Thermo-sensitive poly(VCL-4VP-NVP) ionic microgels: synthesis, cytotoxicity, hemocompatibility, and sustained release of anti-inflammatory drugs

Thermosensitive poly(VCL-4VP-NVP) ionic microgels were prepared by in situ quaternization crosslinking reaction during surfactant free emulsion polymerization (SFEP) with N-vinylcaprolactam (VCL) as the main monomer, 4-vinylpyridine (4VP) as the quaternizable co-monomer, N-vinyl-2-pyrrolidone (NVP) as the second co-monomer and 1,6-dibromohexane (6Br) as the quaternization crosslinker. The obtained ionic microgels were spherical in shape with a narrow size distribution and exhibited thermo-sensitive behavior. These ionic microgels showed low cytotoxicity at concentrations lower than 25 mg mL(-1), excellent hemocompatibility at concentrations up to 1000 mg mL(-1), and could be up taken into the cytoplasm regime of HEK-293 cells without entering the nucleus. It was found that these ionic microgels were suitable for the loading and sustained release of a nonsteroidal anti-inflammatory drug, diclofenac sodium (DS). The drug loading content (DLC) of DS in the microgels could reach ca. 12% with an encapsulation efficiency (EE) of up to 68%. Furthermore, 60% loaded DS could be sustainably released at 37 degrees C from the drug-loaded microgels within 400 min following a first-order exponential kinetics.