Bone morphogenetic protein but not transforming growth factor-beta enhances bone formation in canine diaphyseal nonunions implanted with a biodegradable composite polymer

Salicylic acid-derived poly(anhydride-esters) inhibit bone resorption and formationin vivo

The objective of this study was to investigate the effects of a novel polymer that biodegrades into salicylic acid (SA) on the healing of critical sized long bone defects. Microspheres of the homopolymer, or a copolymer containing 50% less of the SA, were packed into 5-mm mid-diaphyseal defects in rat femurs. Control animals received collagen sponge implants. After 4 and 8 weeks of implantation, bone healing was evaluated using microradiography and quantitative histomorphometry. Four weeks postsurgery, significantly less new bone was formed in both of the polymer groups (p<0.038). Reduced bone loss was also noted with the polymers at this time, although it was not statistically significant. However, at 8 weeks postsurgery, a statistically significant reduction in bone loss was observed in both of the polymer groups compared with controls (p<0.0072). Both polymers seemed to elicit identical tissue responses because there were no differences detected between the homopolymer and copolymer materials at either time point. These results indicate that locally released SA can significantly reduce both bone loss and bone formation in this animal model.

Combination of porous hydroxyapatite and cationic liposomes as a vector for BMP-2 gene therapy

The clinical significance of hydroxyapatite (HAP) as a bone substitute has become apparent in recent years and bone morphogenetic protein (BMP) a substance which induces bone has attracted much attention. In this study, a 1.2 cm diameter bone defects created on rabbit cranium were treated with the BMP-2 gene (cDNA plasmid) introduced with porous HAP after completion of hemostasis and the resultant bone formation was analyzed histopathologically. The amounts of bone formation was compared BMP-2 cDNA plasmids were not combined with cationic liposomes as a vector. Four groups of rabbits were compared. In the HAP group the cranial bone defect was treated with HAP containing 40 microg of liposomes and a dummy gene (PU). The BMP gene HAP group was treated with HAP soaked in liposomes and 10 microg of the BMP-2 gene. In addition, a group was treated with the gene without implanting HAP. Bone formation on the cranial defects was evaluated 3, 6 and 9 weeks after the operation, by X-ray and histopathological examinations. Three weeks after the operation there was vigorous bone formation in the cranial defect in the group which received the BMP-2 gene without HAP, and complete ossification was observed at 9 weeks. In the group which received HAP containing the BMP-2 gene, although new bone formation was evident surrounding the scaffold 3 weeks post-operation, the induced bone tissue did not fill all the pores of the scaffold even at 9 weeks post-operation. These results confirm the clinical usefulness of gene therapy for bone formation, using the BMP-2 gene combined with cationic liposomes as a vector. It is possible that the effects of administering the BMP-2 gene will be improved by specializing the microstructure of scaffold for gene therapy.

A novel osteotropic biomaterial OG-PLG: Synthesis andin vitro release

Statins (e.g., simvastatin) have shown to induce expression of the bone morphogenic protein-2 gene in bone cells, but they are not used clinically because of a lack of a suitable delivery device. The overall objective is to develop optimized statin delivery devices for bone regeneration. The specific objective was to determine the effect of grafting statins to biodegradable poly[lactide-co-glycolide] (PLG) on release kinetics. Simvastatin was grafted to PLG (OG-PLG) and characterized using contact-angle measurements, attenuated total reflectance-Fourier transform infrared, and ultraviolet-visible spectroscopy to determine success of the synthesis. An ultraviolet-visible assay for measuring release of statins and degraded OG-PLG in media was also developed. In vitro release studies using films and scaffolds made with PLG, PLG blended with simvastatin (PLG + Sim), and OG-PLG (simvastatin grafted to PLG) blended into PLG at different concentrations showed that release rate of OG-PLG from films was significantly greater than that of PLG + Sim. However, release rate from scaffolds showed PLG + Sim to be significantly higher than that of OG-PLG. The diffusion-controlled release kinetics of simvastatin from PLG + Sim seems to be more heavily affected by device morphology, whereas the degradation-controlled release kinetics seem to be less affected. In short, release kinetics can be modulated by grafting statins to PLG.

Delivery of Growth Factors Using Gene Therapy to Enhance Bone Healing

OBJECTIVE

To review the delivery of growth factors using gene therapy for enhancing long-bone fracture healing.

STUDY DESIGN

Literature review.

METHODS

MEDLINE and CAB Abstracts literature search (1980-2004).

RESULTS

Non-union and infected non-union are relatively common complications of long-bone fractures in human and veterinary patients. Growth factors are cytokines that regulate many cell functions important in fracture healing. Exogenous growth factors can be delivered to the fracture site as recombinant proteins or using gene therapy. Recombinant human bone morphogenetic protein-2 and -7 (rhBMP-2 and -7), in particular, enhance fracture healing in numerous experimental and clinical studies. Some limitations with use of recombinant proteins may be overcome by use of gene therapy. Gene therapy involves delivery of the growth factor gene to cells at the fracture site using a viral or non-viral vector. The gene is then expressed (protein synthesis) by cells at the fracture site. Delivery of the BMP gene to the fracture site using gene therapy has been evaluated in laboratory animal models of non-union, with favorable results and without complications.

CONCLUSION

Delivery of growth factors, particularly members of BMP family, to the fracture site using gene therapy may be a method to enhance fracture healing. Use of this technology may improve the prognosis for patients with long-bone fractures.

CLINICAL RELEVANCE

Clinical application of gene therapy could improve the prognosis for human and veterinary patients with long-bone fractures, but has not been evaluated clinically.

Different effects of BMP-2 on marrow stromal cells from human and rat bone

Bone morphogenetic proteins (BMPs) promote the differentiation of osteoprogenitor cells, and also induce osteogenesis in bone marrow stromal cells (MSC) from rats and mice. However, compared to results with animal models, BMPs are relatively inefficient in inducing human MSC to undergo osteogenesis, and are much less effective in promoting bone formation in human clinical trials. Previous studies indicated that, while human MSC respond to dexamethasone with elevated levels of the osteoblast marker alkaline phosphatase, most isolates of human MSC fail to show alkaline phosphatase induction in response to BMP-2, BMP-4, or BMP-7. Several other genes known to be induced by BMPs are appropriately regulated; thus, human MSC are capable of some BMP-activated signaling. Analysis of the BMP receptors ALK-3 and ALK-6 indicated that, although ALK-6 mRNA was not expressed in human MSC, overexpressing a constitutively active ALK-6 receptor did not induce elevated alkaline phosphatase. Real-time RT-PCR was used to investigate expression of several osteoblast-related transcription factors in MSC after 6 days' exposure to BMP2 or dexamethasone. Msx-2, a transcription factor that has been reported to inhibit differentiation of osteoprogenitor cells, showed 10-fold elevation in BMP-2-treated human MSC, but not in BMP-2-treated rat MSC. Overexpression of Msx-2 in human and rat MSC, however, did not alter alkaline phosphatase levels, which suggests that absence of BMP-stimulated alkaline phosphatase was not caused by the BMP-2-induced increase in Msx-2. Although Runx2 isoforms have been implicated in control of osteoblast differentiation, levels of this transcription factor were unaffected by BMP treatment. Expression of the FKHR transcription factor, which has been reported to regulate alkaline phosphatase transcription in mouse cells, showed a modest increase in response to BMP-2, but a much greater increase in dexamethasone-treated cells. We propose that BMP regulation of the bone/liver/kidney alkaline phosphatase gene is indirect, requiring expression of new transcription factor(s) that behave differently in rodent and human MSC.

Contact profilometry and correspondence analysis to correlate surface properties and cell adhesion in vitro of uncoated and coated Ti and Ti6Al4V disks

A fundamental goal in the field of implantology is the design of specific devices able to induce a controlled and rapid "osseointegration". This result has been achieved by means of surface modifications aimed at optimizing implant-to-bone contact; furthermore, bone cell adhesion on implant surface has been directly improved by the application of biomolecules that stimulate new tissue formation, thus controlling interactions between biological environment and implanted materials. Actually, methods for biochemical factor delivery at the interface between implant surface and biological tissues are under investigation; a reliable technique is represented by the inclusion of biologically active molecules into biocompatible and biodegradable materials used for coating implant surface. This paper focuses the application of three polymeric materials already acknowledged in the clinical practice, i.e. poly-L-lactic acid (PLLA), poly-DL-lactic acid (PDLA), and sodium alginate hydrogel. They have been used to coat Ti (Ti2) and Ti6Al4V (Ti5) disks; their characteristics have been determined and their performances compared, with specific regard to the ability in allowing osteoblast adhesion in vitro. Moreover, profilometry data analysis permitted to identify a specific roughness parameter (peak density) which mainly controls the amount of osteoblast adhesion.

Evaluation of Ad-BMP-2 for enhancing fracture healing in an infected defect fracture rabbit model

The objective of this study was to evaluate the use of adenoviral transfer of the BMP-2 gene (Ad-BMP-2) for enhancing healing in an infected defect fracture model. A femoral defect stabilized with plates and screws was surgically created in sixty-four skeletally mature New Zealand white rabbits. Experimental groups were: (1) non-infected Ad-luciferase (Ad-LUC, NONLUC), (2) non-infected Ad-BMP-2 (NONBMP), (3) infected Ad-LUC (INFLUC), and (4) infected Ad-BMP-2 (INFBMP). A sclerosing agent was applied to the ends of the bone at surgery to facilitate the development of osteomyelitis. Fracture healing was evaluated radiographically and histologically. Data were analyzed using an ANOVA, with statistical significance set as p<0.05. Rabbits in the non-infected and infected groups that were treated with Ad-BMP-2 had earlier initial- and bridging-callus formation, and a higher overall external callus grade compared to rabbits in the Ad-LUC groups. Rabbits in the Ad-LUC groups had more defect ossification compared to rabbits in the Ad-BMP-2 groups. There was a trend for rabbits in the Ad-BMP-2 group that were euthanized at 2 and 4 weeks after surgery to have more bone and cartilage compared to rabbits in the Ad-LUC group. The results of this study suggest that Ad-BMP-2 enhances the early stages of healing in an infected defect fracture. The results of our study were not as favorable as those reported in previous studies because animals healed by a large bridging callus and not by defect ossification. This could have been a result of the sclerosing agent, which may have damaged the cells in the defect.

Angiogenesis and bone repair

The intimate connection, both physical and biochemical, between blood vessels and bone cells has long been recognized. Genetic, biochemical, and pharmacological studies have identified and characterized factors involved in the conversation between endothelial cells (EC) and osteoblasts (OB) during both bone formation and repair. The long-awaited FDA approval of two growth factors, BMP-2 and OP-1, with angiogenic and osteogenic activity confirms the importance of these two processes in human skeletal healing. In this review, the role of osteogenic factors in the adaptive response and interactive function of OB and EC during the multi-step process of bone repair will be discussed.

Development of a porous poly(L-lactic acid)/hydroxyapatite/collagen scaffold as a BMP delivery system and its use in healing canine segmental bone defect

A hydroxyapatite/collagen (HAC) composite was produced to mimic the natural extracellular matrix of bone, with the collagen serving as a template for apatite formation. A three-dimensional highly porous scaffold was developed by mixing HAC with poly(L-lactic acid) (PLA) using a thermally induced phase separation technique. Naturally derived bovine bone morphogenetic protein (bBMP) was incorporated into the porous HAC-PLA scaffolds, and the composite then was implanted in diaphyseal defects (2 cm in radius) of adult beagle dogs. Controls were implanted with scaffolds without BMP. The dogs were sacrificed at 6 months, at which time biocompatibility, biodegradability, and osteoinduction were evaluated by histologic and radiologic examination and by bone mineral density (BMD) measurements. All defects healed after treatment with BMP combined with HAC-PLA, and BMD at the site of the defect was higher than the BMD of the intact radius. Fibrous union developed in the control group animals. Histologic observation indicated that the presence of BMP not only promoted osteogenesis but that it also accelerated degradation of the biomaterials. Optimized design parameters of a three-dimensional porous biomaterial would give full scope to the role of BMP as an osteoinductive growth factor.

Temporal and spatial expression profiles of BMP receptors and noggin during BMP-2-induced ectopic bone formation

The mechanism of ectopic bone formation has not been clear. After BMP-2 implantation into the back muscles of 198 mice, expression of BMPR-1A, -2, and Noggin was increased during the early phase of the reaction. The results suggest that positive and negative feedback mechanisms modulate ectopic osteogenesis induced by this growth factor.

INTRODUCTION

The expression of bone morphogenetic protein receptors (BMPRs) and Noggin during ectopic bone formation after implantation of BMP-2 into the back muscles of adult mice was investigated in this study.

METHODS

One hundred ninety-eight male ddy mice were divided into groups and received either collagen disks containing BMP-2, collagen disks alone, or sham surgery with no disk implantation. Changes in the temporal and spatial expression profiles of BMPRs and Noggin were examined by Northern blotting, in situ hybridization, Western blotting, and immunohistochemistry.

RESULTS AND CONCLUSIONS

In the BMP group, expression of BMPR-1A, -2, and Noggin mRNA and protein was enhanced 2-4 days after implantation in undifferentiated mesenchymal cells and regenerating muscle fibers located close to the BMP-retaining implants. On day 7, the expression was also observed in cartilage cells, and after day 14, in the osteoblastic cells around bone tissue. The level of expression peaked at day 4 after implantation and persisted at a much lower level during the bone forming process. No significant expression of BMPR-1B was detected at the mRNA and protein levels during the bone-forming reaction. In the BMP free control groups, a mild enhancement of BMPR-2 expression was also noted around the implant, but this was not observed for BMPR-1A, -1B, or Noggin. Upregulated expression of BMPR-1A, -2, and Noggin in undifferentiated mesenchymal cells and regenerating muscle fibers occurs during the early phase of BMP-2-induced bone formation. The coordinate expression of these positive and negative regulators of BMP signaling points to a potential regulatory mechanism for bone induction.

Development of an atrophic nonunion model and comparison to a closed healing fracture in rat femur

Although most fractures heal, some fail to heal and become nonunions. Many animal models have been developed to study problems of fracture healing. The majority of nonunion models have involved segmental bone defects, but this may not adequately represent the biologic condition in which nonunions clinically develop. The objective of the present study is to develop a nonunion model that better simulates the clinical situation in which there is soft tissue damage including periosteal disruption and to compare this model to a standard closed fracture model utilizing identical fracture stabilization, providing a similar mechanical environment. A total of 96 three month old Long Evans rats were utilized. A 1.25 mm diameter K-wire was inserted into the femur in a retrograde fashion, and a mid-diaphyseal closed transverse fracture was created using a standard three-point bending device. To create a nonunion, 48 of the rats received additional surgery to the fractured femur. The fracture site was exposed and 2 mm of the periosteum was cauterized on each side of the fracture. Fracture healing was evaluated with serial radiographs every two weeks. Animals were maintained for intervals of two, four, six or eight weeks after surgery. Specimens from each time interval were subjected to biomechanical and histological evaluation. None of the cauterized fractures healed throughout the eight weeks experimental duration. The radiographical appearance of nonunion models was atrophic. This investigation showed pronounced differences between the experimental nonunions and standard closed fractures both histologically and biomechanically. In conclusion, we have developed a reproducible atrophic nonunion model in the rat femur that simulates the clinical condition in which there is periosteal disruption but no bone defect.

Bone formation in transforming growth factor beta-1-coated porous poly(propylene fumarate) scaffolds

This study determined the bone growth into pretreated poly(propylene fumarate) (PPF) scaffolds implanted into a subcritical size, rabbit cranial defect. PPF scaffolds were constructed by using a photocrosslinking-porogen leaching technique. These scaffolds were then either prewetted (PPF-Pw), treated with RF glow-discharge (PPF-Gd), coated with fibronectin (PPF-Fn), or coated with rhTGF-beta1 (PPF-TGF-beta1). One of each scaffold type was then placed into the cranium of nine rabbits. The rabbits were sacrificed after 8 weeks, and the scaffolds were retrieved for histological analysis. The most bone formation was present in the PPF-TGF-beta1 implants; the newly formed bone had a trabecular appearance together with bone marrow-like tissue. Little or no bone formation was observed in implants without rhTGF-beta1. These histological findings were confirmed by image analysis. Bone surface area, bone area percentage, pore fill percentage, and pore area percentage were significantly higher in the rhTGF-beta1-coated implants than in the noncoated implants. No statistical difference was seen between the PPF-Fn, PPF-Pw, or PPF-Gd scaffolds for these parameters. Quadruple fluorochrome labeling showed that in PPF-TGF-beta1 implants bone formation mainly started in the interior of a pore and proceeded toward the scaffold. We conclude that (a) PPF-TGF-beta1 scaffolds can indeed adequately induce bone formation in porous PPF, and (b) PPF scaffolds prepared by the photocrosslinking-porogen leaching technique are good candidates for the creation of bone graft substitutes.

Effect of phosphodiesterase inhibitor-4, rolipram, on new bone formations by recombinant human bone morphogenetic protein-2

Collagen sponge disks (6 mm diameter, 1 mm thickness) were impregnated with recombinant human bone morphogenetic protein-2 (rhBMP-2) (5 microg/disk) and implanted onto the back muscles of mice. Ten or 20 mg/kg per day of Rolipram, a selective inhibitory agent to phosphodiesterase type 4 (PDE-4), or vehicle, was injected subcutaneously into the host mice for 3 weeks. After treatment, rhBMP-2-induced ectopic ossicles were harvested and examined by radiographic and histologic methods to determine the size, bone quality, and mineral content of the ossicles. The ossicles from a group treated with 20 mg/kg per day Rolipram were significantly larger in size and higher in bone mineral density (BMD) and bone mineral content (BMC) than the control samples. No significant differences were noted in mice treated with 10 mg/kg per day of Rolipram. Histologically, ossicles from the high-dose (20 mg/kg per day) Rolipram-treated group showed densely packed, thicker trabeculae when compared with those from the control group. These experimental results indicate that the PDE-4 inhibitor, Rolipram, may enhance the bone-inducing capacity of BMP-2 in mesenchymal cells. This in turn may result in increased responsiveness to BMP-2 and point to a potential use of PDE-4 inhibitors for the promotion of rhBMP-dependent bone repair.

Osteoinductive molecules in orthopaedics: basic science and preclinical studies

Osteoinductive molecules are characterized by their ability to promote the formation of bone. Most osteoinductive molecules are cytokines, which are extracellular proteins or peptides that mediate cell to cell signaling. Examples of osteoinductive cytokines are certain bone morphogenetic proteins and some growth and differentiation factors. Some osteoinductive molecules are not secreted molecules. LIM mineralization protein-1 is an example of an intracellular osteoinductive molecule. Significant advances have been made in characterizing the molecular composition and mechanism of action of these osteoinductive molecules. Preclinical studies with these molecules have provided better understanding of the doses, formulation, and delivery mechanism necessary for effective bone formation in model systems of spinal fusion and other orthopaedic problems. The current authors will review the most important basic science and preclinical studies involving these osteoinductive molecules.

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.

Implantation of octacalcium phosphate combined with transforming growth factor-beta1 enhances bone repair as well as resorption of the implant in rat skull defects

In our previous study, we reported that synthetic octacalcium phosphate (OCP) enhances bone repair if implanted in rat skull defects. We hypothesized that OCP can be used as an effective carrier for transforming growth factor-beta1 (TGF-beta1) to promote bone repair. We designed the present study to investigate histomorphometrically whether combination with recombinant human TGF-beta1 could promote bone repair caused by OCP per se (Control/OCP). A full-thickness standardized trephine defect was made in the rat parietal bone and OCP combined with recombinant human TGF-beta1 (TGF-beta1/OCP) or Control/OCP was implanted into the defect. Four rats from each group were fixed at 2, 4, and 8 weeks after implantation. Histomorphometrical analysis of the percentage of newly formed bone (n-Bone %) and remaining implants (r-Imp %) in the defect was performed. The statistical analysis showed the n-Bone % of TGF-beta1/OCP was significantly higher than that of the Control/OCP in week 4, whereas the r-Imp % of TGF-beta1/OCP was significantly lower than that of the Control/OCP. The present study demonstrated that OCP can be used as an effective carrier for TGF-beta1 and their combination enhances bone repair as well as resorption of the carrier OCP in the early stage of bone formation.

Enhancement of bone morphogenetic protein-2-induced new bone formation in mice by the phosphodiesterase inhibitor pentoxifylline

Porous collagen disks (6 mm diameter, 1 mm thickness) were impregnated with recombinant human bone morphogenetic protein-2 (rhBMP-2) (5 microg/disk) and implanted onto the back muscles of mice. Pentoxifylline (PTX), which is a methylxanthine-derived inhibitor of phosphodiesterases (PDEs), or vehicle, was injected (5, 25, 50, 100, 200, and 300 mg/kg body weight/day) into the mice subcutaneously once a day for 3 weeks from the day of implantation of the bone morphogenetic protein (BMP)-laden disks. The rhBMP-2-induced ectopic ossicles were harvested and examined using radiographic, histological, and biochemical methods to determine size, bone quality, and calcium content. When compared with controls, ossicles from mice treated with >50 mg/kg per day of PTX were significantly larger in size and had a greater calcium content. However, no differences were noted in mice treated with lower doses (5 and 25 mg/kg per day) of PTX. The temporal sequence of the bone-forming process was unchanged by PTX based on histological examination. The histology of the ossicles from high- and low-dose PTX-treated mice was essentially identical to that observed in the control mice. These experimental results indicate that PTX enhanced the bone-inducing capacity of BMP-2. The underlying mechanism of action most likely involves the inhibition of intracellular phosphodiesterases and a resulting elevation of the intracellular content of cyclic nucleotides. Further studies are warranted to understand how BMP-induced bone formation is pharmacologically modified by PTX.

Porcine fetal enamel matrix derivative enhances bone formation induced by demineralized freeze dried bone allograft in vivo

BACKGROUND

Embryonic enamel matrix proteins are involved in the formation of acellular cementum during development of the periodontal attachment apparatus, suggesting that these proteins might be used clinically to promote periodontal regeneration. At present, it is unknown if these proteins are osteoinductive, osteoconductive, or osteopromotive. To address this question, we examined the ability of a commercially prepared embryonic porcine enamel matrix derivative to induce new bone formation in nude mouse calf muscle, or to enhance the bone induction ability of a demineralized freeze-dried bone allograft (DFDBA).

METHODS

Porcine fetal enamel matrix derivative (EMD) was implanted bilaterally in the calf muscle of 4 male Nu/Nu mice per treatment group (N = 8 implants): 2 mg EMD alone; 4 mg EMD alone; inactive human DFDBA alone; inactive DFDBA + 2 mg EMD; inactive DFDBA + 4 mg EMD; active DFDBA alone; active DFDBA + 2 mg EMD; and active DFDBA + 4 mg EMD. Implants were harvested after 56 days and examined histologically for bone induction using a semi-quantitative score and histomorphometrically for area of new bone, cortical bone, bone marrow, and residual DFDBA.

RESULTS

Implants containing inactive DFDBA, 2 mg EMD, 4 mg EMD, and inactive DFDBA + 2 or 4 mg EMD did not induce new bone. Active DFDBA and active DFDBA + 2 mg EMD induced new bone to a similar extent. In contrast, active DFDBA + 4 mg EMD resulted in enhanced bone induction, area of new bone, and cortical bone. Residual DFDBA was also increased in this group.

CONCLUSIONS

EMD is not osteoinductive. However, it is osteopromotive, due in part to its osteoconductive properties, but a threshold concentration is required.

Bone growth factors

Osteoblastic culture models, experimental, and clinical models have revealed that bone growth factors influence cellular activity. Growth factors including bone morphogenetic proteins, transforming growth factor beta, platelet-derived growth factor, insulin-like growth factors I and II, and acidic and basic fibroblast growth factors, are powerful tools for fracture healing and bone grafting. Understanding the role that bone growth factors play in bone repair is necessary to apply these factors in a clinical setting.