Histological integration of allogeneic cancellous bone tissue treated by supercritical CO2 implanted in sheep bones

Different chemical or physical methods of bone processing have been developed to decrease the antigenicity of allogeneic bone which may delay or prevent graft integration. We have developed a method based on delipidation and deproteination of the bone with a supercritical fluid and hydrogen peroxide. Cylinders of cancellous allogeneic bone treated in this way were implanted for four weeks, four months or eight months in holes drilled in sheep condyles or tibial plateau. Histological sections were then processed and analysed qualitatively and quantitatively using an image analysis software coupled to a light microscope. Measurements were made of the trabecular bone surface (BS/TS), the relative osteoid surface (OS/BS), the active osteoid surface (OS/BS), active resorption surface (Oc.S/BS) and the relative surface of newly formed bone. After four weeks, the control cylinders (non-treated allogeneic bone) had been invaded by cellular tissue composed of lymphocytes and plasmocytes surrounding remnants of the donor bone marrow tissue. The processed cylinders showed osteoid apposition at the surface of their external trabeculae. The trabecular bone and osteoid surfaces were significantly higher in the processed bone sections than in the control bone sections. After four months, most of the control material had been osteolysed and replaced by connective tissue containing lymphocyte islets, while the processed materials showed a large amount of bone synthesized at the surface of implant trabeculae which appeared fragmented and disseminated within the newly formed bone. All the histomorphometric parameters measured were significantly different from those of the control. By eight months, most of the control material had been totally osteolysed with very little bone ingrown in the implantation site. Only one control implant had been integrated. The processed cylinders were difficult to discern from the bone in which they were implanted. The parameters measured on the processed cylinders were significantly higher than those measured on the control sections. IN CONCLUSION: the treatment applied to the bone enhanced allogeneic bone integration and could provide a new kind of tissue treatment for bone banking.     

Biologic attachment of an allograft bone and tendon transplant to a titanium prosthesis

An Achilles tendon allograft with its bony insertion was used to bridge a Titanium implant, containing an endoprosthetic tendon anchor, and the sheep biceps muscle. Twelve sheep were operated on unilaterally and followed up clinically and histologically for 2, 4 (n = 2), 8, and 12 months (n = 4). Full function of the front limb was regained after 8 to 12 weeks. There were no signs of mechanical loosening at all times. The morphologic changes at the bone block and implant fixation site were an initial revascularization of the allograft bone, which was observed at 2 months and enhanced at 4 months but occurred without any evidence of bone remodeling. This was changed in all specimens taken at 8 and 12 months where intensive new bone development, remodeling, and bone ingrowth in the titanium implant was found. Bone mass was shifted significantly to the tendon insertion half of the bone block because of a creeping substitution of the cancellous allograft bone and bone ingrowth to the implant. Overall bone mass slightly decreased with time but resorption of allograft bone outweighed new bone development only at lesser loaded areas. Transplantation of a bone and tendon allograft to an implant resulted in a revitalized, mechanically stable, and biologically anchored compound.     

A case series of ocular disease as the primary manifestation in sarcoidosis

Calcium phosphate ceramics recently have been used for administering therapeutic agents in bone. The present work investigated the efficacy of macroporous biphasic calcium phosphate (MBCP) implants as a matrix for local delivery of human growth hormone (hGH). An initial study showed that the release of 5 microg of hGH loaded onto MBCP cylinders was rapid during the first 48 h and sustained for a total of 11 days. The biological integrity of hGH (88.2%) was checked using a specific bioassay (cellular proliferation of hGH-sensitive Nb2 cells) in comparison with a radioimmunoassay to calculate the proportion of bioactive hGH released. MBCP cylinders then were loaded with 1, 10, and 100 microg of hGH and implanted into rabbit femurs (n = 16) to determine hGH effects on bone ingrowth and ceramic resorption, as evaluated by scanning electron microscopy and image analysis. Results indicated that hGH increased bone ingrowth and ceramic resorption significantly in comparison with contralateral and control implants. Biochemical parameters monitored in rabbit plasma showed that hGH did not produce detectable systemic effects. Thus the use of MBCP appears to be effective for local delivery of hGH and for increasing bone ingrowth.     

Basic fibroblast growth factor promotes bone ingrowth in porous hydroxyapatite

The effect of basic fibroblast growth factor on tissue ingrowth and differentiation in porous hydroxyapatite of coralline origin was studied in a bone chamber model. The hydroxyapatite with or without basic fibroblast growth factor was placed in 22 mm3 titanium bone conduction chambers implanted bilaterally in rat tibiae. Ingrowing bone could enter the cylindrical interior of the chamber only at 1 end. It then penetrated the porous hydroxyapatite inside the chamber. The distance that the ingrown tissue had reached into the material then was measured on histologic slides. Because fibrous tissue always reached further into the material than did bone, both total tissue ingrowth and bone ingrowth distances were measured. In implants supplemented with 0.04 microg basic fibroblast growth factor in a hyaluronate gel carrier, the bone ingrowth distance was increased by 70% at 6 weeks, as compared with paired controls in the contralateral leg. The total tissue ingrowth distance also was increased by 58%. When the dose of basic fibroblast growth factor was increased to 1.0 microg, still using the hyaluronate carrier, there was no difference in bone ingrowth compared with controls, but this dose still increased the total tissue ingrowth. In hydroxyapatite with 1.5 microg basic fibroblast growth factor without hyaluronate gel at 4 weeks, no increase in bone ingrowth was shown, but total tissue ingrowth was increased. At 6 weeks, bone ingrowth and total tissue ingrowth were increased by 41% and 33%, respectively. With a lower dose of 0.15 microg without carrier, only the total ingrowth distance was increased. The results suggest that basic fibroblast growth factor may promote tissue ingrowth into porous hydroxyapatite and that bone ingrowth may be increased by appropriate doses. The hyaluronate gel carrier reduced the optimal dose.     

Acetabular reconstruction with impacted morselized cancellous allografts in cemented hip arthroplasty: a histological and biomechanical study on the goat

Bone defects in total hip arthroplasty revision surgery can be restored with different types of bone graft. The use of impacted morselized allograft chips in combination with cement is the treatment of our choice. To establish the incorporation capacity of the grafts and mechanical stability of the implant, an animal model in the goat was developed. An acetabular defect was created and restored with morselized grafts and a cemented cup. Postoperative performance of the reconstruction was followed both histologically and biomechanically. Histology showed that consolidation of the graft with the host bone bed had occurred within 3 weeks. In the following period a front of vascular sprouts infiltrated the graft. Graft resorption, woven bone deposition, and subsequent remodeling resulted in a new trabecular structure. This structure contained only scarce remnants of the original dead graft material. At the graft-cement interface, graft resorption and new bone formation had resulted in areas of direct vital bone-cement contact. Locally, a soft tissue interface was present. After longer follow-up periods, progressive interface formation and loosening of the cups were found in most animals. Mechanical testing showed that the stability of the reconstruction increased during the first 12 postoperative weeks. Thereafter, the stability decreased, probably by soft-tissue interface formation at the graft cement interface. We conclude that cemented morselized allografts have a high capacity to incorporate. Initial cup stability is adequate to provoke graft incorporation with decreasing stability after the incorporation process has been completed.     

Histological and biomechanical analysis of bone and interface reactions around hydroxyapatite-coated intramedullary implants of different stiffness: a pilot study on the goat

We hypothesized that reduced stem stiffness of orthopaedic implants contributes to a high risk of loosening, since interface stresses and relative motions may exceed a tolerable range. To study this hypothesis, three types of load-bearing implant with different stiffnesses were inserted into the tibia of the goat. Histological analysis was performed of bone repair after insertion of the implant, bone ingrowth, interface disruption and loosening. A finite element model of the configuration provided the quantitative range of interface stresses and relative motions for the present experiment. The implants were made out of stainless steel, hollow titanium and a thin titanium core covered with a polyacetal coating. The stiffness ratios of these implants were approximately 10:4:1, respectively. All implants were coated with a layer of hydroxyapatite (HA) in order to minimize the possible biological effects of the different implant materials. Irrespective of the type of implant, there was a repair phase that lasted 6-12 weeks. The stiff implants functioned well. Large areas of bone bonding to the HA layer were found after the repair phase at 12 weeks postoperatively. After 24 weeks, some signs of loosening were observed. More loosening occurred with the hollow titanium and polyacetal implants, mainly during the repair phase. Three hollow titanium and three polyacetal coated implants survived this period, and were killed after 24 weeks. The integrity of the HA layer at the bone-implant interface of the titanium implants was good. In the polyacetal implants, the repair reaction of the cortical bone was incomplete. Bone ingrowth into HA was largely lacking. In conclusion, we found significant differences in the repair and interface reactions around implants of different stiffness. Stiff implants showed favourable initial interface conditions for bone ingrowth. Intermediate and flexible implants provoked unfavourable interface conditions for initial bone ingrowth. The finite element study showed that the flexible stems produce larger micromotions and higher interface stresses at the bone-prosthesis interface than the stiff stems, indicating an explanation for the histological findings.     

Effect of cisplatin chemotherapy on extracortical tissue formation in canine diaphyseal segmental replacement

The reconstruction of large bone and joint defects after the resection of malignant tumors remains a major challenge. Chemotherapy has significantly lowered the risk of metastasic disease, but complications associated with reconstructive techniques continue to result in late morbidity. In the present study, biomechanical torsion testing, gait analysis, and histomorphometric and scanning electron microscopic evaluations of 24 dogs were used to examine the effects of preoperative and postoperative administration of cisplatin on the biologic fixation of a porous-coated segmental replacement prosthesis. The chemotherapy consisted of four cycles of cisplatin administered at a dosage of 75 mg/m2 preoperatively or postoperatively. The healing was enhanced by use of an autogenous corticocancellous bone graft. The graft was placed evenly around the prosthesis and the adjacent femoral cortex. Mechanical analyses of torsional stiffness, yield strength, and maximum strength revealed no statistically significant differences between the groups at 12 weeks. Such lack of difference was mainly due to the penetration of highly organized fibrous tissue into the porous surface; this provided strong fixation of the implant to bone even in the absence of bone ingrowth. Although bone ingrowth into the prostheses was not affected, electron microscopic, histomorphometric, and radiologic analyses showed a clear difference in the formation of new bone around the prosthesis. Preoperative chemotherapy did not alter the formation of new bone, but specimens from animals treated postoperatively with cisplatin showed significantly less bone graft resorption and less new bone formation. Hence, the effect of cisplatin administration caused only a temporary delay, not a permanent effect, on extracortical capsule formation. The formation of extracortical bone and soft tissue might prevent debris-incised osteolysis and, therefore, prevent late complications by forming a tight capsule around the bone-prosthetic interface.     

Repair of craniofacial defects with hydroxyapatite cement

PURPOSE: The objective of this study was to evaluate the course of healing of craniofacial bone defects when filled with hydroxyapatite cement and to determine whether adding various percentages by weight of demineralized bone powder to the cement will result in enhanced bone formation. MATERIALS AND METHODS: The model for the study was the canine calvarium. The implants were placed into cranial defects and harvested at 3 or 6 months for qualitative evaluation by light microscopy, microradiography, and quantitative histomorphometry. RESULTS: The implantation of hydroxyapatite cement resulted in characteristic replacement of the material with new bone ingrowth. The addition of demineralized bone powder to the hydroxyapatite cement appeared to improve the handling characteristics of the cement; however, improvement in the replacement of the material by bone was not observed. The implantation of only allogeneic demineralized bone showed limited new bone formation within the defect site. CONCLUSIONS: Hydroxyapatite cement formed an effective osseoconductive scaffold for bone replacement. The addition of demineralized bone powder to the cement to serve as a carrier of osseoinductive factors did not result in additional bone being formed.     

Bone ingrowth to implant surfaces in an inflammatory arthritis model

Many studies have shown enhanced bone apposition to implants coated with hydroxyapatite, but the optimum implant texture, especially in abnormal trabecular bone, is unclear. The purpose of this project was to evaluate the histological and mechanical properties of cylindrical implants with three different surface textures that were placed in the cancellous bone of the distal femur of the rabbit after the production of an inflammatory knee arthritis. The three implant surfaces included a beaded surface (Group A), a beaded surface coated with hydroxyapatite (Group B), and a smooth surface coated with hydroxyapatite (Group C). The right knees of 36 rabbits were injected with carrageenan twice a week for 2 weeks. Then bilateral implantations were performed, with 12 rabbits in each group receiving identical implants in the right and left knees. The rabbits were killed 6 weeks after surgery. Mechanical (push-out test) and histomorphometric analyses were performed to determine the quality and quantity of bone ingrowth. In Group A, there was virtually no direct contact (a 20-60-microm clearance) between the bone and the beaded surfaces. Direct contact between the bone and the implant surfaces was seen in Groups B and C. The thickness and number of trabeculae were smaller on the arthritic side than on the control side for all groups but were not different between groups for either the control or the arthritic side. Mechanical testing showed that the shear strength of the interface was weaker on the arthritic side in all groups. The results suggest that inflammatory arthritis induced by carrageenan may influence the quality of local bone (osteopenic changes) and hence compromise the bone apposition and mechanical stability of the interface between the implant and bone.     

A combination of bisphosphonate and BMP additives in impacted bone allografts

OP-1 increases bone ingrowth distance of new bone into allografts (T?gil et al. 2000), but the bone density after incorporation may be reduced by an increase in resorption (H?istner et al. 2000). Bisphosphonates inactivate osteoclasts and can be used to increase allograft bone density after incorporation (Aspenberg and Astrand 2002). A combination of locally-applied bisphosphonate and OP-1 in the graft could therefore be expected to increase both new bone ingrowth and density. We tested this by using a rat bone chamber model. OP-1 alone increased the ingrowth distance of bone. Clodronate increased final bone density greatly, but reduced the ingrowth distance of new bone into grafts that were extremely impacted. This reduction was improved by adding OP-1. Regardless of graft density, combinations of OP-1 and clodronate included a high final bone density, but the ingrowth distances were shorter than with OP-1 alone. These data indicate that new bone and tissue ingrowth into a compacted graft depends on resorption and that resorption is a prerequisite for the stimulating effect of OP-1 in this experimental set-up. Although the problems associated with the use of OP-1 in impaction grafting may be solved by adding a bisphosphonate, some of the benefits of OP-1 can be lost.     

Comparison of hydroxyapatite granules to autogenous bone graft in fusion cages in a goat model

BACKGROUND: With the increased use of fusion cages to achieve lumbar intervertebral fusion, the question arises as to the potential for bone ingrowth from the host bone through the entire cage. Is it even necessary to have an autogenous graft to achieve total bone incorporation? METHODS: Nine adult male goats had fusion cages implanted into three vertebral bodies. The design was Surgical Dynamics/Ray Fusion Cage, measuring 21 mm x 14 mm. In each animal, one fusion cage was filled with autogenous graft, one with hydroxyapatite, porous granules, and the other with nonporous granules. Amount of new bone formation was determined by backscatter electron microscopy at 3 months post implantation in all animals. RESULTS: The histologic section shows that there was total incorporation in all specimens at 3 months. There was slightly more new bone (43%) with the nonporous granules compared with the porous granules (35%). The amount of residual void space was about the same in all specimens, indicating that the amount of new bone formation was similar and not statistically different in cages filled with hydroxyapatite granules versus granules of autogenous bone. CONCLUSION: This study confirms that total incorporation by ingrowth of new bone can be expected in fusion cages. The amount of ingrowth is about the same for autogenous graft versus hydroxyapatite granules. Apparently, it is not necessary to use bone graft to achieve successful bone incorporation if an acceptable biocompatable lattice, such as hydroxyapatite granules, is used.     

Collagen fibers as a temporary scaffold for replacement of ACL in goats

ACL substitutes made of braided or plied purified collagen fibers and cross-linked with hexamethylenediisocyanate were implanted into a total of 14 adult goats to achieve resorption within 8 to 10 months. Two types of collagen fiber prostheses differing in degree of collagen purification were tested. The implants were harvested 2 to 11 months postimplantation, tested for mechanical strength, and evaluated by morphological methods. In the first group (n = 5), the less purified and less cross-linked collagen fiber ACL implant induced fast connective tissue ingrowth. At 6 months postimplantation, 40 to 60% of the collagen implant was resorbed. No studies on breaking strength were done in this group. In the second group, highly purified and more crosslinked ACL implants were less infiltrated by cells and were resorbed only by 10 to 20%. Still, the breaking strength was decreased to 10% of the original implant strength. In the second group, the fixation of the ACL implant in the bone tunnel with a bone wedge was insufficient (n = 6); however, additional fixation with metal screws was successful (n = 3). We conclude that cross-linked collagen fibers alone cannot be used as a safe ACL substitute as they quickly lose mechanical strength despite limited biodegradation.     

Cigarette smoking and breast cancer

OBJECTIVE: To investigate osteoclastic resorption in trabeculae of osteoporotic femoral head. METHODS: Osteoporotic femoral heads were collected from 7 aged women with an average age of 72.4 years, who underwent endoprosthetic replacement for intracapsular hip fracture. Femoral head trabeculae from 3 young adults killed in traffic accidents served as control. The two types of specimens were processed and studied under scanning electron microscope. RESULTS: The trabeculae of femoral head formed round or roundish arch structure. The columnar trabeculae of femoral head in the aged women showed overt osteoclastic resorption, manifested in thinning, tapering and perforation, resulting in formation of icicle-like trabeculae, which then became rounded, lost height and eventually turned into small tubercle. As a result, the inter-trabecular space enlarged markedly. Under high magnification, the trabeculae could be discerned oval, narrow oval or spindle-shaped. Howship resorption lacunae, which varied in size, depth and content, but all revealed punched-out margin. During bone resorption, the inorganic and organic components were successively resorbed. In the Howship lacunae and surrounding areas, newly formed collagen fibrils and bone tissues emerged, signifying reversal and new bone formation phases after bone resorption phase. CONCLUSION: Osteoclastic resorption markedly compromises the structural integrity and strength of the trabeculae of the arch structure of the femoral head in the aged women.     

Effect of flexibility of the femoral stem on bone-remodeling and fixation of the stem in a canine total hip arthroplasty model without cement

The purpose of this study was to compare, with regard to fixation of the implant and femoral bone resorption, two fully porous-coated stems of different stiffnesses in a canine total hip arthroplasty model. A bilateral arthroplasty was carried out with insertion of a titanium-alloy stem (which had stiffness properties comparable with those of the canine femur) on one side and with insertion of a composite stem (which was three to fivefold more flexible than the canine femur) on the contralateral side. Eight femora were evaluated at six months and eight, at eighteen months after the operation, to determine the extent of bone ingrowth, periprosthetic cortical area, intracortical porosity, and bone-remodeling. Despite the markedly greater flexibility of the composite stems, no significant difference could be detected (with the numbers available), with regard to the overall degree of femoral stress-shielding, cortical area, or cortical porosity, between these stems and the stiffer, titanium-alloy stems at either time-period. However, the composite stems had less bone ingrowth and more formation of radiopaque lines than did the titanium-alloy stems. At eighteen months, the values for bone ingrowth were 9.7 +/- 5.38 percent (mean and standard deviation) for the composite stems compared with 28.1 +/- 5.31 percent for the titanium-alloy stems (p = 0.003). Furthermore, the histological sections from the femora containing a composite stem showed radiopaque lines indicative of fibrous ingrowth approximately threefold more often than did those from the femora containing a titanium-alloy stem (p = 0.02).     

Enhancement of bone formation in the setting of repeated tissue deformation

The purpose of this study was to investigate whether the osteoinductive recombinant human bone morphogenetic protein 2, combined with a collagen carrier, could enhance bone formation when exposed to controlled amounts of tissue deformation. Chambers that allow for the multiple harvestings of tissue specimen were used. The devices were implanted in the tibial metaphyses of skeletally mature New Zealand White rabbits. A tissue ingrowth canal in each device either was left empty or filled with a collagen carrier with or without 0.6 microgram of recombinant human bone morphogenetic protein 2. The tissue ingrowth canal was deformed cyclically during a period of 2 minutes daily, according to a previously described deformation protocol. The tissue that developed in the chambers was harvested every 3 weeks. Undecalcified histologic sections of each tissue sample were stained with trichrome and von Kossa stains and subjected to histomorphometric analysis. It was found that deformation decreased the area occupied by bone trabeculae in the empty chambers and carrier controls. The amount of bone formed in the chambers treated with bone morphogenetic protein 2 was significantly greater than that in the chambers subjected to micromotion and left empty or implanted with the collagen carrier. The amount of bone in chambers with motion and bone morphogenetic protein 2 was equal to that in chambers left empty and not subjected to micromotion. Qualitative histologic analysis of the bone formed with bone morphogenetic protein 2 revealed normal bone trabeculae. These findings indicate that bone morphogenetic protein 2 may be useful in augmenting bone formation in conditions that otherwise would favor the formation of fibrous tissue.     

Filling up small bone defects with bone ceramics (hydroxylapatite)

First clinical results using a bovine hydroxyapatite implant to fill up small bony defects after excision of enchondromas or cysts are reported in twelve patients. Incorporation without any problems was completed radiologically after six to eight weeks. Complications did not occur. Avoiding additional surgery harvesting cancellous bone chips at the iliac crest, the use of these bovine hydroxyapatite ceramic seems to be reasonable.     

In vitro crystallisation systems for the study of urinary stone formation

Hydroxyapatite orbital implants undergo early ingrowth of fibrovascular tissue after enucleation. This animal study determined whether control and osteogenin-impregnated hydroxyapatite orbital implants vary in their osteogenic response at 6 and 52 weeks. Rabbits underwent enucleation with implantation of control or osteogenin-impregnated hydroxyapatite spheres. Light microscopy determined fibrovascular ingrowth, and histomorphometry quantitated the amount of bone produced. Osteogenin implants vascularized at a faster rate and contained bony foci by 6 weeks that became confluent at 1 year. Spontaneous osteogenesis was not seen in control animals at 6 weeks. After 1 year they contained bone, although less than in the osteogenin implants. Mixed cell inflammation was observed at the hydroxyapatite-tissue interface in both groups. No inflammation was noted at the interface of hydroxyapatite and bone. These are the first controlled observations that bone-specific differentiation occurs in the pores of spherical hydroxyapatite implants within the soft tissues of the socket. This vascularized process can be enhanced with osteogenin to occur earlier and more uniformly in the implants at one year.     

The use of porous granular hydroxyapatite in secondary orbitocranial reconstruction

The search for the ideal bone-graft substitute has been the focus of many research and clinical studies. Hydroxyapatite is one such material that combines osseointegration with maintenance of implant volume and excellent durability. We present our experience in 29 patients ranging in age from 3 to 22 years (mean age 10.5 years) who underwent secondary orbitocranial reconstruction of large contour defects utilizing porous granular hydroxyapatite. Follow-up ranges from 6 to 72 months (mean 30 months). Indications for secondary surgery included residual bony contour defects of the frontal bone, temporal areas, and superior orbital rims that were present 12 months or more after initial surgery. There was one infection secondary to a chronic seroma necessitating removal of the porous hydroxyapatite, and one patient required revision for underfilling and another for overfilling. Excellent permanent contour improvement was obtained with a smooth skin surface in the remainder of our patients. The contour corrections have been long lasting, without evidence of porous hydroxyapatite resorption or migration.     

Vicryl-mesh wrap for the implantation of hydroxyapatite orbital implants: an animal model

OBJECTIVE: To evaluate host fibrovascularization of hydroxyapatite orbital implants wrapped in sclera or in Vicryl (polyglactin 910) mesh in a rabbit model. NUMBERS: Eight adult New Zealand white rabbits that received hydroxyapatite orbital implants wrapped in homologous donor sclera (four animals) or Vicryl mesh (four animals). INTERVENTIONS: The rabbits had one eye enucleated and then received a 12-mm hydroxyapatite implant wrapped in sclera or Vicryl mesh. Magnetic resonance imaging (MRI) and bone scintigraphy were done to assess host fibrovascularization of the implant 4, 8, 12 and 20 weeks after implantation. Two animals (one in each group) were killed at each of these times, and the implant was removed for histopathological examination. MAIN OUTCOME MEASURES: Enhancement on MRI, uptake on bone scintigraphy, fibrovascularization seen on histopathological examination. RESULTS: The degree of fibrovascularization was substantial in all the specimens but appeared greater in the Vicryl-mesh-wrapped implants in the first 12 weeks after implantation on both histopathological and MRI studies. At 20 weeks these findings were similar in the two groups. A granulomatous foreign-body giant-cell reaction to both the Vicryl mesh and the implant itself was present up to 8 weeks after implantation. Bone scans showed only grade 1+ activity in all the implants. CONCLUSIONS: Host fibrovascularization in the rabbit appears to occur to a greater degree in Vicryl-mesh-wrapped hydroxyapatite implants than in those wrapped in donor sclera during the first 12 weeks after implantation. Vicryl mesh appears to be an acceptable alternative wrap for the hydroxyapatite implant, eliminating the need for donor sclera and its potential risks of transmissible diseases.     

Differential effects of aromatic and charged residue substitutions in the RNA binding domains of the yeast poly(A)-binding protein

A new modified thermal decomposition method is described for preparing a double layered coating on titanium plates which includes an initial perovskite (CaTiO3) layer followed by a hydroxyapatite (HA) layer on top. The characterization of the coating was studied by X-ray diffractometry and infrared spectroscopy and indicated that the double layer consisted of carbonate HA and CaTiO3 and the thickness of the layer was 4 microns. The coating was performed on the inner surfaces of 50-200 microns sized pores and was also consistent in the smallest of the pores even those of 50 microns. Bone formation was examined in canines at 2-32 week intervals and was dominant on coated plates and in large-sized pores before 16 weeks. However, after 16 weeks bone ingrowth was similar in non-coated and coated plates and in all pore sizes. The results indicated that HA could only influence early bone ingrowth, though good bone ingrowth into small pores indicated that HA exhibited enhanced osteocompatibility. Our methodology ensured the stability of the HA layer consequently minimizing the problems associated with HA loss.