Investigating Elastic Modulus and Glass Transition of Gelatin Methacryloyl under Ambient Humidity Using Dynamic Mechanical Analysis and Wrinkling Metrology

The excellent biocompatibility, formability, and moisture-responsive behavior of GelMA (gelatin methacryloyl) films make it an attractive sensing and intelligent material. To better understand the mechanical properties and glass transition behavior of GelMA with a lower water content beyond the range often utilized for biomedical applications, herein, we employed the conventional dynamic mechanical analysis (DMA) in combination with the emerging technique of wrinkling metrology to investigate the mechanical properties and glass transition behavior of thick and thin GelMA films under a moisture-controlled environment. We found that the degree of methacrylation or substitution has a profound effect on the glassy modulus of GelMA films, in particular, for thin film samples. In contrast, the photo-cross-linking leads to only a modest increase in the glassy modulus for both thick and thin GelMA films. Additionally, by utilizing the Gordon-Taylor equation and the Flory-Huggins model, a universal relationship is established for correlating the results of glass transition temperature and the glass transition relative humidity for GelMA and gelatin prepared at different conditions, which provides a convenient tool for predicting the glass transition temperature of GelMA or gelatin when the sample being exposed to relative humidity is known or vice versa.