A growing number of device-related nosocomial infections, elevated hospitalization costs, and patient morbidity necessitate the development of novel antibacterial strategies for clinical devices. We have previously demonstrated a simple, aqueous polydopamine dip-coating method to functionalize surfaces for a wide variety of uses. Here, we extend this strategy with the goal of imparting antifouling and antimicrobial properties to substrates, exploiting the ability of polydopamine to immobilize polymers and induce metal nanoparticle formation. Polydopamine was deposited as a thin adherent film of 4 nm thickness from alkaline aqueous solution onto polycarbonate substrates, followed by grafting of antifouling polymer polyethylene glycol and in situ deposition of silver nanoparticles onto the polydopamine coated polycarbonate substrates. Elemental and morphological surface analyses confirmed successful grafting of polyethylene glycol brushes onto polydopamine-coated substrates, as well as spontaneous silver nanoparticle formation for polydopamine-coated substrates incubated in silver-nitrate solutions. Sustained silver release was observed over at least 7 days from silver-coated substrates, and the release kinetics could be modulated via additional polydopamine overlayers. In vitro functional assays employing gram negative and positive strains demonstrated dual fouling resistance and antibacterial properties of the coatings due to the fouling resistance of grafted polyethylene glycol and antibacterial effect of silver, respectively. Polycarbonate substrates coated only with silver using a method similar to existing commercial coatings provided an antibacterial effect but failed to inhibit bacterial attachment. Taking into account the previously demonstrated substrate versatility of polydopamine coatings, our findings suggest that this strategy could be implemented on a variety of substrate materials to simultaneously improve antifouling and antimicrobial performance.

Cell migration plays a critical role in a wide variety of physiological and pathological phenomena as well as in scaffold-based tissue engineering. Cell migration behavior is known to be governed by biochemical stimuli and cellular interactions. Biophysical processes associated with interactions between the cell and its surrounding extracellular matrix may also play a significant role in regulating migration. Although biophysical properties of two-dimensional substrates have been shown to significantly influence cell migration, elucidating factors governing migration in a three-dimensional environment is a relatively new avenue of research. Here, we investigate the effect of the three-dimensional microstructure, specifically the pore size and Young's modulus, of collagen-glycosaminoglycan scaffolds on the migratory behavior of individual mouse fibroblasts. We observe that the fibroblast migration, characterized by motile fraction as well as locomotion speed, decreases as scaffold pore size increases across a range from 90 to 150 mum. Directly testing the effects of varying strut Young's modulus on cell motility showed a biphasic relationship between cell speed and strut modulus and also indicated that mechanical factors were not responsible for the observed effect of scaffold pore size on cell motility. Instead, in-depth analysis of cell locomotion paths revealed that the distribution of junction points between scaffold struts strongly modulates motility. Strut junction interactions affect local directional persistence as well as cell speed at and away from the junctions, providing a new biophysical mechanism for the governance of cell motility by the extracellular microstructure.

Epidermal growth factor (EGF) receptor-mediated cell migration plays a vital role in invasion of many tumor types. EGF receptor ligands increase invasiveness in vivo, but it remains unclear how consequent effects on intrinsic cell motility behavior versus effects on extrinsic matrix properties integrate to result in net increase of translational speed and/or directional persistence of migration in a 3D environment. Understanding this convolution is important for therapeutic targeting of tumor invasion, as key regulatory pathways for intrinsic versus extrinsic effects may not be coincident. Accordingly, we have undertaken a quantitative single-cell imaging study of glioblastoma cell movement in 3D matrices and on 2D substrata across a range of collagen densities with systematic variation of protease-mediated matrix degradation. In 3D, EGF induced a mild increase in cell speed and a strong increase in directional persistence, the latter depending heavily on matrix density and EGF-stimulated protease activity. In contrast, in 2D, EGF induced a similarly mild increase in speed but conversely a decrease in directional persistence (both independent of protease activity). Thus, the EGF-enhanced 3D tumor cell migration results only partially from cell-intrinsic effects, with override of cell-intrinsic persistence decrease by protease-mediated cell-extrinsic reduction of matrix steric hindrance.

Small-molecule kinase inhibitors often modulate signaling pathways other than the one targeted, whether by direct "off-target" effects or by indirect "pathway cross-talk" effects. The presence of either or both of these classes of complicating factors impedes the predictive understanding of kinase inhibitor consequences for cell phenotypic behaviors involved in drug efficacy responses. To address this problem, we offer an avenue toward comprehending how kinase inhibitor modulations of cell signaling networks lead to altered cell phenotypic responses by applying a quantitative, multipathway computational modeling approach. We show that integrating measurements of signals across three key kinase pathways involved in regulating migration of human mammary epithelial cells, downstream of ErbB system receptor activation by epidermal growth factor (EGF) or heregulin (HRG), significantly improves prediction of cell migration changes resulting from treatment with the small-molecule inhibitors 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) and 2Ј-amino-3Ј-methoxyflavone (PD98059) for both normal and HER2-overexpressing cells. These inhibitors are primarily directed toward inhibition of phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MEK) but are known to exhibit off-target effects; moreover, complex crosstalk interactions between the PI3K/Akt and MEK/extracellular signal-regulated kinase (Erk) pathways are also appreciated. We observe here that treatment with LY294002 reduces migration of HRG-stimulated cells but not EGF-stimulated cells, despite comparable levels of reduction of Akt phosphorylation under both conditions, demonstrating that the target inhibition effect is not unilaterally predictive of efficacy against cell phenotypic response. Consequent measurement of levels of Erk and p38 phosphorylation, along with those for EGF receptor phosphorylation, after LY294002 treatment revealed unintended modulation of these nontargeted pathways. However, when these measurements were incorporated into a partial least-squares regression model, the cell migration responses to treatment were successfully predicted. Similar success was found for the same multipathway model in analogously predicting PD98059 treatment effects on cell migration. We conclude that a quantitative, multipathway modeling approach can provide a significant advance toward comprehending kinase inhibitor efficacy in the face of off-target and pathway cross-talk effects.