Hydrogel is a polymer that carries a high content of water and at the same time is not soluble in water. As a polymer, the substance consists of macromolecules in a three-dimensional network that swell in contact with a solvent while still maintaining cohesion. Hydrogel plays a role in medical technology for wound dressings, lenses and implants.
What is hydrogel?
Due to their biocompatibility and tissue-like mechanical properties, hydrogels are ideal for drug delivery and wound care. Hydrogel is a polymer that contains water and is also water-insoluble. Hydrogel molecules are chemically linked to form three-dimensional networks, for example by ionic or covalent bonds. They can also be physically linked to form a network, for example by entanglement of polymer chains. In water, they swell due to an incorporated and hydrophilic polymer component and thus obtain a high increase in volume. The material cohesion remains unchanged. Hydrogels play a role in a considerable number of biotechnological developments, for example in the form of contact lenses. Their biocompatibility and tissue-like mechanical properties also make them ideal for drug delivery and wound care. In medicine, for example, the term hydrogels also refers to a wound dressing made of gels that have a high water content. The aqueous gels liquefy under the action of mechanical forces. In the meaning of wound dressings, hydrogels are also called hydrophilic gels. In this context, hydrogel should be distinguished from hydrocolloid dressing, which has a matrix of swelling agents.
Forms, types and kinds
A wide variety of types and uses exist of hydrogels. “Smart hydrogels,” for example, are swelling molecular networks that become a gel in solvent and can perform mechanical work through their swelling power. Smart behavior of this type is exhibited only by certain polymer networks that can respond selectively to a gradient of physical environmental variables. Sensitivities can be achieved to temperature, pH, or ion and substance concentration. Other applications of hydrogels in medical technology include soft contact lenses, intraocular lenses and plastic implants. These substances correspond to disperse systems and consist of at least two components. Usually, one of the components is a solid substance such as gelling agents or thickeners. The second component usually corresponds to water, which is used as a dispersant.
Structure and mode of operation
The hydrogel is a gelled liquid, i.e., a gel produced in contact with a suitable swelling agent,l such as cellulose derivative. Unlike oleogels, all hydrogels have a high water content. As a rule, the total water content is between 80 and 90 percent. Hydrogel is normally fat-free and has water-insoluble properties. It is a polymer, i.e. a chemical substance consisting of macromolecules. These macromolecules are made up of a certain number of structural units, also known as constitutional repeating units. The adjective “polymer” literally means “built up from equal parts.” The molecules of a polymer do not have to be identical. Polymer also exists in physiology. These are intracellularly synthesized substances that serve as energy stores in the form of proteins, nucleic acids or similar substances. They fulfill structural cell functions and are also active in metabolism, recognize states and can bring about changes. As biopolymers, polymers are essential for life itself. However, this type of polymer must be distinguished from the artificially synthesized hydrogel. In the hydrogel, the macromolecules are linked by ionic or covalent bonds into a three-dimensional network. Physically, they are entangled to form a network of polymer chains. Due to the polymer components with hydrophilic properties they contain, they usually swell in the presence of water to a considerable increase in volume without losing their cohesion in the network. Medical grade hydrogels are biocompatible and exhibit mechanical properties reminiscent of tissue.
Medical and health benefits
Hydrogels are used to administer locally applied agents, are relevant to implantation techniques, and are used to treat dry wounds or rheumatic lesions. As wound dressings, hydrogels have a cooling effect. In addition, due to the evaporation of water, they exhibit hydrating effects for a short time and at the same time have a drying effect in the long term. Hydrogel wound dressings are not re-lubricating. They may contain an active ingredient and are used in this form to administer certain medications to treat diseases locally. Cooling and drying are desirable, for example, in the context of insect bites, sunburn, sports injuries, rheumatism, and nighttime calf cramps. Hydrogels are now also used in the treatment of various skin diseases. In turn, hydrogels without active ingredients are used for moist wound care and, in this context, are primarily used to keep wounds moist. Such moisturization takes place in the context of dry necroses, but can also support the healing of simple wounds within the granulation or epithelization phase. The gel can either be applied on its own or placed completed under a wound dressing. However, the importance of hydrogels within medicine is not only relevant to wound care. Hydrogels have enabled the invention of soft contact lenses and intraocular lenses, which have been in use since the last century. They have also supported advances in implantation technology. Plastic implants are applied by plastic surgeons to replace damaged or fully destroyed body parts and can also serve to augment existing body parts, such as breast implants for breast augmentation.
