Preparation, characterization and enzyme inhibition of methylmethacrylate copolymer nanoparticles with different hydrophilic polymeric chains

Methylmethacrylate copolymer nanoparticles with different hydrophilic chains were prepared by the free radical polymerization of methylmethacrylate with N-isopropylacrylamide (NIPAAm), N-methacrylic acid (MAA), N-trimethylaminoethylmethacrylate chloride (TMAEMC) or N-dimethylaminoethylmethacrylate hydrochloride (DMAEMC). These particles were characterized by particle size and zeta potential. The polymerization conditions were shown to influence the particle size and surface charge. Particle sizes of MMA–NIPAAm nanoparticles after 3 h of reaction reached constant level at 180 nm. An increasing amount of total monomer (0.5–5%) would result in the nanoparticles of particle size of 115–204 nm for 30% NIPAAm of the total monomer. In the same range of 5–40% NIPAAm of the total monomer, the particle size decreased from 280 to 170 nm. The concentration of the initiator APS up to a concentration of 0.2% for MMA–TMAEMC and 0.1% for MMA–NIPAAm showed no effect on the particle size of the final nanoparticle suspensions, while higher concentration would lead to aggregation in the polymerization process. MMA–NIPAAm nanoparticles were pH-dependent in zeta potential at pH 1–12 values reducing from 12.2 mV to −16.8 mV, respectively. Nanoparticles were incubated with pepsin and trypsin at 37 °C for 20 min and their enzyme inhibition was determined. The activity of pepsin decreased to 27% in the presence of MMA–NIPAAm nanoparticles, and MMA–MAA nanoparticles reduced the activity of trypsin to 39%, respectively.