Hydrogel: synthesis, physicochemical properties, and medical uses.

INTRODUCTION OR BACKGROUND: Hydrogels are three-dimensional polymeric networks capable of absorbing substantial amounts of water while maintaining structural stability. In the biomedical field, hydrogels are widely used because of their high water content, flexibility, and the ability to be chemically modified for diverse applications. Their biocompatibility, biodegradability, porosity, and environmental sensitivity enable them to mimic the extracellular matrix, supporting cell growth and tissue regeneration. SOURCES OF DATA: This review integrates information from existing studies, classifying hydrogels based on their molecular origin, and analyses various reports on their synthesis methods, mechanical properties, and biomedical applications. AREAS OF AGREEMENT: Hydrogels (natural, synthetic, and hybrid) exhibit different mechanical properties, bioactivity levels, and degradation patterns. Functional hydrogels with self-healing, injectable, and stimulus-responsive properties have significantly improved drug delivery and therapeutic performance. AREAS OF CONTROVERSY: Although a standardized framework to evaluate different hydrogel types exists, it remains incomplete. The lack of universally accepted classification criteria and inconsistencies in performance evaluation across studies continue to pose challenges the field. GROWING POINTS: Recent advances in molecular design have led to produce protein/peptide-based, polysaccharide-based, DNA-based, and synthetic hydrogels. These developments highlight the growing importance of integrating molecular-level design with application-driven functionalities. AREAS TIMELY FOR DEVELOPING RESEARCH: Future research should focus on refining hydrogel classification systems, standardizing evaluation methodologies, and exploring multifunctional, responsive hydrogel systems tailored to advanced biomedical applications such as precision drug delivery, tissue engineering, and regenerative medicine.