Supramolecular repair of hydration lubrication surfaces

Supramolecular Polymer Brushes Grafted via Atom Transfer Radical Polymerization from Surfaces Presenting Non-covalent, Host-Guest Complex-Based Initiators

This paper describes the synthesis of supramolecular polymer brushes via surface-initiated polymerization from adamantane-functionalized initiators that are noncovalently bound to β-cyclodextrin- or cucurbit[7]uril-modified substrates. Surface-initiated atom transfer radical polymerization in aqueous media allowed the growth of various hydrophilic polymer brushes with film thicknesses of up to 40 nm from β-cyclodextrin functionalized surfaces. The adamantane moiety not only forms a host-guest complex with β-cyclodextrin, but also with cucurbit[7]uril, which provides opportunities to study the effect of the binding strength of these supramolecular motifs on the film thickness and grafting density of the resulting polymer brushes. Comparison of supramolecular polymer brushes grown from β-cyclodextrin and cucurbit[7]uril-based noncovalent initiators reveals differences in grafting density that are much smaller than expected based on the differences in the solution binding constant of the corresponding host-guest complexes. Both the β-cyclodextrin as well as the cucurbit[7]uril-anchored supramolecular brushes were remarkably robust toward detachment of the polymer grafts. These observations are attributed to the fact that the rates of formation and dissociation of the host-guest complexes are much faster as compared to diffusion of free, detached polymer chains through the polymer brush film. As a result, the surface-grafted polymer brush presents a steric barrier that prevents detachment of individual chains, and also allows surface-initiated polymerization from substrates to which initiators are bound via putatively weak β-cyclodextrin-based host-guest complexes.

Tuning Surface Functions by Hydrophilic/Hydrophobic Polymer Brushes

Polymer brushes, an optimal method for surface modification, have garnered significant interest due to their potential in surface wettability and functions regulation. This review summarizes the recent advancements in functional polymer brush surfaces based on surface wettability regulation. First, the fundamental structure and fabrication methods of polymer brushes, emphasizing the two primary strategies, "grafting-to" and "grafting-from", were introduced, and special attention was accorded to the method of subsurface-initiated atom transfer radical polymerization (SSI-ATRP) for the construction of mechanically robust polymer brushes. Subsequently, we delved into the attributes of the stimuli-responsive polymer brush surface, which can effectuate reversible surface wettability transitions in response to external stimuli. Then, this review also offered an in-depth exploration of the potential applications of polymer brushes based on their surface wettability, including lubrication, drag reduction, antifouling, antifogging, anti-icing, oil-water separation, actuation, and emulsion stability. Lastly, the challenges of polymer brush surfaces encountered in practical applications, including mechanical strength, biocompatibility, recyclability, and preparation efficiency, were addressed, and significant achievements in current research were summarized and insights into future directions were offered. This review intends to provide researchers with a comprehensive understanding of the potential applications of polymer brushes based on surface wettability regulation, and with the development of the polymer brush preparation technology, it will be anticipated that they will assume increasingly pivotal roles in various fields.

Long-lasting comfort ocular surface drug delivery by in situ formation of an adhesive lubricative Janus nanocoating

Topical drug delivery on ocular surface always suffers from frequent administration and low bioavailability due to short drug residence. Despite advances of different adhesive ophthalmic drugs in extending release, cornea and eyelid nonselective adhesion inevitably causes ocular discomfort and even damage. Here, we describe in situ formation of an adhesive lubricative Janus nanocoating (ALJN) to enable long-lasting comfort drug delivery. By iron complexation, an asymmetric ALJN is formed on ocular surface via facile sequential instillation. The adhesive polyphenol inner layer binding with ocular surface enables drug loading and sustained release, while the lubricative zwitterionic polymer outer layer prevents eyelid adhesion to ensure comfort. Following instillation, ALJN retains on ocular surface over 24 hours and reduces blinking frequency to normal level. Moreover, ALJN demonstrates remarkable therapeutic potential in mouse and rabbit models of corneal contusion and alkali burn. This work proposes a comfortable long-lasting topical delivery platform for treating various ocular diseases.

Tribology in Nature: Inspirations for Advanced Lubrication Materials

Friction-induced energy consumption is a significant global concern, driving researchers to explore advanced lubrication materials. In nature, lubrication is vital for the life cycle of animals, plants, and humans, playing key roles in movement, predation, and decomposition. After billions of years of evolution, natural lubrication exhibits remarkable professionalism, high efficiency, durability, and intelligence, offering valuable insights for designing advanced lubrication materials. This review focuses on the lubrication mechanisms of natural organisms and significant advancements in biomimetic soft matter lubrication materials. It begins by summarizing common biological lubrication behaviors and their underlying mechanisms, followed by current design strategies for biomimetic soft matter lubrication materials. The review then outlines the development and performance of these materials based on different mechanisms and strategies. Finally, it discusses potential research directions and prospects for soft matter lubrication materials. This review will be a valuable resource for advancing research in biomimetic lubrication materials.

Mechanically Robust, Superlubricating and Antifouling Bilayer Nanocoating for Micro-Bioimplants via a Dual-Function Metal Coordination Approach

Nanometer-thick ultrathin coatings with superior mechanical strength and desirable lubricating and antifouling performance are critical for the miniaturization of implantable medical devices. However, integrating these properties at the nanoscale remains challenging due to the inherent trade-off between mechanical strength and hydration as well as limitations in coating thickness. In this work, we address these challenges by employing dual-function metal coordination to construct a ∼25 nm thick bilayer structure. Contact mechanics and interfacial molecular force measurements confirm the dual role of vanadium (VIII) ions in forming this bilayer: VIII ions bridge the ligand sites to reinforce the protein bottom layer, and simultaneously anchor the end blocks of the designed ABA triblock hydrophilic polymers to form a hydrated, looping top layer. This VIII-enabled structure demonstrates remarkable load-bearing capacity and lubricating performance (i.e., friction coefficient μ on the order of 10-3 over 100 cycles under ∼10 MPa), while it also exhibits excellent resistance to biofouling in complex biological fluids. This work presents a useful strategy for integrating seemingly incompatible properties into ultrathin coatings, offering the potential for customizing multifunctional surfaces for micro-devices/machines toward bioengineering applications.

Research Progress of Human Biomimetic Self-Healing Materials

Humans can heal themselves after injury, which inspires researchers to develop bionic self-healing materials. Such materials not only equipped with the self-repair capacities akin to those of the human body, but also emulate the mechanical properties of human organs, including the tensile resilience of muscles, the fatigue resistance of skin, and the elevated modulus typical of cartilage. Based on the design concept of imitating the structure of human organs, the bionic self-healing material perfectly solves the problem of poor mechanical properties of self-healing materials caused by weak bond energy and inter-chain flow. This review discusses various organ-inspired self-healing materials in detail, summarizes their synthetic principles and introduces their fascinating mechanical properties. Finally, the application prospects of bionic self-healing polymer materials, such as bio-strain sensors, self-healing anticorrosive coatings, biomedical detection, etc., are outlined. Considering the excellent comprehensive performance and multi-functions of human biomimetic self-healing polymers, more outstanding sustainable materials will be developed, accelerating research progress in self-healing materials and realizing environmentally friendly products in multiple fields.

Lymphocyte-Derived Engineered Apoptotic Bodies with Inflammation Regulation and Cartilage Affinity for Osteoarthritis Therapy

Apoptotic bodies as plentiful extracellular vesicles generated from apoptotic cells play a central role in signal transduction and homeostasis regulation and simultaneously switch death to regeneration to a certain extent. Herein, we designed engineered apoptotic bodies derived from T cells to have the capacity of inflammation regulation and cartilage affinity. The engineered apoptotic bodies as a natural anti-inflammation factor were encapsulated into lubricating hydrogel microspheres to achieve an injectable microsphere complex for the treatment of osteoarthritis (OA). In the above therapeutic system, the engineered apoptotic bodies acted as a biochemical cue to regulate the inflammatory microenvironment and promote chondrocyte cartilage homeostasis, whereas the lubricating hydrogel microspheres served as a biophysical stimulation to effectively reduce the friction of the cartilage surface, restore the cartilage stress, and control the slow delivery of the encapsulated engineered apoptotic bodies by friction degradation. Consequently, the current work creates an injectable and multifunctional therapeutic microsphere to advance cartilage remodeling and OA therapy.

Lubricating Polymer Gels/Coatings: Syntheses and Measurement Strategies

Straightforward design and long-term functionality for tribological considerations has prompted an extensive substitution of polymers for metals across various applications, from industrial machinery to medical devices. Lubrication of and by polymer gels/coatings, essential for ensuring the cost-effective operation and reliability of applications, has gained strong momentum by benefiting from the structural characteristics of natural lubrication systems (such as articular cartilage). The optimal synthetic strategy for lubricating polymer gels/coatings would be a holistic approach, wherein the lubrication mechanism in relation to the structural properties offers a pathway to design tailor-made materials. This review considers recent synthesis strategies for creating lubricating polymer gels/coatings from the molecular level (including polymer brushes, loops, microgels, and hydrogels), and assessing their frictional properties, as well as considering the underlying mechanism of their lubrication.

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.

Zwitterion mediated anti-protein adsorption on polypropylene mesh to reduce inflammation for efficient hernia repair

The effectiveness of polypropylene (PP) mesh is often compromised by severe inflammation. Engineering anti-inflammatory coatings has significant implications for PP mesh to repair unwanted hernias. Here, we presented a facile strategy to develop an anti-fouling coating consisting of zwitterionic poly(carboxybetaine methacrylate) (PCBMA), which could prohibit protein adsorption to endow PP mesh with anti-inflammatory efficacy. The incorporation of PCBMA coating had little impact on the raw features of PP mesh. While the modified mesh PCBMA-PP possessed noticeable hydrophilicity increase and surface charge reduction. The excellent lubricity and surface stability enabled PCBMA-PP to exhibit superior anti-fouling capacity, thus efficiently inhibiting the adsorption of proteins. In vivo experiments showed that incorporating the PCBMA layer could provide PP meshes with outstanding anti-inflammatory effects and tissue compatibility for repairing hernias.

Design, preparation, and characterization of lubricating polymer brushes for biomedical applications

The lubrication modification of biomedical devices significantly enhances the functionality of implanted interventional medical devices, thereby providing additional benefits for patients. Polymer brush coating provides a convenient and efficient method for surface modification while ensuring the preservation of the substrate's original properties. The current research has focused on a "trial and error" method to finding polymer brushes with superior lubricity qualities, which is time-consuming and expensive, as obtaining effective and long-lasting lubricity properties for polymer brushes is difficult. This review summarizes recent research advances in the biomedical field in the design, material selection, preparation, and characterization of lubricating and antifouling polymer brushes, which follow the polymer brush development process. This review begins by examining various approaches to polymer brush design, including molecular dynamics simulation and machine learning, from the fundamentals of polymer brush lubrication. Recent advancements in polymer brush design are then synthesized and potential avenues for future research are explored. Emphasis is placed on the burgeoning field of zwitterionic polymer brushes, and highlighting the broad prospects of supramolecular polymer brushes based on host-guest interactions in the field of self-repairing polymer brush applications. The review culminates by providing a summary of methodologies for characterizing the structural and functional attributes of polymer brushes. It is believed that a development approach for polymer brushes based on "design-material selection-preparation-characterization" can be created, easing the challenge of creating polymer brushes with high-performance lubricating qualities and enabling the on-demand creation of coatings. STATEMENT OF SIGNIFICANCE: Biomedical devices have severe lubrication modification needs, and surface lubrication modification by polymer brush coating is currently the most promising means. However, the design and preparation of polymer brushes often involves "iterative testing" to find polymer brushes with excellent lubrication properties, which is both time-consuming and expensive. This review proposes a polymer brush development process based on the "design-material selection-preparation-characterization" strategy and summarizes recent research advances and trends in the design, material selection, preparation, and characterization of polymer brushes. This review will help polymer brush researchers by alleviating the challenges of creating polymer brushes with high-performance lubricity and promises to enable the on-demand construction of polymer brush lubrication coatings.

Supramolecular Polymer Brushes Grown by Surface-Initiated Atom Transfer Radical Polymerization from Cucurbit[7]uril-based Non-Covalent Initiators

Polymer brushes are densely grafted, chain end-tethered assemblies of polymers that can be produced via surface-initiated polymerization. Typically, this is accomplished using initiators or chain transfer agents that are covalently attached to the substrate. This manuscript reports an alternative route towards polymer brushes, which involves the use of non-covalent cucurbit[7]uril-adamantane host-guest interactions to surface-immobilize initiators for atom transfer radical polymerization. These non-covalent initiators can be used for the surface-initiated atom transfer radical polymerization of a variety of water-soluble methacrylate monomers to generate supramolecular polymer brushes with film thicknesses of more than 100 nm. The non-covalent nature of the initiator also allows facile access to patterned polymer brushes, which can be produced in straightforward fashion by drop-casting a solution of the initiator-modified guest molecules onto a substrate that presents the cucurbit[7]uril host.

Catalysis enabled synthesis, structures, and reactivities of fluorinated S8-corona[n]arenes (n = 8-12)

Previously inaccessible large S8-corona[n]arene macrocycles (n = 8-12) with alternating aryl and 1,4-C6F4 subunits are easily prepared on up to gram scales, without the need for chromatography (up to 45% yield, 10 different examples) through new high acceleration SNAr substitution protocols (catalytic NR4F in pyridine, R = H, Me, Bu). Macrocycle size and functionality are tunable by precursor and catalyst selection. Equivalent simple NR4F catalysis allows facile late-stage SNAr difunctionalisation of the ring C6F4 units with thiols (8 derivatives, typically 95+% yields) providing two-step access to highly functionalised fluoromacrocycle libraries. Macrocycle host binding supports fluoroaryl catalytic activation through contact ion pair binding of NR4F and solvent inclusion. In the solid-state, solvent inclusion also intimately controls macrocycle conformation and fluorine-fluorine interactions leading to spontaneous self-assembly into infinite columns with honeycomb-like lattices.

Outstanding Bio-Tribological Performance Induced by the Synergistic Effect of 2D Diamond Nanosheet Coating and Silk Fibroin

Due to their excellent biocompatibility, outstanding mechanical properties, high strength-to-weight ratio, and good corrosion resistance, titanium (Ti) alloys are extensively used as implant materials in artificial joints. However, Ti alloys suffer from poor wear resistance, resulting in a considerably short lifetime. In this study, we demonstrate that the chemical self-assembly of novel two-dimensional (2D) diamond nanosheet coatings on Ti alloys combined with natural silk fibroin used as a novel lubricating fluid synergistically results in excellent friction and wear performance. Linear-reciprocating sliding tests verify that the coefficient of friction and the wear rate of the diamond nanosheet coating under silk fibroin lubrication are reduced by 54 and 98%, respectively, compared to those of the uncoated Ti alloy under water lubrication. The lubricating mechanism of the newly designed system was revealed by a detailed analysis of the involved microstructural and chemical changes. The outstanding tribological behavior was attributed to the establishment of artificial joint lubrication induced by the cross binding between the diamond nanosheets and silk fibroin. Additionally, excellent biocompatibility of the lubricating system was verified by cell viability, which altogether paves the way for the application of diamond coatings in artificial Ti joint implants.