Quantitative Analysis of Cell Adhesion Studies On Grafted Pnipaam Thermoresponsive Surfaces Synthesized Using ATRP

Environmentally responsive (or “smart”) polymers represent a new approach for controlling biofouling release. Poly (N-isopropyl acrylamide) (PNIPAAm) is a thermoresponsive polymer and acts as a biofouling resistant coating when grafted on to surfaces, as it exhibits a change in its relative hydrophobicity above and below its lower critical solution temperature (LCST ~ 32⁰C). We report grafted PNIPAAm brushes, synthesized using a relatively simple high throughput method which allows atom transfer radical polymerization (ATRP) in presence of air. The grafted surfaces have been characterized using FTIR, XPS, ToF-SIMS, ellipsometry and contact angle measurements. We also quantitatively studied, the adhesion of marine bacteria on these surfaces, both above and below the LCST using a spinning disc apparatus which device applies a linear range of shear forces to cells attached at the interface of a single sample. We have previously demonstrated that our test bacterium, Cobetia marina attaches more readily to PNIPAAm above the LCST (i.e. when the surface is relatively hydrophobic) and is released upon transition to temperatures below the LCST. In this work, C. marina was attached to PNIPAAm grafted surfaces at 37⁰C and subjected to varied detachment forces at 37⁰C, 22⁰C and 4⁰C in artificial sea water. The number of adherent cells decreased non-linearly with applied force and as expected the cell detachment at the interface required lesser shear force at lower temperatures evaluated. The ability to directly correlate a measurable force to bacterial attachment and release represents a step forward in understanding of interactions between PNIPAAm and bacterial cells. These experiments demonstrate the potential of PNIPAAm and similar polymers as possible fouling-release agents, and suggest that grafted PNIPAAm (or similar polymers) may be useful as regenerable fouling-release surfaces.