Using basic thermodynamic principles we derive a Cahn-Hilliard-Darcy model for tumour growth including nutrient diffusion, chemotaxis, active transport, adhesion, apoptosis and proliferation. The model generalises earlier models and in particular includes active transport mechanisms which ensure thermodynamic consistency. We perform a formally matched asymptotic expansion and develop several sharp interface models. Some of them are classical and some are new which for example include a jump in the nutrient density at the interface. A linear stability analysis for a growing nucleus is performed and in particular the role of the new active transport term is analysed. Numerical computations are performed to study the influence of the active transport term for specific growth scenarios.

A porcine model of wound healing was employed to examine the impact of nanocrystalline silver-coated dressings on specific wound healing events. Full-thickness wounds were created on the backs of pigs, contaminated with an experimental inoculum containing Pseudomonas aeruginosa, Fusobacterium sp., and coagulase-negative staphylococci, and covered with dressing products either containing silver or not. Nanocrystalline silver-coated dressings promoted rapid wound healing, particularly during the first several days post-injury. Healing was characterized by rapid development of well vascularized granulation tissue that supported tissue grafting 4 days post-injury, unlike control dressed wounds. The proteolytic environment of wounds treated with nanocrystalline silver was characterized by reduced levels of matrix metalloproteinases. Matrix metalloproteinases have been shown to be present in chronic ulcers at abnormally high levels, as compared with acute wounds, and may contribute to the nonhealing nature of these wounds. Cellular apoptosis occurred at a higher frequency in the nanocrystalline silver-treated wounds than in wounds dressed with other products. The results suggest that nanocrystalline silver may play a role in altering or compressing the inflammatory events in wounds and facilitating the early phases of wound healing. These benefits are associated with reduced local matrix metalloproteinase levels and enhanced cellular apoptosis.

The bioelectric elfect, in which electric fields are used to enhance the efficacy of biocides and antibiotics in killing biofilm bacteria, has been shown to reduce the very high concentrations of these antibacterial agents needed to kill biofilm bacteria to levels very close to those needed to kill planktonic (floating) bacteria Work in many laboratories (16,17,32), including our own (3,12,33), has clearly established that biofilm bacteria are resistant to antibiotics and biocides at levels 500 to 5,000 times higher than those needed to kill planktonic cells of the same species. The mechanism of this inherent resistance of glycocalyx-enclosed biofilm bacteria to antimicrobial agents is not conclusively established but appears to depend on both diffusion limitation (25) and physiological properties associated with low growth rates (8,9,16,17) in biofilm populations. Direct examination of the surfaces of medical devices that have become the foci of device-related bacterial infections shows that these pathogens grow in well-developed adherent biofilms (12), and clinical experience (21) indicates that these chronic infections are highly refractory to antibiotic therapy. Consequently, device-related bacterial infections are aggressively treated with combinations of antibiotics (2, 27), but in many cases, the biofilm-colonized device must still be removed to facilitate the resolution of these infections (21,37).An increasing number of laboratories have begun to examine the effects of electric fields and current densities on biological systems (1,5,15,19,28,31,34,35,38,41), mainly because of interest in the electroporation and electrofusion processes that are very useful in genetic research (31). This body of work has shown that electric fields and currents can be used for electroporation and electrofusion (31), electroosmosis, iontophoresis (6,(13)(14)(15), and the electroinsertion of specific proteins (30). During this work, it has been noted that electric fields and currents can influence the organization of biological membranes (10,28,31,35,40,42) and membrane analogs (1, 18), metabolic and developmental processes within both prokaryotic and eukaryotic cells (19,24,34,38,42) 994-1960. Fax: (406) 994-6098. kilovolt-per-centimeter range, but a significant number (5,13,15,24,36) have also focused on the effects of low-intensity fields and currents on biological systems for which significant effects have been documented, especially embryonic systems (34).We have reported that low-intensity electric fields (field strength of 1.5 to 20 V/cm and current densities of 15 pA/cm2 to 2.1 mA/cm2) can completely override the inherent resistance of biofilm bacteria to biocides (7) and antibiotics (26). This bioelectric effect reduces the concentrations of these antibacterial agents needed to kill biofilm bacteria to 1.5 to 4.0 times those needed to kill planktonic cells of the same species. The present study was undertaken to examine the mechanism of this bioelectric effect, with the working hypothesis that the electric f...

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