Human osteoclast formation and resorptive function on biomineralized collagen

Resorption was observed by SEM, and quantified by measuring resorbed area and volume by optical profilometry, as well as by quantification of Ca2+ concentration in cell culture supernatant. Osteoclasts readily formed resorption pits in cortical bone, resulting in higher Ca2+ concentration in the cell culture medium; however, osteoclast resorption of biomineralized collagen and collagen substrates did not measurably occur.

Activity of key osteoclast enzymes – TRAP, CA-II, and CTS-K – was similar on all substrates, despite phenotypic differences in actin ring formation and functional resorption. Key material property differences may have prevented formation of stable actin rings and resorption, specifically the mesh-like fibrillary structure, relatively low stiffness, and lack of RGD-containing binding domains of the collagen-based membranes versus cortical bone.

This insight can help guide further research toward the optimized design of biomineralized collagen composites as more biomimetic bone-graft substitutes – particularly if they can be readily resorbed by osteoclasts and remodeled into new bone.