Effect of demineralized bone powder on osteoblast-like cells in culture. A potential rapid quality control assay

Delivery of demineralized bone matrix powder using a thermogelling chitosan carrier

Demineralized bone matrix (DBM) powder is widely used for bone regeneration due to its osteoinductivity and osteoconductivity. However, difficulties with handling, its tendency to migrate from graft sites, and lack of stability after surgery can sometimes limit the clinical utility of this material. In this work, the possibility of using a thermogelling chitosan carrier to deliver DBM powder was assessed. The DBM-thermogelling putty improved handling and formed a gel-like composite in situ at body temperature within a clinically relevant time period. The properties of the formed composite, including morphology, porosity, mechanical properties, equilibrium swelling as well as degradability, are significantly influenced by the ratio of DBM to thermogelling chitosan. The in vitro study showed that the alkaline phosphatase activity of C2C12 cells encapsulated in the composite was steadily increased with culture time. The in vivo study showed that increased DBM content in the DBM-thermogelling chitosan induced ectopic bone formation in a nude rat model. The diffusion of growth factor from the DBM-thermogelling chitosan as well as the host-implant interactions are discussed.

A review of osteoinductive testing methods and sterilization processes for demineralized bone

Allogeneic demineralized bone has been used extensively as a clinical graft material because it has osteoinductive and osteoconductive properties. Concerns over processing and terminal sterilization procedures that may reduce performance have led clinicians to call for assurances of product potency. There is extensive experience on effects of demineralized bone in animal and cell culture models with the possibility for future evidence-based standards for release of products. Evaluation of the current state of knowledge leads to the fact that we cannot conclude that performance of different lots of demineralized bone allografts in in vivo or in vitro test systems can be used as a measure of clinical performance. It may be possible to adopt an osteoinductivity standard for release-to-market, but it should be followed by clinical monitoring and further research.

Rapid quantitative bioassay of osteoinduction

We developed a reproducible, relatively rapid bioassay that quantitatively correlates with the osteoinductive capacity of demineralized bone matrix obtained from human long bones. We have found that Saos human osteosarcoma cells proliferate in response to incubation with demineralized bone matrix and that an index of this proliferative activity correlates with demineralized bone matrix-induced osteogenesis in vivo. The bioassay (Saos cell proliferation) had an interassay coefficient of variation of 23 +/- 2% and an intra-assay coefficient of 11 +/- 1%. Cell proliferation was normalized to a standard sample of demineralized bone matrix with a clinically high osteoinductive capacity, which was assigned a value of one. The Saos cell proliferation for each sample was related to the standard and assigned a value placing it into the low (0.00-0.39), intermediate (0.40-0.69), or high (0.70-1.49) osteoinductive index group. Osteoinduction of human demineralized bone matrix was quantitated by expressing new bone formation as a function of the total bone volume (new bone plus the demineralized bone powder). The demineralized bone matrix was placed in pouches formed in the rectus abdominis muscles of athymic rats, and endochondral bone formation was assessed at 35 days following implantation, when marrow spaces in the ossicles were formed by new bone bridging the spaces between demineralized bone matrix particles. The proliferative index correlated with the area of new bone formation in histological sections of the newly formed ossicles. When the proliferative index (the osteoinductive index) was divided into low, intermediate, and high groups, the correlation between it and new bone formation (osteoinduction) was 0.850 (p < 0.0005) in 25 samples of demineralized bone matrix. There was no overlap in the osteoinduction stimulated between the samples with low and high osteoinductive indices. We conclude that the proliferation assay is useful for the routine screening of bone allograft donors for osteoinductive potential. Furthermore, the two-dimensional area of new bone formation, as it relates to total new bone area, is a quantitative measure of osteoinduction.

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.

Cellular reactions to bone-derived material

Demineralized bone has been used as an acceptable alternative to fresh autogenous bone grafting in a variety of clinical reconstructive procedures. With the recent expansion of regional and national tissue banks, more implants are being used in routine applications. Questions raised about the bioactivity of human demineralized bone may be resolved by development of relevant assays for screening a lot of banked tissue. Such a bioassay could be developed based on the effects of osteoinductive materials on cells in vitro. Various effects of culture with demineralized bone or its components have been reported for cell lines or embryonic, fetal, or neonatal rodent and chick tissues and cells. In this study, human dermal fibroblasts and a variety of other cell types expressed features of chondroblastic phenotype when cultured with demineralized bone powder.