Provided herein are polymer-stabilized CaP nanoparticle formulations and related methods of manufacture. In certain embodiments, the methods reliably and selectively form nanoparticles with homogenous size, charge, and morphology. The CaP nanoparticles include calcium ions and phosphate ions with an ionic polymer, thereby forming stable hybrid nanoparticles. The CaP nanoparticle formulations include powders, suspensions and injectable pastes. According to various embodiments, the polymer-stabilized CaP nanoparticles may be polycation-stabilized (CaP/polymer(+) nanoparticles) or polyanion-stabilized (CaP/polymer(-) nanoparticles). The CaP/polymer nanoparticles can be freeze-dried and stored for months with no loss of properties or changes to their morphology.