In this paper, we report on the potential use of atomic force microscopy (AFM) as a tool to measure the intermolecular forces in biofilm structures and to study the effect of silver ions on sessile Staphylococcus epidermidis cell viability and stability. We propose a strategy of destabilizing the biofilm matrix by reducing the intermolecular forces within the extracellular polymeric substances (EPSs) using a low concentration (50 ppb) of silver ions. Our AFM studies on the intermolecular forces within the EPSs of S. epidermidis RP62A and S. epidermidis 1457 biofilms suggest that the silver ions can destabilize the biofilm matrix by binding to electron donor groups of the biological molecules. This leads to reductions in the number of binding sites for hydrogen bonds and electrostatic and hydrophobic interactions and, hence, the destabilization of the biofilm structure.Microorganisms attach to living and nonliving surfaces, including those of indwelling medical devices and potable water system piping, and form biofilms that consist of extracellular polymers. Biofilms are the source of free-floating bacteria in drinking water, which poses a health risk (5). In biomedical areas, biofilms are a common source of medical device-related infections, such as acute bacterial infection of dental plaque (33), catheter-related bloodstream infection (7, 9, 34), and heart valves endocarditis (22). Although antibiotics like vancomycin and tobramycin (8, 23) are used to treat these infections, most of these infections persist. The use of antimicrobial agents and antibiotics for the treatment of these infections is limited, as the biofilms create an environment that enhances antimicrobial resistance (3,16,19). In general, the most important contribution of biofilms' antimicrobial resistance can be related to the properties of extracellular polymeric substances (EPSs), such as diffusion, sorption, water binding, mass transport, and mechanical stability. The EPSs of biofilms contain considerable amounts of polysaccharides, proteins, nucleic acids, and lipid (30), which are responsible for maintaining the structural integrity of the biofilm and providing an ideal matrix for bacterial cell growth (15). Intermolecular interactions between the various functional groups within these macromolecules serve to strengthen the overall mechanical stability of the EPSs and, hence, the survivability of the enclosed microorganisms.It is reported that when silver ions bind to biological molecules containing thio, amino, carboxylate, imidazole, or phosphate groups, they inhibit activities that are vital to the bacteria's regulatory processes and cause bacterial inactivation (26,27). Silver ions also act by displacing other essential metal ions, such as Ca 2ϩ and Zn 2ϩ . Silver cations exhibit broad antimicrobial action at low concentrations, and they are already being used for the treatment of burn wounds (24) and traumatic injuries (6). Silver ions also display low levels of toxicity to humans (1) and are safe agents for the removal of biofilms. B...

This paper describes a multi-step microfluidic device for studying the deformation and extravasation of primary tumor cells. Prior to extravasation, primary tumor cells undergo sequential steps of deformation through the capillaries, before adhering and transmigrating through the endothelial lining and basement membrane. To study this cascade of events, we fabricated a multi-step microfluidic device whose microgaps were coated with Matrigel to mimic the basement membrane. The microchannel was lined with human microvascular endothelial cells (HMECs) to replicate the endothelial lining. Analysis of deformation, biological and migratory capabilities of various tumor cell lines viz. HepG2, HeLa, and MDA-MB 435S were quantified using the fabricated device. After deformation, the cells' viabilities were significantly reduced and their doubling times were simultaneously increased, indicating changes in their biological capability. However, cell deformation did not significantly reduce their cell motility. Cell motility was co-assessed using the cell's migration rate and the overall population's percentage migration under various conditions (no barrier, Matrigel and Matrigel-HMEC). The device was also used to quantify the effects of Matrigel and the endothelial lining on cell migration. Our results suggest that both played an independent role in inhibiting cell extravasation, with the Matrigel significantly slowing down cell movement and the endothelial lining reducing the total number of transmigrated cells.

Three-dimensional (3-D) extracellular matrices (ECM) allow complex biochemical and biophysical interactions between cells and matrices. Unlike 2-D systems, 3-D models provide a better representation of the micro and local environments in living tissues for facilitating the physiological study of cell migration. Here, we report a microfluidic device based on polydimethylsiloxane (PDMS) for monitoring 3-D cell migration across ECM-coated microgaps with real-time light microscopy. We tracked the migration of the invasive MDA-MB-231 (mammary carcinoma) cells and mapped out their migration paths. It enabled us to quantify the percentage of migrated cells as well as migration information of individual cells. This wide spectrum of data acquisition is vital for elucidating the migration capabilities of different type of cells and to understand the basic mechanism involved in cancer metastasis.