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The dynamic surface tension and surface dilational rheology of native collagen (type I, from bovine calf skin) were analyzed in the temperature range from 21 to 34.5 °C. In addition, the effect of heating the collagen solutions up to 90 °C followed by cooling down to room temperature, on surface tension and rheological parameters of the adsorbed layers was studied. As a water-soluble fibrous protein with little exposed hydrophobicity, native collagen is weakly surface active. However, its layers formed by spontaneous adsorption on the water/air surface display exceptional dilational rheology parameters, comparable with those of globular proteins: at high frequency limit (0.1 Hz) the layers are predominantly elastic, with the storage modulus, E′ = 58 mN/m for collagen concentration of 1.3 × 10−5 M (4 g/L). Increasing temperature during adsorption helps to reduce the surface tension, but the resulting layers show diminished surface elastic response. On the other hand, the samples heated at elevated temperatures and measured after cooling down to the room temperature maintain their high surface elasticity. The results suggest that collagen, even in its native form (not processed to gelatin) has a potential to stabilize biocompatible foams/emulsions by forming mechanically strong adsorbed layers.
We describe the adsorption behaviour and rheological properties of a calf skin type I collagen, and of its hydrolysates obtained using a Clostridium histolyticum collagenase (CHC) under moderate conditions (pH 7, 37°C). The effect of CHC concentration (2×10(-9)-2×10(-6)M) and incubation time (35-85min) was studied and optimised to achieve the highest decrease of surface tension and the highest dilational surface viscoelasticity of the adsorbed layers. SDS-PAGE electrophoresis and reverse-phase high performance liquid chromatography (RP-HPLC) were used to characterise the hydrolysis products. The results show that even simple modifications (heat treatment, pH change, partial hydrolysis) of collagen enhances its surface properties, especially in terms of surface dilational elasticity modulus. The use of low enzyme concentration (CHC-to-collagen molar ratio of 4×10(-3)) and short incubation time (<45min) results in moderately hydrolysed products with the highest ability to lower surface tension (γ=53.9mNm(-1)) forming highly elastic adsorbed layers (surface dilational elasticity, E'=74.5mNm(-1)). Copyright © 2015 Elsevier B.V. All rights reserved.
We describe the effect of three synthetic surfactants (anionic – sodium dodecyl sulfate (SDS), cationic – cetyltrimethylammonium bromide (CTAB) and nonionic – Triton X-100 (TX-100)) on surface properties of the type I calf skin collagen at the air/water interface in acidic solutions (pH 1.8). The protein concentration was fixed at 5 × 10⁻⁶ mol L⁻¹ and the surfactant concentration was varied in the range 5 × 10⁻⁶ mol L⁻¹–1 × 10⁻⁴ mol L⁻¹, producing the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:5, 1:10 and 1:20. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic surface tension and surface dilatational moduli of the mixed adsorption layers. Two spectroscopic techniques: UV–vis spectroscopy and fluorimetry allowed us to determine the effect of the surfactants on the protein structure. The thermodynamic characteristic of the mixtures was studied using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC).