Chondroitin Sulfate Solution Research Articles

Effect of stage gas nitriding on corrosion and wear resistance of Ti6Al4V alloy in physiological environment

The wear and corrosion resistance of the Ti6Al4V alloy after gas nitriding combined with stage heat treatment was studied in the physiological environment. It was shown that nitriding temperature at the first stage of the heat treatment mainly effects on the surface quality and microhardness of the treated alloy. The corrosion behaviour of the nitrided Ti6Al4V alloy was studied in Ringer's solution, which simulates the physiological environment of human body. It was shown that the corrosion resistance of the alloy is enhanced by increasing thickness and TiN content in the nitride layer, and improving surface quality. The tribological characteristics of the nitrided Ti6Al4V alloy in a tribo-pair with PE-UHMW were evaluated in a 10 % aqueous solution of chondroitin sulfate, which simulates the synovial fluid. It was established that reducing nitriding temperature at the first stage of the heat treatment improved the wear resistance of the treated alloy due to decrease of the surface roughness and microhardness.

Cartilage extracellular matrix polymers: hierarchical structure, osmotic properties, and function.

Proteoglycans are hierarchically organized structures that play an important role in the hydration and the compression resistance of cartilage matrix. In this study, the static and dynamic properties relevant to the biomechanical function of cartilage are determined at different levels of the hierarchical structure, using complementary osmotic pressure, neutron scattering (SANS) and light scattering (DLS) measurements. In cartilage proteoglycans (PGs), two levels of bottlebrush structures can be distinguished: the aggrecan monomer, which consists of a core protein to which are tethered charged glycosaminoglycan (GAG) chains, and complexes formed of the aggrecan monomers attached around a linear hyaluronic acid backbone. The principal component of GAG, chondroitin sulfate (CS), is used as a baseline in this comparison. The osmotic modulus, measured as a function of the proteoglycan concentration, follows the order CS < aggrecan < aggrecan-HA complex. This order underlines the benefit of the increasing complexity at each level of the molecular architecture. The hierarchical bottlebrush configuration, which prevents interpenetration among the bristles of the aggrecan monomers, enhances both the mechanical properties and the osmotic resistance. The osmotic pressure of the collagen solution is notably smaller than in the proteoglycan systems. This is consistent with its known primary role to provide tensile strength to the cartilage and to confine the aggrecan-HA complexes, as opposed to load bearing. The collective diffusion coefficient D governs the rate of recovery of biological tissue after compressive load. In CS solutions the diffusion process is fast, D ≈ 3 × 10-6 cm2 s-1 at concentrations comparable with that of the GAG chains inside the aggrecan molecule. In CS solutions D is a weakly decreasing function of calcium ion concentration, while in aggrecan and its complexes with HA, the relaxation rate is insensitive to the presence of calcium.

Evaluation of the impact of a course of therapy with an injectable form of chondroitin sulfate on the duration of remission and quality of life in patients with osteoarthritis

Ensuring a long-lasting effect of the therapy and its safety are important tasks in the treatment of patients with osteoarthritis (OA). Parenteral forms of chondroitin sulfate (CS) used for the background therapy of OA are characterized by proven efficacy and safety and, compared to oral forms, have greater bioavailability, faster onset of symptom-modifying effect and maintenance of more stable remission, which can significantly improve patients' quality of life.Objective: to evaluate the clinical efficacy and safety of two-month therapy with injectable CS and the duration of positive dynamics after the end of treatment in patients with knee OA (KOA).Material and methods. The open prospective observational study involved 35 patients (mainly women) aged 50–75 years with stage II–III KOA. All patients were prescribed intramuscular therapy with a CS solution (Mucosat® solution), with the first three injections of 1 ml, followed by 2 ml every second day (25 injections in total). Standard indices and questionnaires were used to assess the main clinical indicators at baseline and over time (14, 30, 60 days, 5 and 8 months after the start of treatment), as well as the results of ultrasound examination of the knee at baseline and at the end of treatment.Results and discussion. 14 days after the start of therapy, a statistically significant decrease in pain was observed applying the visual analogue scale (VAS), and after 2 months, 94% of patients had a significant decrease in knee pain according to VAS, Lequesne index and WOMAC index (total score and components). The KOOS parameters and quality of life according to EQ-5D-3L improved significantly. There was no pain or only minor pain (VAS ≤40 mm) in 54% of patients. The number of patients who had to take nonsteroidal anti-inflammatory drugs (NSAIDs) constantly fell threefold, while occasional use fell fivefold. The thickness of the synovial membrane of the knee joint and the number of patients with signs of synovitis decreased significantly. At 3 and 6 months after the end of therapy, most patients (60%) still had minor pain (≤40 mm according to VAS) and a significantly lower need for NSAIDs compared to baseline. The injectable CS was well tolerated and no adverse drug events were noted.Conclusion. We demonstrated both safety and efficacy and long-term maintenance of the clinical effect (6 months after the end of therapy) of injectable CS in the majority of OA patients, against the background of a low need for NSAIDs.

The effect of sucrose supplementation on chondrocyte viability in porcine articular cartilage following vitrification

Vitrification can extend the banking life of articular cartilage (AC) and improve osteochondral transplantation success. Current vitrification protocols require optimization to enable them to be implemented in clinical practice. Sucrose as a non-permeating cryoprotective agent (CPA) and clinical grade chondroitin sulfate (CS) and ascorbic acid (AA) as antioxidants were investigated for their ability to improve a current vitrification protocol for AC. The aim of this study was to assess the impact of sucrose and CS/AA supplementation on post-warming chondrocyte viability in vitrified AC. Porcine osteochondral dowels were randomly vitrified and warmed with one established protocol (Protocol 1) and seven modified protocols (Protocols 2–8) followed by chondrocyte viability assessment. Sucrose supplementation in both vitrification and warming media (Protocol 4) resulted in significantly higher (p = 0.018) post-warming chondrocyte viability compared to the protocol without sucrose (Protocol 1). There was no significant difference (p = 0.298) in terms of post-warming chondrocyte viability between sucrose-supplemented DMEM + CS solution (Protocol 4) and Unisol-CV (UCV) + CS (Protocol 6) solution. Clinical grade CS and AA contributed to similar post-warming chondrocyte viability to previous studies using research grade CS and AA, indicating their suitability for clinical use. The addition of an initial step (step 0) to reduce the initial concentration of CPAs to minimize osmotic effects did not enhance chondrocyte viability in the superficial layer of AC. In conclusion, sucrose-supplemented DMEM + clinical grade CS (Protocol 4) could be an ideal protocol to be investigated for future use in clinical applications involving vitrified AC.

Development of an in-situ forming, self-healing scaffold for dermal wound healing: in-vitro and in-vivo studies

The importance of the extra-cellular matrix (ECM) for wound healing has been extensively researched. Understanding its importance, multiple ECM mimetic scaffolds have been developed. However, the majority of such scaffolds are prefabricated. Due to their stiffness, prefabricated scaffolds cannot come into direct contact with the basal skin cells at the wound bed, limiting their efficacy. We have developed a unique wound dressing, using chitosan (CH) and chondroitin sulfate (CS), that can form a porous scaffold (CH-CS PEC) in-situ, at the wound site, by simple mixing of the polymer solutions. As CH is positively and CS is negatively charged, mixing these two polymer solutions would lead to electrostatic cross-linking between the polymers, converting them to a porous, viscoelastic scaffold. Owing to the in-situ formation, the scaffold can come in direct contact with the cells at the wound bed, supporting their proliferation and biofunction. In the present study, we confirmed the cross-linked scaffold formation by solid-state NMR, XRD, and TGA analysis. We have demonstrated that the scaffold had a high viscoelastic property, with self-healing capability. Both keratinocyte and fibroblast cells exhibited significantly increased migration and functional markers expression when grown on this scaffold. In the rat skin-excisional wound model, treatment with the in-situ forming CH-CS PEC exhibited enhanced wound healing efficacy. Altogether, this study demonstrated that mixing CH and CS solutions lead to the spontaneous formation of a highly viscoelastic, porous scaffold, which can support epidermal and dermal cell proliferation and bio-function, with an enhanced in-vivo wound healing efficacy.

Rheological Properties of Cartilage Glycosaminoglycans and Proteoglycans

Glycosaminoglycans (GAGs) are molecules that govern the load-bearing and frictional properties of cartilage and the lubricating properties of synovial fluid of joints. Most GAGs in the body form proteoglycans (PGs), and the dominant PG in cartilage is the bottlebrush-shaped aggrecan, comprised of a protein core decorated by GAG side chains consisting mainly of chondroitin sulfate (CS) and keratan sulfate. Additionally, hyaluronic acid (HA) induces aggrecan to self-assemble into complexes having up to 100 aggrecan molecules attached to each HA chain “backbone”. Here, we report the rheological properties of CS, HA, aggrecan, and aggrecan–HA complexes in water and salt solutions. We find that CS solutions are viscous liquids, while HA solutions exhibit viscoelasticity and shear thinning. Specifically, in the case of HA, the storage modulus G′ exceeds the loss modulus G″ at high frequencies (ω) while the reverse is true at low ω. Thus, the rheologies of CS and HA exhibit somewhat distinct viscoelastic properties. Aggrecan, on the other hand, shows a rheology consistent with an incipient “weak gel” in which G′ and G″ cross at a specific ω and follow a power-law scaling over a wide ω range. Moreover, aggrecan samples do not attain an observable plateau in the viscosity under steady shear and low shear rates. Finally, the complexation of aggrecan and HA over a period of 48 h results in a slow evolution (“aging”) in measured rheological properties, with G′ at low ω progressively increases in time, while G″ remains essentially unchanged. This suggests that aggrecan and HA gradually form a macroscopic network in which molecular complexes act as physical cross-links.

A high molecular weight hyaluronic acid biphasic dispersion as potential therapeutics for interstitial cystitis.

Interstitial cystitis (IC) is a progressive bladder disease characterized by increased urothelial permeability, inflammation of the bladder with abdominal pain. While there is no consensus on the etiology of the disease, it was believed that restoring the barrier between urinary solutes and (GAG) urothelium would interrupt the progression of this disease. Currently, several treatment options include intravesical delivery of hyaluronic acid (HA) and/or chondroitin sulfate solutions, through a catheter to restore the urothelial barrier, but have shown limited success in preclinical, clinical trials. Herein we report for the first time successful engineering and characterization of biphasic system developed by combining cross‐linked hyaluronic acid and naïve HA solution to decrease inflammation and permeability in an in vitro model of interstitial cystitis. The cross‐linking of HA was performed by 4‐arm‐polyethyeleneamine chemistry. The HA formulations were tested for their viscoelastic properties and the effects on cell metabolism, inflammatory markers, and permeability. Our study demonstrates the therapeutic effects of different ratios of the biphasic system and reports their ability to increase the barrier effect by decreasing the permeability and alteration of cell metabolism with respect to relative controls. Restoring the barrier by using biphasic system of HA therapy may be a promising approach to IC.

Successful outcomes of a new combined solution of hyaluronic acid, chondroitin sulfate and poloxamer 407 for submucosal injection: animal survival study.

Background and study aims Endoscopic resection requires use of submucosal injection. This study was conducted to assess efficacy and impact on early healing of hyaluronic acid combined with chondroitin sulfate and poloxamer 407 (Ziverel) when used as a solution for submucosal injection. Materials and methods Prospective and comparative study of gastric endoscopic mucosal resection (EMR) with three groups of two Yorkshire pigs. Six submucosal cushions were created in each animal by injecting 2 mL of Ziverel (Group 1) or succinylated gelatin (SG) (Group 2), enabling 12 EMR in each group. Submucosal cushions were created with Ziverel in Group 3, without resection. Electrosurgery unit settings were the same in all cases. EMR defects and injection sites were marked with clips. The animals were sacrificed 7 days later. EMR specimen size and duration of procedure were recorded. EMR specimens and EMR scars and injection sites were evaluated by a blinded pathologist. Results We successfully performed 24 EMR (15 en-bloc and 9 piecemeal, without differences between groups 1 and 2). Mean EMR specimen dimensions were significantly larger in Group 1 (median 19 mm, range 6 – 40 vs 16.6 mm, range 5‑25; P = 0.019), without changing the electrocautery unit settings. Blinded histopathologist assessment of EMR specimens showed less fibrosis in the submucosa and a trend to fewer cautery artifacts with Ziverel and did not identify any significant differences in early healing of resection sites. Conclusion The combination of Ziverel enables EMR and does not negatively affect early healing.

Structure and Cytocompatibility of a Porous Biomimetic Material for Oral Tissue Wound Healing

Composite materials containing natural biocompatible polymers, specific for the extracellular matrix present in the periodontal tissue, are prepared by mixing type I soluble collagen (COL) and fibronectin (FN) as fibrillar proteins and chondroitin sulfate (CS) as polysaccharidic component. The three‐dimensional porous structure is obtained by freeze‐drying process and it is analyzed by scanning electron microscopy (SEM). Specific techniques of immunohistochemistry and transmission electron microscopy (TEM) are used to investigate the distribution and interaction between polymeric components within the scaffold. Light and electron microscopy observations are also performed on solutions of CS and FN to reveal their structural and morphological properties. The cytocompatibility of composite material is tested in gingival fibroblasts and osteoblast cell cultures using quantitative assays of cell viability. The results demonstrate that COL‐CS‐FN composite material has optimal characteristics for further testing as device for oral tissue wound healing.

Green Synthesis of Hierarchically Structured Silver-Polymer Nanocomposites with Antibacterial Activity.

The in situ formation of silver nanoparticles (AgNPs) aided by chondroitin sulfate and the preparation of a hierarchically structured silver-polymer nanocomposite with antimicrobial activity is shown. Green synthesis of AgNPs is carried out by thermal treatment (80 and 90 °C) or UV irradiation of a chondroitin sulfate solution containing AgNO3 without using any further reducing agents or stabilizers. Best control of the AgNPs size and polydispersity was achieved by UV irradiation. The ice-segregation-induced self-assembly (ISISA) process, in which the polymer solution containing the AgNPs is frozen unidirectionally, and successively freeze-drying were employed to produce the chondroitin sulfate 3D scaffolds. The scaffolds were further crosslinked with hexamethylene diisocyanate vapors to avoid water solubility of the 3D structures in aqueous environments. The antimicrobial activity of the scaffolds was tested against Escherichia coli. The minimum inhibitory concentration (MIC) found for AgNPs-CS (chondroitin sulfate) scaffolds was ca. 6 ppm.

Characterization and application of chondroitin sulfate/polyvinyl alcohol nanofibres prepared by electrospinning

Composite nanofibres were prepared by electrospinning from a solution of chondroitin sulfate and polyvinyl alcohol. The chondroitin sulfate/polyvinyl alcohol (CS/PVA) mass ratios of 7/3 has a uniform and smooth morphology, and the average diameter of the nanofibres was 136nm. Combretastatin A-4 phosphate was loaded on the nanofibres and used as a model for testing drug release from the nanofibres crosslinked with glutaric dialdehyde. The morphology and structure of the nanofibres was determined using scanning electron microscopy. In order to assess their possible application to tissue engineering scaffolds, the toxicity and cytocompatibility of the nanofibres were tested by methylthiazolydiphenyl-tetrazolium bromide assay.

Adsorption and Elution of Glucuronic Acid and Chondroitin Sulfate Using Amino-Group-Containing Spherical Gel.

: A spherical gel containing amino groups was prepared using monomers of N,N-dimethylacrylamide and N,N-dimethylaminoethyl methacrylate, with a cross-linker composed of N,N′-methylenebisacrylamide prepared by suspension polymerization for the adsorption of glucuronic acid and chondroitin sulfate. The prepared gel was immersed in glucose, glucuronic acid, and chondroitin sulfate solutions to determine the adsorption performance in batch mode, which demonstrated that 20 % of the chondroitin sulfate was adsorbed to the amino-group-containing gel. The amino-group-containing gel was packed into a column to permeate the chondroitin sulfate-containing solution (0.40 g/L) at pH 2.0, and it adsorbed chondroitin sulfate to the gel at a space velocity of 4.5 h-1. When the space velocity was changed to 1.5 h-1, the amount of chondroitin sulfate increased. When 0.50 M NaCl solution was permeated through the chondroitin-sulfate-adsorbed gel in column mode, 70 % of the chondroitin sulfate was eluted. This spherical gel may be applicable for acidic glycan recovery using batch and permeation modes.

Decellularized kidney in the presence of chondroitin sulfate as a natural 3D scaffold for stem cells.

Use of biological scaffolds and automating the cells directing process with materials such as growth factors and glycosaminoglycans (GAGs) in a certain path may have beneficial effects in tissue engineering and regenerative medicine in future. In this research, chondroitin sulfate sodium was used for impregnation of the scaffolds. It is a critical component in extracellular matrix and plays an important role in signaling pathway; however, little is known about its role within mammalian development and cell linage specification. Due to its porous and appropriate structure and for putting cells in 3D space, the kidney of BALB/c mouse was selected and decellulalized using physical and chemical methods. After decellularization, the scaffold was impregnated in chondroitin sulfate solution (CS) for 24 hr. Then, 60×10(5) human adipose-derived mesenchymal stem cells were seeded on the scaffold to assess their behavior on day 5, 10, 15, 20, and 25. After 48 hr, DAPI staining approved completed decellularized kidney by 1% SDS (sodium dodecyl sulfate). Migration and establishment of a number of cells to the remaining area of the glomerulus was observed. In addition, cell accumulation on the scaffold surface as well as cells migration to the depth of kidney formed an epithelium-like structure. Up to the day 15, microscopic study of different days of seeding showed the gradual adhesion of large number of cells to the scaffold. Glycosaminoglycan could be a right option for impregnation. It is used for smartification and strengthening of natural scaffolds and induction of some behaviors in stem cells.

Development of Bioresorbable Calcium-Phosphate Cements Hybridized with Gelatin Particles and their &lt;i&gt;In Vivo&lt;/i&gt; Evaluation Using Pig’s Tibia Model

Novel bioresorbable calcium-phosphate cement (CPC) with anti-washout property was developed by adding thermally cross-linked gelatin particles as pore generator into a CPC. The CPC was composed of α-tricalcium phosphate (α-TCP) and surface-modified hydroxyapatite (HAp) with inositol phosphate as a chelating agent (IP6-HAp). The bioresorbable CPC hybridized with gelatin particles was successfully fabricated by mixing the aqueous sodium chondroitin sulfate solution including Na2HPO4 and the pre-mixed powders composed of α-TCP (72 mass%), IP6-HAp (18 mass%), and the gelatin particles (10 mass%). The hybridized CPC paste showed initial setting time (IST) of 5 minutes and exhibited anti-washout property. Compressive strength after setting for 24 h reached to 4.2 MPa. An in vivo preliminary study using pig’s tibia model demonstrated that the hybridized CPC could be easily injected and set promptly without washout. In addition, no fragmentation in the specimens was observed after 8 weeks implantation. Moreover, a histological observation (Villanueva bone stain) revealed that almost 80% of the hybridized CPC specimens were resorbed and that immature bones were formed inside the specimens.

Controlled-release triple anti-inflammatory therapy based on novel gastroretentive sponges: Characterization and magnetic resonance imaging in healthy volunteers

The current work aimed to develop novel composite sponges of chitosan (CH)–chondroitin sulfate (CS) as a low-density gastroretentive delivery system for lornoxicam (LOR). This triple anti-inflammatory therapy-loaded matrices are expected to expand and float upon contact with gastric fluids for prolonged times. CH and CS solutions (3%, w/w) were prepared, mixed in different ratios, lyophilized, coated with magnesium stearate and compressed. The CH:CS interpolymer complex (IPC) was evaluated via FT-IR, DSC, and XRD. The compressed-sponges were evaluated for appearance, structure, porosity, pore diameter, density, wetting-time, floating characteristics, adhesion-retention, and LOR-release. The gastroretentivity of the best achieved magnetite-loaded sponges was monitored in healthy volunteers via MRI. The interaction between CH (protonated amino groups) and CS (anionic carboxylate/sulfate groups) proved IPC formation. DSC and XRD studies confirmed loss of LOR crystallinity. The sponges possessed interconnecting porous-network structures. The porosity, mean pore diameter, and bulk density of CH:CS (10:3) IPC sponges were 11.779%, 25.4nm, and 0.670g/mL, respectively. They showed complete wetting within seconds, gradual size-expansion within minutes and prolonged adhesion for hours. Controlled LOR-release profiles were tailored over 12h to satisfy individual patient needs. Monitoring of sponges via MRI proved their gastroretentivity for at least 5h.

Dual-network hydrogels based on chemically and physically crosslinked chitosan/chondroitin sulfate

The formation of a novel type of hydrogel that combines chemically and physically crosslinked networks in a dual-network approach is presented here. Chitosan (CHT) and chondroitin sulfate (CS) were chemically modified with glycidyl methacrylate (GMA) and then crosslinked. The chemical hydrogels (CHT- and CS-gel) were deposited in different vials filled with CS or CHT stock solutions to form the dual-network hydrogels. FTIR, TGA and XRD analyses were used to characterize the chemical and the dual-network hydrogels. The percentages of CS or CHT complexed to the CHT- and CS-gel networks were calculated from the HPLC data. SEM images and swelling assays indicated that the formation of a secondary network by polyelectrolyte complexation changes the morphologies and liquid uptake capacities of the chemical hydrogels. Hence, the data and discussion presented here enable the formation of dual-network hydrogels with very interesting properties, such as the ability to interact with charged specimens (i.e., drugs, proteins or metal ions), a desirable feature for a wide range of applications.

Polysaccharide Films Built by Simultaneous or Alternate Spray: A Rapid Way to Engineer Biomaterial Surfaces

We investigated polysaccharide films obtained by simultaneous and alternate spraying of a chitosan (CHI) solution as polycation and hyaluronic acid (HA), alginate (ALG), and chondroitin sulfate (CS) solutions as polyanions. For simultaneous spraying, the film thickness increases linearly with the cumulative spraying time and passes through a maximum for polyanion/CHI molar charge ratios lying between 0.6 and 1.2. The size of polyanion/CHI complexes formed in solution was compared with the simultaneously sprayed film growth rate as a function of the polyanion/CHI molar charge ratio. A good correlation was found. This suggests the importance of polyanion/polycation complexation in the simultaneous spraying process. Depending on the system, the film topography is either liquid-like or granular. Film biocompatibility was evaluated using human gingival fibroblasts. A small or no difference is observed in cell viability and adhesion between the two deposition processes. The CHI/HA system appears to be the best for cell adhesion inducing the clustering of CD44, a cell surface HA receptor, at the membrane of cells. Simultaneous or alternate spraying of CHI/HA appears thus to be a convenient and fast procedure for biomaterial surface modifications.

UP-01.074 Recurrent Bacterial Cystitis, Bladder Instillation with a Combined Solution of Sodium Halurate and Chondroitin Sulfate (IALURIL): One Year of Follow-Up

Chronic cystitis in women is a big problem. The pathogenesis is not very clear, but the bladder epithelium defect has a fundamental role. In the genesis of bladder flogosis the defect of glycosaminoglycans (GAGs) plays, probably, a role of the “primo movens”. In this study we evaluated the role of bladder instillation with a combined solution of sodium halurate and chondroitin sulphate (IALURIL) in patients with recurrent bacterial cystitis.

Preparation of free-standing films of natural polysaccharides using hot press technique and their surface functionalization with biomimetic apatite

This study demonstrated that gel-like polyion complexes obtained by mixing of aqueous solution of chondroitin sulfate, heparin, and hyaluronic acid with that of chitosan were able to form their free-standing films using hot press treatments. These films, having thicknesses ca. 50 and 100 μm, depending on the spacer thickness, were homogeneous and non-porous at the microscopic level, and were not water-soluble. The present fabrication process required neither cross-coupling agents nor introduction of other functional groups to the polysaccharides. Hydroxyapatite deposition on the film surfaces under body fluid conditions was also achieved.

Experimental Friction Coefficients for Bovine Cartilage Measured with a Pin-on-Disk Tribometer: Testing Configuration and Lubricant Effects

The friction coefficient between wet articular cartilage surfaces was measured using a pin-on-disk tribometer adopting different testing configurations: cartilage-on-pin vs. alumina-on-disk (CA); cartilage-on-pin vs. cartilage-on-disk (CC); and alumina-on-pin vs. cartilage-on-disk (AC). Several substances were dissolved in the phosphate buffered saline (PBS) solution to act as lubricants: 10,000 molecular weight (MW) polyethylene glycol (PEG), 100,000MW PEG, and chondroitin sulfate (CS), all at 100mg/mL concentration. Scanning electron microscopy photographs of the cartilage specimens revealed limited wear due to the experiment. Conducting the experiments in PBS solutions we provide evidence according to which a commercial pin-on-disk tribometer allows us to assess different lubrication mechanisms active in cartilage. Specifically, we find that the measured friction coefficient strongly depends on the testing configuration. Our results show that the friction coefficient measured under CC and AC testing configurations remains very low as the sliding distance increases, probably because during the pin displacement the pores present in the cartilage replenish with PBS solution. Under such conditions the fluid phase supports a large load fraction for long times. By systematically altering the composition of the PBS solution we demonstrate the importance of solution viscosity in determining the measured friction coefficient. Although the friction coefficient remains low under the AC testing configuration in PBS, 100mg/mL solutions of both CS and 100,000MW PEG in PBS further reduce the friction coefficient by ~40%. Relating the measured friction coefficient to the Hersey number, our results are consistent with a Stribeck curve, confirming that the friction coefficient of cartilage under the AC testing configuration depends on a combination of hydrodynamic, boundary, and weep bearing lubrication mechanisms.