Oxidation State of a Polyurethane Membrane after Plasma Etching

Low moduli cell culture substrates can be used to apply dynamic mechanical strain to cells, by surface deformation. Understanding the surface interaction with cells is critical to improving cell adhesion and normal growth. A medical grade polyurethane (PU), Chronoflex AL 80A, was modified by oxygen plasma etching and characterised by X-ray photoelectron spectroscopy. Etching resulted in increased cross-linking at the isocyanate bond and formation of new oxygen moieties. The model, derived from patent data and XPS data of the unetched PU, indicated that the additional oxygen was likely to be hydroxyl and carbonyl groups. Etched membranes enhanced protein adhesion, resulting in full surface coverage compared to unetched PU. The etched PU supported cell adhesion and spreading, while the unetched PU was not conducive to monolayer formation. 1. Introduction The human body comprises tissues with a range of elastic moduli. Improving the response of in vitro cell- and tissue-based investigations can be achieved by culturing cells upon a substrate with a modulus closer to that of living tissue, as opposed to tissue culture polystyrene that has a modulus an order of magnitude greater than smooth muscle, for example, [1]. In addition, dynamic modulation of the substrate can provide mechanical signals that drive differentiation or proliferation. Previously, a stable biocompatible polyurethane (PU), Chronoflex AL 80A (AdvanSource Biomaterials, Wilmington, MA), was tested as a low modulus candidate substrate for a bioreactor capable of subjecting cells to a dynamic mechanical environment [2]. PU was selected as it is more resilient [3] and has a better cell response than similar polymers [4]. It was shown that plasma etching is a key factor to the success of cell adhesion and normal cell growth: the wettability was found to be dependent on etching power and duration, while roughness was more affected by the duration [2]. Therefore the state of oxidation of the PU membrane has been examined, in order to understand the effects of plasma etching on protein and cell adhesion. 2. Method 2.1. Membrane Manufacture and Modification PU membranes were produced as described previously [2]. In brief, polyurethane membranes of thickness ？μm (mean ± standard deviation (SD)) were formed by solvent casting with tetrahydrofuran (10% w/w) and drying in a vacuum oven at 50°C. Surface modification was carried out by etching using an inductively coupled RF-source (13.56？MHz) plasma barrel etcher (Biorad PT7100). The sample chamber was evacuated to 8？Pa, purged with oxygen (grade 2