Evaluation of bone allograft processing methods: Impact on decellularization efficacy, biocompatibility and mesenchymal stem cell functionality

In an ever-aging society the demand for bone-defect filling grafts continues to gain in importance. While autologous grafting still prevails as the gold standard, allografts and xenografts present viable alternatives with promising results. Physiochemical properties of a graft strongly depend on the processing method such as the decellularization protocol. In addition, the physiochemical characteristics are critical factors for a successful integration of the graft after the implantation and might influence mesenchymal stem cell function in therapeutic approaches combining grafts and autologous mesenchymal stem cells (MSCs). Several decellularization methods have been proposed, however it still remains unclear which method results in favorable physiochemical properties or might be preferred in stem cell applications. In the first part of this study we compared two decellularization approaches resulting in chemically processed allografts (CPAs) or sonication-based processed allografts (SPAs). Each decellularization approach was compared for its decellularization efficacy and its influence on the grafts’ surface texture and composition. In the second part of this study biocompatibility of grafts was assessed by testing the effect of extraction medium on MSC viability and comparing them to commercially available allografts and xenografts. Additionally, grafts’ performance in terms of MSC functionality was assessed by reseeding with MSCs pre-differentiated in osteogenic medium and determining cell adhesion, proliferation, as well as alkaline phosphatase (ALP) activity and the degree of mineralization. In summary, results indicate a more effective decellularization for the SPA approach in comparison to the CPA approach. Even though SPA extracts induced a decrease in MSC viability, MSC performance after reseeding was comparable to commercially available grafts based on DNA quantification, alkaline phosphatase activity and quantification of mineralization. Commercial Tutoplast allografts showed overall the best effects on MSC functionality as indicated by extraction biocompatibility testing as well as by comparing proliferation and osteogenic differentiation.