Constructing a biomimetic robust bi-layered hydrophilic lubrication coating on surface of silicone elastomer

Abstract

Silicone elastomers-based materials have been extensively involved in the field of biomedical devices, while their use is extremely restricted due to the poor surface lubricity and inherent hydrophobicity. This paper describes a novel strategy for generating a robust layered soft matter lubrication coating on the surface of the polydimethylsiloxane (PDMS) silicone elastomer, by entangling thick polyzwitterionic polyelectrolyte brush of poly (sulfobetaine methacrylate) (PSBMA) into the sub-surface of the initiator-embedded stiff hydrogel coating layer of P(AAm-co-AA-co-HEMA-Br)/Fe, to achieve a unified low friction and high load-bearing properties. Meanwhile, the stiff hydrogel layer with controllable thickness is covalently anchored on the surface of PDMS by adding iron powder to provide catalytic sites through surface catalytically initiated radical polymerization (SCIRP) method and provides high load-bearing capacity, while the topmost brush/hydrogel composite layer is highly effective for aqueous lubrication. Their synergy effects are capable of attaining low friction coefficient (COFs) under wide range of loaded condition in water environment with steel ball as sliding pair. Furthermore, the influence of mechanical modulus of the stiff hydrogel layer on the lubrication performance of layered coating is investigated, for which the COF is the lowest only when the modulus of the stiff hydrogel layer well matches the PDMS substrate. Surprisingly, the COF of the modified PDMS could remain low friction (COF < 0.05) stably after encountering 50,000 sliding cycles under 10 N load. Finally, the surface wear characterizations prove the robustness of the layered lubricating coating. This work provides a new route for engineering lubricious silicon elastomer with low friction, high load-bearing capacity, and considerable durability.

Brush-Modified Hydrogels: Preparations, Properties, and Applications

“…Hydrogels modified with surface polymer molecular brushes are mainly prepared by atom transfer radical polymerization (ATRP), ,,,, activators regenerated by electron transfer for ATRP (ARGET-ATRP), , or photoinduced electron/energy transfer-RAFT (PET-RAFT) polymerization . The surface modification strategies consist of “grafting onto” and “grafting from”.…”

“…Hydrogels are promising for a broad range of applications given their outstanding properties of swellability, toughness, flexibility, elasticity, viscoelasticity, fatigue resistance, diffusivity, antifouling, and biomimetic environment. − Hydrogel materials with different structures have been designed to implement variable functions, and they have been extensively employed in cell culture, , drug delivery, − tissue scaffolds, − wound dressings, − antifouling materials, − contact lenses, , sensors, flexible and wearable sensing electronics, − lubricating material, − anti-icing, − optical devices, , batteries, , and soft robotics. ,, The chemical composition and the spatial topology of hydrogels determine their properties and functions, which are pivotal for practical applications. The polymer chain of hydrogel with identical compositions can be accommodated in the local environment in various topologies, ranging from linear form to grafted, blocky, star-shaped, bottlebrush, and other complex architectures .…”

“…The mechanical strength of the hydrogels can be finely tuned because of the intense connections of the brush, which compensates for the negative effects of the topological defects within the hydrogels. Alteration of the degree of molecular brush grafting can further regulate the hydrophilic–hydrophobic equilibrium of hydrogels. , Moreover, the grafting density of molecular brushes can be modulated to manipulate the viscoelasticity, load-bearing capacity, lubricity, and friction properties of hydrogels. ,,− The introduction of hydrogen bonds and ionic functional groups in the molecular brush provides a compact structure due to the abundant hydrogen bonding and electrostatic interactions, resulting in double network hydrogels with good compressive properties and low swelling ratio . The hydrogel system, with molecular brush modified on the surface, exhibits good stretchability, toughness, adhesion, and excellent self-healing ability because of the massive hydrogen bonding between the polymer molecular brush and the hydrogel substrate. , Thermosensitive molecular brushes covalently bonded to the surface of the hydrogel amplify the response characteristics of polymer films in aqueous media .…”

Recent progress of bioinspired cartilage hydrogel lubrication materials

“…Fe 3+ induced tridentate metal coordination with the -COOH group in P(AAm-co-AAc) network and act as the second network to enhance the mechanical property. Inspired by this method, Gao et al fabricated a biomimetic bi-layered coating on the surface of polydimethylsiloxane, which was composed of a robust P(AAm-co-AAc)-Fe 3+ hydrogel substrate and an entangling polyzwitterionic polyelectrolyte brush layer on the top surface (Figure 5b) [87]. The COF of the coating could remain low friction (COF <0.05) stably during the friction test of 50,000 sliding cycles under 10 N load, exhibiting excellent anti-wear property.…”

Mussel-Inspired Multicomponent Codeposition Strategy toward Antibacterial and Lubricating Multifunctional Coatings on Bioimplants

“…As for lubricating coating design, natural synovial joints provided an excellent paradigm. Natural joints exhibited extremely efficient lubrication with coefficients of friction (COF) <0.01 under a wide range of contact loads. , The ultralow COF of joints resulted from the hydration lubrication mechanism of charged biomacromolecules on the cartilage surface, which can tightly bound large amounts of water molecules to form a tenacious but fluid-like hydration layer. , Inspired by joint lubrication, a variety of hydrophilic polymer coatings have been explored as promising boundary lubrication layers to reduce the interface friction of bioimplant surfaces. − Charged polymers, especially zwitterionic poly­(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were recognized as the most optimal materials for hydration lubrication. − Recently, Xu et al developed a low friction, nonirritating, and anti-inflammatory hyaluronic acid-based coating on the tracheal tube. The study in animal models demonstrated that the multifunctional coating could effectively relieve the complications of endotracheal intubation. , In addition, Liu et al.…”