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Current progress in 3D printing for cardiovascular tissue engineering
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2015 Biomed. Mater. 10 034002 (http://iopscience.iop.org/1748-605X/10/3/034002) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 169.230.243.252 This content was downloaded on 20/03/2015 at 18:15
Please note that terms and conditions apply.
Biomed. Mater. 10 (2015) 034002
doi:10.1088/1748-6041/10/3/034002
Special SECTION TOPICAL REVIEW
received
16 December 2014
Current progress in 3D printing for cardiovascular tissue engineering
re vised
28 January 2015 accep ted for publication
Bobak Mosadegh, Guanglei Xiong, Simon Dunham and James K Min
9 February 2015
Dalio Institute of Cardiovascular Imaging, Department of Radiology, Weill Cornell Medical College, New York, NY 10021, USA
published
Email: [email protected]
16 March 2015
Keywords: 3D printing, bioprinting, cardiovascular, tissue engineering, cardiology
Abstract 3D printing is a technology that allows the fabrication of structures with arbitrary geometries and heterogeneous material properties. The application of this technology to biological structures that match the complexity of native tissue is of great interest to researchers. This mini-review highlights the current progress of 3D printing for fabricating artificial tissues of the cardiovascular system, specifically the myocardium, heart valves, and coronary arteries. In addition, how 3D printed sensors and actuators can play a role in tissue engineering is discussed. To date, all the work with building 3D cardiac tissues have been proof-of-principle demonstrations, and in most cases, yielded products less effective than other traditional tissue engineering strategies. However, this technology is in its infancy and therefore there is much promise that through collaboration between biologists, engineers and material scientists, 3D bioprinting can make a significant impact on the field of cardiovascular tissue engineering.
1. Introduction Tissue engineering comprises the optimization of three primary components: (i) the type or types of cells being implanted (e.g. somatic, embryonic stem cells, adult stem cells, or induced-pluripotent stem cells) [1], (ii) type of scaffolds supporting the cells (i.e. the mechanical cues provided to the cells), and (iii) type of drugs, extra-cellular matrix (ECM), and growth factors conditioning the cells, (i.e. the chemical cues provided to the cells). In addition, the conditions (e.g. fluid flow, oxygenation, temperature) in which the construct is cultured can have a significant impact on its maturation, making the development of novel bioreactors a major part of tissue engineering [2]. Typically these constructs are fabricated using manual procedures and are therefore limited in the complexity by which materials of varying properties and dimensions can be interfaced. 3D printing provides a means to meet this technological challenge by automating the fabrication process of these materials. 3D printing is an additive manufacturing technique that builds structures, based on a computer-aided design (CAD), by depositing material in a layer-by-layer manner. There are several methods to accomplish the layer-by-layer fabrication depending on the type of material printed [3, 4]. There are four methods of 3D printing that most readily © 2015 IOP Publishing Ltd
a ccommodate biopolymers, which are typically used for providing the scaffolding and/or ECM for tissue engineering applications: (i) selective laser sintering (SLS) [5], (ii) stereolithography (SLA) [6], (iii) fused deposition modeling (FDM) [7], and (iv) pressurebased extrusion (PBE) [8, 9]. SLS uses a CO2 laser to locally raise the temperature of a thin layer of powder so the particles fuse to form a solid object (figure 1(a)). SLA uses UV or visible light to polymerize a thin layer of a solution containing a photocrosslinkable resin (figure 1(b)). FDM melts and extrudes a polymer through a nozzle onto a flat substrate to build up a 3D structure (figure 1(c)). PBE uses a differential pressure, generated by a pressure reservoir upstream or a syringe pump, to drive the material through a nozzle (figure 1(c)). While SLS and SLA are typically faster than FDM and PBE, they both require lasers and optics. SLS is ideal for materials such as ceramics or metals that might require higher temperatures, but the temperatures required for printing can be prohibitive. SLA can be both fast and straightforward, however materials must be available in photocurable chemistries (typically plastics). Both FDM and PBE can be much simpler systems, However, they can be quite slow compared to other methods. FDM is limited to thermally extruded materials (typically thermoplastics), but can be simple, high resolution and produce
Biomed. Mater. 10 (2015) 034002
B Mosadegh et al
Figure 1. Schematic illustration of various modes of 3D printing: (a) SLS: focused CO2 laser heats loose powder of print material to sinter into solid traces, (b) SLA: focused UV light induces chemical change from liquid to solid in bath of precursor liquid, (c) extrusion methods: both heating of molten solids extruded via FDM or pressure based extrusion of viscous liquids.
dense parts. Finally, PBE offers the advantage that most materials with appropriate viscocities for printing can be achieved including hydrogels and direct printing of cells, however, like FDM, it can be quite slow. We refer readers to other reviews regarding which 3D printing methods are useful for different biopolymers [8, 10]. Here, we focus on the use of these techniques specifically for 3D printing for cardiac tissue engineering. For tissue engineering applications, 3D printing serves two main purposes: (i) scaffolds of complex geometries are directly fabricated using biocompatible materials, which may or may not be seeded with cells, and (ii) artificial tissues are directly fabricated with cells encapsulated within the ink, or ‘bioink’, during the printing process [10, 11]. The first purpose of 3D printing uses routine methods for industrial applications, thus allowing the use of commercial printers without any modifications. The second purpose of 3D printing for tissue engineering, however, requires the use of materials not currently used by most industrial users, and therefore custom printers are typically built. Two commercially available bioprinters and services are the 3D-Bioplotter from envision TEC [12] (http:// envisiontec.com/3d-printers/3d-bioplotter/) and the NovoGen MMX Bioprinter from Organovo [13]. The impact of 3D printing on the field of tissue engineering has been most prevalent in applications involving hard 2
tissues with limited cellular involvement (e.g. bone) [14, 15]. This outcome is reasonable since 3D printing is inherently a technique developed for structural fabrication of rigid materials. Furthermore, the complex cues needed to facilitate desired cellular phenotypes are still not well understood. The promise of 3D printing, however, is that once those cues are discovered, this technology will enable such a microenvironment to be built. Already, 3D printing has been shown to build structures at both the nano-scale [16] and macro-scale [17]. There currently, however, is not a single system that can build artificial tissues that span the full range of hierarchical structures observed in vivo. For example, muscle comprises protein filaments, myofibrils, muscle fibers, and fascicles, all of which are well organized and span several orders of magnitude in length. To bridge this gap, novel methods of 3D printing and new classes of bioinks are being developed [3, 4, 18, 19]. In general, bioinks require three characteristics to be useable: (i) biocompatible (i.e. will not induce harm to the host after implantation), (ii) non-cytotoxic (i.e. will not kill or damage cells during printing due to chemical, thermal, or mechanical issues) (iii) printable (i.e. has the proper rheological properties to be extruded or assembled effectively during printing), and (iv) robust (i.e. able to withstand the physical forces of the environment into which it is applied) [3, 4]. According to the Centers for Disease Control and Prevention (CDC) and World Health Organization, cardiovascular disease (CVD) is the number one cause of death for both men and women, and is responsible for killing nearly 30% of people world-wide [20, 21]. CVD is a broad term that refers to disorders of the heart and blood vessels, including coronary heart disease, peripheral arterial disease, rheumatic heart disease, heart failure, arrhythmia, myocardial infarction, and even stroke [22]. Often these diseases are linked to atherosclerosis, a disease in which a build-up of plaque causes inflammation, but other congestive and congenital diseases exist as well [22]. Medications can be effective if administered early, but if the disease progresses, surgical intervention that aims to repair or replace the damaged tissue is often required. Due to a lack of organ donors and adequate synthetic solutions, tissue-engineering approaches are being developed. This review focuses on the use of 3D printing to fabricate tissue-engineered cardiac tissue, but we refer the reader to the following reviews that survey cardiac tissue engineering using other fabrication methods [23–28]. For cardiovascular applications, 3D printing has already been used in a clinical setting to visualize anatomical structures for surgeons [29–31]. For this reason, the NIH has already begun a public resource for the exchange of CAD files, medical images, tutorials and software [32]. These surgical models are made of solid plastic that are not directly useful for tissue engineering purposes. Bioinks, which typically comprise of cells suspended in hydrogels that serve as the ECM, are beginning to be developed and printed directly to form
Biomed. Mater. 10 (2015) 034002
B Mosadegh et al
tissues that can be implanted for cardiovascular tissue engineering [8, 10, 17, 33–35], specifically in the form of myocardial tissue, heart valves, and coronary arteries. Furthermore, 3D printing has the ability to integrate electronics into tissue-engineered constructs to provide additional functionality, such as sensing and actuation. Although currently there is no clinical impact of 3D printed tissues, as techniques are refined and the technology improved in resolution and scale, this technology should yield an unprecedented ability to integrate artificial tissues with native cardiac tissue seamlessly with respect to geometry, mechanical properties, electrical properties, and ability to remodel.
2. 3D printing for myocardial tissue When heart tissue undergoes damage, the heart pumps blood inefficiently due to the loss of contractile muscle tissue (primarily cardiomyocytes) and the formation of stiff scar tissue (due to activated fibroblasts) [36]. The resulting decrease in cardiac output often results in ischemia that can lead to death [37]. One approach to repair the heart is to implant cells at the site of the damaged tissue, a treatment option referred to as cellular therapy [1]. The effectiveness of cellular therapy depends on the ability of the cells to survive the implantation and properly integrate into the heart tissue in a manner that increases cardiac output. Due to the demanding constraints of the heart, cell therapy alone has not been able to cause sufficient regeneration, and therefore techniques of tissue engineering are being explored [37]. There are many combinations of strategies being explored for cardiac tissue engineering, and we refer the readers to the following reviews [36–40]. One of the main limitations to survival of the implanted cells is the immediate availability of oxygen [41]. During in vitro culture, the effective transport of oxygen to cells is facilitated by either, (i) limiting the thickness of the construct of cells to thin slices (
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My IOPscience
Current progress in 3D printing for cardiovascular tissue engineering
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2015 Biomed. Mater. 10 034002 (http://iopscience.iop.org/1748-605X/10/3/034002) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 169.230.243.252 This content was downloaded on 20/03/2015 at 18:15
Please note that terms and conditions apply.
Biomed. Mater. 10 (2015) 034002
doi:10.1088/1748-6041/10/3/034002
Special SECTION TOPICAL REVIEW
received
16 December 2014
Current progress in 3D printing for cardiovascular tissue engineering
re vised
28 January 2015 accep ted for publication
Bobak Mosadegh, Guanglei Xiong, Simon Dunham and James K Min
9 February 2015
Dalio Institute of Cardiovascular Imaging, Department of Radiology, Weill Cornell Medical College, New York, NY 10021, USA
published
Email: [email protected]
16 March 2015
Keywords: 3D printing, bioprinting, cardiovascular, tissue engineering, cardiology
Abstract 3D printing is a technology that allows the fabrication of structures with arbitrary geometries and heterogeneous material properties. The application of this technology to biological structures that match the complexity of native tissue is of great interest to researchers. This mini-review highlights the current progress of 3D printing for fabricating artificial tissues of the cardiovascular system, specifically the myocardium, heart valves, and coronary arteries. In addition, how 3D printed sensors and actuators can play a role in tissue engineering is discussed. To date, all the work with building 3D cardiac tissues have been proof-of-principle demonstrations, and in most cases, yielded products less effective than other traditional tissue engineering strategies. However, this technology is in its infancy and therefore there is much promise that through collaboration between biologists, engineers and material scientists, 3D bioprinting can make a significant impact on the field of cardiovascular tissue engineering.
1. Introduction Tissue engineering comprises the optimization of three primary components: (i) the type or types of cells being implanted (e.g. somatic, embryonic stem cells, adult stem cells, or induced-pluripotent stem cells) [1], (ii) type of scaffolds supporting the cells (i.e. the mechanical cues provided to the cells), and (iii) type of drugs, extra-cellular matrix (ECM), and growth factors conditioning the cells, (i.e. the chemical cues provided to the cells). In addition, the conditions (e.g. fluid flow, oxygenation, temperature) in which the construct is cultured can have a significant impact on its maturation, making the development of novel bioreactors a major part of tissue engineering [2]. Typically these constructs are fabricated using manual procedures and are therefore limited in the complexity by which materials of varying properties and dimensions can be interfaced. 3D printing provides a means to meet this technological challenge by automating the fabrication process of these materials. 3D printing is an additive manufacturing technique that builds structures, based on a computer-aided design (CAD), by depositing material in a layer-by-layer manner. There are several methods to accomplish the layer-by-layer fabrication depending on the type of material printed [3, 4]. There are four methods of 3D printing that most readily © 2015 IOP Publishing Ltd
a ccommodate biopolymers, which are typically used for providing the scaffolding and/or ECM for tissue engineering applications: (i) selective laser sintering (SLS) [5], (ii) stereolithography (SLA) [6], (iii) fused deposition modeling (FDM) [7], and (iv) pressurebased extrusion (PBE) [8, 9]. SLS uses a CO2 laser to locally raise the temperature of a thin layer of powder so the particles fuse to form a solid object (figure 1(a)). SLA uses UV or visible light to polymerize a thin layer of a solution containing a photocrosslinkable resin (figure 1(b)). FDM melts and extrudes a polymer through a nozzle onto a flat substrate to build up a 3D structure (figure 1(c)). PBE uses a differential pressure, generated by a pressure reservoir upstream or a syringe pump, to drive the material through a nozzle (figure 1(c)). While SLS and SLA are typically faster than FDM and PBE, they both require lasers and optics. SLS is ideal for materials such as ceramics or metals that might require higher temperatures, but the temperatures required for printing can be prohibitive. SLA can be both fast and straightforward, however materials must be available in photocurable chemistries (typically plastics). Both FDM and PBE can be much simpler systems, However, they can be quite slow compared to other methods. FDM is limited to thermally extruded materials (typically thermoplastics), but can be simple, high resolution and produce
Biomed. Mater. 10 (2015) 034002
B Mosadegh et al
Figure 1. Schematic illustration of various modes of 3D printing: (a) SLS: focused CO2 laser heats loose powder of print material to sinter into solid traces, (b) SLA: focused UV light induces chemical change from liquid to solid in bath of precursor liquid, (c) extrusion methods: both heating of molten solids extruded via FDM or pressure based extrusion of viscous liquids.
dense parts. Finally, PBE offers the advantage that most materials with appropriate viscocities for printing can be achieved including hydrogels and direct printing of cells, however, like FDM, it can be quite slow. We refer readers to other reviews regarding which 3D printing methods are useful for different biopolymers [8, 10]. Here, we focus on the use of these techniques specifically for 3D printing for cardiac tissue engineering. For tissue engineering applications, 3D printing serves two main purposes: (i) scaffolds of complex geometries are directly fabricated using biocompatible materials, which may or may not be seeded with cells, and (ii) artificial tissues are directly fabricated with cells encapsulated within the ink, or ‘bioink’, during the printing process [10, 11]. The first purpose of 3D printing uses routine methods for industrial applications, thus allowing the use of commercial printers without any modifications. The second purpose of 3D printing for tissue engineering, however, requires the use of materials not currently used by most industrial users, and therefore custom printers are typically built. Two commercially available bioprinters and services are the 3D-Bioplotter from envision TEC [12] (http:// envisiontec.com/3d-printers/3d-bioplotter/) and the NovoGen MMX Bioprinter from Organovo [13]. The impact of 3D printing on the field of tissue engineering has been most prevalent in applications involving hard 2
tissues with limited cellular involvement (e.g. bone) [14, 15]. This outcome is reasonable since 3D printing is inherently a technique developed for structural fabrication of rigid materials. Furthermore, the complex cues needed to facilitate desired cellular phenotypes are still not well understood. The promise of 3D printing, however, is that once those cues are discovered, this technology will enable such a microenvironment to be built. Already, 3D printing has been shown to build structures at both the nano-scale [16] and macro-scale [17]. There currently, however, is not a single system that can build artificial tissues that span the full range of hierarchical structures observed in vivo. For example, muscle comprises protein filaments, myofibrils, muscle fibers, and fascicles, all of which are well organized and span several orders of magnitude in length. To bridge this gap, novel methods of 3D printing and new classes of bioinks are being developed [3, 4, 18, 19]. In general, bioinks require three characteristics to be useable: (i) biocompatible (i.e. will not induce harm to the host after implantation), (ii) non-cytotoxic (i.e. will not kill or damage cells during printing due to chemical, thermal, or mechanical issues) (iii) printable (i.e. has the proper rheological properties to be extruded or assembled effectively during printing), and (iv) robust (i.e. able to withstand the physical forces of the environment into which it is applied) [3, 4]. According to the Centers for Disease Control and Prevention (CDC) and World Health Organization, cardiovascular disease (CVD) is the number one cause of death for both men and women, and is responsible for killing nearly 30% of people world-wide [20, 21]. CVD is a broad term that refers to disorders of the heart and blood vessels, including coronary heart disease, peripheral arterial disease, rheumatic heart disease, heart failure, arrhythmia, myocardial infarction, and even stroke [22]. Often these diseases are linked to atherosclerosis, a disease in which a build-up of plaque causes inflammation, but other congestive and congenital diseases exist as well [22]. Medications can be effective if administered early, but if the disease progresses, surgical intervention that aims to repair or replace the damaged tissue is often required. Due to a lack of organ donors and adequate synthetic solutions, tissue-engineering approaches are being developed. This review focuses on the use of 3D printing to fabricate tissue-engineered cardiac tissue, but we refer the reader to the following reviews that survey cardiac tissue engineering using other fabrication methods [23–28]. For cardiovascular applications, 3D printing has already been used in a clinical setting to visualize anatomical structures for surgeons [29–31]. For this reason, the NIH has already begun a public resource for the exchange of CAD files, medical images, tutorials and software [32]. These surgical models are made of solid plastic that are not directly useful for tissue engineering purposes. Bioinks, which typically comprise of cells suspended in hydrogels that serve as the ECM, are beginning to be developed and printed directly to form
Biomed. Mater. 10 (2015) 034002
B Mosadegh et al
tissues that can be implanted for cardiovascular tissue engineering [8, 10, 17, 33–35], specifically in the form of myocardial tissue, heart valves, and coronary arteries. Furthermore, 3D printing has the ability to integrate electronics into tissue-engineered constructs to provide additional functionality, such as sensing and actuation. Although currently there is no clinical impact of 3D printed tissues, as techniques are refined and the technology improved in resolution and scale, this technology should yield an unprecedented ability to integrate artificial tissues with native cardiac tissue seamlessly with respect to geometry, mechanical properties, electrical properties, and ability to remodel.
2. 3D printing for myocardial tissue When heart tissue undergoes damage, the heart pumps blood inefficiently due to the loss of contractile muscle tissue (primarily cardiomyocytes) and the formation of stiff scar tissue (due to activated fibroblasts) [36]. The resulting decrease in cardiac output often results in ischemia that can lead to death [37]. One approach to repair the heart is to implant cells at the site of the damaged tissue, a treatment option referred to as cellular therapy [1]. The effectiveness of cellular therapy depends on the ability of the cells to survive the implantation and properly integrate into the heart tissue in a manner that increases cardiac output. Due to the demanding constraints of the heart, cell therapy alone has not been able to cause sufficient regeneration, and therefore techniques of tissue engineering are being explored [37]. There are many combinations of strategies being explored for cardiac tissue engineering, and we refer the readers to the following reviews [36–40]. One of the main limitations to survival of the implanted cells is the immediate availability of oxygen [41]. During in vitro culture, the effective transport of oxygen to cells is facilitated by either, (i) limiting the thickness of the construct of cells to thin slices (
