A hydrogel is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. A three-dimensional solid results from the hydrophilic polymer chains being held together by cross-links.[clarification needed] Because of the inherent cross-links, the structural integrity of the hydrogel network does not dissolve from the high concentration of water. Hydrogels are highly absorbent (they can contain over 90% water) natural or synthetic polymeric networks.
Common uses include:
- Scaffolds in tissue engineering. When used as scaffolds, hydrogels may contain human cells to repair tissue. They mimic 3D microenvironment of cells.
- Hydrogel-coated wells have been used for cell culture
- Environmentally sensitive hydrogels (also known as 'Smart Gels' or 'Intelligent Gels'). These hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change.
- Injectable hydrogels which can be used as drug carriers for treatment of diseases or as cell carriers for regenerative purposes or tissue engineering.
- Sustained-release drug delivery systems. Ionic strength, pH and temperature can be used as a triggering factor to control the release of the drug.
- Providing absorption, desloughing and debriding of necrotic and fibrotic tissue
- Hydrogels that are responsive to specific molecules, such as glucose or antigens, can be used as biosensors, as well as in DDS.
- Disposable diapers where they absorb urine, or in sanitary napkins
- Contact lenses (silicone hydrogels, polyacrylamides, polymacon)
- EEG and ECG medical electrodes using hydrogels composed of cross-linked polymers (polyethylene oxide, polyAMPS and polyvinylpyrrolidone)
- Water gel explosives
- Rectal drug delivery and diagnosis
- Encapsulation of quantum dots
- Breast implants
- Granules for holding soil moisture in arid areas
- Dressings for healing of burn or other hard-to-heal wounds. Wound gels are excellent for helping to create or maintain a moist environment.
- Reservoirs in topical drug delivery; particularly ionic drugs, delivered by iontophoresis (see ion exchange resin).
- Materials mimicking animal mucosal tissues to be used for testing mucoadhesive properties of drug delivery systems
Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content. As responsive "smart materials," hydrogels can encapsulate chemical systems which upon stimulation by external factors such as a change of pH may cause specific compounds such as glucose to be liberated to the environment, in most cases by a gel-sol transition to the liquid state. Chemomechanical polymers are mostly also hydrogels, which upon stimulation change their volume and can serve as actuators or sensors.
A short-peptide-based hydrogel matrix, capable of holding about one hundred times its own weight in water. Developed as a medical dressing. The thickness of the fibers was on the order of tens of nm, mimicking the fibrous microenvironment found in the extracellular matrix. Field emission scanning electron microscopy image
Natural hydrogel materials are being investigated for tissue engineering; these materials include agarose, methylcellulose, hyaluronan, Elastin like polypeptides and other naturally derived polymers. Hydrogels show promise for use in agriculture, as they can release agrochemicals including pesticides and phosphate fertiliser slowly, increasing efficacy and reducing runoff, and at the same time improve the water retention of drier soils such as sandy loams.
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