Figure 1.

Network structure of hybrid network, stress relaxing hydrogels. a) Schematic of the chemical structures of the 85 kDa HA-hydrazide, 96 kDa HA-aldehyde, 40 kDa 8-arm PEG-BCN, and the 350 Da benzaldehyde-PEG-azide. b) The reactant groups which form the various bonds within the hydrogel including, the hydrazide and aldehyde groups which form the dynamic hydrazone bond, the hydrazide and benzaldehyde group which react to form a more stable hydrazone bond, and the azide and BCN groups which react to form the permanent triazole bond. c) Upon mixing of the HA-hydrazide and HA-aldehyde a stress relaxing hydrogel is formed. d) Upon mixing the HA-hydrazide with the benzaldehyde-PEG-azide, some of the hydrazide groups can be functionalized with an azide, enabling the reaction between the PEG-BCN and azide groups through a strain promoted cycloaddition. Upon mixing the pre-reacted HA-hydrazide and benzaldehyde-PEG-azide with the HA-aldehyde and PEG-BCN a hybrid network can form between the SPAAC bond and the dynamic hydrazone bond, forming a hydrogel. e) Through the SPAAC formation alone, an elastic hydrogel is formed.