Biorheology最新文献

The rheological properties of synovial fluid (SF) are largely attributed to the presence of high molecular weight hyaluronan (HA). However, rheological differences between SF and pure HA solutions suggest that SF proteins actively contribute towards the bulk viscoelasticity of this biological fluid. Due to various experimental challenges involved with the rheometry of low-viscosity biological fluids, the macromolecular interactions in SF and their relative rheological importance are still a matter of active discussion. Interestingly however, recent evidence suggests that the concentration and structure of proteoglycan 4 (PRG4, also known as lubricin) can directly modulate the viscoelastic properties of HA-PRG4 solutions. The objective of this review is to highlight recent rheological studies that examine the macromolecular interactions between HA and proteins in SF. First, a general overview of the chemical composition of SF and the molecular structure of its key constituents HA and PRG4 is provided. Subsequently, diverse rheological experimental techniques that have been developed to characterize HA solutions are discussed. Finally, rheological investigations of macromolecular interactions between HA, serum proteins, and PRG4 are examined. This review illustrates how diverse rheological techniques can expand our understanding of the composition-structure-function relationships in SF.

Background: Devices gauging viscoelastic properties of blood during coagulation like the thromboelastograph support fundamental research as well as point of care needs. Associated fibrinolysis data are based on endogenous species or plasminogen activator added to a homogeneous sample prior to clot formation. Digestion in a monolithic structure differs from the physical situation of thrombolytic therapy where surface reactions dominate.

Objective: This study aims to develop rheological testing for heterogeneous phase fibrinolysis.

Method: Fibrinolysis rates were determined by phase change of a solid clot induced by autologous plasma/streptokinase (SK) in a rheometer sensitive to viscous damping.

Results: Initial slope or overall change in the logarithmic damping factor indicated fibrinolytic rates. Rates depended on clot geometry, phase volumes, clot composition and SK concentration.

Conclusion: The damped oscillation rheometer can be adapted to determine relative rates of heterogeneous fibrinolysis in vitro.

Background: Systemic arterial pressure (AP) depends on two physiological variables: cardiac output (CO) and total peripheral resistance (TPR). The latter depends on vascular hindrance and blood viscosity (BV). However, the relative contributions of the vascular and rheological factors to TPR remain unclear.

Objective: The aim of our work was to study the haemodynamic and haemorheologic effects of a treatment course with pentoxifylline (PTX) in SHRs in an effort to assess the impact of the rheological factor on TPR and AP.

Methods: The effects of the treatment course with PTX (100 mg/kg/day p.o. for six weeks) on BV, plasma viscosity, haematocrit, erythrocyte aggregation and deformability, mean AP (MAP), stroke volume (SV), CO, and TPR were studied in SHRs and in control Wistar Kyoto (WKY) rats.

Results: PTX-treated SHRs had a lower BV, lower erythrocyte aggregation, and higher erythrocyte deformability index compared with the controls. The TPR level was higher by 43% compared with that in WKY rats and did not differ from the values obtained from control SHRs. In SHRs, moderate and strong positive correlations were found between BV and MAP and between BV and TPR. PTX-treated SHRs did not have any significant correlations between the above mentioned parameters.

Conclusions: Treatment with PTX attenuated whole blood viscosity, but did not affect the AP and hemodynamic parameters in the experimental SHRs compared with the control SHRs. The magnitude of the rheologic effects of PTX was insufficient to cause appreciable decreases in TPR and AP.

Background: Biological cells exhibit complex mechanical properties which determine their responses to applied force.

Objective: We developed an optical method to probe the temporal evolution of power-law rheology of single cells.

Methods: The method consisted in applying optically a constant mechanical torque to a birefringent microparticle bound to the cell membrane, and observing dynamics of the particle's in-plane rotation.

Results: The deformation dynamics of the membrane followed a power law of time, which directly relates to cytoskeletal prestress as reported in the literature. The temporal evolution of this rheological behaviour, over time scales of several minutes, showed strong variations of the exponent on single adherent cells not subject to any specific treatment.

Conclusions: The consistent observation of variations in the exponent suggests that, in their normal activity, living cells modulate their prestress by up to three orders of magnitude within minutes.