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Here we describe an experimental study of the mechanical properties of bacterial biofilms formed from the early dental plaque colonizer Streptococcus mutans. The S. mutans biofilms demonstrated the behavior of rheological fluids, with properties similar to those of organic polymers and other biological fluids. The time-dependent response of the biofilms was modeled on the basis of principles of viscoelasticity theory. The static and dynamic responses were defined in terms of the creep compliance, storage and loss moduli, and viscosity. The creep compliance and stress relaxation functions of S. mutans biofilms were characterized using the Burger model. Implications for developing more effective mechanical removal strategies of dental plaque biofilms are discussed.

Indwelling prostheses and subcutaneous delivery devices are now routinely and indispensably employed in medical practice. However, these same devices often provide a highly suitable surface for bacterial adhesion and colonization, resulting in the formation of complex, differentiated, and structured communities known as biofilms. The University of Washington Engineered Biomaterials group has developed a novel drug delivery polymer matrix consisting of a poly(2-hydroxyethyl methacrylate) hydrogel coated with ordered methylene chains that form an ultrasound-responsive coating. This system was able to retain the drug ciprofloxacin inside the polymer in the absence of ultrasound but showed significant drug release when low-intensity ultrasound was applied. To assess the potential of this controlled drug delivery system for the targeting of infectious biofilms, we monitored the accumulation of Pseudomonas aeruginosa biofilms grown on hydrogels with and without ciprofloxacin and with and without exposure to ultrasound (a 43-kHz ultrasonic bath for 20 min daily) in an in vitro flow cell study. Biofilm accumulation from confocal images was quantified and statistically compared by using COMSTAT biofilm analysis software. Biofilm accumulation on ciprofloxacin-loaded hydrogels with ultrasound-induced drug delivery was significantly reduced compared to the accumulation of biofilms grown in control experiments. The results of these studies may ultimately facilitate the future development of medical devices sensitive to external ultrasonic impulses and capable of treating or preventing biofilm growth via "on-demand" drug release.

Polyvinylidene fluoride (PVDF) is a piezoelectric polymer that has been used in many applications including microphones, transducers, sensors and actuators. The electromechanical properties of PVDF are commonly defined by the constitutive equations of piezoelectricity. This paper presents experimental evidence that the assumptions underlying the theory of piezoelectricity have certain limitations in terms of representing adequately the electromechanical properties of PVDF. It is shown that PVDF tends to demonstrate time-dependent behavior in the form of viscoelastic creep and dielectric relaxation, and measurable energy losses under cyclic loading conditions. Moreover, the response of PVDF strongly depends on temperature and cyclic frequencies.

The paper presents a review in the field of electroactive polymers. It outlines the main classes of electroactive polymers, their properties and applications. Current efforts to synthesize electroactive polymers with novel or improved characteristics along with the challenges, opportunities and future research directions are discussed.