Key Engineering Materials Vols. 330-332

Abstract: In this study, three kinds of photo-reactive polymers, namely positively charged azidophenyl-derived polyallylamine (AzPhPAAm), negatively charged azidophenyl-derived poly(acrylic acid) (AzPhPAAc) and neutral azidophenyl-derived poly(ethylene glycol) (AzPhPEG), were synthesized by introduction of photo-reactive group (-N3) into polyallylamine, poly(acrylic acid) and poly(ethylene glycol), respectively. The structure of the azidophenyl-derived polymers was confirmed by 1H-NMR measurement. All of the photo-reactive polymers can be pattern-grafted on the surface of cells culture plate, which was confirmed by the optical microscopy observation. The contact angle decreased after surface modification by the photo-reactive polymers. Human mesenchymal stem cells (MSC) cultured on the modified surfaces showed different morphology. The cells adhered and spread more on the PAAm- and PAAc-grafted surfaces than on the PEG-grafted surface. The pellets formed on PAAm- and PEG-grafted surfaces in condrogenic differentiation medium were positively stained by safranin O/ fast green. But the pellet formed on PAAc-grafted surface did not show obviously positive staining for safranin O/ fast green. These results indicate that the PAAm- and PEG-grafted surfaces promoted chondrogenic differentiation of MSC.

Abstract: To investigate the mechanical property (shear strength, bending strength and compressive strength) and the interface combinative ability of the composite of bovine bone morphogenetic protein (bBMP) and porous hydroxyapatite (HA) with different pore diameter. HA1 (Φ100-300μm) and HA2 (Φ130-500μm) were used as carriers of bBMP(5mg). The 4 types material (HA1, HA2, bBMP /HA1, bBMP /HA2) were implanted into the femur of 10 dogs (2 dogs each group) for the shear test and 15 dogs (3 dogs each group) for the bending test and compressive test. The shear strength of all kinds of materials were increased as time went on and the shear strength of bBMP/HA1 was highest in four materials. The bending strength of bBMP /HA1 was close to the normal femur in the 24th week. The compressive strength of all materials was lower than the cortex of the dog’s femur until 24th week. The compressive strength of bBMP /HA1 was the highest in four types. The compressive strength of HA2 and bBMP /HA2 was decreased after implantation. Implant of bBMP /HA with 100-300μm diameter had strong bonding with the host bone, and had better mechanical properties than that with 130-500μm diameter. So the porous bBMP /HA (Φ100-300 μm ) could be a useful graft material due to its strength.

Abstract: To evaluate the effectiveness of the cell-material in situ on joint resurfacing, a woven fabric polyglycolic acid (PGA) treated with fresh chondrocytes was used for repairing cartilage defects. Full-thickness defects were created in the weight-bearing surfaces of the femoral intercondylar fossa in a rabbit model. The defect was filled with and without PGA under surgical condition. Before implantation, chondrocytes were co-cultured with PGA for one day. The animals were sacrificed at eight weeks after implantation and evaluated grossly and histological score. Morphological examination showed that for PGA/chondrocytes group, the repaired tissue appeared similar in color and texture to the surrounding articular surface. While for the untreated control, no cartilage-like tissue was observed at all defects, but connective fibrous tissue. Histological analysis revealed neochondrogenesis and clusters of cartilage matrix with specific safranin-O staining for the PGA/cell group. The Gross and histological evaluation indicated a significantly higher score for PGA/cell group than for PGA and control group. These results suggest that the woven fabric PGA may facilitate the formation of cartilage tissues by providing a biodegradable and good-handle vehicle for the delivery to and retention of organized cell matrix constructs in vivo site. It might therefore enhance neochondrogenesis because of the superior biodegradable and biocompatible of PGA scaffold sheet, while the more suitable biological environment might sustain cell growth and in situ cell function, suggesting a promising candidate for functional tissue engineering of clinical environment.

Abstract: The kinetics of tetragonal-to-monoclinic phase transformation (t→m transformation) in the earlier generation zirconia femoral heads was evaluated by X-ray diffractometry, laser microscopy and Raman microprobe spectroscopy. From previous results of hip-simulator study, it was confirmed that phase transformation on the surface of zirconia femoral heads had little influence on wear rate of UHMWPE sockets, and in some zirconia femoral heads, only a slight increase in monoclinic fraction was observed during hip-simulator test. In this study, we suggest that the models of phase transformation progress during tests in hip-simulator and aging tests are different based on both laser microscopic and Raman/fluorescence spectroscopic observation. Besides this finding, this study shows that Raman spectroscopy is a useful technique for the evaluation of the kinetics of phase transformation in femoral heads after both in vitro and in vivo environmental exposure.

Abstract: The ceramic materials Al2O3 and ZrO2 proved successful in hip joint endoprosthetics for more than 20 years. The advantages of these materials are to be found in particular with the very good properties like biocompatibility and wear resistance; thus, they are clearly ahead of conventional materials like metal or PE. The increasing requirements regarding implants can only be realised by means of improvement of the used materials. That is why we surveyed utilisation of new dispersion ceramics consisting of Al2O3 and ZrO2. The first tests were aimed at characterisation of the material regarding material features and measurement of burst load at the hip joint heads. The results showed that both bending strength and burst load of the components could be significantly improved. Thus, the new ZTA dispersion ceramic is perfectly suitable for use with joint endoprosthetics.

Abstract: Wear is the primary cause of failure of joint replacement prostheses. In this paper, the Ultra High Molecular Weight Polyethylene (UHMWPE) as an artificial joint acetabular material was reinforce by nano-ZrO2 particles. The friction and wear properties of ZrO2 - UHMWPE composites sliding against the Co-Cr-Mo alloy were studied under lubrication of distilled water, saline and calf serum. The worn surface is observed by the optics microscope to examine the wear mechanism of the composite. The hardness and wetting angle of the composites were also measured. The result shows that the hardness, wettability, friction and wear resistance were all improved by filing with nano-ZrO2 particles. The 2%ZrO2 - UHMWPE composite had the lowest wear rate.

Abstract: Metallic biomaterials are used as bone plate, dental implant, wire, electrode, and so on. For the purpose of providing the medical services with higher quality, the frictional and wear behavior of Cu47Ti34Zr11Ni8, (Cu47Ti34Zr11Ni8)99Si, Zr41Ti14Cu12.5Ni10Be22.5 and Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glasses (BMG) against ceramic ( Si3N4) at room temperature under dry sliding and lubrication of fresh plasma, distilled water, and physiological saline conditions were investigated on a pin-on-disc testing machine. Under identical sliding condition, the steady state friction coefficients of BMGs were observed with values ranging from 0.6 to 0.9 under dry sliding, 0.5 to 0.8 under lubrication with distilled water, 0.5 to 0.7 under lubrication with physiological saline, and 0.3 to 0.7 under lubrication with fresh plasma, respectively. Wear rates of BMGs indicated significant difference that the Cu-based metallic glasses exhibited higher wear resistance than that of Zr-based glasses. The surface tracks indicated the existence of viscous flow and the material transfer occurred from BMG rod to the ceramic disc. Since tribological properties are not intrinsic properties, those results demonstrated the influences of the environment and the characteristics of BMGs on the frictional behaviors, and furthermore indicated that BMGs may be one of the promising biomaterials in the future.

Abstract: The experience of Alumina ceramic liner fixed in a metallic shell is not new ; From 1983 to 1999 , 555 components of this type with a titanium screw in shell design were implanted . Recently a review of the first 117 cases with a mean follow up of 12 years were presented. No ceramic fracture were recorded. In 1989 a new press fit shell fixation system replaced the screw in design; This material was implanted from 1989 to 1997. The shape of the liner was an angle of 5°40’ , a liner in excess of 2 mm .A centraliser to insure the correct setting. The shell thickness was limited in order to allow the grid fixation One fracture of the rim (Shipping) was discovered during revision surgery performed elsewhere for acetabular loosening; This revision was performed 4 years after a trauma with fracture of the patella in a fore board trauma. No other fracture was recorded with this design (over more than 1500 implanted). Starting in 1997 a new press fit socket was introduced with a sand blasted surface covered with HA. To be able to retain the same liners , the thickness of the shell were increased resulting in a thin Alumina component for the small sizes (50 mm for a 32 mm head.) . In 1999 a slight modification of the design were made. Recessed liner of 1 mm , ancillary material with a system to insure as well polyethylene or alumina liner fixation. At the moment 5 fractures of this design were recorded (one coming from another institution).

Abstract: Two tetragonal (t) zirconia-alumina composites were prepared by adding Al2O3 (20 vol%) into t-ZrO2 solid solutions doped with 3.0 mol% Y2O3, 1.6 mol% Nb2O5, 3.6 mol% CeO2 (Al20Ce) and 5.3 mol% Y2O3, 4.6 mol% Nb2O5 (Al20) as the femoral heads for the total hip replacements. The effect of machining and annealing on the hydrothermal stability and surface roughness of the composites was evaluated by comparing with the commercial 3 mol% Y2O3 stabilized t-ZrO2 (3Y-TZP). Machining was conducted by using the high-precision machine, where the spindle speeds (rpm 9000~18000) and the electroplated wheels (#400, 800) can be easily adjusted. The machined specimens were annealed at temperatures from 900 to 1300 oC and subsequently autoclaved for 5 days at 120oC under 0.3 MPa water vapor pressure. Although the phase stability and surface roughness of the machined composites were found to be inferior, the hydrothermal stability of the annealed and subsequently autoclaved composites was determined to be excellent as compared with that of the commercial 3Y-TZP. The lower phase stability of the machined composites was likely to be due to numerous machining damages (surface defects) of the composites than those of 3Y-TZP.

Abstract: The aim of this study was to record corrosion behaviour of ZTA and ATZ ceramics under hydrothermal conditions and under influence of boiling acids. Ageing was performed for 30 h and for 100 h in an autoclave at 134 °C and at a pressure of 2 bar. The sample surface was characterised with the help of measurements of surface finish, strength and microhardness, as well as by means of determination of wetting angle of contact. Leaching behaviour was analysed by means of scanning electron micrographs and weightings. The results of all tests with ZTA and ATZ ceramics performed in connection with this survey showed positive results, i.e. neither acid treatment nor hydrothermal ageing resulted in significant changes of properties.