The rheological properties of synovial fluid (SF) are largely attributed to the presence of high molecular weight hyaluronic acid (HA). In normal SF, HA has been shown to be an anti-inflammatory molecule able to increase the viscosity and promote endogenous production of HA. The aim of the present report was to investigate the possible effect of HA concentration in rheological properties (elastic modulus, G´ and viscous modulus, G´´) of osteoarthritic equine SF. For this purpose, SF from intercarpal, metacarpophalangeal and distal interphalangeal joint was aspirated by aseptic arthrocentesis from 60 Warmblood horses. For determining HA concentrations in equine SF samples, a commercially available ELISA kit was used. Additionally, full rheological sample characterization was carried out with an AR-G2 rheometer (TA Instruments Ltd., UK) in order to measure the elastic G´ and viscous G´´ moduli, at horse's body (37.5 ºC) temperature. The ANOVA findings revealed statistically significant main effects of the factors Joint Type (p = 0.001), and main effects of covariates Age (p = 0.019) and HA (p < 0.001) on the mean values of logG” and logG' measurements. Interpreting the coefficients of the covariate HA, a positive correlation of HA was detected on the response logG” and logG' measurements. Collectively, these data illustrate the role of HA in equine pathological SF.

Viscosupplementation is the current treatment modality for early stage arthritis and in some cases for delaying joint replacement procedures. Rheological properties similar to that of synovial fluid and high molecular weight have been recognized as the determining factors in hyaluronic acids (HA) therapeutic and analgesic value (1). In this study, the self assembly of peptides into beta-sheet structures in solution (2–4) is explored to develop novel biocompatible injectable joint lubricants. These peptides can be delivered into the joint easily in their low viscosity monomer form, while they are designed to self-assemble in situ under physiological conditions. Four different peptides P11-4, P11-8, P11-9, and P11-12 were designed based on the chemical motif of hyaluronic acid and were found to self-assemble into nematic fluids and gels under physiological conditions. Friction characteristics of these peptides as lubricants were evaluated in a bovine cartilage on cartilage model using a simple pin on plate geometry and under various sliding conditions. Friction tests were carried out using both healthy and damaged bovine cartilage samples, to study the therapeutic effect of these peptides as lubricants. Further, a rheometer with cone-on-plate configuration was used to study these peptides in shear viscosity and oscillatory shear modes to determine their viscoelastic properties. Both the friction properties and rheological behaviour of the peptides were compared to that of a commercially available hyaluronic acid preparation that was tested along with the peptides. Peptide P11-9 was found to have very similar viscoelastic properties to that of HA, and was also the most effective in friction level reduction among the four peptides tested. When compared to HA, P11-9 showed slightly better friction characteristics in all the healthy cartilage models, while HA was the best lubricant in damaged cartilage models when compared to P11-9 and other peptides. The results indicate that these novel self assembling peptides can be developed as a new generation of synthetic viscosupplements for the treatment of early stage arthritis.