A Processing Approach to Tuning the Drug Delivery Characteristics of Calcium Polyphosphate Matrices

Abstract

Amorphous calcium polyphosphate (CPP) has potential as an implantable drug delivery matrix by virtue of a low temperature gelling protocol that has been shown to eliminate burst release and extend drug release time from the matrix. However, a greater understanding of this material’s interaction with aqueous environments is needed to more fully exploit this application. Variations in aqueous exposure were assessed using as-made amorphous CPP as well as CPP processed using established low temperature protocols. Solid-state 31P-NMR along with thermal and X-ray diffraction analyses were used to track resulting structural changes. Exposure to aqueous environments caused a reduction in CPP chain length that was dependant on gel time and mode of exposure. Significantly, increased gel times or water availability further resulted in crystallization events upon drying, except in the presence of a buffered solution. In general, drug elution studies showed an increase in the burst release of vancomycin from CPP disks gelled for extended periods, with matrix-water interactions appearing to be most influential during the drug loading stage. Overall, this study shows that CPP drug delivery matrices can be produced with tailored properties by closely controlling CPP-water interactions during processing.