Hydrogeler

Hydrogels are three-dimensional, hydrophilic polymer networks that can absorb and retain substantial quantities of water while maintaining structure. They can be derived from natural polymers such as alginate, gelatin, chitosan, or cellulose derivatives, or from synthetic polymers such as polyacrylamide, polyethylene glycol (PEG), polyvinyl alcohol, or poly(N-isopropylacrylamide). Because of their high water content and soft, elastic properties, hydrogels resemble biological tissues and are often biocompatible, making them suitable for medical and biosensing applications.

The networks are held together by crosslinks, which may be covalent (chemical crosslinking) or noncovalent/physical (ionic interactions, hydrogen bonding, crystallization). Hydrogels readily swell in water; the degree of swelling is governed by the balance between osmotic driving forces and the elastic constraint of the network, as well as by environmental conditions such as pH, temperature, and ionic strength. They are typically permeable to solutes and can be engineered to control diffusion of drugs or nutrients.

Classification can be by source (natural versus synthetic), by crosslinking mechanism (chemical, physical, or dual), or by responsiveness to stimuli. Stimuli-responsive or "smart" hydrogels alter their swelling or mechanical properties in response to changes in temperature, pH, light, electric or magnetic fields, or enzymes.

Applications span biomedicine (drug delivery, tissue engineering scaffolds, wound dressings, contact lenses), agriculture (soil moisture management), and environmental engineering (water purification, sensors). While hydrogels offer many advantages, challenges remain in mechanical strength, long-term stability, sterilization, and ensuring biocompatibility of additives or crosslinkers.