Ying G, Yan L, Xiulin L, et al. Ultrasound wave auxiliary hydrothermal synthesis technique for magnetic magnetic iron oxide nano ultra-tiny grain. CN101172664; 2008

38.

Hebei Medical University. Jing W, Wei W, Caiqin Y, et al. Hydrothermal synthesis process of magnetic ferroferric oxide nanometer ultrafine particles in


.

48.

Kummitha CM, Malamas AS, Lu ZR. Albumin pre-coating enhances intracellular siRNA delivery of multifunctional amphiphile/ siRNA nanoparticles. Int J Nanomedicine 2012;7:5205-14

17


49.

50.


51.

52.

53.

..

54.

55.

56.

Elzoghby AO, Samy WM, Elgindy NA. Albumin-based nanoparticles as potential controlled release drug delivery systems. J Control Release 2012;157:168-82

Universita Degli Studi Di Urbino Carlo Bo. Magnani M, Antonelli A. Delivery of contrasting agents for magnetic resonance imaging. US2010061937; 2010 Antonelli A, Sfara C, Manuali E, et al. Encapsulation of superparamagnetic nanoparticles into red blood cells as new carriers of MRI contrast agents. Nanomedicine (Lond) 2011;6:211-23 Arias JL, Reddy LH, Othman M, et al. Squalene based nanocomposites: a new platform for the design of multifunctional pharmaceutical theragnostics. ACS Nano 2011;5(2):1513-21 An exciting example on in vitro and in vivo activity of IO-based nanotheranostics.

61.

62.

63.

64.

Donghua University. Chuanglong H, Xiao C, Jinwei H, et al. Preparation method of hollow mesoporous silica nanoparticles. CN102786061; 2012

65.

Mahmoudi M, Shokrgozar MA. Multifunctional stable fluorescent magnetic nanoparticles. Chem Commun (Camb) 2012;48:3957-9

66.

Liapi E, Wabler M, Gilson W, et al. Evaluation of multimodal imageable formulation for thermochemoembolization of liver cancer. Radiological Society of North America 2011 Scientific Assembly and Annual Meeting. Available from: http://archive. rsna.org/2011/11016234.html [Last accessed 4 November 2014] National Chiao Tung University. Chen SY, Hu S, Liu DM. Method of forming a drug nanocarrier having a magnetic shell. US20090285885; 2009

58.

Sungkyunkwan University. Lee DS, Guanghui G, Kim BS, Lee JH. MRI contrast agent using pH sensitive polymeric micelle and dds for diagnosis and therapy using thereof. KR20100030955; 2010

18

60.

Kratz F. Albumin as a drug carrier: design of prodrugs, drug conjugates and nanoparticles. J Control Release 2008;132:171-83

57.

59.

modality MR and optical imaging. J Mater Chem 2010;20:5454-61

67.

68.

.

69.

Lunov O, Syrovets T, Buchele B, et al. The effect of carboxydextran-coated superparamagnetic iron oxide nanoparticles on c-Jun N-terminal kinase-mediated apoptosis in human macrophages. Biomaterials 2010;31:5063-71

.

delivery: cancer therapy by circumventing the skin barrier. Small 2015;11:239-47 In vitro proof of concept of the use of magnetic nanosystems in transdermal drug delivery.

70.

Kim DH, Kim KN, Kim KM, Lee YK. Targeting to carcinoma cells with chitosan- and starch-coated magnetic nanoparticles for magnetic hyperthermia. J Biomed Mater Res A 2009;88:1-11

71.

Cunkelman BP, Chen EY, Petryk AA, et al. Development of a biodegradable iron oxide nanoparticle gel for tumor bed therapy. Proc Soc Photo Opt Instrum Eng 2013;8584:858411

72.

Li L, Jiang W, Luo K, et al. Superparamagnetic iron oxide nanoparticles as MRI contrast agents for non-invasive stem cell labeling and tracking. Theranostics 2013;3:595-615

73.

Banerjee SS, Chen DH. Cyclodextrin conjugated magnetic colloidal nanoparticles as a nanocarrier for targeted anticancer drug delivery. Nanotechnology 2008;19:265602

Li XX, Li KA, Qin JB, et al. In vivo MRI tracking of iron oxide nanoparticlelabeled human mesenchymal stem cells in limb ischemia. Int J Nanomedicine 2013;8:1063-73

74.

Hu SH, Chen SY, Liu DM, Hsiao CS. Core/single-crystal-shell nanospheres for controlled drug release via a magnetically triggered rupturing mechanism. Adv Mater 2008;20:2690-5

Green MD, Snoeck HW. Novel approaches for immune reconstitution and adaptive immune modeling with human pluripotent stem cells. BMC Med 2011;9:51

75.

Moraes L, Vasconcelos-dos-Santos A, Santana FC, et al. Neuroprotective effects and magnetic resonance imaging of mesenchymal stem cells labeled with SPION in a rat model of Huntington’s disease. Stem Cell Res 2012;9:143-55

76.

Ruggiero A, Guenoun J, Smit H, et al. In vivo MRI mapping of iron oxidelabeled stem cells transplanted in the heart. Contrast Media Mol Imaging 2013;8:487-94

77.

Daldrup-Link HE, Nejadnik H. MR imaging of stem cell transplants in arthritic joints. J Stem Cell Res Ther 2014;4:165

78.

Zhao Y, Zhang Z, Wang J, et al. Abdominal hernia repair with a decellularized dermal scaffold seeded with autologous bone marrow-derived mesenchymal stem cells. Artif Organs 2012;36:247-55

79.

Hora´k D, Babicˇ M, Jendelova´ P, et al. Effect of different magnetic nanoparticle coatings on the efficiency of stem cell labeling. J Magn Magn Mater 2009;321:1539-47

Wolf GL, Schmidt KF. Theranosis of macrophage-associated diseases with ultrasmall superparamagnetic iron oxide nanoparticles (USPIO). US2014249413; 2014 Yathindranath V, Hegmann T, van Lierop J, et al. Simultaneous magnetically directed drug convection and MR imaging. Nanotechnology 2009;20:405101 National Yang-Ming University. Liu TY. Nano- and micro-bubbles with ultrasound-triggered release and imaging functionalities. US2014212502; 2014

Meng J, Fan J, Galiana G, et al. LHRH-functionalized superparamagnetic iron oxide nanoparticles for breast cancer targeting and contrast enhancement in MRI. Mat Sci Eng C 2009;29:1467-79 Tai LA, Tsai PJ, Wang YC, et al. Thermosensitive liposomes entrapping iron oxide nanoparticles for controllable drug release. Nanotechnology 2009;20:135101 Chen S, Li Y, Guo C, et al. Temperature-responsive magnetite/PEOPPO-PEO block copolymer nanoparticles for controlled drug targeting delivery. Langmuir 2007;23:12669-76 A complete piece of work on the formulation and in vivo evaluation of a multistimuli-responsive drug nanocarrier based on IOs. Rao YF, Chen W, Liang XG, et al. Epirubicin-loaded superparamagnetic iron-oxide nanoparticles for transdermal

Gao G, Heo H, Lee J, Lee D. An acidic pH-triggered polymeric micelle for dual-



80.


81.

Babicˇ M, Hora´k D, Trchova´ M, et al. Poly(L-lysine)-modified iron oxide nanoparticles for stem cell labeling. Bioconjug Chem 2008;19:740-50 Babicˇ M, Hora´k D, Jendelova´ P, et al. Poly(N,N-dimethylacrylamide)-coated maghemite nanoparticles for stem cell labeling. Bioconjug Chem 2009;20:283-94

resistance threat. ACS Nano 2012;6:2656-64 85.

86.

Takeda S, Mishima F, Fujimoto S, et al. Development of magnetically targeted drug delivery system using superconducting magnet. J Magn Magn Mater 2007;311:367-71 Levy M, Lagarde F, Maraloiu VA, et al. Degradability of superparamagnetic nanoparticles in a model of intracellular environment: follow-up of magnetic, structural and chemical properties. Nanotechnology 2010;21:395103

82.

Sponarova´ D, Hora´k D, Trchova´ M, et al. The use of oligoperoxide-coated magnetic nanoparticles to label stem cells. J Biomed Nanotechnol 2011;7:384-94

87.

83.

Ahrens ET, Bulte JW. Tracking immune cells in vivo using magnetic resonance imaging. Nat Rev Immunol 2013;13:755-63

Lundqvist M, Stigler J, Cedervall T, et al. The evolution of the protein corona around nanoparticles: a test study. ACS Nano 2011;5:7503-9

88.

84.

Mahmoudi M, Serpooshan V. Silver-coated engineered magnetic nanoparticles are promising for the success in the fight against antibacterial

Lartigue L, Wilhelm C, Servais J, et al. Nanomagnetic sensing of blood plasma protein interactions with iron oxide nanoparticles: impact on macrophage uptake. ACS Nano 2012;6:2665-78


89.

Levy M, Luciani N, Alloyeau D, et al. Long term in vivo biotransformation of iron oxide nanoparticles. Biomaterials 2011;32:3988-99

90.

Lartigue L, Alloyeau D, Kolosnjaj-Tabi J, et al. Biodegradation of iron oxide nanocubes: high-resolution in situ monitoring. ACS Nano 2013;7:3939-52

Affiliation

Mazen M El-Hammadi1,2 & Jose L Arias†1 † Author for correspondence 1 University of Granada, Department of Pharmacy and Pharmaceutical Technology, Faculty of Pharmacy, Campus Universitario de Cartuja s/n, 18071 Granada, Spain Tel: +34 958 24 39 02; Fax: +34 958 24 89 58; E-mail: [email protected] 2 Damascus University, Department of Pharmaceutics and Pharmaceutical Technology, Faculty of Pharmacy, Damascus, Syria

19

Iron Oxide Nanozyme: A Multifunctional Enzyme Mimetic for Biomedical Applications.

Galectin-3 inhibitors: a patent review (2008-present).

Composites of Polymer Hydrogels and Nanoparticulate Systems for Biomedical and Pharmaceutical Applications.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery.

Multifunctional to multistage delivery systems: The evolution of nanoparticles for biomedical applications.

Glycosidase inhibitors: a patent review (2008-2013).

Noncanonical self-assembly of multifunctional DNA nanoflowers for biomedical applications.

Dielectrophoresis for Biomedical Sciences Applications: A Review.

Photocontrolled nanoparticle delivery systems for biomedical applications.

Acyltransferase inhibitors: a patent review (2010-present).

PPARγ ligands and their therapeutic applications: a patent review (2008 - 2014).

Preparation and biomedical applications of programmable and multifunctional DNA nanoflowers.

Modulators of complement activation: a patent review (2008 - 2013).

Beyond poly(ethylene glycol): linear polyglycerol as a multifunctional polyether for biomedical and pharmaceutical applications.

Microfabricated tactile sensors for biomedical applications: a review.

Epidermal growth factor receptor inhibitors: a patent review (2010 - present).

Pyrazine derivatives: a patent review (June 2012 - present).

Quinazoline derivatives as anticancer drugs: a patent review (2011 - present).

Comprehensive review on electrospinning of starch polymer for biomedical applications.

Therapeutic applications of lipoic acid: a patent review (2011 - 2014).

3-D Imaging Systems for Agricultural Applications-A Review.

Smart packaging systems for food applications: a review.

A thermostatic system for biomedical applications.

Functional nanoparticles for biomedical applications.