Abstract
The stability of the film poly(n-butyl methacrylate) (PnBMA) with different tacticities, prepared on silicon oxide and exposed to aqueous phosphate-buffered saline with different concentrations of bovine serum albumin (CBSA between 0 and 4.5 mg/mL), was examined at temperatures close to the physiological limit (between 4 and 37 °C) with optical microscopy, contact angle measurements, atomic force microscopy, and time-of-flight secondary ion mass spectrometry. For PBS solutions with CBSA = 0, the stability of atactic PnBMA and dewetting of isotactic PnBMA was observed, caused by the interplay between the stabilizing long-range dispersion forces and the destabilizing short-range polar interactions. Analogous considerations of excess free energy cannot explain the retardation of dewetting observed for isotactic PnBMA in PBS solutions with higher CBSA. Instead, formation of a BSA overlayer, adsorbed preferentially but not exclusively to uncovered SiOx regions, is evidenced and postulated to hinder polymer dewetting. Polymer dewetting and protein patterning are obtained in one step, suggesting a simple approach to fabricate biomaterials with micropatterned proteins.
Highlights
Dewetting is a commonly observed process that occurs when a continuous thin polymer film, which is not in a thermodynamically stable state, breaks up due to interfacial instabilities, initially forming holes that subsequently evolve into droplets.[1]
This study examines the stability of polymer (PnBMA) layers deposited on the silicon oxide surface and immersed in liquids, such as water, phosphate-buffered saline (PBS), and PBS solutions of bovine serum albumin (BSA)
For the purpose of ΔG analysis, the values of surface tension γ and its dispersive and polar components, corresponding to surfaces of the phases that meet at the threephase contact line, are estimated first
Summary
Dewetting is a commonly observed process that occurs when a continuous thin polymer film, which is not in a thermodynamically stable state, breaks up due to interfacial instabilities, initially forming holes that subsequently evolve into droplets.[1]. Article atures.[27] protein adsorption and orientation can be temperature-controlled on PnBMA coatings through a transition from the glassy to the rubbery polymer state, changing polymer nanotopography and elasticity, with negligible changes in electrostatic, dispersion, and polar protein−polymer interactions.[28] This study is an extension of our previous works on PnBMA-grafted brushes[29,30] and explores the films of PnBMA with different tacticities, isotactic and atactic. Analogous experiments performed for isotactic PnBMA films immersed in PBS solutions with different concentrations of bovine serum albumin (BSA) showed retardation of dewetting for the solutions with higher CBSA. This is related to BSA adsorption to various regions of the dewetted surface, with spatial correlation between the protein and the dewetted polymer evidenced by ToF-SIMS: preferential adsorption on uncovered SiOx regions enables protein micropatterning. Increased protein surface density on elevated polymer regions such as rims points to nanotopography effects in protein adsorption.[29]
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