Factors impacting protein adsorption on layer-by-layer assembled stimuli-responsive thin films

Studying the stimuli-response of polyelectrolyte multilayers (PEMs) towards protein adsorption requires coping with the multiplicity of factors influencing interfacial processes. In this study, we report the design of a nanostructured stimuli-responsive coating based on the sequential layer-bylayer assembly of poly(N-isopropylacrylamide) block copolymers with poly (allylamine hydrochloride) and scrutinize its ability to modulate protein adsorption. The results reveal that the stimuli-response of the film towards protein adsorption under T, pH and I changes is strongly influenced by the type of buffer. This latter parameter has indeed a significant impact on the adsorbed amount of proteins, while it has only slight effect on the stimuli-response of free block copolymer, on the mechanism of PEM growth and the properties of the obtained film. In conditions favorable to protein adsorption, the use of anionic buffer leads to the adsorption of an apparent monolayer of proteins, while in zwitterionic buffer, proteins adsorb in a significantly higher amount. This trend may be explained by a more efficient charge screening of macromolecules by zwitterions which reduce the repulsion between proteins, leading to their accumulation at the interface. Finally, the length of the poly(N-isopropylacrylamide) block is shown to be another key factor impacting the amount of adsorbed proteins. The findings reported in this paper provide relevant information and allow the evaluation of stimuli-response of PEM to be carried out under optimized conditions.