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Bone Composite Implants
Oral and Poster Presentations / Journal of Biomechanics 43S1 (2010) S23–S74
especially as hard tissue replacements, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet sufficiently all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. In recent years, many research efforts have been concentrated on the development of surface modification techniques like mechanical, laser, thermal, sol–gel, chemical and electrochemical treatments etc. for titanium and its alloys [1]. Recent works have shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively by appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained [2]. Ti6Al4V alloy has been widely used as a suitable material for surgical implants such as artificial hip joints. These materials possess outstanding corrosion resistance due to a dense and passive oxide film on the surface. Although this alloy is biocompatible, its wear resistance is inadequate. Therefore, grid-blasting method as one of the mechanical modification techniques is used to obtain specific surface topographies and roughness, remove surface contamination, improve the mechanical and biological adhesion in hard tissues. The blasting materials like alumina (Al2 O3 ), zirconia (ZrO2 ), silica (SiO2 ), hydroxyapatite (HA) etc. are frequently used as a blasting media to obtain improved surface properties. The blasting process applied for the surface properties of titanium based implant materials is widely used in medical applications. Nowadays, ZrO2 /SiO2 and HA blasting powders are performed extensively, the surfaces of Ti-based implant materials to modify surface topography and to improve biocompatibility of the Ti-based implant materials. In this study, the surfaces of Ti6Al4V (Grade 5) samples are blasted by different ratio of ZrO2 /HA powders. The blasted samples are characterized by several techniques such as scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), X-ray diffractiometry (XRD), X-ray fluorescence spectrometry (XRF), and profilometry. The blasting process leads to an improvement in the chemical, topographical and biocompatibility characteristics of the samples. The dry sliding wear test of the samples is performed using pin-on disc equipment. The worn surfaces are characterized by SEM to determine the wear characteristic of Ti-based blasted material. Reference(s) [1] Xuanyong Liu, Paul K. Chu, Chuanxian Ding, “Surface modification of titanium, titanium alloys, and related materials for biomedicals applications”, Materials Science and Engineering: R: Reports 47(3–4): pp. 49–121. [2] Yukari Iwaya, Miho Machigashira, Kenji Kanbara, Motoharu Miyamoto, Kazuyuki Noguchi, Yuichi Izumi and Seiji Ban, “Surface Properties and Biocompatibility of Acid-etched-Titanium”, Dental Materials Journal 2008; 27(3): pp. 415–421.
M-14 Design, Preparation and Mechanical Properties of Layered Bionic Artificial Articular Cartilage/Bone Composite Implants Y. Ma1 , Y. Zheng1 , W. Song2 , T. Hu1 , T. Xi1 , X. Huang1 , H. Yang1 . 1 Beijing University of Science and Technology, China; 2 Brunel University, UK Articular cartilage in adults has a limited ability for self-repair in response to injury, wear or disease. Surgical treatments available today usually generate a repair tissue that is insufficient in absorbing or distributing loads and is prone to failure. Consequently, a large number of radical knee joint replacements are performed or repeated each year worldwide. Despite many advances, development of artificial articular cartilages with high biomechanical and biocompatible properties is a still significant challenge. Inspired from the structural characteristics of human’s mature articular cartilage, a kind of layered bionic artificial articular
S57
cartilage/bone composite implants were developed by using various methods of the ultrasonic dispersion, cyclic freezing-melting and radiation cross-linking. The layered bionic artificial articular cartilages were designed and made from different polyvinyl alcohol (PVA)-based biomaterials owing to their desired properties. The surface layer of polyvinyl pyrrolidine (PVP)/PVA blend served as a lubrication layer (Zheng et al., 2008). The bottom of bioglasses (BG)/PVA composites contributed to both bioactivity and mechanical properties (Ma et al., 2010). The middle layer of pure PVA hydrogel acted as a transitional link layer, like a ‘soft cushion’. The composite implants were fabricated by assembling the layered bionic artificial cartilages and the allogeneic bones in vitro. In clinic such composites can be readily implanted to the defect by connecting it with subchondral bone. The mechanical properties of these composite implants, such as elastic modulus and friction coefficient, were studied in this work. In simulated body fluid, the changes of the structure and shear strength at interfaces between artificial cartilage and bone were investigated. The results showed that the stress-strain curves of the composite implants were non-linear. The compression elastic modulus varied within a range of 1.6 to 2.23 MPa, depending on the BG or PVA content as well as the thickness of PVA hydrogel. After the treatment of 60 Co radiation (dose 20 kGy), the highest elastic modulus of the composite was achieved. With PVP content of 40 wt% in PVP/PVA blend, the friction coefficient of the composite implant surface fell to 0.080. In vitro experiments showed that a layer of crystalline bonelike hydroxyapatite carbonate (HCA) was formed at the interface between artificial cartilage and bone as the immersion proceeded, as a result, the shear strength of the interfaces reached 1.21 MPa. Reference(s) [1] Yanxuan Ma, Yudong Zheng, Xiaoshan Huang, Tingfei Xi, Xiaodan Lin, Dongfei Han and Wenhui Song, Mineralization behaviour and interface properties of BG-PVA/bone composite implants in simulated body fluid, Biomedical Materials 5 (2) (2010), 025003. [2] Yudong Zheng, Xiaoshan Huang, Yingjun Wang, Tingfei Xi, Xiaofeng Chen and Hong Xu, The surface lubricative properties of PVA/PVP hydrogels treated with radiation used as artificial cartilage, Applied Surface Science 255(2) (2008), pp. 568–570.
Acknowledgments: This study is financially supported by National Nature Science Foundation of China Project (Grant No. 50773004) M-15 Finite Element Analysis of Porous Bio-Hydrogel With Negative Poisson’s Ratio D. Han1 , Y. Zheng1 , W. Song2 , Y. Ma1 , T. Xi1 . 1 Beijing University of Science and Technology, China; 2 Brunel University, UK Natural auxetic biomaterials can be found in many smart biological systems, such as cytoskeleton membranes of red blood cells, lipid bilayers of cells, cow teat skin, cat skin and organisms in the deep ocean. Use of auxetic feature may help animals to resist the pressure from the environment and reduce the internal stress while preserving their body dimensions. Some efforts have been made to incorporate synthetic auxetic foams into medical implants, such as arterial prostheses and artificial intervertebral discs, in order to reduce the pressure and shear stress to the surrounding soft tissues. However, the low bulk modulus and limited biocompatibility of existing auxetic porous materials hinder the further development of their bio-medical applications. Polymer hydrogels with high water content, high mechanical properites, good chemical stability and durability are promising substitute biomaterials for soft and tough tissue (articular cartilage, artery, ligament etc) for their good biocompatibility in contact with human tissues. So far, hydrogels formed through either the covalent crosslinking or noncovalent physical crosslinking hardly show auxetic behaviour. Meanwhile, all the theoretic models to describe auxetic biomaterials do not fit to hydrogels because of its super entropic elasticity and high water medium content. Only
especially as hard tissue replacements, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet sufficiently all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. In recent years, many research efforts have been concentrated on the development of surface modification techniques like mechanical, laser, thermal, sol–gel, chemical and electrochemical treatments etc. for titanium and its alloys [1]. Recent works have shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively by appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained [2]. Ti6Al4V alloy has been widely used as a suitable material for surgical implants such as artificial hip joints. These materials possess outstanding corrosion resistance due to a dense and passive oxide film on the surface. Although this alloy is biocompatible, its wear resistance is inadequate. Therefore, grid-blasting method as one of the mechanical modification techniques is used to obtain specific surface topographies and roughness, remove surface contamination, improve the mechanical and biological adhesion in hard tissues. The blasting materials like alumina (Al2 O3 ), zirconia (ZrO2 ), silica (SiO2 ), hydroxyapatite (HA) etc. are frequently used as a blasting media to obtain improved surface properties. The blasting process applied for the surface properties of titanium based implant materials is widely used in medical applications. Nowadays, ZrO2 /SiO2 and HA blasting powders are performed extensively, the surfaces of Ti-based implant materials to modify surface topography and to improve biocompatibility of the Ti-based implant materials. In this study, the surfaces of Ti6Al4V (Grade 5) samples are blasted by different ratio of ZrO2 /HA powders. The blasted samples are characterized by several techniques such as scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), X-ray diffractiometry (XRD), X-ray fluorescence spectrometry (XRF), and profilometry. The blasting process leads to an improvement in the chemical, topographical and biocompatibility characteristics of the samples. The dry sliding wear test of the samples is performed using pin-on disc equipment. The worn surfaces are characterized by SEM to determine the wear characteristic of Ti-based blasted material. Reference(s) [1] Xuanyong Liu, Paul K. Chu, Chuanxian Ding, “Surface modification of titanium, titanium alloys, and related materials for biomedicals applications”, Materials Science and Engineering: R: Reports 47(3–4): pp. 49–121. [2] Yukari Iwaya, Miho Machigashira, Kenji Kanbara, Motoharu Miyamoto, Kazuyuki Noguchi, Yuichi Izumi and Seiji Ban, “Surface Properties and Biocompatibility of Acid-etched-Titanium”, Dental Materials Journal 2008; 27(3): pp. 415–421.
M-14 Design, Preparation and Mechanical Properties of Layered Bionic Artificial Articular Cartilage/Bone Composite Implants Y. Ma1 , Y. Zheng1 , W. Song2 , T. Hu1 , T. Xi1 , X. Huang1 , H. Yang1 . 1 Beijing University of Science and Technology, China; 2 Brunel University, UK Articular cartilage in adults has a limited ability for self-repair in response to injury, wear or disease. Surgical treatments available today usually generate a repair tissue that is insufficient in absorbing or distributing loads and is prone to failure. Consequently, a large number of radical knee joint replacements are performed or repeated each year worldwide. Despite many advances, development of artificial articular cartilages with high biomechanical and biocompatible properties is a still significant challenge. Inspired from the structural characteristics of human’s mature articular cartilage, a kind of layered bionic artificial articular
S57
cartilage/bone composite implants were developed by using various methods of the ultrasonic dispersion, cyclic freezing-melting and radiation cross-linking. The layered bionic artificial articular cartilages were designed and made from different polyvinyl alcohol (PVA)-based biomaterials owing to their desired properties. The surface layer of polyvinyl pyrrolidine (PVP)/PVA blend served as a lubrication layer (Zheng et al., 2008). The bottom of bioglasses (BG)/PVA composites contributed to both bioactivity and mechanical properties (Ma et al., 2010). The middle layer of pure PVA hydrogel acted as a transitional link layer, like a ‘soft cushion’. The composite implants were fabricated by assembling the layered bionic artificial cartilages and the allogeneic bones in vitro. In clinic such composites can be readily implanted to the defect by connecting it with subchondral bone. The mechanical properties of these composite implants, such as elastic modulus and friction coefficient, were studied in this work. In simulated body fluid, the changes of the structure and shear strength at interfaces between artificial cartilage and bone were investigated. The results showed that the stress-strain curves of the composite implants were non-linear. The compression elastic modulus varied within a range of 1.6 to 2.23 MPa, depending on the BG or PVA content as well as the thickness of PVA hydrogel. After the treatment of 60 Co radiation (dose 20 kGy), the highest elastic modulus of the composite was achieved. With PVP content of 40 wt% in PVP/PVA blend, the friction coefficient of the composite implant surface fell to 0.080. In vitro experiments showed that a layer of crystalline bonelike hydroxyapatite carbonate (HCA) was formed at the interface between artificial cartilage and bone as the immersion proceeded, as a result, the shear strength of the interfaces reached 1.21 MPa. Reference(s) [1] Yanxuan Ma, Yudong Zheng, Xiaoshan Huang, Tingfei Xi, Xiaodan Lin, Dongfei Han and Wenhui Song, Mineralization behaviour and interface properties of BG-PVA/bone composite implants in simulated body fluid, Biomedical Materials 5 (2) (2010), 025003. [2] Yudong Zheng, Xiaoshan Huang, Yingjun Wang, Tingfei Xi, Xiaofeng Chen and Hong Xu, The surface lubricative properties of PVA/PVP hydrogels treated with radiation used as artificial cartilage, Applied Surface Science 255(2) (2008), pp. 568–570.
Acknowledgments: This study is financially supported by National Nature Science Foundation of China Project (Grant No. 50773004) M-15 Finite Element Analysis of Porous Bio-Hydrogel With Negative Poisson’s Ratio D. Han1 , Y. Zheng1 , W. Song2 , Y. Ma1 , T. Xi1 . 1 Beijing University of Science and Technology, China; 2 Brunel University, UK Natural auxetic biomaterials can be found in many smart biological systems, such as cytoskeleton membranes of red blood cells, lipid bilayers of cells, cow teat skin, cat skin and organisms in the deep ocean. Use of auxetic feature may help animals to resist the pressure from the environment and reduce the internal stress while preserving their body dimensions. Some efforts have been made to incorporate synthetic auxetic foams into medical implants, such as arterial prostheses and artificial intervertebral discs, in order to reduce the pressure and shear stress to the surrounding soft tissues. However, the low bulk modulus and limited biocompatibility of existing auxetic porous materials hinder the further development of their bio-medical applications. Polymer hydrogels with high water content, high mechanical properites, good chemical stability and durability are promising substitute biomaterials for soft and tough tissue (articular cartilage, artery, ligament etc) for their good biocompatibility in contact with human tissues. So far, hydrogels formed through either the covalent crosslinking or noncovalent physical crosslinking hardly show auxetic behaviour. Meanwhile, all the theoretic models to describe auxetic biomaterials do not fit to hydrogels because of its super entropic elasticity and high water medium content. Only