Polymeric crystallization and condensation of calcium polyphosphate glass

Calcium polyphosphate (Ca(PO3)2)n (CPP) is under investigation as a resorbable bone biomaterial. Sintering CPP glass particles in humid air produces a porous, interconnected, degradable, crystalline construct that is suitable for connective tissue engineering applications. Porous CPP constructs sintered at 585 °C dissolved in water more rapidly than those sintered at 950 °C. FTIR, 31P NMR, powder XRD, and density data for CPP glass and fully crystalline fibers were compared with data for the as-sintered and partially dissolved constructs sintered at 585 or 950 °C. The results suggest that condensation continues during sintering, and CPP glass crystallizes in a process analogous to the crystallization of linear organic polymers. During sintering, water vapor caused hydrolytic degradation of the surface polyphosphate chains, forming a surface layer with different dissolution properties than the particle interior. Thus, sintering CPP glass results in a heterogeneous crystalline product that impacts the dissolution rate of CPP as a degradable biomaterial.