The Adsorption Of Bovine Serum Albumin, The Environmental Sensitivity Of The Microgel

Microgel is a kind of polymer colloid suspension with particle diameter from 1nm to 1um. Environmental sensitive hydrogels can respond to the external stimuli such as temperature, pH, ionic strength, electric field, or specific analyte concentration gradients. In addition, hydrogels are also biocompatibility, biodegradation and low toxicity. These unique qualities make them have been used primarily in the biomedical applications such as on-off switches for modulated various drugs, peptides and proteins delivery and tissue engineering. Poly(N-isopropylacrylamide) (PNIPAM) is a well studied microgel which undergos a temperature induced phase transition with a lower critical solution temperature (LCST) at ~32℃. The introduction of ionic monomers to N-isopropylacrylamide (NIPAM) in biomedical research is of great interest due to the similarities in the chemical functionality of protein and microgel.In this work, a group of charged crosslinked pH-temperature sensitive poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)) microgels were synthesized by surfactant-free emulsion polymerization of NIPAM and AAc. AFM images indicated the microgel particles were monodispersed and the diameter of the dried microgel latex particles was about 800nm.The surface-COOH of microgel particles increased with the amount of AAc. The pH and temperature sensitivity of microgels were characterized by the transmittance of microgel suspensions as function of temperature and pH. The LCST of microgel solution was influenced by the content of AAc and MBAAm in microgel polymer significantly. LCST of microgel increased as the content of AAc and MBAAm increases due to their hydrophilic properties. Besides, there was little change of transmittance with the increase of pH value for the pure PNIPAM microgel. However, after incorporation AAc in the PNIPAM, the P(NIPAM-co-AAc) microgel became pH sensitivie In addition, with AAc amount in the copolymer increasing, such pH-sensitivity enhanced.The amount of Bovine Serum Albumin (BSA) adsorption on microgel particles was strongly influenced by the environmental conditions. It was found that high ionic strength leaded to low BSA adsorption due to the decrease of electrostatic interaction between microgel and BSA protein. Moreover, the amount of BSA adsorption was drastically impacted by pH value of medium. The maximum absorption was observed at pH 3~5, while low pH value and basic conditions both induced the rather low absorption. In the experiment of BSA desorption, it was found that the adsorbed BSA protein could be controlled released from P (NIPAM-co-AAc) microgel by adjusting pH value of the suspension.Furthermore, it was found that the properties of original microgel particles wound be changed after they loaded protein. BSA loaded on microgel particles wound make particle surface more hydrophobic, which lead to the LCST of BSA loaded microgel suspensions at pH5 shifted to a lower temperature. At the same time, microgel particle loading BSA was inclined to aggregation due to bridge connection of BSA and microgel. On the other hand, the swellability of P (NIPAM-co-AAc) microgel may be limited by the uptake of protein on the surface of microgel particles, which caused the faintness of the temperature-sensitivity of microgel.