Lubrication by biomacromolecules: mechanisms and biomimetic strategies

Advances in viscosupplementation and tribosupplementation for early-stage osteoarthritis therapy

Joint kinematic instability, arising from congenital or acquired musculoskeletal pathoanatomy or from imbalances in anabolism and catabolism induced by pathophysiological factors, leads to deterioration of the composition, structure and function of cartilage and, ultimately, progression to osteoarthritis (OA). Alongside articular cartilage degeneration, synovial fluid lubricity decreases in OA owing to a reduction in the concentration and molecular weight of hyaluronic acid and surface-active mucinous glycoproteins that form a lubricating film over the articulating joint surfaces. Minimizing friction between articulating joint surfaces by lubrication is fundamental for decreasing hyaline cartilage wear and for maintaining the function of synovial joints. Augmentation with highly viscous supplements (that is, viscosupplementation) offers one approach to re-establishing the rheological and tribological properties of synovial fluid in OA. However, this approach has varied clinical outcomes owing to limited intra-articular residence time and ineffective mechanisms of chondroprotection. This Review discusses normal hyaline cartilage function and lubrication and examines the advantages and disadvantages of various strategies for restoring normal joint lubrication. These strategies include contemporary viscosupplements that contain antioxidants, anti-inflammatory drugs or platelet-rich plasma and new synthetic synovial fluid additives and cartilage matrix enhancers. Advanced biomimetic tribosupplements offer promise for mitigating cartilage wear, restoring joint function and, ultimately, improving patient care.

O-glycans Expand Lubricin and Attenuate Its Viscosity and Shear Thinning

Lubricin, an intrinsically disordered glycoprotein, plays a pivotal role in facilitating smooth movement and ensuring the enduring functionality of synovial joints. The central domain of this protein serves as a source of this excellent lubrication and is characterized by its highly glycosylated, negatively charged, and disordered structure. However, the influence of O-glycans on the viscosity of lubricin remains unclear. In this study, we employ molecular dynamics simulations in the absence and presence of shear, along with continuum simulations, to elucidate the intricate interplay between O-glycans and lubricin and the impact of O-glycans on lubricin's conformational properties and viscosity. We found the presence of O-glycans to induce a more extended conformation in fragments of the disordered region of lubricin. These O-glycans contribute to a reduction in solution viscosity but at the same time weaken shear thinning at high shear rates, compared to nonglycosylated systems with the same density. This effect is attributed to the steric and electrostatic repulsion between the fragments, which prevents their conglomeration and structuring. Our computational study yields a mechanistic mechanism underlying previous experimental observations of lubricin and paves the way to a more rational understanding of its function in the synovial fluid.

Novel biomimetic macromolecules system for highly efficient lubrication, ROS scavenging and osteoarthritis treatment

The early stages of osteoarthritis (OA) in the joints are typically characterized by two key factors: the dysfunction of articular cartilage lubrication and inflammation resulting from the excessive production of reactive oxygen species (ROS). Synthetic injectable macromolecular materials present great potential for preventing the progression of early OA. In this study, to mimic the excellent lubricity of brush-like aggregates found in natural synovial fluid, we develop a novel macromolecular biolubricant (CS-PS-DA) by integrating adhesion and hydration groups onto backbone of natural biomacromolecules. CS-PS-DA exhibits a strong affinity for cartilage surfaces, enabling the formation of a stable lubrication layer at the sliding interface of degraded cartilages to restore joint lubrication performance. In vitro results from ROS scavenging and anti-inflammatory experiments indicate the great advantage of CS-PS-DA to decrease the levels of proinflammatory cytokines by inhibiting ROS overproduction. Finally, in vivo rats OA model demonstrates that intra-cavitary injection of CS-PS-DA could effectively resist cartilage wear and mitigated inflammation in the joints. This novel biolubricant provides a new and timely strategy for the treatment of OA.

Biomimetic chitosan nanoparticles with simultaneous water lubricant and anti-inflammatory

Rheumatoid arthritis (RA) is a chronic inflammatory immune and lubrication dysfunction disease that causes great damage to the joints. Herein, inspired by the unique biochemistry structure and excellent hydration of chondroitin sulfate (CHI) existing in joint system, one kind of novel polysaccharide nanoparticle lubricant, that is chitosan nanoparticles (CS NPs) grafting CHI (CS-CHI), is synthesized by one-step surface chemistry reaction. CHI with negative charges can form hydration layers on the surface of CS NPs, thus improving the lubricity of nanoparticles. Simultaneously, CS-CHI NPs have effective loading and sustained drug release ability for anti-inflammatory drug diclofenac sodium (DS), along with good biocompatibility. Finally, based on a collagen-induced rat RA model, in vitro animals experimental results indicate that the as-synthesized CS-CHI@DS NPs has obvious inhibitory effects on inflammatory factors and can effectively prevent the damaged cartilage from further destruction.

Injectable carboxymethyl chitosan/nanosphere-based hydrogel with dynamic crosslinking network for efficient lubrication and sustained drug release

The typical symptoms of arthritis are inflammation and lubrication deficiency in joints, which increase wear of articular cartilage along with pain of patients. In the present study, one kind of novel macromolecular/microsphere-based injectable hydrogels (CMC-ODex NPs) with dual functionalities of drug release and lubrication, was fabricated via dynamic Schiff base crosslinking network between carboxymethyl chitosan (CMC) and oxidation dextran nanoparticles (ODex NPs). The CMC-ODex NPs hydrogels exhibited typical viscosity-thinning phenomenon at wide range of shear rates and obvious gel-sol transition feature at specific strain. As a result, CMC-ODex NPs hydrogels presented low friction coefficient at the sliding interface of bovine articular cartilages, resulting from the boundary lubrication of hydrogel and the rolling friction effect of ODex NPs. Furthermore, the anti-inflammatory drug (dexamethasone, DXM) encapsulated in ODex NPs exhibited sustainable drug release behavior during the dynamic shearing process, which making CMC-ODex NPs hydrogels possessed good and stable anti-inflammatory effect. CMC-ODex NPs hydrogels was prepared without utilizing any toxic agents, thus demonstrated excellent cytocompatibility. Our experimental results reveal the CMC-ODex NPs hydrogels is promising to be used as functional lubricant for inhibiting the development of arthritis.

Lubricants for osteoarthritis treatment: From natural to bioinspired and alternative strategies

Osteoarthritis is the most common degenerative and highly prevalent joint disease, characterized by progressive loss and destruction of articular cartilage. The damaged cartilage surface has an increased friction, which causes patients to suffer from serious pain. Restoring the lubrication ability of the joint is central to the treatment of osteoarthritis, a key topic in medical research. A variety of lubricants have been designed to reduce friction in joints and promote cartilage tissue repair to alleviate the symptoms of osteoarthritis. Herein, we review the recent progress of lubricants from the three perspectives of natural, bioinspired, and alternative strategies for osteoarthritis treatment, as well as the structural characterization and lubrication properties of such lubricants. Specifically, natural lubricants include glycosaminoglycans, lubricin and lipids in joints, bioinspired lubricants include scaffolds mimicking hyaluronic acid or lubricin, and alternative lubricants include modified lubricants based on hyaluronic acid, lipids, nanoparticles, and peptides. We also discuss the current challenges and long-term perspectives for further research in this area.

Biomimetic chitosan-derived bifunctional lubricant with superior antibacterial and hydration lubrication performances

The lubrication deficiency in joints is a major cause of osteoarthritis. One of the most commonly used treatment means is to inject artificial lubricants, but there is a potential risk of infection during the injection process. Therefore, developing artificial lubricants with dual functions of friction-reduction and antibacterial is urgent. In this work, a novel polysaccharide-derived lubricant with simultaneous anti-bacteria and water-lubrication properties, called CS-MPC-N, is developed by grafting 2‑methacryloyloxylethyl phosphorylcholine (MPC) and nisin peptide onto backbone of chitosan (CS). Compared to the control CS, CS-MPC-N exhibits good lubrication and friction-reduction properties because of its excellent water solubility. Especially, CS-MPC-N shows low friction coefficient (0.03 ∼ 0.05) at the sliding interfaces of artificial joints materials or even natural articular cartilages. Moreover, CS-MPC-N can effectively inhibit the proliferation of Staphylococcus aureu, exhibiting excellent antibacterial effect. This kind of novel polysaccharide-derived lubricant is expected to be used in treating infectious arthritis.

Tribo-corrosive behavior of additive manufactured parts for orthopaedic applications

Background

Additive manufacturing (AM) being an integral component of the production offers a wide variety of applications in the production of different components. The medical industry after the introduction of Additive Manufacturing has resulted in several advancements. The production of intricate patient-specific implants is one of such advancements which greatly assist a surgeon during a surgery. Orthopedic implants apart from possessing good mechanical strength are also expected to exhibit good tribological and corrosion behavior. As a result, the development of various orthopaedic implants and tools has become simple with the use of additive manufacturing.

Objectives and Rationale

In the current paper an effort has been made to discuss actual scientific knowledge on the tribo-corrosive behavior of additive manufactured parts for orthopedic applications. Different studies dealing with the mechanisms of lubrication and friction in synovial joints have also been considered. A special focus has also been laid down to study the corrosive effect of implants on the human body. A section dedicated to texturing of orthopedic implants has also been provided. The paper further elaborates the different research challenges and issues related to the use of additive manufacturing for the production of optimized orthopedic implants.

Conclusion

The study revealed that additive manufacturing has greatly aided in the manufacture of different orthopaedic implants with enhanced properties. However, a detailed study of the effect of processes like friction, wear, lubrication and corrosion in these implants needs to be done. The performance of these implants in the presence of various synovial fluids also needs to be addressed. However, the lack of more biocompatible materials, scalability and cost issues hinder the widespread use of AM in the different orthopaedic applications.

In situ oral lubrication and smoothness sensory perception influenced by tongue surface roughness

BACKGROUND

The human tongue is important in the oral processing of food and in sensory perception. Tongue topography could influence delicate differences in sensory perception. It is hypothesized that tongue surface roughness could alter oral lubrication status and affect perception of smoothness. Fifteen participants with varying levels of tongue surface roughness were recruited and tested. Participants' in situ oral lubrication status without and after consumption of fluid food (milk with varying fat content and maltodextrin solutions with different shear viscosities) was measured. Participants' smoothness sensory scores were also recorded.

RESULTS

The in situ friction coefficient (0.299-1.505) was significantly positively correlated with tongue-surface roughness (54.6-140.0 μm) in all types of test fluid samples across participants. Oral lubrication was significantly decreased when participants consumed the test fluid samples compared with no liquid food consumption, for all test fluid sample types (P < 0.05). No significant differences in in situ friction coefficient were found after participants consumed different test fluid samples, and this was mainly attributed to the limited quantities of fluid residuals in the oral cavity after expectoration. Participants whose tongue surface roughness differed did not exhibit significant differences in smoothness perception with different test fluid samples.

CONCLUSION

Tongue surface roughness has a strong impact on in situ oral lubrication, and fluid food intake reduces in situ oral lubrication significantly. Saliva film and tongue surface roughness might play greater roles in oral lubrication and smoothness sensory perception if fluid is expectorated after consumption. The association between oral physiology and texture perception still needs further elucidation. © 2021 Society of Chemical Industry.

Synovial Joints. Tribology, Regeneration, Regenerative Rehabilitation and Arthroplasty

Synovial joints are unique biological tribosystems that allow a person to perform a wide range of movements with minimal energy consumption. In recent years, they have been increasingly called “smart friction units” due to their ability to self-repair and adapt to changing operating conditions. However, in reality, the elements of the internal structure of the joints under the influence of many factors can degrade rather quickly, leading to serious disease such as osteoarthritis. According to the World Health Organization, osteoarthritis is already one of the 10 most disabling diseases in developed countries. In this regard, at present, fundamental research on synovial joints remains highly relevant. Despite the fact that the synovial joints have already been studied fully, many issues related to their operating, prevention, development of pathology, diagnosis and treatment require more detailed consideration. In this article, we discuss the urgent problems that need to be solved for the development of new pharmacological agents, biomaterials, scaffolds, implants and rehabilitation devices for the prevention, rehabilitation and improvement of the treatment effectiveness of synovial joints at various stages of osteoarthritis.

A bioinspired mucoadhesive restores lubrication of degraded cartilage through reestablishment of lamina splendens

Adsorbed lubricious films composed of biomacromolecules are natively present at all articulating interfaces in the human body where they provide ultralow friction and maintain normal physiological function. Biolubrication gets impaired due to diseases such as osteoarthritis, in which cartilage damage results from alterations in synovial fluid and lamina splendens composition. Osteoarthritis is treated with hyaluronic acid (HA) orally or via intra-articular injection, but due to the poor adsorption of HA on the cartilage surface in the absence of adhesive molecules, pain relief is temporary. Here, we describe how natural lubrication on degraded cartilage surface can be restored with the help of a bioinspired mucoadhesive biopolymer chitosan catechol (Chi-C). Quartz crystal microbalance was used to mimic the formation of lamina splendens in vitro, known as synovial fluid conditioning films (SyCF), and colloidal probe atomic force microscopy was used to measure their nanoscale frictional properties. Clear evidence of glycoprotein (PRG4) recruitment by Chi-C increased the softness of SyCF, which also improved nanoscale lubrication in vitro, decreasing the friction coefficient from 0.06 to 0.03. At the macroscale, cartilage damage induced by Chondroitinase ABC increased the coefficient of friction (COF) from 0.07 ± 0.04 (healthy tissue) to 0.15 ± 0.03 (after tissue damage) in the presence of synovial fluid after sliding for 50 min. After Chi-C treatment of damaged cartilage, the COF fell to 0.06 ± 0.03, which is comparable to healthy cartilage. Chi-C did not adversely affect the metabolic activity of human chondrocytes. This study provides new key insight into the potential for restoring biolubrication through the use of muco-adhesive molecules.