Comparison of plasma-sprayed hydroxyapatite coatings and zirconia-reinforced hydroxyapatite composite coatings: in vivo study

The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has been widely adopted because the HA coating can achieve the firmly and directly biological fixation with the surrounding bone tissue. However, the long-term mechanical properties of HA coatings has been concern for the long-term clinical application. Previous research showed that the concept of adding ZrO2 as second phase to HA significantly increased the bonding strength of plasma-sprayed composite material. The present work aimed to explore the biological properties, including the histological responses and shear strength, between the plasma-sprayed HA and HA/ZrO2 coating, using the transcortical implant model in the femora of canines. After 6 and 12 weeks of implantation, the HA coating revealed the direct bone-to-coating contact by the backscattered electron images (BEIs) of scanning electron microscope (SEM), but the osseointegration was not observed at the surface of HA/ZrO2 coating. For new bone healing index (NBHI) and apposition index (AI), the values for HA implants were significantly higher than that for HA/ZrO2 coatings throughout all implant periods. After push-out test, the shear strength of HA-coated implants were statistically higher than HA/ZrO2 coated implants at 6- and 12-week implantation, and the failure mode of HA/ZrO2 coating was observed at the coating-bone interface by SEM. The results indicate that the firm fixation between bone and HA/ZrO2 has not been achieved even after 12-week implantation. Consequently, the addition of ZrO2 could improve the mechanical properties of coatings, while the biocompatibility was influenced by the different material characteristics of HA/ZrO2 coating compared to HA coatings.     

Processing and in vitro behavior of hydroxyapatite coatings prepared by electrostatic spray assisted vapor deposition method

Hydroxyapatite (HA) bioactive coatings are often used to improve bone attachment and reduce corrosion of metal prosthesis implants. This paper reports the preparation of HA coatings onto titanium substrates using a novel electrostatic spray assisted vapor deposition (ESAVD)-based method. The deposited coatings are characterized using a combination of Fourier transform infrared spectrometer, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and scratch test. The results confirm that well-crystallized HA coatings can be produced directly via the single-step ESAVD process, without further heat-treatment. The in vitro behavior of the as-deposited HA coating in simulated body fluid (SBF) is also presented. After 14-day immersion in SBF, the adhesion of the HA coating to the substrate increases significantly.     

Preliminary beta-tricalcium phosphate coating prepared by discharging in a modified body fluid enhances collagen immobilization onto titanium

Because of its excellent scaffold properties toward bone cells, collagen has been recognized as a promising extracellular matrix protein for surface modification of titanium implants. Hydroxyapatite (HA) coatings have been investigated as a preliminary coating for collagen immobilization on titanium implants. However, the composition of HA-collagen is recognized as being difficult, and while many studies have suggested that biodegradable beta-tricalcium phosphate (beta-TCP) has better osteoconductivity than HA, the efficiency of preliminary beta-TCP coating for collagen immobilization on titanium surfaces has yet to be evaluated. This investigation aimed to evaluate the applicability of HA and beta-TCP coatings, prepared by discharging in modified body fluids, as preliminary collagen coatings. To increase collagen induction on preliminary HA and beta-TCP coatings, we used a new cathodic polarization method. X-ray photoelectron spectroscopy revealed that the bonding strength between the collagen NH(+) amino groups of collagen and phosphate (PO(4) (3-)) was greater on the beta-TCP coating than the HA coating. The preliminary beta-TCP coating was tightly crosslinked with RCOO(-) carboxyl groups of the collagen molecules and showed high cellular responses, even in the early stage of cell cultivation. Thus, this coating was found to be more effective than HA as a preliminary coating for collagen immobilization on titanium implants.     

Comparison of plasma-sprayed hydroxyapatite coatings and hydroxyapatite/tricalcium phosphate composite coatings: in vivo study

This study aimed to compare biological properties, including osteoconduction, osseointegration, and shear strength, between plasma-sprayed hydroxyapatite (HA) and HA/tricalcium phosphate (TCP) coatings, using a transcortical implant model in the femora of canines. After 3 and 12 weeks of implantation, the implants with surrounding bone were assessed histologically in undecalcified sections in backscattered electron images (BEIs) under a scanning electron microscope (SEM). After short-term (3 week) follow-up, both coatings conducted new bone formation and revealed direct bone-to-coating contact. The HA/TCP coating could not enhance early host-to-coating responses. At 12 weeks, serious dissolution of the HA/TCP coatings evidently occurred. By the new bone healing index (NBHI) and apposition index (AI), we found no significant difference between HA/TCP-coated implants and HA-coated implants throughout all implant periods. At 12 weeks of implantation, some particles dissociated from the HA/TCP coating were found within the remodeling canal. After push-out measurements, the shear strength and failure mode of HA/TCP-coated implants were similar to those of HA-coated implants, and no statistical differences were found between either coating. Consequently, this study indicates that HA/TCP coatings have excellent biological response and may be considered suitable bioactive ceramic coatings for short-term clinical use.     

In vivo behaviour of hydroxyapatite coatings on titanium implants: a quantitative study in the rabbit

The aim of this study was to evaluate quantitatively the behaviour of in vivo hydroxyapatite coated implants (HA) in the rabbit over time, and to compare the results with observations made on titanium plasma spray implants (TPS). Results were analysed according to the percentage of bone contact. Eighteen HA cylindrical implants (3.25 x 8 mm) and 6 TPS cylindrical implants from Steri-Oss were placed in the epiphysis of the femur in 24 white rabbits. Each rabbit received one implant. Three rabbits with one HA implant (n = 3) and 1 rabbit with one TPS implant (n = 1) were sacrificed after implantation periods of 2, 4, 6, 8, 10 and 12 months. Implants were cut along the long axis and prepared for histological and histomorphometrical evaluations. Measurements of coating thickness and percentage of bone contact were performed with scanning electron microscopy analysis on the sides of the implant, in 3 different types of bone, namely cortical, trabecular and marrow. In cortical bone, dense bone was apposed to the HA implants: from 92.3 +/- 5.5% at 2 months to 89.6 +/- 6.5% at 1 year, with no significant regression of HA thickness (P = 0.37). TPS coating showed less bone contact, but thickness was stable (P = 0.46). In trabecular zone, where bone contact was less pronounced, a significant regression of HA coatings thickness (P < 0.05) was observed. Nevertheless TPS coatings were stable (P = 0.81). Histomorphometrical results demonstrated that a highly significant regression (P < 0.0001) of HA thickness was observed in the marrow area, where the bone-to-implant contact never exceeded 7.6% from 2 to 12 months. TPS coating did not reveal any sign of resorption (P = 0.88), despite a rare bone contact. Histological analysis revealed inflammatory and giant cells, principally in the marrow area in contact with HA coating, but always in restrictive numbers. We conclude that bone contact protected the HA coating from resorption.     

磁控溅射制备HA/Ti6Al4V复合材料种植体体外生物活性研究

研究了射频磁控溅射法制备的HA/Ti6Al4V复合材料种植体在模拟体液(Simulated body fluid,SBF)环境下的生物活性。利用扫描电镜(SEM)、能谱分析(EDS)、红外光谱(FTIR)及X-射线衍射(XRD)分析了该种植体涂层在模拟体液中浸泡前后的表面形貌、界面结合状态、晶体结构和相组成的变化,结果表明:该种植体涂层在模拟体液中存在溶解和新生物质在其表面沉积相伴的过程。其中,HA涂层表面的新生物质是一种缺钙型且含有CO32-的类骨磷灰石,其n(Ca)/n(P)比值约为1.56,晶粒小,结晶度低,接近于非晶态,这与自然骨中无机相的结构成分相似,因此具有良好生物相容性和生物活性。     

Osteointegration of biomimetic apatite coating applied onto dense and porous metal implants in femurs of goats

Biomimetic calcium phosphate (Ca-P) coatings were applied onto dense titanium alloy (Ti6Al4V) and porous tantalum (Ta) cylinders by immersion into simulated body fluid at 37 degrees C and then at 50 degrees C for 24 h. As a result, a homogeneous bone-like carbonated apatitic (BCA) coating, 30 microm thick was deposited on the entire surface of the dense and porous implants. Noncoated and BCA-coated implants were press-fit implanted in the femoral diaphysis of 14 adult female goats. Bone contact was measured after implantation for 6, 12, and 24 weeks, and investigated by histology and backscattered electron microscopy (BSEM). After 6 weeks, bone contact of the BCA-coated Ti6Al4V implants was about 50%. After 12 and 24 weeks, bone contact was lower in comparison with the 6-week implantations at, respectively 24 and 39%. Regarding the BCA-coated porous Ta implants, bone contacts were 17, 30, and 18% after 6, 12, and 24 weeks, respectively. However, bone contact was always found significantly higher for BCA-coated dense Ti6Al4V and porous Ta cylinders than the corresponding noncoated implants. The results of this study show that the BCA coating enhances the bone integration as compared to the noncoated implants.     

Characteristics of hydroxyapatite coated titanium porous coatings on Ti-6Al-4V substrates by plasma sprayed method

A porous metal coating applied to solid substrate implants has been shown, in vivo, to anchor implants by bone ingrowth. Calcium phosphate ceramics, in particular hydroxyapatite [Ca(10)(PO(4))(6)(OH)(2), HA], are bioactive ceramics, which are known to be biocompatible and osteoconductive, and these ceramics deposited on to porous-coated devices may enhance bone ingrowth and implant fixation. In this study, bi-feedstock of the titanium powder and composite (Na(2)CO(3)/HA) powder were simultaneously deposited on a Ti-6Al-4V substrate by a plasma sprayed method. At high temperature of plasma torch, the solid state of Na(2)CO(3) would decompose to release CO(2) gas and then eject the molten Ti powder to induce the interconnected pores in the coatings. After cleaning and soaking in deionized water, the residual Na(2)CO(3) in the coating would dissolve to form the open pores, and the HA would exist at the surface of pores in the inner coatings. By varying the particle size of the composite powder, the porosity of porous coating could be varied from 25.0 to 34.0%, and the average pore size of the porous coating could be varied to range between 158.5 and 202.0 microm. Using a standard adhesive test (ASTM C-633), the bonding strength of the coating is between 27.3 and 38.2 MPa. By SEM, the HA was observed at the surface of inner pore in the porous coating. These results suggest that the method exhibits the potential to manufacture the bioactive ceramics on to porous-coated specimen to achieve bone ingrowth fixation for biomedical applications.     

In vivo evaluation of plasma-sprayed wollastonite coating

Wollastonite coatings were prepared by plasma spraying. The bioactivity of wollastonite coatings was investigated in vivo by implanting in dog's muscle, cortical bone and marrow, respectively. The behaviour of bone tissue around wollastonite coatings were examined by histological and SEM observation. After 1 month in the muscle, a bone-like apatite layer was found to form on the surface of the wollastonite coating. When implanted in cortical bone, histological observation demonstrated that bone tissue could extend and grow along the surface of the wollastonite coating. The coating bonded directly to the bone without any fibrous tissue, indicating good biocompatibility and bone conductivity. SEM and EDS analysis revealed that bone did not bond to wollastonite coating directly, but through a Ca/P layer. This suggested that the formation of bone-like apatite layer was very important for bonding to the bone tissue. The amount of bone-implant contact was also measured. Wollastonite coating was shown to stimulate more bone formation on its surface than titanium coating after implantation for 1 month, enhancing the short-term osseointegration properties of implant. The test in marrow indicated that wollastonite coatings could induce new bone formation on their surface showing good bone inductivity property.     

Bond strength,compositional, and structural properties of hydroxyapatite coating on Ti,ZrO2-coated Ti,and TPS-coated Ti substrate

The effect of titanium plasma-sprayed (TPS) and zirconia (ZrO(2))-coated titanium (Ti) substrates on the adhesive, compositional, and structural properties of plasma-sprayed hydroxyapatite (HA) coatings were evaluated. X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, surface roughness, and adhesive strength were used to characterize the coatings. Apatite-type and alpha-tricalcium phosphate phases were observed for all HA coatings. A structural change due to the absence of a 960 cm(-1) peak during FTIR analysis was observed for all HA coatings. The coating surfaces appeared rough and melted, with surface roughness correlating to the size of the starting powder. No significant difference in the Ca/P ratio of HA on Ti and TPS-coated Ti substrates was observed. However, the Ca/P ratio of HA on ZrO(2)-coated Ti substrate was significantly increased. Interfaces between all coatings and substrates were observed to be dense and tightly bound, except for HA coatings on TPS-coated Ti substrate interface. However, an intermediate TPS or ZrO(2) layer between the HA and Ti substrate resulted in a lower adhesive strength as compared to HA on Ti substrate.     

Bone bonding to hydroxyapatite and titanium surfaces on femoral stems retrieved from human subjects at autopsy

The success of clinical results obtained with many hydroxyapatite (HA)-coated prosthetic designs has deflected attention from the need to extend the life of the HA coating on the device. In the current study the percentages of HA and titanium surfaces to which bone was bonded, on HA-coated and non-coated titanium femoral stems retrieved from human subjects, were evaluated. Plasma-sprayed hydroxyapatite (PSHA)-coated devices demonstrated wide variability in the percentage of the PSHA coating remaining on the stems. The coating was missing from a substantial portion of a stem after only about 6 months of implantation. The percentage of revealed metal to which bone was bonded was significantly less than the percentage of the HA coating demonstrating such bonding. The revealed metal to which bone was bonded was comparable to the same value for a separate group of non-PSHA-coated titanium stems. If HA-coatings degrade over time precipitous decline in performance may occur even after several functional years. Many ultrastructural features of the bone bonded to the HA coatings on these implants from human subjects were comparable to those found on HA-coated devices implanted in a canine model.     

Enhanced osteoblast adhesion on hydrothermally treated hydroxyapatite/titania/poly(lactide-co-glycolide) sol-gel titanium coatings

Sol-gel processing was used to coat titanium substrates with hydroxyapatite (HA), TiO2, and poly(DL-lactic-glycolic acid). Coating surface characteristics were analyzed with XRD, EDS, AFM, SEM, and water contact angle measurements which indicated that the coatings had a high degree of crystallinity and good resistance to cracking. Coatings were also evaluated by cytocompatibility testing with osteoblast-like cells (or bone-forming cells). The cytocompatibility of the HA composite coatings prepared in the present in vitro study was compared to that of a traditional plasma-sprayed HA coating. Results showed that osteoblast-like cell adhesion was promoted on the novel HA sol-gel coating compared to the traditional plasma-sprayed HA coating. In addition, hydrothermal treatment of the sol-gel coating improved osteoblast-like cell adhesion. Since osteoblast adhesion is a necessary prerequisite for subsequent formation of bone, these results provided evidence that hydrothermally sol-gel processed HA may improve bonding of titanium implants to juxtaposed bone and, thus, warrants further investigation.     

Physicochemical study of plasma-sprayed hydroxyapatite-coated implants in humans

This study represents the first report of the physical and chemical changes occurring in coatings of failed hydroxyapatite (HA)-coated titanium implants obtained from a comprehensive, multicenter human dental implant study. A total of 53 retrieved samples were obtained and compared with unimplanted controls with the same manufacturer and similar manufacture dates. Forty-five retrieved implants were examined for surface characteristics and bulk composition. Implants were staged based on implantation history: stage 1 (implants retrieved between surgical placement and surgical uncovering), stage 2 (implants retrieved at surgical uncovering and evaluation), stage 3 (implants retrieved between surgical uncovering evaluation and occlusal loading), and stage 4 (implants retrieved after occlusal loading). Scanning electron microscopy showed progressive coating thinning with implantation time. At later stages, bare Ti metal was detected by energy-dispersive X-ray analysis and electron spectroscopy for chemical analysis. Increases in Ti and Al (2-7.5 atm % each) were detected at the apical ends of all stage 4 samples. In unimplanted coatings, X-ray diffraction analysis demonstrated the presence of amorphous calcium phosphate, beta-tricalcium phosphate, tetracalcium phosphate, and calcium oxide in addition to large hydroxyapatite crystals (c axis size, D002 = 429 +/- 13 A; a axis size, D300 = 402 +/- 11 A, a/c aspect ratio 0.92). The nonapatitic phases disappeared with increased implantation time, although there was a persistence of amorphous calcium phosphate. Bulk coating chemical analysis showed that Ca/P ratios for implant controls (1.81 +/- 0.01) were greater than stoichiometric HA (1.67) and decreased for implant stages 3 and 4 (1.69 +/- 0.09 and 1.67 +/- 0.09, respectively), explained by the dissolution of the non apatitic phases. Crystal sizes also changed with implantation times, being smaller than the control at all but stage 4. Fourier transform infrared analyses agreed with these results, and also indicated the accumulation of bone (protein and carbonate-apatite) in the retrieved coatings. The accumulation of bone was not stage dependent. These findings indicate that there was some biointegration with the surrounding bone, but the greatest changes occurred with the HA coating materials, their loss, and chemical change.     

The effect of polyelectrolyte multilayer coated titanium alloy surfaces on implant anchorage in rats

Advances have been achieved in the design and biomechanical performance of orthopedic implants in the last decades. These include anatomically shaped and angle-stable implants for fracture fixation or improved biomaterials (e.g. ultra-high-molecular-weight polyethylene) in total joint arthroplasty. Future modifications need to address the biological function of implant surfaces. Functionalized surfaces can promote or reduce osseointegration, avoid implant-related infections or reduce osteoporotic bone loss. To this end, polyelectrolyte multilayer structures have been developed as functional coatings and intensively tested in vitro previously. Nevertheless, only a few studies address the effect of polyelectrolyte multilayer coatings of biomaterials in vivo. The aim of the present work is to evaluate the effect of polyelectrolyte coatings of titanium alloy implants on implant anchorage in an animal model. We test the hypotheses that (1) polyelectrolyte multilayers have an effect on osseointegration in vivo; (2) multilayers of chitosan/hyaluronic acid decrease osteoblast proliferation compared to native titanium alloy, and hence reduce osseointegration; (3) multilayers of chitosan/gelatine increase osteoblast proliferation compared to native titanium alloy, hence enhance osseointegration. Polyelectrolyte multilayers on titanium alloy implants were fabricated by a layer-by-layer self-assembly process. Titanium alloy (Ti) implants were alternately dipped into gelatine (Gel), hyaluronic acid (HA) and chitosan (Chi) solutions, thus assembling a Chi/Gel and a Chi/HA coating with a terminating layer of Gel or HA, respectively. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bones’ response to polyelectrolyte surfaces in vivo. 48 rats were randomly assigned to three groups of implants: (1) native titanium alloy (control), (2) Chi/Gel and (3) Chi/HA coating. Mechanical fixation, peri-implant bone area and bone contact were evaluated by pull-out tests and histology at 3 and 8 weeks. Shear strength at 8 weeks was statistically significantly increased (p < 0.05) in both Chi/Gel and Chi/HA groups compared to the titanium alloy control. No statistically significant difference (p > 0.05) in bone contact or bone area was found between all groups. No decrease of osseointegration of Chi/HA-coated implants compared to non-coated implants was found. The results of polyelectrolyte coatings in a rat model showed that the Chi/Gel and Chi/HA coatings have a positive effect on mechanical implant anchorage in normal bone.     

Biological performance of biomimetic calcium phosphate coating of titanium implants in the dog mandible

The aim of the present study was to analyze the in vivo effect of biomimetic calcium phosphate coating of titanium implants on periimplant bone formation and bone-/implant contact. Five types of implants were used: 1) Ti6Al4V implants with a polished surface; 2) Ti6Al4V implants with collagen coating; 3) Ti6Al4V implants with a mineralized collagen layer; 4) Ti6Al4V implants with sequential coating of hydroxyapatite (HA) and collagen; and 5) Ti6Al4V implants with HA coating only. All implants had square cross sections with an oblique diameter of 4.6 mm and were inserted press fit into trephine burr holes of 4.6 mm in the mandibles of ten beagle dogs. The implants of five animals each were evaluated after a healing period of 1 month and 3 months, respectively, during which time sequential fluorochrome labeling of bone formation had been performed. Bone formation was evaluated by morphometric measurement of the newly formed bone around the implants and the percentage of implant bone contact. After 1 month, there was a significantly higher percentage of mean bone/implant contact in the HA-coated implants compared to those with polished surface and those with the collagen-coated surface. After 3 months, these differences were not present anymore. Bone apposition was significantly higher next to implants with sequential HA/collagen coating compared to polished surfaces and mineralized collagen layer. It is concluded that biomimetic coating of titanium implants with HA has shown the clearest trend to increase bone-implant contact in the early ingrowth period. The addition of collagen to an HA coating layer may hold some promise when used as sequential HA/collagen coating with mineralized collagen as the surface layer.     

In vivo comparison of the osseointegration of vacuum plasma sprayed titanium- and hydroxyapatite-coated implants

For the last 15 years, orthopedic implants have been coated with hydroxyapatite (HA) to improve implant fixation. The osteoconductive effect of HA coatings has been demonstrated in experimental and clinical studies. However, there are ongoing developments to improve the quality of HA coatings. The objective of this study was to investigate whether a rough and highly crystalline HA coating applied by vacuum plasma spraying (VPS) had a positive effect on the osseointegration of special, high-grade titanium (Ti) implants with the same surface roughness. Ti alloy implants were coated (VPS) with special, high-grade Ti or HA. The osseointegration of the implants was evaluated by either light microscopy or pullout tests after 1, 2, and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep. The interface shear strength increased significantly over all time intervals. By 4 weeks, values had reached approximately 10N/mm(2). However, the difference between the coatings was not significant at any time interval. Direct bone-implant contact was significantly different between the coatings after 2 and 4 weeks, and reached 46% for Ti and 68% for HA implants by 4 weeks. This study indicates that the use of a rough and highly crystalline HA coating, applied by VPS, enhances early osseointegration. Accelerated establishment of secondary implant fixation decreases the risk of early loosening.     

Mechanical stability of two-step chemically deposited hydroxyapatite coating on Ti substrate: effects of various surface pretreatments

The success of implants in orthopaedic and dental load-bearing applications crucially depends on the initial biological fixation of implants in surrounding bone tissues. Using hydroxyapatite (HA) coating on Ti implant as carrier for bone morphogenetic proteins (BMPs) may promote the osteointegration of implants; therefore, reduce the risk of implant failure. The goal of this study was to develop an HA coating method in conditions allowing the incorporation of protein-based drugs into the coating materials, while achieving a mechanical stable coating on Ti implant. HA coatings were deposited on six different groups of Ti surfaces: control (no pretreatment), pretreated with alkali, acid, heat at 800°C, grit blasted with Al?O?, and grit blasted followed by heat treatment. HA coating was prepared using a two-step procedure. First step was the chemical deposition of a monetite coating on Ti substrate in acidic condition at 75°C and the second step was the hydrolysis of the monetite coating to HA. Coatings were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The roughness of substrates and coatings was measured using profilometry technique. The mechanical stability of the coatings deposited on the pretreated substrates was assessed using scratch test. The coatings deposited on the grit-blasted Ti surface demonstrated superior adhesive properties with critical shearing stress 131.6 ± 0.2 MPa.     

Early bone apposition in vivo on plasma-sprayed and electrochemically deposited hydroxyapatite coatings on titanium alloy

Three different implants, bare Ti-6Al-4V alloy, Ti-6Al-4V alloy coated with plasma-sprayed hydroxyapatite (PSHA), and Ti-6Al-4V alloy coated with electrochemically deposited hydroxyapatite (EDHA), were implanted into canine trabecular bone for 6 h, 7, and 14 days, respectively. Environmental scanning electron microscopy study showed that PSHA coatings had higher bone apposition ratios than those exhibited by bare Ti-6Al-4V and EDHA coatings after 7 days; however, at 14 days after implantation, EDHA and PSHA coatings exhibited similar bone apposition ratios, much higher than that for bare Ti-6Al-4V. The ultrastructure of the bone/implant interface observed by transmission electron microscope showed that the earliest mineralization (6 h-7 days) was in the form of nano-ribbon cluster mineral deposits with a Ca/P atomic ratio lower than that of hydroxyapatite. Later-stage mineralization (7-14 days) resulted in bone-like tissue with the characteristic templating of self-assembled collagen fibrils by HA platelets. Though adhesion of EDHA coatings to Ti-6Al-4V substrate proved problematical and clearly needs to be addressed through appropriate manipulation of electrodepositon parameters, the finely textured microstructure of EDHA coatings appears to provide significant advantage for the integration of mineralized bone tissue into the coatings.     

Bone bonding behavior of the hydroxyapatite containing glass-titanium composite prepared by the Cullet method.

Bioactive composites composed of hydroxyapatite containing glass (HA-G) as a coating and titanium (Ti) or titanium alloy implants as a substrate were prepared by the Cullet method. This method results in the HA-G coating layer on the substrate with a compositional gradient in HA concentration. The results of in vitro and in vivo experiments investigating the characteristics of the composite materials are reported and discussed in this article. In vitro evaluations confirmed that the Cullet method was suitable for the preparation of the functionally gradient composite implants with higher reliable quality. In vivo experiments permitted evaluation of bonding strength of these composite implants to living bone tissue. Mechanical pull-out tests indicated that the implants bonded to living bone at least as firmly as those by the conventional method, and that the adhesion between the HA-G coating layer and metal substrate was well integrated and strongly maintained in vivo. SEM observations with EDX and a histological study of the interface between the HA-G-Ti composite implants and bone tissue revealed not only that the implants bonded to bone directly without any intervening tissue but that bone ingrowth into the HA-G layer occurred. The HA-G-Ti composite implants demonstrate both biocompatible and osteoconductive characteristics, and may be expected to obtain good and lasting results when applied clinically.     

Electrohydrodynamic coating of metal with nano-sized hydroxyapatite

Electrohydrodynamic spray deposition of a hydroxyapatite (HA) suspension consisting of nano-particles has been used to create a hydroxyapatite coating comprising of nanostructured surface topography. Preliminary coating experiments were carried out on an Al substrate and 30 s was found to be the most appropriate coating time. HA coating on titanium for this duration was found to be well-bonded to the substrate after heat-treatment. A thickness of 2 mum was achieved in 30 s and formation of a bone-like apatite on the surface was detected after incubation of the heat-treated coated Ti in simulated body fluid. Therefore, we have uncovered a new procedure by which nano-biomaterials can be deposited on real orthopedic substrates to prepare bioactive thin coatings in a simple and easy manner.