Study of synthesis parameters on the physical properties and morphology of smart PNIPAAm hydrogels

Bone loss is common in human old age and new materials that promote bone regeneration are an active line of research. In the present work, seven smart hydrogels based on PNIPAAm were synthesized with the prospective to be used in tissue engineering as a scaffold for bone growth. By changing the stoichiometric concentrations of the reagents and the synthesis parameters, hydrogels with different physical properties and morphology were obtained. Swelling, degradation properties, and crystallinity were analyzed. Physical properties were characterized using ¹H-NMR, FTIR, and TGA. The results showed that the swelling degree (degree of mass expansion) varied at room temperature from 1,400% for less rigid hydrogels to 550% for stiffer hydrogels. With heating to body temperature, swelling decreases to 300% and 200%, respectively. The samples presented three-dimensional morphology, but they acquired different structures according to the magnetic stirring during the synthesis process. The crosslink and initiator concentrations have an important effect on the polymeric structure and thermal stability of the hydrogels. The PNIPAAm synthesized using 8.9 and 15.7 mol % of MBA are the most promising compounds to be used in the future as a scaffold for biomedical applications due to their high thermal stability, satisfactory 3D surface morphology, and shrinking-swelling property.