Healthy synovial fluids (SFs) are complex fluids consisting of biopolymers, globule proteins, and lipids and regarded as superlubricants to provide nearly life-long low friction and wear protection ...of synovial joints in mammals. In this paper, we report that the intricate lubricious mixture can be simulated by the aggregation of hyaluronic acid (HA) and hydrogel particles in aqueous suspensions. In the HA aqueous suspensions added with synthetic polymer microgels, we have effectively captured the bulk rheological properties of healthy SFs. It is also confirmed by light scattering and fluorescence microscopic characterization that added hydrogel particles can enhance the HA network by hydrogel-mediated hydrogen bonding, leading to the fractal HA-hydrogel aggregating networks in aqueous suspensions. The potential application of HA-hydrogel particle aggregates as biomimetic superlubricants is supported by the comparable low friction at high load to that of healthy SFs.
The conformational structure of a polyelectrolyte chain in dilute aqueous solution is strongly coupled with its surrounding electrostatic environment. With the introduction of branched topology, the ...distribution of counterions in the vicinity of a polyelectrolyte chain becomes highly inhomogeneous, giving rise to complex structures of branched polyelectrolytes in dilute aqueous solution. To directly probe the local electrostatic conditions near a branched polyelectrolyte in aqueous solutions, star-shaped poly(2-vinylpyridine) (P2VP) polymers with precise labeling of one single fluorophore at different locations, for example, the star center or the terminal group of one arm, were synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization of vinyl-terminated P2VP macromonomers. Using fluorescence correlation spectroscopy (FCS) combined with photon counting histogram (PCH) analysis, the conformational structures and local electric potential of P2VP star polyelectrolytes were investigated in dilute aqueous solutions of varied pH at a single molecule level. Despite the same hydrodynamic radius of P2VP stars, pH-sensitive fluorophores labeled at different locations sensitively differentiated the higher electric potential at the star center from the lower electric potential at the periphery in dilute aqueous solutions.
A facile and low-cost method is developed to functionalize engineering metal membrane supports, such as stainless steel (SS), with epoxy-containing polymer poly(glycidyl methacrylate) (PGMA) to ...produce a versatile and universal platform for subsequent surface modification. With a PGMA anchoring layer, we have demonstrated that hydrogel particles, such as polyacrylamide-co-poly(acrylic acid) (PAM-co-PAA), can be subsequently grafted to form functional polymer membranes for rapid and efficient oil–water separation. By contact angle and AFM measurement, we have confirmed that PAM-co-PAA hydrogel particle layer grafted on a PGMA-modified SS surface exhibits excellent selectivity as required for liquid–liquid separation, showing high affinity to water but not to oils as an ideal membrane for oil–water separation. To evaluate the separation efficiency, a simple flow-through device is employed to separate free-floating oil from water in the mixture of varied initial oil volume fraction and oil composition. Under substantially high pump flow rate up to 1.3 L/min, PAM-co-PAA hydrogel treated SS mesh can achieve excellent separation efficiency with less than 5% oil or water in the respective filtrate at the flux of as high as 540 m3/(m2·h) and retentate at the flux of 1.95 m3/(m2·h). This separation efficiency is better than, or comparable to, the maximal performance achieved using conventional gravity methods at much lower flow rate. Similar approach could be also adapted to graft superhydrophobic and superoleophilic polymer membranes with PGMA-treated engineering support to separate water from oil.
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We report on studies of lipid transfer rates between different morphology nanoparticles and lipids with different length acyl chains. The lipid transfer rate of dimyristoylphosphatidylcholine ...(di-C14, DMPC) in discoidal “bicelles” (0.156 h–1) is 2 orders of magnitude greater than that of DMPC vesicles (ULVs) (1.1 × 10–3 h–1). For both bicellar and ULV morphologies, increasing the acyl chain length by two carbons going from di-C14 DMPC to di-C16, dipalmitoylphosphatidylcholine (DPPC) causes lipid transfer rates to decrease by more than 2 orders of magnitude. Results from small angle neutron scattering (SANS), differential scanning calorimetry (DSC), and fluorescence correlation spectroscopy (FCS) are in good agreement. The present studies highlight the importance of lipid dynamic processes taking place in different morphology biomimetic membranes.
Using the method of Frantz and Salmeron to cleave mica Tribol. Lett. 5, 151 (1998) we investigate alkane fluids in a surface forces apparatus and confirm several predictions of molecular dynamics ...(MD) simulation. An oscillatory force-distance profile is observed for the methyl-branched alkane, squalane. Boundary slip is inferred from the frictional sliding of molecularly thin fluids and also from the hydrodynamic flow of thicker films. These findings resolve the paradox that prior experiments disagreed with these aspects of MD predictions, and demonstrate that exceptionally low energy dissipation is possible when fluids move past solid surfaces that are sufficiently smooth.
Bacterial ribonucleoprotein bodies (BR-bodies) are non-membrane-bound structures that facilitate mRNA decay by concentrating mRNA substrates with RNase E and the associated RNA degradosome machinery. ...However, the full complement of proteins enriched in BR-bodies has not been defined. Here, we define the protein components of BR-bodies through enrichment of the bodies followed by mass spectrometry-based proteomic analysis. We find 111 BR-body-enriched proteins showing that BR-bodies are more complex than previously assumed. We identify five BR-body-enriched proteins that undergo RNA-dependent phase separation in vitro with a complex network of condensate mixing. We observe that some RNP condensates co-assemble with preferred directionality, suggesting that RNA may be trafficked through RNP condensates in an ordered manner to facilitate mRNA processing/decay, and that some BR-body-associated proteins have the capacity to dissolve the condensate. Altogether, these results suggest that a complex network of protein-protein and protein-RNA interactions controls BR-body phase separation and RNA processing.
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•Bacterial RNP body (BR-body) proteomics identifies 111 proteins enriched in BR-bodies•BR-bodies associate with an interconnected network of RNP condensates•BR-body condensation is modulated by its interaction network•RNA is required for rapid BR-body condensation
Nandana et al. present liquid chromatography-mass spectrometry proteomics data of bacterial RNP bodies, revealing that they contain >100 proteins including the RNA degradosome. Through the complex network of protein-protein and protein-RNA interactions, this proteome has diverse regulatory interactions with the core scaffold RNase E that impact BR-body assembly and function.
We present a high throughput (maximum flow rate approximately 10 microl/min or linear velocity approximately 3 mm/s) continuous bio-particle sorter based on 3D traveling-wave dielectrophoresis ...(twDEP) at an optimum AC frequency of 500 kHz. The high throughput sorting is achieved with a sustained twDEP particle force normal to the continuous through-flow, which is applied over the entire chip by a single 3D electrode array. The design allows continuous fractionation of micron-sized particles into different downstream sub-channels based on differences in their twDEP mobility on both sides of the cross-over. Conventional DEP is integrated upstream to focus the particles into a single levitated queue to allow twDEP sorting by mobility difference and to minimize sedimentation and field-induced lysis. The 3D electrode array design minimizes the offsetting effect of nDEP (negative DEP with particle force towards regions with weak fields) on twDEP such that both forces increase monotonically with voltage to further increase the throughput. Effective focusing and separation of red blood cells from debris-filled heterogeneous samples are demonstrated, as well as size-based separation of poly-dispersed liposome suspensions into two distinct bands at 2.3 to 4.6 microm and 1.5 to 2.7 microm, at the highest throughput recorded in hand-held chips of 6 microl/min.
Enhanced layering is observed when molecularly thin films of a simple globular molecular fluid (octamethylcyclotetrasiloxane) are confined between step-free sheets of mica cleaved to be free of ...nanoparticulates produced by using a hot platinum wire. In addition, the linear shear responses depend on history. Films formed by rapid compression or under the action of shear display a large effective viscosity, but films formed by quasistatic compression display unprecedented low friction.
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