The Small Molecule Components of Human Synovial Fluid and Bovine Calf Serum that Correlate with Cobalt Chrome (CoCrMo) Wear

Background:Implant wear in joint replacements is influenced by the chemical and physical properties of human synovial fluid (HSF). In vitro testing for implant wear uses 25% weight bovine calf serum (25BCS) to substitute for HSF, due to similar rheology and total protein content. However, previous studies have shown differences in the macromolecular composition. We aimed to evaluate the differences in small molecule composition between fluids and correlate these differences with their effects on implant material wear.Methods:HSF was harvested from osteoarthritis patients undergoing primary knee replacement (n=14). Nuclear magnetic resonance (NMR) spectroscopy with linear regression modelling analysed the metabolites present in HSF and commercially sourced 25BCS and investigated the differences. Wear properties of the fluids were evaluated using a validated quantitative laboratory bench-test utilising a cobalt/chromium/molybdenum (CoCrMo) ball oscillating against a CoCrMo disc and analysing the resulting wear scar. The variation in metabolite levels in both HSF and 25BCS was correlated to the wear properties of the fluids.Results:Differences in the levels of metabolites, lipids, and glycosaminoglycans (GAG) were observed between HSF and 25BCS: significance was confirmed by O-PLS-DA (p<0.05). The wear of CoCrMo was found to strongly correlate with the macromolecules GAG and proteins that potentially bind to glucose and citrate. Conclusions:The small molecule concentration differences between the fluids questions the validity of 25BCS as a model for wear analysis. The demonstration of variable metabolites present in HSF which correlate with material wear has implications for implant failure and targeted therapeutic manipulation of these metabolites. Trial Registration:Ethical approval was granted by the NRES Committee London, Chelsea, UK on the 12th May 2015. The study was performed in accordance with the ethical standards in the 1964 Declaration of Helsinki.

Rheologic Behavior of Bovine Calf Serum

Recent studies have illuminated the rheological behavior of synovial fluid and the role of protein and hyaluronan (HA). However, with respect to artificial joint replacement in standardized wear simulations, bovine serum is used as fluid test medium. Little is known about the rheological characteristics of bovine serum, which are needed for precise tribological investigations. The steady shear viscosity η of bovine calf serum is determined for protein concentrations used in standardized wear simulations depending on shear rate γ˙ and temperature T. Additionally, the density of the serum is determined for both protein concentrations. The results show shear thinning behavior of bovine calf serum with a nearly Newtonian behavior in the range of high shear rates. Within the range of high shear rates, mean viscosities of η = 0.82–0.88 mPa·s were found for protein concentrations of 20 g/L and mean viscosities of η = 0.88–0.94 mPa·s for 30 g/L, decreasing with temperature. Densities of 1.004–1.005 g/cm3 and 1.007–1.008 g/cm3 were found for 20 and 30 g/L protein concentrations, respectively.

Wear Behavior Characterization of Hydrogels Constructs for Cartilage Tissue Replacement

This paper aims to characterize the wear behavior of hydrogel constructs designed for human articular cartilage replacement. To this purpose, poly (ethylene glycol) diacrylate (PEGDA) 10% w/v and gellan gum (GG) 1.5% w/v were used to reproduce the superior (SUP) cartilage layer and PEGDA 15% w/v and GG 1.5% w/v were used to reproduce the deep (DEEP) cartilage layer, with or without graphene oxide (GO). These materials (SUP and DEEP) were analyzed alone and in combination to mimic the zonal architecture of human articular cartilage. The developed constructs were tested using a four-station displacement control knee joint simulator under bovine calf serum. Roughness and micro-computer tomography (µ-CT) measurements evidenced that the hydrogels with 10% w/v of PEGDA showed a worse behavior both in terms of roughness increase and loss of uniformly distributed density than 15% w/v of PEGDA. The simultaneous presence of GO and 15% w/v PEGDA contributed to keeping the hydrogel construct’s characteristics. The Raman spectra of the control samples showed the presence of unreacted C=C bonds in all the hydrogels. The degree of crosslinking increased along the series SUP < DEEP + SUP < DEEP without GO. The Raman spectra of the tested hydrogels showed the loss of diacrylate groups in all the samples, due to the washout of unreacted PEGDA in bovine calf serum aqueous environment. The loss decreased along the series SUP > DEEP + SUP > DEEP, further confirming that the degree of photo-crosslinking of the starting materials plays a key role in determining their wear behavior. μ-CT and Raman spectroscopy proved to be suitable techniques to characterize the structure and composition of hydrogels.

Whole Ovine Ovaries as a Model for Human: Perfusion with CryoprotectantsIn VivoandIn Vitro

These experiments were performed to test the perfusion of ovine as a model for human ovaries by cryoprotectantsin vivoat high temperature when the permeability of capillaries is high and when blood is insensibly replaced by the solution of cryoprotectants. By our hypothetical supposition, ovaries could be saturated by cryoprotectants before their surgical removal. The objective was to examine the effectiveness of perfusion of ovine ovaries with vascular pediclein vivoandin vitro.Arteria ovaricawas cannuled and ovaries were perfused by Leibovitz L-15 medium + 100 IU/mL heparin + 5% bovine calf serum + 6% dimethyl sulfoxide + 6% ethylene glycol + 0.15 M sucrose + Indian inkin vivoandin vitro. In the first and second cycle of experiments, ovaries (n=13andn=23) were perfusedin vivoandin vitro, respectively, during 60 min with the rate of perfusion 50 mL/h (0.8 mL/min). It was established within vivoperfusion that only about 10% of ovarian tissues were perfused due to an appearance of multiple anastomoses when the perfusion medium goes fromarteria ovaricatoarteria uterinawithout inflow into the ovaries. It was concluded thatin vitroperfusion of ovine intact ovaries with vascular pedicle by freezing medium is more effective than this manipulation performedin vivo.