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The crosslinks which bond the polymers of a hydrogel fall under two general categories: physical hydrogels and chemical hydrogels. Chemical hydrogels have covalent cross-linking bonds, whereas physical hydrogels have non-covalent bonds.
Crosslinking is the process of joining two or more polymer chains. Both chemical and physical crosslinking exists. In addition, both natural polymers such as proteins or synthetic polymers with a high affinity for water may be used as starting materials when selecting a hydrogel. [1]
Similar to physical solidification, some chemical crosslinking methods have been developed to produce hydrogel fibers. And the key for the achievement of hydrogel production through the chemical crosslinking method is the effective separation between the formed network and the tube wall.
In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.
Hirst et al. [22] showed that the solubility of the gelators in media can be modified by tuning the peripheral protecting groups of the gelators, which in turn controls the gel point and the concentrations at which crosslinking takes place (See Table 2 for data). Gelators that have higher solubility in medium show less preference for crosslinking.
Gelation can occur either by physical linking or by chemical crosslinking. While the physical gels involve physical bonds, chemical gelation involves covalent bonds. The first quantitative theories of chemical gelation were formulated in the 1940s by Flory and Stockmayer. Critical percolation theory was successfully applied to gelation in 1970s.
A wide range of nanoparticles, such as carbon-based, polymeric, ceramic, and metallic nanomaterials can be incorporated within the hydrogel structure to obtain nanocomposites with tailored functionality. Nanocomposite hydrogels can be engineered to possess superior physical, chemical, electrical, thermal, and biological properties. [23] [26]
Poly(2-hydroxyethyl methacrylate) (pHEMA) is a polymer that forms a hydrogel in water. Poly (hydroxyethyl methacrylate) (PHEMA) hydrogel for intraocular lens (IOL) materials was synthesized by solution polymerization using 2-hydroxyethyl methacrylate as raw material, ammonium persulfate and sodium pyrosulfite (APS/SMBS) as catalyst, and triethyleneglycol dimethacrylate (TEGDMA) as cross ...