Modification of hysteresis behaviors of protein monolayer and the corresponding structures with the variation of protein surface charges

Lysozyme Influence on Monolayers of Individual and Mixed Lipids

Fatty acids, cholesterol, and phospholipids are amphiphilic compounds of biological interest, which form ordered monolayers mimicking biomembranes, and can be studied with the Langmuir technique using surface pressure-area isotherms and compressibility plots. Proteins are also components of biomembranes or are present in body fluids. In this study, the influence of lysozyme on different films of a fatty acid (stearic acid or oleic acid), cholesterol, a phospholipid (dipalmitoylphosphatidylcholine, DPPC, or palmitoyloleoylphosphatidylcholine, POPC), and mixtures of them is presented using a 0.9% saline solution as subphase. Results show that the presence of lysozyme alters the lipid monolayer formation in an important way at the beginning (low surface pressures) and the middle (intermediate surface pressures) parts of the isotherm. At high surface pressures, the phospholipids DPPC and POPC and the saturated fatty acid, stearic acid, expel lysozyme from the surface, while oleic acid and cholesterol permit the presence of lysozyme on it. The mixtures of oleic acid-DPPC also expel lysozyme from the surface at high surface pressures, while mixtures of oleic acid-POPC and cholesterol-POPC permit the presence of lysozyme on it. The compressibility of the monolayer is affected in all cases, with an important reduction in the elastic modulus values and an increase in the fluidity, especially at low and intermediate surface pressures.

Covalent immobilization of the phytic acid-magnesium layer on titanium improves the osteogenic and antibacterial properties

In order to improve early osseointegration and long-term survival rate of implants, a multifunctional titanium surface that promotes osteogenesis and antibacterial properties is expected. Incorporation of bioactive trace elements such as magnesium ions was proved a promising method to improve osseointegration of titanium. Phytic acid has strong chelating ability with multivalent cations, which has been used in surface modification. Moreover, phytic acid was proved antibacterial potential. Herein, to improve the osteogenic and antibacterial properties, a phytic acid-magnesium (PA-Mg) layer was introduced on titanium using phytic acid as a cross-linker molecule. No obvious changes of the surface characterization were observed by scanning electron microscopy and atomic force microscopy. X-ray photoelectron spectroscopy confirmed that the PA-Mg layer covalently bond to the Ti surface, and the thickness of the PA-Mg layer was about 150 nm. Besides, improved hydrophilic and more protein adsorption were observed on Ti-PA-Mg. Notably, a relatively controlled magnesium release was also observed on Ti-PA-Mg. Human bone mesenchymal stem cells showed better adhesion, proliferation, and osteogenic differentiation on Ti-PA-Mg samples, indicating improved biocompatibility and osteoinductivity. Moreover, Ti-PA-Mg had better antibacterial properties against porphyromonas gingivalis than Ti. Overall, the PA-Mg layer on Ti surface improved the osteogenic and antibacterial properties, which may have promise for use in dental implantation.

Behaviour of protein (BSA)-lipid (DMPA) mixed monolayer on the spreading order of the individual component

Surface pressure (π) - mean molecular area (A) isotherms of protein (BSA) - lipid (DMPA) mixed films are examined by varying their ratio and altering the spreading order of BSA and DMPA on the water surface to study the protein-lipid interactions and the corresponding structures and patterns at different interfacial conditions. π-A isotherms and compression-decompression isotherm cycles of protein-lipid mixed monolayers below and above of the isoelectric point of BSA (pI ≈ 4.8) are also examined. Below the isoelectric point of BSA (pH ≈ 4.0), i.e., when BSA is weakly hydrophobic and has net positive charge shows low hysteresis irrespective of the spreading order of the molecules. However, at pH ≈ 7.0, i.e., when the overall charge of BSA is negative and is strongly hydrophobic the protein-lipid mixed films display higher hysteresis value. Besides the properties of the isotherms, the surface morphology and secondary conformations of protein inside the mixed films are obtained from X-ray reflectivity, atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy respectively after depositing the mixed films on solid substrates. Nearly similar information is obtained after altering the spreading order of BSA and DMPA, which indicates that the spreading of molecules on the water surface is one of the better ways of forming the lipid-protein mixed film at the air-water interface.