Nonleaching Antibacterial Glass Surfaces via “Grafting Onto”: The Effect of the Number of Quaternary Ammonium Groups on Biocidal Activity

Antimicrobial surfaces were prepared using the “grafting onto” technique. Well-defined block copolymers containing poly(2-(dimethylamino)ethyl methacrylate) and poly(3-(trimethoxysilyl)propyl methacrylate) segments (PDMAEMA/PTMSPMA) and corresponding random copolymers were prepared via atom transfer radical polymerization (ATRP), followed by covalent attachment to a glass surface through reaction of the trimethoxysilyl groups with surface silanol groups. The density of quaternary ammonium (QA) groups available to bind small molecules in solution increased with polymer solution concentration and immobilization time. For the PDMAEMA97-b-PTMSPMAxdiblock copolymers with a fixed length of PDMAEMA segment (degree of polymerization (DP) = 97) and varied lengths of PTMSPMA segments, maximal available surface charge was observed when the ratio of DPPDMAEMA to DPPTMSPMA was 5:1. The tertiary amino groups in immobilized PDMAEMA segments were reacted with ethyl bromide to form QA groups. Alternatively, block copolymers with prequaternized PDMAEMA segments were attached to surfaces. Biocidal activity of the surfaces with grafted polymers versus Escherichia coli (E. coli) increased with the density of available QA units on the surface. The number of bacteria killed by the surface increased from 0.06 × 105 units/cm2 to 0.6 × 105 units/cm2, when the density of surface QA increased from 1.0 × 1014 unit/cm2 to 6.0 × 1014 unit/cm2. The killing efficiency of QA on all surfaces was similar with ∼1 × 1010 units of QA needed to kill one bacterium. The AFM analysis indicated that grafting onto the surface resulted in small patches of highly concentrated polymer. These patches appear to increase the killing efficiency as compared to surfaces prepared by grafting onto with the same average polymer density but with a uniform distribution.