Hydrogels: sources and applications-an overview
Hydrogels are crosslinked three-dimensional polymer network materials with hydrophilic structures that can absorb and retain large amounts of water and/or biological fluids without dissolving, owing to the physical and chemical nature of their crosslinks. They play significant roles in various industrial and environmental applications. In many applications, natural hydrogels have gradually been replaced by synthetic hydrogels because of their superior water absorption capacity, longer lifetime, and diverse sources of raw chemical materials. The main functions of hydrogels are important and diverse, including high water absorption and retention, controlled drug delivery, biocompatibility, soft-tissue-mimicking behavior, swelling and deswelling ability, selective permeability, mechanical support, and environmental remediation. Hydrogels are commonly classified according to their origin, composition, crosslinking type, responsiveness, and structure. They have different applications, particularly in biomedical and healthcare fields, hygiene and personal care products, industrial and engineering applications, agriculture, environmental remediation, and nanotechnology. The literature on hydrogels has expanded considerably, especially in scientific research fields. Therefore, this review examines various publications and technical reports focusing on hydrogel products from an engineering perspective to summarize the technological dimensions of this rapidly advancing multidisciplinary research field. This review aims to summarize and evaluate the preparation, classification, and recent applications of hydrogels, emphasizing their transition from simple water absorbing materials to tailored smart systems. It also highlights the relationship between structural design and functional performance in different sectors, such as drug delivery, wound healing, oil-water separation, and agricultural water management. Finally, the review addresses current challenges and proposes future research directions to improve hydrogel stability, responsiveness, and biocompatibility.