Diagnostic platform for synovial fluid analysis based on viscoelastic and dielectric properties
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Joints of vetrebrates are encapsulated in a lubricant, the synovial fluid, consisting of a blood dialysate enriched by hyaluronan (HA), a glycosaminoglycan produced in the surrounding tissue. In case of an experienced trauma or diseases like osteoarthtitis and rheumatoid arthritis, the composition of the synovial fluid is altered, e.g. by lower molecular weight of HA, lower concentration, or a contamination with red blood cells. Up to now, small amounts of synovia are extracted and analysed by optical techniques and simple filament breakup tests for are performed for viscosity estimation. Classical methods for measuring the viscoelastic properties require more sample volume than can be punctuated from a single joint, and the fluid is not stable when exposed to air . Our novel diagnostic approach consists of (1) a fluidic two-phase system where an immiscible carrier fluid ensures encapsulation to air (2) two electrodynamic plate resonators to measure the viscoelastic storage and loss moduli  (3) the same two metallic plates used as electrodes for electrical impedance spectroscopy (EIS). The required sample volume is below 10 µl, a quantity that is readily available from joint punctation. The combination of shear-wave viscometry and electrical impedance spectroscopy is unique and opens up a variety of novel diagnostic measures. Figure 1 shows the assembled system. Figure 2(a) shows the electrical impedance measurement of deionized water, a 10 mg/ml purified sodium hyaluronate (Hyonate, Bayer), and a canine synovia sample. Figure 2(b) shows the resonance spectra of the bottom and top resonators - at higher viscoelastic moduli the mechanical coupling by shear-waves would be visible in a transmissive measurement (not shown here). A low viscous silicone fluid was used as the encapsulation liquid. In an ongoing veterinary preclinical study, the ability to detect pathological alterations in the synovia is demonstrated.