ARGET-ATRP synthesis and characterization of PNIPAAm brushes for quantitative cell detachment studies

Abstract

Stimuli responsive (or "smart") polymer brushes represent a non-toxic approach for achieving release of biofouling layers. Thermo-responsive poly(N-isopropylacrylamide) (PNIPAAm) polymer brushes have been shown to modulate bacterial adhesion and release through transition between temperatures above and below the lower critical solution temperature (LCST ~32 °C) of PNIPAAm in water. In this article, we describe a convenient method to synthesize grafted PNIPAAm brushes over large areas for biological studies using a relatively simple and rapid method which allows atom transfer radical polymerization (ATRP) in presence of air using the activator regenerated electron transfer (ARGET) mechanism. PNIPAAm brushes were characterized using X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, Fourier transform infrared spectroscopy, ellipsometry, and contact angle measurements. Our studies demonstrate that uniform, high purity PNIPAAm brushes with controlled and high molecular weight can be easily produced over large areas using ARGET-ATRP. We also report the use of a spinning disk apparatus to systematically and quantitatively study the detachment profiles of bacteria from PNIPAAm surfaces under a range (0-400 dyne/cm(2)) of shear stresses.

Fig. 1

a Schematic of the ARGET–ATRP reaction. b ARGET–ATRP of PNIPAAm from initiator immobilized on a silicon wafer in presence of air

Fig. 2

Ellipsometric thickness of grafted PNIPAAm brush measured in dry state for different polymerization times by (a) use of tin 2-ethylhexanoate as the reducing agent, and (b) use of ascorbic as the reducing agent. The standard deviation for each measurement is within the size of the data point

Fig. 3

High resolution XPS C1 s spectra of PNIPAAm grafted surfaces synthesized using (a) tin(II) 2-ethylhexanoate and (b) and ascorbic acid

Fig. 4

Time-of-flight secondary ion mass spectroscopy positive ion spectra of (a) ARGET–ATRP grafted PNIPAAm brush formed using ascorbic acid as a reducing agent, and (b) spin coated PNIPAAm on silicon substrates

Fig. 5

Fraction of adherent C. marina cells on PNIPAAm grafted glass coverslip substrate as a function of shear rate applied at different temperature (inverted filled triangles 37 °C, filled circles 25 °C, filled diamonds 4 °C) using the spinning disk device using spinning disk device. Errors bars are within the size of the data point symbols