Nanoscale organization of collagen and mixed collagen-pluronic adsorbed layers

Adsorption of collagen (300 nm length, 1.5 nm diameter) on poly(ethylene terephthalate) and the influence of Pluronic PE6800, a triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer, were investigated by the combination of three techniques. The adsorbed amounts of the two adsorbates were determined by radiolabeling. X-ray photoelectron spectroscopy was used to get quantitative information on the adsorbed layer. Selected samples were observed by atomic force microscopy (AFM) under water and in air; data on morphology, mechanical resistance, and molecular interactions were obtained. In the absence of Pluronic, two collagen layer morphologies were observed. Under water, at an adsorbed amount equal to half the maximum, collagen formed a dense granular layer; at the maximum adsorbed amount (equivalent to six layers of lying molecules), the adsorbed layer was soft, appeared as a pattern of elongated structures, and showed adhesion of the AFM probe with rupture lengths as long as several hundred nanometers. This was attributed to collagen molecules or bundles protruding into the solution. After fast drying, the collagen layer was smooth with a low surface fraction occupied by holes at the lower protein adsorbed amount, while it showed spindle-shape relief features at the maximum adsorbed amount. In the presence of Pluronic, the amount of adsorbed collagen was reduced considerably, due to rapid adsorption of the surfactant. In these conditions, the collagen layer obtained from high protein concentration solutions was also constituted by granules and was very sensitive to the alteration by the AFM probe.