4-arm PEG Azide (4-arm PEG-N3) is a multiarm PEG derivative which has -N3 at each PEG end and can be cross-linked into PEG hydrogels. Azide groups are useful for coupling via click chemistry reactions with alkynes. PEG hydrogels have a variety of applications in medical devices and regenerative medicine, and are especially of interest for controlled release of drugs, for 2D and 3D cell culture, and for wound sealing and healing. Nanosoft Polymers 4 arm PEGs are synthesized by ethoxylation of pentaerythritol (4 ARM PEG). The number of ethylene oxide units in the PEG chain may not be equal for all arms.