Gels or gelators are jelly-like substances that can be soft and weak or strong and hard in composition, while displaying a degree of elasticity. If the surface of a gel is slightly displaced, it will spring back to its original position. Gels can be man-made but also occur naturally, such as the enzymatic gel that covers the skin of the long-finned pilot whale, protecting it from organisms creating colonies on its surface.
Because hydrogels have a degree of flexibility similar to natural tissue, they are often used as scaffolds in tissue engineering and may contain human cells in order to repair tissue. Hydrogels consist of more than 99 percent of water and are superabsorbent. The practical uses of hydrogels include breast implants, granules for holding soil moisture in arid areas and dressings for burns and hard-to-heal wounds.
Organogels or organic gelulators are noncrystalline, nonglassy, thermoplastic solid materials composed of a liquid organic phase entrapped in a three-dimensionally, cross-linked network. Organogels are frequently found in food processing, pharmaceuticals and cosmetics.
Xerogels are solids formed from gels that do not suffer from shrinkage in the process. Xerogels generally retain a high degree of porosity. Rubber and gelatin are examples of xerogels.
Aerogels are low-density materials created when the liquid component of a gel has been replaced by nitrogen or air. This results in very low density solids that are highly effective as thermal insulators. Aerogels are used as vehicles for drug prophylaxis.