Study of selective protein adsorption on stimuli-responsive polymer brushes

Protein adsorption is the first step when a solid surface gets in contact with a biological fluid, and its effect can be either beneficial or detrimental. The control of this phenomenon has important im- plications in biomaterials science, biofouling, food industry or biosensors. Surface modification with stimuli-responsive polymer brushes offers promising perspectives to control protein adsorption. Thin coatings of these «smart materials» can indeed be chemically modified in a certain biological aim, such as to stimulate the adsorption or the desorption of proteins. This study aims at developing mixed polymer brushes sensitive to the ionic strength and the pH of the surrounding medium, in order to tune their properties toward selective protein adsorption from a mixture, such as human blood plasma containing serum albumin, globulins and fibrinogen. In this study, complex stimuli-responsive polymer brushes were developed, composed of poly(2-(di- methylamine)ethyl methacrylate) (PDMAEMA) and poly(ethylene oxide) (PEO), according to the «grafting to» approach on a gold substrate. PDMAEMA is a weak positively-charged polyelectrolyte at pH 7.4 and PEO is a neutral protein-repellent polymer. First, the coated polymer brushes were characterized using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM), water contact angle and streaming potential measurements, and revealed the presence of both polymers on the surface. Protein adsorption was then studied at biological pH 7.4 and ionic strength 10−3M, using quartz crys- tal microbalance (QCM). Desorption was carried out by rinsing with a sodium chloride solution at pH 9.0 and ionic strength 0.15M. The switchable behavior of the polymer brushes depending on the conditions allowed to demonstrate partial reversibility of protein adsorption. Adsorption of mixed protein solutions was then studied by ToF-SIMS using principal component anal- ysis (PCA), in order to identify the adsorbed proteins and to investigate the selectivity of polymer brushes. Adsorption from solutions of human serum albumin (HSA), fibrinogen (Fb), lysozyme (Lys) and/or avidin (Avi) was studied and discussed. PCA revealed selective adsorption of HSA from an HSA/Avi solution. The obtained results showed that polymer brushes exhibit promising properties towards the control of protein adsorption, and offer many perspectives in biomaterials science and bioengineering.