Calvarial bone regeneration using osteogenin

Comparison of Autogenous Tooth Materials and Other Bone Grafts

Autogenous odontogenic materials are a new, highly biocompatible option for jaw restoration. The inorganic component of autogenous teeth acts as a scaffold to maintain the volume and enable donor cell attachment and proliferation; the organic component contains various growth factors that promote bone reconstruction and repair. The composition of dentin is similar to that of bone, which can be a rationale for promoting bone reconstruction. Recent advances have been made in the field of autogenous odontogenic materials, and studies have confirmed their safety and feasibility after successful clinical application. Autogenous odontogenic materials have unique characteristics compared with other bone-repair materials, such as the conventional autogenous, allogeneic, xenogeneic, and alloplastic bone substitutes. To encourage further research into odontogenic bone grafts, we compared the composition, osteogenesis, and development of autogenous odontogenic materials with those of other bone grafts. In conclusion, odontogenic bone grafts should be classified as a novel bone substitute.

The Recent Revolution in the Design and Manufacture of Cranial Implants: Modern Advancements and Future Directions

Large format (i.e., >25 cm) cranioplasty is a challenging procedure not only from a cosmesis standpoint, but also in terms of ensuring that the patient's brain will be well-protected from direct trauma. Until recently, when a patient's own cranial flap was unavailable, these goals were unattainable. Recent advances in implant computer-aided design and 3-dimensional (3-D) printing are leveraging other advances in regenerative medicine. It is now possible to 3-D-print patient-specific implants from a variety of polymer, ceramic, or metal components. A skull template may be used to design the external shape of an implant that will become well integrated in the skull, while also providing beneficial distribution of mechanical force in the event of trauma. Furthermore, an internal pore geometry can be utilized to facilitate the seeding of banked allograft cells. Implants may be cultured in a bioreactor along with recombinant growth factors to produce implants coated with bone progenitor cells and extracellular matrix that appear to the body as a graft, albeit a tissue-engineered graft. The growth factors would be left behind in the bioreactor and the graft would resorb as new host bone invades the space and is remodeled into strong bone. As we describe in this review, such advancements will lead to optimal replacement of cranial defects that are both patient-specific and regenerative.

Transforming growth factor beta 1 augments calvarial defect healing and promotes suture regeneration

BACKGROUND

Repair of complex cranial defects is hindered by a paucity of appropriate donor tissue. Bone morphogenetic protein 2 (BMP2) and transforming growth factor beta 1 (TGFβ1) have been shown separately to induce bone formation through physiologically distinct mechanisms and potentially improve surgical outcome for cranial defect repair by obviating the need for donor tissue. We hypothesize that a combination of BMP2 and TGFβ1 would improve calvarial defect healing by augmenting physiologic osteogenic mechanisms.

METHODS/RESULTS

Coronal suturectomies (3×15 mm) were performed in 10-day-old New Zealand White rabbits. DermaMatrix™ (3×15mm) patterned with four treatments (vehicle, 350 ng BMP2, 200 ng TGFβ1, or 350 ng BMP2+200 ng TGFβ1) was placed in suturectomy sites and rabbits were euthanized at 6 weeks of age. Two-dimensional (2D) defect healing, bone volume, and bone density were quantified by computed tomography. Regenerated bone was qualitatively assessed histologically. One-way analysis of variance revealed significant group main effects for all bone quantity measures. Analysis revealed significant differences in 2D defect healing, bone volume, and bone density between the control group and all treatment groups, but no significant differences were detected among the three growth factor treatment groups. Qualitatively, TGFβ1 treatment produced bone with morphology most similar to native bone. TGFβ1-regenerated bone contained a suture-like tissue, growing from the lateral edge of the defect margin toward the midline. Unique to the BMP2 treatment group, regenerated bone contained lacunae with chondrocytes, demonstrating the presence of endochondral ossification.

CONCLUSIONS/SIGNIFICANCE

Total healing in BMP2 and TGFβ1 treatment groups is not significantly different. The combination of BMP2+TGFβ1 did not significantly increase bone healing compared with treatment with BMP2 or TGFβ1 alone postoperatively at 4 weeks. We highlight the potential use of TGFβ1 to regenerate calvarial bone and cranial sutures. TGFβ1 therapy significantly augmented bony defect healing at an earlier time point when compared with control, regenerated bone along the native intramembranous ossification pathway, and (unlike BMP2 alone or in combination with TGFβ1) permitted normal suture reformation. We propose a novel method of craniofacial bone regeneration using low-dose, spatially controlled growth factor therapies to minimize potentially harmful effects while maximizing local bioavailability and regenerating native tissues.

Repair of critical size defects in the rat cranium using ceramic-reinforced PLA scaffolds obtained by supercritical gas foaming

Bioresorbable scaffolds made of poly(L-lactic acid) (PLA) obtained by supercritical gas foaming were recently described as suitable for tissue engineering, portraying biocompatibility with primary osteoblasts in vitro and interesting mechanical properties when reinforced with ceramics. The behavior of such constructs remained to be evaluated in vivo and therefore the present study was undertaken to compare different PLA/ceramic composite scaffolds obtained by supercritical gas foaming in a critical size defect craniotomy model in Sprague-Dawley rats. The host-tissue reaction to the implants was evaluated semiquantitatively and similar tendencies were noted for all graft substitutes: initially highly reactive but decreasing with time implanted. Complete bone-bridging was observed 18 weeks after implantation with PLA/ 5 wt % beta-TCP (PLA/TCP) and PLA/5 wt % HA (PLA/HA) scaffolds as assessed by histology and radiography. We show here for the first time that this solvent-free technique provides a promising approach in tissue engineering demonstrating both the biocompatibility and osteoconductivity of the processed structures in vivo.

Bone repair in rat mandible by rhBMP-2 associated with two carriers

This study evaluated the quantity and quality of newly formed bone, stimulated by rhBMP-2 in combination with monoolein or chitosan gel as carriers, in critical bone defects created in 36 Wistar rat mandibles. Two weeks after surgery, the animals were anesthetized with 37.5% urethane submitted to perfusion and the hemi-mandibles removed for histological and histomorphometrical analysis. The results showed that there was a statistical difference between groups of animals receiving or not rhBMP-2 (p<0.05). Newly formed bone was more intense in the occlusal region, followed by the basal and middle regions, respectively. Both carriers, monoolein and chitosan gels were adequate for defect filling and control of protein release.

Macroscopical, histological, and morphometric studies of porous bone-replacement materials in minipigs 8 months after implantation

OBJECTIVE

The aim of this investigation was to test the induction of bone formation and biodegradation of different biomaterials based on calcium phosphate (CaP). Up to now, hydroxyapatite and beta-tricalcium phosphate ceramics have routinely been sintered at temperatures of 1300 degrees C. The new CaP biomaterials tested are fabricated by a sol-gel process at only 700 degrees C.

STUDY DESIGN

Critical-size defects (>5 cm(3)) in the mandible of 15 adult Goettingen minipigs were filled with 1 of the 2 new types of CaP biomaterials, or with 1 of 2 well-known old-type ceramics, or with a gelatin sponge (in the control group). Macroscopical, histological, and morphometric examination of the former defect areas were made 8 months postoperatively.

RESULTS

Eight months after implantation of the new CaP biomaterials, complete bone formation was observed in the defect area, and at the same time, the foreign material was resorbed almost completely. After implantation of the classical types of ceramics, only incomplete bone formation and a lesser resorption rate of the foreign bodies were noted. The difference in the bone formation rate was significant: more than 93% for the new CaP biomaterials versus less than 58% for the classical types of ceramics (P < 0.01).

CONCLUSION

The biological behavior of the new CaP biomaterials was better than that of the old-type sintered ceramic bone-grafting materials. These new CaP matrices are suitable for filling bone defects and are of interest for dentists, including implantologists, craniomaxillofacial and orthopedic surgeons, as well as traumatologists.

Prefabricated vascularized bone flap: a tissue transformation technique for bone reconstruction

In this study, an attempt was made to transform a muscle vascularized pedicle raised on host vessels into a vascularized bone flap, using recombinant human bone morphogenetic protein 2 (rhBMP-2). The purpose of this study was to produce new bone vascularized in nature to increase the survival rate of the subsequently grafted bone and to fabricate the newly formed bone into the desired shape. Silicone molds in the shape of a rat mandible were used to deliver rat bone matrix impregnated with or without rhBMP-2. A muscle pedicle the same size as the mold was raised on the saphenous vessels in the rat thigh and then sandwiched in the center of the silicone molds. The molds were sliced in half and each section was filled with rat bone matrix that was impregnated either with 25 microg of rhBMP-2 for the experimental group or with diluting material alone for the control group. The sandwiched flaps were then secured by tying them to the adjacent muscles and were harvested at 2 and 4 weeks after surgery. Three and six rats were used in the control and experimental groups at each time point, respectively. Bone formation was assessed in the ex vivo specimens by macroscopic, radiologic, and histologic evaluation. Macroscopically, the continuation of the vascular pedicle was clearly visible for both the control and experimental muscle flaps. However, no evidence of muscle-tissue transformation was observed in the control flaps, whereas all the flaps treated with rhBMP-2 produced new bone that replicated the shape of the mold exactly and had saphenous vessels supplying the newly formed bone. This study demonstrates that this experimental model has the potential to be therapeutically applied for effective bone reconstruction.

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

BACKGROUND

The purpose of the present study was to create an effective bone-graft substitute for the treatment of a diaphyseal nonunion.

METHODS

A standardized nonunion was established in the midportion of the radial diaphysis in thirty mongrel dogs by creating a three-millimeter segmental bone defect (at least 2 percent of the total length of the bone). The nonunion was treated with implantation of a carrier comprised of poly(DL-lactic acid) and polyglycolic acid copolymer (50:50 polylactic acid-polyglycolic acid [PLG50]) containing canine purified bone morphogenetic protein (BMP) or recombinant human transforming growth factor-beta (TGF-beta1), or both, or the carrier without BMP or TGF-beta1. Five groups, consisting of six dogs each, were treated with implantation of the carrier alone, implantation of the carrier with fifteen milligrams of BMP, implantation of the carrier with 1.5 milligrams of BMP, implantation of the carrier with fifteen milligrams of BMP and ten nanograms of TGF-beta1, or implantation of the carrier with ten nanograms of TGF-beta1. At twelve weeks after implantation, the radii were examined radiographically and the sites of nonunion were examined histomorphometrically.

RESULTS

We found that implantation of the polylactic acid-polyglycolic acid carrier alone or in combination with ten nanograms of TGF-beta1 failed to induce significant radiographic or histomorphometric evidence of healing at the site of the nonunion. The radii treated with the carrier enriched with either 1.5 or fifteen milligrams of BMP showed significantly increased periosteal and endosteal bone formation on histomorphometric (p < 0.05) and radiographic (p < 0.02) analysis.

CONCLUSIONS

Bone formation in a persistent osseous defect that is similar to an ununited diaphyseal fracture is increased when species-specific BMP incorporated into a polylactic acid-polyglycolic acid carrier is implanted at the site of the nonunion. TGF-beta1 at a dose of ten nanograms per implant did not induce a similar degree of bone formation or potentiate the effect of BMP in this model.

CLINICAL RELEVANCE

The biodegradable implant containing BMP that was used in the present study to treat diaphyseal nonunion is an effective bone-graft substitute.

Surface roughness modulates the response of MG63 osteoblast-like cells to 1,25-(OH)(2)D(3) through regulation of phospholipase A(2) activity and activation of protein kinase A

Implant surface roughness influences osteoblast proliferation, differentiation, and local factor production. Moreover, the responsiveness of osteoblasts to systemic hormones such as 1, 25-(OH)(2)D(3) is altered by the effects of surface roughness; on the roughest Ti surfaces the effects of roughness and 1, 25-(OH)(2)D(3) are synergistic. Prostaglandin E(2) (PGE(2)) appears to be involved in mediating the effects of surface roughness on the cells, as well as in the response to 1,25-(OH)(2)D(3). However, it is not yet known through which signaling pathways surface roughness exerts its effects on the response of osteoblasts to 1, 25-(OH)(2)D(3). The present study examined the potential role of protein kinase A (PKA), phospholipase A(2)(PLA(2)), and protein kinase C (PKC) in this process. MG63 osteoblast-like human osteosarcoma cells were cultured on cpTi disks with R(a) values of 0. 54 microm (PT), 4.14 microm (SLA), or 4.92 microm (TPS). PKA was inhibited by adding H8 to the cultures; similarly, PLA(2) was inhibited with quinacrine or activated with melittin, and PKC was inhibited with chelerythrine. Inhibitors or activators were included in the culture media through the entire culture period or for the last 24 h of culture. In addition, cultures were treated for 24 h with inhibitors or activators in the presence of 1,25-(OH)(2)D(3). The effects on cell number and alkaline phosphatase specific activity were determined after 24 h; PKC activity was determined after 9 min and at 24 h. Cell number was reduced on rough surfaces, and alkaline phosphatase activity was increased. 1,25-(OH)(2)D(3) had a synergistic effect with surface roughness on alkaline phosphatase. However, neither surface roughness nor 1,25-(OH)(2)D(3) had an effect on PKC. H8 treatment for 24 h inhibited cell number and alkaline phosphatase on all surfaces; however, when it was present throughout the culture period, the PKA inhibitor had no effect on cell number, but decreased alkaline phosphatase-specific activity. H8 reduced the 1,25-(OH)(2)D(3)-mediated effect on cell number and alkaline phosphatase. Quinacrine inhibited cell proliferation and alkaline phosphatase on all surfaces and further reduced the 1,25-(OH)(2)D(3)-dependent decreases in both parameters. Melittin had no effect when applied for 24 h and did not modify the 1,25-(OH)(2)D(3) effect; however, when present throughout the culture period, it caused a decrease in proliferation and an increase in enzyme activity. Chelerythrine, the PKC inhibitor, only inhibited cell proliferation when it was present throughout the entire culture period. However, it decreased alkaline phosphatase in cultures treated for 24 h, but increased enzyme activity when it was present for the entire culture period. The results indicate that surface roughness and 1,25-(OH)(2)D(3) both mediate their effects through PLA(2) which catalyzes the rate-limiting step in PGE(2) production. Further downstream, PGE(2) activates PKA. Surface roughness-dependent effects are also mediated through PKC, but only after the cells have reached confluence and are undergoing phenotypic maturation. The effect of surface roughness on responsiveness to 1,25-(OH)(2)D(3) is mediated through PLA(2)/PKA and not through PKC.

Osteochondral progenitor cells in acute and chronic canine nonunions

This study examined the ability of cells isolated from early healing segmental defects and from tissue from chronic nonunions to support bone and cartilage formation in vivo and their response to transforming growth factor-beta1 in vitro. Ostectomies (3 mm) were created in the radial diaphysis of four dogs. The dogs were splinted 3-5 days postoperatively and then allowed to bear full weight. At 7 days, tissue in the defect was removed and any periosteum was discarded; cells in the defect tissue were released by enzymatic digestion. The dogs were splinted again and allowed to bear full weight for 12 weeks. Radiographs confirmed a persistent nonunion in each dog. Defect tissue was again removed, any periosteum was discarded, and cells were isolated. Cells were also obtained from the defect tissue by nonenzymatic means with use of explant cultures. One-half of the tissue and one-half of any preconfluent, first-passage cultures were shipped to Cleveland by overnight carrier. At second passage, cells were loaded into ceramic cubes and implanted into immunocompromised mice for 3 or 6 weeks. Harvested cubes were examined histologically for cartilage and bone with use of a semiquantitative scoring system. Confluent fourth-passage cultures of 7 and 84-day defect tissue cells were cultured with 0.03-0.88 ng/ml transforming growth factor-beta1 for 24 hours, and [3H]thymidine incorporation and alkaline phosphatase specific activity were determined. Donor-dependent differences were noted in the rate at which defect cells achieved confluence; in general, cells from 7-day tissue divided most rapidly. Seven-day defect cells formed less bone and at a slower rate than was seen in the ceramic cubes containing samples from day 84. Cells derived enzymatically behaved similarly to those from explant cultures. Ceramic cubes contained fibrous connective tissue, cartilage, bone, and fat, indicating that multipotent cells were present. Stimulation of [3H]thymidine incorporation in response to transforming growth factor-beta1 was donor dependent and variable; only two of six separate isolates of cells exposed to it had measurable alkaline phosphatase activity (which was relatively low), and none of the cultures exhibited an increase in response to transforming growth factor-beta1 for 24 hours. This indicates that mesenchymal progenitor cells are present in the healing defect tissue at 7 and 84 days and that the relative proportion of osteochondroprogenitor cells is greater at the later time. The response to transforming growth factor-beta1 is typical of multipotent mesenchymal cells but not of committed chondrocytes or osteoblasts, indicating that these committed and differentiated cells are not present in early stages of healing and suggesting that their differentiation is inhibited in chronic nonunion.

Fixation of the craniofacial skeleton with butyl-2-cyanoacrylate and its effects on histotoxicity and healing

Butyl-2-cyanoacrylate is an easily applied, biocompatible, bioresorbable polymer glue that provides an alternative to conventional rigid fixation techniques. Our aim was to determine if cyanoacrylate fixation of the bone flap in a rabbit craniotomy model provides the healing and strength afforded by plate and screw fixation. We also investigated the inflammatory responses of adjacent tissues including the scalp, cranium, and brain. A unilateral parietal bone flap was elevated in 33 adult New Zealand rabbits. The bone was fixed in position with cyanoacrylate (n = 13), fixed with a microplate and screws (n = 14), or was replaced without fixation (sham-control, n = 6). Normal scar formation and no residual polymer were found in scalp specimens. Neuropathologic analysis identified the presence of residual polymer on the surface of 2 of the 13 rabbit brains. Histopathologic analysis of the bone flap-to-skull interface revealed no difference in the degree but rather in the quality of inflammation and healing between the plate and screw and polymer fixation groups. Microdensitometric analysis of the bone gap revealed nearly equivalent bone density in the cyanoacrylate and plated groups, tending to less density in the sham group (p = 0.11 and 0.09, respectively). An additional study focusing on neurotoxicity was performed in 20 adult rabbits with 3-week and 11-week recovery periods and similarly found the absence of a marked inflammatory response to the polymer. In conclusion, bone healing and soft-tissue inflammation were comparable between cyanoacrylate and plate and screw fixation groups. Although butyl-2-cyanoacrylate glue fixation may provide a reasonable alternative to hardware fixation, further investigations are necessary to identify its ideal utilization.

[Osteoinduction and -reparation]

Traumata, diseases, developmental deformities, and tumor resections frequently cause bone defects and atrophies. In general, three different mechanisms exist by which bone restoration can be achieved: (1) osteogenesis initiated by vital, osteoblastic cells of autografts; (2) osteoconduction (or creeping substitution); and (3) osteoinduction. The latter mechanism means the differentiation of pluripotent, mesenchymal-type cells (located in a recipient bed with strong regenerative capacity) into cartilage- and bone-forming progenitor cells under the influence of inductive bone morphogenetic proteins (BMPs). Some BMPs are physiologically included in low concentrations as organic components in bone tissue. They can diffuse from demineralized bone implants into the recipient bed and induce a differentiation into new bone tissue. Nine different BMPs have been isolated, characterized, and cloned. Some of these possess inductive properties and can initiate new bone formation in muscle tissue or in bone defects. In the future recombinant BMPs will be available in unlimited quantities. This will lead to completely new therapeutic concepts in reconstructive bone surgery.

Growth factors in surgery

Surgical reconstruction of functional and aesthetic defects is often compromised by donor-tissue limitations and wound-healing constraints--problems that can potentially be overcome by peptide growth factor therapy. The effectiveness of growth factor therapy in animal models and in limited human clinical trials has been realized. Epidermal growth factor (EGF), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), platelet-derived wound-healing formula (PDWHF), transforming growth factor (TGF), the bone morphogenetic proteins (BMPs), and general considerations of growth factor therapy are reviewed.

Healing of a segmental defect in the rat femur with use of an extract from a cultured human osteosarcoma cell-line (Saos-2). A preliminary report

Devitalized extracts from cultured human osteosarcoma cells (Saos-2) can induce ectopic bone formation. The ability of an extract from Saos-2 cells to stimulate healing of an operatively created four-millimeter defect in the femoral diaphyses of rats was compared with that of collagen and that of autogenous bone graft. Forty adult rats were randomized into four groups of ten each. In Group 1 (controls), no material was placed in the defect; in Group 2, the defect was filled with pure bovine collagen; in Group 3, it was filled with autogenous graft obtained by morseling of the resected segment of the femur; and in Group 4, it was filled with ten milligrams of extract from Saos-2 cells that was mixed with an equal amount of bovine collagen. Five rats from each group were killed at four weeks and the remaining five, at eight weeks. Each femoral defect was analyzed radiographically and histologically for osseous healing. There was no evidence of healing at either four or eight weeks in Groups 1 and 2. Although there was some new-bone formation in Group 3, none of the defects had united at eight weeks. There was early, almost complete union in all five four-week specimens in Group 4 and complete healing of the defect in four of the five rats assessed at eight weeks. The Saos-2 cell extract was found to be the most effective agent, promoting union by mature lamellar bone within eight weeks.

Repair of human skull defects using osteoinductive bone alloimplants

To estimate the efficacy of cranioplasty in clinical practice, autolyzed, antigen-extracted, allogenic (AAA) bone was prepared from cortical bones of human organ donors. AAA bone implants consisted of completely demineralized bone powder, completely demineralized pliable bone chips, surface-demineralized bone chips with pliable crevices, surface-demineralized rigid bone chips, or combinations thereof. 21 patients received AAA bone cranioplasties and were followed-up for between 12 and 58 months (average: 29 months). No infection or rejection of any of the AAA bone implants occurred. X-ray assessments as well as bone scintigraphies revealed osseous integration and remodelling of the AAA bone implants with minimal resorption, with the exception of completely demineralized AAA bone chips which showed partial resorption (2 cases). However, the partial resorption of completely demineralized AAA bone chips ceased after the implants had been remodelled. In 4 cases, the osteosynthesis material was removed between 10 and 18 months after the cranioplasty. In another case, a re-entry was necessary because of recurrence of an intracranial tumor. All of these five AAA bone reconstructions showed bleeding surfaces and osseous consolidations at the time of re-entry. A bone biopsy taken from one of these cranioplasties showed osteoinduction on the surface of the AAA bone implants. This first clinical review of cranial reconstructions using osteoinductive AAA bone implants emphasizes the therapeutical application of AAA bone for cranioplasty. Large AAA bone chips from human skull bones facilitate the reproduction of the skull's convexity especially when combined with preoperative stereolithography-based planning.

Experimental study on demineralized bone matrix (DBM) and coral as bone graft substitutes in maxillofacial surgery

Three different bone substitutes were implanted in a standardized nasal bone defect in 30 Wistar rats. The results were assessed at 2 months by macroscopic examination, contact radiography, and histologic analysis. Demineralized osseous implants sterilized by ethylene oxide induced bone formation in 90% of the the cases, as no heat-treated graft showed any bone formation. Coralline grafts were osteointegrated in 50% of the cases, but osteoconduction was not sufficient to achieve complete bone repair. This study implies that ethylene oxide sterilization does not impair biologic properties of demineralized grafts, but further studies on more evolved animal species are necessary before human implantation.

Immediate reconstruction of massive cranio-orbito-facial defects with allogeneic and alloplastic matrices in baboons

40 cranio-orbito-facial osseous defects were created in 20 adult male baboons (Papio ursinus) to test the effectiveness of an allogeneic and an alloplastic matrix implant for the functional and morphological repair of the disassembled craniofacial complex. In each animal, one defect was reconstructed with a craniofacial bone segment harvested from donor adult baboons, and processed so as to obtain autolysed antigen-extracted allogeneic (AAA) bone matrix, preserving the bone morphogenetic protein (BMP) activity essential for bone induction. The contralateral defect was implanted with spherical macrobeads of polymethylmethacrylate (PMMA) coated with poly-2-hydroxyethylmethacrylate (PHEMA), and sintered into a porous molded implant, replicating the structural anatomy of the avulsed osseous segment. Histological analysis was carried out on undecalcified and decalcified bone sections prepared from specimens harvested at 3, 6 and 12 months after surgery. In AAA bone, the morphogenetic response was characterized by vascular invasion and mesenchymal cell aggregation after partial resorption of the implanted matrix. This was followed by bone deposition at the osteotomy interfaces and within the medullary spaces of the implanted AAA bone. Although bone ingrowth did occur in some PMMA/PHEMA specimens, the majority of implants showed fibrous union at the recipient interfaces. The limited bone ingrowth may be related to narrow interconnections between larger porous spaces after chemical synthesis of the two polymeric components. Osteogenesis in AAA bone appeared consistent with osteoconductive invasion from the viable bone at the recipient interfaces. In addition, the finding of a delicate trabecular-like bone, appositional to the central areas of the implanted matrix, suggests bone formation by induction.

Biotechnology and bone graft substitutes

Trauma, disease, developmental deformities, and tumor resection frequently cause bone defects that seriously challenge the skills of orthopedic and maxillofacial surgeons. Currently, repairing osseous deficiencies involves various medical surgical techniques, including autogenous grafts, allografts, internal and external fixation devices, electrical stimulation, and alloplastic implants. The existing technology, though effective in many cases, still is beset with numerous difficulties and disadvantages. A critical need for improved treatment methods exists today. Biotechnology now provides access to new bone repair concepts via administration of protein growth and morphogenic factors. Implantable device and drug delivery system technologies also have advanced. The converging biopharmaceutical, device, and delivery technologies represent an opportunity to improve the quality of health care for individuals with orthopedic and maxillofacial deficiencies. This report reviews current concepts in fracture healing and bone repair and examines existing treatment modalities. It also addresses novel protein drugs that stimulate osseous regeneration and delivery systems for these drugs.

Mineralization of dentinal collagen sheets complexed with alkaline phosphatase and integration with newly formed bone following subperiosteal implantation over osseous defects in rat calvaria

We addressed the question to what extent alkaline phosphatase (ALP) can induce mineralization of a collagenous matrix implanted subperiosteally, and how the graft interacts with the underlying bone. Bovine intestinal ALP was bound to sheets of guanidine-extracted, demineralized bovine dentin by using the crosslinking agent 1-ethyl-3(3-dimethylaminopropyl)carbodiimide.HCl. The complexes (with active enzyme) and control grafts (no enzyme) were implanted over osseous defects in opposite halves of rat calvaria. After time intervals varying from 3-12 weeks, the calvaria were processed for light and electron microscopic examination and histomorphometric analysis. The ALP-containing sheets (but not their controls) rapidly accumulated mineral crystals. As the complexes mineralized, osteoblasts appeared and formed a layer of bone in direct contact with the grafted material. The results indicate that ALP induced the deposition of mineral crystals, and strongly suggest that it is this mineral component which influenced the formation of bone.

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)

Regeneration of calvarial defects by a composite of bioerodible polyorthoester and demineralized bone in rats

A study was performed to evaluate regeneration of defects in rat calvaria either unfilled or filled with a bioerodible polyorthoester only, demineralized bone only, or a composite of both. At 4 weeks, histological and radiographic studies showed that defects filled with a composite of bioerodible polyorthoester and demineralized bone or demineralized bone alone were bridged by bone. Unfilled defects or defects filled with polyorthoester only did not heal. The polyorthoester caused slight inflammation that subsided by 3 weeks, and only traces of the filler could be detected at 4 weeks. The polyorthoester provided local hemostasis when used either alone or in composites with demineralized bone. The composite implant was moldable, easily contoured, and technically easier to use than demineralized bone alone.