The invention is directed toward porous composites for application to a bone defect site to promote new bone growth. The inventive porous composites comprise a biocompatible polymer and a plurality of particles of bone-derived material, inorganic material, bone substitute material or composite material. In certain embodiments, the porous composites are prepared using a method that includes a supercritical fluid (e.g., supercritical carbon dioxide) treatment. The invention also discloses methods of using these composites as bone void fillers.