Current and Future Prospective of Injectable Hydrogels—Design Challenges and Limitations

Injectable hydrogels (IHs) are smart biomaterials and are the most widely investigated and versatile technologies, which can be either implanted or inserted into living bodies with minimal invasion. Their unique features, tunable structure and stimuli-responsive biodegradation properties make these IHs promising in many biomedical applications, including tissue engineering, regenerative medicines, implants, drug/protein/gene delivery, cancer treatment, aesthetic corrections and spinal fusions. In this review, we comprehensively analyze the current development of several important types of IHs, including all those that have received FDA approval, are under clinical trials or are available commercially on the market. We also analyze the structural chemistry, synthesis, bonding, chemical/physical crosslinking and responsive release in association with current prospective research. Finally, we also review IHs' associated future prospects, hurdles, limitations and challenges in their development, fabrication, synthesis, in situ applications and regulatory affairs.