Comparative Study on the Lubrication Mechanism and Performance of Two Representative Ionic and Nonionic Self-Adhesive Polymer Coatings.

Surface modification of lubricating coatings on biomedical devices is a pivotal strategy to improve the overall performance and clinical efficacy, significantly reducing friction between devices and human tissues and mitigating tissue damage during intervention and long-term implantation. Recently, various hydrophilic polymeric materials have been used for achieving surface functionalization, endowing the biomedical device with excellent superlubrication performance. N-Vinylpyrrolidone (NVP) and 2-methacryloyloxyethyl phosphorylcholine (MPC) are two typical representatives of nonionic and zwitterionic materials. However, there is still a research gap in a comparative study of the lubrication mechanisms and properties between them. In this study, a bioinspired and dopamine-assisted codeposition technique was used to fabricate biomimetic hydrophilic coatings, including P(DMA-NVP) and P(DMA-MPC), on polyurethane. To achieve a thorough comparative analysis of the self-adhesive coating performance, 3 M ratios of the copolymers were synthesized and comprehensive material evaluations were conducted. Additionally, surface morphology, hydrophilicity, and lubrication at both the microscale and macroscale were performed. It was found that both hydrophilic coatings exhibited good stability. The P(DMA-MPC) coating, due to the ability to attract and bind a large number of water molecules, demonstrated superior lubrication effects compared to the P(DMA-NVP) coating. The study provides an in-depth understanding of the lubrication behavior of the self-adhesive coatings to enhance the functionality and application in biomedical engineering.

Understanding mechanisms behind the oily mouthcoating perception of pure vegetable oils using tribology.

Tribology is the science of measuring friction between surfaces. While it has been widely used to investigate texture sensations of food applications, it is seldom applied in pure edible oil systems. In this research, we measured friction, viscosity, and solid fat content (SFC) of nine vegetable oils at 30 and 60°C. Polarized static microscopy was used to assess crystal formation between 60 and 30°C. Descriptive sensory analysis and quantification of oral oil coatings were performed on the oils at 60°C. Expressing the friction factor of oil over the Hersey number (calculated using high sheer-viscosity values) showed no differences in friction between 30 and 60°C, except for shea stearin. Static microscopy revealed crystallization occurred at 30°C for shea stearin, whereas no or few crystals were present for other oils. At 30°C, friction at 1 × 10-2 m/s showed an inverse correlation with SFC (R = -0.95) and with high shear rate viscosity (R = -0.84), as well as an inverse correlation (R = -0.73) with "oily mouthcoating" perception. These results suggest that friction could be a predictor of fat-related perceptions of simple oil systems. Additionally, we hypothesize that the presence of crystals in oils could lower friction via a ball-bearing lubrication mechanism.

Alterations in articular cartilage frictional properties in the setting of acute gouty arthritis.

The tribological behaviour of articular cartilage plays a key role in joint motion; however, there is a gap in research on the effect of hyperuricemic joint fluid on cartilage friction behaviour in acute gouty arthritis. In this study, we carried out a fixed-load scratch experiment to compare the friction and wear of articular cartilage under the lubrication of gouty arthritis arthritic fluid and normal human arthritic fluid, and the results showed that the cartilage friction coefficient of patients with acute gouty arthritis was significantly larger than that of normal human beings, and that the cartilage friction coefficient decreased with the elevation of normal load and sliding speed, and the change with the sliding speed varied more differently from that of normal human beings, and that the cartilage surface wear was more severe after prolonged friction. The wear and tear of the cartilage surface is more severe after prolonged friction. Patients with gouty arthritis should reduce the sudden speed changes such as fast running and variable speed running to maintain the stability of the cartilage surface friction coefficient.

Enzymatic digestion does not compromise sliding-mediated cartilage lubrication.

Articular cartilage's remarkable low-friction properties are essential to joint function. In osteoarthritis (OA), cartilage degeneration (e.g., proteoglycan loss and collagen damage) decreases tissue modulus and increases permeability. Although these changes impair lubrication in fully depressurized and slowly slid cartilage, new evidence suggests such relationships may not hold under biofidelic sliding conditions more representative of those encountered in vivo. Our recent studies using the convergent stationary contact area (cSCA) configuration demonstrate that articulation (i.e., sliding) generates interfacial hydrodynamic pressures capable of replenishing cartilage interstitial fluid/pressure lost to compressive loading through a mechanism termed tribological rehydration. This fluid recovery sustains in vivo-like kinetic friction coefficients (µk<0.02 in PBS and <0.005 in synovial fluid) with little sensitivity to mechanical properties in healthy tissue. However, the tribomechanical function of compromised cartilage under biofidelic sliding conditions remains unknown. Here, we investigated the effects of OA-like changes in cartilage mechanical properties, modeled via enzymatic digestion of mature bovine cartilage, on its tribomechanical function during cSCA sliding. We found no differences in sliding-driven tribological rehydration behaviors or µk between naïve and digested cSCA cartilage (in PBS or synovial fluid). This suggests that OA-like cartilage retains sufficient functional properties to support naïve-like fluid recovery and lubrication under biofidelic sliding conditions. However, OA-like cartilage accumulated greater total tissue strains due to elevated strain accrual during initial load application. Together, these results suggest that elevated total tissue strains-as opposed to activity-mediated strains or friction-driven wear-might be the key biomechanical mediator of OA pathology in cartilage. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) decreases cartilage's modulus and increases its permeability. While these changes compromise frictional performance in benchtop testing under low fluid load support (FLS) conditions, whether such observations hold under sliding conditions that better represent the joints' dynamic FLS conditions in vivo is unclear. Here, we leveraged biofidelic benchtop sliding experiments-that is, those mimicking joints' native sliding environment-to examine how OA-like changes in mechanical properties effect cartilage's natural lubrication. We found no differences in sliding-mediated fluid recovery or kinetic friction behaviors between naïve and OA-like cartilage. However, OA-like cartilage experienced greater strain accumulation during load application, suggesting that elevated tissue strains (not friction-driven wear) may be the primary biomechanical mediator of OA pathology.

Formation of small-granule starch oleogels based on capillary force: Impact of starch surface lipids on lubrication performance.

Starch granule oleogels were prepared and their rheological properties were precisely tuned using the capillary bridging phenomenon. The addition of a small amount of water to an oily suspension of starch granules can lead to starch granule bridging and network formation, transitioning it from a fluid-like to a gel-like state. Small-granule starches with high specific surface area and interfacial area exhibited a greater number of liquid bridges and stronger starch granules interactions, making them more prone to forming structurally stable oleogel systems. By increasing the content of water and starch granule, the starch oleogels exhibited three distinct structural states: pendular state (water ≤ 3.28 %, starch ≤ 17.85 %), pendular bridging network (water: 4.92 %, starch: 24.59 %), and capillary aggregates (water ≥ 6.56 %, starch > 24.59 %). Furthermore, the influence of starch granule surface lipids on the lubrication performance of the oleogel system was investigated. Surface roughness increased after extraction of surface lipids, and the friction coefficient also showed a significant increase. Overall, capillary suspension system can potentially be used to design novel fat food products, and our findings have established the correlation between starch granule surface properties and sensory perception in food, providing valuable insights for adjusting the oral processing characteristics of food.

Biomimetic zwitterionic copolymerized chitosan as an articular lubricant.

Restoration of the lubrication functions of articular cartilage is an effective treatment to alleviate the progression of osteoarthritis (OA). Herein, we fabricated chitosan-block-poly(sulfobetaine methacrylate) (CS-b-pSBMA) copolymer via a free radical polymerization of sulfobetaine methacrylate onto activated chitosan segment, structurally mimicking the lubricating biomolecules on cartilage. The successful copolymerization of CS-b-pSBMA was verified by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and 1H nuclear magnetic resonance. Friction test confirmed that the CS-b-pSBMA copolymer could achieve an excellent lubrication effect on artificial joint materials such as Ti6Al4V alloy with a coefficient of friction as low as 0.008, and on OA-simulated cartilage, better than the conventional lubricant hyaluronic acid, and the adsorption effect of lubricant on cartilage surface was proved by a fluorescence labeling experiment. In addition, CS-b-pSBMA lubricant possessed an outstanding stability, which can withstand enzymatic degradation and even a long-term storage up to 4 weeks. In vitro studies showed that CS-b-pSBMA lubricant had a favorable antibacterial activity and good biocompatibility. In vivo studies confirmed that the CS-b-pSBMA lubricant was stable and could alleviate the degradation process of cartilage in OA mice. This biomimetic lubricant is a promising articular joint lubricant for the treatment of OA and cartilage restoration.

In vitro drug release and cartilage interface lubrication properties of biomimetic polymers.

Osteoarthritis is a degenerative disease that is widely found in the elderly population, with a trend towards a younger age group in recent years. In the early stages of arthritis, patients are treated with hyaluronic acid injections and anti-inflammatory drugs. However, it has been found that hyaluronic acid can only play a supportive role and does not have a lubricating effect, and due to the absence of blood vessels, nerves, and lymphatic vessels in the articular cartilage, the oral anti-inflammatory drugs cannot reach the interface of the inflammatory joints adequately, and the drug utilisation rate is low. Herein, we designed and prepared a brush-like bionic lubricant for joint lubrication and drug loading. The poly(2-methyl-2-oxazoline) branched chain was grafted onto the hyaluronic acid main chain by ring-opening polymerisation and graft polymerisation to form a brush-like bionic lubricin containing multiple hydrophilic groups, which was self-assembled to encapsulate the drug by using its multi-branched special structure for drug loading. The friction behaviour tests on the articular cartilage surface showed that the prepared bionic lubricin has excellent lubrication effect, with a minimum friction coefficient of 0.036 close to the lubrication effect of natural synovial fluid, which is mainly due to the hydrophilic groups on its molecular chain that can adsorb the water molecules and form a hydration layer at the cartilage interface, which plays the role of hydration lubrication. In addition, in vitro drug release studies showed that the synthesised drug-loading biomimetic lubricin had a certain drug release capacity, and the maximum drug release rate could reach 77.8 % at 72 h. The synthesis of this bionic lubricant with dual functions of lubrication and drug release provides a new idea for the treatment of osteoarthritis.

Exogenous Collagen Crosslinking is Highly Detrimental to Articular Cartilage Lubrication.

Healthy articular cartilage is a remarkable bearing material optimized for near-frictionless joint articulation. Because its limited self-repair capacity renders it susceptible to osteoarthritis (OA), approaches to reinforce or rebuild degenerative cartilage are of significant interest. While exogenous collagen crosslinking (CXL) treatments improve cartilage's mechanical properties and increase its resistance to enzymatic degradation, their effects on cartilage lubrication remain less clear. Here, we examined how the collagen crosslinking agents genipin (GP) and glutaraldehyde (GTA) impact cartilage lubrication using the convergent stationary contact area (cSCA) configuration. Unlike classical configurations, the cSCA sustains biofidelic kinetic friction coefficients (µk) via superposition of interstitial and hydrodynamic pressurization (i.e., tribological rehydration). As expected, glutaraldehyde- and genipin-mediated CXL increased cartilage's tensile and compressive moduli. Although net tribological rehydration was retained after CXL, GP or GTA treatment drastically elevated µk. Both healthy and "OA-like" cartilage (generated via enzymatic digestion) sustained remarkably low µk in saline- (≤0.02) and synovial fluid-lubricated contacts (≤0.006). After CXL, µk increased up to 30-fold, reaching values associated with marked chondrocyte death in vitro. These results demonstrate that mechanical properties (i.e., stiffness) are necessary, but not sufficient, metrics of cartilage function. Furthermore, the marked impairment in lubrication suggests that CXL-mediated stiffening is ill-suited to cartilage preservation or joint resurfacing.

High-density zwitterionic polymer brushes exhibit robust lubrication properties and high antithrombotic efficacy in blood-contacting medical devices.

High-performance catheters are essential for interventional surgeries, requiring reliable anti-adhesive and lubricated surfaces. This article develops a strategy for constructing high-density sulfobetaine zwitterionic polymer brushes on the surface of catheters, utilizing dopamine and sodium alginate as the primary intermediate layers, where dopamine provides mussel-protein-like adhesion to anchor the polymer brushes to the catheter surface. Hydroxyl-rich sodium alginate increases the number of grafting sites and improves the grafting mass by more than 4 times. The developed high-density zwitterionic polymer brushes achieve long-lasting and effective lubricity (µ<0.0078) and are implanted in rabbits for four hours without bio-adhesion and thrombosis in the absence of anticoagulants such as heparin. Experiments and molecular dynamics simulations demonstrate that graft mass plays a decisive role in the lubricity and anti-adhesion of polymer brushes, and it is proposed to predict the anti-adhesion of polymer brushes by their lubricity to avoid costly and time-consuming bioassays during the development of amphoteric polymer brushes. A quantitative influence of hydration in the anti-adhesion properties of amphiphilic polymer brushes is also revealed. Thus, this study provides a new approach to safe, long-lasting lubrication and anticoagulant surface modification for medical devices in contact with blood. STATEMENT OF SIGNIFICANCE: High friction and bioadhesion on medical device surfaces can pose a significant risk to patients. In response, we have developed a safer, simpler, and more application-specific surface modification strategy that addresses both the lubrication and anti-bioadhesion needs of medical device surfaces. We used dopamine and sodium alginate as intermediate layers to drastically increase the grafting density of the zwitterionic brushes and enabled the modified surfaces to have an extremely low coefficient of friction (µ = 0.0078) and to remain non-bioadhesive for 4 hours in vivo. Furthermore, we used molecular dynamics simulations to gain insight into the mechanisms behind the superior anti-adhesion properties of the high-density polymer brushes. Our work contributes to the development and application of surface-modified coatings.

On the interdependence of insertion forces, insertion speed, and lubrication: Aspects to consider when testing cochlear implant electrodes.

OBJECTIVES: During the insertion of cochlear implant (CI) electrode arrays, forces occur which may cause trauma and poorer hearing outcomes. Unfortunately, research groups investigating factors influencing insertion forces come to contradicting results, especially regarding insertion speed. This study was conducted to investigate the origin of these contradicting results and to determine how different testing conditions influence experimental findings. METHODS: Repeated, automated insertions with three different FLEX28 CI electrode arrays (MED-EL, Innsbruck, Austria) were performed into a newly developed, anatomically correct and 3D-printed mean scala tympani phantom. The testing protocol for each electrode included variations in insertion speed (v = 0.1-2.0 mm/s) and lubrication (90%, 50%, and 10% liquid soap), resulting in 51 insertions per electrode array and a total of 153 insertions. RESULTS: The test setup and protocol allowed for repeatable insertions with only minimal change in the morphology of the insertion force profiles per testing condition. Strong but varying dependencies of the maximal insertion forces and work were found regarding both lubrication and speed: work-speed dependency is constant for the 10% lubricant, negative for the 50% lubricant and positive for the 90% lubricant. CONCLUSION: Our results can explain part of the contradicting results found within previous studies by translating interrelations known from lubricated rubber friction to the field of CI electrode array insertion. We show that the main driver behind measured bulk forces are most likely the generated friction forces, which are strongly dependent on insertion speed and lubrication. The employed test setup allows for conducting repeatable and comparable insertion studies, which can be recapitulated by other centers due to the detailed explanation of the test setup as well as the developed and freely available insertion phantom. This study hence represents another important step toward standardizing CI array insertion testing.

Elbow dimensions in quadrupedal mammals driven by lubrication regime.

Synovial joints, such as the elbow, experience different lubrication regimes, ranging from fluid film to boundary lubrication, depending on locomotion conditions. We explore the relationship between the elbow lubrication regime and the size of quadrupedal mammals. We use allometry to analyze the dimensions, contact stress, and sliding speed of the elbow in 110 quadrupedal mammals. Our results reveal that the average diameter and width of the distal humerus are scaled [Formula: see text], which allowed us to estimate a consistent contact pressure and sliding speed across mammals. This consistency likely promotes fluid film lubrication regardless of body mass. Further, the ratio between the diameter and width is about 0.5 for all analyzed taxa, which is a good compromise between loading capacity and size. Our study deepens our understanding of synovial joints and their adaptations, with implications for the development of treatments, prostheses, and bioinspired joint designs.

Calcium ions have a detrimental impact on the boundary lubrication property of hyaluronic acid and lubricin (PRG-4) both alone and in combination.

Cartilage demineralisation in Osteoarthritis (OA) patients can elevate calcium ion levels in synovial fluid, as evidenced by the prevalence of precipitated calcium phosphate crystals in OA synovial fluid. Although it has been reported that there is a potential connection between elevated concentrations of calcium ions and a deterioration in the lubrication and wear resistance of cartilage tissues, the mechanism behind the strong link between calcium ion concentration and decreased lubrication performance is unclear. In this work, the AFM friction, imaging, and normal force distance measurements were used to investigate the lubrication performances of hyaluronic acid (HA), Lubricin (LUB), and HA-LUB complex in the presence of calcium ions (5 mM, 15 mM, and 30 mM), to understand the possible mechanism behind the change of lubrication property. The results of AFM friction measurements suggest that introducing calcium ions to the environment effectively eliminated the lubrication ability of HA and HA-LUB, especially with relatively low loading applied. The AFM images indicate that it is unlikely that structural or morphological changes in the surface-bound layer upon calcium ions addition are primarily responsible for the friction results demonstrated. Further, the poor correlation between the effect of calcium ions on the adhesion forces and its impact on friction suggests that the decrease in the lubricating ability of both layers is likely a result of changes in the hydration of the HA-LUB surface bound layers than changes in intermolecular or intramolecular binding. This work provides the first experimental evidence lending towards the relationship between bone demineralisation and articular cartilage degradation at the onset of OA and the mechanism through which elevated calcium levels in the synovial fluid act on joint lubrication.

Insight into the hydration friction of lipid bilayers.

Hydration layers formed on charged sites play crucial roles in many hydration lubrication systems in aqueous media. However, the underlying molecular mechanism is not well understood. Herein, we explored the hydration friction of lipid bilayers with different charged headgroups at the nanoscale through a combination of frequency-modulation atomic force microscopy and friction force microscopy. The nanoscale friction experiments showed that the hydration friction coefficient and frictional energy dissipation of a cationic lipid (DPTAP) were much lower than those of zwitterionic (DPPE) and anionic (DPPG) lipids. The hydration layer probing at the surfaces of different lipid bilayers clearly revealed the relationship between the charged lipid headgroups and hydration layer structures. Our detailed analysis demonstrated that the cationic lipid had the largest hydration force in comparison with zwitterionic and anionic lipids. These friction and hydration force results indicated that the difference of the lipid headgroup charge resulted in different hydration strengths which led to the difference of hydration friction behaviors. The findings in this study provide molecular insights into the hydration friction of lipid bilayers, which has potential implications for the development of efficient hydration lubrication systems with boundary lipid bilayers in aqueous media.

Modulating mechanobiology as a therapeutic target for synovial fibrosis to restore joint lubrication.

OBJECTIVES: Fibroses are disorders linked to persistence of myofibroblasts due to biochemical (e.g., Transforming growth factor-ß) and biophysical cues (e.g., a stiff microenvironment). In the context of osteoarthritis, fibrotic changes in the joint-lining synovium have been linked with disease progression. The objective of this study was to probe synovial fibroblast mechanobiology and how essential functions (i.e., lubrication) are altered in fibrotic environments. DESIGN: Both ex vivo and in vitro synovium models were assessed for fibrotic and lubrication biomarkers to better understand the role of mechanobiology and lubrication. Additionally, in vitro, work on small molecules targeting mechanobiology was assessed. RESULTS: Our results indicated that modulating mechanobiology could rescue the fibrotic phenotype instigated by stiffening microenvironment that resulted in altered lubricant expression. A small molecule therapeutic, fasudil, blocked ROCK-mediated contractility and this inhibition of the fibrotic mechano-response of synovial fibroblasts restored proper lubrication function, providing insight into mechanisms of disease progression as well as a new avenue for therapeutic development. CONCLUSION: This study identifies synovial fibrosis as a condition that potentially has joint-wide deficits through inhibiting lubrication. Additionally, modulating mechanobiology (i.e., ROCK-mediated contractility) may pose a potential target for small molecule therapies that can be delivered to the joint space. CLASSIFICATION: Applied Biological Sciences.

Worsened punch sticking by external lubrication with magnesium stearate.

External lubrication of tooling with magnesium stearate (MgSt) is a common strategy to eliminate punch sticking when compressing powders with a high sticking propensity, such as many pure active pharmaceutical ingredients (APIs). We found that it actually led to aggravated punch sticking at low compaction pressures. This counterintuitive phenomenon was explained based on interplay of forces among the punch tip, MgSt, and API. The explanation is supported by the observed effects of pressure and mechanical properties of APIs on this phenomenon.

The role of membrane components on the oleosome lubrication properties.

HYPOTHESIS: Oleosomes are natural oil droplets with a unique phospholipid/protein membrane, abundant in plant seeds, from which they can be extracted and used in emulsion-based materials, such as foods, cosmetics and pharmaceutics. The lubrication properties of such materials are essential, on one hand, due to the importance of the in-mouth creaminess for the consumed products or the importance of spreading the topical creams. Therefore, here, we will evaluate the lubrication properties of oleosomes, and how these properties are affected by the components at the oleosome membrane. EXPERIMENT: Oleosomes were extracted, and their oral lubricating properties were evaluated using tribology. To understand the influence of the oil droplet membrane composition, reconstituted oleosomes were also studied, with membranes that differed in protein/lecithin ratio. Additionally, whey protein- and lecithin-stabilised emulsions were used as reference samples. Confocal laser scattering microscopy was used to study the samples visually before and after tribological analysis. FINDINGS: Oleosomes followed a ball-bearing mechanism, which was probably related to their high physical stability due to the presence of membrane proteins. When the membrane protein concentration at the surface was reduced, the droplet stability weakened, leading to plating-out lubrication. Following our results, we elucidated the oleosome lubrication mechanism and showed their possible control by changing the membrane composition.

Successful Formulation Window for the design of pharmaceutical tablets with required mechanical properties.

Pharmaceutical tablet formulations combine the active ingredient with processing aids and functional components. This paper evaluates compressibility based predictive models for binary and ternary formulations to establish an acceptable range of tablet compression parameters that satisfy prescribed quality target criteria for tablets including minimum tablet strength and processing constraints such as maximum ejection stress and maximum compaction pressure. The concept of Successful Formulation Window (SFW) is introduced. A methodology is proposed to determine the SFW for a given formulation based on compaction simulator data collected for individual formulation components. The methodology is validated for binary and ternary mixtures and lubricated formulations. The SFW analysis was developed to support tablet formulation design to meet mechanical requirements.

Effects of tableting process parameters and powder lubrication levels on tablet surface temperature and moisture content.

Punch sticking is a recurrent problem during the pharmaceutical tableting process. Powder moisture content plays a key role in the buildup of sticking; it evaporates due to increased tablet temperature, accumulates at the punch-tablet interface, and causes sticking through capillary force. This study investigated the effects of compaction pressure (CP), compaction speed (CS), and lubrication level (magnesium stearate (MgSt) ratio) on tablet surface temperature (TST) and tablet surface moisture content (TSMC). TST and TSMC were measured with an infrared thermal camera and near-infrared sensor, respectively. Microcrystalline cellulose was used as the tableting powder and MgSt as the lubricant. The low range of CS values (16-32 mm/s) considered in this study did not have significant effects on TST and TSMC. MgSt ratio had a significant positive effect on TST; this may be explained by the increase in powder blend effusivity with the addition of MgSt. However, MgSt ratio did not have a significant effect on TSMC. CP had a significant positive effect on both TST and TSMC. Increased CP induced higher heat generation through particle deformation and friction during the compaction phase, leading to increased TST. Furthermore, the water vapor diffusion rate through the powder bed might have increased due to the rise in thermal energy and led to further moisture accumulation at the tablet-punch interface, causing the significant positive effect of CP on TSMC. This result may explain the occurrence of sticking regardless of the CP applied during the tableting process.

A polymer network architecture provides superior cushioning and lubrication of soft tissue compared to a linear architecture.

We report the relationships between linear vs. network polymer architecture and biomechanical outcomes including lubrication and cushioning when the polymers are applied to the surface of articulating knee cartilage. Aqueous formulations of the bioinspired polymer poly(2-methacryloyloxylethyl phosphorylcholine) (pMPC) exhibit tuneable rheological properties, with network pMPC exhibiting increased elasticity and viscosity compared to linear pMPC. Application of a polymer network, compared to a linear one, to articulating tissue surfaces reduces friction, lessens tissue strain, minimizes wear, and protects tissue - thereby improving overall tissue performance. Administration of the network pMPC to the middle carpal joint of skeletally mature horses elicits a safe response similar to saline as monitored over a 70 day period.

Investigation on hydrodynamic lubrication effect of micro groove seal in pharmaceutical kettle.

To improve the lubrication conditions of the seal in the pharmaceutical kettles, a specific shape groove with micrometer level on the sealing end face is set up to fully utilize the fluid dynamic pressure effect under given working conditions. A numerical model is developed to solve the pressure distribution in the micro groove, where any groove shape can be used. The numerical form of the model is derived using the principle of mass conservation without considering the film thickness derivative term, and the coordinate transformation is introduced to adapt to the curved shape of the groove. The cavitation phenomenon is taken into account in the flow field of the seal, and the JFO cavitation model is introduced to modify the Reynolds equation. The diversity of groove shapes is considered, and the node adsorption method is adopted to approximate the groove shape. The model is established based on the principle of mass conservation, which can adapt to any different groove shapes and has a strong scalability. By mathematical modeling and solving, the performances of the micro groove seal under different groove shapes are analyzed, providing a basis for the micro groove design of seal in pharmaceutical kettles.