Histomorphometric and microhardness assessments of sheep cortical bone surrounding titanium implants with different surface treatments

Several factors influence the healing process and the long-term mechanical stability of cementless fixed implants, such as bone remodeling and mineralization processes. Histomorphometric and bone hardness measurements were taken in implants inserted in sheep femoral cortical bone at different times to compare the in vivo osseointegration of titanium screws (diam.; 3.5 x 7 mm length) with the following surface treatments: machined (Ti-MA); acid-etched (Ti-HF); HA vacuum plasma spray (Ti-HA); and Ca-P anodization followed by a hydrothermal treatment (Ti-AM/HA). Ti-MA and Ti-AM/HA implants presented the lowest (Ra = 0.20 +/- 0.01 microm) and highest (Ra = 1.97 +/- 0.64 microm) significant (p < 0.0005) roughness value, respectively. Bone-to-implant contact of Ti-HF was lower than that of the other surface treatments at both experimental times (8 weeks: -20%, ns; 12 weeks: -30%, p < 0.01). Significant differences in MAR (mineral apposition rate) were also found between the different experimental times for Ti-MA (115%, p < 0.01) and Ti-HF (57%, p < 0.01), demonstrating that bone growth had slowed inside the screw threads of Ti-HA and Ti-AM/HA after 12 weeks. No bone microhardness changes in preexisting host bone were found, while Ti-MA showed the lowest value for the inner thread area at 8 weeks (HV(200 microm)= 49.8 +/- 3.8 HV). These findings confirm that osseointegration may be accelerated by adequate surface roughness and bioactive ceramic coating such as Ca-P anodization followed by a hydrothermal treatment, which enhance bone interlocking and mineralization.     

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.     

Novel carbon fiber composite for hip replacement with improved in vitro and in vivo osseointegration

A novel composite femoral stem has been developed to match cortical stiffness and achieve fixation by osseointegration with the primary goal to reduce cortical bone loss associated with stress shielding. The femoral stem consists of three distinct material layers: the first is a long carbon fiber (CF) in a polyamide 12 (PA12) polymer matrix (PA12/CF); the second is a PA12/HA (hydroxyapatite) interface; and the third is a plasma-sprayed coating of HA. In vitro studies with MG63 cells indicated that the HA surface supported improved proliferation and differentiation of osteoblast-like cells as determined by alkaline phosphatase activity and osteocalcin production when compared with Ti-6Al-4V (Ti64). In vivo studies comparing the composite and Ti64 rods in the rabbit femur demonstrated significantly higher bone apposition to the composite than Ti64 rods. The results of this study indicate that the invasion of surrounding bone cells and thus osteointegration together with its bone-matching mechanical properties make the PA12/CF/HA stem a promising hip replacement candidate.     

Osteointegration of femoral stem prostheses with a bilayered calcium phosphate coating

Our purpose was to evaluate the osteointegration of bilayered calcium phosphate (CaP)-coated femoral hip stems in a canine model. A first layer of hydroxyapatite (HA) 20 microm thick and a superficial layer of Biphasic Calcium Phosphate (BCP) 30 microm thick were plasma-sprayed on to the proximal region of sandblasted Ti6Al4V prostheses. Bilayered CaP-coated and non-coated canine femoral stems were implanted bilaterally under general anesthesia in 6 adult female Beagle dogs. After 6 and 12 months, a significant degradation of the bilayered coating occurred with a remainder of 33.1+/-12.4 and 23.6+/-9.2 microm in thickness, respectively. Lamellar bone apposition was observed on bilayered coated implants while fibrous tissue encapsulation was observed on non-coated femoral stems. The bone-implant contacts (BIC) were 91+/-3% and 81+/-8% for coated and 7+/-8% and 8+/-12% for non-coated implants, at 6 and 12 months, respectively. Our study supports the concept of a direct relationship between the biodegradation of CaP coating and the enhanced osteointegration of titanium prostheses. A bilayered CaP coating might therefore enhance bone apposition in the early stages because of the superior bioactivity of the BCP layer while the more stable HA layer might sustain bone bonding over long periods.     

In vivo bone response to 3D periodic hydroxyapatite scaffolds assembled by direct ink writing

The in vivo bone response of 3D periodic hydroxyapatite (HA) scaffolds is investigated. Two groups of HA scaffolds (11 mm diameter x 3.5 mm thick) are fabricated by direct-write assembly of a concentrated HA ink. The scaffolds consist of cylindrical rods periodically arranged into four quadrants with varying separation distances between rods. In the first group, HA rods (250 microm in diameter) are patterned to create pore channels, whose areal dimensions are 250 x 250 microm(2) in quadrant 1, 250 x 500 microm(2) in quadrants 2 and 4, and 500 x 500 microm(2) in quadrant 3. In the second group, HA rods (400 microm in diameter) are patterned to create pore channels, whose areal dimensions of 500 x 500 microm(2) in quadrant 1, 500 x 750 microm(2) in quadrants 2 and 4, and 750 x 750 microm(2) in quadrant 3. Each group of scaffolds is partially densified by sintering at 1200 degrees C prior to being implanted bilaterally in trephine defects of skeletally mature New Zealand White rabbits. Their tissue response is evaluated at 8 and 16 weeks using micro-computed tomography, histology, and scanning electron microscopy. New trabecular bone is conducted rapidly and efficiently across substantial distances within these patterned 3D HA scaffolds. Our observations suggest that HA rods are first coated with a layer of new bone followed by subsequent scaffold infilling via outward and inward radial growth of the coated regions. Direct-write assembly of 3D periodic scaffolds composed of micro-porous HA rods arrayed to produce macro-pores that are size-matched to trabecular bone may represent an optimal strategy for bone repair and replacement structures.     

Characterization of nano hydroxyapatite/collagen surfaces and cellular behaviors

Osseointegration at the bone-implant interface is a prerequisite for endosseous implants to succeed in achieving and maintaining their long-term stability in bone tissue. The achievement of osseointegration is significantly affected by surface nature of implants. To optimize osseointegration, this study presents the characterization of synthesized nanocrystalline hydroxyapatite (nano HA) and in vitro studies on nano HA, nano-HA/collagen, and titanium surfaces. Voids were found within the grain of nano HA, which consisted of the shell and the core. The finding assists the clarification of microstructures of nano HA. By low-temperature mixing nano-HA sol with collagen gel (nano-HA/collagen 80:20), nano HA, and nano-HA/collagen coated on pure titanium or porous anodic titanium oxides resulted in higher wettability and lower roughness. The in vitro studies showed that porous structures produced by anodic oxides on titanium served as positive anchorage sites for cell filopodia to connect, and nano HA decreased cell attachment of osteoblasts and induced well-developed long filopodia and broad lamellipodia, thereby enhancing cellular motility. Collagen involvement enhanced cell adhesion to nano HA. Cell reactions to nano HA, nano-HA/collagen, native, and porous titanium surfaces provide some guidance for an optimal osseointegration by their application in surface modifications for implants.     

Evaluation of titanium plasma-sprayed and plasma-sprayed hydroxyapatite implants in vivo

In this study, bone interfacial strength and bone contact length at the plasma-sprayed hydroxyapatite (HA) and titanium plasma-sprayed (TPS) implants were evaluated in vivo. Non-coated titanium (Ti) implants were used as controls. Cylindrical coated or non-coated implants (4.0mm diameter by 8mm long) were implanted in the dogs' mandibles. Loading of the implants was performed at 12 weeks after implantation. At 12 weeks after implantation (prior to loading) and 1 year after loading, implants were evaluated for interfacial bone-implant strength and bone-implant contact length. No significant differences in interfacial bone-implant strength for all groups at 12 weeks after implantation and after 1 year loading in normal bone were found. However, bone contact length for HA implants was significantly higher than the TPS and Ti implants for both periods tested (12 weeks after implantation and 1 year after loading). It was concluded that TPS implants exhibited similar pull-out strength compared to the HA implants. In addition, the lower bone contact length on the TPS surface compared to HA surfaces did not affect the interfacial bone-implant strength for both implants.     

Comparative in vivo evaluation of porous and dense duplex titanium and hydroxyapatite coating with high roughnesses in different implantation environments

Ti (PG60) and Ti plus HA (HPG60) dense coatings with ultrahigh roughness (Ra: 74 +/- 8 microm and 53 +/- 18 microm, respectively) were compared to high Ti (Ti60) and Ti plus HA (HT60) high roughened porous coatings (Ra: 40 +/- 7 microm and 36 +/- 3 microm, respectively). Surfaces were implanted in cortical and trabecular bone of young adult (YOUNG), aged (AGED) and estrogen-deficient sheep (OVX) and analyzed by means of histology, histomorphometry and push-out tests 3 months after implantation. A significantly lower value in affinity index (AI) of PG60 when compared to TI60 (p < 0.01) was observed in cortical bone. In trabecular bone, lower values in AI were found in TI60 and PG60 when compared to their HA-coated surfaces (p < 0.0005). Bone ingrowth (BI) of TI60 and PG60 was significantly lower than that of the HA-coated surfaces in trabecular bone (p < 0.05). Significantly lower values in BI in OVX sheep in comparison to YOUNG sheep in both cortical and trabecular bone were observed (p < 0.05). Data showed that high roughness and Ti and HA-coated surfaces are suitable for aged and osteoporotic patients. HA coatings represent the most successful strategy in trabecular bone.     

Preparation and osteocompatibility of hydroxyapatite coated on titanium from the reaction of sputtered CaO and vaporized P2O5

Hydroxyapatite (HA) and other calcium phosphates were synthesized on titanium plates by a solid-gas state reaction of sputtered CaO and vaporized P(2)O(5). The calcium phosphates formed were HA, beta-tricalcium phosphate (beta-TCP; Ca(3)(PO(4))(2)), beta-calcium pyrophosphate (beta-PYR; Ca(2)P(2)O(7)), and beta-calcium metaphosphate (beta-MET; Ca(2)(PO(3))(2)). Their formation depended on the ratio of the sputtered CaO and the reacting P(2)O(5). For a mole ratio of CaO/P(2)O(5)=4 (Ca/P=2), an HA film was synthesized. The surface roughness increased by over seven times after the solid-gas state reaction from Ra = 0.16+/-0.02 microm (for the CaO film) to Ra = 1.15+/-0.25 microm (for the reacted film). The synthesized HA film-coated titanium plates and control non-coated titanium plates were implanted in the femora of two dogs for a period of two, four and 12 weeks, and observed using a soft X-ray radiograph and histological sections. New bone formation was observed without any connective tissue at four weeks around the HA film, whereas over the 12 week experimental period, there was no new bone formation around the control and connective tissue was observed over all periods, reaching a thickness of more than 200 microm at 12 weeks.     

Inhibition of Ni release from NiTi alloy by hydroxyapatite,alumina, and titanium sputtered coatings

To alleviate the effects of Ni allergy from NiTi alloy implants, hydroxyapatite (Ca10(PO4)6(OH)2; HA), alumina (Al2O3), or titanium (Ti) was coated onto NiTi alloy plates to form 1-microm thick films using radio frequency magnetron sputtering. The coatings on the plates were characterized using XRD. After the plates had been immersed in physiological saline for periods of one, four, or eight weeks, the concentration of Ni ions released in each solution was detected using a microwave induced plasma mass spectrometer. After eight weeks, the concentration of Ni ions released from the non-coated, the Ti-coated, the HA-coated, and the alumina-coated plates were 238, 19.7, 183, and 106 ppb, respectively. The bonding strength of the Ti film, the HA film, and the alumina film to the NiTi substrate were 3.8 +/- 1.2, 2.6 +/- 0.7, and 3.1 +/- 1.2 MPa, respectively.The non-coated, the HA-coated, the alumina-coated, and the Ti-coated plates were implanted into the femurs of a dog for four weeks for histological observation. In case of the non-coated plates, connective tissue more than 300 microm thick was observed, whereas for the coated plates the thickness of the connective tissue was around 100 microm.     

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 removal torque of titanium screw inserted in rabbit tibia treated by dual acid etching

Chemical acid etching alone of the titanium implant surface have the potential to greatly enhance osseointegration without adding particulate matter (e.g. TPS or hydroxyapatite) or embedding surface contaminants (e.g. grit particles). The aims of the present study were to evaluate any differences between the machined and dual acid etching implants with the removal torque as well as topographic analysis. A total of 40 custom-made, screw-shaped, commercially pure titanium implants with length of 5 mm and an outer diameter of 3.75 mm were divided into 4 groups, 10 screws in each, and chemical modification of the titanium implant surfaces were achieved using HF and HCl/H(2)SO(4) dual acid etching. The first exposure was to hydrofluoric acid and the second was to a combination of hydrochloric acid and sulfuric acid. The tibia metaphysics was exposed by incisions through the skin, fascia, and periosteum. One implant of each group was inserted in every rabbit, 2 in each proximal tibia metaphysics. Every rabbit received 3 implants with acid etched surfaces and 1 implant with a machined surface. Twelve weeks post-surgically, 7 rabbits were sacrificed, Subsequently, the leg was stabilized and the implant was removed under reverse torque rotation with a digital torque gauge (Mark-10 Corporation, USA) (Fig. 1). Twelve weeks after implant placement, the removal torque mean values were the dual acid etched implants (24%HF+HCl/H(2)SO(4), group C) required a higher average force (34.7 Ncm), than the machined surface implants (group A) (p=0.045) (Mann-Whiteney test). Scanning electron micrographs of acid etching of the titanium surface created an even distribution of very small (1-2 microm) peaks and valleys, while machining of the titanium surface created typical microscopically grooved surface characteristics. Nonetheless, there was no difference in surface topography between each acid etched implant groups. Therefore, chemically acid etching implant surfaces have higher strengths of osseointegration than machined implant surfaces. There is less correlation between removal torque and the difference in HF volume%.     

Bone growth in rapid prototyped porous titanium implants

Two porous titanium implants with a pore size diameter of 800 and 1200 microm (Ti800 and Ti1200) and an interconnected network were manufactured using rapid prototyping. Their dimensions and structure matched those of the computer assisted design. The porosity of the implants was around 60%. Their compressive strength and Young's modulus were around 80 MPa and 2.7 GPa, respectively. These values are comparable to those of cortical bone. The implants were implanted bilaterally in the femoral epiphysis of 15 New Zealand White rabbits. After 3 and 8 weeks, abundant bone formation was found inside the rapid prototyped porous titanium implants. For the Ti1200 implants, bone ingrowth was (23.9 +/- 3.5)% and (10.3 +/- 2.8)%, respectively. A significant statistical difference (p < 0.05) was found for bone ingrowth in the Ti1200 between the two delays. The percentage of bone directly apposited on titanium was (35.8 +/- 5.4)% and (30.5 +/- 5.0)%. No significant difference was found for bone-implant contact between the different time periods and pore sizes. This work demonstrates that manufacturing macroporous titanium implants with controlled shape and porosity using a rapid prototyping method is possible and that this technique is a good candidate for orthopedic and maxillofacial applications.     

Long-term study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures: a 2-4-year follow-up study in rabbits

Biodegradation of hydroxyapatite (HA)/poly(L-lactide)(PLLA) composite bone implant rods was studied with the use of two types of HA particles as reinforcing fillers: uncalcined HA (u-HA) or calcined HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA containing 30 or 40% (w/w) HA were implanted in the distal femur of 21 rabbits, and specimens were examined by light microscopy, scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM) 2-4 years later. For u-HA/PLLA, trabecular bone bonding directly onto the rod was maintained for up to 2 years. By 3 years, surface collapse had begun, and the implants were shrinking. By 4 years, they had shrunk further, with complete bone encapsulation. The u-HA particles were small and needle shaped in the peripheries, and TEM confirmed their resorption. The cross-sectional area after 4 years decreased by 23.3+/-8.4%. The mean ratio of bony ingrowth to the initial cross-sectional area around the shrunken rods was 6.7+/-1.3 %. The viscosity molecular weight of PLLA reduced from 2 x 10(5) to less than 1 x 10(3). Thus, most of the PLLA had released from the rods. The c-HA/PLLA implants also showed good osteoconductivity, but shrinkage and infiltration of histiocytes were less. No osteolytic or osteoarthritic changes were found.     

阳极氧化伴水热处理制备纯钛羟基磷灰石薄涂层

为了解纯钛阳极氧化伴水热处理的技术路线及羟基磷灰石薄涂层在体内的成骨效应，以钛片为阳极，β－磷酸甘油钠和醋酸钙为电解质，经200－400V直流电解15min，维持电流密度≤50mA/cm^2，而后经280℃－300℃水热处理2h，取光滑，喷砂表面作对照，分别植入12只兔股骨内，枯术后4，8，16周取出带种植体骨块制作磨片，观察新骨生成情况及术后8周光滑和涂层种植体的界面超微结构，并作表面能谱分析，结果发现水热处理后，钛片表面出现了羟基磷灰石涂层，动物实验显示涂层种植体8周后编织骨的转化和成熟较快，未见剥脱的羟基磷灰石碎片，其表面的钙，磷含量在种植后增加明显，这说明阳极氧化伴水热处理可以制备出纯钛表面羟基磷灰石薄涂层，其早期促编织骨形成作用明显，可以加快编织骨转化成板层骨。     

Osseointegration of sandblasted or anodised hydrothermally-treated titanium implants: mechanical,histomorphometric and bone hardness measurements

The improvement of the implant-bone interface is still an open problem in the long-term mechanical stability of cementless fixed implants. Mechanical, histomorphometric and bone hardness measurements were performed in sheep femoral cortical bone implants at 8 and 12 weeks from surgery to compare in vivo the osseointegration of titanium screws (psi 3.5 mm x 7 mm length) with two different surface treatments: sandblasting with 70-100 microm HA followed by acid etching with HNO3 (Group A) and Ca-P anodization followed by a hydrothermal treatment (Group B). No significant differences were found for maximum push-out force and interfacial strength between groups at both experimental times. No significant difference was observed for Bone Ingrowth between groups at both experimental times, while the Affinity Index of Group B was significantly higher (7.5%, p<0.05) and lower (10.2%, p<0.05) than that of Group A at 8 and 12 weeks, respectively. Finally, a significant increase in bone microhardness measured within 200 microm from the interface and inside the thread depth of Group A was observed between the two experimental times (p<0.05). In conclusion, present findings show that osseointegration may be accelerated by adequate surface roughness and bioactive ceramic coating such as current tested treatments which enhance bone interlocking and mineralization.     

RGD-coated titanium implants stimulate increased bone formation in vivo

Numerous studies have demonstrated that peptide modified surfaces influence short- and long-term cell responses such as attachment, shape and function in vitro. These responses are mediated via cell receptors known as integrins which bind specifically to short peptide sequences from larger proteins. Integrins transduce information to the nucleus through several cytoplasmic signalling pathways. Little is known, however, about the ability of peptide-coated surfaces to influence cell responses in vivo. The present study was designed to evaluate the quality and quantity of the new bone formed in response to titanium rods surface-coated with the peptide sequence Arg-Gly-Asp-Cys (RGDC) using gold-thiol chemistry and implanted in rat femurs. Histomorphometric analysis of cross-sections perpendicular to the implant long axis showed a significantly thicker shell of new bone formed around RGD-modified versus plain implants at 2 weeks (26.2 +/- 1.9 vs. 20.5 +/- 2.9 microm; P < 0.01). A significant increase in bone thickness for RGD implants was also observed at 4 weeks while bone surrounding controls did not change significantly in thickness (32.7 +/- 4.6 vs. 22.6 +/- 4.0 microm; P < 0.02). Mechanical pull-out testing conducted at 4 weeks revealed the average interfacial shear strength of peptide modified rods was 38% greater than control rods although this difference was not statistically significant. These pilot data suggest that an RGDC peptide coating may enhance titanium rod osseointegration in the rat femur. Long-term studies and evaluation of other peptides in larger animal models are warranted.     

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.     

Interaction between topography and coating in the formation of bone nodules in culture for hydroxyapatite- and titanium-coated micromachined surfaces

Rat osteoblast cultures were maintained from 24 h to 6 weeks on hydroxyapatite (HA)- or titanium (Ti)-coated smooth and micromachined grooved substrata in medium supplemented with L-ascorbic acid-2-phosphate and beta-glycerophosphate to promote mineralization. The HA coatings, approximately 1 microm thick, were characterized using X-ray diffraction, surface roughness, and scanning electron microscopy (SEM). Osteoblasts elongated, aligned, and moved in the direction of the grooves on both Ti and HA grooved surfaces. HA surfaces produced significantly more bone-like nodules than Ti surfaces. All grooved substrata produced significantly more nodules than smooth surfaces. These results are consistent with the hypothesis that substrata can increase osteogenesis by formation of an appropriate microenvironment. There was also a statistically significant interaction between topography and chemistry in the formation of mineralized nodules. A strong correlation (r = 0.958) between alkaline phosphatase (Alk-P) at 2 weeks and nodule counts at 6 weeks was observed, suggesting that Alk-P may possibly be used as a leading indicator of osteogenesis on microfabricated surfaces. The results of this study indicate that surface topography and chemistry can affect osteogenesis, and that interactions between chemistry and topography can occur.     

Ability of zirconia double coated with titanium and hydroxyapatite to bond to bone under load-bearing conditions

As a preclinical study, we evaluated the ability of hydroxyapatite and titanium on zirconia (HTOZ) to bond to bone under load-bearing conditions in animal experiments. HTOZ, HA, and Ti on Co-Cr alloy (HTOC) and Ti on Co-Cr alloy (TOC) were implanted into the weight-bearing portion of the femoral condyles of nine beagle dogs. Femurs were extracted 4, 12, and 52 weeks after implantation and examined mechanically by pullout testing, and histologically by toluidine blue staining, SEM, and calculation of the affinity index. The interfacial shear strengths (mean+/-SD) of the HTOZ, HTOC, and TOC groups were 4.42+/-0.453, 3.90+/-0.903, and 4.08+/-0.790 MPa at 4 weeks; 6.82+/-2.64, 6.00+/-1.88, and 6.63+/-1.63 MPa at 12 weeks; and 13.98+/-1.94, 11.95+/-1.51, and 10.78+/-0.83 MPa at 52 weeks. There were no significant differences in the interfacial shear strengths between the three groups at any time. Affinity indices (mean+/-SD) obtained from SEM images of the HTOZ, HTOC, and TOC groups were 49.6+/-6.52%, 43.3+/-10.43%, and 23.7+/-3.95% at 4 weeks; 55.0+/-6.72%, 51.5+/-3.07%, and 28.6+/-4.09% at 12 weeks; and 59.1+/-6.73%, 63.0+/-6.40%, and 34.3+/-6.72% at 52 weeks. HA-coated implants (HTOZ, HTOC) had significantly higher affinity indices than non-HA-coated implants (TOC) at all times. HTOZ has the ability to bond to bone equivalent to HTOC and TOC. HTOZ is an excellent material for components of cementless joint prostheses.