A compaction route for low temperature processing of porous calcium polyphosphate matrices

Porous condensed calcium phosphate matrices intended for skeletal tissue engineering applications are currently produced using high temperature processing methods that may ultimately limit their versatility in these applications. The aim of this study was to investigate a compaction route in conjunction with controlled water uptake for obtaining these porous matrices at ambient temperature. Here, cold isostatic pressing (CIP) and uniaxial compression ("pelleting") strategies were evaluated using a range of amorphous and crystalline calcium polyphosphate (CPP) panicle sizes. Compaction procedures were supplemented by addition of controlled volumes of water prior to compaction, or exposure of the pre-compacted matrix to a high humidity environment. These initial studies demonstrate that CPP compacts strong enough for handling and shaping can be produced from amorphous powders provided water is introduced directly or atmospherically during processing, with tensile strengths approaching 6 MPa for higher density (∼80%) compacts. Additional studies are required to optimize these processing conditions while also assessing the resulting degradation properties of these matrices. Ultimately, this processing strategy may enable physical incorporation and subsequent local delivery of putative biological agents required for effective bone regenerative therapy.