Polyethylene Glycol Chemically Modified Soy Protein Isolate Hydrogel

Soy protein isolate (SPI), a kind of plant protein, has attracted comprehensive interests in many fields due to its sustainability, low cost, functionality, biocompatibility and tunable degradability. However, SPI needs to take an appropriate modification to meet the requirement of practical use because of the weak intermolecular interactions among the polypeptide chains due to its globular protein nature. Therefore, we designed a chemical modification method to change the aggregation state of SPI molecular chains and prepared a SPI-based hydrogel thereafter. Firstly, polyethylene glycol monomethyl ether (mPEG-CHO) was synthesized by Tempo-BAIB method, achieving an average oxidation degree of 56%. Then, mPEG was successfully grafted onto SPI through Schiff's base reaction between mPEG-CHO and the amino groups in SPI molecular chains, followed by a reduction reaction from NaCNBH4. It was found that such a PEG modified SPI solution (10%) was able to form a hydrogel at 37 degrees C spontaneously. In the meantime, it showed that with the increase in grafting ratio, the gelation time can be within 30 min. Such a characteristic make this SPI-based hydrogel an injectable hydrogel, which may have the considerable potential in the biomedicine field. However, the mechanical properties of current PEG modified SPI hydrogel is still not high enough (storage modulus of 300 Pa), so further effort should be taken to make it meet the requirement of real applications.