Characterization of hyaluronic acid and synovial fluid in stagnation point elongational flow

Abstract

Hyaluronic acid (HA) is an important biomacromolecule, which fulfils a number of vital physiological functions (especially in the joint synovial fluid) and also has consumer and pharmaceutical applications. HA solution properties have already been quite thoroughly characterized in response to steady shear flows but are less well understood in highly deforming extensional flows. In this study, flow-induced birefringence measurements are made as a function of the strain rate in planar elongational flow at the stagnation point of a cross-slot device using HA solutions of a range of molecular weights (0.9×10(6) g mol(-1)≤Mw≤4.8×10(6) g mol(-1)) and at dilute concentrations. The results provide macromolecular relaxation times, molecular weight distributions and the extensional viscosities and Trouton ratios of the fluids. The HA relaxation time is found to vary as τ∼Mw1.8, which is consistent with a partially solvated, expanded coil. An intrinsic Trouton ratio is defined, which varies as [Tr]∼Mw2. The measurement of birefringence with strain rate is shown to be highly sensitive to the molecular weight distribution and can resolve subtle changes due to macromolecular degradation and the presence of fracture products. Mechanical degradation experiments in the cross-slots indicate midchain scission of HA macromolecules, strongly suggesting near full extension of the high-molecular weight fraction in the stagnation point extensional flow field. Taken together the results suggest a possible method for analysis of the HA in synovial fluid, and this concept is tested using synovial fluid obtained from porcine tarsal joint.

Relaxation time of dilute polymer solutions: A microfluidic approach

“…PBS contains mainly 138 mM of NaCl and 2.7 mM of KCl, and is a widely used physiological buffer for biological samples [37,43]. The molecular weight dispersity of HA samples similar to that used here is typically reported to be within the range 1.1 < M w =M n < 1.2 [47,48,54]. The solution was stirred continuously for 2 days to reach sample uniformity.…”

“…2(c)]. The occurrence of the coil-stretch transition is predicted when the Weissenberg number [50,52,54]. By finding the critical strain rate _ c above which birefringence is observed, the relaxation time can be consequently evaluated as k ext ¼ 0:5=_ c : The first nonzero value of the birefringence when increasing the strain rate is considered as the onset of flow-induced birefringence, and used for the evaluation of k ext :…”

“…The ratio of d=H > 10 provides a close approximation to a 2D extensional flow field. More details on the OSCER device are available in a number of previous publications [19,20,54].…”

Synovial Fluid Response to Extensional Flow: Effects of Dilution and Intermolecular Interactions

“…In a recent paper, Haward [13] performed a detailed study of the extensional response of dilute HA solutions over a range of molecular weights, 0.9 MDa ≤ M W ≤ 4.8 MDa and concentrations, 0.01 wt.% ≤ c ≤ 0.07 wt.%. Flow-induced birefringence (FIB) measurements were made as a function of the strain rate, , imposed at the stagnation point of a microfluidic cross-slot device.…”

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.…”