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The human body involves a large number of systems subjected to contact stresses and thus experiencing wear and degradation. The limited efficacy of existing solutions constantly puts a significant financial burden on the healthcare system, more importantly, patients are suffering due to the complications following a partial or total system failure. More effective strategies are highly dependent on the availability of advanced functional materials demonstrating excellent tribological response and good biocompatibility. In this article, we review the recent progress in implementing two-dimensional (2D) materials into bio-applications involving tribological contacts. We further summarize the current challenges for future progress in the field., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The present study focuses on friction evaluation of the polyvinyl alcohol (PVA) hydrogel layer, an anticipative material for cartilage replacement. The experiments were carried out in a ball-in-socket configuration using a pendulum hip simulator. The friction coefficients of ceramic-on-hydrogel pairs were compared with those of commercial implants (metal/ceramic heads vs UHMWPE, HXPE and metal/ceramic sockets). The effects of hydrogel ageing and hydration were studied, among others. The use of PVA inserts caused up to 98% reduction in friction coefficient compared to original hip pairs. The application of PVA for local or even complete cartilage replacement seems to be an outstanding opportunity in implantology. • Friction investigation of hip implants with PVA hydrogel insert. • Testing of real conformal contact using pendulum hip joint simulator. • Comparison of friction with conventional hip replacement materials. • Friction-speed dependence of PVA hydrogel using rheometer. • Up to 80 times lower friction for hydrogel-inserted implants. [ABSTRACT FROM AUTHOR]

This work investigates the effects of kinematic conditions, configuration, viscoelasticity, and lubricant viscosity on friction in lubricated compliant contacts. Experimental data were also used to develop a numerical simulation capable of predicting fluid friction in compliant contacts. Mini Traction Machine (MTM) in the ball-on-disc configuration was used to successfully gain insight into the behaviour of compliant contacts, allowing the investigation of the mentioned effects. The findings have confirmed that viscoelastic effects are present in all configurations, being soft-on-hard (S/H), hard-on-soft (H/S) and soft-on-soft (S/S), where they seem to be more profound in the configurations using compliant discs. The experimental data also suggest that the slide-to-roll ratio affects rolling friction in all configurations which is contrary to current literature. [Display omitted] • Compliant contacts were investigated using MTM in a ball-on-disc configuration. • Kinematic conditions were studied using different values of the slide-to-roll ratio. • Ball-on-disc configurations were studied in soft-hard, hard-soft and soft-soft configurations. • The slide-to-roll ratio was found to affect rolling friction in compliant contacts. • Configurations affect the viscoelastic response and thus the whole Stribeck curve. [ABSTRACT FROM AUTHOR]

Hyaluronan (HA) is widely used for eye drops as lubricant to counteract dry eye disease. High and low molecular weight HA are currently used in ophthalmology. However, a large portion of the current literature on friction and lubrication addresses articular (joint) cartilage. Therefore, eye drops compositions based on HA and its derivatized forms are extensively characterized providing data on the tribological and mucoadhesive properties. The physiochemical properties are investigated in buffers used commonly in eye drops formulations. The tribological investigation reveals that amphiphilic HA-C12 decreases the friction coefficient. At the same time, the combination of trehalose/HA or HAC12 enhances up to eighty-fold the mucoadhesiveness. Thus, it is predicted a prolonged residence time on the surface of the eye. The incorporation of trehalose enhances the protection of human keratinocytes (HaCaT) cells, as demonstrated in an in-vitro cell-desiccation model. The presence of trehalose increases the friction coefficient. Medium molecular weight HA shows significantly lower friction coefficient than high molecular weight HA. This research represents a first, wide array of features of diverse HA forms for eye drops contributing to increase the knowledge of these preparations. The results here presented also provide valuable information for the design of highly performing HA-formulations addressing specific needs before preclinic. [ABSTRACT FROM AUTHOR]

Hyaluronic acid (HA) injections represent one of the most common methods for the treatment of osteoarthritis. However, the clinical results of this method are unambiguous mainly because the mechanism of action has not been clearly clarified yet. Viscosupplementation consists, inter alia, of the improvement of synovial fluid rheological properties by injected solution. The present paper deals with the effect of HA molecular weight on the rheological properties of its solutions and also on friction in the articular cartilage model. Viscosity and viscoelastic properties of HA solutions were analyzed with a rotational rheometer in a cone–plate and plate–plate configuration. In total, four HA solutions with molecular weights between 77 kDa and 2010 kDa were tested. The frictional measurements were realized on a commercial tribometer Bruker UMT TriboLab, while the coefficient of friction (CoF) dependency on time was measured. The contact couple consisted of the articular cartilage pin and the plate made from optical glass. The contact was fully flooded with tested HA solutions. Results showed a strong dependency between HA molecular weight and its rheological properties. However, no clear dependence between HA molecular weight and CoF was revealed from the frictional measurements. This study presents new insight into the dependence between rheological and frictional behavior of the articular cartilage, while such an extensive investigation has not been presented before. [ABSTRACT FROM AUTHOR]

A healthy natural synovial joint is very important for painless active movement of the natural musculoskeletal system. The right functioning of natural synovial joints ensures well lubricated contact surfaces with a very low friction coefficient and wear of cartilage tissue. The present paper deals with a new method for visualization of lubricating film with simultaneous measurements of the friction coefficient. This can contribute to better understanding of lubricating film formation in a natural synovial joint. A newly developed device, a reciprocating tribometer, is used to allow for simultaneous measurement of friction forces with contact visualization by fluorescence microscopy. The software allowing for snaps processing and subsequent evaluation of fluorescence records is developed. The evaluation software and the follow-up evaluation procedure are also described. The experiments with cartilage samples and model synovial fluid are carried out, and the new software is applied to provide their evaluation. The primary results explaining a connection between lubrication and friction are presented. The results show a more significant impact of albumin proteins on the lubrication process, whereas its clusters create a more stable lubrication layer. A decreasing trend of protein cluster count, which corresponds to a decrease in the thickness of the lubrication film, is found in all experiments. The results highlight a deeper connection between the cartilage friction and the lubrication film formation, which allows for better understanding of the cartilage lubrication mechanism. [ABSTRACT FROM AUTHOR]

The paper introduces an experimental investigation of frictional behaviour of materials used for joint replacements. The measurements were performed using a ball-on-disc tribometer, while four material combinations were tested; metal-on-metal, ceramic-on-ceramic, metal-on-polyethylene, and ceramic-on-polyethylene, respectively. The contact was lubricated by pure saline and various protein solutions. The experiments were realized at two mean speeds equal to 5.7 mm/s and 22 mm/s and two slide-to-roll ratios, −150% and 150%. It was found that the implant material is the fundamental parameter affecting friction. In general, the metal pair exhibited approximately two times higher friction compared to the ceramic. In particular, the friction in the case of the metal varied between 0.3 and 0.6 while the ceramic pair exhibited friction within the range from 0.15 to 0.3 at the end of the test. The lowest friction was observed for polyethylene while it decreased to 0.05 under some conditions. It can be also concluded that adding proteins to the lubricant has a positive impact on friction in the case of hard-on-hard pairs. For hard-on-soft pairs, no substantial influence of proteins was observed. The effect of kinematic conditions was found to be negligible in most cases. [ABSTRACT FROM AUTHOR]

The present paper explores the effect of viscosupplementation on the friction of articular cartilage depending on the rheology of viscosupplements. The experiments were realized on rotational rheometers and a tribometer in pin-on-plate configuration. Five commercially available viscosupplements and their mixtures with synovial fluid were tested. The results showed differences by the order of magnitudes between viscosupplements viscosity and no viscoelastic properties in some of them. The friction was substantially affected by the addition of viscosupplement into the model synovial fluid. In most cases, mixtures of synovial fluid and viscosupplement even showed similar friction as clear viscosupplements. This study is the basis for a better understanding of the short-term changes in articular cartilage frictional behavior after the viscosupplementation of synovial joint. • Rheological analysis of HA-based viscosupplements and their mixtures with synovial fluid. • Frictional behaviour of HA solutions within the model of synovial joint. • Substantial differences in the rheological properties of individual viscosupplements. • No clear dependency between HA viscosity and friction within the contact. • Lubrication regime influenced by HA molecular weight. [ABSTRACT FROM AUTHOR]