Extensional flow of hyaluronic acid solutions in an optimized microfluidic cross-slot device

Abstract

We utilize a recently developed microfluidic device, the Optimized Shape Crossslot Extensional Rheometer (OSCER), to study the elongational flow behavior and rheological properties of hyaluronic acid (HA) solutions representative of the synovial fluid (SF) found in the knee joint. The OSCER geometry is a stagnation point device that imposes a planar extensional flow with a homogenous extension rate over a significant length of the inlet and outlet channel axes. Due to the compressive nature of the flow generated along the inlet channels, and the planar elongational flow along the outlet channels, the flow field in the OSCER device can also be considered as representative of the flow field that arises between compressing articular cartilage layers of the knee joints during running or jumping movements. Full-field birefringence microscopy measurements demonstrate a high degree of localized macromolecular orientation along streamlines passing close to the stagnation point of the OSCER device, while micro-particle image velocimetry is used to quantify the flow kinematics. The stress-optical rule is used to assess the local extensional viscosity in the elongating fluid elements as a function of the measured deformation rate. The large limiting values of the dimensionless Trouton ratio, Tr $ O(50), demonstrate that these fluids are highly extensional-thickening, providing a clear mechanism for the load-dampening properties of SF. The results also indicate the potential for utilizing the OSCER in screening of physiological SF samples, which will lead to improved understanding of, and therapies for, disease progression in arthritis sufferers. V C 2013 AIP Publishing LLC. [http://dx

Instabilities in stagnation point flows of polymer solutions

“…This is partly due to the large mass of the disaccharide HA repeat unit and the inherent rigidity it confers to the HA backbone structure, and also because HA is a polyelectrolyte with a rather expanded coil size under equilibrium conditions. For the HA solutions the relaxation times are determined directly from flow-induced birefringence measurements made in the OSCER device, as described by Haward et al 16 These values are in good agreement with those made on similar solutions in a CaBER device. 51 In Table I we also include the details of the dilute polymer solution studied by Haward et al.…”

“…The numerical optimization, design, fabrication and experimental operation of the OSCER device has been described in detail in a number of recent publications [8][9][10]16 and will not be repeated here. To visualize flow instabilities in the device, we use fast polarizing electro-optical modulation techniques to image the full-field flow-induced birefringence (FIB), which arises as polymer molecules unravel in the planar extensional flow field and the polymer solutions become optically anisotropic in local regions of high polymer orientation.…”

“…[11][12][13][14][15] In FIB experiments within the OSCER device (as within conventional cross-slots), a sharply localized birefringent strand can be observed along the outflowing symmetry plane for Wi > 0.5, indicating the development of significant optical anisotropy among macromolecules that pass near the stagnation point. 8,10,16 Moreover, along the symmetry planes of the OSCER device (the x = 0 and y = 0 planes) there is zero shear, and hence the flow field in these regions provides a purely planar extensional deformation to fluid elements. The OSCER device therefore largely satisfies the requirements to be considered as a true extensional rheometer, and we have already demonstrated its use as such in a number of recent publications.…”

“…The OSCER device therefore largely satisfies the requirements to be considered as a true extensional rheometer, and we have already demonstrated its use as such in a number of recent publications. 8,10,16 FIG. 1.…”

Extensional rheometry of cellulose ether solutions: flow instability

“…CaBER measurements are relatively time-efficient and require less sample volume (\1 ml) compared to the techniques such as capillary extrusion (Cogswell 2003), opposed jet flow (Patruyo et al 2002) and filament stretching rheometry (FiSER) (Bhardwaj et al 2007). It is noteworthy that Cross-slot rheometry also offers some of the abovementioned advantages of CaBER, and has been used for cellulosic fluids (Sharma et al 2015) and hyaluronic acid solutions (Haward et al 2013;Haward 2014). From the perspective of processability, breaking up of an initially stable fluid filament is a process which has commercial applications such as spraying and atomization of pesticides, applying paints and adhesives, coating and food processing operations e.g.…”