Crosslinking-controlled biopolymer biomaterials for tissue engineering and regenerative medicine: network chemistry, processing, and mechanistically informed validation

Crosslinking is often treated as a technical step used to stabilize biopolymer scaffolds, yet in regenerative biomaterials it is a primary design variable that simultaneously controls network mechanics, viscoelasticity, swelling, molecular transport, degradation, ligand accessibility, and cell-material interactions. This Review examines crosslinked biopolymer biomaterials for tissue engineering and regenerative medicine through that network-centered perspective. Collagen and gelatin, hyaluronic acid, silk fibroin, chitosan, alginate, fibrin, and related matrices are considered with emphasis on how covalent, photoinduced, enzymatic, ionic, physical, and dynamic covalent crosslinking generate distinct biological microenvironments. We analyze how crosslinking is coupled to processing routes including extrusion bioprinting, electrospinning, freeze-drying, injectable hydrogel formation, and porous-scaffold fabrication, and why the timing of network formation can be as important as nominal polymer composition. We propose a mechanistically informed evidence chain connecting material definition to hydrated-state properties, cellular response, ex vivo or in vivo behavior, and tissue-specific regenerative outcomes. Particular attention is given to quantitative network characterization, reproducibility, sterilization, storage, aging-related property drift, and controls needed to distinguish genuine network effects from formulation confounders. Clinical trials, patient data, patent landscapes, regulatory pathways, commercialization, and product-development strategies are intentionally excluded. Crosslinking should be designed and reported as a multidimensional regulator of the regenerative microenvironment rather than as a single measure of scaffold stability.