Injectable Hydrogels as Three-Dimensional Network Reservoirs for Osteoporosis Treatment

Despite tremendous progresses made in the field of tissue engineering over the past several decades, it remains a significant challenge for the treatment of osteoporosis (OP) due to the lack of appropriate carriers to improve the bioavailability of therapeutic agents and the unavailability of artificial bone matrix with desired properties for the replacement of damaged bone regions. Encouragingly, the development of injectable hydrogels for the treatment of OP has attracted increasing attention in recent years because they can serve either as a reservoir for various therapeutic species or as a perfect filler for bone injuries with irregular shapes. However, the relationship between the complicated pathological mechanism of OP and the properties of diverse polymeric materials lacks elucidation, which clearly hampers the clinical application of injectable hydrogels for the efficient treatment of OP. To clarify this relationship, this article summarized both localized and systematic treatment of OP using an injectable hydrogel-based strategy. Specifically, the pathogenesis of OP and the limitations of current treatment approaches were first analyzed. We further focused on the use of hydrogels loaded with various therapeutic substances following a classification standard of the encapsulated cargoes for OP treatment with an emphasis on the application and precautions of each category. A concluding remark on existing challenges and future directions of this rapidly developing research area was finally made. Impact statement Effective osteoporosis (OP) treatment remains a significant challenge due substantially to the unavailability of appropriate drug carriers and artificial matrices with desired properties to promote bone repair and replace damaged regions. For this purpose, this review focused on the development of diverse injectable hydrogel systems for the delivery of various therapeutic agents, including drugs, stem cells, and nucleic acids, for effective increase in bone mass and favorable osteogenesis. The summarized important guidelines are believed to promote clinical development and translation of hydrogels for the efficient treatment of OP and OP-related bone damages toward improved life quality of millions of patients.