Synthesis, characterization and drug release properties of thermosensitive poly(N-isopropylacrylamide) microgels

This study was aimed at optimizing the structure and properties of poly(N-isopropylacrylamide) (PNIPAAm) microgels prepared by inverse suspension polymerization. The influence of the oil-to-water phase ratio, the concentration of emulsifier, and the monomer-to-crosslinker molar ratio on selected properties of the PNIPAAm microgels was examined. Regularity of the microgels shape was estimated by optical microscopy. Laser diffraction technique was used to determine the microgels mean size and size distribution. Equilibrium swelling ratio was studied gravimetrically. Morphology of microgels was followed by SEM. Volume phase transition temperature of PNIPAAm microgels was determined by differential scanning calorimetry. The results obtained imply that the mean diameter of microgels and their equilibrium swelling ratio highly depend on the concentration of emulsifier in oil phase and the crosslinking degree of PNIPAAm. The crosslinking degree of PNIPAAm has no substantial effect on the volume phase transition temperature that is demonstrated to be around 33 degrees C even after complete heating-cooling-heating cycle. In addition, it was confirmed that the swollen microgels have a porous, honeycomb-like structure. Release profiles of procaine hydrochloride from the PNIPAAm microgels confirmed their potential to be considered as efficient matrices in drug release applications