Grafting of cationic molecules to hyaluronic acid improves adsorption and cartilage lubrication.

Synovial fluid lubricates articular joints by forming a hydrated layer between the cartilage surfaces. In degenerative joint diseases like osteoarthritis (OA), the synovial fluid is compromised, which leads to less effective innate lubrication and exacerbated cartilage degeneration. Studies over the years have led to the development of partially or fully synthetic biolubricants to reduce the coefficient of friction with cartilage in knee joints. Cartilage-adhering, hydrated lubricants are particularly important to provide cartilage lubrication and chondroprotection under high normal load and slow speed. Here, we report the development of a hyaluronic acid (HA)-based lubricant functionalized with cationic branched poly-L-lysine (BPL) molecules that bind to cartilage via electrostatic interactions. We surmised that the electrostatic interactions between the BPL-modified HA molecules (HA-BPL) and the cartilage facilitate localization of the HA molecules to the cartilage surface. The number of BPL molecules on the HA backbone was varied to determine the optimal grafting density for cartilage binding and HA localization. Collectively, our results show that our HA-BPL molecules adhered readily to cartilage and were effective as a lubricant in cartilage-on-cartilage shear measurements where the modified HA molecules significantly reduce the coefficient of friction compared to phosphate-buffered saline or HA alone. This proof-of-concept study shows how the incorporation of cartilage adhering moieties, such as cationic molecules, can be used to enhance cartilage binding and lubrication properties of HA.

The effect of salbutamol sulphate inhalation (an anti-asthmatic medication) on the surfaces of orthodontic Archwires.

OBJECTIVES: This study aimed to compare the surface roughness and friction of different orthodontic archwires after exposure to salbutamol sulphate inhalation, an anti-asthmatic medication. METHODS: Orthodontic archwires (stainless-steel [StSt], nickel-titanium [NiTi], beta-titanium [ß-Ti], and copper-NiTi [Cu-NiTi]) were equally divided into two groups. The exposed groups were subjected to 20 mg salbutamol sulphate for 21 days and kept in artificial saliva. The control groups were only kept in artificial saliva. Surface changes were visualized using scanning electron microscopy (SEM). The average surface roughness (Ra) was evaluated using atomic force microscopy (AFM), and friction resistance forces were assessed using a universal testing machine. Statistical analyses were performed using t-tests and ANOVA followed by post hoc tests. RESULTS: Salbutamol sulphate did not change the surface roughness of StSt and NiTi archwires (p > .05). However, the change in the surfaces of ß-Ti and Cu-NiTi archwires was significant (p < .001). The frictional forces of exposed StSt, NiTi, and Cu-NiTi archwires did not change (p > .05). However, the frictional forces of ß-Ti archwires increased significantly after exposure to salbutamol sulphate (p = .021). Brushing with fluoride after exposure to salbutamol sulphate increased the frictional forces of ß-Ti only (p = .002). CONCLUSIONS: Salbutamol sulphate inhalation significantly affected the surface texture of ß-Ti and Cu-NiTi orthodontic archwires and increased the friction of ß-Ti archwires. These deteriorating effects were not detected on the surface of StSt and NiTi archwires. Therefore, we suggest that ß-Ti and copper titanium archwires should be used cautiously in individuals under salbutamol sulphate inhalation treatment.

Tribological Properties of Micropored Poly(2-hydroxyethyl methacrylate) Hydrogels in a Biomimetic Aqueous Environment.

The applications of hydrogels in tissue engineering as implants have rapidly grown in the last decade. However, the tribological properties of hydrogels under physiologically relevant conditions, especially those of textured hydrogels, have remained largely unknown due to the complexity of their mechanical and chemical properties. In this study, we experimentally investigated the tribological properties of micopored poly(2-hydroxyethyl methacrylate) (pHEMA) with the lateral pore dimensions varied compared to untextured pHEMA, the most commonly used hydrogel in ophthalmology, under physiologically relevant conditions. The pHEMA specimens were slid against a smooth glass curve under varying loads (6-60 mN, leading to an average contact pressure of 10-21 kPa) and sliding speeds (1-10 mm/s) in phosphate-buffered saline (pH 7.4) at 33 °C to mimic the physiological conditions in human eyes. At relatively low loads and sliding speeds (e.g., 6 mN and 1 mm/s), the micopored pHEMA did not reduce the dissipated frictional energy significantly. However, at relatively high loads and sliding speeds (e.g., 60 mN and 100 mm/s), the micopored pHEMA resulted in significantly lower frictional energy (reduced by up to 68%) dissipation than the untextured pHEMA. The effect was more pronounced with the micropores with smaller dimensions. These are attributed to the greater amount and retentivity of the interfacial fluid supported by the free water squeezed out of the micropores with the smaller dimensions under the higher load and sliding speed. These results suggest that the use of micropore texturing on hydrogels in practice, such as for ocular applications, can be leveraged to reduce friction and wear under physiological conditions and hence lower the chance of inflammation near eye implants or keratoprosthesis.

Role of MUC1 in lubrication of pleural mesothelial cells cultured on fibrine gel.

To elucidate the role of sialomucin in friction reduction, we investigated the sliding friction of pleural mesothelial cells monolayers cultured on fibrine gel. These measurements were performed on normal (4/4 RM-4) and on tumor (CARM-L1 TG3) cell lines. The effect of treatment with neuraminidase, which removes sialic acid from sialomucin, and of dexamethasone, which has shown to increase sialomucin expression, were also assessed. Furthermore, the expression of the main form of cell-surface-associated mucin (MUC1) present in the mesothelium, was assessed by western blot and immunofluorescence, under different experimental conditions. Expression of MUC1 was not significantly different in the two cell lines. Moreover, dexamethasone did not increase the expression of MUC1. Coefficient of kinetic friction (µ) was significantly higher in tumor cells than in normal cells. Neuraminidase increased µ in both cell lines. These results suggest that sialomucin may play a role in reducing the friction of pleural mesothelial cells.

The influence of cigarette smoke on colour stability and friction property of aesthetic orthodontic wires-In vitro study.

OBJECTIVE: To evaluate the colour stability and friction property of aesthetic orthodontic wires when exposed to cigarette smoke. MATERIALS AND METHODS: Forty-eight samples of aesthetic orthodontic wires (0.019″×0.025″) were allocated to three experimental groups according to their brand (n=8): GAD (Aditek™); GTP (TP Orthodontics™); GRM (Rocky Mountain™) and their respective control groups (GC) (n=8). Samples were exposed to 2 cycles of smoke in a hermetic chamber while GCs were stored in artificial saliva at 37°C. Colour analysis (CIEL*a*b* colour space and NBS units) was performed on 5mm wire segments with the Vita Easyshade Compact spectrophotometer. The friction analysis was performed in a universal test machine, in segments of 5cm wires tied to ceramic brackets with maximum values recorded in N/cm. The comparison between groups was performed with the ANOVA/Tukey test (a=0.05) and the effect of the time evaluated with ANOVA-MR with Bonferroni correction (a=0.016). RESULTS: GTP and GRM did not show significant colour and friction property variations and did not differ from GC during the study (P>0.05). However, GAD was significantly sensitive to colour changes (T1-T0-L*: -4.09±1.06; a*: 2.25±0.39; b*: 1.70±0, (T2-T0-L* 0.66±0.92; a*: 2.76±0.35) and friction (T2-T0: 2.07±1.00N/cm) (P<0.016). CONCLUSION: Exposure to cigarette smoke may alter the mechanical and optical properties of aesthetic orthodontic wires.

Bioinspired Hyaluronic Acid/Phosphorylcholine Polymer with Enhanced Lubrication and Anti-Inflammation.

Under pathological conditions, the joint is not well lubricated, which inevitably leads to osteoarthritis. Currently, in clinics injection of hyaluronic acid (HA) as an intra-articular viscosupplement is one of the main methods for alleviation of osteoarthritis. However, the viscosity of HA reduces dramatically under high shear rate due to the shear-thinning effect. Therefore, it is crucial to enhance the lubrication property of HA in order to treat osteoarthritis effectively. In this study, we successfully grafted 2-methacryloyloxyethyl phosphorylcholine (MPC), which is a zwitterionic biomaterial with excellent hydration lubrication, onto the HA with two different molecular weights (HAMPC) to enhance lubrication. The lubrication test performed using an atomic force microscope showed that, compared with HA, the friction coefficient of HAMPC was greatly reduced under various conditions. The in vitro test demonstrated that HAMPC was biocompatible and could upregulate cartilage anabolic genes while simultaneously downregulating cartilage catabolic proteases and pain-related genes. Importantly, high molecular weight HAMPC exhibited improved the capability to regulate these genes compared with low molecular weight HAMPC. In conclusion, the high molecular weight HAMPC developed herein, with enhanced lubrication and anti-inflammation, may be a promising polymer for the treatment of osteoarthritis.

Influence of the Punch Speed on the Die Wall/Powder Kinematic Friction During Tableting.

Influence of the compaction speed on the final tablet properties is an important challenge during the scale-up of a solid dosage form. This strain rate sensitivity is generally attributed to the time dependent deformation behavior of the powder. In this work, we studied the influence of the speed on another important factor during compaction: friction between the tablet/powder and the die. An original experimental methodology was developed to study the evolution of the kinematic friction coefficient between the tablet and the die as a function of the sliding speed of the tablet on the die wall. This methodology made it possible to separate the speed used to make the tablet from the speed used to measure the friction coefficient. Results indicate that the kinematic coefficient of friction increases with the sliding speed following a logarithmic trend. This trend was observed for 4 different pharmaceutical excipients. Moreover, it was proved that the speed dependency is an intrinsic property of the friction between a tablet and a die lubricated using magnesium stearate.

Biomimetic proteoglycans can molecularly engineer early osteoarthritic cartilage in vivo.

Biomimetic proteoglycans (BPGs) have the potential to treat osteoarthritis (OA) given that these molecules mimic the structure and properties of natural proteoglycans, which are significantly reduced in OA. We examined the effects of BPGs injected into the intra-articular space in an in vivo OA rabbit knee model and evaluated the effect on histological response, joint friction, and BPG distribution and retention. Rabbits underwent ACL transection to create an arthritic state after 5 weeks. OA rabbits were treated with BPGs or Euflexxa® (hyaluronic acid) intra-articular injections. Non-OA rabbits were injected similarly with BPGs; contralateral joints served as controls. The progression of OA and response to injections were evaluated using Mankin and gross grading systems indicating that mild OA was achieved in operated joints. The coefficient of friction (COF) of the intact knee joints were measured using a custom pendulum friction apparatus, showing that OA joints and OA + Euflexxa® joints demonstrated increased COF than non-operated controls, while BPG-injected non-OA and OA + BPGs were not significantly different from non-OA controls. Injected fluorescently labeled BPGs demonstrated that BPGs diffused into cartilage with localization in the pericellular region. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:403-411, 2019.

Tribological evaluation of biomedical polycarbonate urethanes against articular cartilage.

This research investigated the in-vitro wear and friction performance of polycarbonate urethane (PCU) 80A as they interact with articular cartilage, using a customised multidirectional pin-on-plate tester. Condyles were articulated against PCU 80A discs (Bionate® I and Bionate® II) (configuration 1) and the results arising from these tests were compared to those recorded during the sliding of PCU pins against cartilage plates (configuration 2). Configuration 1 produced steadily increasing coefficient of friction (COF) (up to 0.64 ±â€¯0.05) and had the same trend as the cartilage-on-stainless steel articulation (positive control). When synovial fluid rather than bovine calf serum was used as lubricant, average COF significantly decreased from 0.50 ±â€¯0.02-0.38 ±â€¯0.06 for condyle-on-Bionate® I (80AI) and from 0.41 ±â€¯0.02-0.24 ±â€¯0.04 for condyle-on-Bionate® II (80AII) test configurations (p < 0.05). After 15 h testing, the cartilage-on-cartilage articulation (negative control) tests showed no cartilage degeneration. However, different levels of cartilage volume loss were found on the condyles from the positive control (12.5 ±â€¯4.2 mm3) and the PCUs (20.1 ±â€¯3.6 mm3 for 80 AI and 19.0 ±â€¯2.3 mm3 for 80AII) (p > 0.05). A good correlation (R2 =0.84) was found between the levels of average COF and the volume of cartilage lost during testing; increasing wear was found at higher levels of COF. Configuration 2 showed low and constant COF values (0.04 ±â€¯0.01), which were closer to the negative control (0.03 ±â€¯0.01) and significantly lower than configuration 1 (p < 0.05). The investigation showed that PCU is a good candidate for use in hemiarthroplasty components, where only one of the two articulating surfaces is replaced, as long as the synthetic material is implanted in a region where migrating cartilage contact is achieved. Bionate® II showed better tribological performance, which suggests it is more favourable for use in hemiarthroplasty design.

On medical treatment for ureteral stone expulsion.

There is evidence that α-adrenoceptor (α-AR) antagonists facilitate the passage of ureteric stones, but the mechanism behind this effect has not been established. If one accepts that it is the friction between a ureteral stone and the mucosa that hampers the passage of the stone, and that the passage traumatizes the mucosa, the aim of treatment must be to reduce this friction. Elevated pressure above an obstructing stone results in an increase in tension in the wall of the upper urinary tract, including the tension at stone level, which causes an increase in friction and ureteric colic. Reducing pressure, by low but adequate fluid intake, non-steroidal anti-inflammatory drugs (NSAIDs), or α-AR antagonists that reduce the friction and give pain relief, seems to be rational. When the stone is pressed downwards by a high pressure the mucosa forms a bar ahead of the stone. These factors reduce the ureteral lumen and hamper the passage of both urine and the stone. The swelling can be reduced by NSAIDs. Filling of the ureter ahead of the stone reduces the friction between the stone and the ureteral mucosa. Evacuation of the urine ahead of the stone by effective peristaltic activity increases this friction. α-AR antagonists that reduce peristalsis may therefore be used to reduce the friction and consequently allow the stones to pass more often and earlier. For very early stone expulsion, a combination of NSAIDs and α-AR antagonists may be useful. There is no evidence that spasm influences the passage of ureteral stones.

Unraveling the Correlations between Conformation, Lubrication, and Chemical Stability of Bottlebrush Polymers at Interfaces.

In the present study, we monitored the conformation and chemical stability of a hydrophilic bottlebrush (BB) polymer in pure water and buffered saline solutions. We correlated these parameters to lubricating and wear protecting properties. Using the surface forces apparatus (SFA), we show that the BB polymer partially adsorbs on mica surfaces and extends half its contour length toward the aqueous media. This conformation gives rise to a strong repulsive interaction force when surfaces bearing BB polymer chains are pressed against each other. Analysis of these repulsive forces demonstrated that the adsorbed polymer chains could be described as end-attached elastic rods. After 2 months of aging at temperatures ranging from 4 to 37 °C, partial scission of the BB polymer's lateral chains was observed by gel permeation chromatography with a half-life time of the polymer of at least two years. The thickness of the BB polymer layer assessed by SFA appeared to quickly decrease with aging time and temperature, which was mainly caused by the adsorption to the substrate of the released lateral chains. The gradual loss of the BB polymer lateral chains did not significantly impact the tribological properties of the BB polymer solution nor its wear protection capacity. The friction coefficient between mica surfaces immersed in the BB polymer solution was µ = 0.031 ± 0.002, was independent of the aging conditions, and remained constant up to an applied pressure P = 0.2 to 0.25 MPa. Altogether, this study demonstrates that, besides the gradual loss of lateral chains, the BB polymer is still able to perform adequately as a lubricant and wear protecting agent over a time period suitable for in vivo administration.

An in vitro study of cartilage-meniscus tribology to understand the changes caused by a meniscus implant.

Active lifestyles increase the risk of meniscal injury. A permanent meniscus implant of polycarbonate urethane (PCU) is a promising treatment to postpone/prevent total knee arthroplasty. Study of the changes in articular cartilage tribology in the presence of PCU is essential in developing the optimum meniscus implant. Therefore, a cartilage-meniscus reciprocating, sliding model was developed in vitro, mimicking the stance and swing phases of the gait cycle. The meniscus was further replaced with PCU and surface-modified PCUs (with C18 chains, mono-functional polydimethylsiloxane groups and mono-functional polytetrafluoroethylene groups) to study the changes. The coefficient of friction (COF) was calculated, and cartilage wear was determined and quantified histologically. The cartilage-meniscus sliding resulted in low COF during both stance and swing (0.01< COF <0.12) and low wear of cartilage (scores <1). The cartilage-PCU sliding, during stance, revealed similar low COFs. But during swing, the COFs were high (average ∼1, maximum 1.6), indicating a breakdown in interstitial fluid pressurization lubrication and non-effective activation of the boundary lubrication. This may lead to wear of cartilage in long term. However, under the tested conditions the wear of cartilage against PCUs was not higher than its wear against meniscus, and the cartilage was occasionally damaged. The COF decreased with increasing the contact pressure (as-per a power equation) up to 1MPa. The changes in the surface modification of PCU did not affect PCU's tribological performance.

Reduction of friction by recombinant human proteoglycan 4 in IL-1α stimulated bovine cartilage explants.

A boundary lubricant attaches and protects sliding bearing surfaces by preventing interlocking asperity-asperity contact. Proteoglycan-4 (PRG4) is a boundary lubricant found in the synovial fluid that provides chondroprotection to articular surfaces. Inflammation of the diarthrodial joint modulates local PRG4 concentration. Thus, we measured the effects of inflammation, with Interleukin-1α (IL-1α) incubation, upon boundary lubrication and PRG4 expression in bovine cartilage explants. We further aimed to determine whether the addition of exogenous human recombinant PRG4 (rhPRG4) could mitigate the effects of inflammation on boundary lubrication and PRG4 expression in vitro. Cartilage explants, following a 7 day incubation with IL-1α, were tested in a disc-on-disc configuration using either rhPRG4 or saline (PBS control) as a lubricant. Following mechanical testing, explants were studied immunohistochemically or underwent RNA extraction for real-time polymerase chain reaction (RT-PCR). We found that static coefficient of friction (COF) significantly decreased to 0.14 ± 0.065 from 0.21 ± 0.059 (p = 0.014) in IL-1α stimulated explants lubricated with rhPRG4, as compared to PBS. PRG4 expression was significantly up regulated from 30.8 ± 19 copies in control explants lubricated with PBS to 3330 ± 1760 copies in control explants lubricated with rhPRG4 (p < 0.001). Explants stimulated with IL-1α displayed no increase in PRG4 expression upon lubrication with rhPRG4, but with PBS as the lubricant, IL-1α stimulation significantly increased PRG4 expression compared to the control condition from 30.8 ± 19 copies to 401 ± 340 copies (p = 0.015). Overall, these data suggest that exogenous rhPRG4 may provide a therapeutic option for reducing friction in transient inflammatory conditions and increasing PRG4 expression. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:580-589, 2017.

Tactile friction of topical formulations.

BACKGROUND: The tactile perception is essential for all types of topical formulations (cosmetic, pharmaceutical, medical device) and the possibility to predict the sensorial response by using instrumental methods instead of sensory testing would save time and cost at an early stage product development. Here, we report on an instrumental evaluation method using tactile friction measurements to estimate perceptual attributes of topical formulations. METHODS: Friction was measured between an index finger and an artificial skin substrate after application of formulations using a force sensor. Both model formulations of liquid crystalline phase structures with significantly different tactile properties, as well as commercial pharmaceutical moisturizing creams being more tactile-similar, were investigated. Friction coefficients were calculated as the ratio of the friction force to the applied load. The structures of the model formulations and phase transitions as a result of water evaporation were identified using optical microscopy. RESULTS: The friction device could distinguish friction coefficients between the phase structures, as well as the commercial creams after spreading and absorption into the substrate. In addition, phase transitions resulting in alterations in the feel of the formulations could be detected. A correlation was established between skin hydration and friction coefficient, where hydrated skin gave rise to higher friction. Also a link between skin smoothening and finger friction was established for the commercial moisturizing creams, although further investigations are needed to analyse this and correlations with other sensorial attributes in more detail. CONCLUSION: The present investigation shows that tactile friction measurements have potential as an alternative or complement in the evaluation of perception of topical formulations.

Influence of treatment of vulvovaginal atrophy with intravaginal prasterone on the male partner.

OBJECTIVE: The aim was to analyze the opinion of the male partner of women treated for vulvovaginal atrophy (VVA) with intravaginal 0.50% DHEA (prasterone), thus providing information on both members of the couple. METHODS: On a voluntary basis, in a prospective, randomized, double-blind and placebo-controlled phase-III clinical trial, the male partner filled a questionnaire at baseline and at 12 weeks stating his observations related to his penis and intercourse before and after VVA treatment. RESULTS: Sixty-six men having a partner treated with intravaginal DHEA and 34 others having a partner treated with placebo answered the questionnaires. Concerning the feeling of vaginal dryness of their female partner, the severity score following DHEA treatment improved by 81% (0.76 units) over placebo (p = 0.0347). Thirty-six percent of men having a partner treated with DHEA did not feel the vaginal dryness of the partner at the end of treatment compared to 7.8% in the placebo group. When analyzing the situation at 12 weeks compared to baseline, an improved score of 1.09 units was the difference found for the DHEA group compared to 0.76 for the placebo group (p = 0.05 vs. placebo). In the DHEA group, 38% of men scored very improved compared to 18% in the placebo group. No adverse event has been reported. CONCLUSION: The male partner had a very positive evaluation of the treatment received by his female partner.

Comparison of friction and wear of articular cartilage on different length scales.

The exceptional tribological properties of articular cartilage are still far from being fully understood. Articular cartilage is able to withstand high loads and provide exceptionally low friction. Although the regeneration abilities of the tissue are very limited, it can last for many decades. These biomechanical properties are realized by an interplay of different lubrication and wear protection mechanisms. The deterioration of cartilage due to aging or injury leads to the development of osteoarthritis. A current treatment strategy focuses on supplementing the intra-articular fluid with a saline solution containing hyaluronic acid. In the work presented here, we investigated how changing the lubricating fluid affects friction and wear of articular cartilage, focusing on the boundary and mixed lubrication as well as interstitial fluid pressurization mechanisms. Different length and time scales were probed by atomic force microscopy, tribology and profilometry. We compared aqueous solutions with different NaCl concentrations to a viscosupplement containing hyaluronic acid (HA). In particular, we found that the presence of ions changes the frictional behavior and the wear resistance. In contrast, hyaluronic acid showed no significant impact on the friction coefficient, but considerably reduced wear. This study confirms the previous notion that friction and wear are not necessarily correlated in articular cartilage tribology and that the main role of HA might be to provide wear protection for the articular surface.

Effects of hyaluronic acid and γ-globulin concentrations on the frictional response of human osteoarthritic articular cartilage.

Synovial fluid plays an important role in lubricating synovial joints. Its main constituents are hyaluronic acid (HA) and γ-globulin, acting as boundary lubricants for articular cartilage. The aim of the study was to demonstrate the concentration-dependent effect of HA and γ-globulin on the boundary-lubricating ability of human osteoarthritis (OA) cartilage. Normal, early and advance stage articular cartilage samples were obtained from human femoral heads and in presence of either HA or γ-globulin, cartilage frictional coefficient (µ) was measured by atomic force microscopy (AFM). In advanced stage OA, the cartilage superficial layer was observed to be completely removed and the damaged cartilage surface showed a higher µ value (∼ 0.409) than the normal cartilage surface (∼ 0.119) in PBS. Adsorbed HA and γ-globulin molecules significantly improved the frictional behavior of advanced OA cartilage, while they were ineffective for normal and early OA cartilage. In advanced-stage OA, the concentration-dependent frictional response of articular cartilage was observed with γ-globulin, but not with HA. Our result suggested that HA and γ-globulin may play a significant role in improving frictional behavior of advanced OA cartilage. During early-stage OA, though HA and γ-globulin had no effect on improving frictional behavior of cartilage, however, they might contribute to disease modifying effects of synovial fluid as observed in clinical settings.

Use of biomimetic hexagonal surface texture in friction against lubricated skin.

Smooth contact pads that evolved in insects, amphibians and mammals to enhance the attachment abilities of the animals' feet are often dressed with surface micropatterns of different shapes that act in the presence of a fluid secretion. One of the most striking surface patterns observed in contact pads of these animals is based on a hexagonal texture, which is recognized as a friction-oriented feature capable of suppressing both stick-slip and hydroplaning while enabling friction tuning. Here, we compare this design of natural friction surfaces to textures developed for working in similar conditions in disposable safety razors. When slid against lubricated human skin, the hexagonal surface texture is capable of generating about twice the friction of its technical competitors, which is related to it being much more effective at channelling of the lubricant fluid out of the contact zone. The draining channel shape and contact area fraction are found to be the most important geometrical parameters governing the fluid drainage rate.

Calcium phosphate particulates increase friction in the rat knee joint.

OBJECTIVE: Basic calcium phosphate (BCP) particulates are commonly found in cartilage and synovial fluid of osteoarthritis (OA) joints with the amount of BCP correlating with knee OA severity. How cartilage mineralization affects joint degeneration has yet to be determined. The objective of this study was to determine whether BCP in the synovial fluid affects the rat knee joint coefficient of friction (COF). METHODS: The COFs of knees from both hind limbs of four mature male rats were measured post mortem using a pendulum apparatus with an infrared tracking system. The three conditions evaluated were (1) the naïve state, (2) after the injection of 100 µL of phosphate buffered saline (PBS) (sham) and (3) after the injection of 100 µL of a 1 mg/mL BCP suspension. The decrease in the pendulum amplitude (decay) was fit using two friction models: (1) a one parameter Stanton linear decay model and (2) a two parameters combination Stanton linear decay and viscous damping exponential decay model. RESULTS: The COF increased 17.6% after injection of BCP compared to the naïve (P = 0.0012) and 16.0% compared to the saline injected (P = 0.0018) joints as derived from the one parameter model. The COF did not differ between naïve and saline injected joints. Results from the two parameters model showed a similar increase in COF after injection of BCP while the viscous damping was not significantly different between conditions. CONCLUSIONS: The increased joint friction with BCP particulates suggests BCPs may play a role in articular surface degradation and OA development.

Pleural mesothelium lubrication after phospholipase treatment.

Coefficient of kinetic friction (µ) of rabbit pleural mesothelium increased after short treatment of specimens with phospholipase C. This increase was removed by addition of a solution with hyaluronan or sialomucin, as previously shown in post-blotting Ringer or after short pronase treatment. After phospholipase µ decreased with increase in sliding velocity, but at highest velocity it was still greater than control; this difference was removed by addition of hyaluronan or sialomucin, as in post-blotting Ringer or after short pronase treatment. Hyaluronan placed on specimen before phospholipase treatment reduced increase in µ by protecting phospholipids from enzyme, as shown by others for alveolar and synovial phospholipids. Samples of parietal pleura stained with silver nitrate showed that mesothelial cells were not disrupted by short phospholipase treatment. Instead, they were disrupted if this treatment was preceded by a short pronase treatment; but even after this disruption addition of hyaluronan or sialomucin brought µ back to control.