Surface-grown bacteria and production of an extracellular polymeric matrix modulate the assembly of highly cohesive and firmly attached biofilms, making them difficult to remove from solid surfaces. Inhibition of cell growth and inactivation of matrix-producing bacteria can impair biofilm formation and facilitate removal. Here, we developed a novel nonleachable antibacterial composite with potent antibiofilm activity by directly incorporating polymerizable imidazolium-containing resin (antibacterial resin with carbonate linkage; ABR-C) into a methacrylate-based scaffold (ABR-modified composite; ABR-MC) using an efficient yet simplified chemistry. Low-dose inclusion of imidazolium moiety (∼2 wt %) resulted in bioactivity with minimal cytotoxicity without compromising mechanical integrity of the restorative material. The antibiofilm properties of ABR-MC were assessed using an exopolysaccharide-matrix-producing (EPS-matrix-producing) oral pathogen (Streptococcus mutans) in an experimental biofilm model. Using high-resolution confocal fluorescence imaging and biophysical methods, we observed remarkable disruption of bacterial accumulation and defective 3D matrix structure on the surface of ABR-MC. Specifically, the antibacterial composite impaired the ability of S. mutans to form organized bacterial clusters on the surface, resulting in altered biofilm architecture with sparse cell accumulation and reduced amounts of EPS matrix (versus control composite). Biofilm topology analyses on the control composite revealed a highly organized and weblike EPS structure that tethers the bacterial clusters to each other and to the surface, forming a highly cohesive unit. In contrast, such a structured matrix was absent on the surface of ABR-MC with mostly sparse and amorphous EPS, indicating disruption in the biofilm physical stability. Consistent with lack of structural organization, the defective biofilm on the surface of ABR-MC was readily detached when subjected to low shear stress, while most of the biofilm biomass remained on the control surface. Altogether, we demonstrate a new nonleachable antibacterial composite with excellent antibiofilm activity without affecting its mechanical properties, which may serve as a platform for development of alternative antifouling biomaterials.

SynopsisThe mechanism of craze initiation and growth and its relationship to mechanical properties has been studied in thin films of styrene-butadiene-styrene (SBS) block copolymers. Optical microscopy and transmission electron microscopy were used to examine three copolymers which had a spherical rubber domain morphology but varied in rubber content from 20 to 50%. With increasing rubber content, the crazes became longer and less numerous. Widening of the crazes was at least partially responsible for the higher strains achieved in the copolymers, especially for the composition with the highest rubber content where the crazes widened to form micronecks. Transmission electron microscopy revealed that craze initiation and growth at the craze tip occurred by cavitation in the polystyrene phase. Cavitation of the continuous phase rather than the rubber domains was attributed to the concentration of chainend flaws in the polystyrene. Crazes in the block copolymers followed a meandering pathway and the boundaries between c r d and uncrazed material were indistinct. Incorporation of fibrillated rubber particles into the craze fibrils strengthened the craze. At higher rubber content, the craze widened in the stress direction by voiding and fibrillation, which produced a cellular morphology.

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and so forth. References and Notes(1) The Langevin forces strictly defined have a covariance matrix proportional to a friction matrix R', but the yi are the random numbers required in a polymer simulation. See ref 2.ABSTRACT: Gels of atactic polystyrene (aPS) in carbon disulfide were formed in the temperature range from 0 to -100 "C. The shear modulus was measured as a function of temperature, concentration, and molecular weight, and a master curve of the data was constructed. The modulus vs. temperature behavior of the aPS gels resembles that of un-cross-linked polymers in the rubbery plateau regime. It is proposed that physical associations act as cross-links and impart elastic properties to the gel network. A molecular weight between associations of 2700 was obtained by using rubber elasticity theory and a simple chain end correction factor for aPS gels of 200 g/L concentration in the plateau region. This defines the minimum molecular weight required for gel formation at this concentration. A more refined statistical approach that accounts for the polymer not included in the network gave a value of 5000. The molecular weight of the chain segment between associations increased as the temperature approached Tgel in a manner that was independent of molecular weight.