Used in bioconjugation to link proteins, peptides, or nanoparticles via thiol-reactive chemistry. The four-arm structure enables crosslinking for hydrogel formation, useful in tissue engineering and drug delivery. Provides water solubility and biocompatibility. Commonly used to modify surfaces or create scaffolds in regenerative medicine. Also applied in creating stable, long-circulating formulations in pharmaceuticals due to its stealth properties.