| Stumili-responsive polymer coatings have attracted tremendous research interest in the last decade due to their highly adjustable physicochemical properties. These properties have enabled applications in both mechanical engineering and biomedical engineering as coatings for microfluidic devices and for orthopedic implants.This dissertation presents the specific research and exploration of novel responsive polymer coatings such as responsive polymer brushes and layer-by-layer (LbL) hydrogels as effective tools to regulate surface wettability, to control bacterial adhesion, or to kill bacteria upon contact thus preventing biofilm formation. First, we successfully grafted polymer brushes of polyacrylic acid (PAA), polymethacrylic acid (PMAA), poly(2-ethylacrylic acid) (PEAA), and their corresponding N-isopropylacrylamide (NIPAM) copolymers via reversible addition fragmentation chain-transfer (RAFT) polymerization onto silicon substrates. We investigated the effects of monomer hydrophobicity, which dictates surface wettability, on the hydrogen bonding of polymer brushes. By using Fourier-transform infrared spectroscopy (FTIR), we found that copolymer brush composition was significantly influenced by the bulkiness of poly (2-alkylacrylic acid) (PaAA) functional groups. Contact angle measurements indicated that copolymer brushes of P(AA-co-NIPAM) and P(MAA-co-NIPAM) were pH responsive but not temperature responsive, however the P(EAA-co-NIPAM) brush had dual pH and temperature responsiveness. Next, we constructed novel pH responsive LbL hydrogels of PaAA (PaAALbL) on both non-patterned and micropillar-patterned substrates. We found that swelling and wettability of PaAALbL hydrogels correlated as a function of pH. All PaAALbL hydrogels exhibited large amplitude and reversible wettability transitions under physiological conditions. Moreover, contact angles of all PaAALbL hydrogels increased dramatically at low pH on roughened silicon substrates, except for hydrophilic PMAALbL hydrogels. Lastly, we evaluated the anti-adhesion and antibacterial activities of PaAALbL hydrogels on non-patterned substrates. Using various analytical methods, we found that hydrophobic PaAALbL hydrogels were capable of reducing bacterial adhesion as well as being able to kill bacteria upon contact. In addition, they displayed a selective bio-adhesive property towards human osteoblast cells. This makes PaAALbL hydrogels ideal coating candidates for microfluidic devices and biomedical implants. |
