Repulsive surfaces and lamellar lubrication of synovial joints.

Surface-active phospholipid (SAPL) secreted in the synovial joint plays an important role in cartilage integrity. In healthy joints, phospholipid multibilayers coat the cartilage surface, providing boundary lamellar-repulsive hydration lubrication. Current mechanism for lubrication of synovial joints, as well as the physical and chemical nature of the cartilage surface is discussed. Friction between phospholipid (PL) bilayers attached to cartilage surfaces is considered including a discussion on the recent observation of an extreme friction reduction as a consequence of a less charged hydrophilic cartilage surface. It is proposed that the highly efficient lubrication occurring in natural joints arises from the presence of negatively charged cartilage surfaces. The lamellar-repulsive mechanisms for the reduction of friction is supported by phospholipid lamellar phases and charged macromolecules residing between contacting cartilage surfaces at pH ∼7.4.

Study of Hydration Repulsion of Zwitterionic Polymer Brushes Resistant to Protein Adhesion through Molecular Simulations.

The fabrication of antifouling zwitterionic polymer brushes represents a leading approach to mitigate nonspecific adhesion on the surfaces of medical devices. This investigation seeks to elucidate the correlation between the material composition and structural attributes of these polymer brushes in preventing protein adhesion. To achieve this goal, we modeled three different zwitterionic brushes, namely, carboxybetaine methacrylate (CBMA), sulfobetaine methacrylate (SBMA), and (2-(methacryloyloxy)ethyl)-phosphorylcholine (MPC). The simulations revealed that elevating the grafting density enhances the structural stability, hydration strength, and resistance to protein adhesion exhibited by the polymer brushes. PCBMA manifests a more robust hydration layer, while PMPC demonstrates the slightest interaction with proteins. In a comprehensive evaluation, PSBMA polymer brushes emerged as the best choice with superior stability, enhanced protein repulsion, and minimally induced protein deformation, resulting in effective resistance to nonspecific adhesion. The high-density SBMA polymer brushes significantly reduce the level of protein adhesion in AFM testing. In addition, we have pioneered the quantitative characterization of hydration repulsion in polymer brushes by analyzing the hydration repulsion characteristics at different materials and graft densities. In summary, our study provides a nuanced understanding of the material and structural determinants influencing the capacity of zwitterionic polymer brushes to thwart protein adhesion. Additionally, it presents a quantitative elucidation of hydration repulsion, contributing to the advancement and application of antifouling polymer brushes.

Mitigation of protein fouling by magnesium ions and the related mechanisms in ultrafiltration process.

Although protein is an important membrane foulant in the water body that may be significantly affected by the coexisting common cation magnesium (Mg2+), the effect of Mg2+ on protein fouling is rarely reported. In this context, this study selected bovine serum albumin (BSA) as the model foulant, and investigated its fouling characteristics at different Mg2+ concentrations (0-100 mM). Filtration tests showed that the protein fouling can be significantly mitigated by adding Mg2+, and the specific filtration resistance (SFR) of pure BSA (3.56 × 1014 m kg-1) was at least 5 times that of BSA-Mg2+ solutions (0.5-100 mM). In addition, an optimal Mg2+ concentration exists, which can achieve the lowest BSA SFR. A series of characterizations indicated that the main contributors to the differences in BSA SFR were the changes in BSA adhesion capacity and the thickness and structure of the foulant layer. Basically, the above results were attributed to the hydration repulsion effect of Mg2+, which prevented tight adhesion of foulants to the membrane. Moreover, the lowest BSR SFR at 1 mM Mg2+ was achieved not only by the hydration repulsion effect but also by the particle size compression due to the conformational change of BSA molecules. This combined effect led to the lowest foulant retention on the membrane surface and delivered to the lowest SFR. This study conducts a thorough inspection into the specific effect of Mg2+ on protein fouling and provides a fresh insight into protein fouling control in the UF process.

Hydration repulsion between membranes and polar surfaces: simulation approaches versus continuum theories.

A review of various computer simulation approaches for the study of the hydration repulsion between lipid membranes and polar surfaces is presented. We discuss different methods and compare their advantages and limitations. We consider interaction pressures, interaction thermodynamics, and interaction mechanisms. We take a close look at the influence of the experimental boundary conditions and at repulsion mechanisms due to the unfavorable overlap of interfacial water layers. To this end, we analyze several distinct water order parameters in simulations of interacting polar surfaces and compare the results to the predictions of simple continuum theories.