Equilibrium protein adsorption on nanometric vegetable-oil hybrid film/water interface using neutron reflectometry

TL;DR

This study investigates protein adsorption on nanometric vegetable-oil hybrid films at the water interface using neutron reflectometry, revealing multilayer adsorption and minimal film penetration, which informs biocompatibility optimization.

Contribution

It provides the first detailed neutron reflectometry analysis of protein adsorption on nanometric vegetable-oil hybrid films, highlighting multilayer formation and the effects of salt and protein concentration.

Findings

Adsorption at oil-water interface is 3-4 times higher than at air-water interface.

Proteins form multilayer structures with specific thicknesses (~30 Å and 55-60 Å).

Oil film remains intact with minimal protein penetration.

Abstract

Nanofilms of thickness of about two nanometers have been formed at the air-water interface using functionalized castor oil (ICO) with cross-linkable silylated groups. These hybrid films represent excellent candidates for replacing conventional polymeric materials in biomedical applications, but they need to be optimized in terms of biocompatibility which is highly related to protein adsorption. Neutron reflectivity has been used to study the adsorption of two model proteins, bovine serum albumin and lysozyme, at the silylated oil (ICO)-water interface in the absence and presence of salt at physiologic ionic strength and pH and at different protein concentrations. These measurements are compared to adsorption at the air-water interface. While salt enhances adsorption by a similar degree at the air-water and the oil-water interface, the impact of the oil film is significant, with adsorption at the oil-water interface three-to four-fold higher compared to the air-water interface. Under these conditions, the concentration profiles of the adsorbed layers for both proteins indicate multilayer adsorption: The thickness of the outer layer (oil-side) is close to the dimension of the minor axis of the protein molecule, ~ 30 {\AA}, suggesting a side-way orientation with the long axis parallel to the interface. The inner layer extends to 55-60 {\AA}. Interestingly, in all cases, the composition of oil film remains intact without significant protein penetration into the film. The optimal adsorption on these nanofilms, 1.7-2.0 mg$\bullet$m-2 , is comparable to the results obtained recently on thick solid cross-linked films using quartz crystal microbalance and atomic force microscopy, showing in particular that adsorption at these ICO film interfaces under standard physiological conditions is non-specific. These results furnish useful information towards the elaboration of vegetable oil-based nanofilms, in direct nanoscale applications or as precursor films in the fabrication of thicker macroscopic films for biomedical applications. 2