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THOUGHTS AND PROGRESS The limitations of this study are a small sample size and not having a nonuremic control group. Results based on a larger sample would be more representative and could be extrapolated on a larger population of HD patients. CONCLUSION Our study contributes to understanding the importance of testosterone in HD patients. We found that testosterone is associated with hemoglobin in male and female HD patients. However, other larger studies are needed, basic as well as clinical, to find out how testosterone acts on endocrine processes in hemodialysis patients and its correlation with cardiovascular diseases. Answers to those questions would contribute to improved treatment, survival, and quality of life of HD patients. Conflict of Interest: We declare that we have no conflict of interest. REFERENCES 1. Parker JP, Beime GJ, Desai JN, Raich PC, Shahidi NT. Androgen-induced increase in red-cell 2,3diphosphoglycerate. N Engl J Med 1972;287:381–3. 2. Sheashaa H, Abdel-Razek W, El-Husseini A, Mohamed Taha N, Elbaz M, Sobh M. Use of nandrolone decanoate as an adjuvant for erythropoietin dose reduction in treating anemia in patients on hemodialysis. Nephron Clin Pract 2005;99: c102–6. 3. Buttner R, Bollheimer LC, Zietz B, et al. Definition and characterization of relative hypo- and hyperleptinemia in a large Caucasian population. J Endocrinol 2002;175:745–56. 4. Bachman E, Feng R, Travison T, et al. Testosterone suppresses hepcidin in men: a potential mechanism for testosteroneinduced erythrocytosis. J Clin Endocrinol Metab 2010;95: 4743–7. 5. Moriyama Y, Fischer JW. Increase in erythroid colony formation in rabbits following the administration of testosterone. Proc Soc Exp Biol Med 1975;149:178–80. 6. Carrero JJ, Barany P, Yilmaz MI, et al. Testosterone deficiency is a cause of anemia and reduced responsiveness to erythropoiesis-stimulating agents in men with chronic kidney disease. Nephrol Dial Transplant 2012;27:709–15. 7. Ferrucci L, Maggio M, Bandinelli S, et al. Low testosterone levels and the risk of anemia in older men and women. Arch Intern Med 2006;166:1380–8. 8. Anantharaman P, Schmidt RJ. Sexual function in chronic kidney disease. Adv Chronic Kidney Dis 2007;14:119–25. 9. Bhatia V, Chaudhuri A, Tomar R, Dhindsa S, Ghanim H, Dandona P. Low testosterone and high C-reactive protein concentrations predict low hematocrit in type 2 diabetes. Diabetes Care 2006;29:2289–94. 10. Grossmann M, Panagiotopolou S, Sharpe K, et al. Low testosterone and anaemia in men with type 2 diabetes. Clin Endocrinol (Oxf) 2009;70:547–53. 11. Shaldon S, Koch KM, Oppermann F, Patyna WD, Schoeppe W. Testosterone therapy for anemia in maintenance dialysis. Br Med J 1971;3:212–5. 12. Kidney Disease: Improving Global Outcomes (KDIGO) Anemia Work Group. KDIGO clinical practice guideline for anemia in chronic kidney disease. Kidney Int Suppl 2012;2: 279–335.
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13. Carrero JJ, Steinvinkel P. The vulnerable man: impact of testosterone deficiency on the uraemic phenotype. Nephrol Dial Transplant 2012;27:4030–41. 14. Griggs RC, Kingston W, Jozefowich RF, Herr BE, Forbes G, Halliday D. Effect of testosterone on muscle mass and muscle protein synthesis. J Appl Physiol 1989;66:498–503. 15. Carrero JJ, Qureshi AR, Parini P, et al. Low serum testosterone increases mortality risk among male dialysis patients. J Am Soc Nephrol 2009;20:613–20. 16. Carrero JJ, Qureshi AR, Nakashima A, et al. Prevalence and clinical implications of testosterone deficiency in men with end-stage renal disease. Nephrol Dial Transplant 2011;26:184– 90.
Fabrication of Low-Cost, Cementless Femoral Stem 316L Stainless Steel Using Investment Casting Technique *†Mohd Yusof Baharuddin, †Sh-Hussain Salleh, ‡Andril Arafat Suhasril, §Ahmad Hafiz Zulkifly, ¶Muhammad Hisyam Lee, **Mohd Afian Omar, ††Ab Saman Abd Kader, †Alias Mohd Noor, †Arief Ruhullah A. Harris, and †Norazman Abdul Majid *Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Lembah Pantai, Kuala Lumpur; †Centre for Biomedical Engineering Transportation Research Alliance; ‡Department of Materials Engineering, Faculty of Mechanical Engineering; ¶Department of Mathematical Sciences, Faculty of Science; ††Transportation Research Alliance, Universiti Teknologi Malaysia, Skudai, Johor; §Department of Orthopaedic, Traumatology & Rehabilitation, Kuliyyah of Medicine, International Islamic University Malaysia, Kuantan, Pahang; and **Advanced Materials Research Center (AMREC), SIRIM Berhad, Kulim, Kedah, Malaysia Abstract: Total hip arthroplasty is a flourishing orthopedic surgery, generating billions of dollars of revenue. The cost associated with the fabrication of implants has been increasing year by year, and this phenomenon has burdened the patient with extra charges. Consequently, this study will focus on designing an accurate implant via implementing the reverse engineering of three-dimensional morphological study based on a particular population. By using finite element analysis, this study will assist to predict the outcome and could become a useful tool for preclinical testing of newly designed implants. A prototype is then fabricated using 316L stainless steel by applying investment casting techniques that reduce manufacturing cost
doi:10.1111/aor.12222 Received June 2013; revised September 2013. Address correspondence and reprint requests to Professor Sh-Hussain Salleh, Centre for Biomedical Engineering Transportation Research Alliance, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia. E-mail: [email protected] Artif Organs, Vol. 38, No. 7, 2014
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without jeopardizing implant quality. The finite element analysis showed that the maximum von Mises stress was 66.88 MPa proximally with a safety factor of 2.39 against endosteal fracture, and micromotion was 4.73 μm, which promotes osseointegration. This method offers a fabrication process of cementless femoral stems with lower cost, subsequently helping patients, particularly those from nondeveloped countries. Key Words: Implant—Hip replacement—Cementless hip—Investment casting.
Total hip arthroplasty (THA) is recognized as the most successful orthopedic surgery to restore the function of the hip joint lost to degenerative diseases such as osteoarthritis and rheumatoid arthritis. The major issues in femoral stems that lead to replacement surgery are fixation stability, aseptic loosening, inappropriate design, wear, and stress shielding (1). Several implant manufacturers have modified the stem to better suit the peculiar hip morphology of the Asian population particularly in terms of the metaphyseal region, femoral head offset size, and isthmus diameter. In general, Asians have smaller builds and different lifestyles that contribute to the differences in the femoral morphology. The University of Fukui has developed a cementless hip stem in accordance with the morphology of the Japanese population focusing on dysplastic hip osteoarthritis that showed successful results in the medium term (2–4). The primary emphasis was the metaphyseal region with a view to preventing micromotion, loosening, and stress shielding predominantly at the proximal calcar. In addition, nonlinear threedimensional finite element analysis was used to simulate physiological loading to predict the early outcome of the implant that allows them to rectify any problems that arise in the design process. Custom-made femoral stems have become an alternative solution to differences in hip morphology. The main reason is that a universal stem with collodiaphyseal angle of 135° does not match all femoral types. Generally, commercial off-the-shelf implants are designed using a western dataset, which differs from Asian morphology. Variable sizes are not the optimal solution to this problem, as similar designs still apply, leading to a geometrical mismatch between the stem and the patient. Bigger stems risk more cancellous bone in the endosteal canal, along with over reaming and bone fractures. On the other hand, smaller stems cause under sizing, aseptic loosening, and bone atrophy. Consequently, a custommade stem has been chosen as it is tailored in line with individual morphology, and optimized fitting and filling in endosteal canal provides better fixation stability and promotes osseointegration. However, increments in cost and time are other factors that Artif Organs, Vol. 38, No. 7, 2014
need to be considered. This phenomenon has led to a newly designed femoral stem based on specific characteristics of the population. The excellent results shown by the University of Fukui prove that this approach could be applied in cementless femoral stem development. Cutting-edge technology in three-dimensional reverse engineering helps to produce an accurate implant that is well suited to the actual morphology of the bone. In this present study, we fabricated a cementless hip stem that not only optimally fits and fills the medullary canal but also reduces the cost of the implant itself. This systematic methodology is based on a three-dimensional morphological analysis of the Malaysian population and is based on a precise implant designed to comply with the patient’s anatomy. The performance of nonlinear finite element analysis was used to predict the outcome and to rectify design flaws, allowing for the development of a prototype cementless stem and the fabrication of this stem using investment casting techniques. The 316L stainless steel is chosen over titanium and cobalt chrome as it is cheaper in price and its properties are widely accepted as an orthopedic prosthesis (1). Despite the advantages of its mechanical properties, there are several concerns regarding these metallic alloys. First, toxic effects (with release of metal ions) are caused by leaching, wear, and corrosion (5). Sivakumar and Rajeswari (6) reported that 90% of the implants failure made by this alloy is ascribable to pitting and crevice corrosion attack. However, Yang and Ren (7) suggested nickel element replacement with high-nitrogen that produced a stable austenitic phase, high strength and good plasticity, better corrosion and wear resistance, and superior biocompatibility. Second, the fatigue strength of 316L stainless steel is inferior to cobalt chrome alloy and titanium alloy. Several studies reported the fatigue strength of 316L stainless steel at 107 cycles (8–11). The stress/life (S/N) curves from fatigue test using Eagle’s medium at 37°C for 316L stainless steel illustrated maximum stress of 320 MPa after 107 cycles (8). Despite its material properties, the implant design also made a crucial contribution to features of fatigue failure (5). Khanuja et al. (12) pointed out that the excellent survival rates of a cementless femoral stem are attributed to the stem’s geometrical design rather than the choice of material and fixation surface. In this study, the femoral stem is designed based on local anatomical features, and deliberate considerations are taken into account before fabrication. We believe that finite element analysis might become a useful tool for preclinical testing of newly designed implants. The finite element could become a “safety measure” for
THOUGHTS AND PROGRESS new stems before clinical trials. As the cost of the cementless stem has increased each year, aligned with the increment of THA performed worldwide, we are highlighting a methodology that is reproducible and could help to reduce the cost without jeopardizing quality. It is strongly hypothesized that this method would be beneficial particularly to nondeveloped countries such as those in Asia, which may not be able to afford the hip implant surgery costs that increase each year. MATERIALS AND METHODS We prospectively acquired the computed tomography (CT) images from 60 healthy hips prior to designing the cementless femoral stem in accordance with the peculiar morphology of the Asian population (13– 16). The design process used a three-dimensional femora model that provides more anthropometric
De-waxing shell in firing furnace at 800°C
Wax implant invested into ceramic slurry, and stuccoed with layers of zirconla sand to form shell
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information and accurate measurement. The cementless femoral stem was designed to optimally fit and fill the endosteal canal as shown in Fig. 1. Interquartile range descriptive analysis was used as the stem design profile, and nonlinear finite element analysis was conducted to predict the outcome of the early stage after the surgery according to the standard protocol of virtual implantation (2–4). After designing the stem based on the morphology analysis, we performed finite element analysis using different software such as Marc/Mentat software (MSC Software, Santa Ana, CA, USA). The finite element model for the cementless femoral stem consisted of 4226 nodes and 13 241 elements, whereas the “virtual surgery femora” consisted of 7946 nodes and 41 900 elements. The 3D femora model chosen for finite element study was the “average” femora from the previous study (13–16). The material properties of the cementless femoral stem were assigned as 316L stainless steel
316L molten stainless steel (at 1600°C) poured into implant shell
Knock out shell after cooling, sand blast with nano size silicon carbide
Design of cementless femoral sand blast on morphology study
FIG. 1. Fabrication process of the low cost cementless femoral stem of 316L stainless steel using investment casting technique.
Wax injection into the mould to form pattern. The pouring cup, sprue and riser were wax welded on pattern
Implant mould using silicone rubber compound
Cementless femoral stem using rapid prototype machine
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with a Young’s Modulus of 200 GPa and a Poisson’s ratio of 0.3 (2). In addition, the femora were assumed as isotropic and linear elastic, with bone properties determined according to the CT datasets’ gray level values.The correlation proposed by Carter and Hayes between the modulus of elasticity of the bone, E, and its apparent density was used in this study as shown in Eq. 1 (17). The cancellous and cortical bones are assumed merely at different ends of a continuum spectrum.
E = 3790 ρ3
(1)
The physiological loading mimicked stair climbing with an assumed body weight of 71 kg, given forces Fx = −709.2 N, Fy = 600.8 N, Fz = 1553.2 N, and applied moment of Mx = −123.9 Nm, My = 25 Nm (2). The finite element model was completely restrained distally. This present study will look at stress shielding, micromotion, and displacement. We proposed a new investment casting technique that may decrease the existing cost and time consumed during the fabrication process of the cementless femoral stem. The implant’s prototype was converted from three-dimensional stereo lithographic formats into slices 0.085-mm thick using a rapid prototype machine (ZPrinter 310, 3D Systems, Rock Hill, SC, USA). The prototype is then depowdered, infiltrated with resin to ensure its durability, and allowed to dry. The silicone rubber compounds (RTV560, Momentive Performance Materials Inc., Albany, New York, USA) for high–low temperature potting, encapsulating, and sealing were used as the mould. This silicon elastomer is mixed homogenously with dibutyl tin dilaurate, which acts as a regular curing agent. The RTV560 base compound might continuously retain elastomeric properties up to 260°C and up to 316°C for a short duration, which is suitable during the wax injection process. The investment casting process commenced by injecting the melted wax into the silicone rubber compound mould producing the implant’s casting that are called patterns. These patterns were then attached (wax welded) to another three parts: (i) pouring cup (bigger size funnel shape than pattern that is attached at the proximal region to allow molten metal to flow inside the shell); (ii) sprue (smaller size funnel that connects the pouring cup and pattern); and (iii) riser (cylindrical shape attached at distal part to allow uniform flow of molten metal). The more general method that uses the central sprue to produce the wax patterns was not utilized, resulting in reducing the amount of molten Artif Organs, Vol. 38, No. 7, 2014
316L stainless steel to be used later and decreasing the fabrication cost. The pattern is injected into the ceramic slurry, a mixture of 25% colloidal silica and zirconia sand (ASTM 325), which is stirred homogenously nonstop until the process is finished. Using coarser aluminum silicate sand (ASTM 20–70), a six-layer shell is formed before it is finally dipped into the ceramic slurry to seal it. The shell must be well built to endure high temperatures in the calcined process that later takes place in the firing furnace at 800°C for 2 h to remove the wax residue. The 316L stainless steel is heated in an induction furnace (Inductotherm Group, Victoria, Australia) at 1600°C. The molten metal is poured through the pouring cup into the shell by using the standard gravity and pouring method. After the 2-h cooling, the shell is knocked out, and other parts are removed using a metal saw blade. The prototype is subsequently sand blasted using 2.0 bar, 180 μm silicon carbide mesh using a blasting machine (CSMG25/Adhesion, CemeCon, Wuerselen, Germany). The prototype surface roughness is measured using a hybrid surface contour machine (Formtracer CS-5000, Mitutoyo America Company, IL, USA). The parameters are set to a measured length of 5 mm, a measurement pitch of 0.0010 mm, speed 0.1 mm/s, roughness pitch of 0.0005 mm, and a cutoff at 0.8. We measured two different regions, proximal and distal, and divided the region into five areas. RESULTS The three-dimensional morphology analysis provided sufficient information regarding the periosteal and endosteal canal size of the femora. In this study, we used these parameters for our newly designed femoral stem: femoral head offset (FHO), the isthmus position, collo-diaphyseal angle (CDA), and endosteal canal diameter at certain levels especially in the metaphyseal region. The FHO showed 30.55 mm horizontally and 52.72 mm vertically with CDA 130.68° and isthmus position at 112.83 mm from the center of the lesser trochanter. We found that the maximum stress was 66.88 MPa at the proximal region, and minimum stress was 7.75 × 10−12 Pa at distal region as illustrated in Fig. 2. In addition, the maximum value for micromotion was 4.73 μm and displacement of 6.47 μm. The surface roughness of the cementless femoral stem was shown to be 7.287 μm proximally and 1.613 μm distally. DISCUSSION From the finite element analysis, we discovered that the stress was normally distributed at the
THOUGHTS AND PROGRESS a Pa
b mm
607
c mm
6.000e+005
4.726e−003
1.051e−003
5.400e+005
4.253e−003
9.861e−004
4.800e+005
3.780e−003
9.210e−004
4.200e+005
3.308e−003
8.559e−004
3.600e+005
2.835e−003
7.908e−004
3.000e+005
2.363e−003
7.257e−004
2.400e+005
1.890e−003
6.606e−004
1.800e+005
1.418e−003
5.955e−004
1.200e+005
9.451e−004
5.304e−004
6.000e+004
4.726e−004
4.653e−004
0.000e+000
0.000e+000
4.002e−004
metaphyseal region when the limit was scaled to 600 000 Pa, which is vital for primary stability fixation, as it helps to prevent stress shielding at the calcar region. The safety factor computed for this newly designed stem was 2.39, which does not favor endosteal canal fractures. On the other hand, the maximum value for micromotion was less than 20 μm, which ensured the osseointegration between bone–stem interfaced and prevented fibrous tissue formation (not more than 150 μm). In this study, we managed to produce five-stem implants with femoral balls that cost less than $300. The final product is then sandblasted using silicon carbide with a particle size of 180 μm to improve roughness and to promote osseointegration between the bone–implant interface. The study done by Rønold et al. (18) demonstrated better bone ingrowth with only blasted implants compared with acid etching using in situ tensile tests. In addition, the optimal surface roughness expressed as the arithmetic mean deviation is determined to be within a range of 3.62–3.90 μm (18). However, a negative correlation was found while using sand particles bigger than 200 μm for blasting and this did not improve stem fixation (18). Another concern is the use of coating material in the cementless femoral stem especially at the metaphyseal region. Coating material normally has a coarser surface and porous properties that help to increase primary fixation stability and to enhance bone ingrowth. Hydroxyapatite has become a popular coating material for orthopedic implants due to its properties (bioactive calcium phosphate) that reinforce the bone–implant interface mechanical loading. Still, Yoon et al. (19) found no statistical differences in clinical, radiographic, or survival distribution while assessing the effect of hydroxyapatite/
FIG. 2. Finite element analyses for implant prototype: (a) equivalent von Mises stress, (b) micromotion, (c) displacement.
tricalcium phosphate coating on a multilock femoral stem. In this study, coating material was not used based on our belief that the surface roughness of the implant (7.29 μm proximally, 1.61 μm distally) is sufficient for bone ingrowth and the implant’s fixation found in the finite element analysis done prior. Nevertheless, further study is required prior to clinical trial and hopefully this might kick-start the fabrication of low cost cementless femoral stems especially in nondeveloped countries. CONCLUSION We would like to reemphasize the methodical investment casting technique using 316L stainless steel in the fabrication of cementless femoral stems that would reduce cost without endangering the implant’s superiority.Three-dimensional morphology analysis and finite element analysis assisted the researchers and orthopedic surgeons to predict an early result and to correct the problems at the femoral stem design stage. This newly designed femoral stem is more particularly suited to Asians, preventing geometrical mismatch and enhancing better fixation within the femora endosteal canal that may contribute to a longer implant lifetime. Acknowledgments: The authors would like to thank the Foundry Laboratory, Universiti Teknologi Malaysia (UTM) for providing the research facilities especially to Mr. Wan who voluntarily helped during the fabrication process. This research work has been supported by UTM’s Tier 1/Flagship Research Grant, University of Malaya, Ministry of Science and Technology Malaysia (MOSTI), and the Ministry of Higher Education (MOHE). Artif Organs, Vol. 38, No. 7, 2014
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Conflict of Interest: The authors report no conflicts of interest in this work.
Enhanced Beam-Steering-Based Diagonal Beamforming Algorithm for Binaural Hearing Support Devices
REFERENCES 1. Sivarasu S, Beulah P, Mathew L. Novel approach for designing a low weight hip implant used in total hip arthroplasty adopting skeletal design techniques. Artif Organs 2011;35:663–6. 2. Ando M, Imura S, Omori H, Okumura Y, Bo A, Baba H. Nonlinear three-dimensional finite element analysis of newly designed cementless total hip stems. Artif Organs 1999;23:339– 46. 3. Kawahara H, Kokubo Y, Yayama T, et al. Metaphysealloading anterolaterally-flared femoral stem in cementless total hip arthroplasty: five- to eleven-year follow-up evaluation. Artif Organs 2010;34:377–83. 4. Kokubo Y, Uchida K, Oki H, et al. Modified metaphysealloading anterolaterally flared anatomic femoral stem: fiveto nine-year prospective follow-up evaluation and results of three-dimensional finite element analysis. Artif Organs 2013; 37:175–82. 5. Hendra H, Dadan R, Djuansjah JRP. Chapter 17: metals for biomedical applications. In: Fazel-Rezai R, ed. Biomedical Engineering—From Theory to Applications. Croatia: InTech Pub, 2011;411–30. 6. Sivakumar M, Rajeswari S. Investigations of failures in stainless steel orthopaedic implant devices: pit induced stress corrosion cracking. J Mater Sci Lett 1992;11:1039–42. 7. Yang K, Ren Y. Nickel-free austenitic stainless steels for medical applications. Sci Technol Adv Mater 2010;11:1– 13. 8. Okazaki Y. Comparison of fatigue properties and fatigue crack growth rates of various implantable metals. Materials (Basel) 2012;5:2981–3005. 9. Okazaki Y, Gotoh E. Corrosion fatigue properties of metallic biomaterials in Eagle’s medium. Mater Trans 2002;43:2949– 55. 10. Teoh S. Fatigue of biomaterials: a review. Int J Fatigue 2000;22:825–37. 11. Semlitsch M, Willert HG. Properties of implant alloys for artificial hip joints. Med Biol Eng Comput 1980;18:511–20. 12. Khanuja HS, Vakil JJ, Goddard MS, Mont MA. Cementless femoral fixation in total hip arthroplasty. J Bone Joint Surg Am 2011;93:500–9. 13. Baharuddin MY, Zulkifly AH, Lee MH, Kadir MRA, Saat A, Aziz AA. Three dimensional morphometry of the femur to design the total hip arthroplasty for Malay population. Adv Sci Lett 2013;19:2982–7. 14. Baharuddin MY, Zulkifly AH, Lee MH, Kadir MRA, Saat A, Aziz AA. Three dimensional morphometry of proximal femoral medullary canal in Malays. Adv Sci Lett 2013;19: 3582–7. 15. Baharuddin MY, Kadir MRA, Zulkifly AH, Saat A, Aziz AA, Lee MH. Morphology study of the proximal femur in Malay population. Int J Morphol 2011;29:1321–5. 16. Baharuddin MY, Zulkifly AH, Kadir MRA, Saat A, Aziz AA, Lee MH. Morphometric study of the acetabular in Malay population normal hips and its clinical applications. J Med Sci 2011;11:213–9. 17. Carter D, Hayes WC. The behavior of bone as a two-phase porous structure. J Bone Joint Surg 1977;59A:954–62. 18. Rønold HJ, Lyngstadaasb SP, Ellingsena JE. Analysing the optimal value for titanium implant roughness in bone attachment using a tensile test. Biomaterials 2003;24:4559– 64. 19. Yoon KS, Kim J, Lee JH, Kang SB, Seong NH, Koo KH. A randomized clinical trial of cementless femoral stems with and without hydroxyapatite/tricalcium phosphate coating. An 8- to 12-year follow-up study. J Arthroplasty 2007;22:504–8. Artif Organs, Vol. 38, No. 7, 2014
*1Jun Chang Lee, *1Kyoung Won Nam, *Kyeongwon Cho, †Sangmin Lee, ‡Dongwook Kim, §Sung Hwa Hong, *Dong Pyo Jang, and *In Young Kim *Department of Biomedical Engineering, Hanyang University; §Department of Otolaryngology-Head and Neck Surgery, Samsung Medical Center, Seoul; †Department of Electronic Engineering, Inha University, Incheon; and ‡Bio & Health Lab, Samsung Advanced Institute of Technology, Yongin, Korea Abstract: In order to improve speech intelligibility for hearing-impaired people in various listening situations, it is necessary to diversify the possible focusing directions of a beamformer. In a previous report, the concept of binaural beam-steering that can focus a beamformer in diagonal directions was applied to a binaural hearing aid; however, in the previously proposed protocol, the effective frequency range for consistent diagonal beam-steering was limited to the 200–750 Hz range, which is far narrower than that of normal speech signals (200–4000 Hz). In this study, we proposed a modified binaural diagonal beam-steering technique that can reduce the focusing-direction deviations at high input frequencies up to 4000 Hz by introducing a new correction factor to the original protocol that can reduce the differences in gradient between the signal and the noise components at frequencies up to 4000 Hz. In simulation tests, the focusing effect of the proposed algorithm was more consistent than conventional algorithms. The deviations between the target and the focusing directions were reduced 27% in the left device and 6% in the right device with 45° steering at a 4000 Hz input signal, and were reduced 3% in the left device and 25% in the right device with 135° steering. On the basis of the experimental results, we believe that the proposed algorithm has the potential to help hearing-impaired people in various listening situations. Key Words: Beamforming—Beamsteering—Spatial noise reduction—Hearing aids.
People with normal hearing can distinguish a desired speech signal from environmental noises in noisy situations. However, for people with sensorineural hearing impairment, their ability to do so is decreased by deteriorated hearing levels and reduced spectral resolution of the auditory system
doi:10.1111/aor.12219 Received July 2013, revised September 2013. Address correspondence and reprint requests to Dr. In Young Kim, Department of Biomedical Engineering, Hanyang University, Seoul 133-791, Korea. E-mail: [email protected] 1 Jun Chang Lee and Kyoung Won Nam contributed equally to this article and should therefore be regarded as equivalent first authors.
THOUGHTS AND PROGRESS The limitations of this study are a small sample size and not having a nonuremic control group. Results based on a larger sample would be more representative and could be extrapolated on a larger population of HD patients. CONCLUSION Our study contributes to understanding the importance of testosterone in HD patients. We found that testosterone is associated with hemoglobin in male and female HD patients. However, other larger studies are needed, basic as well as clinical, to find out how testosterone acts on endocrine processes in hemodialysis patients and its correlation with cardiovascular diseases. Answers to those questions would contribute to improved treatment, survival, and quality of life of HD patients. Conflict of Interest: We declare that we have no conflict of interest. REFERENCES 1. Parker JP, Beime GJ, Desai JN, Raich PC, Shahidi NT. Androgen-induced increase in red-cell 2,3diphosphoglycerate. N Engl J Med 1972;287:381–3. 2. Sheashaa H, Abdel-Razek W, El-Husseini A, Mohamed Taha N, Elbaz M, Sobh M. Use of nandrolone decanoate as an adjuvant for erythropoietin dose reduction in treating anemia in patients on hemodialysis. Nephron Clin Pract 2005;99: c102–6. 3. Buttner R, Bollheimer LC, Zietz B, et al. Definition and characterization of relative hypo- and hyperleptinemia in a large Caucasian population. J Endocrinol 2002;175:745–56. 4. Bachman E, Feng R, Travison T, et al. Testosterone suppresses hepcidin in men: a potential mechanism for testosteroneinduced erythrocytosis. J Clin Endocrinol Metab 2010;95: 4743–7. 5. Moriyama Y, Fischer JW. Increase in erythroid colony formation in rabbits following the administration of testosterone. Proc Soc Exp Biol Med 1975;149:178–80. 6. Carrero JJ, Barany P, Yilmaz MI, et al. Testosterone deficiency is a cause of anemia and reduced responsiveness to erythropoiesis-stimulating agents in men with chronic kidney disease. Nephrol Dial Transplant 2012;27:709–15. 7. Ferrucci L, Maggio M, Bandinelli S, et al. Low testosterone levels and the risk of anemia in older men and women. Arch Intern Med 2006;166:1380–8. 8. Anantharaman P, Schmidt RJ. Sexual function in chronic kidney disease. Adv Chronic Kidney Dis 2007;14:119–25. 9. Bhatia V, Chaudhuri A, Tomar R, Dhindsa S, Ghanim H, Dandona P. Low testosterone and high C-reactive protein concentrations predict low hematocrit in type 2 diabetes. Diabetes Care 2006;29:2289–94. 10. Grossmann M, Panagiotopolou S, Sharpe K, et al. Low testosterone and anaemia in men with type 2 diabetes. Clin Endocrinol (Oxf) 2009;70:547–53. 11. Shaldon S, Koch KM, Oppermann F, Patyna WD, Schoeppe W. Testosterone therapy for anemia in maintenance dialysis. Br Med J 1971;3:212–5. 12. Kidney Disease: Improving Global Outcomes (KDIGO) Anemia Work Group. KDIGO clinical practice guideline for anemia in chronic kidney disease. Kidney Int Suppl 2012;2: 279–335.
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13. Carrero JJ, Steinvinkel P. The vulnerable man: impact of testosterone deficiency on the uraemic phenotype. Nephrol Dial Transplant 2012;27:4030–41. 14. Griggs RC, Kingston W, Jozefowich RF, Herr BE, Forbes G, Halliday D. Effect of testosterone on muscle mass and muscle protein synthesis. J Appl Physiol 1989;66:498–503. 15. Carrero JJ, Qureshi AR, Parini P, et al. Low serum testosterone increases mortality risk among male dialysis patients. J Am Soc Nephrol 2009;20:613–20. 16. Carrero JJ, Qureshi AR, Nakashima A, et al. Prevalence and clinical implications of testosterone deficiency in men with end-stage renal disease. Nephrol Dial Transplant 2011;26:184– 90.
Fabrication of Low-Cost, Cementless Femoral Stem 316L Stainless Steel Using Investment Casting Technique *†Mohd Yusof Baharuddin, †Sh-Hussain Salleh, ‡Andril Arafat Suhasril, §Ahmad Hafiz Zulkifly, ¶Muhammad Hisyam Lee, **Mohd Afian Omar, ††Ab Saman Abd Kader, †Alias Mohd Noor, †Arief Ruhullah A. Harris, and †Norazman Abdul Majid *Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Lembah Pantai, Kuala Lumpur; †Centre for Biomedical Engineering Transportation Research Alliance; ‡Department of Materials Engineering, Faculty of Mechanical Engineering; ¶Department of Mathematical Sciences, Faculty of Science; ††Transportation Research Alliance, Universiti Teknologi Malaysia, Skudai, Johor; §Department of Orthopaedic, Traumatology & Rehabilitation, Kuliyyah of Medicine, International Islamic University Malaysia, Kuantan, Pahang; and **Advanced Materials Research Center (AMREC), SIRIM Berhad, Kulim, Kedah, Malaysia Abstract: Total hip arthroplasty is a flourishing orthopedic surgery, generating billions of dollars of revenue. The cost associated with the fabrication of implants has been increasing year by year, and this phenomenon has burdened the patient with extra charges. Consequently, this study will focus on designing an accurate implant via implementing the reverse engineering of three-dimensional morphological study based on a particular population. By using finite element analysis, this study will assist to predict the outcome and could become a useful tool for preclinical testing of newly designed implants. A prototype is then fabricated using 316L stainless steel by applying investment casting techniques that reduce manufacturing cost
doi:10.1111/aor.12222 Received June 2013; revised September 2013. Address correspondence and reprint requests to Professor Sh-Hussain Salleh, Centre for Biomedical Engineering Transportation Research Alliance, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia. E-mail: [email protected] Artif Organs, Vol. 38, No. 7, 2014
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without jeopardizing implant quality. The finite element analysis showed that the maximum von Mises stress was 66.88 MPa proximally with a safety factor of 2.39 against endosteal fracture, and micromotion was 4.73 μm, which promotes osseointegration. This method offers a fabrication process of cementless femoral stems with lower cost, subsequently helping patients, particularly those from nondeveloped countries. Key Words: Implant—Hip replacement—Cementless hip—Investment casting.
Total hip arthroplasty (THA) is recognized as the most successful orthopedic surgery to restore the function of the hip joint lost to degenerative diseases such as osteoarthritis and rheumatoid arthritis. The major issues in femoral stems that lead to replacement surgery are fixation stability, aseptic loosening, inappropriate design, wear, and stress shielding (1). Several implant manufacturers have modified the stem to better suit the peculiar hip morphology of the Asian population particularly in terms of the metaphyseal region, femoral head offset size, and isthmus diameter. In general, Asians have smaller builds and different lifestyles that contribute to the differences in the femoral morphology. The University of Fukui has developed a cementless hip stem in accordance with the morphology of the Japanese population focusing on dysplastic hip osteoarthritis that showed successful results in the medium term (2–4). The primary emphasis was the metaphyseal region with a view to preventing micromotion, loosening, and stress shielding predominantly at the proximal calcar. In addition, nonlinear threedimensional finite element analysis was used to simulate physiological loading to predict the early outcome of the implant that allows them to rectify any problems that arise in the design process. Custom-made femoral stems have become an alternative solution to differences in hip morphology. The main reason is that a universal stem with collodiaphyseal angle of 135° does not match all femoral types. Generally, commercial off-the-shelf implants are designed using a western dataset, which differs from Asian morphology. Variable sizes are not the optimal solution to this problem, as similar designs still apply, leading to a geometrical mismatch between the stem and the patient. Bigger stems risk more cancellous bone in the endosteal canal, along with over reaming and bone fractures. On the other hand, smaller stems cause under sizing, aseptic loosening, and bone atrophy. Consequently, a custommade stem has been chosen as it is tailored in line with individual morphology, and optimized fitting and filling in endosteal canal provides better fixation stability and promotes osseointegration. However, increments in cost and time are other factors that Artif Organs, Vol. 38, No. 7, 2014
need to be considered. This phenomenon has led to a newly designed femoral stem based on specific characteristics of the population. The excellent results shown by the University of Fukui prove that this approach could be applied in cementless femoral stem development. Cutting-edge technology in three-dimensional reverse engineering helps to produce an accurate implant that is well suited to the actual morphology of the bone. In this present study, we fabricated a cementless hip stem that not only optimally fits and fills the medullary canal but also reduces the cost of the implant itself. This systematic methodology is based on a three-dimensional morphological analysis of the Malaysian population and is based on a precise implant designed to comply with the patient’s anatomy. The performance of nonlinear finite element analysis was used to predict the outcome and to rectify design flaws, allowing for the development of a prototype cementless stem and the fabrication of this stem using investment casting techniques. The 316L stainless steel is chosen over titanium and cobalt chrome as it is cheaper in price and its properties are widely accepted as an orthopedic prosthesis (1). Despite the advantages of its mechanical properties, there are several concerns regarding these metallic alloys. First, toxic effects (with release of metal ions) are caused by leaching, wear, and corrosion (5). Sivakumar and Rajeswari (6) reported that 90% of the implants failure made by this alloy is ascribable to pitting and crevice corrosion attack. However, Yang and Ren (7) suggested nickel element replacement with high-nitrogen that produced a stable austenitic phase, high strength and good plasticity, better corrosion and wear resistance, and superior biocompatibility. Second, the fatigue strength of 316L stainless steel is inferior to cobalt chrome alloy and titanium alloy. Several studies reported the fatigue strength of 316L stainless steel at 107 cycles (8–11). The stress/life (S/N) curves from fatigue test using Eagle’s medium at 37°C for 316L stainless steel illustrated maximum stress of 320 MPa after 107 cycles (8). Despite its material properties, the implant design also made a crucial contribution to features of fatigue failure (5). Khanuja et al. (12) pointed out that the excellent survival rates of a cementless femoral stem are attributed to the stem’s geometrical design rather than the choice of material and fixation surface. In this study, the femoral stem is designed based on local anatomical features, and deliberate considerations are taken into account before fabrication. We believe that finite element analysis might become a useful tool for preclinical testing of newly designed implants. The finite element could become a “safety measure” for
THOUGHTS AND PROGRESS new stems before clinical trials. As the cost of the cementless stem has increased each year, aligned with the increment of THA performed worldwide, we are highlighting a methodology that is reproducible and could help to reduce the cost without jeopardizing quality. It is strongly hypothesized that this method would be beneficial particularly to nondeveloped countries such as those in Asia, which may not be able to afford the hip implant surgery costs that increase each year. MATERIALS AND METHODS We prospectively acquired the computed tomography (CT) images from 60 healthy hips prior to designing the cementless femoral stem in accordance with the peculiar morphology of the Asian population (13– 16). The design process used a three-dimensional femora model that provides more anthropometric
De-waxing shell in firing furnace at 800°C
Wax implant invested into ceramic slurry, and stuccoed with layers of zirconla sand to form shell
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information and accurate measurement. The cementless femoral stem was designed to optimally fit and fill the endosteal canal as shown in Fig. 1. Interquartile range descriptive analysis was used as the stem design profile, and nonlinear finite element analysis was conducted to predict the outcome of the early stage after the surgery according to the standard protocol of virtual implantation (2–4). After designing the stem based on the morphology analysis, we performed finite element analysis using different software such as Marc/Mentat software (MSC Software, Santa Ana, CA, USA). The finite element model for the cementless femoral stem consisted of 4226 nodes and 13 241 elements, whereas the “virtual surgery femora” consisted of 7946 nodes and 41 900 elements. The 3D femora model chosen for finite element study was the “average” femora from the previous study (13–16). The material properties of the cementless femoral stem were assigned as 316L stainless steel
316L molten stainless steel (at 1600°C) poured into implant shell
Knock out shell after cooling, sand blast with nano size silicon carbide
Design of cementless femoral sand blast on morphology study
FIG. 1. Fabrication process of the low cost cementless femoral stem of 316L stainless steel using investment casting technique.
Wax injection into the mould to form pattern. The pouring cup, sprue and riser were wax welded on pattern
Implant mould using silicone rubber compound
Cementless femoral stem using rapid prototype machine
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with a Young’s Modulus of 200 GPa and a Poisson’s ratio of 0.3 (2). In addition, the femora were assumed as isotropic and linear elastic, with bone properties determined according to the CT datasets’ gray level values.The correlation proposed by Carter and Hayes between the modulus of elasticity of the bone, E, and its apparent density was used in this study as shown in Eq. 1 (17). The cancellous and cortical bones are assumed merely at different ends of a continuum spectrum.
E = 3790 ρ3
(1)
The physiological loading mimicked stair climbing with an assumed body weight of 71 kg, given forces Fx = −709.2 N, Fy = 600.8 N, Fz = 1553.2 N, and applied moment of Mx = −123.9 Nm, My = 25 Nm (2). The finite element model was completely restrained distally. This present study will look at stress shielding, micromotion, and displacement. We proposed a new investment casting technique that may decrease the existing cost and time consumed during the fabrication process of the cementless femoral stem. The implant’s prototype was converted from three-dimensional stereo lithographic formats into slices 0.085-mm thick using a rapid prototype machine (ZPrinter 310, 3D Systems, Rock Hill, SC, USA). The prototype is then depowdered, infiltrated with resin to ensure its durability, and allowed to dry. The silicone rubber compounds (RTV560, Momentive Performance Materials Inc., Albany, New York, USA) for high–low temperature potting, encapsulating, and sealing were used as the mould. This silicon elastomer is mixed homogenously with dibutyl tin dilaurate, which acts as a regular curing agent. The RTV560 base compound might continuously retain elastomeric properties up to 260°C and up to 316°C for a short duration, which is suitable during the wax injection process. The investment casting process commenced by injecting the melted wax into the silicone rubber compound mould producing the implant’s casting that are called patterns. These patterns were then attached (wax welded) to another three parts: (i) pouring cup (bigger size funnel shape than pattern that is attached at the proximal region to allow molten metal to flow inside the shell); (ii) sprue (smaller size funnel that connects the pouring cup and pattern); and (iii) riser (cylindrical shape attached at distal part to allow uniform flow of molten metal). The more general method that uses the central sprue to produce the wax patterns was not utilized, resulting in reducing the amount of molten Artif Organs, Vol. 38, No. 7, 2014
316L stainless steel to be used later and decreasing the fabrication cost. The pattern is injected into the ceramic slurry, a mixture of 25% colloidal silica and zirconia sand (ASTM 325), which is stirred homogenously nonstop until the process is finished. Using coarser aluminum silicate sand (ASTM 20–70), a six-layer shell is formed before it is finally dipped into the ceramic slurry to seal it. The shell must be well built to endure high temperatures in the calcined process that later takes place in the firing furnace at 800°C for 2 h to remove the wax residue. The 316L stainless steel is heated in an induction furnace (Inductotherm Group, Victoria, Australia) at 1600°C. The molten metal is poured through the pouring cup into the shell by using the standard gravity and pouring method. After the 2-h cooling, the shell is knocked out, and other parts are removed using a metal saw blade. The prototype is subsequently sand blasted using 2.0 bar, 180 μm silicon carbide mesh using a blasting machine (CSMG25/Adhesion, CemeCon, Wuerselen, Germany). The prototype surface roughness is measured using a hybrid surface contour machine (Formtracer CS-5000, Mitutoyo America Company, IL, USA). The parameters are set to a measured length of 5 mm, a measurement pitch of 0.0010 mm, speed 0.1 mm/s, roughness pitch of 0.0005 mm, and a cutoff at 0.8. We measured two different regions, proximal and distal, and divided the region into five areas. RESULTS The three-dimensional morphology analysis provided sufficient information regarding the periosteal and endosteal canal size of the femora. In this study, we used these parameters for our newly designed femoral stem: femoral head offset (FHO), the isthmus position, collo-diaphyseal angle (CDA), and endosteal canal diameter at certain levels especially in the metaphyseal region. The FHO showed 30.55 mm horizontally and 52.72 mm vertically with CDA 130.68° and isthmus position at 112.83 mm from the center of the lesser trochanter. We found that the maximum stress was 66.88 MPa at the proximal region, and minimum stress was 7.75 × 10−12 Pa at distal region as illustrated in Fig. 2. In addition, the maximum value for micromotion was 4.73 μm and displacement of 6.47 μm. The surface roughness of the cementless femoral stem was shown to be 7.287 μm proximally and 1.613 μm distally. DISCUSSION From the finite element analysis, we discovered that the stress was normally distributed at the
THOUGHTS AND PROGRESS a Pa
b mm
607
c mm
6.000e+005
4.726e−003
1.051e−003
5.400e+005
4.253e−003
9.861e−004
4.800e+005
3.780e−003
9.210e−004
4.200e+005
3.308e−003
8.559e−004
3.600e+005
2.835e−003
7.908e−004
3.000e+005
2.363e−003
7.257e−004
2.400e+005
1.890e−003
6.606e−004
1.800e+005
1.418e−003
5.955e−004
1.200e+005
9.451e−004
5.304e−004
6.000e+004
4.726e−004
4.653e−004
0.000e+000
0.000e+000
4.002e−004
metaphyseal region when the limit was scaled to 600 000 Pa, which is vital for primary stability fixation, as it helps to prevent stress shielding at the calcar region. The safety factor computed for this newly designed stem was 2.39, which does not favor endosteal canal fractures. On the other hand, the maximum value for micromotion was less than 20 μm, which ensured the osseointegration between bone–stem interfaced and prevented fibrous tissue formation (not more than 150 μm). In this study, we managed to produce five-stem implants with femoral balls that cost less than $300. The final product is then sandblasted using silicon carbide with a particle size of 180 μm to improve roughness and to promote osseointegration between the bone–implant interface. The study done by Rønold et al. (18) demonstrated better bone ingrowth with only blasted implants compared with acid etching using in situ tensile tests. In addition, the optimal surface roughness expressed as the arithmetic mean deviation is determined to be within a range of 3.62–3.90 μm (18). However, a negative correlation was found while using sand particles bigger than 200 μm for blasting and this did not improve stem fixation (18). Another concern is the use of coating material in the cementless femoral stem especially at the metaphyseal region. Coating material normally has a coarser surface and porous properties that help to increase primary fixation stability and to enhance bone ingrowth. Hydroxyapatite has become a popular coating material for orthopedic implants due to its properties (bioactive calcium phosphate) that reinforce the bone–implant interface mechanical loading. Still, Yoon et al. (19) found no statistical differences in clinical, radiographic, or survival distribution while assessing the effect of hydroxyapatite/
FIG. 2. Finite element analyses for implant prototype: (a) equivalent von Mises stress, (b) micromotion, (c) displacement.
tricalcium phosphate coating on a multilock femoral stem. In this study, coating material was not used based on our belief that the surface roughness of the implant (7.29 μm proximally, 1.61 μm distally) is sufficient for bone ingrowth and the implant’s fixation found in the finite element analysis done prior. Nevertheless, further study is required prior to clinical trial and hopefully this might kick-start the fabrication of low cost cementless femoral stems especially in nondeveloped countries. CONCLUSION We would like to reemphasize the methodical investment casting technique using 316L stainless steel in the fabrication of cementless femoral stems that would reduce cost without endangering the implant’s superiority.Three-dimensional morphology analysis and finite element analysis assisted the researchers and orthopedic surgeons to predict an early result and to correct the problems at the femoral stem design stage. This newly designed femoral stem is more particularly suited to Asians, preventing geometrical mismatch and enhancing better fixation within the femora endosteal canal that may contribute to a longer implant lifetime. Acknowledgments: The authors would like to thank the Foundry Laboratory, Universiti Teknologi Malaysia (UTM) for providing the research facilities especially to Mr. Wan who voluntarily helped during the fabrication process. This research work has been supported by UTM’s Tier 1/Flagship Research Grant, University of Malaya, Ministry of Science and Technology Malaysia (MOSTI), and the Ministry of Higher Education (MOHE). Artif Organs, Vol. 38, No. 7, 2014
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Conflict of Interest: The authors report no conflicts of interest in this work.
Enhanced Beam-Steering-Based Diagonal Beamforming Algorithm for Binaural Hearing Support Devices
REFERENCES 1. Sivarasu S, Beulah P, Mathew L. Novel approach for designing a low weight hip implant used in total hip arthroplasty adopting skeletal design techniques. Artif Organs 2011;35:663–6. 2. Ando M, Imura S, Omori H, Okumura Y, Bo A, Baba H. Nonlinear three-dimensional finite element analysis of newly designed cementless total hip stems. Artif Organs 1999;23:339– 46. 3. Kawahara H, Kokubo Y, Yayama T, et al. Metaphysealloading anterolaterally-flared femoral stem in cementless total hip arthroplasty: five- to eleven-year follow-up evaluation. Artif Organs 2010;34:377–83. 4. Kokubo Y, Uchida K, Oki H, et al. Modified metaphysealloading anterolaterally flared anatomic femoral stem: fiveto nine-year prospective follow-up evaluation and results of three-dimensional finite element analysis. Artif Organs 2013; 37:175–82. 5. Hendra H, Dadan R, Djuansjah JRP. Chapter 17: metals for biomedical applications. In: Fazel-Rezai R, ed. Biomedical Engineering—From Theory to Applications. Croatia: InTech Pub, 2011;411–30. 6. Sivakumar M, Rajeswari S. Investigations of failures in stainless steel orthopaedic implant devices: pit induced stress corrosion cracking. J Mater Sci Lett 1992;11:1039–42. 7. Yang K, Ren Y. Nickel-free austenitic stainless steels for medical applications. Sci Technol Adv Mater 2010;11:1– 13. 8. Okazaki Y. Comparison of fatigue properties and fatigue crack growth rates of various implantable metals. Materials (Basel) 2012;5:2981–3005. 9. Okazaki Y, Gotoh E. Corrosion fatigue properties of metallic biomaterials in Eagle’s medium. Mater Trans 2002;43:2949– 55. 10. Teoh S. Fatigue of biomaterials: a review. Int J Fatigue 2000;22:825–37. 11. Semlitsch M, Willert HG. Properties of implant alloys for artificial hip joints. Med Biol Eng Comput 1980;18:511–20. 12. Khanuja HS, Vakil JJ, Goddard MS, Mont MA. Cementless femoral fixation in total hip arthroplasty. J Bone Joint Surg Am 2011;93:500–9. 13. Baharuddin MY, Zulkifly AH, Lee MH, Kadir MRA, Saat A, Aziz AA. Three dimensional morphometry of the femur to design the total hip arthroplasty for Malay population. Adv Sci Lett 2013;19:2982–7. 14. Baharuddin MY, Zulkifly AH, Lee MH, Kadir MRA, Saat A, Aziz AA. Three dimensional morphometry of proximal femoral medullary canal in Malays. Adv Sci Lett 2013;19: 3582–7. 15. Baharuddin MY, Kadir MRA, Zulkifly AH, Saat A, Aziz AA, Lee MH. Morphology study of the proximal femur in Malay population. Int J Morphol 2011;29:1321–5. 16. Baharuddin MY, Zulkifly AH, Kadir MRA, Saat A, Aziz AA, Lee MH. Morphometric study of the acetabular in Malay population normal hips and its clinical applications. J Med Sci 2011;11:213–9. 17. Carter D, Hayes WC. The behavior of bone as a two-phase porous structure. J Bone Joint Surg 1977;59A:954–62. 18. Rønold HJ, Lyngstadaasb SP, Ellingsena JE. Analysing the optimal value for titanium implant roughness in bone attachment using a tensile test. Biomaterials 2003;24:4559– 64. 19. Yoon KS, Kim J, Lee JH, Kang SB, Seong NH, Koo KH. A randomized clinical trial of cementless femoral stems with and without hydroxyapatite/tricalcium phosphate coating. An 8- to 12-year follow-up study. J Arthroplasty 2007;22:504–8. Artif Organs, Vol. 38, No. 7, 2014
*1Jun Chang Lee, *1Kyoung Won Nam, *Kyeongwon Cho, †Sangmin Lee, ‡Dongwook Kim, §Sung Hwa Hong, *Dong Pyo Jang, and *In Young Kim *Department of Biomedical Engineering, Hanyang University; §Department of Otolaryngology-Head and Neck Surgery, Samsung Medical Center, Seoul; †Department of Electronic Engineering, Inha University, Incheon; and ‡Bio & Health Lab, Samsung Advanced Institute of Technology, Yongin, Korea Abstract: In order to improve speech intelligibility for hearing-impaired people in various listening situations, it is necessary to diversify the possible focusing directions of a beamformer. In a previous report, the concept of binaural beam-steering that can focus a beamformer in diagonal directions was applied to a binaural hearing aid; however, in the previously proposed protocol, the effective frequency range for consistent diagonal beam-steering was limited to the 200–750 Hz range, which is far narrower than that of normal speech signals (200–4000 Hz). In this study, we proposed a modified binaural diagonal beam-steering technique that can reduce the focusing-direction deviations at high input frequencies up to 4000 Hz by introducing a new correction factor to the original protocol that can reduce the differences in gradient between the signal and the noise components at frequencies up to 4000 Hz. In simulation tests, the focusing effect of the proposed algorithm was more consistent than conventional algorithms. The deviations between the target and the focusing directions were reduced 27% in the left device and 6% in the right device with 45° steering at a 4000 Hz input signal, and were reduced 3% in the left device and 25% in the right device with 135° steering. On the basis of the experimental results, we believe that the proposed algorithm has the potential to help hearing-impaired people in various listening situations. Key Words: Beamforming—Beamsteering—Spatial noise reduction—Hearing aids.
People with normal hearing can distinguish a desired speech signal from environmental noises in noisy situations. However, for people with sensorineural hearing impairment, their ability to do so is decreased by deteriorated hearing levels and reduced spectral resolution of the auditory system
doi:10.1111/aor.12219 Received July 2013, revised September 2013. Address correspondence and reprint requests to Dr. In Young Kim, Department of Biomedical Engineering, Hanyang University, Seoul 133-791, Korea. E-mail: [email protected] 1 Jun Chang Lee and Kyoung Won Nam contributed equally to this article and should therefore be regarded as equivalent first authors.
