Synergistic Interactions of a Synthetic Lubricin-Mimetic with Fibronectin for Enhanced Wear Protection

A review of current advancements for wound healing: Biomaterial applications and medical devices

Wound healing is a complex process that is critical in restoring the skin's barrier function. This process can be interrupted by numerous diseases resulting in chronic wounds that represent a major medical burden. Such wounds fail to follow the stages of healing and are often complicated by a pro‐inflammatory milieu attributed to increased proteinases, hypoxia, and bacterial accumulation. The comprehensive treatment of chronic wounds is still regarded as a significant unmet medical need due to the complex symptoms caused by the metabolic disorder of the wound microenvironment. As a result, several advanced medical devices, such as wound dressings, wearable wound monitors, negative pressure wound therapy devices, and surgical sutures, have been developed to correct the chronic wound environment and achieve skin tissue regeneration. Most medical devices encompass a wide range of products containing natural (e.g., chitosan, keratin, casein, collagen, hyaluronic acid, alginate, and silk fibroin) and synthetic (e.g., polyvinyl alcohol, polyethylene glycol, poly[lactic‐co‐glycolic acid], polycaprolactone, polylactic acid) polymers, as well as bioactive molecules (e.g., chemical drugs, silver, growth factors, stem cells, and plant compounds). This review addresses these medical devices with a focus on biomaterials and applications, aiming to deliver a critical theoretical reference for further research on chronic wound healing.

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.

An Accelerated Wound-Healing Surgical Suture Engineered with an Extracellular Matrix

A suture is a ubiquitous medical device to hold wounded tissues together and support the healing process after surgery. Surgical sutures, having incomplete biocompatibility, often cause unwanted infections or serious secondary trauma to soft or fragile tissue. In this research, UV/ozone (UVO) irradiation or polystyrene sulfonate acid (PSS) dip-coating is used to achieve a fibronectin (FN)-coated absorbable suture system, in which the negatively charged moieties produced on the suture cause fibronectin to change from a soluble plasma form into a fibrous form, mimicking the actions of cellular fibronectin upon binding. The fibrous fibronectin coated on the suture can be exploited as an engineered interface to improve cellular migration and adhesion in the region around the wounded tissue while preventing the binding of infectious bacteria, thereby facilitating wound healing. Furthermore, the FN-coated suture is found to be associated with a lower friction between the suture and the wounded tissue, thus minimizing the occurrence of secondary wounds during surgery. It is believed that this surface modification can be universally applied to most kinds of sutures currently in use, implying that it may be a novel way to develop a highly effective and safer suture system for clinical applications.

Dynamics of Synovial Fluid Aggregation under Shear

The synovial fluid (SF) that lubricates articular joints exhibits complex rheological and tribological properties due to the interactions and behaviors of its various molecular components. Under shear, SF films abruptly thicken by more than 300% and large, dense aggregates form within the fluid. In this study, we used the Surface Force Apparatus to elucidate which SF components are involved in this shear-induced transformation by (i) determining which (if any) of all major SF components replicate the behavior of SF under shear and (ii) observing the effect of removing implicated components from SF by enzymatic digestion. While most previous studies of SF have focused on the tribological roles of lubricin or hyaluronic acid, our results indicate that albumin is a key contributor to the formation of aggregates in SF under shear. Our results also suggest that SF aggregation is associated with efficient surface protection against wear. As our findings are based on experiments involving rigid, nonporous surfaces, they may be used to investigate shear-mediated aggregation mechanisms occurring during the lubrication of artificial joints, ultimately advancing our current vision of implant design.

Synergy between Zwitterionic Polymers and Hyaluronic Acid Enhances Antifouling Performance

Challenges associated with nonspecific adsorption of proteins on sensor surfaces have steered the development of novel antifouling materials and strategies. Inspired by human synovial fluid composition and structure, we designed synergistic antifouling coatings with mixtures of hyaluronic acid (HA) and a zwitterionic bottlebrush polymer (BB). Using a fast and convenient online surface modification method, the polymers were immobilized on the Au surface, significantly increasing its hydrophilicity. Using surface plasmon resonance (SPR), a 10:1 ratio of HA to BB was found optimal to provide the best antifouling performance. Bovine serum albumin (BSA) adsorption on HA-BB coated surfaces was 0.2 ng/cm², which was 60 times lower than BB or HA alone and 25 times lower than the commonly accepted ultralow adsorption limit (<5 ng/cm²), demonstrating the synergistic effect of HA and BB against nonspecific protein adsorption. This was found to be independent of BSA concentration up to physiological concentrations. Furthermore, the antifouling performance of HA-BB coated surfaces was tested against milk and serum, showing almost 92% lower protein adsorption than that on bare surfaces, suggesting the potential efficacy of this antifouling coating in real life settings.

Boundary mode lubrication of articular cartilage with a biomimetic diblock copolymer

We report the design of a diblock copolymer with architecture and function inspired by the lubricating glycoprotein lubricin. This diblock copolymer, synthesized by sequential reversible addition-fragmentation chain-transfer polymerization, consists of a cationic cartilage-binding domain and a brush-lubricating domain. It reduces the coefficient of friction of articular cartilage under boundary mode conditions (0.088 ± 0.039) to a level equivalent to that provided by lubricin (0.093 ± 0.011). Additionally, both the EC₅₀ (0.404 mg/mL) and cartilage-binding time constant (7.19 min) of the polymer are comparable to purified human and recombinant lubricin. Like lubricin, the tribological properties of this polymer are dependent on molecular architecture. When the same monomer composition was evaluated either as an AB diblock copolymer or as a random copolymer, the diblock effectively lubricated cartilage under boundary mode conditions whereas the random copolymer did not. Additionally, the individual polymer blocks did not lubricate independently, and lubrication could be competitively inhibited with an excess of binding domain. This diblock copolymer is an example of a synthetic polymer with lubrication properties equal to lubricin under boundary mode conditions, suggesting its potential utility as a therapy for joint pathologies like osteoarthritis.

Two compartment pharmacokinetic model describes the intra-articular delivery and retention of rhprg4 following ACL transection in the Yucatan mini pig

Treatment of the injured joint with rhPRG4 is based on recent observations that inflammation diminishes expression of native PRG4. Re-establishing lubrication between pressurized and sliding cartilage surfaces during locomotion promotes the nascent expression of PRG4 and thus intra-articular (IA) treatment strategies should be supported by pharmacokinetic evidence establishing the residence time of rhPRG4. A total of 21 Yucatan minipigs weighing ∼55 kg each received 4 mg of ¹³¹ I-rhPRG4 delivered by IA injection 5 days following surgical ACL transection. Animals were sequentially euthanized following IA rhPRG4 at 10 min (time zero), 24, 72 h, 6, 13 and 20 days later. The decay of the ¹³¹ I-rhPRG4 was measured relative to a non-injected aliquot and normalized to the weight of cartilage samples, menisci and synovium, and known cartilage volumes from each compartment surface obtained from representative Yucatan minipig knees. Decay of ¹³¹ I-rhPRG4 from joint tissues best fit a two-compartment model with an α half-life (t_1/2α ) of 11.28 h and β half-life (t_1/2β ) of 4.81 days. The tibial and femoral cartilage, meniscii, and synovium retained 7.7% of dose at 24 h. High concentrations of rhPRG4 were found in synovial fluid (SF) that was non-aspiratable and resided on the articular surfaces, removable by irrigation, at 10 min following ¹³¹ I-rhPRG4 injection. Synovial fluid K21 exceeded K12 and SF t_1/2β was 28 days indicating SF is the reservoir for rhPRG4 following IA injection. Clinical Significance: rhPRG4 following IA delivery in a traumatized joint populates articular surfaces for a considerable period and may promote the native expression of PRG4. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:386-396, 2019.

A synthetic polymeric biolubricant imparts chondroprotection in a rat meniscal tear model

Intra-articular injection of hyaluronic acid (HA) is used to treat osteoarthritis (OA) as a viscosupplement, yet it only provides short-term benefit because HA is cleaved by hyaluronidase and cleared out of the joint after several days. Therefore, we developed a new polymer biolubricant based on poly-oxanorbornane carboxylate to enhance joint lubrication for a prolonged time. Rheological and biotribological studies of the biolubricant reveal viscoelastic properties and coefficient of friction equivalent and superior to that of healthy synovial fluid, respectively. Furthermore, in an ex vivo bovine cartilage plug model, the biolubricant exhibits superior long-term reduction of friction and wear prevention compared to saline and healthy synovial fluid. ISO 10993 biocompatibility tests demonstrate that the biolubricant polymer is non-toxic. In an in vivo rat medial meniscal tear OA model, where the performance of the leading HA viscosupplement (Synvisc-one®) is comparable to the saline control, treatment with the biolubricant affords significant chondroprotection compared to the saline control.

A hyaluronic acid binding peptide-polymer system for treating osteoarthritis

Hyaluronic acid (HA) is found naturally in synovial fluid and is utilized therapeutically to treat osteoarthritis (OA). Here, we employed a peptide-polymer cartilage coating platform to localize HA to the cartilage surface for the purpose of treating post traumatic osteoarthritis. The objective of this study was to increase efficacy of the peptide-polymer platform in reducing OA progression in a mouse model of post-traumatic OA without exogenous HA supplementation. The peptide-polymer is composed of an HA-binding peptide (HABP) conjugated to a heterobifunctional poly (ethylene glycol) (PEG) chain and a collagen binding peptide (COLBP). We created a library of different peptide-polymers and characterized their HA binding properties in vitro using quartz crystal microbalance (QCM-D) and isothermal calorimetry (ITC). The peptide polymers were further tested in vivo in an anterior cruciate ligament transection (ACLT) murine model of post traumatic OA. The peptide-polymer with the highest affinity to HA as tested by QCM-D (∼4-fold greater binding compared to other peptides tested) and by ITC (∼3.8-fold) was HABP2-8-arm PEG-COLBP. Biotin tagging demonstrated that HABP2-8-arm PEG-COLBP localizes to both cartilage defects and synovium. In vivo, HABP2-8-arm PEG-COLBP treatment and the clinical HA comparator Orthovisc lowered levels of inflammatory genes including IL-6, IL-1B, and MMP13 compared to saline treated animals and increased aggrecan expression in young mice. HABP2-8-arm PEG-COLBP and Orthovisc also reduced pain as measured by incapacitance and hotplate testing. Cartilage degeneration as measured by OARSI scoring was also reduced by HABP2-8-arm PEG-COLBP and Orthovisc. In aged mice, HABP2-8-arm PEG-COLBP therapeutic efficacy was similar to its efficacy in young mice, but Orthovisc was less efficacious and did not significantly improve OARSI scoring. These results demonstrate that HABP2-8-arm PEG-COLBP is effective at reducing PTOA progression.