Tissue response to composite ceramic hydroxyapatite/demineralized bone implants

This study evaluated the tissue reactions to two materials: ceramic hydroxyapatite (CHA), and a composite material of demineralized bone powder (DBP) and CHA (ratio of 4:1) in a collagen vehicle. The materials were tested in a subcutaneous pocket, a mandibular onlay, and in a calvarial onlay model. Specimens were evaluated histologically at 7, 10, 14, and 21 days postimplantation. Ceramic hydroxyapatite, implanted subcutaneously, elicited a fibrous response with minimal inflammation, but did not induce bone formation. In specimens of subcutaneously implanted composite material, induced bone was evident in association with the DBP. In CHA onlay specimens, there was a small amount of reactive bone extending from the host bone into the implant. In composite onlays, bone filled the entire body of the implant. The results of this study indicate that CHA particles were not osteoinductive in heterotopic sites and that osteoconductive ingrowth was minimal in onlays. Bone was induced by DBP even when mixed with CHA particles and implanted in subcutaneous and intraosseous sites. It was concluded that composite implants may provide a means of combining the osteoinductive properties of DBP with the bulk and structural support of osteoconductive CHA particles.     

Accelerated endochondral osteoinduction in the absence of bone matrix particles in a rat model system.

Ethanol-precipitated proteins obtained from demineralized rat bone powder (DBP) by 4M guanidine-HCl extraction have been shown to reproducibly induce ectopic endochondral bone formation when subcutaneously implanted in rats in the absence of bone matrix particles. Histologic and biochemical analysis revealed a temporal sequence of chondrocyte differentiation, calcified cartilage formation, neovascularization, osteoblast differentiation, bone formation, osteoclastic bone remodeling, and hematopoietic marrow development that is complete by 21 days. In contrast to previous reports, these results clearly show an osteoinductive response independent of the presence of insoluble extracellular bone matrix. Compared with conventional DBP implants, the guanidine-extractable protein (GE) produces an accelerated and more robust osteoinductive response. Histologically, the initial chondrogenic response at days 6 to 9 is greatly amplified. Alkaline phosphatase specific activity peaks at day 9, several days earlier than for DBP, and is sixfold higher. Calcium accumulation in GE implants at day 12 is fivefold greater than with DBP, and all mineral is localized within the matrix of newly calcified cartilage and new bone. Osteoclasts are up to ninefold more abundant in the rapidly remodeling GE ossicle, making space for hematopoietic marrow. Delivery of GE coprecipitated with inert bone matrix particles was also more effective than DBP, although the response was somewhat attenuated compared with GE alone. Bony filling of 4-mm defects in rat mandibular rami was elicited by 10 mg of GE and followed an endochondral process with increased neovascularization compared with DBP and unimplanted controls. This guanidine-extractable protein fraction should prove useful for inducing quantities of chondrocytes and osteoclasts for in vitro study, and for analysis of osteoinductive requirements.(ABSTRACT TRUNCATED AT 250 WORDS)     

Implant system for guiding a new layer of bone. Computed microtomography and histomorphometric analysis in the rabbit mandible

Objective: To prove the concept that an implant system with osteoconductive surface characteristics and an osteoinductive scaffold material has the capacity to guide vertical supracrestal bone growth in a rabbit mandible onlay model.
Material and methods: Thirteen adult white New Zealand rabbits each received custom-designed dental implants. All implants had sandblasted, acid-etched (SLA^™) surfaces, with the coronal aspect (3 mm) of each implant was left outside the lateral aspect of posterior mandibular bone, but covered by periosteum, muscle, subcutaneous tissue, and skin. Bone formation around implants placed adjacent to osteoinductive demineralized bone matrix (DBM) scaffolds were compared with contralateral implants without scaffolds in six rabbits using micro-CT imaging. Bone formation around implants with scaffolds from seven additional rabbits was measured using both micro-CT imaging and quantitative histology.
Results: At 8 weeks, new supracrestal bone was seen adjacent to all implants placed with DBM and two implants without DBM. The mean supracrestal bone heights achieved for implants with and without DBM scaffolds as measured by micro-CT was 2.1±0.9 and 0.8±0.9 mm, respectively ( P =0.008). Histomorphometric analysis illustrated that supracrestal bone-to-implant contact for implants with DBM scaffolds was 58.1±14% and that mean supracrestal bone height was 2.4±0.6 mm.
Conclusions: Successful implant-guided supracrestal osteogenesis has been demonstrated in a rabbit model with the combined use of osteoconductive implant surfaces, an osteoinductive scaffold, and a device that prevents soft tissue downgrowth and provides scaffold stabilization.     

Superior effect of MD05, beta-tricalcium phosphate coated with recombinant human growth/differentiation factor-5, compared to conventional bone substitutes in the rat calvarial defect model

BACKGROUND: MD05 consists of beta-tricalcium phosphate (beta-TCP) coated with recombinant human growth/differentiation factor-5 (rhGDF-5) and is under evaluation as an osteoinductive and osteoconductive bone graft material for use in dental and maxillofacial applications. The objective of this study was to compare the bone regenerative properties of MD05 with those of conventional commercially available bone substitutes. METHODS: Full-thickness, 6-mm diameter, calvarial critical-size defects (two per animal) were created in adult Sprague-Dawley rats. Groups of rats were implanted with the following: 1) MD05; 2) bovine bone mineral; 3) bovine bone mineral with collagen; 4) bovine bone mineral with synthetic peptide, 5) beta-TCP (from two different manufacturers); or 6) no filling material (sham controls). Blinded macroscopic analysis, histopathologic analysis, and histomorphometric analysis were carried out 6 weeks after implantation. RESULTS: New bone formation assessed histomorphometrically was about five times greater with MD05 than with the other bone substitutes tested, and bone repair was well advanced in MD05-filled defects after 6 weeks. The extent of fibrous tissue and residual implant were significantly lower in the MD05 group. In contrast to the other materials, the use of MD05 was associated with the complete osseous bridging of the defect and with the presence of normal bone marrow. The osteoinductive effect of rhGDF-5 was apparent from the more pronounced bone ingrowth observed with MD05 compared to the beta-TCP carrier alone. All implants showed good biocompatibility. CONCLUSION: MD05 achieved superior bone regeneration compared to conventional materials and is a promising new bone substitute for dental and maxillofacial applications.     

膜结合骨形成蛋白和单独用膜引导种植体周围骨组织再生的比较研究

为研究单纯用膜及膜结合ＢＭＰ修复与种植体有关的骨缺损的愈合速度及界面情况，应用ＨＡ喷涂钛种植体植入伴有裂状缺损的拔牙窝内。实验分两组进行，一组用聚四氟己烯膜（ＰＥＴＥ膜）结合ＢＭＰ，另一组单纯用聚四氟己烯膜。术后２、４、８、１２周分别行大体，Ｘ线，光镜观察。结果发现：单纯用膜能促进种植体周围新骨生成，而膜结合ＢＭＰ处理的种植体骨修复启动早，骨界面愈合速度较单纯用膜可提前约４～６周。两种方法为扩大种植体的适应证范围，解决植床质和量问题提供了可能     

A comparative study of osseointegration of Avana implants in a demineralized freeze-dried bone alone or with platelet-rich plasma.

PURPOSE: The purpose of this study was to assess the efficacy of demineralized bone powder (DBP) alone or combined in a mixture with platelet-rich plasma (PRP) used to enhance osseointegration of dental implants in a dog model. MATERIALS AND METHODS: Tissue integration was assessed using standard histomorphometric methods at 6 and 12 weeks after surgery. A total of 30 Avana dental implants (SooMin Synthesis Dental Materials Co, Busan, Korea) were inserted in the animals. They were self-tapping screw implants, 10 mm in length and 4 mm in diameter, made of commercially pure titanium. A titanium implant was then placed centrally in each defect. In each dog, the defects were treated with 1 of the following 3 treatment modalities:1) no treatment (control), 2) grafting with DBP, or 3) grafting with DBP and PRP. RESULTS: Histologic analysis showed that all of the bone defects surrounding the implants that were treated with DBP, with and without PRP, were filled with new bone. The defects that were not treated (control) showed new bone formation only in the inferior threaded portion of the implants. Histomorphometric results revealed a higher percentage of bone contact with DBP and PRP compared with control and DBP. CONCLUSION: These results suggested that bone defects around titanium implants can be treated successfully with DBP and that PRP may improve bone formation.     

Effects of preservation on the osteoinductive capacity of demineralized bone powder allografts

Demineralized bone powder (DBP) has repeatedly been shown to serve as an osteoinductive material. The aim of this study was to investigate the effects of different methods of storage of DBP on its osteoinductive property. Forty-five Long Evan rats were used in this study. Twenty rats were used as donors; the diaphyses of their femoral bones were used for the preparation of DBP. The DBP was divided into four portions that were either lyophilized or frozen at -70 degrees C, -4 degrees C, or kept at room temperature (25 degrees C). All samples were stored under the specified condition for six months. At the time of implantation, fresh DBP was prepared and used as a control. Twenty-five rats were divided equally into five groups. Each group received an implant of either one of the differently preserved and stored samples of DBP or fresh DBP. The animals were killed 60 days following implantation. The implants were excised and processed to obtain 5 micron thick decalcified sections and 3 micron thick undecalcified sections. Semicomputerized histomorphometry was used for the quantification of the newly-formed bone in each implant. Newly-formed bone was detected in all experimental and control groups and there were no statistically significant differences between the various groups. It was concluded that DBP retains its osteoinductivity after lyophilization or preservation at -70 degrees C, -4 degrees C, and 25 degrees C for a period of up to six months, and that the different methods of preservation did not significantly affect the amount of the induced newly-formed bone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Osteoinduction in rhesus monkeys using demineralized bone powder allografts

This experiment tested the osteoinductivity of demineralized bone powder (DBP) in nonhuman primates. Six DBP implants were implanted subcutaneously close to the pectoralis major muscle in each of four rhesus monkeys. Excisional biopsies were obtained 20, 40, and 72 days after implantation and were processed for light and electron microscopy. Decalcified and undecalcified sections of the implants were studied. Large numbers of undifferentiated mesenchymal and fibroblast-like cells were observed around and within the DBP matrix particles on day 20. Cartilage formation was also evident at that time and had increased by day 40, when chondroid bone also appeared. By day 72, the implants showed mature (lamellar) and immature (woven and chondroid) bone and bone marrow formation. Areas of DBP that were incorporated within the induced bone contained empty lacunae and stained similarly to mineralized bone. It was concluded that allogenic DBP can induce bone formation in monkeys. The results justify the use of DBP as a bone-banked material to induce bone formation in humans.     

Experience with freeze-dried PGLA/HA/rhBMP-2 as a bone graft substitute.

We investigated bone induction by recombinant human bone morphogenetic protein-2 in rodents. The purpose of this study was to evaluate the osteoinductive potential of a resorbable bone substitute fabricated from freeze-dried poly(glycolic acid-co-lactic acid) (PGLA) mixed with hydroxyapatite particles incorporated with bone morphogenetic protein-2 in skull defects of rats (FD-PGLA/HA/rhBMP-2). The FD-PGLA/HA/rhBMP-2 composite or as a control, the FD-PGLA/HA by itself were implanted in skull defects (psi 8 mm) of rats. The samples were harvested at 2 or 4 weeks postoperatively and were studied radiographically and histologically. Four weeks after implantation, the FD-PGLA/HA/rhBMP-2 discs were completely replaced by newly-formed bone possessing bone marrow. In contrast, the defects implanted with FD-PGLA/HA were filled only with fibrous connective tissue. The results suggest that the FD-PGLA/HA/rhBMP-2 composite could be an optimum bone substitute with osteoinductive potential and could function as an alternative bone graft material for autogenous bone in humans.     

骨形成蛋白与胶原膜联合应用促进即刻种植体周骨组织再生的实验研究

目的 比较单独应用胶原膜和胶原膜与人骨形成蛋白（ｈＢＭＰ）联合应用引民即刻种植体周骨缺隙骨再生的效果。方法 将复合有ｈＢＭＰ和ｈＢＭＰ的相同种植体分别植入１２只成年杂种狗下颌拨牙窝,覆盖胶原膜。于术后２、４、８、１２周每次处死狗３只,取格,扫描电子显微镜观察。结果 在种植体周骨缺隙部,有ｈＢＭＰ组２周时即有大量新骨形成,８周时骨缺隙完全由成熟的骨质充填,而无ｈＢＭＰ组,１２周时种植体周骨缺隙由仍未     

Bone augmentation using rhGDF-5-collagen composite

The aim of this study was to evaluate the effectiveness of local application of growth differentiation factor-5 (GDF-5)-collagen composite on bone augmentation on the rat calvaria. GDF-5-collagen composite is made from recombinant human GDF-5 (rhGDF-5) and purified bovine type I atelocollagen. The GDF-5 solution was mixed with 0.3% atelocollagen acid solution, and the mixture was lyophilized. The spongy lyophilized material was pressed into the shape of a minidisk to make the GDF-5-collagen composite. The GDF-5-collagen composite contained 1, 10, or 100-microg rhGDF-5. The control collagen composite contained 0-microg rhGDF-5. The GDF-5-collagen composite or control collagen composite was inserted beneath the calvarial periosteum of 4-week-old rats. At 3 weeks after implantation, the implants containing 1-microg rhGDF-5 had mostly induced new bone formation on the cranial side. In the implants containing 10- microg rhGDF-5, bone formation had proceeded to the center of the GDF-5-collagen composite from the periosteal and the cranial sides, and bone marrow was seen focally. The augmented bone showed a connected trabecular structure with abundant vascularization. The implants containing 100-microg rhGDF-5 were nearly entirely replaced by new bone with bone marrow, and the augmented bone was firmly connected with the original bone. Neither cartilage nor bone formation was found in the control collagen composite. Thus, we conclude that the GDF-5-collagen composite may be a superior biomaterial for bone augmentation and this composite could be useful as a local osteoinductive device.     

Bone formation in transforming growth factor beta-I-loaded titanium fiber mesh implants

The osteoconductive properties of porous titanium (Ti) fiber mesh with or without a calcium phosphate (Ca-P) coating and osteoinductive properties of noncoated Ti fiber mesh loaded with recombinant human Transforming Growth Factor beta-1 (rhTGF-beta1) were investigated in a rabbit non-critical size cranial defect model. Nine Ca-P-coated and 18 non-coated porous titanium implants, half of them loaded with rhTGF-beta1, were bilaterally placed in the cranium of 18 New Zealand White rabbits. At 8 weeks postoperative, the rabbits were sacrificed and the skulls with the implants were retrieved. Histological analysis demonstrated that in the TGF-beta1-loaded implants, bone had been formed throughout the implant, up to its center, whereas in the non-loaded implants only partial ingrowth of bone was observed. Bone formation had a trabecular appearance together with bone marrow-like tissue. No difference in ingrowth could be observed between the non-TGF-beta1-loaded non-coated implants and the Ca-P-coated ones. All histological findings were confirmed by image analysis: 97% ingrowth was seen in the rhTGF-beta1-loaded implants, while only 57% and 54% ingrowth was observed in the non-loaded Ca-P-coated and non-coated implants, respectively. Bone surface area and bone fill were significantly higher in the rhTGF-beta1-loaded implants (1.37 mm2 and 36%, respectively) than in the non-loaded implants (0.57 mm2 and 26%). No statistical difference was found for any parameter between the Ca-P-coated and noncoated implants. Quadruple fluorochrome labeling showed that in the Ti and Ti-CaP implants mainly bone guidance had occurred from the former defect edge, while in the Ti-TGF-beta1 implants bone formation had mainly started in the center of a pore and proceeded in a centrifugal manner. Our results show that: (1) the combination of Timesh with TGF-beta1 can induce orthotopic bone formation; (2) Ti-fiber mesh has good osteoconductive properties; (3) a thin Ca-P coating, as applied in this study, does not seem to further enhance the bone-conducting properties of a titanium scaffold material.     

牙种植术钻孔骨碎作植骨的临床研究

目的:评价在牙种植术中,钻备种植窝时收集到的自体骨颗粒单独或与Bio-Oss人工骨混合作为骨移植材料应用的临床效果。方法:34例52枚牙种植术的病例分成四组。第一组(对照组)22枚植体,单纯植入种植体,种植区无植入自体骨或人工骨。第二组6枚植体,植入螺纹种植体后,在部分暴露的植体处植入Bio-Oss人工骨。第三组8枚植体,收集种植术中准备植体窝时,在各种钻针上的自体骨颗粒,植入种植体周骨量不足区域。第四组16枚植体,自各种钻针上收集到的自体骨颗粒与Bio-Oss人工骨混合,植入种植体周骨缺损区。记录I、II期手术种植体周围骨组织高度。结果:植入术后3-12个月,II期手术时,实验组有新生骨形成,第四组(即Bio-Oss人工骨与自体骨颗粒混合物植入组),新生骨形成的量较其余组别多。结论:研究表明牙种植术中钻备种植窝时收集到的自体骨颗粒可作为有效的植骨材料,这种简单的方法避免从他处手术获得自体骨,对扩大牙种植适应症有重要意义。RRRR     

Alveolar ridge and sinus augmentation utilizing platelet-rich plasma in combination with freeze-dried bone allograft: case series

BACKGROUND: Alveolar bone regeneration is frequently necessary prior to placement of implants. Efforts to improve wound healing have focused on factors that may enhance bone formation following guided bone regeneration (GBR) techniques alone or in combination with bone replacement graft materials. Recent reports suggest that platelet-rich plasma (PRP), presumably high in levels of peptide growth factors, may enhance the formation of new bone when used in combination with autogenous graft material. METHODS: In this report, the clinical and radiographic results are presented on 15 consecutively treated patients using autologous PRP in combination with freeze-dried bone allograft (FDBA) for sinus elevation and/or ridge augmentation. FDBA and PRP (0.5 g/2cc PRP) were mixed and placed as a composite graft material. A gel formed by mixing autologous thrombin-rich plasma with PRP (1:4 ratio) was used to cover the graft material. Core biopsies of grafted areas were obtained in several patients as part of implant site preparation and were evaluated histologically to determine site maturation. RESULTS: Of 36 implant fixtures, 32 (89%) were considered clinically successful demonstrating complete bone coverage of the implant, no mobility, and a normal radiographic appearance at the time of re-entry and 12 months post-implant exposure. Four implants were removed due to mobility at the time of surgical exposure. Histologic evaluation of biopsy specimens revealed numerous areas of osteoid and bone formation around FDBA particles, with no evidence of inflammatory cell infiltrate. CONCLUSIONS: These clinical and histological findings suggest that ridge augmentation and sinus grafting with FDBA in combination with PRP provide a viable therapeutic alternative for implant placements. Future studies are necessary to determine whether PRP enhances new bone formation or maturation with bone replacement allografts.     

Effect of polylactic acid on osteoinduction of demineralized bone: preliminary study of the usefulness of polylactic acid as a carrier of bone morphogenetic protein

To evaluate the usefulness of polylactic acid (PLA), a bioabsorbable and plastic polymer, as a carrier of bone morphogenetic protein (BMP), a preliminary study has been carried out to investigate any negative effect of PLA on osteoinduction of demineralized bone (DB). PLA (10,600mol. wt) was mixed with DB particles (1– 1.5 mm square) prepared from rat femurs and laid subcutaneously on the intercostal muscle of 4-week-old Wistar rats. The PLA/DB pellets were harvested at 2, 4, 8 and 24 weeks after the operation, and prepared for light microscopic examination. Histological examination revealed cartilage formation at 2 weeks and new bone formation at 4 weeks. Extensive bone and marrow formation were observed at 24 weeks. PLA was gradually absorbed and completely disappeared at 24 weeks to be replaced by connective tissue. These results demonstrate that PLA does not have a negative influence on the osteoinductive activity and that PLA could well be a promising bioabsorbable carrier of BMP.     

重组人骨形成蛋白-2/珊瑚复合人工骨的动物实验研究

本研究将重组人骨形成蛋白－２（ｒｈＢＭＰ－２）和珊瑚以一定的方式复合后,植入小鼠股部肌袋和兔颅骨标准大小缺损,以单纯珊瑚植入作对照,术后不同时间取材,通过组织学方法检测其骨诱导活性和骨修复能力．结果显示：ｒｈＢＭＰ－２／珊瑚复合人工骨植入小鼠肌袋１周,诱导软骨形成,３周,形成编织骨,６周,形成含骨髓的板层骨,同时,珊瑚被部分降解吸收;复合人工骨植入兔颅骨缺损后,以引导成骨和诱导成骨双重机制完成骨修复过程,术后１２周,植入物完全被成熟的骨组织取代,其骨修复效果明显优于单纯的珊瑚．此复合人工骨具有骨传导和骨诱导活性,骨修复能力较强,是一种较理想的新型生物性植骨材料     

Bone reformation and implant integration following maxillary sinus membrane elevation: an experimental study in primates

Background: Recent clinical studies have described maxillary sinus floor augmentation by simply elevating the maxillary sinus membrane without the use of adjunctive grafting materials. Purpose: This experimental study aimed at comparing the histologic outcomes of sinus membrane elevation and simultaneous placement of implants with and without adjunctive autogenous bone grafts. The purpose was also to investigate the role played by the implant surface in osseointegration under such circumstances. Materials and Methods: Four tufted capuchin primates had all upper premolars and the first molar extracted bilaterally. Four months later, the animals underwent maxillary sinus membrane elevation surgery using a replaceable bone window technique. The schneiderian membrane was kept elevated by insertion of two implants (turned and oxidized, Brånemark System®, Nobel Biocare AB, Göteborg, Sweden) in both sinuses. The right sinus was left with no additional treatment, whereas the left sinus was filled with autogenous bone graft. Implant stability was assessed through resonance frequency analysis (Osstell^TM, Integration Diagnostics AB, Göteborg, Sweden) at installation and at sacrifice. The pattern of bone formation in the experimental sites and related to the different implant surfaces was investigated using fluorochromes. The animals were sacrificed 6 months after the maxillary sinus floor augmentation procedure for histology and histomorphometry (bone‐implant contact, bone area in threads, and bone area in rectangle). Results: The results showed no differences between membrane‐elevated and grafted sites regarding implant stability, bone‐implant contacts, and bone area within and outside implant threads. The oxidized implants exhibited improved integration compared with turned ones as higher values of bone‐implant contact and bone area within threads were observed. Conclusions: The amount of augmented bone tissue in the maxillary sinus after sinus membrane elevation with or without adjunctive autogenous bone grafts does not differ after 6 months of healing. New bone is frequently deposited in contact with the schneiderian membrane in coagulum‐alone sites, indicating the osteoinductive potential of the membrane. Oxidized implants show a stronger bone tissue response than turned implants in sinus floor augmentation procedures.     

Ectopic bone formation after implantation of a slow release system of polylactid acid and rhBMP-2

Objectives: The present study was conducted to test the hypothesis that preshaped polylactic acid (PLA) implants loaded with recombinant human bone morphogenic protein 2 (rhBMP-2) can induce bone formation in a rat ectopic model.
Materials and methods: Two groups of porous cylindrical poly- dl -lactic acid implants of 8-mm diameter were produced by gas foaming with CO₂, incorporating 48 and 96 μg rhBMP-2, respectively, into each implant. Blank PLA implants were used as controls. The release of BMPs and the induction of alkaline phosphatase were assessed in vitro . Osteoinduction in vivo was tested by insertion of 15 implants from each group into the gluteal muscles of Wistar rats. Five implants from each group were retrieved after 6, 13 and 26 weeks and assessed using flat panel volume detector computed tomography and light microscopy.
Results: Both groups of implants showed increased release of rhBMP-2 during the first 24–48 h, with a slightly higher amount being released from the implants with 48 μg. Release during subsequent intervals was <100 ng/72 h in the low-concentration group and >100 ng in the group with 96 μg rhBMP-2. Implants with 95 μg rhBMP-2 exhibited bone formation in vivo on the outside of the implants across the observation period of 26 weeks with invasion of bone into the pores, whereas implants with 48 μg rhBMP-2 failed to induce the formation of bone tissue. No bone formation was found in the control implants.
Conclusions: The results suggest that release rates of rhBMP-2 for ectopic bone induction have to be >100 ng/72 h to maintain the osteoinductive activity of the tested porous PLA implants. This slow release system may have impact on alveolar bone augmentation procedures when used as individually preformed osteoinductive implants.     

The effect of Emdogain and platelet-derived growth factor on the osteoinductive potential of hydroxyapatite tricalcium phosphate

The aim of this study was to determine whether hydroxyapatite β-tricalcium phosphate (HA-TCP) either alone or coated with Emdogain (EMD) or recombinant human platelet-derived growth factor-BB (rhPDGF-BB) becomes osteoinductive in the murine thigh muscle model for osteoinduction. Twenty CD1 adult male mice had gelatin capsules implanted into the thigh muscle of both hind limbs. The capsules were either empty or contained one of the following: uncoated particulate HA-TCP, EMD-coated HA-TCP or rhPDGF-BB-coated HA-TCP. The implant sites were assessed histologically at 4 and 8 weeks. A semi-quantitative histological examination was performed to assess the inflammatory changes, reparative processes and osteoinduction within the graft site. At both 4 and 8 weeks, histological analysis failed to demonstrate any osteoinductive activity in any of the specimens from the experimental groups. A minimal chronic inflammatory response and foreign body reaction around the implanted materials was seen which reduced over time. The HA-TCP particles were embedded within fibrous connective tissue and were encapsulated by a dense cellular layer consisting of active fibroblasts and occasional macrophages with the thickness of this layer decreasing over time. The results of this study suggest that the use of commercially available HA-TCP alone or in combination with EMD or rhPDGF-BB is biocompatible but not osteoinductive in the murine thigh muscle model of osteoinduction. Coating HA-TCP with EMD or rhPDGF-BB does not enhance its osteoinductive potential.     

Bone augmentation by recombinant human BMP-2 and collagen on adult rat parietal bone.

A composite of recombinant human bone morphogenetic protein-2 (rhBMP-2) and collagen was implanted beneath the cranial periosteum of 10-month-old rats to observe bone development and absorbent change of carrier collagen. The rhBMP-2/collagen onlay implant resulted in active bone formation and the augmented bone was connected directly with the original bone, whereas the collagen alone resulted in neither bone nor cartilage. The ossification process in the rhBMP-2/collagen occurred directly through bone formation, similar to intramembranous ossification. The carrier collagen fibers were found in the woven bone and were completely absorbed at 8 weeks in the presence of rhBMP-2, while the collagen alone implant remained encapsulated by a thin, fibrous connective tissue. Our results indicate that rhBMP-2/collagen is an effective material as a biological onlay implant, showing osteoinductive properties and being completely replaced by new bone. Carrier collagen not only plays a role in rhBMP-2 delivery, but also provides a cell anchorage for cell differentiation and remains as an artificial matrix in woven bone.