*4.3. Preparation and Characterization of P(OEGMA-co-MEO2MA) Microgels-Based Thermosensitive Hydrogel*

The thermosensitive P(OEGMA-co-MEO2MA) hydrogels were prepared through the thermal induction method [29].

A certain amount of P(OEGMA-co-MEO2MA) microgel samples were weighed and dissolved in phosphate buffered saline (PBS) to obtain a final solution with mass fraction of 3.0 wt%. Then, they were placed in a physiological temperature environment, which was higher than their VPTTs. The formation process of thermosensitive hydrogel from microgels and its stability and shrinkage were observed by the inverted method and recorded by camera. The gelation time was defined as the time point at which the inverted hydrogel no longer flowed visually.

To quantitatively analyze the shrinkage degree of the obtained hydrogels, we calculated the ratio of the volume of the obtained hydrogel at certain time point (Vt) to the initial volume (V0) by measuring with a ruler. The thermosensitive hydrogel sample with minimum shrinkage was screened out for the next cell experiments.
