Inhibition of lens epithelial cell growth via immobilisation of hyaluronic acid on atmospheric pressure plasma modified polystyrene

Abstract

Naturally occurring macromolecules have the potential for providing non-fouling coatings on substrates based on a steric entropic principle. In order for this effect to occur, the macromolecules that adhered to the surface must have the correct chemical conformation. This article reports on the immobilisation of hyaluronic acid (HA) onto polystyrene substrates for the purpose of repelling cellular adhesion thereon. In order to create a polystyrene surface capable of adhering HA in the required orientation substrates were treated by atmospheric pressure plasma processing in air. The resulting oxidised surfaces were then aminated by the chemisorption of the 3-aminopropyltrimethoxysilane (APTMS) linker molecule. Three distinct chemical states were found for the APTMS amine group: a neutral, a protonated and a hydrogen bonded state, as determined by X-ray photoelectron spectroscopy (XPS). Carbodiimide coupling of HA at two different macromolecular concentrations (1 mg cm⁻³ and 3 mg cm⁻³) to the aminated surfaces on oxidized polystyrene resulted in covalent immobilisation of the polysaccharide. The chemistry and topography of the polymer surface at each stage of the coating process were analysed by a combination of XPS, ToF-SIMS, and AFM. XPS demonstrates that HA was successfully grafted to the aminated PS surfaces. The degree of chemical homogeneity on the surfaces was determined by ToF-SIMS. Changes in topography resulting from the immobilization process were evident in the AFM images. In vitro studies of the response of human lens epithelial cells (LEC) to the HA-modified polystyrene indicated a significant reduction in cell numbers at all time points post-seeding compared to the control. These results coupled with the surface analysis data indicate that the immobilization method based on atmospheric plasma activation of the polymer surface creates a HA layer with a steric conformation capable of inhibiting cellular attachment.