Interface of covalently bonded phospholipids with a phosphorylcholine head: characterization, protein nonadsorption, and further functionalization.

Surface anchored poly(methylhydrosiloxane) (PMHS) thin films on oxidized silicon wafers or glass substrates were functionalized via the SiH hydrosilylation reaction with the internal double bonds of 1,2-dilinoleoyl-sn-glycero-3-phosphorylcholine (18:2 Cis). The surface was characterized by X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, and scanning electron microscopy. These studies showed that the PMHS top layer could be efficiently modified resulting in an interfacial high density of phospholipids. Grafted phospholipids made the initially hydrophobic surface (θ = 106°) very hydrophilic and repellent toward avidin, bovine serum albumin, bovine fibrinogen, lysozyme, and α-chymotrypsin adsorption in phosphate saline buffer pH 7.4. The surface may constitute a new background-stable support with increased biocompatibility. Further possibilities of functionalization on the surface remain available owing to the formation of interfacial SiOH groups by Karstedt-catalyzed side reactions of SiH groups with water. The presence of interfacial SiOH groups was shown by zeta potential measurements. The reactivity and surface density of SiOH groups were checked by fluorescence after reaction of a monoethoxy silane coupling agent bearing Alexa as fluorescent probe.

Increase of fibrin gel elasticity by enzymes: a kinetic approach.

Two enzymes, thrombin and transglutaminase, both participate in the formation of fibrin networks and contribute to the mechanical strength of biogels. A theoretical model built from the available kinetic data showed that a competition may take place between the two enzymes for their common substrate, fibrinogen. To evidence this phenomenon experimentally, the concentrations of the reactants were varied and the rheological properties of the resulting fibrin gels explored. The elasticity of the gels was not a singular function of the transglutaminase concentration, the optimum being also related to fibrinogen and thrombin concentrations. Thrombin concentration influenced the kinetics of gelation, but not the evolution of the mechanical properties of the gel. An indirect relationship between gel elasticity and thrombin concentration was observed upon covalent binding. The liquid phase inside the gel contained a high amount of soluble proteins when a high transglutaminase concentration was used. The impact of this competition between the two enzymes, demonstrated here for the first time, is evaluated for biomaterial elaboration.