Current State of DBM

Since 2005, demineralized bone matrices (DBMs) are subject to the 510(k) premarket approval process, during which they must demonstrate the potential to induce bone formation. However, differences between lots of DBM from the same supplier can be significant, and the manner in which producers test each lot to ensure some degree of osteoinductivity varies considerably. Some companies rely on in vivo assays, and others use in vitro assays of biomarkers as a surrogate. In addition, some producers of DBM might test it after acid removal and early processing, but others might perform terminal product testing after the addition of a carrier and final aseptic processing or sterilization. How well in vitro assays correlate with established animal models is a topic of debate in the literature, and no generally accepted in vitro assay is currently available. In hopes of eliminating the need for animal testing, our research group demonstrated that mesenchymal stem cell (MSCs) can be used to determine which bone graft extenders induced markers for bone formation.1 However, we found this approach potentially problematic for two reasons: (A) some products tend to dissolve so quickly in culture that MSCs have little surface area to which to adhere, and (B) some DBM formulations and nonorganic carriers are so basic or acidic that they are cytotoxic and kill the MSCs (Figure 1). Buffering has not proved helpful for the most basic products (bioactive glass). This work shows that surgeons should be conscious of pH issues because placing cells from autograft or bone marrow aspirate in contact with products that do not have a near physiologic pH on the “back table” for long periods might lead to cell death.Figure 1: Average pH value of substrates buffered in human plasma over 48 hours, with pH after buffering in phosphate-buffered saline shown in parentheses.The rat muscle pouch continues to be the preferred method of documenting osteoinductivity, and standardized methods have been described (ASTM 2529-13). It makes the most sense to perform the test on the final product of each lot of DBM, as it would be done clinically, as this is the only way to account for all variables in the manufacturing process. Although this does not guarantee clinical success, it is the most pragmatic way to ensure that each lot has the potential to induce bone formation after final processing.

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