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PubMed1996

Friction, not texture, dictates grip forces used during object manipulation.

1. Three men and seven women, 25-40 yr of age, were asked to use the thumb and index fingers to grasp, lift, and hold the armature of a linear motor generating a 2.0-N opposing force (simulating an object weighing approximately 200 g) for 2 s. The surface in contact with the fingers was composed of smooth or polyamide plastic etched with 1.0-mm high Braille beads separated at 2.0- or 3.0-mm intervals measured from apex to apex. The surfaces were left either untreated or coated with talc, water, or sucrose films designed to change the coefficient of friction with the skin. Talc reduced the coefficient of friction, whereas water and sucrose both increased the friction against the skin. In all, 12 surface conditions were used to evaluate the effects of texture and friction on the grip force during lifting and holding. 2. For all subjects the inverse coefficient of friction was associated with proportionately scaled increases in grip force, regardless of surface texture. The peak lifting force as well as the static force used to hold the object stationary were significantly correlated with the inverse of the coefficient of friction. When coatings were applied to dissimilar surface textures to produce similar coefficients of friction, the grip force profiles were nearly identical. When strong adhesives increased the friction of the smooth surface compared with textured surfaces, grip forces decreased as friction increased. That is, although the untreated smooth surface had less friction than either of the two textured surfaces, the addition of sucrose increased the smooth surface friction to a higher level than either of the similarly treated textured surfaces. As a result, the effect of surface friction could be dissociated from the effect of either surface texture or coating. Friction appears to be a more important factor in determining the grip force than either texture or surface films at least for the range of textures and coatings examined in this study.

Adhesiveness↗
PubMed1999

The influence of continuous sliding and subsequent surface wear on the friction of articular cartilage.

Reciprocating motion friction tests were conducted upon cartilage-on-metal contacts while subjected to a constant load. Initial friction coefficients were compared with repeat friction coefficients following a sufficient load removal period. The repeat friction coefficients were marginally higher than the initial values and both were primarily dependent on the loading time. It was concluded that while a wear component had been identified, which modestly increased friction coefficients, the overriding parameter influencing friction was loading time. The authors postulate that fluid phase load carriage (being dependent on loading time) within the articular cartilage is largely responsible for low friction coefficients in the mixed and boundary lubrication regimes. This mechanism has been referred to as biphasic lubrication. Both synovial fluid and Ringer's solution were used as lubricants. Over the assessed 120 min loading time friction coefficients rose from 0.005 (for both lubricants) after 5 s to 0.50 and 0.57 for synovial fluid and Ringer's solution respectively. Synovial fluid was found to significantly reduce friction coefficients compared to Ringer's solution over broad ranges of the assessed loading times (p < 0.05). Stylus and non-contacting laser profilometry were successfully employed to provide reliable, quantitative and accurate measures of surface roughness. Laser profilometry before and after a continuous sliding friction test revealed a significant increase in surface roughness from Ra = 0.8 (+/- 0.2) micron to Ra = 2.1 (+/- 0.2) microns, (p < 0.0005); confirming that surface wear was occurring. Scanning electron microscopy (SEM) revealed the typical highly orientated collagen fibres of the superficial tangential zone. Environmental SEM (ESEM) of fully hydrated cartilage specimens provided largely featureless images of the surface which suggested that sample preparation for conventional SEM was detrimental to the authenticity of the cartilage surface appearance using SEM. Two distinct acellular, non-collagenous surface layers were identified using ESEM and transmission electron microscopy (TEM); respectively referred to as the boundary layer and surface lamina. The phospholipid/glycoprotein based boundary layer will provide boundary lubrication during intimate contact of opposing cartilage surfaces. The surface lamina, being a continuum of the proteoglycan interfibrillar matrix, is present to prevent fibrillation of the underlying collagen fibres. Both layers may contribute to the time dependent frictional response of articular cartilage. Although laser profilometry did reveal surface wear which was consistent with a small increase in friction, the primary variable controlling the friction coefficient was the period of loading.

Animals↗
PubMed1994

The dynamic frictional resistance between orthodontic brackets and arch wires.

Limited published research on friction deals mainly with conventional stainless steel brackets and arch wires. However, the clinician can choose from a range of modern materials in determining arch wire and bracket combinations. This study quantifies the dynamic frictional force of sliding between different modern orthodontic brackets and arch wires. From the multitude of factors involved in the frictional process, the following were selected for investigation: arch wire material, bracket material, bracket-to-arch wire angulation, and lubrication (artificial saliva). The frictional force involved in sliding a ligated arch wire through a bracket slot was measured with a universal materials testing machine. A four-way analysis of variance was used to assess the results. Of the four factors investigated, all were found to have a significant influence on friction. Polycarbonate brackets showed the highest friction and stainless steel brackets the lowest. Friction increased with bracket-to-arch wire angulation. Lubrication significantly reduced friction. A range of 0.9 to 6.8 N frictional force was recorded. The actual force values recorded were most useful for comparing the relative influence of the factors tested on friction, rather than as a quantitative assessment of friction in vivo. The forces observed suggest that friction may be a significant influence on the amount of applied force required to move a tooth in the mouth. Hence, arch wire and bracket selection may be an important consideration when posterior anchorage is critical.

Aluminum Oxide↗
PubMed2006

Friction dynamics of trocars.

BACKGROUND: In minimally invasive surgery, force feedback information on tissue manipulation is altered by friction between the instrument and the sealing mechanism of the trocar. It is unknown how the different sealing mechanisms of currently available trocars influence the friction forces. The current study investigated the dynamic changes in friction for various trocars at different instrument velocities. METHODS: The friction characteristics for six common types of trocars were determined. A force sensor was attached to the shaft of a standard 5-mm disposable grasper to measure the forces required to move it through the trocars. Movement velocity and direction of the shaft were controlled by a servomotor. In addition, whether moistening the shaft reduced friction was tested. RESULTS: The friction depended on the type of trocar, the movement velocity, and the movement direction, and varied between 0.25 and 3.0 N. Specifically, trocars with narrow sealing caps (i.e., high normal force onto the shaft) and trocars with thick sealing caps (i.e., large contact area) generate a high amount of friction. Moistening the shaft reduced friction 15% to 45%. For most trocars, large fluctuations in forces occur when the movement starts or when the direction reverses. The magnitude of these fluctuations varied between 0.2 and 2.5 N. CONCLUSIONS: For some trocars, friction can be as great as the forces associated with instrument-tissue interaction. At movement reversals, friction fluctuates due to deformations of the rubber and silicon parts of the sealing mechanism. Such high variance can deteriorate surgical performance during high precision tasks (e.g., tissue manipulation) that typically involve many changes in movement direction. Comparisons of the investigated trocars indicate that the friction magnitude and variance can be reduced easily by changing the properties of the sealing cap or by lubricating the instruments.

Equipment Design↗
PubMed1996

Relative friction minimization in fixed orthodontic bracket appliances.

The biomechanical and mathematical analysis of friction on an arch wire/bracket combination and the wire supports has demonstrated that there is an optimal relationship, i.e. minimal friction forces, between the bracket width and the distance between the adjacent brackets on the neighboring teeth. With this optimal situation, less force will develop for a given deflection of the arch wire. This, in turn, will lead to fewer frictional effects when the friction forces are assumed to be proportional to the concentrated perpendicular forces on the arch wire. As long as the contacting surface can be regarded as a point, Coulomb's law of friction can be applied in its simplest form. Relative friction minimization can thereby be qualitatively and quantitatively obtained by linear theory for any specified angulation, wire properties and coefficients of friction. Literature stating that narrow brackets will lead to less friction for specified angulation cannot be confirmed according to the presented analysis. The other extreme statement 'Use the widest bracket possible' also cannot be used in principle. Since the analysis shows a mathematical relationship between most of the relevant design variables of an arch wire/bracket combination and the magnitude of friction forces, empirical results can be sorted and ranked by their physical figures instead of by statistical distribution. In addition, it is possible to make recommendations about the appropriate bracket sizes for various cases. The dependences of the coefficients of friction themselves on material, surface roughness, lubrication, etc. are not investigated here. These factors are also very relevant, especially in reduction of the absolute magnitude of frictional forces, but this problem is left to tribologists.

Biomechanical Phenomena↗
PubMed2006

Influence of hyaluronic acid on the time-dependent friction response of articular cartilage under different conditions.

Therapeutic lubricant injections of hyaluronic acid are a relatively recent treatment for osteoarthritis. Their efficacy, however, in vivo has been subject to much debate. Frictional properties of cartilage-cartilage contacts under both static and dynamic loading conditions have been investigated, using healthy cartilage and cartilage with a physically disrupted surface, with and without the addition of a therapeutic lubricant, hyaluronic acid. Most of the cartilage friction models produced typical time-dependent loading curves, with a rise in static friction with loading time. For the dynamic loading conditions the rise in friction with loading time was dependent on the spatial (and time) variation in the load on the cartilage plate. For sliding distances of 4 mm or greater, when the cartilage plate was unloaded during sliding, the dynamic friction remained low whereas, with shorter sliding distances, the dynamic friction increased with increasing loading time. Static friction was higher than dynamic friction (under the same tribological conditions). The 'damaged' cartilage models produced higher friction than healthy cartilage under equivalent tribological conditions. It was shown that hyaluronic acid was an effective boundary lubricant for articular cartilage under static conditions with both healthy and damaged cartilage surfaces. Hyaluronic acid was less effective under dynamic conditions. However, these dynamic conditions had low friction values with the control lubricant because of the effectiveness of the intrinsic biphasic lubrication of the cartilage. It was only under the tribological conditions in which the cartilage friction was higher and rising with increasing loading time because of depletion of the intrinsic biphasic lubrication, that the role of hyaluronic acid as an effective therapeutic lubricant was demonstrated.

Animals↗
PubMed2006

Static frictional resistances of polycrystalline ceramic brackets with metal slot inserts.

AIMS: To compare the static frictional resistances of polycrystalline ceramic brackets with a gold slot insert (Desire), a stainless steel slot insert (Clarity), a conventional polycrystalline ceramic bracket (Transcend 6000) and a stainless steel bracket (Ultratrimm). METHODS: Twenty five brackets of each type were tested by sliding against straight lengths of 0.019 x 0.025 inch rectangular stainless steel wire. During the tests the brackets and wire were lubricated with artificial saliva. Static frictional forces at three different binding angulations (0, 5 and 10 degrees) were measured for all brackets. RESULTS: Statistically significant increases in static frictional resistance were found as the bracket/wire angulation increased from 0 through 5 to 10 degrees for all bracket types. At angulations below the critical binding angle the Ultratrimm brackets produced the greatest friction and the Transcend 6000 brackets produced the least friction. As the angulation increased the Transcend 6000 brackets produced greater friction than the other brackets. At the highest angulation (10 degrees), the Ultratrimm brackets produced significantly less friction and the Transcend 6000 brackets produced significantly more friction than the other brackets. The Desire and Clarity brackets produced comparable results: there were no statistically significant differences between these two brackets for static friction at any of the angulations. CONCLUSIONS: Polycrystalline ceramic brackets with either stainless steel or gold slot inserts produced similar static frictional resistances to sliding. At binding angulations, the brackets with inserts demonstrated consistently lower static frictional resistances than a conventional ceramic bracket.

Ceramics↗
PubMed2006

Physiological and psychophysical responses in handling maximum acceptable weights under different footwear--floor friction conditions.

A study on combined manual materials-handling tasks performed on floors under three friction levels was conducted. Eight male subjects participated in the study. The maximum acceptable weight of handling, including lifting, carrying for 3m, lowering, and walking 3m back at twice per minute was determined. The subject then performed the same tasks for 10 min. Heart rate, Vo2, energy efficiency, perceived sense of slip, and rating of perceived exertion for whole body strain were measured. The results showed that the effects of friction level on the maximum acceptable weights of handling, perceived sense of slip, Vo2, and energy efficiency were statistically significant (p<or=0.0006). As the friction level increased from low to high, the maximum acceptable weights of handling increased from 8.15 to 9.34 kg. The energy efficiency on the low friction condition (12.58 kg/L/min) was significantly lower than those of the medium (15.73 kg/L/min) and high (15.38 kg/L/min) friction conditions. The perceived sense of slip was the highest (5.44) on the low-friction condition, followed by the medium-friction condition (3.58), and last the high-friction condition (1.84). The implication of this study was that friction level should be regarded as one of the major environmental factors in designing MMH tasks as it affected both physiological and psychophysical responses of the subjects. Low-friction footwear-floor interface should be avoided as it resulted in not only high scores of perceived sense of slip but also in low-energy efficiency utilized in the body.

Adult↗
PubMed2003

Friction coefficient of skin in real-time.

BACKGROUND/PURPOSE: Friction studies are useful in quantitatively investigating the skin surface. Previous studies utilized different apparatuses and materials for these investigations but there was no real-time test parameter control or monitoring. Our studies incorporated the commercially available UMT Series Micro-Tribometer, a tribology instrument that permits real-time monitoring and calculation of the important parameters in friction studies, increasing the accuracy over previous tribology and friction measurement devices used on skin. METHODS: Our friction tests were performed on four healthy volunteers and on abdominal skin samples. A stainless steel ball was pressed on to the skin with at a pre-set load and then moved across the skin at a constant velocity of 5 mm/min. The UMT continuously monitored the friction force of the skin and the normal force of the ball to calculate the friction coefficient in real-time. Tests investigated the applicability of Amonton's law, the impact of increased and decreased hydration, and the effect of the application of moisturizers. RESULTS: The friction coefficient depends on the normal load applied, and Amonton's law does not provide an accurate description for the skin surface. Application of water to the skin increased the friction coefficient and application of isopropyl alcohol decreased it. Fast acting moisturizers immediately increased the friction coefficient, but did not have the prolonged effect of the slow, long lasting moisturizers. CONCLUSION: The UMT is capable of making real-time measurements on the skin and can be used as an effective tool to study friction properties. Results from the UMT measurements agree closely with theory regarding the skin surface.

2-Propanol↗
PubMed1996

Frictional resistance between orthodontic brackets and archwires in the buccal segments.

Orthodontic sliding mechanics using preadjusted brackets is a popular approach for achieving incisor retraction. A distally directed force slides the archwire through brackets and tubes in the buccal segments. Friction in the buccal segments contributes resistance to the force required to achieve tooth movement, and techniques to reduce friction reduce the potential for anchorage loss. This in vitro study used an Instron testing machine to assess frictional forces for three types of 0.022 x 0.028 inch brackets: preadjusted stainless steel premolar brackets (Standard Straight Wire, "A" Company, Inc, San Diego, Calif), Activa brackets ("A" Company Inc, San Diego, Calif), and Speed brackets (Strite Industries Ltd), combined with five wire sizes (0.018, 0.020, 0.016 x 0.022, 0.018 x 0.025 and 0.019 x 0.025 inch). A model with one attached molar bracket and one or two premolar brackets simulated the buccal segments. Activa brackets produced the least friction for all wires tested. Speed brackets with round wires showed little frictional force while rectangular wires gave rise to higher forces, at levels similar to those recorded with two Standard Straight Wire brackets. Static friction for round wires in standard brackets was found to be 178-275 gm-force. The ratio of static to dynamic friction was remarkably consistent in all tests. Different methods of ligation were compared for their effect on static friction. Ligation with loosely placed ligatures or stretched modules reduced frictional forces in Standard Straight Wire brackets, the reduction being greatest for round archwires. Frictional forces recorded from archwires secured with elastomeric modules showed a steady reduction over a 3-week period, depending on how long the module had been in position on the bracket.

Dental Stress Analysis↗
PubMed2005

Friction of orthodontic elastomeric ligatures with different dimensions.

The aim of this study was to evaluate in vitro the effect of variations in the size of elastomeric ligatures on the static frictional resistance generated by orthodontic sliding mechanics under dry condition. Frictional forces generated by elastomeric ligatures treated with a lubricating material (silicone) were analyzed as well. An Instron testing machine was used to assess the static frictional forces of a 0.019 x 0.025-inch stainless steel rectangular wire that was ligated to a molar convertible tube and to three stainless steel 0.022-inch pre-adjusted brackets with elastomeric ligatures with different dimensions: small, medium, and large. The static friction produced by two prototypes of silicone-lubricated elastomeric ligatures was also measured. The small and medium elastomeric ligatures produced significantly less friction than the large ligatures. No statistically significant difference was found between small and medium ligatures. The decrease in frictional forces of small and medium modules had to be ascribed mainly to the smaller thickness of both ligatures with respect to large ligatures. The lubricated elastomeric ligatures generated significantly smaller frictional forces than nonlubricated elastomeric ligatures with different dimensions. The variation in the dimensions of the elastomeric ligatures is able to influence the static frictional resistance generated by orthodontic sliding mechanics in the buccal segments. The use of small and medium elastomeric ligatures determines a 13-17% decrease in static friction compared with large ligatures. Silicone-lubricated modules can reduce static friction by 23-34% with respect to the small and medium nonlubricated elastomeric ligatures and by 36-43% compared with nonlubricated large ligatures.

Analysis of Variance↗
PubMed2006

Physical friction is under-recognized as an irritant that can cause or contribute to contact dermatitis.

BACKGROUND: The role of physical friction as an irritant in the causation of contact dermatitis is under-recognized. Frictional dermatitis is defined as an eczematous process in which physical frictional trauma contributes to the induction of a dermatitis process. OBJECTIVES: To examine the clinical background of patients in whom friction was contributing to dermatitis. METHODS: Over a 30-month period during which 2700 new patients were seen, frictional irritancy was identified as playing a role in the dermatosis in 31 cases: in 27 of these, case notes were evaluated for a range of parameters. RESULTS: Physical friction was identified as causing or contributing to the dermatitis in 18 men and nine women, mean age at onset 42 years. The hands, usually the fingers of the dominant hand, were affected in all but two cases. Occupational frictional activities were found in 25 cases: commonly handling small metal components, paper, cardboard or fabric, and driving. Potential frictional activities in hobbies were noted in 12 cases. Wet work irritancy contributed in four cases (15%). Patch testing showed relevant contact allergies as cofactors in seven of 25 subjects tested (26%). Psoriasis was a cofactor in four (15%), and atopic dermatitis in 11. The study was selective, being based in a teaching hospital clinic with a special interest in contact dermatitis. Frictional irritancy is often one of several factors contributing to dermatitis. CONCLUSIONS: The contribution of friction to contact dermatitis is under-recognized probably because dermatologists do not think about the potential for physical forces to induce eczematous changes in the skin.

Adult↗
PubMed2003

Modeling of biomedical interfaces with nonlinear friction properties.

Proper isotropic and anisotropic friction constitutive equations are developed based on previous friction measurements at cancellous bone-porous coated implant interfaces exhibiting nonlinear load-displacement curves. The simulated friction response is dependent on relative tangential displacements in both orthogonal directions. The interface constitutive matrix contains cross-stiffness terms identical in isotropic friction but different in anisotropic friction. These terms are due mainly to nonlinearity in response and vanish in unidirectional friction along a principal direction and in cases with Coulomb or linear friction. The interface ultimate resistance is evaluated by an elliptic criterion which becomes circular in isotropic cases. These constitutive relations are implemented in a finite element program which is employed to analyze a bone cube sliding on top of a porous-surfaced metallic plate, an experimental model used in our earlier measurements. The results for both isotropic and anisotropic frictions demonstrate the coupling between two orthogonal directions. The direction of resultant displacement under a variable load coincides with that of the load only when the friction is isotropic with coupling terms considered. In anisotropic friction, the resultant displacement occurs in a direction different from that of loading. Our previous bi-directional measurements corroborate well the findings of this study.

Anisotropy↗
PubMed2005

[A study of frictional resistance of archwires and ligating methods].

PURPOSE: To study the effect of 4 archwires and 2 ligating methods on the frictional resistance. METHODS: The static and dynamic friction of different combinations of 4 archwires and 6 preadjusted brackets and 2 ligating methods in the buccal segments were tested in the dry state. The friction was tested by the load cell in the LJ-500 testing machine. Orthogonal experiment design was performed in this study. The data were analysed by analysis of variance and regression analysis using the statistical analysis system. RESULTS: The smallest frictional resistance in 4 different archwires was produced by combination of 0.018 x 0.025 inch stainless rectangular wire and all preadjusted brackets. The biggest frictional resistance in 4 different archwires was produced by combination of 0.019 x 0.025 inch stainless rectangular wire and all preadjusted brackets. The static friction of combination of 0.020 inch stainless round wire and all preadjusted brackets were higher than 0.018 inch stainless round wire. The dynamic friction of combination of 0.018 inch stainless round wire and all preadjusted brackets were higher than 0.020 inch stainless round wire. Among 4 kinds of stainless wires, the ratio of dynamic to static friction of 0.018 inch round wire appeared the highest, followed by 0.018 x 0.025 inch rectangular wire, 0.020 inch round wire and 0.019 x 0.025 inch rectangular wire. Elastomeric ring ligature produced higher friction and the ratio of dynamic to static friction than stainless steel ligature. CONCLUSIONS: 0.018 inch stainless steel round wire was not suitable for sliding mechanics in this study. One should pay attention to anchorage control in using 0.019 x 0.025 inch rectangular wire. Elastomeric ring ligature was not advantageous for sliding of brackets and wires in the dry state.

Dental Stress Analysis↗
PubMed1995

Development of human precision grip. IV. Tactile adaptation of isometric finger forces to the frictional condition.

The adaptation of the grip forces to the frictional condition between the digits and an object relies on feedforward sensorimotor mechanisms that use tactile afferent input to intermittently update a sensorimotor memory that controls the force coordination, i.e., the ratio between grip force (normal to the grip surface) and load force (tangential to the grip surface). The present study addressed the development of these mechanisms. Eighty-nine children and 15 adults lifted an instrumented object with exchangeable grip surfaces measuring the grip and load forces. Particularly in trials with high friction (sandpaper), the youngest children used a high grip force to load force ratio. Although this large safety margin against slips indicated an immature capacity to adapt to the frictional condition, higher grip forces were produced for more slippery material (silk versus sandpaper). The safety margin decreased during the first 5 years of age, in parallel with a lower variability in the grip force and a better adaptation to the current frictional condition. The youngest children (18 months) could adapt the grip force to load force ratio to the frictional condition in a series of lifts when the same surface structure was presented in blocks of trials, but failed when the surface structure was unpredictably changed between subsequent lifts. The need for repetitive presentation suggests a poor capacity to form a sensorimotor memory representation of the friction or an immature capacity to control the employed ratio from this representation. The memory effects, reflected by the influences of the frictional condition in the previous trial, gradually increased with age. Older children required a few lifts and adults only one lift to update their force coordination to a new friction. Hence, the present finding suggests that young children use excessive grip force, a strategy to avoid frictional slips, to compensate for an immature tactile control of the precision grip.

Adolescent↗
PubMed2006

A comparison of different ligation methods on friction.

INTRODUCTION: An elastomeric module with a polymeric coating has been developed to reduce the friction of sliding mechanics. This in-vitro study examined the stability of the coating and compared the frictional properties of coated modules with those of other common ligation methods. METHODS: Six ligation methods (regular uncoated, slick [coated], conventional silver, easy-to-tie, silicone-impregnated, and standard silver modules) were used with standard stainless steel brackets and 0.019 x 0.025-in archwires, and resistance to movement was measured. Two self-ligating (Speed [Strite Industries, Cambridge, Ontario, Canada] and Damon 2 [Sybron Dental Specialities Ormco, Orange, Calif]) brackets were also tested. RESULTS: The Damon 2 self-ligating brackets produced less friction than the other ligation methods, followed by the coated modules. There was no significant difference between the frictional resistance of brackets ligated with regular uncoated, silicone-impregnated, and easy-to-tie modules. Speed self-ligating brackets produced less friction than regular uncoated, conventional silver, and standard silver modules. The frictional properties of coated modules were not significantly affected by repeating the test 5 times or by storage in saliva for a week. CONCLUSIONS: Damon 2 brackets produced no recordable friction of ligation. Coated modules produced 50% less friction than all other ligation methods except Damon 2. The coating was resistant to the simulated effects of the oral environment. Different methods of human saliva application were found to affect the frictional properties of the coating.

Analysis of Variance↗
PubMed2006

Chondroitin sulfate reduces the friction coefficient of articular cartilage.

The objective of this study was to investigate the effect of chondroitin sulfate (CS)-C on the frictional response of bovine articular cartilage. The main hypothesis is that CS decreases the friction coefficient of articular cartilage. Corollary hypotheses are that viscosity and osmotic pressure are not the mechanisms that mediate the reduction in the friction coefficient by CS. In Experiment 1, bovine articular cartilage samples (n=29) were tested in either phosphate buffered saline (PBS) or in PBS containing 100mg/ml of CS following 48h incubation in PBS or in PBS+100mg/ml CS (control specimens were not subjected to any incubation). In Experiment 2, samples (n=23) were tested in four different solutions: PBS, PBS+100mg/ml CS, and PBS+polyethylene glycol (PEG) (133 or 170mg/ml). In Experiment 3, samples (n=18) were tested in three solutions of CS (0, 10 and 100mg/ml). Frictional tests (cartilage-on-glass) were performed under constant stress (0.5MPa) for 3600s and the time-dependent friction coefficient was measured. Samples incubated or tested in a 100mg/ml CS solution exhibited a significantly lower equilibrium friction coefficient than the respective PBS control. PEG solutions delayed the rise in the friction coefficient relative to the PBS control, but did not reduce the equilibrium value. Testing in PBS+10mg/ml of CS did not cause any significant decrease in the friction coefficient. In conclusion, CS at a concentration of 100mg/ml significantly reduces the friction coefficient of bovine articular cartilage and this mechanism is neither mediated by viscosity nor osmolarity. These results suggest that direct injection of CS into the joint may provide beneficial tribological effects.

Animals↗
PubMed2001

The effect of disc thickness and trauma on disc surface friction in the porcine temporomandibular joint.

The pathomechanics of osteoarthritis in the human temporomandibular joint (TMJ) are unknown. Compromised lubrication is a potential factor, but, lubrication within even the normal TMJ is not understood completely. Weeping lubrication is a concept that may be applicable to the TMJ. A characteristic of weeping lubrication is a slow increase in friction during static loading. The rate of increase in friction is related to the rate of lateral movement of synovial fluid away from the loading area. The TMJ disc is expected to be the main source of TMJ lubrication. This study tested two variables, disc thickness and magnitude of trauma to the disc, as factors that can affect the rate of flow of synovial fluid and thus alter lubrication of the disc surfaces. To test these variables, TMJ disc surface friction was measured before and after an impulse load. Before the impulse load, all discs demonstrated a gradual increase in friction during light static loading. The rate of increase in friction was inversely related to the disc thickness (R(2)=0.75). After an impulse load of known magnitude and peak force, disc surface friction was higher. The magnitude of this surface friction was correlated with the magnitude of the impulsive blow (R(2)=0.89) and the area of surface damage (R(2)=0.85). Disc thickness was a significant factor in determining the minimal impulse needed to produce higher surface friction (R(2)=0.99). These results confirm that disc thickness and trauma to the disc affect surface friction in the TMJ, and therefore may be important factors in compromised lubrication and the development of osteoarthritis.

Animals↗