The effect of cross-linker concentration on the physical properties of poly(dimethyl acrylamide-co-stearyl acrylate)-based shape memory hydrogels

Chemically cross-linked shape memory hydrogels were synthesized, and their physical properties were studied. The gels were made from a hydrophilic monomer, i.e., N,N-dimethyl acrylamide (DMAA), and a hydrophobic monomer, i.e., stearyl acrylate (SA). The properties were characterized by varying the concentration of the cross-linker methylene bisacrylamide (MBAA), whereas the concentrations of other chemical components were held constant. It was observed that the mechanical properties strongly depended on the cross-linker concentration. The cross-linked hydrogels showed improved toughness compared to the hydrogel counterparts without cross-linking. Thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC spectra of dried samples exhibited a complex crystalline nature, while swollen samples showed homogeneous crystallinity. The experimental results of DSC and TGA suggested that there was no significant influence of MBAA concentration on the crystallinity and thermal properties of swollen SMG hydrogels.