Biological assessment of the bone-screw interface after insertion of uncoated and hydroxyapatite-coated pedicular screws in the osteopenic sheep

The sheep seems to be a promising model of osteoporosis and biomaterial osteointegration in osteopenic bone. The long-term ovariectomized sheep model was used for the biological investigation of bone healing around uncoated and hydroxyapatite (HA)-coated pedicle screws in osteopenic bone. Four sheep were ovariectomized and four sheep were sham-operated. Twenty-four months after surgery, the animals were implanted with uncoated and HA-coated stainless steel screws in the lumbar vertebral pedicles. Four months later, bone-to-implant contact, bone ingrowth, and bone hardness were measured around screws. Uncoated stainless steel presented significantly (p < 0.0005) lower bone-to-implant contact in healthy and osteopenic bone compared with HA-coated stainless steel. HA significantly improved bone ingrowth in healthy bone (p < 0.05) compared with uncoated stainless steel. Osteopenia significantly (p < 0.05) reduced the area of bone ingrowth around the screw threads for both types of implants. In the inner thread area, bone microhardness significantly increased (p < 0.05) in HA-coated surface versus uncoated for healthy and osteopenic bone. HA coating significantly enhances bone-to-implant contact also in osteopenic bone in comparison with uncoated stainless steel surfaces. Bone ingrowth and mineralization are ameliorated by the osteoconductive HA coating. However, osteopenia seems to greatly influence bone ingrowth processes around the implanted screws regardless of the characteristics of the material surface.     

An investigation of the effects of hydroxyapatite coatings on the fixation strength of cortical screws

Hydroxyapatite (HA) are commonly applied to orthopaedic implants for acceleration of osteointegration and so overcoming the loosening problems such as in cortical screws. Electrophoretic deposition (EPD) of hydroxyapatite was applied for coating of cortical screws in this work. The effects of hydroxyapatite-coated and uncoated cortical screws on insertion and extraction torque were investigated through in vivo experiments. Three groups of screws were undertaken: first group with no coating, second group coated with HA and the third group coated with HA+interlayer, a synthetic calcium silicate compound. Five sheep were operated, and 60 cortical (20 x 3) screws from those of groups were implanted in cortical femurs to observe the effect of HA and interlayer on screws. Results show that as an alternative to plasma spray coating method, the EPD process enables to produce a quick, easy, cheap and uniform adjustable coating layer. Also from biomechanical and SEM examinations, HA coating by EPD method of cortical screws resulted in extremely improved fixation with reduced risk of loosening problem.     

The effect of zoledronic acid incorporated in a poly(D,L-lactide) implant coating on osteoblasts in vitro

Bisphosphonates such as zoledronic acid (ZOL) are used in diseases associated with osteoclast-mediated bone loss. However, their antiresorptive activity is partly due to their effect on osteoblasts. Local application might increase the therapeutical fence and their local efficiency and reduce systemic side effects. Aim of the study was to investigate the effect of ZOL on human osteoblasts like cells in vitro with special focus on the synthesis of factors mediating osteoclast differentiation (RANKL, OPG). ZOL was incorporated in an implant coating based on poly(D,L-lactide) (PDLLA) in different concentrations (10-150 microM). Control groups were treated with uncoated implants, PDLLA-coated implants, and ZOL pure substance in corresponding concentrations. After an experimental period of 144 h, primary human osteoblasts were stained with alamar blue and cell viability was measured. Procollagen I synthesis, osteoprotegerin (OPG) secretion, and soluble receptor activator of nuclear factor-kappaB ligand (sRANKL) were analyzed. Results showed that cell viability was not affected when treated with doses equivalent up to 100 microM ZOL-coated implants (ZOL-CI). Procollagen I synthesis was highest when treated with 50 microM ZOL-CI. OPG increased significantly in the 10 microM ZOL-CI group, whereas sRANKL decreased significantly with different concentrations of ZOL-CI. Higher concentrations or exposure to the pure substance showed a decrease in cell viability, collagen I, OPG, and sRANKL synthesis. In conclusion, exposure to specific concentrations of ZOL-CI showed a beneficial effect on osteoblast differentiation and protein synthesis without influencing their proliferation. Changes in sRANKL and OPG production may contribute to the inhibition of osteoclastic bone resorption. This local antiresorptive effect might be clinically useful in osseous implant integration and fracture healing.     

Biologic effects of surface roughness and fluorhydroxyapatite coating on osteointegration in external fixation systems: an in vivo experimental study

The concomitant influence of surface roughness and fluorhydroxyapatite (FHA) coating of titanium (Ti) implants on bone response was investigated. For this purpose, titanium screw-shaped implants with a lower degree (Y371) and a higher degree (TiPore300) of surface roughness, coated with FHA and uncoated, were transversally inserted into the diaphyses of sheep tibiae for 12 weeks. Four sheep received Y371 (group A) and Y371 + FHA (group B) screws and four sheep received TiPore300 (group C) and TiPore300 + FHA (group D) screws. For each type of material, the morphology and microstructure of implant-facing bone were evaluated. The host bone of each tibia was used as a control. In all groups the bone tissue did not reach a complete maturation. The higher degree of roughness, perhaps due to an excessive irregularity of the surface, induced the worst osteointegration: a fibrous tissue layer between screw and new bone tissue was often present. Nevertheless, as viewed by XRD, no crystallographic change of the apatite lattice was observed in any of the implants. In contrast, the microhardness value, an index of bone mineralization, was higher in the uncoated screws and decreased progressively in the following order: group C > group A > group B > group D. The association of plasma spraying with roughness treatment constitutes a complex system that seems to interfere with bone mineralization. A chemical change of the surface, perhaps with more Ti release or more coating degradation, could be responsible for such impairment. The authors emphasize the necessity for simultaneous evaluation of surface topography and chemistry as well as an improvement in plasma-spraying and post-processing techniques and in standard procedures for materials characterization.     

Prevention of pin track infection in external fixation with silver coated pins: clinical and microbiological results

Pin tract infection is a frequent complication of external fixation; according to literature its frequency ranges from 2-30%. The recent introduction of silver coating of polymeric materials was found to decrease bacterial adhesion; its clinical use with Foley catheters and central venous catheters led to significant results. To verify the ability of the same silver coating to decrease the bacterial colonization on external fixation screws, a prospective randomized study was carried out on 24 male patients; a total of 106 screws were implanted in the lower limb to fix femoral or tibial diaphyseal fractures: 50 were coated with silver and 56 were commercially available stainless steel screws. Although the coated screws resulted in a lower rate of positive cultures (30.0%) than the uncoated screws (42.9%), this difference was not statistically significant (p = 0.243). The clinical behavior of the coated screws did not differ from that of the uncoated ones. Furthermore, the implant of silver-coated screws resulted in a significant increase in the silver serum level. These results led us to consider it ethically unacceptable to continue this investigation.     

Composite resorbable polymer/hydroxylapatite composite screws for fixation of osteochondral osteotomies

The aim of this study was to evaluate biomechanically the healing of an osteochondral fragment created in the distal sheep femur in response to fixation with a resorbable composite screw made of polylactide and hydroxylapatite. Pure poly(L-lactide) screws were used for comparison. At follow-up times of 4 or 8 weeks, specimens were examined with standard radiography, biomechanics, and histology. The intact contralateral femur served as a control. Only minimal signs of polymer degradation were seen in the histologic specimens. At 8 weeks, most osteotomies had healed completely and there was no difference in compressive strength and elastic modulus of cylindrical cores between the two types of biodegradable implants used. The width of the repair tissue at the tissue-implant interface was 250+/-50 micro m representing a clear transition zone of newly formed trabecular bone separating the implant from the surrounding plexiform bone. We conclude that relatively large polylactide implants, blended with hydroxyapatite, are capable of fixing an osteochondral fragment in an animal model. Biomechanical data assessing the quality of the bone formed at the osteotomy sites were found to be equivalent when compared to the control poly(L-lactide) implants of similar design and size. In addition, hydroxylapatite composite implants showed benign tissue responses and good implant osteointegration. Results suggest that hydroxylapatite composite screw implants can be used for similar indications as pure poly(L-lactide) implants in current clinical use.     

Tibial implants: biomechanical and histomorphometric studies of hydroxyapatite-coated and uncoated stainless steel and titanium screws in long-term ovariectomized sheep.

This study was designed to evaluate osteointegration of HA-coated and uncoated titanium and stainless steel screws in the cortical bone of long-term (24 months) ovariectomized sheep (OVX group), in comparison with Sham-aged sheep (control group). The screws were tested biomechanically (extraction torque) and histomorphometrically (affinity index: Al) 12 weeks after their implantation in tibial diaphyses. Tibial cortical bone parameters showed significant differences between the groups, showing a reduction of the selected parameters in the OVX group. ANOVA showed significant effects for both material and ovariectomy factors on obtained extraction torque (material: F=159.26, p < 0.0005; ovariectomy: F=20.04, p < 0.0005) and Al data (material: F=8.04, p < 0.001; ovariectomy: F=7, 17, p < 0.05). In both groups the extraction torque for coated screws of both materials was significantly higher than for uncoated screws, and uncoated titanium had a better extraction torque than uncoated stainless steel. In the OVX group, the HA-coated stainless steel and titanium Al data were significantly higher than uncoated Al data. In conclusion, the biomechanical and histomorphological results obtained suggest employing HA-coated screws in the presence of osteopenic cortical bone.     

A biomechanical and histological analysis of standard versus hydroxyapatite-coated pins for external fixation

This sheep study was designed to make a comparative evaluation of two external fixation pin types each with and without hydroxyapatite (HA) coating. The two pins had different taper, pitch, and self drilling capabilities. Twenty Orthofix standard, self-tapping pins (group A), 20 Orthofix HA-coated, self-tapping pins (group B), 20 X-caliber, self-drilling, self-tapping pins (group C), and 20 X-caliber HA-coated, self-drilling, self-tapping pins (group D) were selected. Four pins were implanted in the right femurs of 20 adult sheep that were euthanized at 6 weeks. Mean pin insertion torque was 2745 +/- 822 Nmm in group A, 2726 +/- 784 Nmm in group B, 2818 +/- 552 Nmm in group C, and 2657 +/- 732 Nmm in group D (ns). Mean pin extraction torque was 1567 +/- 541 Nmm in group A, 2524 +/- 838 Nmm in group B, 1650 +/- 650 Nmm in group C, and 2517 +/- 726 Nmm in group D. HA-coated pins (group B and D) had a significantly greater mean pin extraction torque compared to similar uncoated pins (group A and C) (p < 0.0005). Histological analysis showed good osteointegration of the two coated pin types. This study shows that HA-coating is more important for optimal pin fixation than the particular combination of design parameters used in each pin type.     

异种生物骨钉界面的成骨能力

背景：牛皮质骨作为异种皮质骨材料应用最为广泛,但其免疫原性反应严重,从而可能导致内固定失败。 目的：观察3种不同皮质骨螺钉在动物体内的转归,及不同材料骨钉的生物力学性能以及免疫原性反应差异。 方法：脱脂、脱细胞、灭菌及诱导活性修饰处理制备牛皮质骨生物界面螺钉及普通方式处理后的消毒牛骨钉及消毒羊骨钉。再将3种骨钉植入健康18只山羊股骨中段进行生物学性能观察。 结果与结论：Lane组织学评分生物界面骨螺钉>消毒羊骨钉>消毒牛骨钉(P < 0.01)。生物力学实验行初始界面刚度载荷及界面刚度比较,3组差异无显著性意义(P > 0.05);12周时,生物界面骨螺钉>两组消毒钉(P< 0.05);24周时,生物界面骨螺钉>消毒羊骨钉>消毒牛骨钉(P < 0.01)。提示,生物界面骨螺钉的初始力学性能不低于消毒牛骨,且能较长时间保持稳定的力学性能;生物界面骨螺钉具有一定的成骨作用,与宿主骨组织结合后,产生了更强的界面力学性能。     

Short term in vivo biocompatibility testing of biodegradable poly(D,L-lactide)--growth factor coating for orthopaedic implants

Fracture healing can be stimulated by exogenous application of growth factors. Using porcine and rat models the efficacy of locally delivered IGF-I and TGF-beta1 from an implant coating has been demonstrated. A thin and biomechanical stable biodegradable poly(D,L-lactide) was used to coat implants and serve as a drug carrier. Due to reports of possible foreign body reactions caused by polymer materials in orthopedic surgery, this study investigated the biocompatibility of the polylactide implant coating and the locally released growth factors during the time course of rat tibial fracture healing (days 5, 10, 15, and 28 after fracture). Monocytes/macrophages and osteoclast were detected using an monoclonal antibody against ED1 (comparable to CD68 in mice and human). The antibody ED1 stains monocytes, macrophages and osteoclast in the bone marrow and in the newly formed fracture callus. A moderate density of the monocytes/macrophages was seen in the proximal part of the medullary canal, but almost no cells were detectable in the region distal to the fracture. The amount of stained cells increased during the observation time with a maximum at days 10 and 15 followed by a decrease at day 28. No differences were detectable between the investigated groups from day 5 to 15 post fracture indicating, that the used poly(D,L-lactide) or the incorporated growth factors do not evoke an elevated immunological response compared to the uncoated titanium implant at the investigated time points. A significantly higher amount of ED1 positive cells was measured 28 days after fracture in the control group compared to the groups with the coated implants. In conclusion, no indication of a foreign body reaction due to the use of the polylactide or the growth factors was found indicating a good short-term biocompatibility of this bioactive coating.     

钛涂层317L接骨板螺钉与放射骨界面的光镜观察

目的：光镜观察钛涂层317L接骨板螺钉与放射骨界面。方法：钛涂层317L接骨板螺钉植入经9MeV电子线照射30Gy后4周的犬右下颌骨体部作为实验组,以未喷涂钛层的317L接骨板螺钉作为对照组。术后3、6、12周用光镜观察接骨板螺钉与放射下颌骨界面。结果：钛涂层317L接骨板螺钉与骨面呈骨整合界面结合关系,新骨形成快;未喷涂钛层的317L接骨板螺钉与骨面呈纤维性界面结合关系,新骨形成缓慢,有一厚纤维组织层。结论：在犬下颌部照射30Gy相同条件下,钛涂层317L接骨板螺钉生物相容性明显优于未喷涂钛层317L接骨板螺钉。     

Bone regeneration in segmental defects with resorbable polymeric membranes: IV. Does the polymer chemical composition affect the healing process?

Diaphyseal segmental defects 10 mm in length in the radii of 36 skeletally mature rabbits were covered with tubular microporous membranes prepared from poly(L/D-lactide) (18 rabbits) and poly(L/DL-lactide) (18 rabbits) to determine whether chemical composition of the membrane affected the bone healing in the defect. The results of a previous study in which similar defects of the rabbits radii were not covered with membranes or covered with poly(L-lactide) membranes were used as controls. The control defects were rapidly filled with overlying muscle and soft tissues, producing a radio-ulnar synostosis. The osseous activity of control defects was limited to the bone ends. The defects covered with membranes were progressively filled with new bone. At 1 year, complete bone regeneration in the defects covered with the poly(L/D-lactide) membrane was found in 16 cases, no regeneration in 1 animal and pseudoarthrosis in 1 animal. For the poly(L/DL-lactide) membrane there was complete bone regeneration in 17 cases (1 animal died during surgery). The quality of the interface between the new bone and the membrane seemed to be affected by the chemical structure of the polylactides used for membranes preparation. For poly(L/D-lactide), the connective tissue layer entirely separated the new bone from the polymeric membrane. This has been observed before for poly(L-lactide) membranes. In the case of poly(L/DL-lactide) the new bone was formed in some places in direct contact with the membrane and the membrane fragments were osteointegrated. The differences in chemical composition of the polylactide membranes did not have an evident effect on the bone regeneration process in segmental defects of the rabbit radii.     

骨转移瘤的溶骨与成骨机制研究进展

骨骼是一种动态重塑的组织,终身以骨质溶解和骨质形成的方式进行骨骼动态重塑循环。骨微环境适宜实体肿瘤定植与生长。实体肿瘤骨转移发生率高,骨转移瘤可以导致明显溶骨性和(或)成骨性骨病灶,如乳腺癌主要以溶骨性病灶为典型,前列腺癌主要以成骨性病灶为主。骨转移瘤的骨骼生理以过度溶骨和(或)成骨为中心。溶骨和成骨的主要机制相互区别独立,本质上均为溶骨与成骨的相关因子打破机体正常骨骼重塑动态循环：RANK-RANKL-OPG系统、甲状旁腺激素相关肽和转移生长因子β参与溶骨,Wnts、内皮素1、甲状旁腺激素相关肽和骨形态发生蛋白参与成骨。骨转移瘤的溶骨与成骨效应都属于正反馈性"恶性循环"。本综述在理解正常骨骼生理与骨骼重塑动态循环的基础上重点阐述骨转移瘤的溶骨和成骨生理机制。探索骨转移瘤的溶骨和成骨生理机制可以为研究者研发靶向药物提供契机。     

Effect of RGD coating on osteocompatibility of PLGA-polymer disks in a rat tibial wound

Osteocompatibility of porous polylactic-glycolic acid (PLGA) disks coated with synthetic peptides was assessed in 5-mm diameter unicortical tibial osseous wounds in rats. The coatings consisted of various ratios of peptides including the tripeptide arginine-glycine-aspartic acid (RGD) and the inactive arginine-glycine-glutamic acid (RGE). When left empty, the tibial wounds healed spontaneously with proliferation of intramedullary woven bone within 1 week. The reactive bone was resorbed, and by 3 weeks, the cortical wound was healed with lamellar bone, and the medullary space was repopulated with marrow. When PLGA disks were implanted there was a delay in repair with reduced bone fill and no bone bridging at 3 weeks. When disks were coated with increasing amounts of RGD peptide, there was a biphasic effect on osteocompatibility and on osseous ingrowth. Evaluation at 10 days showed a dose-dependent increase, with 1.5-fold greater osteocompatibility (p < 0.05) and 1.6-fold more osseous ingrowth into the polymer (p < 0.01) than uncoated disks. With more RGD and with undiluted RGE, osteocompatibility and osseous ingrowth were the same as with uncoated disks. At 3 weeks, there were no significant differences among all the groups. These data indicate that RGD coating enhanced early stages of osteocompatibility and ingrowth.     

Macrophages at the skeletal tissue-device interface of loosened prosthetic devices express bone-related genes and their products

Aseptic loosening of prosthetic arthroplasty is the most common reason for implant failure in adult orthopaedic reconstruction. At the interface of aseptic loosened prostheses, there is an abundance of particle-activated macrophages and other inflammatory cells. The role of these particle-laden macrophages in the osteogenic arm of the remodeling skeleton in this pathological condition is poorly understood. Molecular signaling by mesenchymal cells and mononuclear inflammatory cells residing in the interfacial tissues between bone and cement or prosthetic material of aseptically loosened joint prostheses was studied using in situ hybridization and immunohistochemical techniques. We found that a range of collagenous and noncollagenous matrix proteins, including osteopontin, osteocalcin, bone sialoprotein, and type I collagen, were produced in the periprosthetic tissue by foamy macrophages, as well as nearby osteogenic cells. The former accumulated in profusion in the three zones of interfacial tissues: pseudomembranous, fibrous, and osseous. Spindle mesenchymal cells in the fibrous zone failed to express any of the osteogenic mRNAs or proteins sought. The expression of bone-related genes and proteins by foamy macrophages at the interface of an aseptic loosened prosthesis may contribute to the disturbance of bone remodeling at this site.     

Effect of hydroxyapatite coating and polymethylmethacrylate on stainless steel implant-site infection with Staphylococcus epidermidis in a sheep model

We aimed to study the influence of hydroxyapatite (HA) coating and polymethylmethacrylate (PMMA) cement on the risk of development of stainless steel implant-site infection with Staphylococcus epidermidis in a sheep model. Uncoated, HA-coated, and PMMA-cemented stainless steel implants were inserted in the left femur of 30 sheep. For each type of implant, sheep were inoculated with S. epidermidis in the intramedullary canal and one non-inoculated group was used as control. After 6 weeks, infection was evaluated using clinical, radiological, bacteriological, and histological criteria. Radiological and clinical results were normal. Cultures were negative in the control sheep. In the inoculated sheep, interposition tissue and bone cultures were positive in 2 of 6 uncoated, 6 of 6 HA, and 6 of 6 PMMA implants with a mean bacteria count of 5.2 +/- 1.17, 3.5 +/- 0.7, and 3.9 +/- 0.9 log10 cfu/g, respectively (NS), for interposition tissue, and 4 +/- 0.01, 2.9 +/- 0.6, and 2.5 +/- 1.3 log10 cfu/g, respectively (NS) for bone. The polymorphonuclear leukocyte (PMN) score (mean number of PMN per 10 different microscopic high-power fields >or=5) in interposition tissue was >or=3 in 6 of 6 HA, significantly different from uncoated (3 of 6) and PMMA (2 of 6) groups (p = 0.04). The HA and PMMA inoculated groups had a higher infection rate than the uncoated inoculated group (p = 0.06). In this experimental sheep model of S. epidermidis infection at the bone-biomaterial interface, HA seems to be at higher risk of infection compared with uncoated or PMMA-cemented stainless steel, when inoculation is intramedullary and contemporary with implantation.     

Osteointegration of hydroxyapatite-coated and uncoated titanium screws in long-term ovariectomized sheep.

This study was designed to evaluate the osteointegration of HA-coated and uncoated titanium screws in the cortical bone of long-term (24 months) ovariectomized sheep (OVX group) compared to sham-aged sheep (Control group). At 12 weeks after implantation, the screws were tested biomechanically (extraction torque) and histomorphometrically (affinity index: AI) in both femoral and tibial diaphyses. Cancellous bone status was assessed by iliac crest biopsy. BMD of the L5 vertebra and a histomorphological study of the femoral and tibial shafts were performed to acquire data on cortical bone. A significant difference was found between the OVX and Control groups for BMD (p<0.0005), and a significant reduction in the cancellous bone area was observed in the OVX group. Femoral and tibial cortical bone parameters showed significant differences between the groups. The type of material selected (femurs: p<0.0005; tibiae: p<0.0005) and ovariectomy (femurs: p<0.005; tibiae: p<0.005) had a significant effect on the extraction torque. AI results were related to the presence or absence of ovariectomy (p<0.05) and strictly depended on the material implanted in the femur and tibia (p<0.0005). In conclusion, at implantation OVX sheep showed a significant loss of trabecular and cortical bone versus sham-aged sheep. The biomechanical and histomorphological results achieved suggest employing HA-coated screws in the presence of osteopenic cortical bone.     

Axial Vibration of Threaded External Fixation Pins: Detection of Pin Loosening

The hypothesis of this study was that a nondestructive vibrational method could detect bone lysis at the external fixation pin–bone interface prior to current clinical and radiographic methods. In vitro models were used to simulate changes observed during pin loosening in vivo. Fixation pin axial natural frequency decreased with decreasing tensile modulus of the material into which it was implanted. In a live animal study the right tibia of 12 dogs was fractured and stabilized with a four-pin unilateral external fixation frame. The axial natural frequency of each pin was measured and radiographs were taken at 0, 2, 4, 6, 8, and 10 weeks after surgery. The natural frequency did not change when the first radiographic changes around the interface were observed. Pins were palpably stable at this point. As loosening progressed, the natural frequency did decrease. Frequency and quasistatic tests of dissected pin–bone structures revealed a good correlation between natural frequency and pin–bone interface stiffness. In addition, the measurement of natural frequency was more sensitive to bone structure changes at the pin–bone interface than low-load quasi-static stiffness. Therefore, a nondestructive vibration technique could be used instead of low-load quasistatic tests for assessing the pin–bone interface ex vivo.     

Osseointegration of alumina with a bioactive coating under load-bearing and unloaded conditions

The aim of the study was to evaluate the osseointegration of Al(2)O(3) coated with a bioactive glass ceramic (BioveritI), in a load-bearing implant model in sheep in comparison to uncoated Al(2)O(3) and to a minimally loaded situation. Both types of implants were inserted into the proximal tibia (load-bearing model) and in a drill hole defect into the tibia diaphysis (minimally loaded model). Under load-bearing conditions, the coating resulted in significantly higher interfacial shear strength and a high amount of mineralized bone in direct contact to the implant surface. In contrast, the uncoated Al(2)O(3) was surrounded by a thick connective tissue layer corresponding to low interfacial shear strength. In the minimally loaded model, however, there was rather a tendency of lower interfacial shear strength in the case of the coated implants. This finding corresponds to the histological results, which showed mineralized bone in the interface of uncoated Al(2)O(3), whereas in the case of the coated implants a thin layer of osteoid was observed. It was suggested that the osseointegration of Al(2)O(3) could be improved by the coating under load-bearing conditions, under which uncoated Al(2)O(3) ceramics cannot directly bind to bone.     

The effect of surface macrotexture and hydroxylapatite coating on the mechanical strengths and histologic profiles of titanium implant materials

A mechanical and histological evaluation of uncoated and hydroxylapatite-coated titanium implant materials was performed. Cylindrical implants of uncoated commercially pure (CP) titanium and hydroxylapatite-coated Ti-6Al-4V alloy were studied using a transcortical model, with implants evaluated after periods of 3, 5, 10, and 32 weeks. All implants had a surface macrotexture consisting of a series of semicircular annular grooves, approximately 750 micron in maximum depth. The attachment characteristics of interface shear stiffness and interface shear strength were determined by mechanical push-out testing. Nondecalcified histologic and microradiographic techniques, with implants in situ, were used to evaluate the response to the implant materials and the presence of the surface macrotexture. Mechanical testing results indicated that the hydroxylapatite-coated implants exhibited significantly greater values of maximum interface shear strength than the uncoated implants after all time periods. Interface shear stiffness was also significantly greater at all time periods for the hydroxylapatite-coated implants as compared to the uncoated implants. Histological evaluation after 3 weeks revealed an osteoid layer covering on all areas coated with the hydroxylapatite material; mineralization of this layer appeared to be complete after 10 weeks. In all cases, longer-term implants demonstrated mineralization of interface bone directly onto the hydroxylapatite coating, and in no case was a fibrous layer observed between the hydroxylapatite coating and the interface bone. Sections from the uncoated CP titanium implants revealed a thin fibrous layer present in nearly all areas. Only isolated regions of direct bone-implant apposition were observed for the uncoated implants. The presence of this fibrous tissue layer, however, apparently did not adversely affect the development of considerable attachment strength. The results from this study indicate that the hydroxylapatite coating can significantly increase the attachment strength of implants which rely upon bone apposition for fixation. In addition, the hydroxylapatite coating provides an osteophilic surface for bone deposition, and allows for a more rapid development of implant-bone attachment.