Calcified microspheres as biological entities and their isolation from bone

Calcified microspheres, about 1 microm in diameter, appear at sites of bone formation where they invest the collagenous matrix, become confluent and disappear. Evidence that the particle boundaries are not lost with compaction but merely deformed is supported in section by the granular histochemical staining of the inorganic phase for bone salt, lipid, fibronectin and acid phosphatase in osteomalacic, acid-etched and normal human bone. Their persistence as discrete objects is confirmed by the application of methods for their isolation from the collagenous matrix of immature mouse calvarium and mature bovine femur. Five methods have been used to extract them and include (i) biochemical, (ii) chemical, (iii) mechanical, (iv) pyrogenous and (v) biological separation. Under the optical microscope, all isolates consisted of similar discrete objects and bridged assemblies, whose birefringence varied with treatment. After decalcification, their organic 'ghosts' remained. Each isolated microsphere had a complex substructure of clusters of non-collagenous calcified filaments surrounding a less dense centre. The filaments were 5 nm in diameter with a 5 nm periodicity and regular fine interfilamentous connections. It is concluded that the microspheres are independent, complex, pervasive and central to the containment (i.e. packaging) of calcium phosphate in bone. Their extraction will enable further analysis.

Demineralized bone implants for nonunion fractures, bone cysts, and fibrous lesions

Demineralized bone implants were used to treat eight patients with fracture nonunion, five patients with bone cysts, and eight patients with fibrous lesions. Five of the eight patients with nonunions had had previous unsuccessful attempts at reconstruction. After fixation and implantation with either human or bovine demineralized bone, all eight fractures healed. For those patients with nonunion fractures, mean followup time was 8 years, 5 months, and longest followup was 15 years, 3 months. The cystic lesions in five patients included three typical aneurysmal bone cysts and two recurrent unicameral bone cysts. The aneurysmal bone cysts had excellent healing and bone remodeling. The two unicameral bone cysts were repacked more densely after 1 year and healed. For these patients with bone cysts, the mean followup time was 12 years, 5 months, and longest followup was 15 years, 1 month. The various fibrous lesions in seven of the eight patients were healed within 6 months, with only one requiring repacking. For these patients with fibrous bone lesions, the mean followup time was 9 years, 8 months, and longest followup was 14 years. A biopsy of the lesions in five patients was performed and in two cases showed osteoblasts and new bone around small particles of the implants. These results with long term followup show that allogeneic or xenogeneic demineralized bone implants offer a reasonable alternative for the treatment of typical nonunion fractures, bone cysts, and fibrous lesions of bone.

Xenogeneic ossicular implants: an experimental study of heterotopic, demineralized, lyophilized, porcine implants in the guinea-pig

This study was done to compare the outcome of porcine ossicular implants in the middle ear and the subcutaneous dorsal region of the guinea-pig to those of allo-implants implanted in parallel in the dorsal region. The implants were heteropic, xenogeneic, demineralized (HCl), lyophilized and sterilized. The evaluation was histological (light microscopy and scanning electron microscopy) and immunological (immunofluorescence staining). Fifty-four guinea-pigs were implanted in the middle ear and 14 of them were also implanted subcutaneously in the dorsal region with xeno-implants and allo-implants. The middle ear implants were found to be constantly reossified and coated with normal mucosa with only a minimal immune reaction. In contrast, the dorsal xeno-implants were found to be the target of mononucleic infiltration, fibrous encapsulation and an influx of immunoglobulins resulting in segregation. The corresponding allo-implants were found to be partially reoccupied and reossified. These findings highlight the value of HCl demineralization in the induction of non-species-specific Bone Morphogenetic Protein and the failure of attempts at immuno-despecification. It appears that the fate of the implant depends less on its antigenic load than on the site of implantation. In this regard the middle ear is apparently very advantageous. The very good short-term tolerance and recovery observed in the middle ear xeno-implant suggest that these implants offer sufficiently good results to warrant clinical testing.

New formulations of demineralized bone matrix as a more effective graft alternative in experimental posterolateral lumbar spine arthrodesis

STUDY DESIGN

A rabbit model of posterolateral intertransverse process spine arthrodesis was used.

OBJECTIVE

To determine the efficacy of two new formulations of demineralized bone matrix.

SUMMARY OF BACKGROUND DATA

The flowable gel form of Grafton (Osteotech, Eatontown, NJ) demineralized bone matrix has been shown to have osteoinductive properties in various models and currently is used clinically as bone graft material in posterolateral lumbar spine arthrodesis. Two new formulations of Grafton, one made of flexible sheets (Flex) and the other made in a malleable consistency (Putty), have improved handling characteristics compared with the gel form.

METHODS

In this study, 108 New Zealand white rabbits underwent bilateral posterolateral intertransverse spine arthrodesis at L5-L6 using autogenous iliac crest bone graft alone (control), one of the new forms of demineralized bone matrix (DBM; made from rabbit bone) alone or in combination with autogenous iliac crest bone. Rabbits were killed 6 weeks after surgery. The lumbar spines were excised, and fusion success or failure was determined by manual palpation and radiography. Specimens also were processed for undecalcified histologic analysis.

RESULTS

Manual palpation of the harvested lumbar spines revealed that the fusion rates of the Flex-DBM/Auto group (9/9, 100%) and Putty-DBM/Auto group (10/10, 100%) were superior (P < 0.01) to those of the Auto/control group (3/9, 33%). As a stand-alone graft substitute, Flex-DBM performed superiorly with a fusion rate of 11/11 (100%) compared with that of Putty-DBM (10/12, 83%) and Gel-DBM (7/12, 58%). The devitalized version of Flex-DBM had a fusion rate of 4/11 (36%), which was comparable with the devitalized Putty-DBM rate of 4/12 (33%). Both were superior (P < 0.05) to the devitalized Gel-DBM rate of 0/12 (0%). More mature fusions with greater amounts of trabecular bone were present radiographically and histologically in rabbits that received all forms of demineralized bone matrix than in those in which autograft was used.

CONCLUSIONS

The new flexible sheet and malleable putty forms of demineralized bone matrix were effective as graft extender and graft enhancer in a model of posterolateral lumbar spine fusion. These newer formulations of Grafton appear to have a greater capacity to form bone than the gel form or autogenous bone graft alone in this model.

Results from demineralized bone creep tests suggest that collagen is responsible for the creep behavior of bone

Cortical and trabecular bone have similar creep behaviors that have been described by power-law relationships, with increases in temperature resulting in faster creep damage accumulation according to the usual Arrhenius (damage rate approximately exp (-Temp.-1)) relationship. In an attempt to determine the phase (collagen or hydroxyapatite) responsible for these similar creep behaviors, we investigated the creep behavior of demineralized cortical bone, recognizing that the organic (i.e., demineralized) matrix of both cortical and trabecular bone is composed primarily of type I collagen. We prepared waisted specimens of bovine cortical bone and demineralized them according to an established protocol. Creep tests were conducted on 18 specimens at various normalized stresses sigma/E0 and temperatures using a noninvasive optical technique to measure strain. Denaturation tests were also conducted to investigate the effect of temperature on the structure of demineralized bone. The creep behavior was characterized by the three classical stages of decreasing, constant, and increasing creep rates at all applied normalized stresses and temperatures. Strong (r2 > 0.79) and significant (p < 0.01) power-law relationships were found between the damage accumulation parameters (steady-state creep rate d epsilon/dt and time-to-failure tf) and the applied normalized stress sigma/E0. The creep behavior was also a function of temperature, following an Arrhenius creep relationship with an activation energy Q = 113 kJ/mole, within the range of activation energies for cortical (44 kJ/mole) and trabecular (136 kJ/mole) bone. The denaturation behavior was characterized by axial shrinkage at temperatures greater than approximately 56 degrees C. Lastly an analysis of covariance (ANCOVA) of our demineralized cortical bone regressions with those found in the literature for cortical and trabecular bone indicates than all three tissues creep with the same power-law exponents. These similar creep activation energies and exponents suggest that collagen is the phase responsible for creep in bone.

Accelerating bone formation and earlier healing after using demineralized bone matrix for limb lengthening in rabbits

We studied the effects of grafting with demineralized bone matrix during lengthening of the tibia in young Japanese White rabbits. The demineralized bone matrix was made from frozen cortical bone harvested from other rabbits. A 5-mm gap was created in the tibial diaphysis by a subperiosteal osteotomy; a maximum of 20 mm (2-3 mm/day) of tibial lengthening was reached in a week with use of an external fixator. The control group of 20 rabbits did not receive an implant; the group of 21 experimental rabbits received an implant of demineralized bone matrix in the surgical gap. The control group failed to demonstrate radiographic callus 5 weeks after surgery, and nonunion was persistent after 1 year. In the group with demineralized bone matrix, new radiodensity was demonstrated within the lengthening gap at 3 weeks, with a gradual increase in bone density to 85% that of the intact tibia after 12 weeks. Bone union was seen within 1 year for all experimental animals for whom the external fixator was removed 8 weeks after the procedure. These bones showed normal bone structure histologically. The lengthening was carried out at a rapid distraction rate of 2-3 mm/day; therefore, this method allows for satisfactory bone formation at a faster rate than normal.

The role of trabecular demineralized bone in combination with perichondrium in the generation of cartilage grafts

The use of a composite graft of bovine trabecular demineralized bone matrix (DBM) and perichondrium has been found a reliable method for in vivo generation of cartilage. In the present study, the mechanism whereby this commercially available matrix increases cartilage formation was investigated. First, the time course of cartilage formation in vivo, in the combined implant of perichondrium and DBM in the rabbit ear was studied, with special focus on tissue reactions to DBM. DBM was colonized by macrophages from day 3 post-operatively, reaching a maximum after 2 weeks. Only a minimal number of neutrophils was found. After 3 weeks the DBM appeared to be resorbed. In the first week the DBM was invaded with chondroblasts, and chondrogenesis occurred between the first and second week of implantation. After 3 weeks, the initially formed islets of cartilage had fused. Next, the chondrogenic capacity of DBM itself was investigated by implantation of DBM without perichondrium. This never resulted in cartilage formation. Immunohistochemistry showed only a faint staining of the DBM for growth factors. This indicates a minimal chondrogenic effect of DBM alone and the requirement of perichondrium as cell provider. In order to define the conditions which cause chondrogenesis in composites of perichondrium and DBM, a series of in vitro culture experiments was performed in which the in vivo situation was mimicked step by step. The basic condition was perichondrium cultured in medium with 10% FCS. In this condition, cartilage formation was variable. Because in the in vivo situation both DBM and macrophages can release growth factors, the effect of IGF1, TGFbeta2 or OP1 added to the culture medium was tested. Neither the incidence nor the amount of cartilage formation was stimulated by addition of growth factors. Perichondrium wrapped around DBM in vitro gave cartilage formation in the perichondrium but the incidence and amount were not significantly stimulated compared to cultures of perichondrium without DBM. However, cartilage-like cells were found in the DBM suggesting an effect of DBM on perichondrium-derived cells. Finally, macrophages and/or blood were added to the composite DBM-perichondrium to mimic the in vivo situation as close as possible. However, no effect of this treatment was found. In conclusion, this study indicates that DBM itself has few chondrogenic qualities but functions merely as a spacer for cell ingrowth. The fast resorption of DBM by macrophages in vivo seems of importance for the cartilage forming process, but in vitro the presence of macrophages (in combination with blood) could not enhance chondrogenesis.

Osteoinduction by demineralised bone

Bone contains several growth factors, including bone morphogenetic proteins (BMPs), transforming growth factor beta (TGF-beta), insulin-like growth factors I and II (IGF-I and IGF-II), platelet derived growth factor (PDGF) and basic and acidic fibroblast growth factor (bFGF and aFGF). The BMPs are the only factors known to provoke bone formation heterotopically by making undifferentiated mesenchymal cells differentiate into osteoblasts (osteoinduction). Much of our knowledge of osteoinduction derives from studies in rodents of heterotopically implanted demineralised bone which contains various growth factors, including BMPs. This model has been used to examine the effect on osteoinduction of different factors, including the type of host soft tissue, age and species of donor and recipient, demineralisation procedure, storage and sterilisation procedures, experimental diabetes, dietary factors, hormones, growth factors, caffeine, biphosphonates, indomethacin and biomaterials. Demineralised bone enhances bone formation experimentally in various animal models, including cranio-maxillofacial reconstructions, healing of diaphyseal defects, and spinal fusion; demineralised bone has also been used in a limited way clinically. However, sufficient osteoinduction in humans may require a higher concentration of BMPs and other growth factors than those found in demineralised bone.

Osteoinduction of human demineralized bone: characterization in a rat model

The increasing clinical use of human demineralized bone matrix has brought about the desire to understand better the osteoinductivity of these graft materials. The rat heterotopic model has been used successfully to show the sequence of events involved in the endochondral ossification process resulting in osteoinduction. In this study, the osteoinductive potential of human demineralized bone powder was assessed, using immune compromised rats (athymic rnu/rnu) to avoid problems associated with cross species incompatibilities. Implants were placed in subcutaneous or intermuscular sites. This model is characterized to provide a basis for routinely determining the performance of human demineralized bone powder. Demineralized bone powder was prepared from rat and human cortical bone according to a strict protocol. The lack of response to guanidine HCl extracted (noninductive) demineralized bone showed the selectivity of the assay. The same lots of human and rat demineralized bone were tested in sequential experiments during a 1-year period. These results showed reproducible induction of the demineralized bone powder between experiments. Combining demineralized bone with the guanidine HCl extracted demineralized bone in varying ratios tested the sensitivity of the assay. These results showed an increase in bone formation with increasing quantities of active demineralized bone and established the ability of the bioassay to differentiate between the various levels of active (osteoinductive) demineralized bone powder. With this model, consistent performance of demineralized bone powder processed by well controlled methods was seen.

In- and out-flows of elements in bones embedded in reference soils

Possible exchanges of elements between bone and the surrounding soil after being embedded underground for 2 years were estimated. Bone pieces were samples from human vertebrae without any treatments after resection. Sixteen elements were determined by atomic emission mass spectrometry. These were divided into three types; Type I, an in-flow in which elements increased, as in Fe, Al and Ba; type II, a balanced decrease in which changes were found in S, Mg and Zn; and type III, an out-flow in which elements, such as Ca and P, entered into bones from embedded soils. These exchanges depended on the varying nature of soils and also on the time underground. The exchanges were progressed in duration of the time after burial. Data obtained are possible references to judge the time-lapse after burial of bones in relating to characters of soils embedded, and to identify proper bone elements from containment elements.

Efficacy of perichondrium and a trabecular demineralized bone matrix for generating cartilage

A pedicled auricular perichondrial flap wrapped around trabecular demineralized bovine bone matrix can generate an autologous cartilage graft. In earlier experimental studies, it was demonstrated that this graft could be used for nasal and cricoid reconstruction. It was assumed that the vascularization of the perichondrial flap was obligatory, but it was never proven that the flap should be pedicled. Moreover, for clinical use, the dimensions of the auricle would set restrictions to the size of the graft generated. Therefore, the possibility to generate cartilage with a composite graft of a free perichondrial flap wrapped around demineralized bovine bone matrix, by using young New Zealand White rabbits, was studied. This composite graft was implanted at poorly (subcutaneously in the abdominal wall; n = 12), fairly (subcutaneously in the pinna; n = 12), and well-vascularized sites (quadriceps muscle; n = 12). As a control, trabecular demineralized bovine bone matrix was implanted without perichondrial cover. Half of these grafts (n = 6) were harvested after 3 weeks, and the remaining grafts (n = 6) after 6 weeks of implantation. In histologic sections of these grafts, the incidence of cartilage formation was scored. Furthermore, the amount of newly formed cartilage was calculated by computerized histomorphometry. Trabecular demineralized bovine bone matrix without perichondrial cover demonstrated early resorption; no cartilage or bone was formed. In demineralized bovine bone matrix wrapped in perichondrium, early cartilage formed after 3 weeks at well- and fairly vascularized sites. No cartilage could be detected in grafts placed at a poorly vascularized site after 3 weeks; minimal cartilage formed after 6 weeks. In summary, the highest incidence of cartilage formed when trabecular demineralized bovine bone matrix was wrapped either in a pedicled auricular perichondrial flap or in a free perichondrial flap, which was placed at a well-vascularized site. Second, a significantly higher percentage of the total area of the graft was cartilaginized at well-vascularized sites after 3 weeks. The newly generated cartilage contained collagen type II and proteoglycans with hyaluronic acid binding regions, whereas collagen type I was absent, indicating the presence of hyaline cartilage. This study demonstrates that new cartilage suitable for a graft can be generated by free perichondrial flaps, provided that the site of implantation is well vascularized. Consequently, the size of such a graft is no longer limited to the dimensions of the auricle.

The correlation between immune rejection and osteoinduction of allogeneic bone grafting

OBJECTIVE

To evaluate the relationship between the immune rejection and the osteoinductive potential of bone allograft.

METHODS

Allogeneic and syngeneic fresh bone, autolyzed antigen-extracted bone, bone matrix gelatin and demineralized bone matrix were implanted into the muscle of mice, and immunological tests, histological observation and alkaline phosphatase assay were performed.

RESULTS

Three and 6 weeks after implantation, all kinds of allogeneic implants activated immune rejection, among them, fresh bone induced the most vigorous immune rejection and bone matrix gelatin caused the weakest response. Allogeneic autolyzed antigen-extracted bone, bone matrix gelatin and demineralized bone matrix inhibited proliferation of the lymphocytes in vitro and bone matrix gelatin had the most powerful inhibiting effect. Both allogeneic and syngeneic autolyzed antigen-extracted bone, bone matrix gelatin, and demineralized bone matrix induced heterotopic osteogenesis in vivo and bone matrix gelatin had the best osteoinductive capacity.

CONCLUSION

There is a negative correlation between immune rejection to bone allograft and osteoinductive capacity of the graft.

In vitro osteoinduction of demineralized bone

Among numerous available materials for osseous repair and reconstruction, those presenting osteoinductive characteristics and promoting bone regeneration are preferable. Fresh autologous bone is one of the most effective, but it has some disadvantages and risks. Demineralized bone matrix (DBM) is considered to be a valid alternative, because it seems to show osteogenic potential, ascribed to the presence of bone morphogenetic proteins. In addition it can be prepared without difficulty and preserved without losing osteoinductive properties. The aim of the study was to evaluate the osteoinductive ability of xenogenic DBM, by testing DBM powder obtained from rabbit long bones, in cell culture of murine fibroblasts, alone or associated with electromagnetic field (EMF), that are known to exhibit biologic effects on cells: in particular they are used in orthopedics to improve bone formation. At the end of experiment, alkaline phosphatase (ALP) activity, calcium levels and cell proliferation and morphology were evaluated. A statistically significant stimulation of ALP activity and cell proliferation and a morphological change of fibroblasts were found. The results obtained show how DBM and EMF have different effects on cells, and that together they have synergic action toward bone induction.

Demineralized bone matrix supplied by bone banks for a carrier of recombinant human bone morphogenetic protein (rhBMP-2): a substitute for autogeneic bone grafts

Four commercially available preparations of demineralized freeze-dried human bone powders (DFDB) were investigated for endogenous bone morphogenetic protein (BMP) as observed by osteoinductive activity. Composites of DFDB without and with 1 microgram or 10 micrograms of recombinant human bone morphogenetic protein-2 (rhBMP-2) were implanted into the hindquarter muscles of Swiss-Webster mice. The four batches of DFDB without rhBMP-2 were placed also in hindquarter muscles of athymic mice. Three weeks after implantation, the area of induced bone and cartilage formation was measured by radiographic and histomorphometric methods. In normal mice, without rhBMP-2, DFDB implants induced development of dense fibrous connective tissue with minimal, if any, new bone. In athymic mice, DFDB induced development of small patches of appositional new bone. In contrast, in normal mice, composites of DFDB and rhBMP-2 induced development of large areas of heterotopic bone and bone marrow formation. The bone morphogenetic response occurred with a statistically significant difference (p < 0.0001) between implants of 1 microgram and the 10-microgram rhBMP-2 composites. Thus, DFDB from all four bone banks demonstrated comparable capacity to serve as a carrier for rhBMP-2.

Ethene oxide and bone induction. Controversy remains

There is controversy as to whether ethene oxide ("ethylene oxide", EO) sterilization destroys the bone-inducing capacity of demineralized bone matrix (DBM) or not. Correctly performed studies seem to support both opinions. Bone conductive properties of fresh frozen, defatted bone grafts are greatly impaired by EO sterilization, whereas purified inductive proteins resist EO. Studies showing destruction of osteoinductive capacity used nonpulverized DBM, whereas the others used powder. This could be the key to resolving the controversy, because if EO treatment reduces the cells' ability to penetrate a cortical graft and to reach inductive proteins inside it, it may appear noninductive after EO sterilization, even though BMP molecules may be intact. On the other hand, cells could easily penetrate the powder implants. We compared the effect of EO sterilization on the inductive capacity of demineralized cortical bone with that of DBM powder, using allogeneic material in rats. Cortical pieces lost all inductive capacity by EO sterilization, whereas the powder yielded a calcium content which was at best one fourth of the unsterilized. The concentrations of residual EO, ethene chlorohydrin and ethene glucol at implantation were far below approved levels. Another difference between studies is the humidity during EO treatment. In our hands, humidification reduced bone yield by half. In conclusion, EO sterilization may impair the biological performance of bone inductive implants by reducing cell penetration into bulk material. However, DBM powder, when correctly sterilized, also yielded scanty amounts of bone.

Identification of lysyl oxidase and TRAMP as the major proteins in dissociative extracts of the demineralized collagen matrix of porcine dentine

Carbonated apatite (dahllite) is formed within and between collagen fibrils in the mineralization of connective tissues. However, the mechanism of crystal nucleation at these sites has not been resolved. To identify non-collagenous proteins that may be involved in the nucleation process we have utilized a dissociative extraction procedure to isolate proteins associated non-covalently with the de-mineralized collagen matrix of dentine isolated from tooth roots of adult porcine incisors. Following extraction of dentine fragments with 4M GuHCl (G1-extract) and 0.5M EDTA (E-extract), de-mineralized collagen matrix-associated proteins were isolated with a second series of extractions with 4M GuHCl (G2-extract). Analysis of the G2-extracts on SDS-PAGE revealed two major 32 kDa and 24 kDa protein bands, comprising > 80% of the extracted non-collagenous proteins. The 32 kDa protein was purified by FPLC on hydroxyapatite and Mono Q resins, followed by HPLC reverse-phase chromatography. Small amounts of 26 kDa and 6 kDa proteins, which appear to represent proteolytically processed, disulphide-linked fragments of the 32 kDa protein, co-eluted with the major protein. The 32 kDa protein was identified as lysyl oxidase from amino acid sequence analysis of a 13 kDa CNBr peptide obtained from protein purified by preparative electrophoresis on SDS-PAGE. Fractionation of the 24 kDa protein on FPLC Mono Q resin generated < 5 closely eluting protein peaks. The proteins from these peaks were similar in size, staining properties, amino acid composition and CNBr digestion patterns. Each protein was immunoreactive with antibodies raised against a tyrosine-rich acidic matrix protein (TRAMP), reported previously to co-purify with lysyl oxidase. These studies, therefore, show that lysyl oxidase, which is important in collagen cross-link formation, and proteins with properties of TRAMP, a protein that can modulate collagen fibrillogenesis, are the major proteins in dissociative extracts of de-mineralized porcine dentine.

Dermatan sulfate proteoglycans from the mineralized matrix of the avian eggshell

The eggshell of the chicken is a useful model to study matrix components which affect biomineralization. As an extension of our previous immunohistochemical work which suggested the presence of dermatan sulfate proteoglycans in the mineralized region of the eggshell, a study was undertaken to characterize these molecules biochemically. After demineralization with HCl and extraction with 4 M guanidinium chloride containing protease inhibitors, the extract was partitioned by anion exchange chromatography. Step elution with 0.25 M and 1.0 M sodium chloride resulted in the generation of two fractions, both of which contain chondroitinase-sensitive proteoglycans with molecular weights estimated at 200,000 by gel electrophoresis. The proteoglycans in each fraction have core proteins with molecular weights of approximately 120,000 and glycosaminoglycans with average molecular weights of 22,000. Based on differential sensitivity to chondroitinase ABC and AC II, these glycosaminoglycans contain a small proportion of dermatan sulfate. The disaccharide compositions of these glycosaminoglycans differ for the proteoglycans eluted with 0.25 M and 1.0 M sodium chloride. Those eluted with lower sodium chloride are enriched in unsulfated chondroitin and have much more 4-sulfated than 6-sulfated disaccharides; those eluted with 1.0 M sodium chloride contain primarily 4-sulfated disaccharides, a small amount of 6-sulfated disaccharides, and less unsulfated disaccharides than the proteoglycans eluted with 0.25 M sodium chloride. The large difference in the proportions of unsulfated chondroitin may be the reason for the elution at different sodium chloride concentrations. Both of the anion exchange column fractions contain other proteins in addition to the proteoglycans. These proteins are not separated from the proteoglycans by a second anion exchange column or by molecular sieve chromatography under dissociative conditions. Of particular interest is the observation that the eggshell proteoglycans and their core proteins are recognized by a monoclonal antibody which recognizes an epitope on the core protein of avian versican. This suggests that, in spite of the large differences in the sizes of the core proteins of versican and the eggshell proteoglycans, these core proteins share some homology. Because anionic molecules are thought to be important regulators of biomineralization, and because preparations like those analyzed in this study have been shown to influence in vitro calcium carbonate crystallization, the eggshell proteoglycans may play a role in eggshell mineralization.

Osteoinductive potential of demineralized rat bone increases with increasing donor age from birth to adulthood

Demineralized allogenic bone implanted in the subcutis or muscle of rodents causes formation of heterotopic bone by osteoinduction. The osteoinductive response may be weaker in primates than in rodents. It was suggested that the osteoinductive response of demineralized bone for clinical use could be enhanced by using young donors, because studies have indicated that the osteoinductive response is reduced in demineralized bone of old versus young donors. However, these findings may not represent a gradual decline in the osteoinductive property of bone matrix throughout the life span. We evaluated quantitatively, by uptake of strontium 85, the osteoinductive effect of demineralized bone matrix from newborn, 8-week-old (adolescent), and 8-month-old (adult) male Wistar rats implanted in the abdominal muscles of 8-week-old male Wistar rats. The osteoinductive response increased significantly with increasing donor age. The results of the present study, weighed with those of previous studies, indicate that the osteogenic potential of the bone matrix increases from newborn to adulthood but decreases in the aged rat. This may be due to changes in concentration of essential growth factors (e.g., bone morphogenetic proteins) resulting from maturational changes from birth to adulthood and osteoporotic changes occurring in later years. The results do not support the contention that young donors of demineralized bone are preferable to adult donors.

Ultrasound characterization of bone demineralization

Quantitative ultrasound (QUS) assessment of bone may permit an assessment of bone properties currently not available by bone densitometry techniques. To explore the effects of the quantity of bone mineral on acoustic parameters, we carried out an in vitro study of the impact of demineralization on attenuation of ultrasound in trabecular bone. Ten fresh cubes of trabecular bone obtained from bovine distal femurs were progressively demineralized using formic acid solution. The progression of demineralization was controlled by monitoring the specimen bone mineral density (BMD) using dual x-ray absorptiometry (DXA). At five stages of demineralization-0% (baseline), 25%, 50%, 75%, and 100% (all mineral removed)-the US properties of the specimens were assessed (Walker Sonix UBA 575+). The US parameters investigated were broadband ultrasound attenuation (BUA) and ultrasound attenuation in bone (UAB). Both DXA and QUS measurements were made along the three orthogonal axes of each cube. Our results demonstrated significant variability in both BUA and UAB along the three principle axes of the cubes whereas BMD did not differ in the different directions. A strong but nonlinear correlation was found between BMD and US attenuation. A reduction in BMD to 50% of the baseline values resulted in BUA (UAB) reduction to 25% and 19%, respectively. A random effect model analysis supported a multiplicative relationship between BMD and the US parameters. US attenuation is a sensitive indicator of bone mineral changes with nonlinear dependence on bone mineral loss. Bone collagen structure reinforced by hydroxyapatite crystal accounts for fundamental US characteristics. Ultrasound attenuation associated with trabecular orientation is basically dominated by the mineral spread in a collagen framework.

Experimental posterolateral lumbar spinal fusion with a demineralized bone matrix gel

STUDY DESIGN

A controlled rabbit model of lumbar posterolateral intertransverse process arthrodesis was used to evaluate a bone graft substitute.

OBJECTIVE

To determine the efficacy of demineralized bone matrix gel as an autograft extender, using different ratios of demineralized bone matrix to autograft and to determine the efficacy of demineralized bone matrix as an autogenous bone graft enhancer by adding it to the usual quantity of autograft.

SUMMARY OF BACKGROUND DATA

Autogenous bone is considered the most effective bone graft material for posterolateral lumbar arthrodesis, yet nonunions occur in up to 30% of patients. In addition, donor site complications may occur in 25-30% of patients. This has prompted the search for and investigation of bone graft extenders, enhancers, and substitutes. Commercially available demineralized bone matrix gel is one possible graft extender and enhancer, which, unlike mineralized allografts, has osteoinductive properties. Although the gel is in common use, the efficacy of demineralized bone matrix when used for posterolateral spine arthrodesis has not been examined in prospective clinical studies. Furthermore, no known animal studies have tested demineralized bone matrix gel in a posterolateral arthrodesis model.

METHODS

Forty-seven New Zealand white rabbits underwent bilateral posterolateral spine arthrodesis at L5-L6 using autogenous iliac crest bone graft alone or in combination with demineralized bone matrix. Four groups were formed on the basis of the ratio of autograft to demineralized bone matrix: autograft alone (3 mL), 100:0 group; autograft (3 mL) and demineralized bone matrix (1.5 mL), 100:50 group; autograft (1.5 mL) and demineralized bone matrix (1.5 mL), 50:50 group; and autograft (0.75 mL) and demineralized bone matrix (2.25 mL), 25:75 group. Rabbits were killed 6 weeks after surgery. Inspection, manual palpation, radiographic film, and histologic evaluation were used to assess fusion.

RESULTS

All groups had similar fusion rates (66-73%) based on manual palpation. Rabbits implanted with demineralized bone matrix had more mature fusion masses, evidenced by the greater trabecular bone formation seen on radiographic film and histologic study.

CONCLUSIONS

Demineralized bone matrix was effective as a graft extender when used in up to a 3:1 ratio with autograft in a rabbit posterolateral spine fusion model. When less than the standard volume of autograft was used, the addition of demineralized bone matrix gel lead to fusion success rates comparable to those of the standard amount of autograft alone. However, demineralized bone matrix did not increase the frequency of successful fusion when added to the standard amount of autograft.

Induction in vivo of cartilage grafts for craniofacial reconstruction

In the craniofacial region, defects of cartilage structures are preferably reconstructed with autologous cartilage. Donor-site morbidity related to the creation of a new defect elsewhere, and a lack of growth potential of the graft--mandatory in children--have stimulated investigators to find other ways to generate new "extra" cartilage. Several biomaterials have been tested as a matrix for the ingrowth of (peri)chondroblasts in experimental animals. In young (growing) rabbits we have developed a process of heterotopic cartilage induction with the use of a demineralized (bovine) bone matrix which is enfolded in a pedicled flap of ear perichondrium for at least three weeks. During this period the demineralized matrix is colonized by macrophages and polymorphonuclear cells which start a process of complete biodegradation of the material. Simultaneously, the collagen matrix is invaded by mesenchymal cells, originating from the perichondrium and differentiating into chondroblasts and later, into chondrocytes forming the intercellular substance. The developing, very young cartilage could be demonstrated as collagen type II, thus, hyaline cartilage. When applied with its adherent perichondrium as a graft, it merges easily with the more matured host cartilage and even appears to be capable of further growth. Therefore, it seems suitable for the reconstruction of a cartilaginous defect in growing cartilaginous structures like the nasal septum or the larynx.

Insulin-like growth factor I increases bone formation in old or corticosteroid treated rats

We studied bone induction in subcutaneous implants of demineralized bone matrix with or without insulin-like growth factor I (IGF-I) in aged or corticosteroid-treated rats. Each rat carried one pair of implants, one control and one experiment implant, containing IGF-I dissolved in a hyaluronan solution for slow release. The rats were killed after 3 weeks and the results were evaluated by measuring the calcium content of implants. Young (6-7 weeks) and old (19-27 months) rats were used. A group of young rats was treated for 1 week with subcutaneous injections of 140 micrograms/kg dexamethasone daily. Old rats produced only approximately 1% as much bone as young rats. Local delivery of IGF-I did not increase bone formation in young rats. In old rats, bone formation was increased by IGF-I, 3000 ng/implant. Corticosteroids reduced bone formation in young rats. This effect was partially reversed by local administration of IGF-I.

Improved osteoinduction of cortical bone allografts: a study of the effects of laser perforation and partial demineralization

Massive cortical bone allografts have been found to incorporate slowly into host bone and thus are subject to complications such as nonunion, fatigue fracture, and infection. To better understand and improve the process of osteoinduction in these types of bone grafts, a new experimental model was developed with use of diaphyseal cortical bone grafts from rat tibiae that were prepared by partial demineralization and drilling of 0.33 mm diameter holes with a pulsed, 2.94 microns wavelength, erbium:yttrium-aluminum-garnet laser. Six types of grafts were analyzed: untreated (Type I), demineralized 25 microns deep (Type II), demineralized 150 microns deep (Type III), laser perforated (Type V), laser perforated and then demineralized 25 microns deep (Type V), and laser perforated and then demineralized 150 microns deep (Type VI). The graft was orthotopically transplanted in the tibia of an adult Sprague-Dawley rat and followed for as long as 4 months. Histologic evaluation at 1 and 4 months postoperatively with use of hematoxylin and eosin staining confirmed that there was new bone growth in Types II, III, V, and VI grafts. The amount of growth was estimated by comparing bone mineral density before implantation with values obtained after retrieval of the graft. These measurements were correlated to histomorphometric analysis of graft incorporation. The results show that the processes of partial demineralization (p < 0.000001) and laser perforation with partial demineralization (p < 0.000001) were both significant in enhancing bone growth in this model. New bone growth was significantly increased when the grafts were prepared with extensive demineralization (p < 0.015). This study demonstrates that osteogenesis in cortical bone grafts can be fostered through the process of partial demineralization and laser perforation. To the extent that minimal partial demineralization and laser perforation allow maintenance of structural integrity while altering the osteoinductive properties in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts may be improved.

[The effects of microwave heating on osteoinduction of demineralized bone matrix in rabbits]

In order to study the change of the autograft demineralized bone matrix, twenty-four new-Zealand rabbits were randomly divided into four groups of 2, 4, 8, 12 week by sacrified time, each group had 7, 7, 5, 5 rabbits. Autoradiography was done for 2 rabbits in 2, 4 weeks respectively. The tibiae were removed by amputation at knee joint level, then they were cleansed of marrow and periosteun, cut into six pieces in length of 0.8 cm heated with microwave. Demineralized bone matrix were made by defated and decalcified, and implanted into abdomenal walls autograft. The results showed that the implants heated at 45 degrees C 30 min had same osteoinduction as control group. The 65 degrees C 30 minutes heating may reduce implant's osteoinduction slightly. The osteoinduction of the groups heated 75 degrees C for 30-60 minutes were impaired severely. The implants boiled at 100 degrees C 30 minuts had no osteoinduction at all, 65 degrees C 30 minutes may be a "safty" limit when heat treatment on bone clinically. Otherwise, bone formation ability would be reduced and remodelling was delayed.

The biological effect of natural bone mineral on bone neoformation on the rabbit skull

The aim of this study was to evaluate the effect of deproteinized bovine bone graft material on new bone formation in a guided bone regeneration model system. In 20 rabbits, a periosteal skin flap was raised uncovering the calvaria. A form stable hemispherical dome made of poly-lactic acid (PLA) was placed onto the roughened calvaria. Prior to placement, the dome was either filled with peripheral blood alone (control group, 8 rabbits), or with blood and OsteoGraf/N-300 (test group, 12 rabbits). The wound was closed for primary healing. Morphometric assessment of 1- and 2-month undecalcified histologic specimens revealed better tissue fill in the test domes at 1 month (test 99%, control 55%) (P < 0.05) and 2 months (t, 100%; c, 82%). The fraction of the new bone within the regenerated tissue was higher in the test specimens at 1 month (t, 22%; c, 12%) (P < 0.05) and 2 months (t, 34%; c, 24%). The fraction of the entire space underneath the domes occupied by bone was higher in the test at 1 month, but higher in the controls at 2 months. The fraction of the bone substitute material in contact with bone increased from 1 month (34% +/- 14) to 2 months (45% +/- 5). The surface fraction of osteoblast layers was tendentially higher in the test at 1 month but higher in the control specimens at 2 months. In both test and control, initially woven bone was formed which underwent subsequent remodeling. Cellular degradation of the deproteinized bone graft was frequently detected. It is concluded that deproteinized bovine bone mineral has osteoconductive properties and can initially accelerate new bone formation during guided bone regeneration by increased recruitment of osteoblasts.

Osseous repair of a lateral periodontal cyst

THE LATERAL PERIODONTAL CYSTS is a slow-growing radiolucent, developmental lesion occurring most frequently in males during the sixth decade. As part of the differential diagnosis, it must be distinguished from the collateral keratocyst and the gingival cyst of adults as well as other entities. Speculation remains as to the lateral periodontal cyst's developmental origin. Whether it is from reduced enamel epithelium, remnants of dental lamina, or cell rests of Malassez remains to be determined. The following longitudinal case report describes the review of literature and clinical and histologic findings as well as unusual treatment of a through-and-through perforating lateral periodontal cyst. Due to the large bony defect left after the cyst's removal, a decalcified freeze-dried bone graft was placed to close the defect. The repair of the lesion was followed for 30 months.

[The effect of calcium content in bovine cancellous bone as carrier on expression of tumor necrosis factor-alpha gene in mice]

We investigated the expression of tumor necrosis factor-alpha (TNF alpha) gene in the area of implanted calf cancellous bone with different calcium content and the influence of calcium salts on local cellular immunity. The particles of mineralized and partially demineralized bone were implanted in the mouse's muscle pouch, and removed 3, 5, 10 and 20 days after implantation of the bone particles. The specimens were processed for determining the expression of mRNA encoding TNF alpha, which was performed by a nonradioactive in situ hybridization technique. The expression of TNF alpha mRNA was markedly higher in the mineralized bone group than in the partially demineralized bone group (P < 0.01). The positive rate of TNF alpha gene expression was highest by 10 days after implantation. There was a strong hybridization signal localization to the cytoplasm of morphologically identifiable monocytes and multinucleated giant cells. Similar activity was detected in the cytoplasm or nuclei of mesenchymal cells, fibroblasts as well as striated muscle fibers. This finding suggests that the calcium content in calf cancellous bone possesses a significantly stimulative effect on TNF alpha mRNA expression, and calcium salts may be of importance for the modulation of local cellular immunity.

A clinical evaluation of guided tissue regeneration with a bioabsorbable matrix membrane combined with an allograft bone graft. A series of case reports

THE PURPOSE OF THIS STUDY was to evaluate the clinical effectiveness of a surgical technique in treating periodontal defects. The technique combined tetracycline treatment of a root planed root, grafting of the osseous defect with a demineralized freeze-dried bone allograft combined with tetracycline and the placement of a bioabsorbable matrix membrane, made of polylactic acid softened with citric acid ester. Thirty defects were treated in 27 patients. Statistically significant changes, as a result of the surgical procedure, were observed in marginal recession (mean: 0.5 mm), probing depth reductions (mean: 5.7 mm), and attachment level gain (mean: 5.2 mm). No statistically significant difference existed between the results in the furcation and non-furcation groups. The defects with probing depths > or = 10 mm had a greater mean probing depth reduction (7.4 mm) and mean attachment level improvement (7.2 mm) than the defects with < 10 mm probing depths (probing depth reduction 4.5 mm and attachment level gain 3.9 mm). The proposed surgical procedure seemed to be an effective method to treat periodontal defects.

Long-term outcome of extensive skull reconstruction using demineralized perforated bone in Siamese twins joined at the skull vertex

The successful use of cortical demineralized perforated bone in the treatment of extensive skeletal defects in children is exemplified by this case involving Siamese twins joined at the skull vertex. Four years following extensive skull reconstruction using demineralized perforated bone, an examination revealed successful calvarial reconstruction in one twin. The other twin required additional implants of demineralized perforated bone to fill in defects. However, a histologic examination taken following this additional procedure revealed that these implants neither caused tissue reaction over a 4-year period, nor showed signs of resorption. Bony remodeling and new bone formation were in progress. Compared with other bone substitutes, demineralized perforated bone has proven to be effective in the treatment of large skull defects in children.

Ethylene oxide does not extinguish the osteoinductive capacity of demineralized bone. A reappraisal in rats

We examined the influence of ethylene oxide (EO) and gamma irradiation on the osteoinductive capacity of demineralized bone. Demineralized bone powder prepared from Wistar rats was exposed to EO (55 degrees C or 40 degrees C) or gamma irradiation (25 KGy) or was preserved in ethanol. Sterilely-prepared bones served as controls. The powder was packed in a gelatin capsule and implanted for 6 weeks in muscles of 6-week-old female rats. Exposure of demineralized bone particles to EO 55 degrees C resulted in an almost complete loss of osteoinductivity. Irradiated bones lost about 40% of their osteoinductive capacity, while sterilization with EO at 40 degrees C resulted in only a slight alteration of the osteoinductivity, as assessed by the recovered weight ratio, calcium content, alkaline phosphatase activity measurements and histomorphometry. Ethanol treatment had no influence on the new bone yield when compared to controls. As EO exposure at 40 degrees C is a true sterilization procedure, it can be recommended in a clinical setting for its small effect on osteoinductive capacity as assessed experimentally in rats.

Utilization of type I collagen gel, demineralized bone matrix, and bone morphogenetic protein-2 to enhance autologous bone lumbar spinal fusion

Autologous bone grafts are currently considered "gold standard" material for achieving long-term spinal arthrodesis. The present study was performed to determine whether demineralized bone matrix (DBM), type I collagen gels, or bone morphogenetic protein-2 (BMP-2) can improve autologous bone spinal fusions. Using a unilateral decompression-contralateral fusion technique in dogs, each of these materials was added to an autologous bone graft. Volumetric analysis, histological analysis, and biomechanical testing were performed to assess the effectiveness of each material. The DBM had an inhibitory effect on solid bone fusion of the spine, whereas the type I collagen gels improved the bony interface between the graft and the host spine. The BMP-2 strongly enhanced the amount of bone deposition at the fusion site and increased the number of intervertebral levels that were solidly fused. This study strongly supports the use of BMP-2 as an additive to autologous bone grafts in spine stabilization.

Improved method for examination of microvascular structures in bone tissue

Scanning electron microscopy of methylmethacrylate vascular corrosion casts was used for the morphologic examination of the microvascular system in bone. The methylmethacrylate used for vascular casting was prepared by prepolymerization with ultraviolet light. To approximate the viscosity of blood in the microcirculation, where the hematocrit of blood is lower than in the rest of the circulation, a viscosity between that of plasma and full blood was chosen for the casting material. Neither the ultraviolet prepolymerization of methylmethacrylate nor the choice of a viscosity this low has been used in microcorrosion casting in bone before. Further preparation of the tissue followed 2 directions: (1) complete maceration and decalcification of the specimens, thereby exposing all the vascular structures for detailed examination. By this procedure, it was possible to show detailed and sharp impressions of the vascular bed, and to show, for the first time, the vascular loop from a cutting cone; and (2) maceration without decalcification of the specimens, which is suitable for examination of relations between the microvascular system and the bone tissue. This technique enables studies of the role of the vascular system in bone remodeling and of the involvement of vascular structures in bone disorders. This improved technique for examination of microvascular structures in bone enables detailed studies of the vascular system and its relation to active remodeling sites in bone.

Visualization of crystal-matrix structure. In situ demineralization of mineralized turkey leg tendon and bone

A technique to correlate the ultrastructural distribution of mineral with its organic material in identical sections of mineralized turkey leg tendon (MTLT) and human bone was developed. Osmium or ethanol fixed tissues were processed for transmission electron microscopy (TEM). The mineralized tissues were photographed at high, intermediate, and low magnifications, making note of section features such as fibril geometry, colloidal gold distribution, or section artifacts for subsequent specimen realignment after demineralization. The specimen holder was removed from the microscope, the tissue section demineralized in situ with a drop of 1 N HCl, then stained with 2% aqueous vanadyl sulfate. The specimen holder was reinserted into the microscope, realigned with the aid of the section features previously noted, and rephotographed at identical magnification used for the mineralized sections. A one to one correspondence was apparent between the mineral and its demineralized crystal "ghost" in both MTLT and bone. The fine structural periodic banding seen in unmineralized collagen was not observed in areas that were fully mineralized before demineralization, indicating that the axial arrangement of the collagen molecules is altered significantly during mineralization. Regions that had contained extrafibrillar crystallites stained more intensely than the intrafibrillar regions, indicating that the noncollagenous material surrounded the collagen fibrils. The methodology described here may have utility in determining the spatial distribution of the noncollagenous proteins in bone.

A new approach to the treatment of true-combined endodontic-periodontic lesions by the guided tissue regeneration technique

Clinicians often have difficulty in the diagnosis and treatment of the combined endodontal and periodontal (endo-perio) lesion. A case of an endo-perio true-combined lesion on a maxillary premolar was first treated with conventional endodontic therapy. Periodontal surgery was then completed, which included scaling and root planing and apical curettage on the tooth. The facial bony defect was then filled with a decalcified freeze-dried bone allograft mixed with tetracycline powder. A non-resorbable Teflon membrane was then used to cover the bone material and the periodontal flap sutured over this. This combined treatment resulted in minimal probing depth (2 mm), maximal clinical attachment gain (8 mm), as well as radiographic evidence of alveolar bone gain. This case report demonstrates that proper diagnosis, followed by removal of etiological factors and utilizing the guided tissue regeneration technique combined with osseous grafting, will restore health and function to a tooth with severe attachment loss caused by an endo-perio lesion.

Influence of smoking on long-term clinical results of intrabony defects treated with regenerative therapy

This retrospective study compares the short-term (1 year) and long-term (2 to 5 year) clinical results of regenerative therapy in clinical private practice using a bone allograft for the treatment of intrabony defects in smokers and non-smokers. A total of 110 intrabony lesions were treated with demineralized freeze-dried bone allograft (DFDBA) following thorough defect debridement and root preparation in 53 patients (15 cigarette smokers and 38 non-smokers). Assessments of clinical attachment level (CAL) and probing depth (PD) were recorded at pre-treatment, 1 year post-treatment, and 2 to 5 years post-treatment. At 1 year post-treatment, significant gains in mean CAL were maintained for both smokers (2.7 mm) and non-smokers (3.4 mm). Similarly, significant reductions in mean PD were observed for smokers (3.0 mm) and non-smokers (3.8 mm) at the 1-year follow-up. However, when comparing relative improvements in clinical measures, smokers were found to exhibit significantly poorer treatment results (i.e., sites exhibited less CAL gain) at 1 year and 2 to 5 years follow-up. Relative to pre-treatment scores, differences in improvements observed for CAL at the 1-year evaluation (29.2% for smokers and 42.5% for non-smokers) were sustained in the subgroup of patients at 2 to 5 years follow-up (31.3% for smokers and 41.8% for non-smokers). Similar but non-significant trends were observed for relative reductions in probing depth for smokers and non-smokers at 1 year (41.9% for smokers and 49.3% for non-smokers) and 2 to 5 years follow-up (43.9% for smokers and 48.3% for non-smokers) for the subgroup of patients followed beyond 1 year. These results suggest that smoking adversely affects treatment outcome, as measured by gains in clinical attachment levels of intrabony defects treated by regenerative therapy using DFDBA.

Expression of extracellular matrix macromolecules around demineralized freeze-dried bone allografts

In the present study histochemical techniques were used to identify specific macromolecular components of the extracellular matrix associated with the tissue reaction to demineralized freeze-dried bone allografts (DFDBA) placed under barrier membranes for ridge augmentation. Small biopsies were obtained from tissues underneath the membranes at various times after placement of the DFDBA and processed for routine immunohistochemistry. Sections were stained with antibodies to osteocalcin, collagen type I, collagen type III, decorin, and biglycan. Non-immune serum, irrelevant antibodies, and omission of the primary antibodies served as negative controls. Histologic examination of the biopsies revealed allograft particles surrounded by well-formed fibrous connective tissue with little or no evidence of new bone formation. Vital autogenous bone fragments were present in the peripheral portions of the biopsies and served as positive controls for comparative purposes with the DFDBA particles. Only 7 out of the 20 biopsies studied were found to have any signs of bone formation around the DFDBA particles and in these such bone formation was irregular and inconsistent around the DFDBA particles. Around the periphery of the allograft particles, osteocalcin, collagen type I, collagen type III, decorin, and biglycan all showed relatively strong staining. Osteocalcin staining was also noted within the vital bone matrix but not in the surrounding fibrous connective tissue. Decorin, biglycan, collagen type I, and collagen type III were also found within the vital bone matrix. None of these antibodies stained the DFDBA particles. The unremarkable osteogenic response of the tissues to the DFDBA particles after healing periods of up to 12 months raises questions as to the predictability of these agents in inducing new bone.

Demineralized bone matrix mediates differentiation of bone marrow stromal cells in vitro: effect of age of cell donor

Bone maintenance requires a continuous source of osteoblasts throughout life. Its remodeling and regeneration during fracture repair is ensured by osteoprogenitor stem cells which are part of the stroma of the bone marrow (BM). Many investigators have reported that in cultured BM stromal cells there is a cell population that will differentiate along an osteogenic lineage if stimulated by the addition of osteogenic inducers, such as dexamethasone (dex), beta-glycerophosphate (beta-GP), transforming growth factor beta-1 (TGF-beta 1) and bone morphogenetic protein-2 (BMP-2). Here we report the effects of demineralized bone matrix (DBM) on the osteogenic differentiation of BM stromal cells in vitro, using morphological criteria, alkaline phosphatase (AP) activity, and calcium accumulation. DBM and DBM-conditioned medium (DBMcm) enhanced bone formation in the presence of dex and beta-GP, whereas DBM particles caused changes in the cell phenotype. Temporal expression of total and skeletal AP by BM stromal cells from 4-week-old rats showed a biphasic pattern enhanced by DBM and suggesting the presence of two cell populations. In one population, AP synthesis reaches a maximum during the first week in culture, following which cells either die or loose their ability to synthesize AP. A second, less abundant population begins to proliferate and synthesize AP during the second and third weeks. The synthesis of AP, which often decreases by the third week, can be maintained at high levels only if DBM is added to the cultures. BM stromal cells isolated from 24- and 48-week-old rats showed a decrease or loss of this biphasic AP expression pattern compared with cells isolated from 4-week-old rats. The addition of DBM to cultures derived from 24- and 48-week-old rats stimulated mostly the second cell population to synthesize AP, suggesting that DBM contains a factor(s) that acts on a specific bone marrow cell population by increasing the proliferation of active cells or inducing the differentiation of dormant cells.

The tensile behavior of demineralized bovine cortical bone

Bone is frequently modeled as a two-phase composite of hydroxyapatite mineral crystals dispersed throughout an organic collagen matrix. However, because of the numerous limitations (e.g. small sample size, poor strain measuring techniques, rapid demineralization with acids) of previous mechanical tests of bone with its hydroxyapatite chemically removed, we have determined new, accurate data on the material properties of the demineralized bone matrix for use in these composite models. We performed tensile tests on waisted specimens of demineralized bovine cortical bone from six humeral diaphyses. Specimens were demineralized over 14 days with a 0.5 M disodium EDTA solution that was replaced daily. Atomic absorption spectrophotometry was used to track the demineralization process and to determine the effectiveness of our demineralization protocol. Mechanical tests were performed at room temperature under displacement control at an approximate strain rate of 0.5% per s. We imposed nine preconditioning cycles before a final ramp to failure, and measured gauge length displacements using a non-invasive optical technique. The resulting stress-strain curves were similar to the tensile behavior observed in mechanical tests of other collagenous tissues, exhibiting an initial non-linear 'toe' region, followed by a linear region and subsequent failure without evidence of yielding. We found an average modulus, ultimate stress, and ultimate strain of 613 MPa (S.D. = 113 MPa), 61.5 MPa (S.D. = 13.1 MPa), and 12.3% (S.D. = 0.5%), respectively. Our average modulus is approximately half the value frequently used in current composite bone analyses. These data should also have clinical relevance because the early strength of healing fractured bone depends largely on the material properties of the collagen matrix.

[An experimental study on the relationship between BMP's activity and its carrier]

To find out the relationship between human bone morphogenetic protein's activity and its carrier and to document the clinical application of BMP, we investigated six kinds of BMP carrier's influence upon hBMP's osteogenic activity with small sample size at first. Then three kinds of carriers selected from the six, added with the seventh carrier, were investigated with large sample size. The result showed that the compound of hBMP and hDDBM had best osteogenic ability. The human bone matrix had been formerly demineralized and extracted without hBMP. The hDDBM showed porous structure under SEM, its mean pore's diameter was 127 +/- 34 microns. It was demonstrated that the function of demineralized bone matrix extracted without BMP (i.e. DDBM) was related not only to its pore's diameter, but to the fibrolike matter in it as well. With the method of BMP bioassay, BMP was composited with carrier, then the compound was injected into the calf of mouse. This made BMP's bioassay become simple and reliable.

Chondroinduction of human dermal fibroblasts by demineralized bone in three-dimensional culture

We designed and tested a three-dimensional device composed of demineralized bone powder (DBP) packed within a bilaminate sponge as an in vitro model for chondroinduction induced by DBP. Control bovine articular chondrocytes deposited cartilage matrix when cultured in these sponges. Human dermal fibroblasts that were seeded onto the composite sponge migrated through the collagen lattice and attached to the particles of DBP. Fibroblasts surrounding the DBP deposited a fine, granular extracellular matrix characterized by metachromatic staining similar to that deposited around the bona fide chondrocytes. Immunohistological analysis showed that the matrix contained chondroitin delta Di-4 sulfate, chondroitin delta Di-6 sulfate, and keratan sulfate epitopes. These components accumulated during the culture period, as quantified by immunochemical analysis of extracted matrix. In contrast, fibroblasts cultured in collagen sponges without DBP did not produce such a cartilage matrix. Control bovine chondrocytes produced these matrix molecules when cultured in the presence or absence of DBP. Thus this composite three-dimensional device facilitated evaluation of chondroinduction in human dermal fibroblasts in vitro.

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.

[Experimental study on repair of mandibular defect by allogenic decalcified bone compounded with autogeneic bone marrow in rabbits]

Twenty adult rabbits were used in our experiment. The bone defects were made at the lower border of the bilateral mandible. A compound bone graft (allogenic decalcified bone with autogeneic bone marrow, ADB) was implanted in the right bone defect as the experimental group. The left mandible was taken as the control group and autogeneic cancellous bone was grafted. The process of new bone formation was evaluated by X-ray plain film, 99Tc-PYP Scintigraphy, histological, and histochemical, and transmmission electronic microscope examinations. The results demonstrated histogically that ADB induced new bone formation. The quantity of new bone produced by compound bone graft in the experimental group was much more than that in control group (P < 0.05). The compound bone graft can promote and accelerate bone defect healing.

Kinetics of cortical bone demineralization: controlled demineralization--a new method for modifying cortical bone allografts

We investigated the kinetics of hydrochloric acid demineralization of human cortical bone with the objective of developing a method of controlled demineralization for structural bone allografts. It is known that the demineralization of cortical bone is a diffusion rate limited process with a sharp advancing reaction front. The demineralization kinetics of human cortical bone, described as the advance of the reaction front versus immersion time, were determined by measuring extraction of bone mineral in both planar and cylindrical geometries. Mathematical models based on diffusional mass transfer were developed to predict this process. The experimental data fit well with the behavior predicted by the model. The model for planar geometry is applicable to controlled demineralization of cortical bone allografts of irregular shapes such as cortical struts. The model for cylindrical geometry is appropriate when curved surfaces are involved such as in diaphyseal bone allografts. This method of demineralization has direct application to clinical modification of cortical bone allografts to potentially enhance their osteoinductive properties.

Change in trabecular architecture as measured by fractal dimension

The objective of this work was to expose dried trabecular bone material to a decalcifying environment and to quantify the change in the spatial distribution of the bone with a fractal measure. Digitized radiographic images were produced from four separate slices of human vertebral bone as they dissolved within a solution of nitric acid. Pixel data from a region of interest (ROI) within the trabecular bone were used to estimate the time-dependent change in fractal dimension of the ROI as the bone dissolved. Results demonstrated that a change in the spatial distribution of trabecular material may be expressed in terms of a concurrently changing estimate of the fractal dimension.

Prevascularized bone graft cultured in sintered porous beta-Ca2P2O7 with 5 wt% Na4P2O7.10H2O addition ceramic chamber

Autogenous bone transfer is an important part of reconstructive plastic surgery. Presently available techniques have the disadvantages of limitation of available donor site, loss of donor tissue and the possibility of donor defect or deformity. In the present study, a vascularized bone graft was created and cultured in the groin area of the New Zealand rabbit. The cylindrical ceramic chambers, 15 mm in length, 6 mm in outer diameter and 3 mm in inner diameter, were prepared by the addition of sintered porous beta-Ca2P2O7 with 5 wt% Na4P2O7.10H2O. In the first group, the chambers impregnated with autogenous bone fragments and allogenous demineralized bone matrix with volume ratio 1:1 were cultured in the rabbit's groin area with saphenous vessels passing through. In the second group, the chambers were treated by the same procedures as the first group but without saphenous vessels passing through. In the third group, the chambers were not impregnated, and were cultured in the groin area with saphenous vessels. After 2, 4, 6, 8 and 12 wk of operation, the animals were killed with an overdose of intravenous pentobarbital. The viability of the osseous tissue in the chamber was evaluated by histological examination, microangiograms and fluorochrome incorporation for the three groups. The autogenous bone chips could survive and retain their osteogenic properties while packed into the sintered porous beta-Ca2P2O7 (with 5 wt% Na4P2O7.10H2O addition) ceramic chamber and implanted in the rabbit groin area up to 12wk. However, even at the longest time periods, considerable amounts of dead bone were present in the chambers. In addition, we observed bone resorption in the three groups up to 12 wk, which might be attributed to lack of physiological stress. There were significant differences in new bone formation and osseous cell viability among the three groups. The prevascularized vessels and autogenous bone chips were both necessary for the formation of new bone and osteogenic property in the chamber under these heterotopic circumstances. The biodegradable ceramic used in this study was gradually absorbed and dissolved in the physiological environment. However, the degradation debris of the ceramic caused no injury to the new bone formation. These findings support the concept of creating a preformed vascularized bone graft to reconstruct segmental bone defects.