ABSTRACT
The reversible manipulation of the helix screw sense in surface-grafted poly(beta-phenethyl-L-aspartate) (PPELA) films by means of external stimuli was investigated. Ringopening polymerization of beta-phenethyl-L-aspartate N-carboxyanhydride initiated from primary amino-functionalized silicon and quartz substrates results in surface-grafted PPELA films in which the end-grafted polypeptide chains have a right-handed alpha-helical conformation. Upon annealing of the film at 150 degrees C for 30 min, a helix screw sense inversion takes place and the grafted chains adopt a left-handed pi-helical conformation. In the solid state, this left-handed pi-helical form is completely stable and cannot be changed by reheating and/or cooling. Upon immersion of the annealed grafted film in chloroform or other helicogenic solvents, the grafted polypeptide chains completely revert to their original right-handed alpha-helical form. Successive annealing and solvent treatment steps show that this helix sense inversion cycle can be repeated many times.
ABSTRACT
Using a chemical cross-linking procedure, surface-grafted polyglutamate films with a permanently perpendicular helix orientation were prepared. A surface-grafted alpha-helical polyglutamate film containing polymerizable side groups was synthesized by ring-opening terpolymerization of 50 molar% gamma-methyl-L-glutamate N-carboxyanhydride (NCA), 30% gamma-stearyl-L-glutamate NCA and 20% gamma-4-vinylbenzyl-L-glutamate NCA initiated from a silicon substrate functionalized with primary amino groups. The average tilt angle of the end-grafted helices in this film is approximately 66 degrees , indicating a nearly parallel helix orientation with respect to the substrate surface. After swelling of the grafted terpolyglutamate film in stearyl methacrylate and subsequent radical cross-linking, the average helix tilt angle decreases to about 11 degrees, indicating an almost perpendicular helix orientation. The film thickness increases accordingly from 151 A before to approximately 390 A after cross-linking. Extensive solvent treatment of the cross-linked film shows that the perpendicular helix orientation is permanent.
ABSTRACT
A method is presented to prevent microbial adhesion to solid surfaces exploiting the unique properties of polymer brushes. Polyacrylamide (PAAm) brushes were grown from silicon wafers by atom transfer radical polymerization (ATRP) using a three-step reaction procedure consisting of immobilization of a coupling agent gamma-aminopropyltriethoxysilane, anchoring of an ATRP initiator 4-(chloromethyl)benzoyl chloride, and controlled radical polymerization of acrylamide. The surfaces were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ellipsometry, and contact-angle measurements. The calculated grafting density pointed to the presence of a dense and homogeneous polymer brush. Initial deposition rates, adhesion after 4 h, and detachment of two bacterial strains (Staphylococcus aureus ATCC 12600 and Streptococcus salivarius GB 24/9) and one yeast strain (Candida albicans GB 1/2) to both PAAm-coated and untreated silicon surfaces were investigated in a parallel plate flow chamber. A high reduction (70-92%) in microbial adhesion to the surface-grafted PAAm brush was observed, as compared with untreated silicon surfaces. Application of the proposed grafting method to silicone rubbers may offer great potential to prevent biomaterials-centered infection of implants.
