The present invention provides compositions and methods for providing controllable local delivery of a therapeutic agent to promote bone formation. In certain embodiments, the invention is used as a treatment for a subject with osteoporosis, bone cancer or bone fracture. The invention provides a therapeutic agent that is tethered to a polymer to form a therapeutic-tethered macromer, where the therapeutic agent is controllably released from the conjugate by degradation of the tether. In certain embodiments, the therapeutic agent is an inhibitor of GSK3β. In certain embodiments, the composition of the invention is specifically targeted to a site in need of bone formation.