Rheological Properties and Its Effect on the Lubrication Mechanism of PVP K30 and PVP 40-50 G as Artificial Synovial Fluids

The effect of polyvinylpyrrolidone (PVP) on the rheological properties of joint prostheses is still unclear, despite its good lubricity and biocompatibility. In the present work, PVP K30 and PVP 40-50 G solutions at different concentrations were analyzed for rheological and lubrication properties. The rheological properties of the samples were measured at a shear rate range of 0–1800 s−1 (advanced air bearing rheometer Bohlin Gemini 2 and Plate MCR 72/92 rheometer for PVP30 and PVP 40-50 G, respectively). It was found that both the viscosity and shear stress of the samples reduced with a shear rate increase. PVP 40-50 G/sterile water showed higher viscosity as compared to the PVP K30/sterile water sample at a lower shear rate. However, at a higher shear rate, the PVP K30 sample produced better results. Further numerical study results showed the pressure and molecular viscosity distributions. The inclusion of PVP improved the load caring capacity and hence, it is a promising lubrication additive for artificial joints.

A unified description of gravity- and kinematics-induced segregation forces in dense granular flows

Particle segregation is common in natural and industrial processes involving flowing granular materials. Complex, and seemingly contradictory, segregation phenomena have been observed for different boundary conditions and forcing. Using discrete element method simulations, we show that segregation of a single particle intruder can be described in a unified manner across different flow configurations. A scaling relation for the net segregation force is obtained by measuring forces on an intruder particle in controlled-velocity flows where gravity and flow kinematics are varied independently. The scaling law consists of two additive terms: a buoyancy-like gravity-induced pressure gradient term and a shear rate gradient term, both of which depend on the particle size ratio. The shear rate gradient term reflects a kinematics-driven mechanism whereby larger (smaller) intruders are pushed toward higher (lower) shear rate regions. The scaling is validated, without refitting, in wall-driven flows, inclined wall-driven flows, vertical silo flows, and free-surface flows down inclines. Comparing the segregation force with the intruder weight results in predictions of the segregation direction that match experimental and computational results for various flow configurations.

Preparation and Rheology of Magnetorheological Fluid Using Six Kinds of Fumed Silica as Stabilizing Additives

In this study, magnetorheological fluid (MRF) was prepared with several kinds of hydrophobic fumed silica in order to improve MRF stability while maintaining desirable fluidity. We conducted steady flow measurements and oil separation tests under gravity and centrifugal conditions. The linkage of fumed silica particles was also observed morphologically by transmission electron microscopy. We found that the MRF sedimentation stability correlated with viscosity in the lower shear rate range. The oil separation ratio improved with the addition of the fumed silicas examined in this study. The surface characteristics of the silica particles affected the stabilization ability. The addition of hydrophobic fumed silica can desirably increase MRF magnetic properties.

Rheological Characterization of Polyethylene Oxide (PEO): An Experimental Steady State and Transient Analysis

In this paper, the rheological characteristics of aqueous PEO (Polyethylene oxide) solution with very high molecular weight 4 × 106 g/mol is investigated. Shear flow measurements were carried out in steady and transient modes. The unique behavior of PEO is found to be heavily dependent on the input shear rate and the mechanism of data generation. Generally, PEO is found to be shear-thinning throughout the experiments, but at the start of the experiments at low shear rates, minimum input shear value also affects the shear-thinning behavior. In this study, we investigate the critical method of applying input shear to the samples in the lower shear rate regime. Surprisingly, different input methods yield different results. Viscosity curves obtained through shear flow experiments are found to be significantly dependent on the input method of shear rate. Experimental measurements were validated by Cross and Carreau-Yasuda models.

Properties of EPDM/PP thermoplastic vulcanizates produced by an intermeshing-type internal mixer comparing with a co-rotating twin-screw extruder

A unique technology for producing thermoplastic vulcanizate (TPV) has been developed using an intermeshing-type internal mixer (ITM). TPV produced by the ITM was compared with that produced using a co-rotating twin screw extruder (Co-TSE) to assess the former’s commercial possibilities. TPV, originating from ethylene-propylene-diene monomer (EPDM) and polypropylene (PP), was produced by both machines with equal filled volumes, same shear rate, and same specific mechanical energy. Results indicate that ITMs can be used to produce TPV with mechanical properties comparable to those of TPV produced by Co-TSE. TPV can be produced with a lower shear rate with ITM compared to Co-TSE. A long residence time can be maintained in the mixing chamber of the ITM, allowing high conversion of the cross-linking reaction and resulting in better elastic recovery properties due to the higher cross-linking density. However, this resulted in higher viscosity of TPV produced by ITM.

An Investigation on the Aggregation and Rheodynamics of Human Red Blood Cells Using High Performance Computations

Studies on the haemodynamics of human circulation are clinically and scientifically important. In order to investigate the effect of deformation and aggregation of red blood cells (RBCs) in blood flow, a computational technique has been developed by coupling the interaction between the fluid and the deformable RBCs. Parallelization was carried out for the coupled code and a high speedup was achieved based on a spatial decomposition. In order to verify the code’s capability of simulating RBC deformation and transport, simulations were carried out for a spherical capsule in a microchannel and multiple RBC transport in a Poiseuille flow. RBC transport in a confined tube was also carried out to simulate the peristaltic effects of microvessels. Relatively large-scale simulations were carried out of the motion of 49,512 RBCs in shear flows, which yielded a hematocrit of 45%. The large-scale feature of the simulation has enabled a macroscale verification and investigation of the overall characteristics of RBC aggregations to be carried out. The results are in excellent agreement with experimental studies and, more specifically, both the experimental and simulation results show uniform RBC distributions under high shear rates (60–100/s) whereas large aggregations were observed under a lower shear rate of 10/s.

Dynamics of shear-induced migration of spherical particles in oscillatory pipe flow

The large-amplitude oscillatory flow of a suspension of spherical particles in a pipe is studied at low Reynolds number. Particle volume fraction and velocity are examined through refractive index matching techniques. The particles migrate toward the centre of the pipe, i.e. toward regions of lower shear rate, for bulk volume fractions larger than 10 %. Steady results are in agreement with available experimental results and discrete-particle simulations for similar geometries. The dynamics of the shear-induced migration process are analysed and compared against the predictions of the suspension balance model using realistic rheological laws.

Variable Reduction Of Thrombus Formation In The Blood Of Patients Treated With Oral Factor Xa and Thrombin Inhibitors: Pathophysiologic and Therapeutic Implications

Background Warfarin, an oral anti-vitamin K anticoagulant, effectively prevents venous thrombosis in patients at risk, but requires constant laboratory monitoring to maintain a therapeutic range and reduce bleeding complications. For many indications, oral inhibitors of coagulation factor (F) Xa and thrombin (FIIa) have proven at least as effective as warfarin with comparable risk of bleeding complications, but with the advantage of administration in a fixed dose without laboratory monitoring. Although rare, thrombosis may still occur in treated patients and bleeding remains a potentially serious complication. Aims The assumption that an equal dose of an anticoagulant drug can achieve a comparable antithrombotic effect in different patients implies that an appropriate test of efficacy should yield results within a relatively narrow range of values. Thus, we measured the volume of platelet aggregates and fibrin deposited onto thrombogenic surfaces exposed to flowing blood to compare the antithrombotic effect of rivaroxaban (Riv), a FXa inhibitor, and dabigatran (Dab), a thrombin inhibitor, with that of warfarin (Warf) in patients undergoing total knee or hip replacement and treated to prevent deep vein thrombosis. Methods Blood containing 0.011 M trisodium citrate was recalcified with 5 mM CaCl2 and perfused at the wall shear rate of 300 and 1500 s-1 over a surface coated with fibrillar collagen type I, or at 300 s-1 over recombinant tissue factor (TF). Platelet aggregates and fibrin were detected in situ through distinct fluorochromes and the respective volumes were measured from stacks of confocal optical sections. We tested 12 normal controls, 12 patients treated with Warf (INR between 1.94 and 2.90), 10 patients treated with Riv and 10 with Dab between 8 and 16 days from the initiation of therapy. Statistical analysis was performed using one-way analysis of variance. Results On the collagen surface at the lower shear rate of 300 s-1, the blood of Warf patients yielded an average volume of deposited fibrin significantly lower not only of control (P<0.001) but also Riv and Dab patients (P<0.01); the latter two were not different from control. All 12 Warf samples, but only 5/10 Riv and 4/10 Dab, were below the lower limit of normal values. In contrast, at the higher shear rate of 1500 s-1 the average fibrin volume was significantly lower than control in Warf (P<0.001) as well as Riv and Dab (P<0.01) blood. Notably, at both lower and higher shear rate the average volume of platelet aggregates was not decreased in Warf, Riv or Dab blood; rather, the tendency was to increased. On the TF surface, stable thrombus formation in flowing blood could only be assessed at the lower shear rate of 300 s-1, since even the reactivity of normal samples was negligible at 1500 s-1; thus we focused on blood from Riv and Dab treated patients who showed only an insignificant reduction of fibrin formation at 300 s-1 on the collagen surface. In contrast, thrombus volume in the blood of Riv and Dab treated patients was decreased on the TF surface under the same flow conditions. In the case of Dab, the average volume of both platelet aggregates and fibrin was significantly lower (P<0.01) than in control blood; with Riv, fibrin volume was also significantly reduced (p<0.01), but that of platelet aggregates was not. Of note, the volume of fibrin formed in Dab samples was only one third of that in Riv samples. Summary/Conclusions The significance of findings obtained with a test of thrombus formation in ex vivo flowing blood and the potential value for interpreting the evidence provided by clinical trials remain to be established prospectively. This notwithstanding, it is apparent that different agents have different anticoagulant effects, and those administered in a “one fits all” dose and without laboratory monitoring lead to a greater inter-individual variability of results. The influence of the thrombogenic surface on the ex vivo anticoagulant potency of drugs with distinct coagulation targets suggests that treating or preventing different thrombotic disorders may require a selective choice among therapeutic agents targeting specific coagulation pathways and physiologic inhibitors. Disclosures: No relevant conflicts of interest to declare.

Effects of Amines on Chemical and Physical Behaviors of Viscous Precursor Sols to Indium Gallium Zinc Oxide

ABSTRACTWe synthesized viscous precursors to indium gallium zinc oxide (IGZO) using three kinds of alcoholamines, ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA), by a simple process. The viscous precursors are obtained just by vigorous stirring of alcoholamine and urea in an aqueous solution containing the metal nitrates during heating at 150-160 °C. The precursor containing EA (EA-precursor) is a pale-orange suspension containing aggregates of the metal hydroxides and shows pseudoplastic flow. The precursors containing DEA (DEA-precursor) and TEA (TEA-precursor) are transparent pale-yellow and dark-orange sols, respectively. They give Newtonian flow in the lower shear rate and pseudoplastic flow in the higher shear rate. Higher concentration of metal salts leads to higher viscosity of the precursors. According to thermogravimetry-differential thermal analysis (TG-DTA) for the EA- and DEA-precursors, evaporation of alcoholamine occurs at around each boiling point and subsequently formation of metal oxides occur at around 300 °C. In the case of the TEA-precursor, formation of metal oxides occurs before pyrolysis of TEA attributed to the higher boiling point of TEA. The thin IGZO film, which is prepared by spin-coating of the diluted DEA-precursor and subsequent sintering at 450 °C for 30 min, shows 0.02 cm2 ·V-1s-1 of the mobility and 10-5 of the on/off ratio. The highly viscous DEA-precursor containing high concentration of metal ions allows patterning in an area of 100 cm2 onto a surface of a silicon wafer with screen printing.

Study on the Rheological Behavior of Neat PLA Chips and PLA Composites for Meltblowing Nonwovens

The PLA/tourmaline composites were prepared by co-extrusion of PLA chips and tourmaline fillers. Rheological behavior of PLA chips and PLA/tourmaline composites were analyzed using a capillary rheometer. Experimental results showed that the rheological curves complex viscosity of the PLA chips exhibited a non-Newtonian flow behaviour. Complex viscosity of the PLA chips decreased with the temperature increasing. A non-Newtonian flow behaviour was observed in all the PLA/tourmaline composites samples at lower shear rate. The complex viscosity of PLA blends increased with the input of tourmaline. The viscous flow activation energy of PLA/tourmaline blend melts decreased compared with that of neat PLA chips. Keyword: Rheological behavior; poly(lactic acid); tourmaline; meltblowing