Thiolated Polymers in 3D Bioprinting: Control of Gelation

Thiolated polymers represent a versatile class of bioinks for extrusion-based 3D bioprinting, combining cytocompatibility with tunable crosslinking chemistry and dynamic redox-responsive behaviour. This review consolidates recent advances in thiomer chemistry, focusing on synthetic strategies that modulate thiol reactivity through pKa adjustment, neighboring-group interactions, and redox control. Crosslinking mechanisms such as oxidative disulfide formation, thiol-ene, thiol-yne, and thiol-polyphenol reactions are compared in terms of their impact on gelation. External triggers, including small-molecule and polymeric crosslinkers, light activation, oxidants, enzymatic systems, as well as hybrid dual-stage systems, are discussed for their capacity to achieve controlled gelation and long-term stability. A comprehensive printability framework links chemical design to performance metrics such as gel point, modulus build-up rate, collapse angle, filament fusion index, fidelity ratio, and shear thresholds that maintain cell viability. Redox-driven reversibility provides additional adaptability through self-healing and stress-relaxation mechanisms. Applications span soft tissue and cartilage regeneration, vascularized and multicellular constructs, hemostatic adhesives, and extracellular matrix-mimetic scaffolds for stem-cell culture. These developments collectively establish design principles for balancing gelation kinetics, shape fidelity, and biological functionality in thiomer-based bioinks.