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.

Lubricin (PRG-4) anti-fouling coating for surface-enhanced Raman spectroscopy biosensing: towards a hierarchical separation system for analysis of biofluids.

Surface-enhanced Raman Spectroscopy (SERS) is a powerful optical sensing technique that amplifies the signal generated by Raman scattering by many orders of magnitude. Although the extreme sensitivity of SERS enables an extremely low limit of detection, even down to single molecule levels, it is also a primary limitation of the technique due to its tendency to equally amplify 'noise' generated by non-specifically adsorbed molecules at (or near) SERS-active interfaces. Eliminating interference noise is thus critically important to SERS biosensing and typically involves onerous extraction/purification/washing procedures and/or heavy dilution of biofluid samples. Consequently, direct analysis within biofluid samples or in vivo environments is practically impossible. In this study, an anti-fouling coating of recombinant human Lubricin (LUB) was self-assembled onto AuNP-modified glass slides via a simple drop-casting method. A series of Raman spectra were collected using rhodamine 6G (R6G) as a model analyte, which was spiked into NaCl solution or unprocessed whole blood. Likewise, we demonstrate the same sensing system for the quantitative detection of L-cysteine spiked in undiluted milk. It was demonstrated for the first time that LUB coating can mitigate the deleterious effect of fouling in a SERS sensor without compromising the detection of a target analyte, even in a highly fouling, complex medium like whole blood or milk. This feat is achieved through a molecular sieving property of LUB that separates small analytes from large fouling species directly at the sensing interface resulting in SERS spectra with low background (i.e., noise) levels and excellent analyte spectral fidelity. These findings indicate the great potential for using LUB coatings together with an analyte-selective layer to form a hierarchical separation system for SERS sensing of relevant analytes directly in complex biological media, aquaculture, food matrix or environmental samples.

Potential Pulse-Facilitated Active Adsorption of Lubricin Polymer Brushes Can Both Accelerate Self-Assembly and Control Grafting Density.

Self-assembled lubricin (LUB) monolayers are an effective antiadhesive coating for biomedical applications. Long deposition times and limited control over the monolayer grafting density remain impediments to commercialization and applications in advanced sensor technologies. This work describes a novel potential pulse-facilitated coating method that reduces coating times to mere seconds while also providing high-level control over the achieved grafting density. This is the first time that the potential pulse-facilitated method is applied for direct assembling of a large and complex polyelectrolyte.

Lubricin as a tool for controlling adhesion in vivo and ex vivo.

The ability to prevent or minimize the accumulation of unwanted biological materials on implantable medical devices is important in maintaining the long-term function of implants. To address this issue, there has been a focus on materials, both biological and synthetic, that have the potential to prevent device fouling. In this review, we introduce a glycoprotein called lubricin and report on its emergence as an effective antifouling coating material. We outline the versatility of lubricin coatings on different surfaces, describe the physical properties of its monolayer structures, and highlight its antifouling properties in improving implant compatibility as well as its use in treatment of ocular diseases and arthritis. This review further describes synthetic polymers mimicking the lubricin structure and function. We also discuss the potential future use of lubricin and its synthetic mimetics as antiadhesive biomaterials for therapeutic applications.

Antifouling Strategies for Electrochemical Biosensing: Mechanisms and Performance toward Point of Care Based Diagnostic Applications.

Although there exist numerous established laboratory-based technologies for sample diagnostics and analyte detection, many medical and forensic science applications require point of care based platforms for rapid on-the-spot sample analysis. Electrochemical biosensors provide a promising avenue for such applications due to the portability and functional simplicity of the technology. However, the ability to develop such platforms with the high sensitivity and selectivity required for analysis of low analyte concentrations in complex biological samples remains a paramount issue in the field of biosensing. Nonspecific adsorption, or fouling, at the electrode interface via the innumerable biomolecules present in these sample types (i.e., serum, urine, blood/plasma, and saliva) can drastically obstruct electrochemical performance, increasing background "noise" and diminishing both the electrochemical signal magnitude and specificity of the biosensor. Consequently, this review aims to discuss strategies and concepts used throughout the literature to prevent electrode surface fouling in biosensors and to communicate the nature of the antifouling mechanisms by which they operate. Evaluation of each antifouling strategy is focused primarily on the fabrication method, experimental technique, sample composition, and electrochemical performance of each technology highlighting the overall feasibility of the platform for point of care based diagnostic/detection applications.

Lubricin (PRG4) Antiadhesive Coatings Mitigate Electrochemical Impedance Instabilities in Polypyrrole Bionic Electrodes Exposed to Fouling Fluids.

Surface fouling is a major problem faced by bionic implants (e.g., cochlear implants, pacemakers), where the adsorption of unwanted biomolecules has a detrimental effect on interfacial charge transfer processes, which severely impairs their capacity to sense and transmit electrical signals with high fidelity. Polypyrrole (PPy) is a conductive polymer whose naturally high impedance, ionic and electric conductivity, mechanical "softness", and biocompatibility make it a leading candidate for next-generation neural electrode interfaces. However, PPy (and related conductive polymer) surfaces are susceptible to surface fouling upon exposure to biological fluids (e.g., blood, perilymph, saliva), which compromises performance and shortens its expected working lifespan. Here, we report the ability of lubricin (LUB) coatings, a rapidly self-assembling, biological antiadhesive glycoprotein, to mitigate the harmful electrochemical effects caused by the surface fouling of electrochemically grown PPy films. LUB, a biological antiadhesive glycoprotein, undergoes rapid self-assembly and adheres strongly to most interfaces, including PPy, resulting in an easy-to-apply and highly efficacious coating. The LUB-coated PPy electrodes are electrochemically characterized, and its antifouling properties are assessed against concentrated solutions of bovine serum albumin (BSA) and following long-term exposure to artificial perilymph (AP). Periodic impedance measurement conducted over 6 days in AP solution demonstrates the high stability and capacity of the LUB coatings to maintain stable impedance values under real-world mimicking conditions.