Transmembrane bone morphogenesis across multiple-walled diffusion chambers. New evidence for a diffusible bone morphogenetic property

Effects of demineralization mode and particle size of allogeneic bone powder on its physical and chemical properties

At present, the commonly used allogeneic bone powder in the clinic can be divided into nondemineralized bone matrix and demineralized bone matrix (DBM). Commonly used demineralizers include acids and ethylene diamine tetraacetic acid (EDTA). There may be some diversities between them. Also, the size of the bone particle can affects its cell compatibility and osteogenic ability. We produced different particle sizes i.e., < 75, 75-100, 100-315, 315-450, 450-650, and 650-1000 μm, and treated in three ways (nondemineralized, demineralized by EDTA, and demineralized by HCl). Scanning electron microscopy showed that the surface of the samples in each group was relatively smooth without obvious differences. The results of specific surface area and porosity analysis showed that they were significantly higher in demineralized bone powder than in nondemineralized bone powder, however, there was no significant difference between the two decalcification methods. The content of hydroxyproline in nondemineralized bone powder and EDTA-demineralized bone powder had no statistical difference, while HCl-demineralization had statistical significance compared with the former two, and the content increased with the decrease of particle size. The protein and BMP-2 extracted from HCl demineralized bone powder were significantly higher than that from nondemineralized bone powder and EDTA demineralized bone powder, and there were differences among different particle sizes. These results suggested the importance of demineralization mode and particle size of the allogenic bone powder and provided guidance for the choice of the most appropriate particle size and demineralization mode to be used in tissue bioengineering.

Discovery of Heterotopic Bone-Inducing Activity in Hard Tissues and the TGF-β Superfamily

Bone is a unique organ because it can be experimentally induced in soft tissues by implanting a single growth factor, bone morphogenetic protein (BMP). Heterotopic bone-inducing activity was found in demineralized bone matrix in 1965. The characterization of this activity in bone enabled the purification and molecular cloning of BMPs and showed that they are members of the transforming growth factor-β (TGF-β) superfamily. Assay systems developed for this bone-inducing activity revealed the molecular mechanisms of the intracellular signaling of members of the superfamily, including BMPs. Moreover, they are being applied to elucidate molecular mechanisms and to develop novel therapeutics for a disease caused by an abnormality in BMP signaling.

Effects of fresh mineralized dentin and cementum on socket healing: a preliminary study in dogs

Objectives

Dentin is composed of many minerals and growth factors. Based on this composition, we studied its effect as a possible regenerative material for alveolar healing.

Materials and Methods

This study was conducted using four 2.5-year-old mongrel dogs (male; weight, 25 to 30 kg). The third mandibular premolars were carefully mobilized with a dental elevator and then removed using forceps. The crown portions of the extracted teeth were removed with cutters, and the root portions of the remaining teeth were collectively trimmed as closely as possible to 350 to 500 µm. Dentin and cementum (DC) chips harvested from the extracted teeth were soaked in blood and packed into the fresh sockets (autograft). Biopsies were performed at the ends of day 14 and day 56 following implantation. Data were expressed as mean±standard deviation and compared with t-test results.

Results

The ratio of S_A(bone) to total area of each probe was determined and was 170±16 µm² for the control group and 71±14 µm² for the DC group, a significant difference (P<0.05).

Conclusion

DC particulate grafts offered no improvement in bone regeneration in alveolar extraction sockets.

Demineralization of the contacting surfaces in autologous onlay bone grafts improves bone formation and bone consolidation

BACKGROUND

Autologous bone grafts are usually well consolidated after 4 to 5 months but can be incompletely interlocked with the native bone. This study investigated the effect of acid demineralization of the graft-bed interface on graft consolidation.

METHODS

Onlay bone grafts were performed on the calvaria of 36 guinea pigs. Half of the animals had the graft-bed contacting surfaces demineralized with 50% citric acid (pH 1.0) for 3 minutes (test group). The other half received no demineralization (control group). The bone grafts were immobilized by a resorbable membrane glued to the recipient bed with cyanoacrylate. After 7, 30, and 90 days, specimens (n = 6) were obtained for light microscopy. Data from qualitative analysis and computerized histomorphometry were statistically processed at a significance level of 5%.

RESULTS

Osteogenesis was not seen at the interface after 7 days. After 30 days, the test group showed 34.39% ± 13.4% of the interface area filled with mineralized tissue, compared to 17.14% ± 8.6% in the control group (P = 0.026). After 90 days, the mean percentages of mineralized tissue at the interface in the test and control specimens were 54.00% ± 11.23% and 38.65% ± 7.76% (P = 0.041), respectively. Within groups, a higher percentage of the area filled with mineralized tissue was seen at 90 days compared to 30 days (P = 0.004 for control and 0.041 for test).

CONCLUSIONS

Demineralization of the contacting surfaces between autologous bone graft and bone bed improved new bone formation and bone consolidation. These data need to be confirmed in humans.

The in vitro elution of BMP-7 from demineralized bone matrix

Demineralized bone matrix (DBM) grafts induce new bone formation by locally releasing matrix-associated growth factors, such as bone morphogenetic proteins (BMPs), to the surrounding tissue after implantation. However, the release kinetics of BMPs from DBM lack characterization. Such information can potentially help to improve processing techniques to maximize graft osteoinductive potential, as well as increase understanding of the osteoinductive process itself. We produced DBM with three particle size ranges from bovine cortical bone, i.e., <106, 106-300, and 300-710 μm and extracted 1.5 g of each size range in 40 ml of Sorensen's buffer at room temperature for up to 168 h. The BMP-7 concentration of the DBM and the buffer were measured at each time point using enzyme-linked immunosorbant assay. Based on measurement of the concentration of BMP-7 in the buffer, the 0-8 h elution rate was high, i.e., 3.3, 2.9, and 2.2 ng BMP-7/g DBM h, and for the 8-168 h interval was much lower, at 0.039, 0.15, and 0.11 ng BMP-7/g DBM h for the three size ranges, respectively. By 168 h, there was no indication that elution was nearing completion. Measurement of the residual BMP-7 remaining in the DBM as a function of time yielded unexpected results, i.e., after the BMP-7 content of the DBM declined for the first 4-6 h, it paradoxically increased for the remaining interval. We propose a two-compartment model to help explain these results in terms of the possible distribution of BMP-7 in bone matrix.

A rationale for delivery of osteoinductive proteins

Highly pure, recombinant human osteoinductive proteins make it possible to consider programmable osteoneogenesis. Until recently, it was believed that a bioresorbable excipient or physiologic solution would suffice to transport osteoinductive agents from source to wound. After considering surgical requirements, particular bone wound circumstances, scarcity of collateral circulation, phenotype plasticity of mesenchymal progenitor cells, and the morphogens' pleiotrophic effects, it becomes clear that the issue of controlled, programmable osteoneogenesis is a more complicated proposition than can be addressed solely by application of osteoinductive protein. The essential characteristics of a manufactured bone graft substitute (BGS) device are dictated by demands placed on such a device by the surgeons who will employ them and the cells that will occupy them. This review outlines a design process for BGS devices that (1) begins by surveying BGS requirements gathered from the literature from 1991 to 1995, (2) briefly reviews recent in vitro studies of rhBMP-2 and OP- 1, (3) describes commonly encountered circumstances of recipient wound beds, (4) describes behaviors of mesenchymal cells involved in connective tissue repair and regeneration, and (5) concludes with a rationale for design of an osteoinductive bone graft substitute. Emerging from this process is a composite device consisting of a bioresorbable structural polymer, a filamentous velour of hyaluronan (HY), and an osteoinductive protein. The structural polymer, D,D-L,L-polylactic acid, fabricated in the architecture of cancellous bone, is capable of maintaining its structural and architectural properties after being thoroughly saturated with water. Within its interstices is located a filamentous velour of hyaluronan which, when fully hydrated, becomes a viscoelastic gel. It is anticipated that the osteoinductive protein will either be carried on the dried hyaluronic acid velour or in solution via the viscoelastic HY gel.

Off-label use of recombinant human bone morphogenetic protein-2 (rhBMP-2) for reconstruction of mandibular bone defects in humans

PURPOSE

The off-label use of recombinant human bone morphogenetic protein-2 (rhBMP-2) for the treatment of mandibular bone defects was evaluated in 5 patients. The rhBMP-2 was used as an alternative to autogenous bone grafting.

PATIENTS AND METHODS

A total of 5 patients had mandibular defects reconstructed with rhBMP-2, 1.5 mg/mL, soaked collagen sponges alone or in combination with bone marrow cells and allogenic cancellous bone chips. Four of the patients had mandibular continuity defects and the fifth patient had 2 large bone cavities following removal of dentigerous cysts. Radiographs and clinical examinations were used to evaluate healing. The longest patient follow-up was 22 months after reconstruction.

RESULTS

Radiographic and clinical assessments revealed bone regeneration and restoration of the mandibular defects in 3 of the 5 patients. The rhBMP-2 failed in 2 patients with continuity defects. Both patients with failed rhBMP-2 grafts were successfully repaired using autogenous harvested from the iliac crest.

CONCLUSION

Mandibular bone defects can be successfully reconstructed using rhBMP-2 soaked sponges with and without including bone marrow cells and allogenic bone. Further studies are needed to determine the ideal combination of components that will predictably and reliably regenerate bone in different types of bone defects.

Use of Recombinant Human Bone Morphogenetic Protein-2 as an Adjunct in Posterolateral Lumbar Spine Fusion

INTRODUCTION

This study determines whether recombinant human bone morphogenetic protein-2 (rhBMP-2) (12 mg at the rate of 1.5 mg/mL) delivered on an absorbable collagen sponge with an added bulking agent can increase posterolateral lumbar spine fusion success rates and decrease time for fusion with autogenous bone grafts.

METHOD

A prospective, single institution, clinical case-matched, radiographic, cohort study was undertaken. A total of 52 patients underwent posterolateral lumbar arthrodesis with pedicle screw instrumentation. The experimental group (n=41) underwent placement of Iliac crest bone graft (ICBG) with InFUSE (12 mg/level at the rate of 1.5 mg/mL). The control group (n=11) consisted of sex-matched patients, consecutively collected over the same time period with an instrumented posterolateral arthrodesis and ICBG placed in the intertransverse space.

OUTCOME MEASURES

Thin-cut (2 mm) axial, coronal, and sagittal reconstructions were blindly evaluated for evidence of bridging bone and cortication of the fusion mass by 3 separate reviewers. Fusions were graded and an overall score was given to the quality of the fusion mass.

RESULTS

Fifty patients (ICBG alone n=11; ICBG/rhBMP-2 n=39) were available for CT evaluation at 2-year follow-up. An overall 97% (68/70 levels; Definite+Probably Fused) fusion rate in the rhBMP-2 group was achieved as compared to the 77% fusion rate (17/22 levels) in the ICBG alone group (P<0.05). In the rhBMP-2 group, 92% of the patients (36/39 patients) received an overall excellent subjective fusion rating as compared to 27% (3/11) in the control group (P<0.05). There was no computed tomographic evidence of soft-tissue ossification, dural ossification, or laminar bone regrowth in any patient.

CONCLUSIONS

The adjunctive use of rhBMP-2 and ICBG seems to be safe and results in significantly larger and more consistent posterolateral fusion masses.

The Hydration Characteristics of Demineralized and Nondemineralized Allograft Bone: Scientific Perspectives on Graft Function

Demineralized bone matrix grafts are osteoinductive due to the increase in bioavailability of bone morphogenetic proteins that occurs from demineralization. The manner by which demineralization increases their bioavailability, however, is not known with certainty. It is known that the mineral phase of bone masks the proteins of the organic matrix. Proteins depend on their interaction with water for their three-dimensional conformation, biologic activity, and stability. It is possible that demineralization allows a more complete hydration of bone matrix, changing the local environment and allowing the bone morphogenetic proteins to desorb and form a concentration gradient, signaling the appropriate cell types to begin the process of bone regeneration. Under similar test conditions, it was discovered that hydration of demineralized bone matrix powder produces a strong exotherm on the order of 14 degrees C whereas hydration of bone powder produces a smaller exotherm of about 2 degrees C. The details of the hydration reactions of demineralized bone matrix and bone were investigated by measuring the exotherm produced under varying conditions. The results suggest that bone mineral does mask, or limit, the ability of the organic matrix to interact with water. An understanding of the hydration characteristics of demineralized bone matrix can also help in the development of carrier systems that optimize osteoinductive potential.

Cartilage and bone tissue engineering for reconstructive head and neck surgery

The loss of cartilage and bone because of congential defects, trauma and after tumor resection is a major clinical problem in head and neck surgery. The most prevalent methods of tissue repair are through autologous grafting or using implants. Tissue engineering applies the principles of engineering and life sciences in order to create bioartificial cartilage and bone. Most strategies for cartilage tissue engineering are based on resorbable biomaterials as temporary scaffolds for chondrocytes or precursor cells. Clinical application of tissue-engineered cartilage for reconstructive head and neck surgery as opposed to orthopedic applications has not been well established. While in orthopedic and trauma surgery engineered constructs or autologous chondrocytes are placed in the immunoprivileged region of joints, the subcutaneous transplant site in the head and neck can lead to strong inflammatory reactions and resorption of the bioartificial cartilage. Encapsulation of the engineered cartilage and modulation of the local immune response are potential strategies to overcome these limitations. In bone tissue engineering the combination of osteoconductive matrices, osteoinductive proteins such as bone morphogenetic proteins and osteogenic progenitor cells from the bone marrow or osteoblasts from bone biopsies offer a variety of tools for bone reconstruction in the craniofacial area. The utility of each technique is site dependent. Osteoconductive approaches are limited in that they merely create a favorable environment for bone formation, but do not play an active role in the recruitment of cells to the defect. Delivery of inductive signals from a scaffold can incite cells to migrate into a defect and control the progression of bone formation. Rapid osteoid matrix production in the defect site is best accomplished by using osteoblasts or progenitor cells.

Tissue engineering in otorhinolaryngology

Tissue engineering is a field of research with interdisciplinary cooperation between clinicians, cell biologists, and materials research scientists. Many medical specialties apply tissue engineering techniques for the development of artificial replacement tissue. Stages of development extend from basic research and preclinical studies to clinical application. Despite numerous established tissue replacement methods in otorhinolaryngology, head and neck surgery, tissue engineering techniques opens up new ways for cell and tissue repair in this medical field. Autologous cartilage still remains the gold standard in plastic reconstructive surgery of the nose and external ear. The limited amount of patient cartilage obtainable for reconstructive head and neck surgery have rendered cartilage one of the most important targets for tissue engineering in head and neck surgery. Although successful in vitro generation of bioartificial cartilage is possible today, these transplants are affected by resorption after implantation into the patient. Replacement of bone in the facial or cranial region may be necessary after tumor resections, traumas, inflammations or in cases of malformations. Tissue engineering of bone could combine the advantages of autologous bone grafts with a minimal requirement for second interventions. Three different approaches are currently available for treating bone defects with the aid of tissue engineering: (1) matrix-based therapy, (2) factor-based therapy, and (3) cell-based therapy. All three treatment strategies can be used either alone or in combination for reconstruction or regeneration of bone. The use of respiratory epithelium generated in vitro is mainly indicated in reconstructive surgery of the trachea and larynx. Bioartificial respiratory epithelium could be used for functionalizing tracheal prostheses as well as direct epithelial coverage for scar prophylaxis after laser surgery of shorter stenoses. Before clinical application animal experiments have to prove feasability and safety of the different experimental protocols. All diseases accompanied by permanently reduced salivation are possible treatment targets for tissue engineering. Radiogenic xerostomia after radiotherapy of malignant head and neck tumors is of particular importance here due to the high number of affected patients. The number of new diseases is estimated to be over 500,000 cases worldwide. Causal treatment options for radiation-induced salivary gland damage are not yet available; thus, various study groups are currently investigating whether cell therapy concepts can be developed with tissue engineering methods. Tissue engineering opens up new ways to generate vital and functional transplants. Various basic problems have still to be solved before clinically applying in vitro fabricated tissue. Only a fraction of all somatic organ-specific cell types can be grown in sufficient amounts in vitro. The inadequate in vitro oxygen and nutrition supply is another limiting factor for the fabrication of complex tissues or organ systems. Tissue survival is doubtful after implantation, if its supply is not ensured by a capillary network.

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.

Healing of autogenous intramembranous bone in the presence and absence of homologous demineralized intramembranous bone

This study was designed to examine the osteogenecity of demineralized bone matrix (DBM) prepared from intramembranous (IM) bone and to quantitatively assess the amount of new bone formed by IM autogenous bone grafts with or without DBM(IM). Forty-two defects were created in 42 New Zealand White rabbits. Twenty-one defects were grafted with IM bone alone, and the other 21 defects were grafted with composite IM-DBM(IM). Eleven rabbits, 22 defects were used as controls, where 11 defects were left empty (passive control) and the other 11 defects were filled with rabbit skin collagen (active control). Tissues were retrieved on days 1, 2, 3, 4, 5, 6, 7, and 14 for qualitative and quantitative analysis. Cells involved in the healing of composite IM and IM-DBM(IM) bone grafts were identified. No cartilage cells were detected during the healing of either grafts. Appearance of small blood vessels into the newly formed matrix was seen on day 5 in IM bone grafts and on day 4 in composite IM-DBM(IM) bone graft. Quantitative analysis was performed by means of image analysis on 100 sections of tissues retrieved after 14 days. Approximately 204% more new bone was formed in defects grafted with composite IM-DBM(IM) than in those grafted with IM bone alone (P <.0001). No bone was formed across the defects in either active or passive controls. In conclusion, DBM(IM) significantly increases the osteogenicity of IM bone grafts.

Bone morphogenetic protein excipients: comparative observations on poloxamer

Clinicians await the availability of synthetic bioimplants that will replace the need for autogeneic bone grafts in bone reconstructive surgery. For more than a decade, researchers have evaluated delivery vehicles for the tissue morphogen bone morphogenetic protein. The object of this investigation was to measure induced bone development when bone morphogenetic protein was delivered by human tendon collagen, human demineralized bone matrix, hydroxyapatite, a composite of human tendon collagen and human demineralized bone matrix (tendon collagen + demineralized bone matrix), Poloxamer 407, and a composite of human demineralized bone matrix and Poloxamer 407. Sixty-three adult male Swiss Webster mice (Harlan Sprague-Dawley, Indianapolis, Ind.) received 126 implants. The animals were divided into seven groups of nine animals, depending on carrier (six carriers plus the positive control group) used. Each animal received a bone morphogenetic protein-enhanced carrier in one hindquarter muscle mass, with the contralateral leg being implanted with the carrier alone. Implants were evaluated by quantitative radiomorphometry validated by histologic methods. Radiographically, no significant differences were identified among any of the implants evaluated (p > 0.05). Histomorphometric analysis demonstrated that Poloxamer 407 was significantly (p < 0.05) better at delivering bone morphogenetic protein than the other carriers involved in this investigation. The new bone developed in a tubular or spherical shape. Interaction of endogenous and exogenous delivery systems seems to be essential for optimal transmission of bone morphogenetic protein. The importance of the excipient to deliver bone morphogenetic protein and develop a bone morphogenetic protein concentration gradient has been emphasized by other investigators and confirmed by our research on poloxamer. With further research on the physicochemical mechanisms of localization and transmission of bone morphogenetic protein, it may be possible to avoid hazardous operations with autogeneic bone.

Osteogenic protein versus autologous interbody arthrodesis in the sheep thoracic spine. A comparative endoscopic study using the Bagby and Kuslich interbody fusion device

STUDY DESIGN

Using an in vivo interbody arthrodesis model, the efficacy of the Bagby and Kuslich (BAK) device packed with recombinant human osteogenic protein-1 (rhOP-1) was evaluated.

OBJECTIVES

To compare the efficacy of osteogenic protein with that of autograft for interbody arthrodesis, with fusion success based on biomechanical, histologic, and radiographic analyses.

SUMMARY OF BACKGROUND DATA

The use of recombinant human bone morphogenetic proteins (rhBMPs) as osteoinductive bone graft substitutes or expanders has recently gained considerable research interest, particularly when applied in posterolateral arthrodesis. However, whether these results can be extrapolated to a successful interbody spinal arthrodesis remains uncertain.

METHODS

Twelve sheep underwent a multilevel thoracic spinal decompression by thoracoscopic approach. Three noncontiguous destabilization sites (T5-T6, T7-T8, T9-T10) were prepared and randomly treated as follows. Control group treatments were nonsurgical, destabilization alone, and empty BAK. Experimental groups were treated with autograft alone, BAK device packed with autograft, or BAK device packed with rhOP-1. Four months after surgery, interbody fusion status was quantified by biomechanical testing, computed tomography, microradiography, and histomorphometry.

RESULTS

Results of biomechanical analysis showed statistically higher segmental stiffness levels when comparing the control and experimental groups with four of the five testing methods (P < 0.05). Computed tomography and microradiography characterized destabilization alone as producing one fusion in six preparations; the empty BAK, two in six;, autograft alone, four in eight; BAK with autograft, five in eight; and BAK with rhOP-1 group, six in eight-all evidenced by woven trabecular bone spanning the fusion sites. Histomorphometry yielded significantly more trabecular bone formation at the fusion sites in the three experimental groups than in the two control groups (P < 0.05).

CONCLUSIONS

Interbody spinal fusions showing biomechanical and histomorphometric equivalency to autologous fusions have been achieved with rhOP-1. The functional unit stability and histologic osteointegration evidenced by the BAK/rhOP-1 complex shows this interbody arthrodesis technique to be a viable alternative toconventional autologous iliac crest, thereby obviating the need for an iliac crest donor site and associated patient morbidity.

Bone morphogenetic protein induced repair of compartmentalized segmental diaphyseal defects

In adult rabbits, mid-diaphyseal segments of the radius or ulna were excised to produce defects greater than the critical size for spontaneous bone repair. The defects were enveloped in sleeves composed of nonbiodegradable expanded polyfluoroethylene (ePTFE), pore size 30, 60, 90 microns, and compared with sleeves of three biodegradable materials. Bone morphogenetic protein and associated noncollagenous bone matrix protein (BMP/NCP) or recombinant human morphogenetic protein (rhBMP-2) were implanted inside the sleeves. Albumin was implanted for a control system. Without intracompartmental BMP, only about 10%-15% of the defect was repaired by bone growth extending from the bone ends into the sleeves composed of ePTFE, pore size 30 microns. With sleeves with pore size 60 or 90 microns and intracompartmental BMP/NCP, 54%-96% regeneration occurred within 8 weeks after the operation. Sleeves of biodegradable nonimmunogenic materials such as polyorthoester (POE) and polylactic-polyglycollic acids (PLA/PGA) permitted 86%-98% restoration of bone continuity, but only when BMP was present in the lumen. With puncture holes (0.5 mm in diameter), implants of BMP/NCP in the 30-micron PTFE sleeve produced transmembrane external callus formation and bone regeneration to 147%. Sleeves composed of aorta first calcified, then induced complete intracompartmental bone regeneration. Atelocollagen sleeves incited a low-grade inflammatory cell reaction and did not promote complete regeneration. Under conditions presently undisclosed segments of the ulna bridged with ePTFE, were incompletely paired, even with intracompartmental BMP/NCP. Puncture holes of 0.5 mm admitted ingrowth of capillaries and introduced local conditions favorable for the response to BMP/NCP. BMP/NCP may promote proliferation of nutrient vessels and differentiation of bone marrow stroma cells between the open bone ends. For further investigation, the hypothesis to be examined is that the optimum response to BMP/NCP and rhBMP-2 would emerge in compartments containing first a high concentration gradient and second proliferating perivascular cells.

Endogenous bone morphogenetic protein expression in transplants of urinary bladder

Bone morphogenetic proteins (BMP) were identified in full-thickness autogeneic implants of the urinary bladder by monoclonal antibody BMP immunohistochemistry and by in situ hybridization of BMP-2, -4, and -5 mRNAs. Within the first week after transplantation, BMP mRNAs were expressed in uroepithelial cytoplasm and basement membranes of proliferating cells. About the second week, BMP-2, -4, and -5 mRNA expression and monoclonal antibody BMP-2 synthesis were colocalized in the sites of conversion of transitional to columnar epithelium. In close association with basement membrane, mesenchymal-type cells migrated, proliferated, and formed osteogenetic condensations. The areas of condensation were composed of densely packed cells with high nucleocytoplasmic ratios and high mitotic activity, and resembled periosteum of growing membrane bone. For the first 3 to 4 weeks, the bone deposits grew rapidly in size on surfaces of columnar uroepithelial basement membrane. After 4 to 5 weeks, the growth was constrained by enclosure in a thick, dense, periosteum-like fibrous tissue, completely separated from basement membrane. Serial observations are submitted herewith as circumstantial evidence that bone development is a product of mutual interaction of uroepithelium and mesenchymal-type cells across basement membranes in response to endogenous BMP-2, -4, and -5. Neither BMP-2, -4, -5 mRNA nor monoclonal antibody BMP-2 was detected in the lamina propria, smooth muscle, or fibrous tissue.

Bone morphogenetic proteins: background and implications for oral reconstruction. A review

For over 30 years now, research has been carried out to isolate and purify bone morphogenetic protein (BMP), a substance which has been shown to induce heterotopic bone formation in various animal species. Recent advances in the fields of developmental biology, molecular biology, genetics and wound healing, have shown that the BMPs are not only responsible for postfetal bone induction (including normal bone remodeling, healing and repair), but are also critical during embryogenesis, not only in regards to the skeletal system, but quite possibly in the morphogenesis and pattern formation of other tissues and organs as well. Therefore, BMPs have the potential as a therapeutic utility in orthopedic and dento-alveolar reconstruction.

[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.

Osteoinductive potential of freeze-dried, biodegradable, poly (glycolic acid-co-lactic acid) disks incorporated with bone morphogenetic protein in skull defects of rats

Biodegradable, porous, polymer implant disks with an osteoinductive potential were prepared by a freeze-drying technique by incorporating bovine bone morphogenetic protein (BMP) in poly (glycolic acid-co-lactic acid) (PGLA). The PGLA disks with and without BMP were implanted in rat skull defects, and the defect sites were studied radiographically and histologically for 2 and 4 weeks after implantation. A quantitative radiographic analysis showed significantly thicker radiopacity for the disks with BMP than those without BMP (P < 0.01). After 2 weeks, chondrogenesis and new bone formation were observed on the BMP-incorporated disks. After 4 weeks, PGLA was completely replaced by new bone in the defects with implantation of the BMP-incorporated disks, whereas the defects implanted with PGLA alone were filled with fibrous connective tissue. The results suggest that BMP-incorporated PGLA is an ideal bone substitute with osteoinductive potential.

Integration of endochondral bone grafts in the presence of demineralized bone matrix

The use of endochondral bone grafts (EC) and demineralized bone matrix (DBM), which contains a potent osteoinductive matrix, may promote the repair of nonregenerative defects. The purpose of the current work is to assess qualitatively and quantitatively the effect of DBM on the healing of EC bone grafts and to compare it to the healing of EC bone grafts alone. Twenty-four defects in rabbit skulls were filled with EC bone grafts alone, DBM alone, or combined EC and DBM. Histologic and immunohistologic changes were examined in 2 weeks. The amount of new bone formation was quantified by image analysis. Healing of all the groups was characterized by the presence of a cartilage intermediate stage. In the EC bone grafts alone, healing was localized to the host bone/graft interface. In the composite group, amalgamation of the new bone, DBM, and bone graft progressed throughout the whole width and depth of the defect, uniting the graft to the recipient bed. The amount of new bone formed was significantly greater (47%) in the composite group than the EC group. In conclusion, DBM powder augments the bone-induction capacity of the recipient bed as well as the bone graft. The composite EC bone grafts and added DBM possess properties required for an effective graft material and merit further clinical evaluation.

Effect of freeze-dried poly-L-lactic acid discs mixed with bone morphogenetic protein on the healing of rat skull defects

Porous poly-L-lactic-acid discs were prepared by a freeze-drying method (FDPLLA). During preparation of the discs, semipurified bone morphogenetic protein (BMP) was mixed with the poly-L-lactic acid (500 micrograms BMP per disc). The discs were implanted in the skull defects of rats and retrieved after 2 or 4 weeks. With the FDPLLA/BMP discs, new bone formation was observed at 2 weeks after implantation. On the other hand, plain FDPLLA discs failed to produce new bone formation even at 4 weeks after implantation. Calcium content of the retrieved FDPLLA/BMP discs was statistically higher than that of plain FDPLLA discs. These results suggest that FDPLLA may be an effective delivery system for BMP and that the FDPLLA/BMP disc may potentially have usefulness as a bone graft substitute.

Osteoinductive, morphologic, and biomechanical properties of autolyzed, antigen-extracted, allogeneic human bone

Autolyzed, antigen-extracted, allogeneic (AAA) bone was prepared from human cortical bone and its morphologic, biomechanical, and osteoinductive properties were compared with untreated (frozen) as well as lyophilized human bone. Scanning electron microscopy revealed removal of inorganic calcium phosphates and persistence of shrunken collagen fibrils on the surface of AAA bone matrix. Biomechanical testing of differently prepared bone samples showed that lyophilization increased both the modulus of elasticity (P < .00001) and the compressive strength (P < .00001). Depending on the depth of decalcification in the preparation of AAA bone, both measured values decreased in rehydrated AAA bone compared with untreated bone (P < .00001). Completely demineralized and rehydrated AAA bone was soft, flexible, and showed very little compressive strength. Differences in biomechanical behavior between samples drilled longitudinally or perpendicularly to the diaphyseal bone axis were observed. Xenogeneic human bone samples were implanted in muscle pouches of Sprague-Dawley rats for 6 weeks. AAA bone implants showed chondrogenesis and osteogenesis in 50% of the cases, while untreated or lyophilized bone implants induced no new cartilage or bone formation. As decalcification exposed xenogeneic organic matrix components, AAA bone implants provoked the highest inflammatory reaction. When AAA bone samples were implanted in immunosuppressed rats, the inflammatory reaction was suppressed and 94% of the implants showed endochondral bone formation. The chondroinductivity of the bone samples also was tested in vitro using neonatal rat muscle tissue to avoid interference with inflammatory cells and secreted cytokines. In this assay, 68% of AAA bone samples induced chondroneogenesis, while untreated as well as lyophilized bone samples failed to induce any cartilage formation. The results clearly demonstrate that AAA bone has osteoinductive properties. Biomechanical stability of AAA bone implants depends on the degree of demineralization. Thus, they can be prepared in an appropriate manner for different indications in oral and maxillofacial surgery.

Bone induction by demineralized bone particles: long-term observations of the implant-connective tissue interface

Allogeneic demineralized bone (DB) powder was applied to subcutaneous pockets and cranial defects of rats and histological, histomorphometrical, and radiological evaluation was performed one to 52 weeks after implantation. In both type of implants cartilage formation was observed after 1 week between DB particles and in former vascular channels and cervices within the particles. Foci of bone formation were observed after 2 weeks in the center of the implant. Remineralization of DB particles only occurred in close contact with the new bone tissue by which they became incorporated, indicating that remineralization of DB is a continuation of a process which has started in live bone. At all times, the interface between implant and connective tissue of the host consisted of a layer of non-remineralized DB particles embedded in fibrous connective tissue. This rim was thinner at the dura-mater-side in the cranial implants, compared with the skin-side of the same implants as well as all sides of the subcutaneous implants. The rim became thinner with time but never disappeared completely. The outer contour of the mineralized implant sometimes ran right through a DB particle. A critical concentration of bone-inducing agent leaking from DB particles seems to be necessary for bone induction. We suggest that at the interface of the implant and loose connective tissue this concentration is never reached, which results in maintenance of the rim.

Ectopic induction of cartilage and bone by water-soluble proteins from bovine bone using a polyanhydride delivery vehicle

Controlled release delivery vehicles for water-soluble osteogenic proteins from demineralized bovine bone matrix were constructed using polyanhydride polymers. The water-soluble proteins were isolated from a 4 M guanidine hydrochloride extract of bone matrix. The water-soluble proteins possessed Chondrogenic Stimulating Activity (CSA) when tested in stage 24 chick limb bud cell cultures, but were incapable of inducing cartilage or bone in vivo when implanted intramuscularly into mice by themselves. The polyanhydride polymers alone were also incapable of inducing ectopic cartilage or bone. However, when the water-soluble proteins were incorporated into the polymeric delivery vehicle, the combination was capable of inducing cartilage and bone up to 50% of the time. These results demonstrate that it is possible to use polyanhydride polymers as controlled-release delivery vehicles for soluble bioactive factors that interact with a local cell population.

Bone transplantation

According to one principle of surgery, the transplantation of vital tissue is the best method of reconstructing a defect. Because of absent immunologic reactions, high osteogenic potency, and preserved stability, transplantation of autogenous bone shows the best results. Necrosis of transplanted bone, leading inevitably to absorption and remodeling of the graft, can be avoided if microsurgically vascularized autogenous bone segments are transferred. Disadvantages are the low availability and the necessity of additional operations. As an alternative, deep-frozen allogeneic bone is used. However, this kind of bone shows delayed incorporation based on cellular and humoral immune reactions, and it is also installed into the host bed after overcoming the immune barrier. The risk of microbiological contamination or transmission of unrecognized germs such as HIV is a cause of great expense in bone banking techniques. If one succeeds in reducing (a) the immunologic defense reaction and (b) the risk of infection by sterilization or disinfection without damaging the osteoinductive proteins of bone matrix, the rate of complications can be lowered. Demineralized bone matrix can be used if biomechanical stability is not required. Its ability to induce osteogenesis without a major immune reaction or the risk of transmitting diseases justifies its clinical application. Further intensive research in these areas is unavoidable.

In vivo analysis of the half-life of the osteoinductive potential of demineralized bone matrix using diffusion chambers

Subcutaneous implantation of demineralized bone matrix (DBM) from rat initiates a sequence of developmental events that results in endochondral bone formation. This investigation examined the modification of the osteoinductive potential of DBM during the initial stages of this developmental cascade. Diffusion chambers (DC), constructed with filters of known pore size, permitting or excluding cells from entering the chambers, and containing DBM were subcutaneously implanted into Long-Evans male rats for specific time periods (1-7 days). DC were recovered and the osteoinductive potential of the matrix from these chambers was then tested by subcutaneous implantation and assaying the resulting day 11 plaque tissue enzymatically for alkaline phosphatase activity, and histologically for evidence of chondrogenesis and osteogenesis. The possible modification of DBM by local systemic factors (enzymatic degradation) or contact by polymorphonuclear leukocytes (PMNs) was also investigated. We have concluded from this study that the osteoinductive potential of DBM has a half-life of 5-7 days following implantation and although the enzymes collagenase, elastase, and trypsin abolished this activity, pepsin significantly enhanced it. Culture of PMNs with matrix prior to its implantation appeared to have little effect. Furthermore, during the initial stages of matrix-induced endochondral bone formation, DBM serves as both the instructive inducer and permissive substratum required in this process.

Ectopic induction of cartilage and bone by water-soluble proteins from bovine bone using a collagenous delivery vehicle

A controlled-release delivery vehicle for water-soluble osteogenic proteins from demineralized bone matrix was constructed using purified type I collagen. The water-soluble proteins were isolated from a 4 M GdnHCl extract of bone matrix. Although the water-soluble proteins were capable of inducing cartilage formation in vitro, they were incapable of inducing cartilage or bone in vivo when implanted intramuscularly into mice in the absence of an appropriate delivery vehicle. The collagen-based delivery vehicle alone was also incapable of inducing osteogenesis in vivo. However, when the water-soluble proteins were incorporated into the delivery vehicle, the combination was capable of inducing cartilage and bone 76% of the time. These results demonstrate that it is possible to formulate a controlled-release delivery vehicles for soluble bioactive factors which upon release interact with local responsive cells.

Osteoinduction by implants of demineralized allogeneic bone matrix is diminished in vitamin D-deficient rats

Experimental heterotopic bone formation was produced by subcutaneous implants of demineralized allogeneic bone matrix (DABM) in vitamin D-deficient (-D) animals that were either not treated or given vitamin D3 (+D) or 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) to determine the role of vitamin D and its most active metabolite in osteoinduction and implant remodeling. Histologically, implants in both +D and -D groups caused a similar acute inflammatory response, formation of a fibrous capsule, and chondrogenesis by 1 to 2 weeks after implantation. However, by 3 weeks after implantation implants in the -D animals had formed less bone matrix, had developed a defect in matrix mineralization, had reduced bone forming and bone resorbing surfaces, and had altered bone architecture resulting from defective bone remodeling. The altered histology in -D animals was not corrected by 10 weeks after implantation. Treatment of vitamin D-deficient rats with 1,25(OH)2D3, 65 pmol/day for 3 weeks, corrected both the defect in mineralization and the abnormal histology. The results indicate that (1) vitamin D deficiency does not alter either the timing or the sequence of histologic events associated with osteoinduction but dramatically reduces the magnitude of the response, (2) vitamin D deficiency not only impairs mineralization but also reduces bone formation and resorption, and (3) 1,25(OH)2D3 mimics all of the actions of vitamin D with regard to correcting the abnormal osteoinductive response and bone histomorphometry.

Regeneration of an enchondroma defect under the influence of an implant of human bone morphogenetic protein

A 29-year-old woman with an enchondroma that was expanding and eroding the palmar cortex of the middle phalanx was successfully treated by curettage and implantation of bone morphogenetic protein. The metaphysis and cortex were repaired by lamellar bone within 2 months. The medulla was completely filled with trabecular bone by 9 months. The full range of motion and normal functions of finger and hand joints were restored, and there was no recurrence or abnormalities at follow-up visits 2 1/2 years after the operation.

Influence of 1 alpha-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 on experimentally induced heterotopic ossification in rats

We report the effects of 1 alpha-OH-D3 and 24,25(OH)2D3, either alone or combined, on new bone formation induced by demineralized cortical bone matrix transplanted extraskeletally to the abdominal muscle wall in rats. 1 alpha-OH-D3 was administered orally in dosages of 0.1 microgram, 24,25(OH)2D3 in dosages of 0.2 micrograms, and, in the combined procedure, in the same dosages as mentioned above per day and rat. The amount of induced new bone in respect of organic matter, mineral content and 45Ca activity increased in all treatment groups, compared with controls. The differences between the groups treated separately with 1 alpha-OH-D3 or 24,25(OH)2D3 were insignificant. The differences in the combined treatment group were not so profound, but differed considerably compared with controls. However, 1 alpha-OH-D3 showed more prominent effects on the mineralization of implanted grafts, while 24,25(OH)2D3 especially promoted the production of organic material of the newly formed bone.

Traumatic myositis ossificans in the masseter muscle

Traumatic myositis ossificans in the left masseter muscle of a 25-year-old man is described. The lesion, which extended intramuscularly from the lateral surface of the zygomatic bone to the mandibular angle, was resected by an intraoral approach. The specimen was composed of mature cortical bone in the outer portion and spongy bone, including degenerated muscle fibers and marrow spaces, in the inner portion. At the lower end of the specimen was a sequence of bone formation involving fibrous connective tissue, cartilage, woven bone, and mature lamellar bone with many osteoblasts. Clinicopathologic features of 26 reported cases of traumatic myositis ossificans of the maxillofacial region are reviewed, and the pathogenesis of the disease is discussed.

Connective tissue regeneration to periodontally diseased roots, planed and conditioned with citric acid and implanted into the oral mucosa

This investigation used autogenous submucosal implants of root sections to study the connective tissue healing to periodontally diseased roots which had previously been planed and demineralized with citric acid. Eighteen implants were performed, with each being removed 2 to 24 weeks after implantation. The results showed new connective tissue attachment to the old cementum and to the dentin. After 18 weeks, in all specimens new cementum had formed on the dentin, with collagen fibers attached to it. No deposition of new cementum on the old cementum was noted. The formation of new cementum on roots placed in an environment without periodontal ligament cells might be ascribed to the inductive principle of demineralized dentin. The results suggest that a diseased root which has been planed and conditioned with citric acid is likely to form a new connective tissue attachment, even if it is placed in an environment without periodontal ligament cells. They also suggest that the factor inhibiting potential new connective tissue attachment is the condition of the root surface, rather than the lack of an adjacent progenitor cell population.

Effect of interferon on heterotopic new bone formation in mice

To study the effect of interferon (IFN) on bone induction and new bone formation, heterotopic bone was induced by implanting pieces of demineralized bone matrix in soft tissue of mice. Mouse IFN was given as daily subcutaneous injections of 2 X 10(5) IU/mouse. Treatment was started one week before bone matrix implantation and continued until sacrifice. As a measure of chondrogenesis in the implants short-term incorporation of 35sulphur administered 11 days after implantation was measured. The amount of mineralized tissue formed in connection with the implant was estimated by 45calcium incorporation 20 days after implantation. There was no indication of a negative effect of IFN on bone induction, new bone formation, or metabolism of orthotopic bone. This is in agreement with our findings in the clinical use of IFN after reconstructive surgery in osteosarcoma.

Histological investigation of bone induction by demineralized allogeneic bone matrix: a natural biomaterial for osseous reconstruction

The objective of the study was to delineate the histological sequence of events associated with bone formation induced in extraosseous sites by implants of demineralized allogeneic bone matrix (DABM) in order to provide a more complete basis for the clinical use of the natural biomaterial for osseous reconstruction. The rat was the experimental animal model. Implants were prepared by demineralization of diaphyseal cortical rat bone in 0.6N HCl for 18-24 h. A total of 104 specimens, 4 mm square, were implanted both subcutaneously and intramuscularly in 26 rats for periods of 3 days to 22 weeks. Histological evaluation revealed a sequence of events that at 3 days displayed an inflammatory response to surgical trauma and after 6 weeks exhibited the formation of a mature lamellar ossicle with central marrow which was maintained through 22 weeks. Resorption of the DABM, first evident at 1 week, was accompanied by the appearance of chondroblast in vascular canals and in crevices in the implant. Osteoblastic activity, initially seen at 2 weeks, appeared to be associated with capillary and blood vessel formation around the implant and within enlarged resorptive cavities within the specimens. Calcification occurred in the cartilaginous matrix and osteoid and within the implanted matrix. The osteoinductive process comprises (1) the inflammation/granulation/scar formation processes elicited by implantation of a material, (2) the resorptive response elicited by DABM, and (3) the process of induction of nonosseous mesenchymal cells to differentiate to chondroblasts and osteoblasts. The results of the present study support previous investigations demonstrating the bone-inducing property of DABM and provide further evidence for the potential value of this natural biomaterial for use in osseous reconstruction.

Reconstruction of osseous defects with freeze-dried allogeneic and autogenous bone. Clinical and histologic assessment

Freeze-dried allogeneic bone combined with autogenous particulate cancellous bone and marrow was used for reconstruction in 56 patients. With the exception of 3 patients who had infection postoperatively, the patients had complete acceptance of the composite graft system. Histologic examination at 2, 3, 12, 18, and 24 months demonstrated early incorporation, revascularization, resorption of the freeze-dried component, and formation of a bone ossicle that continued to remodel and form mature lamellar bone. This study suggests that freeze-dried allogeneic bone can serve as a latticework along which osteocompetent cells can proliferate, that composite grafts are readily accepted and will form a satisfactory and predictable bone ossicle over a considerable defect, and that freeze-dried allogeneic bone induces the host mesenchymal cells to differentiate into mature osteoblasts and aids in the formation of a long-lasting functional bone graft.

Osteoinduction within porous polysulfone implants at extraosseous sites using demineralized allogeneic bone matrix

The objective of this study was to determine if bone induction could occur in implants of porous polysulfone (PPSF) impregnated with particles of demineralized allogeneic bone matrix (DABM). DABM-PPSF composites were fabricated by inserting DABM particles into PPSF specimens. The porous implants were produced by sintering polysulfone particles (850-1180 micron in diameter). DABM particles were prepared by demineralizing rat cortical bone in 0.6N HCl at 4 degrees C for 18-24 h. A composite DABM-PPSF specimen and three "controls" were implanted subcutaneously at abdominal sites in 30 adult Sprague-Dawley rats. The three controls were whole DABM (4 X 4 X 1 mm), particulate DABM (1 X 1 X 1 mm), and porous polysulfone (5 X 5 X 1 mm). Microradiographic and histological evaluation of DABM-PPSF composites revealed chondrogenesis within the pores of the specimens at 10 days, followed by ossification and fatty marrow production at 21 and 43 days. This histological sequence was similar to that seen with DABM controls. The tissue response to porous polysulfone did not prevent the osteoinductive process. These results suggest that an osteoinductive material such as DABM may be useful in augmenting the implantation of porous implants at osseous sites in which the potential for bone regeneration is limited.

Bone cell differentiation and growth factors

Bone morphogenetic protein and bone-derived growth factors are biochemical tools for research on induced cell differentiation and local mechanisms controlling cell proliferation. Bone morphogenetic protein irreversibly induces differentiation of perivascular mesenchymal-type cells into osteoprogenitor cells. Bone-derived growth factors are secreted by and for osteoprogenitor cells and stimulate DNA synthesis. Bone generation and regeneration are attributable to the co-efficiency of bone morphogenetic protein and bone-derived growth factors.

Healing following implantation of healthy roots, with and without periodontal ligament tissue, in the oral mucosa

This investigation, involving 44 patients, studied the physiological interactions of human dentine and cementum with the connective tissue of the oral mucosa by means of 26 autogenous implants of root fragments without periodontal ligament, and 18 implants with periodontal ligament. The implants together with the adjacent tissues were removed between the 3rd and 26th week after implantation. The implants without periodontal ligament failed to form cementum or bone-like tissue and in the 26th week they still showed resorption. Ten implants with periodontal ligament showed deposition of cementum with collagen fibers attached to it after the 12th week. The formation of new attachment with new cementum deposition on the dentine or on the old cementum could be ascribed to the influence of cells of the remaining periodontal ligament on the implanted root fragments.

The reaction of the dura to bone morphogenetic protein (BMP) in repair of skull defects

Trephine defects in the adult rat skull 0.8 cm in diameter, which do not spontaneously heal, were filled with a bovine bone morphogenetic protein (BMP) fraction. The defects healed not only by bony ingrowth from the trephine rim, but also by proliferation of pervascular mesenchymal-type cells (pericytes) of the dura mater. Under the influence of BMP, dural pericytes differentiated into chondroid and woven bone. Between three and four weeks postimplantation, sinusoids formed and the woven bone remodelled into lamellar bone. Concurrently, blood-borne bone marrow cells colonized the bone deposits, and the diploe were restored. Demonstrating that it is soluble in interstitial fluid, and diffusible across a nucleopore membrane (which isolated the bony margins of the skull), BMP induced new bone formation in the underlying dura and complete repair of the defect. The response of the dura to the BMP fraction produced more new bone than the response to allogeneic bone matrix. The BMP-induced repair was dose dependent; the quantity of new bone was proportional to the dose of the implanted BMP.

Dentin matrix gelatin (DMG) as a possible "universal" grafting material in periodontics

The ideal of periodontal surgery is the total regeneration of the lost periodontal complex. A promising new osseous grafting material is Dental Matrix Gelation (DMG). DMG was prepared by a method similar to that of Conover and Urist (1979). This consisted of sequential extraction in 1:1 chloroform-methanol, 25 degrees C for 1 hour; 0.6 N HCl, 2 degrees C for 24 hours with constant agitation; 2 M CaCl2, 2 degrees C for 1 hour; 0.5 M EDTA pH 7.4, 2 degrees C for 1 hour; washed in distilled water 1 hour. Twelve rats were anesthetized, had heads shaved, midline flaps reflected, and 2 mm holes drilled through the right and left parietal bones. This type of osseous defect normally heals only by fibrous scarring and has been used to define osteoinductive materials. The DMG was cut into pieces about 1 mm square and placed into the right side defect while the left side remained open as a control. The animals were sacrificed on a schedule of two rats every 2 weeks until the 10th week when four rats were killed. The results showed complete osseous closure of the DMG site while the control healed by fibrous scarring. DMG seems to have strong osteoinductive power, and used allogenically has great potential as a commercially viable implant material.

Osteogenesis and leukopoiesis within diffusion-chamber implants of isolated bone marrow subpopulations

The developmental potential of isolated rabbit bone marrow cell populations was examined following autogeneous implantation into diffusion chambers. After 4 weeks, the implants were harvested and processed for light and electron microscopy. More total tissue was formed in abdominally implanted chambers than in corresponding femoral chambers. Two of the separated marrow cell populations produced significantly greater amounts of fibrous connective tissue, cartilage, and bone than did whole-marrow controls. These two populations, which were defined by density gradients of 1.050-1.055 gm/cm3 and 1.064-1.067 gm/cm3, consistently produced a fibrous connective tissue nodule in which were found dispersed foci of hyaline cartilage and woven bone. The denser population was distinguished further by the presence of leukopoietic foci in several of the implant chambers. Cartilage foci were found predominantly towards the center of the tissue nodules, whereas bone was dominant towards the periphery. Blood vessels, osteoclasts, bone remodeling, and mature lamellar bone were found only in those chambers which had been penetrated by the host's vascular system. The results indicate that 1) normal marrow tissue contains two separate osteoprogenitor cell populations; 2) these two progenitor populations represent separate osteogenic and chondrogenic capabilities; 3) one of these populations possesses a leukopoietic as well as an osteogenic potential; and 4) a competent vascular system is essential for the remodelling of bone into mature bone organs.