Surface tension of protein and insoluble lipids at the air-aqueous phase interface

The surface activity of bovine serum albumin (BSA) in water and aqueous solutions of ethanol (0.5, 1.0, and 2.0 M) and sucrose (0.5 and 1.0 M) has been investigated over a range of protein concentrations (5–1.10⁻⁵, % w/w). The surface tension data were determined by the Wilhelmy plate method. Surface data at low protein concentrations indicate a low surface activity, which rises to a plateau as the monolayer is saturated at higher protein concentrations. The protein concentration and surface tension at the plateau depend on the aqueous phase composition. The effect of aqueous phase composition on BSA-lipid interactions has been investigated by spreading an insoluble lipid (monostearin or monoolein) on a film of BSA previously adsorbed on the interface. The existence of protein-lipid interactions depends on the protein/lipid ratio. The surface activity of mixed BSA-lipid films is determined by the lipid because the surface pressure of the mixed film is the same as the lipid equilibrium spreading pressure, and the monolayer is not saturated by BSA. However, the surface activity of mixed BSA-lipid films is determined by BSA as the monolayer is saturated by the protein.     

Protein and lipid films at equilibrium at air-water interface

The surface activity of β-casein, caseinate, and a whey protein isolate in aqueous solutions has been investigated over a range of protein concentrations (1·10⁻⁵ to 5% w/w) at pH 5 and 7. The surface pressure data were determined by the Wilhelmy plate method. Surface pressure data at low protein concentration indicate a low surface activity that rises to a plateau as the monolayer is saturated at higher protein concentrations. The protein concentration and the surface pressure at the plateau depend on the pH and the type of protein in the aqueous phase. Protein-monoglyceride interactions were investigated by spreading an insoluble monoglyceride (monopalmitin, monoolein, or monolaurin) on a film of protein previously adsorbed on the interface at equilibrium. The existence of protein-monoglyceride interactions depends on the interfacial composition and on the protein/monoglyceride ratio. The surface activity of mixed protein-monopalmitin and protein-monoolein films is determined by the lipid as the surface pressure of the mixed film is the same as the monoglyceride equilibrium spreading pressure, and the monolayer is not saturated by the protein. However, the protein determines the surface activity of mixed protein-monopalmitin and protein-monoolein films as the protein saturates the monolayer. For protein and monolaurin mixed films, protein determines the surface activity over the range of protein-monolaurin compositions due to monolaurin dissolution in the bulk aqueous phase.     

Wettability and surface free energy of bovine serum albumin films

Measurements of the contact angle for water, glycerol, formamide, ethylene glycol, and diiodomethane on polymethyl methacrylate covered by adsorptive bovine serum albumin (BSA) films were made. Adsorption was performed from solutions in the concentration range 0–100 g/L. From the obtained contact angles the Lifshitz-van der Waals components and the values of the electron-acceptor and electrondonor parameters of the acid-based components of the films were calculated for six triplets of liquids. The biggest changes in the BSA film structure occurred under a monolayer coverage (i.e., at BSA concentrations of <2.5 g/L). On the basis of the contact angles of glycerol, ethylene glycol, and formamide it was concluded that the density of BSA polar groups was almost constant. The surface density of the hydrophobic part of the BSA film also seemed constant regardless of the concentration of the solution from which the BSA adsorptive film was created. This conclusion could be drawn from the almost constant contact angle of diiodomethane.     

磺酸盐型双基表面活性剂的合成与表面性能

以壬基酚和甲醛为原料,合成了一种新型的磺酸盐型双基表面活性剂(Gemini-A)。利用元素分析、红外光谱确定了Gemini-A的结构。研究了Gemini-A水溶液的润湿性,比较了Gemini-A与传统表面活性剂的增溶能力。试验结果表明,Gemini-A水溶液具有较低的表面张力(33.51 mN/m)和临界胶束浓度(0.141 mmol/L)及良好的润湿性,显示出了较好的表面性能,具有很强的增溶能力,是符合3次采油要求的表面活性剂。     

Study of the adsorption process of bovine serum albumin on passivated surfaces of CoCrMo biomedical alloy

Adsorption of bovine serum albumin (BSA) on CoCrMo surface was studied by electrochemical techniques in order to determine the mechanism of protein adsorption at different surface conditions (which are reached by considering different passivation times) in phosphate buffered solution (PBS). At open circuit potential (OCP), adsorption kinetic was influenced by surface passivation when passivation time was lower than 1 h, whereas, at higher passivation times, no apparent modification in the kinetic mechanisms of adsorption was observed. On the other hand, at a passive applied potential, the BSA addition decreased the passivation kinetics of the process at all the passivation times.     

Synthesis and characterization of poly(N-vinyl pyrrolidone-alt-maleic anhydride): Conjugation with bovine serum albumin

Alternate N-vinyl pyrrolidone/maleic anhydride (NVPMA) copolymers were obtained by radical solution polymerization in dioxane with various MA contents in the monomer feed. The conversion of each monomer was monitored by proton nuclear magnetic resonance spectroscopy (¹H NMR), and the kinetics investigation showed that both monomers had identical polymerization rates if both monomers were present in the reaction mixture. The presence of excess NVP in the polymerization medium increased the kinetics of the polymerization and the molar masses of the resulting polymers. This increase was attributed to a cosolvent effect due to NVP, which is a better solvent for the polymer than dioxane. The hydrolysis rate constant of the polymers increased with pH, and NVPMA copolymers were more prone to hydrolysis (by a factor 10) than the methyl vinyl ether ones. Finally, the immobilization of bovin serum albumin (BSA) was investigated. A 25 mM phosphate buffer (pH 5.5) was the best medium to covalently bind 5 BSA molecules onto a 29 kDa NVPMA copolymer and 13 BSA molecules onto a 58 kDa sample, with grafting efficiencies > 90%. Noncovalent interactions with the hydrolyzed form of the polymer and BSA occured at pHs lower than the isoelectric point of BSA, and the resulting complexes were insoluble in water. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3327–3337, 2001     

ATRP in the design of functional materials for biomedical applications

Atom Transfer Radical Polymerization (ATRP) is an effective technique for the design and preparation of multifunctional, nanostructured materials for a variety of applications in biology and medicine. ATRP enables precise control over macromolecular structure, order, and functionality, which are important considerations for emerging biomedical designs. This article reviews recent advances in the preparation of polymer-based nanomaterials using ATRP, including polymer bioconjugates, block copolymer-based drug delivery systems, cross-linked microgels/nanogels, diagnostic and imaging platforms, tissue engineering hydrogels, and degradable polymers. It is envisioned that precise engineering at the molecular level will translate to tailored macroscopic physical properties, thus enabling control of the key elements for realized biomedical applications.