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

Abstract

In this study, a microfluidic cross-slot device is used to examine the extensional flow response of diluted porcine synovial fluid (PSF) samples using flow-induced birefringence (FIB) measurements. The PSF sample is diluted to 10× 20× and 30× its original mass in a phosphate-buffered saline and its FIB response measured as a function of the strain rate at the stagnation point of the cross-slots. Equivalent experiments are also carried out using trypsin-treated PSF (t-PSF) in which the protein content is digested away using an enzyme. The results show that, at the synovial fluid concentrations tested, the protein content plays a negligible role in either the fluid's bulk shear or extensional flow behaviour. This helps support the validity of the analysis of synovial fluid HA content, either by microfluidic or by other techniques where the synovial fluid is first diluted, and suggests that the HA and protein content in synovial fluid must be higher than a certain minimum threshold concentration before HA-protein or protein-protein interactions become significant. However a systematic shift in the FIB response as the PSF and t-PSF samples are progressively diluted indicates that HA-HA interactions remain significant at the concentrations tested. These interactions influence FIB-derived macromolecular parameters such as the relaxation time and the molecular weight distribution and therefore must be minimized for the best validity of this method as an analytical technique, in which non-interaction between molecules is assumed.

Rheological behaviour of vitreous humour

“…Although we are not aware of any comparable studies in the literature, it is instructive to compare our results with some studies with HA solutions (Ambrosio et al 1999;Maleki et al 2007), which is believed to be one of the main components of the liquid phase, and with some biological fluids in which the main constituent is HA (Bingol et al 2010;Fam et al 2009;Haward 2014;Haward et al 2013). HA solutions are shear thinning and both the values and the characteristics of the flow curve are dependent of the concentration of HA, the molecular weight, the molecular conformation of HA, and, consequently, the interactions between them (Ambrosio et al 1999;Bingol et al 2010;Fam et al 2009;Haward 2014;Haward et al 2013;Maleki et al 2007).…”

Microfluidic extensional rheometry using stagnation point flow

“…If the relationship between molecular weight and coil-stretch relaxation time for the polymer is known (or can be determined), then the molecular weight distribution can be computed from the birefringence. 15,126,133,[169][170][171] The technique has been termed "hydrodynamic chromatography" and shows high sensitivity to high molecular weight tails of distributions (where Dn increases rapidly with _ e). High molecular weight tails are highly important rheologically and difficult to resolve using conventional techniques such as gel-permeation chromatography.…”

“…7. 13,15,126,171 The ability to characterize the extensional properties of such fluids has been a long standing challenge and may lead to improved understanding of the development of conditions such as osteoarthritis, cystic fibrosis, oral mucositis, Sj€ ogren's, and asthma, in which fluid rheology is drastically altered from its healthy state. [178][179][180][181][182] In addition, the characterization of biological fluid samples under extensional deformations should enable improved design and formulation of the prosthetic fluids that are used in the palliative treatment of many such conditions.…”

Stagnation point flows in analytical chemistry and life sciences

“…95,96 Using birefringence measurements, the molecular weight distribution of a polymer blend can be calculated if the molecular weight and coil-stretch relaxation time are known. 97,98 Investigations on this phenomenon have been predominantly performed using the Couette-type apparatus with the solution contained within the annular gap concentric cylinders. 99 However, observed polymer birefringence in these ows only slightly deform the polymer chains with a uniform intensity between the inner and outer cylinder.…”