Resolution of the Vertical and Horizontal Heterogeneity of Adsorbed Collagen Layers by Combination of QCM-D and AFM

Abstract

Collagen (type I from calf skin) adsorption on polystyrene (PS) and plasma-oxidized polystyrene (PSox) was studied, using a quartz crystal microbalance with energy dissipation measurements (QCM-D) and atomic force microscopy (AFM) in tapping mode. Radio-labeled collagen was used to measure the adsorbed amount and the ability of adsorbed collagen to exchange with molecules in the solution. The results show that the collagen adlayer consists of two parts: a dense and thin sheet in which fibrils are formed (directly observed by AFM) and an overlying thick layer (up to 200 nm) containing protruding molecules or bundles which are in very low concentration but modify noticeably the local viscosity. The thickness and viscosity of the semi-liquid adlayer both increase with adsorption time and collagen concentration. Fibril formation near the surface also increases with time and collagen concentration and occurs more readily on PS compared to PSox. Radiochemical measurements show that this may be related to the larger mobility of molecules adsorbed on PS, presumably owing to a smaller number of binding points.

Understanding and controlling type I collagen adsorption and assembly at interfaces, and application to cell engineering

“…Collagen adsorption is essentially irreversible on both substrate, with a desorption in buffer of about 20%. However, exchange of adsorbed molecules by molecules from the solution is observed on PS, where desorption in the presence of collagen is of about 45%, but not on PSox [21]. This further confirms that the collagen-substrate interaction is stronger on PSox compare to PS.…”

“…On PSox, collagen molecules would rather lie along the substrate plane, increasing the interaction with the substrate, and decreasing the mobility of molecules, which cannot assemble in such conditions. QCM-D results (not shown here) [21] obtained for collagen adsorption on PS and PSox revealed unusually high f (≈600 Hz on PS; ≈300 Hz on PSox) and D (≈150 × 10 −6 on PS; 100 × 10 −6 on PSox) values, especially on PS. This is attributed to the length of the collagen molecule (≈300 nm), which can extend in solution and trap water in the adsorbed layer.…”

“…On images obtained under water, some aggregates are terminated by a rootlike structure [18]. This appears even more clearly when imaging is performed on dried samples [21]. This observation points to the formation of fibrils starting from partly adsorbed collagen molecules, whose free segments would assemble.…”

Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers

“…2b also allows obtaining qualitative information on energy/entropy balance in the adsorption process. 28 High DD values in this plot indicate that the energetic factors predominate, while low DD values indicate that entropy is the factor that controls the adsorption process. The results obtained by ellipsometry are in good qualitative agreement with those obtained from D-QCM and they are in agreement with the results obtained for other similar systems.…”

Viscoelastic adlayers of collagen and lysozyme studied using quartz crystal microbalance with dissipation monitoring

“…In fact, no conformational change is caused for CSC by a simple 1:1 electrolyte, namely NaCl, as briefly mentioned in Section 3.3. Besides, some AFM work [21] shows that the bundled structure of collagen is well retained after the adsorption on a solid surface in the presence of 0.15 M salt. As long as the bundle remains unchanged, it is quite possible that the each constituent collagen molecule keeps its native triple helix structure.…”