Mechanical and histological evaluations of cobalt-chromium alloy and hydroxyapatite plasma-sprayed coatings in bone

This study evaluated the mechanical and histological behavior of cobalt-chromium (CoCr) alloy and hydroxyapatite (HA) plasma-sprayed coatings in canine cortical bone after 6 and 12 weeks of implantation, using CoCr alloy as the substrate. the substrate was bond-coated with microtextured CoCr alloy coating to ensure adherence between the substrate and top coats. A macrotextured CoCr alloy top coat with surface roughness R _a=34.25±5.50 m was produced to create suitable pores ranging from 25 m to 200 m for bone ingrowth. For HA top coat, a relatively smooth surface (R _a=15.14±3.21 m) was prepared for bone apposition. Shear testing of bone/implant interfaces showed that the CoCr alloy top coat exhibited significantly lower (p<0.01) mean shear strength than the HA top coat at each time interval. The maximum shear strength was 10.88±0.38 MPa for HA-coated implants 12 weeks post-implantation. After histological evaluations, substantial differences in the extent of new bone formation and the types of implant/bone contact were found between two kinds of implants. Direct bone-to-HA coating contact was consistently observed, while a layer of fibrous tissue intervening at the bone-CoCr alloy coating interface was found. Occasionally, partial dissolution of HA coating was seen after 12 weeks of implantation. The results of this study suggested that plasma-sprayed macrotextured CoCr coatings may not be an effective alternative for biological fixation.     

Biomechanical assessment of bone ingrowth in porous hydroxyapatite

Porous hydroxyapatite (Endobon®) specimens were implanted into the femoral condyle of New Zealand White rabbits for up to 6 months. After sacrifice, specimens were sectioned for histology and mechanical testing, where the extent of reinforcement by bony ingrowth was assessed by compression testing and fixation was assessed by push-out testing. From histological observations, it was established that the majority of bone ingrowth occurred between 10 day and 5 weeks after implantation and proceeded predominantly from the deep end of the trephined defect, with some integration from the circumferential sides. At 3 months, the implants were fully integrated, exhibiting bony ingrowth, vascularization and bone marrow stroma within the internal macropores. After 5 weeks, the mean ultimate compressive strength of retrieved implants (6.9 MPa) was found to be greater than that of the original implant (2.2 MPa), and by 3 months the fully integrated implants attained a compressive strength of approximately 20 MPa. Push-out testing demonstrated that after 5 weeks in vivo, the interfacial shear strength reached 3.2 MPa, increasing to 7.3 MPa at 3 and 6 months.     

Absorbable self-reinforced polylactide (SR-PLA) composite rods for fracture fixation: strength and strength retention in the bone and subcutaneous tissue of rabbits

The strength and strength retention of self-reinforced (SR) absorbable polylactic acid composite rods were evaluated after intramedullary and subcutaneous implantation in rabbits. Rods made of poly-l-lactic acid (SR-PLLA) and of poly-dl-lactic acid + poly-l-lactic acid composite (SR-PDLLA/PLLA) were used. The molecular mass (M _v) of PLLA was 260.000 and that of PDLLA 100.000. The bending and shear strengths were measured after a follow-up of 1–48 weeks. The initial bending strength of the SR-PLLA rods was 250–271 MPa and the shear strength was 94 98 MPa. After intramedullary and subcutaneous implantation of 12 weeks the bending strength of the SR-PLLA implants was 100 MPa. At 36 weeks the bending strength had decreased to the level of the strength of cancellous bone (10–20 MPa). There were no changes in the shear strength during 12 weeks hydrolysis. The initial bending strength of SR-PDLLA/PLLA implants was 209 MPa and during the follow-up the implants lost their bending and shear strength faster than the SR-PLLA implants. The present investigation gave us the impetus to continue the studies with the fixation of experimental cortical bone osteotomies with SR-PLLA intramedullary rods.     

Histomorphological, histomorphometrical and biomechanical analysis of ceramic bone substitutes in a weight-bearing animal model

It was the purpose of this investigation to prove the biomechanical properties, the osteoconductive capacity and the degradation rate of tricalcium phosphate ( TCP), a neutralized glass ceramics (GB9N) and a composite material (GB9N+copolymers). In a weight-bearing animal model six substitutes each were implanted in the medial tibial head of the right lower leg of adult Merino-sheep in a standardized surgical technique. After nine months the implants were harvested and prepared for histomorphological and histomorphometrical investigations (undecalcified Masson Goldner staining). For additional biomechanical testing of the specimens, non-operated bone blocks from the contralateral tibia as well as native implants served as controls. No significant differences for the maximum fracture load as well as for the yield strength were detected between harvested specimens and bone blocks from the contralateral tibia. However there were marked differences to ceramics that were not implanted. All substitutes showed osteoconduction, leading to a continuous ingrowth of new formed bone. However in the composite material soft tissue could be identified within the scaffold and there were signs of ongoing bone remodeling, nine months after implantation. The bone per tissue volume of -TCP in conjunction to new bone (=percentage of trabecular bone volume plus percentage of residual substitute) was higher than for GB9N and the composite material. Nine months after implantation the percentage of residual -TCP was 48%, it was 32% for GB9N and 28% for the composite.The intention of further studies should be to accelerate the degradation rates of substitutes and to improve biomechanical properties of implants by either modifying the chemical composition or combining materials with agents as, e.g. growth factors.     

In vivo studies of the ceramic coated titanium alloy for enhanced osseointegration in dental applications

This paper reports the effect of the various ceramic coatings viz., hydroxyapatite (HA) and partially stabilized zirconia (PSZ) on the bond strength between the bone and implant, and cell compatibility of screw-shaped Ti-6Al-7Nb dental implants. Electrophoretic deposition technique (EPD) was used to obtain a uniform coating of one of the three types of ceramic layers (HA, PSZ and 50%HA + 50%PSZ) on the screws. Structural investigations were carried out on the prepared HA powder and the modified surfaces of the Ti-6Al-7Nb alloy using different techniques, namely X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The in vivo studies were performed by the implantation of screw-shaped uncoated and coated implants in the tibia of white New Zealand rabbits. To understand the bone-implant interface, biomechanical test was carried out after 2, 6 and 18 weeks healing periods. There was increased mechanical strength (torque value) of bone-implant interface with time, and the highest increment in the bond strength was recorded for implants coated with a 50% HA and 50% PSZ. Histological results show that the coated Ti-6Al-7Nb screws after 18 weeks of the implantation seem to be well-tolerated by the bone since no adverse tissue reaction was evident. However, there was a faster reaction of bone towards the coated implants compared to the uncoated one. The histochemical stain studies shows higher cellular activity and mature bone formation on all the samples.     

Long-term evaluation of titania-based ceramics compared with commercially pure titanium in vivo

Fifty-four cylinders (2.8 mm in diameter) machined from hot isostatically pressed titania (TI) and titania-hydroxyapatite (TI/HA-15 vol%) sintered at 925°C, as well as commercially pure titanium (c.p. Ti), were implanted in the fermoral cortical bone of New Zealand white rabbits for 1, 3 and 12 months. The shear strength between bone and implant was measured by a push-out test. The TI/HA composite showed a significantly higher bonding strength to bone compared to c.p. Ti at all times, while no differences were observed between TI and c. p. Ti at 1 and 3 months after implantation. Titania-based materials had a significantly higher bonding strength than that of c.p. Ti one year after implantation. The results indicate that bioactivity of HA in TI/HA composite contributes to the early bone apposition reflected by high bonding strength, while the stability of the oxide, determines the development of long-term bonding strength. Both effects may be explained by the level and type of ions released from the ceramic implant. HA has a positive conduction to bone ingrowth while TI has a limited interaction to the bone apposition due to the extraordinary low ion release in vivo. Under light microscopy, similar patterns of bone-implant interfaces were seen from titania-based materials and c.p. Ti in 3-month samples, indicating high biocompatibility of these materials. However, histological evaluation by light microscope cannot identify the differences between physical contact and chemical bonding of implant-bone interface, and thus does not give information on bonding mechanism and the level of shear stresses developed.     

A new composite made of polyurethane and glass ceramic in a loaded implant model: a biomechanical and histological analysis

The biocompatibility and osseous integration of a new composite material made of polyurethane and a calcium silicophosphate ceramic was investigated in a loaded implant model in sheep and compared to that of commercially pure titanium. Six months after implantation, interfacial shear strength was higher between the titanium and bone than between the composite and bone. After 2 years, however, the shear strength was significantly higher in the composite group. Histologically, both implants were surrounded by bone and fibrous tissue and there were no signs of inflammation. Direct contact of bone on the composite surface increased significantly with time, whereas there was no time-dependent increase of bone contact on titanium. It can be concluded that the biocompatibility and osseous integration of the composite was very good in the loaded implant model used. It is therefore suggested that the new composite is a promising biomaterial for orthopaedic implants.     

A histological evaluation of the effect of hydroxyapatite coating on interfacial response

The effect of hydroxyapatite (HA) coating on cortical bone apposition around press-fit inserted implants and implants surrounded by a gap was investigated. Uncoated and HA-coated titanium implants were inserted in burr holes with three different diameters in the tibia of rabbits. Implantation time was four months. The histological evaluation demonstrated that after four months implantation the interfacial bone reaction appeared to be identical for HA-coated and non-coated implants with various degrees of surgical fit. Although after four months the interface showed the same response, there still might be an initial advantage of the HA-interface with bony tissue.     

Mechanical and histological assessment of uncoated and HA- or Ti-coated PE and POM plugs implanted in rabbits

The surface material and surface structure of orthopaedic implants are considered to be key parameters for clinical success. The goal of this study was to assess mechanical and histological aspects of uncoated and coated polymer plugs implanted transcortically into the femurs of rabbits for 6, 9, and 12 weeks. Cylindrical plugs (diameter 3×12 mm) made of ultra-high molecular weight polyethylene (UHMW-PE) or polyoxymethylene (POM) uncoated or coated with hydroxyapatite (HA) or titanium (Ti) were analysed in a push-out test to determine the interface shear strength. Compared to uncoated PE plugs, coated PE implants were always significantly better in interface strength (up to a factor of 20). HA-coated PE plugs reached their final shear strength after a shorter period of implantation (at 6 weeks) than Ti-coated plugs, but both finally yielded the same strength (at 12 weeks). With a thin Ti-plasma coating, the increase of interface strength of POM plugs was much smaller than the increase found in PE implants coated with a different technique. Microscopic analysis suggested that interface failure initially occurred between coating and bone. Histology revealed a stable, bony integration of all plug types. The increase in interface shear strength could not be explained by histological findings and must be caused mainly by the different surface structures of the implants or coatings.     

Long-term soft tissue reaction to various polylactides and their in vivo degradation

Cylindrical pins made from poly(L-lactide), poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5% were implanted in the subcutaneous tissue of sheep. The tissue reaction to the implanted materials and their in vivo degradation was investigated at 1,3,6 and 12 months. The capsule formed around the polylactide implants consisted of fibroblasts, fibrocytes, phagocytes, a few foreign body giant cells and polymorphonuclear cells. For all three polylactides used, the cellular response was most intensive during the first 6 months of implantation and significantly subsided at 1 year. The thickness of the capsule was 200 m at 1 month, increased to 200–600 m at 6 months, and decreased to 100 to 200 m at 1 year, depending on the material used. The tissue reaction was more intense for poly(L/D-lactide) than for poly(L/DL-lactide) and poly(L-lactide). The drop in molecular weight of the implants was highest after 1 month of implantation (70 to 95%). Irrespective of the extensive reduction of the molecular weight at 1 month, none of the polymers used was completely resorbed at 1 year. The most advanced resorption was observed for poly(L/D-lactide). Despite molecular weight reduction, the poly(L-lactide) implants had maintained 70% of their initial bending strength and 95% of their shear strength at 3 months. The poly (L/D-lactide) and poly(L/DL-lactide) had maintained only 26 to 27% of their initial bending strength and 26 to 31% of the initial shear strength, respectively. The crystallinity of all the materials increased after implantation as compared with nonimplanted materials. The overall crystallinity increase and the final crystallinity reached by the materials at 1 year was, however, lowest for poly(L/DL-lactide) as compared with the other two polylactides.     

炭基复合材料与人骨的力学性能对比分析

选用3种炭基复合材料,分别为采用化学气相沉积（CVD）工艺和CVD/浸渍复合工艺制备的2种C/C复合材料以及采用CVD/熔融渗硅（MSI）工艺制备的C/C-SiC复合材料,通过对比分析3种炭基复合材料与人骨的微观结构和力学性能,研究了所选用的3种炭基复合材料作为新型骨折内固定材料的可行性。结果表明:3种炭基复合材料与人骨均具有纤维增强、多孔基体的微观结构形态。在力学性能方面,3种炭基复合材料的弹性模量与人骨都较为接近,其中C/C-SiC复合材料的力学性能与人骨最为接近,分别为弯曲强度213.0 MPa、剪切强度19.3 MPa、压缩强度228.1 MPa,有望成为理想的接骨板材料。CVD和CVD/浸渍工艺制备的C/C复合材料,弯曲强度分别仅为161.8 MPa和174.6 MPa,低于人骨的弯曲强度,后期可通过改进坯体结构和制备工艺等方法来使其力学性能与人骨相匹配。      

Evaluation of tricalciumphosphate/ hydroxyapatite cement for tooth replacement: an experimental animal study

A calciumphosphate cement, consisting mainly of tricalciumphosphate (85% -TCP and 15% -TCP), was inserted in 16 surgical defects created in the tibia of goats. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) showed that after 3 months of implantation the -TCP was transformed to hydroxyapatite (HA). Histological evaluation revealed that the presence of cement stimulated the ingrowth of bone compared with unfilled cavities. Active resorption and remodelling of cement particles was observed. The cement did not evoke an inflammatory reaction. At 6 months after implantation no further changes in the composition of the cement occurred. All remaining material was surrounded by mature bone.     

喷涂功率对碳/碳复合材料表面羟基磷灰石涂层的影响

采用等离子喷涂技术在碳/碳复合材料表面制备了羟基磷灰石(HA)涂层,采用电子拉伸机和自制装置测定了不同喷涂功率下涂层与基体的抗剪强度,采用扫描电镜观察了涂层表面、剪切断裂表面的形貌,采用电子探针分析了试样截面的形貌和成分线分布.结果表明:随着喷涂功率的增加,涂层中HA颗粒的熔化程度和涂层与基体的抗剪强度均增加,涂层与基体的界面属于机械结合,其剪切断裂的形式主要有界面失效和涂层内部失效两种.     

Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites

A novel biocomposite of carbon fiber (CF) reinforced hydroxyapatite (HA)/polylactide (PLA) was prepared by hot pressing a prepreg which consisting of PLA, HA and CF. The prepreg was manufactured by solvent impregnation process. Polymer resin PLA dissolved with chloroform was mixed with HA. After reinforcement CF bundle was impregnated in the mixture, the solvent was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 170°C for 20 min. A study was carried out to investigate change in mechanical properties of CF/HA/PLA composites before and after degradation in vitro. The composites have excellent mechanical properties. A peak showed in flexural strength, flexural modulus and shear strength aspects, reaching up 430 MPa, 22 GPa, 212 MPa, respectively, as the HA content increased. Degraded in vitro for 3 months, the flexural strength and flexural modulus of the CF/HA/PLA fell 13.2% and 5.4%, respectively, while the shear strength of the CF/HA/PLA composites remains at the 190 MPa level. The SEM photos showed that there were gaps between the PLA matrix and CF after degradation. Water uptake increased to 5%, but the mass loss rate was only 1.6%. The pH values of the PBS dropped less than 0.1. That’s because the alkaline of HA neutralize the acid degrades from PLA, which can prevent the body from the acidity harm.     

A histological and histomorphometrical evaluation of screw-type calciumphosphate (Ca-P) coated implants; an in vivo experiment in maxillary cancellous bone of goats

The bone response to different calcium phosphate (Ca-P) coated implants was evaluated in a goat animal model. Two types of plasma spray coatings were applied to a commercially pure titanium (cpTi) tapered, conical screw-design implant (BioComp^®); hydroxyapatite (HA-PS) and a dual coating, consisting of FA and HA (FA/HA-PS). In addition an amorphous RF magnetron sputter coating (Ca-P-a) and uncoated implants were investigated. Forty-eight implants were inserted in the maxilla of 12 adult female goats. After implantation periods of 3 and 6 months, the bone implant interface was evaluated histologically and histomorphometrically. After both implantation periods all plasma spray coated implants were maintained. On the other hand three Ca-P-a and two cpTi implants were lost. Histological examination revealed a better bone response to both plasma spray coated implants. Histomorphometrical evaluation confirmed this finding. At 3 and 6 months significantly higher percentages of bone contact (p<0.001, ANOVA) were measured for both plasma spray coated implants than for the cpTi and Ca-P-a implants, while no significant difference (p<0.05) existed between both implantation periods. Degradation of both plasma spray coatings was observed. Supported by the results, it is concluded that, although Ca-P coatings can improve the performance of dental implants, the presence of a Ca-P coating is not the only important factor for bone healing around implants placed in low density trabecular bone.     

Plasma spraying of zirconia-reinforced hydroxyapatite composite coatings on titanium: Part I Phase, microstructure and bonding strength

Plasma-sprayed hydroxyapatite (HA) coatings applied to metal substrates can induce a direct chemical bond with bone and hence achieve biological fixation of the implant. However, the poor bonding strength between HA and substrate has been of concern to orthopaedists. In this study, two submicrometre ZrO2 powders stabilized with both 3 and 8 mol% Y2O3 (TZ3Y and TZ8Y, respectively) were incorporated in a plasma-sprayed HA coating on Ti-6Al-4V substrate to investigate the change in phase, microstructure and bonding strength. The results show that ZrO2 composite coatings contain more unmelted particles and greater porosity. During plasma spraying, ZrO2 reacts with the CaO in HA to form CaZrO3 and accelerates HA decomposition to -TCP and Ca4P2O9. Nevertheless, bonding strength increases with increase of ZrO2 content in the range 0 to 10 wt% studied. The higher Y2O3-containing TZ8Y apparently exerts a greater strengthening effect than the lower Y2O3-containing TZ3Y.     

Bilayered calcium phosphate coating to promote osseointegration of a femoral stem prosthesis

A bilayered bioactive-gradient coating, consisting of a superficial layer of biphasic calcium phosphate (BCP) and a deep layer of hydroxyapatite (HA), promotes faster osseointegration and higher shear strength in non-loading conditions than do monolayer BCP or HA coatings. This study evaluated the biofunctionality of this coating in weight-bearing conditions at 6 and 12 months. The coating was plasma-sprayed on the metaphyseal portion of a sandblasted Ti6Al4V canine femoral prosthesis implanted using the surgical press-fit technique. An identical uncoated stem served as the control. Metaphyseal bone-to-implant apposition was increased for coated (90% and 80% respectively at 6 and 12 months) as compared to uncoated implant (7% at 6 and 12 months). Limited bone apposition was observed at the diaphyseal level. After 12 months, the uncoated implant interface consisted of well-organized, active fibrous tissue, whereas only inactive fibrous tissue interposition was observed at diaphyseal levels of the coated implant. At 6 months, the mineralization apposition rate (MAR) was similar, regardless of implant or bone structures. At 12 months, a significant decrease of MAR was observed around the uncoated implant. Transmission electron microscopy studies of the interface showed precipitation of biological apatite crystals in close association with mineralized collagenous bone matrix. Our results suggest a direct relationship between bioactivity and enhanced bone formation. The sandwich coating used is effective in promoting massive metaphyseal osseointegration, which ensures mechanical stability for early weight-bearing and should prevent long-term complications.     

Improved electrochemical performance of nitrocarburised stainless steel by hydrogenated amorphous carbon thin films for bone tissue engineering

In this study, hydrogenated amorphous carbon thin films, structurally similar to diamond‐like carbon (DLC), were deposited on the surface of untreated and plasma nitrocarburised (Nitrocarburizing‐treated) stainless steel medical implants using a plasma‐enhanced chemical vapour deposition method. The deposited DLC thin films on the nitrocarburising‐treated implants (CN+DLC) exhibited an appropriate adhesion to the substrates. The results clearly indicated that the applied DLC thin films showed excellent pitting and corrosion resistance with no considerable damage on the surface in comparison with the other samples. The CN+DLC thin films could be considered as an efficient approach for improving the biocompatibility and chemical inertness of metallic implants.Inspec keywords: tissue engineering, bone, biomedical materials, electrochemistry, amorphous state, carbon, hydrogen, thin films, plasma CVD, adhesion, corrosion resistance, surface hardeningOther keywords: electrochemical performance, plasma nitrocarburised stainless steel medical implants, hydrogenated amorphous carbon thin films, bone tissue engineering, plasma‐enhanced chemical vapour deposition method, adhesion, corrosion resistance, biocompatibility, chemical inertness, metallic implants, C:H     

In vivo osteocompatibility of lotus-type porous nickel-free stainless steel in rats

The bone response to lotus-type porous nickel-free stainless steels implants was investigated using Sprague-Dawley rats. The implants were inserted in the femora and tibiae of rats (n = 60) and bone formation inside the pores of the implants was followed up to 12 weeks. Bone ingrowth in transverse histological sections was calculated using an image analysis program. Shear strength of the bone–implant interface was evaluated by the push-out test. Histological examination showed that bone grew into apparent direct contact with the implant surface and into the pores, which sizes were between 70–650 μm. At 12 weeks, maximum compressive shear strengths of 24 ± 1 MPa were obtained; these values are substantially higher than the typical shear strength achieved by porous-coated materials. These results clearly indicate that lotus-type porous structure allowed bone cells and tissue to invade the implant throughout superficial porous spaces, which resulted in an efficient biological fixation responsible for the mechanical stability at the implantation site.     

Carbon fibre-cement adhesion in carbon fibre reinforced cement composites

The addition of small amounts of short carbon fibres to cement causes a great increase in the composite material toughness and tensile, flexural, and impact strength. In order to understand how cement properties are improved by carbon fibres and to understand the level of adhesion and interfacial failure mode which are necessary to obtain optimum carbon fibre reinforced cement (CFRC) properties, various admixtures were included in cement and CFRC. Their effects on the carbon fibre-cement adhesion and the composite material properties were determined using fibre pull-out and composite material flexural tests. The addition of latex to CFRC, and hot water curing of CFRC dramatically increase fibre-matrix adhesion. Both latex (with an anti-foam agent) and hot water curing increase flexural strength by 40% over adhesion changes the failure mode from fibre pull-out to fibre rupture. Optimum strength and toughness of CFRC result from an intermediate level of fibre-matrix adhesion.