Crosslink

Crosslink is a term used in chemistry, materials science, and biology to describe a bond or linkage that connects two molecular chains or network nodes, integrating them into a larger, interconnected structure. The concept is central to the formation of polymer networks, gels, and composite materials, where the presence and density of crosslinks determine mechanical properties, stability, and behavior under stress or solvent exposure.

In polymer chemistry, crosslinking links polymer chains to form three-dimensional networks. This generally increases rigidity, thermal and chemical resistance, and reduces solubility and swelling. Crosslinks can be covalent bonds formed by bifunctional or multifunctional reagents, or they can arise from ionic or noncovalent interactions such as hydrogen bonding. Common methods include chemical crosslinking with reagents like glutaraldehyde or carbodiimides, UV or heat-induced radical crosslinking, ionic crosslinking (for example Ca2+ with alginate), and enzymatic crosslinking using transglutaminase. In hydrogels, the balance between permanent and reversible crosslinks controls viscoelastic properties, swelling behavior, and degradation rates.

In biology and biochemistry, crosslinking stabilizes protein complexes or cellular structures for analysis. Chemical crosslinkers fix interactions for microscopy or mass spectrometry, and crosslinking mass spectrometry helps map proximities within and between proteins. In chromatin studies, formaldehyde crosslinking links DNA to associated proteins to enable techniques such as ChIP and chromosome conformation capture.

In industry and materials engineering, crosslink density is a key parameter that governs performance in rubbers, plastics, coatings, and composites. Dynamic or reversible crosslinks can impart reprocessability and self-healing, while permanent crosslinks yield rigid, heat-resistant materials.