Bioceramics 17

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Authors: G. Göller, Faik N. Oktar, Simeon Agathopoulos, D.U. Tulyaganov, José Maria F. Ferreira, E.S. Kayali, Ismail Peker
Abstract: The influence of sintering temperature on densification, microstructure and the mechanical properties of bovine hydroxyapatite (BHA), produced by a calcination method, was investigated. Densification and mechanical properties increased over increasing sintering temperature in the range between 1000°C and 1300°C, and there are evidences of optimum sintering temperature at 1200°C. The measured mechanical properties indicate sintered BHA-bodies as interesting biomaterials for further investigation in biomedical applications.
Authors: Akari Takeuchi, Chikara Ohtsuki, Masanobu Kamitakahara, Shinichi Ogata, Masao Tanihara, Toshiki Miyazaki, Masao Yamazaki, Yoshiaki Furutani, Hisao Kinoshita
Abstract: Porous a-tricalcium phosphate (a-TCP) ceramics are attractive as a novel bioresorbable material for bone repair, since they can be easily fabricated through conventional sintering of b-TCP at high temperature. However, the solubility of a-TCP is too high to keep its body until the bone defect is repaired completely. Coating of the a-TCP porous body with organic polymer is a way to reduce the degradation rate. In the present study, biodegradation of a-TCP porous body coated with silk sericin was evaluated in vivo. Bone repair at the defect made in rabbit tibia was nearly completed after 4 weeks. Higher density of cortical bone was estimated for a-TCP coated with sericin than for mere a-TCP. The a-TCP porous body coated with sericin is expected as a material that show less degradation than mere a-TCP, and may result in suitable bone repair.
Authors: A.B. Diggs, J.W. Halloran, S.J. Hollister
Abstract: This paper describes the investigation into the use of cathodoluminescence for distinguishing HA and β-TCP phases within the biphasic calcium phosphate ceramic microstructure. Polished samples were scanned using SEM-CL at an accelerating voltage in the range of 10-15 keV with a beam current of 5-10 nA. The grayscale images produced reveal distinctive patterns for each composition. EDS and EPMA suggest chemical differences among the contrasting regions. Image analysis of voxel values indicate that areas of bright contrast correspond to β-TCP grains with phase amounts confirmed by XRD.
Authors: Y. Cao, Bo Zhang, Li Ping Wang, Qiang Lin, Xu Dong Li, C.Y. Bao, Ji Yong Chen, Bang Cheng Yang, L. Yang, Xing Dong Zhang
Abstract: Plasma-sprayed hydroxyapatite coating on metal substrate has been prepared, two kinds of post-treatment methods have been used: (1) Heating in air at 650°C for 30 min, (2) Heating in water vapor at 125°C, 0.15Mpa for 6 hours. XRD showed that the nanocrystals of HA coating increased after water vapor treated. The interfacial tensiles strength between HA and the substrate were 45.0±1.82MPa, 39.1±1.27MPa and 30.3±1.61MPa for as-received coatings, water vapor treated coatings and heated in air coatings respectively. After 3 months implant in dogs limbs, the push-out strength between implants and bone were 11.27±2.71 MPa, 11.63±3.11MPa, 23.92± 2.01MPa and 18.8±1.82 MPa for pure Ti implants, as-received coating implants, water vapor treated implants and heated in air implants respectively. The results showed that the water vapor post treated HA coating have better mechanical behavior in vitro and in vivo.
Authors: Cláudia M.S. Ranito, Fernando A. Costa Oliveira, João P. Borges
Abstract: Hydroxyapatite, often in the form of synthetic porous blocks, has been used in the repair of bone defects for over 20 years owing to its biocompatibility and osseoconductive behaviour. Bone ingrowth requires the existence of open and interconnected pores with diameters larger than 150 µm for proper circulation of nutrients. Hence, currently available materials are characterised by poor mechanical properties. Collapse of such products is therefore a major source of concern to surgeons using these weak materials in bone surgery. There is a need to develop stronger highly porous structures through adequate control over the size, shape and volume fraction of pores. In this work, highly porous open-cell hydroxyapatite foams were fabricated by the polymer foam replication process, where two types of polyurethane (PU) foams were infiltrated with optimised slurries containing appropriate binders and ceramic particles, followed by the removal of excess slurry, burning out of the polymer to leave a ceramic replica of the polyurethane and finally high temperature sintering. Open-cell HAP foams with porosities of about 80% were obtained, i.e. 30% higher than that determined for commercial ones (50%). Many of the commercial foam cells approach 500 µm in diameter whereas the developed foam cell size ranged from 300 up to 500 µm. The ultimate compressive strength of the developed foams (1-2 MPa) was found to be higher than that recorded for the commercial ones (0.7 MPa) indicating that these foams can more easily be modelled in theatre. Both the elastic moduli and the compressive strength of the developed foams were found to increase with increasing of the relative density, in accordance with the predictions of available micro-mechanical models.
Authors: F.P. Cox, Michael J. Pomeroy, M.E. Murphy
Abstract: A commercially available hydroxyapatite (HA) was sintered for a number of sintering temperatures and times between 1150°C to 1350°C and 0 to 12 hours respectively. Full density was reached after sintering for 1.5 hours at 1250°C and a maximum microhardness of 4.9GPa was achieved after 6 hours at 1300°C. Significant grain growth occurred but did not seem to influence the microhardness observed. Significant decomposition was observed after sintering at 1350°C for 1.5 which lead to major decreases in microhardness. An activation energy for grain growth of 286 kJ.mol-1 was calculated which is substantially higher than that previously noted for HA.
Authors: J.P. Gittings, I.G. Turner, A.W. Miles
Abstract: Calcium phosphate (CaP) ceramics possessing an interconnecting porosity network in the appropriate size range for vascularisation offer the possibility of providing a structural matrix for replacement of diseased or damaged bone. Such bioceramics must possess sufficient mechanical strength to avoid failure whilst offering a bioactive surface for bone regeneration. The objective of the current study was to produce a hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramic that imitated the orientated trabecular structure found in cancellous bone. The structure-property relationship of these bioceramics was then analysed. It was hypothesised that the mechanical properties would be linked to the shape of the pore structure due to the orientation of the open porous scaffolds (OPS) produced. OPS bioceramics possessed an interconnected macroporosity network of 40-70% by volume with bending strengths of 0.30MPa ± 0.01MPa and apparent densities of 0.35g/cm3 ± 0.05g/cm3. Typically, pore sizes in the range of 150-300µm were produced. The fabrication of CaP OPS resulted in a wide range of macroporosity in the correct size range for osseointegration to occur. Elongating the pore structure did not affect the total porosity of the bioceramics. Strengths were low due to microcrack formation on sintering and not due to the shape of the pores present in the scaffold as initially hypothesised.
Authors: Koji Ioku, Giichiro Kawachi, Nakamichi Yamasaki, Hirotaka Fujimori, Seishi Goto
Abstract: Porous plates of hydroxyapatite (Ca10(PO4)6(OH)2; HA) with about 0.5 to 5 mm in thickness and porous HA granules of about 40 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA plates with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 20 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 to 0.5 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.
Authors: Luis M. Rodríguez-Lorenzo, Blanca Vázquez, Julio San Román
Abstract: Hydroxyapatite has been frequently described as an osteoconductive but not osteoinductive material based on failure to observe bone formation in nonbony sites. Bisphosphonates (BPs) are stable pyrophosphate analogs, that enhance the proliferation, differentiation and bone forming activity of osteoblasts and are potent inhibitors of bone resorption. In this paper, the modification of a calcium hydroxyfluor carbonate apatite with sodium alendronate and (4-(aminomethyl)benzene)bisphosphonic acid is described. The surface modification is carried out by refluxing the apatite in a bisphosphonate acetone solution. Modified particles are characterized by thermal analysis, ATR-IR spectroscopy and contact angle between other techniques. A weight loss between 150 and 500°C can be observed for the modified apatites. IR spectra show the appearance of bisphosphonate bands on modified powders. The surface energy of the modified apatite is reduced up to a 74% from the total apatite value after the alendronate surface modification with a decrease of 58% of the polar component main responsible of the cellular interaction of biomaterials.
Authors: Marc Long, Charles Martin, Mike Cooper
Abstract: This study investigated the strength of several bone graft substitute (BGS) granular products under compression in a confined fixture characteristic of packing into a contained surgical bone defect. The compressive strength values for columns of granules made of tricalcium phosphate (TCP, dense), calcium carbonate / hydroxyapatite (CC/HA, porous) and ultraporous TCP (TCPu, ultra porous) were 2063.8 ±177.6N, 115.3 ±7.4N, and 40.5 ±8.3, respectively. As a result of their higher strength, the TCP granules did not appreciably reduce in volume after packing. The CC/HA and TCPu granules appreciably reduced in volume after packing, with the final packed volumes being 68% and 41%, respectively, of their original volumes. Based on these results the TCP synthetic bone substitute granules are better able to resist crushing and retain their original volume and osteoconductive capacity during packing in a bone defect than the other BGS granules tested in this study. These properties give the dense granules with a six-arm, interlocking shape superior robustness during handling and implantation compared to other BGS scaffolds produced by porous granules, morsels or blocks, while producing a comparable osteoconductive, resorbable scaffold with interconnected porosity.

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