crosslinking

Crosslinking is the process of connecting individual polymer chains or molecular strands to form a three-dimensional network. This connection can be covalent, yielding durable, permanently bound networks, or noncovalent, resulting in more flexible or reversible structures. The density of crosslinks—how many connections exist per chain—controls the physical properties of the material, including stiffness, elasticity, thermal stability, and swelling behavior.

In synthetic polymers and materials science, crosslinking creates networks known as thermosets and gels. Chemical crosslinking uses multifunctional reagents that bridge chains, such as diamines or diepoxides; radiation-induced crosslinking uses ionizing radiation to generate bonds without added chemicals; enzymatic crosslinking uses enzymes to form bonds between specific amino or other functional groups. Noncovalent crosslinking relies on hydrogen bonding, ionic interactions, or metal coordination and can yield reversible networks. The choice of method and crosslink density affects mechanical strength, chemical resistance, permeability, and degradability, with applications ranging from hydrogels for contact lenses or drug delivery to structural polymers and elastomers.

In biology and medicine, crosslinking plays essential roles in tissue structure and function. Enzymes such as lysyl oxidase form covalent crosslinks in collagen and elastin, enhancing extracellular matrix stiffness. Crosslinking is also used in sample preparation and imaging to stabilize biological structures. DNA can suffer interstrand crosslinks from certain chemicals or drugs, which block replication and transcription and are exploited in chemotherapy.

In biotechnology and engineering, crosslinked hydrogels are used for wound dressings, tissue engineering scaffolds, and controlled-release systems. Crosslink density and the nature of the crosslinks determine swelling, porosity, diffusion of solutes, and the material’s response to stimuli.