Hydrogels for in vivo biomedical applications: recent advances and future perspectives

Hydrogels are water-rich, three-dimensional polymeric networks that closely mimic the physical and mechanical properties of native tissues, making them highly suitable for biomedical applications. Among these, in vivo applications are particularly significant, as they involve direct interactions with the internal physiological environment to support diagnosis, therapy, and tissue regeneration. Given the rapid advancements and growing complexity of in vivo hydrogel technologies, a comprehensive and up-to-date overview is needed to contextualize current progress and guide future research. This review begins by introducing the hydrogel selection and key properties of medical-grade hydrogels, including their mechanical performance, biocompatibility, and responsiveness. We then examine recent advances in in vivo applications, with an emphasis on 3D bioprinted hydrogels for tissue reconstruction, hydrogel-based implantable electronics for sensing and stimulation, implantable hydrogel adhesives, and hydrogel systems for wound healing and regenerative therapies, such as cartilage repair and neural regeneration. We also highlight hydrogel platforms for drug delivery and microneedle-based systems designed for biosensing and controlled therapeutic release. Throughout this discussion, we analyze the material properties and performance requirements specific to each in vivo use case. Finally, we outline key challenges such as immune compatibility, mechanical stability, and long-term functionality, and provide perspectives on strategies to accelerate clinical translation and enhance the functional versatility of hydrogel technologies. This review aims to offer valuable insights and inspiration for researchers seeking to advance the development of hydrogel-based in vivo biomedical applications.