Polymer-calcium phosphate composites for use as an injectable bone substitute

Medical procedures to address bone related injury are prevalent in the United States, with around 900,000 hospitalizations due to fractures and over 800,000 grafting procedures annually. Calcium phosphates (CPs) are particularly promising as bone substitute materials, due to their similarity to hydroxyapatite, the mineral component of bone. In addition to being non-toxic, they are biocompatible, not recognized as foreign in the body, and most importantly, exhibit bioactive behavior. CPs are integrated into bone tissue by the same ongoing processes active in remodeling healthy bone, through the resorption and deposition of bone mineral. This leads to an intimate physicochemical bond between CP implants and bone, termed osseointegration. CPs are also known to support osteoblast adhesion and proliferation. This unique bioactivity is highly desirable and hence CP compounds are widely studied and used as bone replacements or as coatings on implants. However, the inability to sculpt the bulk materials to conform to irregular defects and the possibility of the granules migrating from the implant site has resulted in the formulation of self-setting calcium phosphate cements (CPCs).