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PubMed2002

Nanofriction behavior of cluster-assembled carbon films.

We have characterized the frictional properties of nanostructured carbon films grown by supersonic cluster beam deposition via an atomic force-friction force microscope (AFM-FFM). The experimental data are discussed on the basis of a modified Amonton's law for friction, stating a linear dependence of friction on load plus an adhesive offset accounting for a finite friction force in the limit of null total applied load. Molecular dynamics simulations of the interaction of the AFM tip with the nanostructured carbon confirm the validity of the friction model used for this system. Experimental results show that the friction coefficient is not influenced by the nanostructure of the films nor by the relative humidity. On the other hand the adhesion coefficient depends on these parameters.

Carbon↗
PubMed1998

The lubricating ability of biomembrane models with dipalmitoyl phosphatidylcholine and gamma-globulin.

Two kinds of friction tests were conducted to investigate the lubricating effect of the injection of amphiphilies on the osteoarthritic joint. The effects of the addition of L alpha-dipalmitoyl phosphatidyl-choline (L alpha-DPPC) riposomes and gamma-globulin in a saline solution of sodium hyaluronate (HA) were evaluated through pendulum friction tests. The frictional characteristics of pig shoulder joints were confirmed to depend on the viscosity of the lubricants only in the physiologically low load condition and in the condition immediately after loading. Detergent (polyoxyethylene p-t-octylphenyl ether) was successfully used to remove adsorbed films from the articular surfaces. The friction coefficient of natural synovial joints was significantly increased in a mode of mixed lubrication with the HA solution of 0.2 g/dl by the treatment of the surface with the detergent. The addition of L alpha-DPPC riposomes or gamma-globulin significantly improved the boundary lubricating ability of the articular surfaces treated with the detergent, depending on the quantity of those additives. It appears that the L alpha-DPPC riposomes and gamma-globulin can form protective films on the articular surfaces like a biomembrane. Moreover, the reciprocating frictional behaviour in sliding pairs of pig articular cartilages and glass plates was studied in order to elucidate the tribological role of those constituents in the boundary lubricating film on the articular surface. Pig synovial fluid and water solutions of HA were used as lubricants. The synovial fluid had superior lubricating ability compared to the HA solution of equivalent viscosity under a physiologically high load condition. This fact seems to be responsible for the boundary lubricating ability of constituents other than hyaluronic acid. Langmuir-Blodgett (LB) films of L alpha-DPPC on the glass plate were kept at a low and stable friction coefficient, depending on the number of film layers. In conditions of mixed films with L alpha-DPPC and gamma-globulin, the frictional behaviour was improved by increasing the quantity of gamma-globulin. A model is proposed in which the effective adsorbed films are composed of proteins, phospholipids and other conjugated constituents on the articular surfaces to be accurate in describing the boundary lubricating mechanism. The mechanism is controlled by hydrophobic groups in those amphiphilies.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Biomechanical analysis of arch-guided molar distalization when employing superelastic NiTi coil springs.

Two typical treatment situations (distalization of a last molar, distalization of a molar with the guiding arch fixed on the most distal abutment tooth) were simulated experimentally using the Orthodontic Measurement and Simulation System (OMSS). For this purpose an upper first molar was guided along steel arches with differing cross sections (0.016" x 0.022"/0.41 mm x 0.56 mm; 0.017" x 0.025"/0.43 mm x 0.64 mm) using a nickel-titanium (NiTi) compression spring. The 6 NiTi springs investigated differed in their design and in the type of force delivery. The force application that was eccentric with respect to the center of resistance caused a conflict situation between the tube and the guiding arch through rotations of the molar. Although the force level of the springs was almost constant, the orthodontically effective forces measured fluctuated due to frictional losses. With progressing distalization the mean frictional forces increased, reaching values between 50 and 80% of the applied force of the compression springs. Simultaneously fluctuations in the frictional losses increased. Lower frictional losses were determined with a 0.016" x 0.022", than with a 0.017" x 0.025" guiding arch. Fixing the arch on the 3rd molar resulted in higher frictional losses compared to the distalization of a last molar. There were intensive interactions of the compression springs with the guiding arch and the tube. This resulted in extreme frictional losses even in the initial phase of the movement and in a complete stop to the distalizing movement in extreme cases. After removal of the convertible, the freedom of the molar movement could be regulated by the tension of the ligature wire. The friction varied accordingly. The distalization rate was not influenced by the force delivered by the compression spring. Small forces are biologically more favorable and thus should be preferred.

Analysis of Variance↗
PubMed2001

Prediction of electrophoretic mobilities. 4. Multiply charged aromatic carboxylates in capillary zone electrophoresis.

The electrophoretic mobilites of aromatic carboxylates and sulfonates at zero ionic strength were correlated with models incorporating both hydrodynamic and dielectric friction. The hydrodynamic friction was predicted using either the Hückel spherical ion model or the Perrin ellipsoidal model. Dielectric friction is the charge-induced drag caused by the reorientation of the solvent dipoles in response to the analyte charge. Based on the Hubbard-Onsager and Zwanzig expressions, the dielectric friction is related to z2/V. Expressions incorporating both the hydrodynamic and dielectric frictional terms successfully predicted infinite-dilution mobilities to within 4.4%. The influence of dielectric friction ranged from 3-8% of the overall drag for singly charged analytes to 39% of the total frictional drag for 1,2,4,5-benzenetetracarboxylate.

Journal Article↗
PubMed2000

Numerical study of stress distribution in sheared granular material in two dimensions

We simulate the response of dense granular material to shear. Our simulations use a micromechanical model which includes realistic material models for each deformable grain, and a Coulomb friction model for interactions between grains. We measure the probability density function (PDF) governing the volume distribution of stress for monodisperse and polydisperse samples, circular and polygonal grains, and various values of microscopic friction coefficients, yield stresses, and packing fractions. Remarkably, PDF's are similar in form for all cases simulated, and similar to those observed in experiments with granular materials under both compression and shear. Namely, the simulations yield an exponential probability of large stresses above the mean. The relationship between distributions of boundary tractions and volume distributions of stress is discussed. The ratio of normal and tangential components of traction on the boundary defines a bulk frictional response, which is shown to increase with the intergranular friction coefficient. However, the bulk friction is always larger than the intergranular friction for densely packed samples. Bulk friction is also strongly dependent on grain size distribution and shape. New observations of force-chain banding during recrystallization, of slip systems in monodisperse samples, and of the effects of plastic yield, are also presented.

Journal Article↗
PubMed1982

Accurate repositioning of the human thumb against unpredictable dynamic loads is dependent upon peripheral feed-back.

1. The strategy of accurate movement of the human thumb has been studied in nine subjects. An open-loop hypothesis, which states that a new final position is defined by re-setting the agonist/antagonist spring constants, was tested2. Subjects were trained to flex the top joint of the thumb rapidly through 20 deg in about a third of a second from a fixed starting position against a load. Occasionally, and unpredictably, the viscous friction of the load was altered prior to it's being moved. The spring hypothesis predicts that such a change in load should have no effect on final position accuracy.3. Under normal conditions no final position error developed when the viscous friction was increased. A small overshoot occurred when the viscous friction was decreased.4. The electromyogram recorded from surface electrodes over the belly of flexor pollicis longus in the forearm revealed an increase in activity in response to an increase in viscous friction and a decrease in activity when the viscous friction was reduced.5. When the joint and cutaneous afferents from the thumb were anaesthetized, the e.m.g. response to a change in viscous friction was severely attenuated and consistent final position errors developed.6. Even though the compensatory open-loop muscle properties went some way towards maintaining accuracy, the change in final position error that occurred as a result of thumb anaesthesia correlated well (r = 0.84) with the amount of muscle e.m.g. response that was lost.7. The latency of the e.m.g. response to a change in viscous friction was compared to that of a voluntary response by asking the subject to push down or let go upon perception of the load change. Approximately the first 100 ms of the e.m.g. response was unaffected by the voluntary intervention of the subject.8. We conclude that the spring hypothesis does not explain human thumb movement. It is argued that the long-latency stretch reflex machinery is responsible for some automatic compensation for unexpected interference with movement.

Adult↗
PubMed2000

Investigation into the tribological condition of acetabular tissue after bipolar joint replacement hip surgery.

The aim of this research was to investigate the tribological condition of acetabular tissue before and after bipolar hip surgery. Articular cartilage was taken from the femoral head of patients undergoing primary joint replacement as a control. Tissue was also taken from the acetabular cups of patients undergoing revision hip surgery after primary bipolar surgery and compared with the control cartilage. The biomechanical characteristics of the two tissue types were tested using friction and compression tests. The friction tests were carried out on a sliding friction rig under nominal contact stresses of 0.5 and 4 MPa. The compression tests were carried out under a 0.8 MPa contact stress. The majority of the bipolar patients produced friction coefficients that were significantly higher than those produced by the control group, and the compression tests highlighted that the tissue from the bipolar patients produced a much greater rate of increase in displacement compared with the control cartilage. Histology showed major differences between the control cartilage and the bipolar tissue. The control cartilage showed a healthy collagen structure with a good distribution of proteoglycan whereas the majority of the bipolar tissue had lost tissue architecture and had a sparse fibrous structure. The high friction coefficients with the bipolar tissue imply that the frictional torque at the outer head of the bipolar prosthesis would be large compared with the inner bearing frictional torque. It was therefore predicted that the motion of the bipolar prosthesis should occur at the inner bearing.

Acetabulum↗
PubMed1983

Human blood oscillating axially in a tube.

Experiments were performed to study the rheological response of human blood at hematocrit ratios of 0 to 0.45 in axial oscillatory flow in a tube of uniform bore. Three principal regimes of flow were identified, depending on the amplitude of oscillation. At the highest amplitudes (and therefore the largest range of shear rates in the blood) there was turbulent motion and the friction coefficient increased in proportion to the square of the hematocrit. At small amplitudes the friction decreased with increase in amplitude, the rate of decrease increasing with hematocrit. At intermediate amplitudes the friction increased in proportion to the square of the hematocrit. Glutaraldehyde fixation of the red cells caused increase in the friction, and reduced the rate of decrease of friction with amplitude at small amplitudes. With a stenosis of very modest degree and span the friction in normal blood increased disproportionately, and a small blind hole in the lumen of the stenosis caused additional and disproportionate increase in friction.

Blood Physiological Phenomena↗
PubMed2000

The role of cough and hyperventilation in perpetuating airway inflammation in asthma.

Air flowing through a pipe exerts frictional stress on the walls of the pipe. Frictional stress of more than 40 N/m2 (velocity equivalent of air 113 m/s) is known to cause acute endothelial damage in blood vessels. The frictional stress in airways during coughing may be much greater, however, since the velocity of air may be as high as speed of sound in air. We suggest that high levels of frictional stress perpetuate airway inflammation in airways which are already inflamed and vulnerable to frictional stress-induced trauma in patients with asthma. Activities associated with rapid ventilation and higher frictional stress (e.g. exercise, hyperventilation, coughing, sneezing and laughing) cause asthma to worsen whilst activities that reduce frictional stress (Yoga 'Pranayama', breathing a helium-oxygen mixture and nasal continuous positive airway pressure) are beneficial. Therefore control of cough may have anti-inflammatory benefits in patients with asthma.

Asthma↗
PubMed2003

Tribological behavior of artificial hip joint under the effects of magnetic field in dry and lubricated sliding.

In recent years, there is an increasing utilization and demand to use magnetic fields in bioengineering applications due to its beneficial effects. Although in the last decade more attention has been given by tribologists to the electromagnetic processes taking place between sliding surfaces, which influence the tribological behaviors, but no attention has been concern with the sliding surfaces of the artificial implant joints. Therefore, the present work aims to elucidate the tribological behavior of an artificial joint implant under the effect of magnetic fields. Experimental investigation was carried out on a specially designed and constructed hip simulator on which the variations in the coefficients of friction and wear rates of the sliding surfaces were evaluated under the influence of a medium strength magnetic field suitable to apply in the human body. A realistic Ti-alloy implanted stem was used with an inserted head made from surgical grade stainless steel. This head was allowed to rub against UHMWPE sockets. The utilized type of prosthesis was "The JRI Modular Muller Standard-Total Hip Design". The performed experimental tests were conducted under both dry and lubricated sliding conditions using physiological saline solution. The designed simulator allows the coefficients of friction and the wear rates to be evaluated under realistic physiological loading and motion cycles encountered during normal walking of the human body. Comparative results are presented between the artificial joint performance in the presence and absence of the applied magnetic field. The experimental results have indicated that the presence of a medium strength magnetic field of 270 Gauss strength between rubbing surfaces resulted in high beneficial reductions in friction and wear rate of UHMWPE sliding on stainless steel either under dry or saline lubricating conditions. Therefore recommendation was forward to subject artificial implants made of stainless steel/UHMWPE combination of material to such medium strength magnetic field in animal clinical trials aiming to prolong the implant life. Scanning investigation of rubbing surfaces has revealed that the transfer of polymer to the counterface plays a dominant role in dictating the frictional and wear behaviors under dry sliding condition. Smooth molecular profile of the polymer-transferred leads to progressive reductions in friction and wear while the lumpy polymer transfer, formed at the beginning of sliding, increases both friction coefficient and wear. Two action mechanisms dominate the sliding process; adhesive and abrasive mechanisms. The presence of saline lubricant retards the formation of the beneficial polymer transfer thus leading to faster abrasion of the polymeric counterface which explains the relatively rapid and progressive increases in friction and wear.

Biocompatible Materials↗
PubMed1986

The principles of pressure drop in long segment stenosis.

With Doppler echocardiography, determination of pressure gradients at the region of valvular stenoses with the aid of the modified Bernoulli equation has been shown feasible in clinical and experimental studies. The Bernoulli equation neglects frictional losses and prerequisites laminar flow across the stenosis such that it would not appear applicable for long segment stenoses in the cardiovascular system. To evaluate pressure drop in a long segment stenosis, the full form of the energy balance equation, encompassing frictional losses and localized velocity profile, must be taken into consideration. Frictional losses occur in the region of flow contraction, the stenosis itself and at the expansion area. Assuming a reasonably square edge at the contraction and expansion, losses in these areas, and, employing the Fanning friction factor, losses in the stenosis can be calculated. Investigation of the theoretically-derived frictional loss equation in an in vitro model of a long segment stenosis with various stenosis lengths and diameters showed a good correlation between manometrically determined pressure gradients and those calculated according to the Bernoulli equation and the frictional loss equation. On use of the frictional loss equation, the pressure gradients, however, were only slightly underestimated while those rendered by the Bernoulli equation were clearly underestimated. In vitro data suggest that a long segment stenosis existed when the obstructive length was greater than twice the obstructive diameter for each 10,000 Reynolds numbers.

Blood Pressure↗
PubMed1985

Lubrication and surface chemical properties of ophthalmic solutions.

Surface chemical and lubrication parameters such as contact angle, surface tension, and coefficient of friction, together with viscosity, were measured for commercial ophthalmic solutions. A sensitive friction-testing instrument was employed to measure the coefficient of friction between low-energy polymeric surfaces, e.g., polymethylmethacrylate (PMMA). The viscosity of ten commercial tear substitutes employed in the present study ranged from 2 to 25 cp. The results showed that there is no correlation between the coefficient of friction and viscosity, surface tension, or contact angle of these tear substitutes. The coefficient of friction of tear substitutes appears to depend upon the structure, conformation, and adsorption characteristics of polymer as well as surface characteristics of sliding surfaces. A systematic study was undertaken to evaluate the effect of speed and load on the coefficient of friction between different sliding surfaces, namely PMMA/nylon and PMMA/PMMA. The analysis of data established that our system was operating in the region of "boundary lubrication." In general, a PMMA/PMMA system exhibited a lower coefficient of friction as compared with the PMMA/nylon system.

Lubrication↗
PubMed2002

Effect of particle-particle shearing on the bioleaching of sulfide minerals.

The biological leaching of sulfide minerals, used for the production of gold, copper, zinc, cobalt, and other metals, is very often carried out in slurry bioreactors, where the shearing between sulfide particles is intensive. In order to be able to improve the efficiency of the bioleaching, it is of significant importance to know the effect of particle shearing on the rate of leaching. The recently proposed concept of ore immobilization allowed us to study the effect of particle shearing on the rate of sulfide (pyrite) leaching by Thiobacillus ferrooxidans. Using this concept, we designed two very similar bioreactors, the main difference between which was the presence and absence of particle-particle shearing. It was shown that when the oxygen mass transfer was not the rate-limiting step, the rate of bioleaching in the frictionless bioreactor was 2.5 times higher than that in a bioreactor with particle friction (shearing). The concentration of free suspended cells in the frictionless bioreactor was by orders of magnitude lower than that in the frictional bioreactor, which showed that particle friction strongly reduces the microbial attachment to sulfide surface, which, in turn, reduces the rate of bioleaching. Surprisingly, it was found that formation of a layer of insoluble iron salts on the surface of sulfide particles is much slower under shearless conditions than in the presence of particle-particle shearing. This was explained by the effect of particle friction on liquid-solid mass transfer rate. The results of this study show that reduction of the particle friction during bioleaching of sulfide minerals can bring important advantages not only by increasing significantly the bioleaching rate, but also by increasing the rate of gas-liquid oxygen mass transfer, reducing the formation of iron precipitates and reducing the energy consumption. One of the efficient methods for reduction of particle friction is ore immobilization in a porous matrix.

Bioreactors↗
PubMed2007

Differential tissue-on-tissue lubrication by ophthalmic formulations.

Tissue-on-tissue friction testing was used to determine how instillation of hydrophilic polymer-containing formulations between the "blinking" tissues would compare with lubrication by saline, alone, or an oil-emulsion preparation. Best results were obtained for a formulation that contained active demulcents polyethylene glycol (PEG 400) and propylene glycol (PG), as well as a gellable polymer hydroxypropyl guar (HP-Guar) in a borate-buffered solution, in comparison with hydroxypropylcellulose-containing and carboxymethylcellulose-containing formulations. Superior performance of all the formulations was found for lubricating tissue-on-tissue couples, compared with metal-oxide-to-metal oxide interfaces, or metal oxide-to-tissue interfaces. A reciprocating pin-on-disc type friction/wear test device articulated the intimal faces of preserved human umbilical cord vein segments under increasing loads during simulated continuous "eye-blinking" with addition of increasing weights up to 60 g/cm2, simulating maximal eyelid force on the orbital globe. The tissue-on-tissue couples moved from liquid phase lubrication to boundary lubrication. After residual formulations were rinsed away with saline, persistence of low friction at the highest loads was indicative of formulation substantivity. Human umbilical cord vein segments were utilized in saline-wetted tissue-on-tissue couples that showed variable starting coefficients of friction in the range 0.2-0.4, producing moderate tearing and disruption of the interfacial layers above the medial collagen zone. The best-performing formulations instilled to the tissues pre-wetted with saline apparently reacted separately with each tissue face to produce a lower final and persistent coefficient of friction of about 0.05. Scanning electron microscopy and light microscopy of these guar-modified tissue specimens showed only a few superficial tissue disruptions, and some interphase swelling consistent with polymer uptake. The frictional values for lubricated couples having non-tissue members were considerably higher than the coefficients of friction measured for the similarly lubricated tissue-on-tissue couples, emphasizing the requirement that appropriate simulations are critical to obtaining clinically predictive data.

Cornea↗
PubMed2006

Optimization of surface modifications of extrasynovial tendon to improve its gliding ability in a canine model in vitro.

Previous studies have shown that the carboxyl groups in hyaluronic acid (HA) could be activated by 1-ethy 1-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) to form intermediate O-acylisoureas, which can chemically bind to exposed amino groups on the tendon surface, leading to improved gliding ability. However, the optimal ratio and concentrations of the components in this chemical mixture were not investigated. The purpose of this study was to optimize the constituents of this tissue engineering approach to tendon surface modification, to reduce friction and improve durability. Peroneus longus (PL) tendons (n=40) were harvested from adult mongrel dogs along with the A2 pulley obtained from the ipsilateral hind paw. After the gliding resistance of the normal PL tendon was measured, the tendons were treated under varying concentrations of HA (0.5, 1, and 2%) and EDC/NHS (0.05, 0.25, and 1%) mixed with a 10% gelatin. Tendon friction was measured for 1000 cycles of simulated flexion/extension motion. Following testing, the residual HA on the tendon surface was evaluated by immunohistochemisty. The gliding resistance of the untreated PL tendons had a mean value of 0.087+/-0.021 N. After surface treatment, there was no significant difference in friction due to HA concentration alone, but the concentration of EDC/NHS and the interaction between HA concentration and EDC/NHS concentration had a significant effect on friction. Regardless of HA concentration, the friction after 1000 cycles was significantly decreased in preparations which included a 1% concentration of EDC/NHS. The tendons with lower gliding resistance presented a smoother surface on light microscopy and maintained more residual HA on the tendon surface. By varying the relative concentrations of HA, EDC, and NHS it is possible to optimize the effect of surface treatment on friction and durability in a canine extrasynovial tendon in vitro.

Animals↗
PubMed2003

Finite element analysis to determine implant preload.

STATEMENT OF PROBLEM: The nature of the forces used to clamp implant components together, and how they are generated and sustained, is lacking in the literature. PURPOSE: This study examined the dynamic nature of developing the preload in an implant complex using finite element analysis. METHODS: The implant complex was modeled in accordance with the geometric designs for the Nobel Biocare implant systems. A thread helix design for the abutment screw and implant screw bore was modeled to create the geometric design for these units of the implant systems. Using the software programs HyperWorks and LS3D-Dyna, 2 3-dimensional finite element models of (1) a Branemark System 3.75 x 10-mm titanium Mark III implant, a CeraOne titanium abutment, a Unigrip gold alloy abutment screw, and (2) a Replace Select System 4.30 x 10-mm titanium implant, a Straight Esthetic titanium abutment, and a TorqTite titanium abutment screw were created. Modeling the threads to the machining specifications permitted simulation of screw tightening. The abutment screws were subjected to a tightening torque in increments of 1 Ncm from 0 to 64 Ncm using ABAQUS software. Using these models, the effect of the coefficient of friction on the development of preload amount in the implant complex during and after abutment screw tightening was determined. In the first experiment, the coefficient of friction was set to 0.20 between the titanium bearing surface of the abutments and the implant bearing surfaces, and 0.26 between the gold abutment screw and the titanium implant screw bore. In the second experiment, the coefficient of friction was varied; the titanium implant and titanium abutment bearing surfaces were set to a coefficient of friction of 0.20, whereas the Mark III gold and the Replace Select titanium abutment screws and their respective titanium screw bores in the implants were set to 0.12. The preload amount (N) was determined from the finite element analysis. RESULTS: The stress distribution pattern clearly demonstrated a transfer of preload force from the screw to the implant during tightening. A preload of 75% of the yield strength of the abutment screw was not established using the recommended tightening torques. CONCLUSION: Using finite element analysis, a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied in the presence of a coefficient of friction of 0.26 resulted in a lower than optimum preload for the abutment screws. To reach the desired preload of 75% of the yield strength, using a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied, the coefficient of friction between the implant components should be 0.12.

Dental Abutments↗
PubMed2001

Constituents and pH changes in protein rich hyaluronan solution affect the biotribological properties of artificial articular joints.

The relationship between the coefficient of friction and pH value or protein constituents of lubricating fluid, together with viscosity, were studied within a bearing surface model for artificial joint, ultra-high molecular weight polyethylene (UHMWPE) against stainless steel (SUS), using a mechanical spectrometer. Four lubricants were tested in this study: sodium hyaluronate (HA), HA with albumin, HA with gamma-globulin, and HA with (L)alpha-dipalmitoyl phosphatidylcholine ((L)alpha-DPPC). The coefficient of friction between UHMWPE and SUS in HA with albumin or HA with gamma-globulin varied from 0.035 to 0.070 depending on angular velocity and pH. The coefficient of friction in HA or HA with (L)alpha-DPPC varied from 0.023 to 0.045 depending on angular velocity and pH. The variation in pH for HA with albumin had a large effect on the coefficient of friction at low range of angular velocity with viscosity independence. The variation in pH for HA with gamma-globulin had a large effect on the coefficient of friction with viscosity dependence at high angular velocity. The addition of (L)alpha-DPPC showed a small effect on the coefficient of friction at low angular velocity. This study confirms that the presence of albumin in the lubricant promotes pH dependence and viscosity independence of the tribological properties at low speed while the presence of globulin promotes pH and viscosity independence at low speed and promotes pH and viscosity dependence at high speed in the lubrication of UHMWPE against SUS. This study supports the clinical hypothesis that the effect of constituents and pH changes in periprosthetic fluid for the lubrication is a clue toward resolving many complications after total joint replacement.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2002

Remodeling of the gliding surface after flexor tendon repair in a canine model in vivo.

Maintaining a smooth lubricated surface between the flexor tendon and sheath after tendon repair is very important for restoration of digit function. We studied the tendon surface after tendon repair mechanically in a canine model in vivo by measuring frictional force. One hundred and twenty flexor digitorum profundus (FDP) tendons were lacerated to 80% of their cross-section and repaired with either a modified Kessler (MK) or Becker (MGH) repair. The postoperative therapeutic regimen was either synergistic wrist and digit motion (SWM) or passive digit flexion and extension with the wrist fixed in 45 degrees of flexion (FIX). The dogs were sacrificed at one, three, or six weeks postoperatively. Thirty six FDP tendons from normal paws served as the control group, with each control tendon tested in two different conditions: intact and immediately after partial laceration and repair (0 time), making a total of five different timing points (intact, 0 time, one week, three weeks, and six weeks) for each repair type and each postoperative therapy. Frictional force between tendon and proximal pulley was evaluated after breaking any adhesions. Compared to intact tendons, friction was significantly increased immediately after tendon repair. The friction of the MK repair was significantly less than that of the MGH repair at all time and therapy groups, except at six weeks in the SWM group. For the MGH repair, at six weeks friction in the SWM group was significantly less than friction in the FIX group. This study showed that postoperative tendon gliding depends on the method of tendon repair and the postoperative therapy regimen. Furthermore, we have demonstrated that the gliding surface after tendon repair remodels with time.

Animals↗