Zhejiang University Yang Wei academician / Harvard University lock Zhigang academician "NSR" review: functional hydrogel coating.

Hydrogels are natural or synthetic polymer networks that dissolve in water and can be mechanically, chemically and electrically compatible with living tissue. Since the invention of hydrogel contact lenses in 1960, in-depth research and development of medical water gels has been carried out. Recently, functional hydrogel coatings with controlled thickness and toughness have been implemented on a variety of substrates

. Hydrogel-coated substrates combine the advantages of hydrogels (e.g. lubricity, biosynorbability and anti-bioscaling properties) with the advantages of substrates (e.g. stiffness, toughness and strength). The application and function of functional hydrogel coating were reviewed by the team of Yang Wei academicians of Zhejiang University and the lock Zhigang academicians of Harvard University, the method of coating various substrates with different functional hydrogels with strong viscosity, and the testing to evaluate the adhesion between functional hydrogel coatings and substrates. The development prospect of functional hydrogel coating is given. The review was published in the National Science Review under the title "Functional Hydrogel Coatings."
hydrogels are aggregations of water molecules and hydropolymer networks. High water content allows hydrogels to dissolve and transmit ions and many small molecules. Polymer networks are usually sparsely interlinked, resulting in soft and elastic hydrogels. Natural and synthetic hydrogels come in a wide variety of polymer topology and chemical composition, making them highly adaptable to a wide range of applications. Functional hydrogels mimic the function of biological tissue chemically, mechanically and electrically. Established medical applications for functional hydrogels include tissue engineering, wound dressings, contact lenses and drug delivery. Hydrogels also play a key role in stretchable devices and soft robots such as muscle-like movers, hydrogel fish, soft displays, stretchable ion electronics, skin sensors, and more. A key challenge in hydrogel applications is to achieve a strong bond between the hydrogel and other materials. Although hydrogels have long been developed as adhesives for wound closure, their adhesion is limited to less than 10J/m2.
Functional Hydrogel Application
Hydrogel Coating Function and Application
Drug Control Release: Based on hydrogel drug delivery is controlled in space and time, improving the accuracy of drug distribution and producing fewer side effects. The characteristic size of the hydrogel determines the possible route of delivery. The rate at which the drug is released depends on the spread of the drug to surrounding tissues and can be accelerated by constructing a hydrogel coating using a biodegradable polymer network. In addition, the release rate of the drug can be effectively regulated by regulating the molecular interaction between the hydrogel polymer network and the drug.
lubrication: some biological surfaces, such as cartilage in animal joints, are essentially hydrogels made up of fibrous collagen and protein polysaccharine. Synthetic hydrogel surface has non-adhesive suspension chain, can achieve a very low coefficient of friction, water gel's friction behavior and solids are very different, it is affected by several factors, including the chemical structure of hydrogel, sliding surface properties and measurements.
anti-fouling: bioscales are surface contamination caused by the adhesion of organisms and their by-products. The surface bioscales of implantable medical devices are caused by the adhesion of microorganisms or thrombosis media caused by the reaction of foreign actiles. Bioscales limit the life of implanted medical devices and may even cause them to be removed and replaced. Hydrogel, as a well-known hydro-hydro-material, can greatly improve the hydro-hydro-hydrogenicity of the coating surface. Hydrogels commonly used as biodeface coatings for implantable medical devices include polyethylene alcohol (PVA), polyglycol (PEG) and natural polysaccharides such as crustaceans and glucosaccharides.
coating of nerve electrodes: organisms mainly use ions to conduct electrical signals, while machines use only electrons. Hydrogel ion electronics is a new research field, and hydrogel-based ion cables mimic the function of axons in terms of ion conductivity. In medical applications, hydrogel ion conductors inherit the bio-compatible nature of hydrogels and are ideal for neuroelectronic conductive coatings.
sensing: The diversity of hydrogel chemistry enables it to respond widely to a variety of stimuli such as temperature, pH, magnetic fields and chemicals, such as deformation and changes in transparency. The application of stimulating responsive hydrogels in the field of soft starters and soft measurements is very attractive. Stimulating response hydrogel coatings combine with other substrates or devices to create new sensing systems.
: as a stimulating response hydrogel that drives the active material, it has a large driving deformation under the influence of external stimulation. By using a network of stimulus-responsive polymers for hydrogel formation, embedding active components in hydrogel substates, and designing structures with chambers or channels for hydraulic or air pressure drive, it is easy to achieve the stimulating response of hydrogels. Active hydrogels in the form of coatings are mostly based on stimulating responsive polymer networks. Under stimulation, changes in the composition of the polymer network or crosslink density can lead to the swelling/deflation of the hydrogel, which can lead to the expansion or contraction of the drive.
resistant to marine biomass: The sunken surface of the marine environment is subject to the accumulation of marine dirt, such as algae, diatoms and barnacles known as marine life dirt. Pollution of marine life slows down ships, resulting in additional energy consumption and ship maintenance costs. Coating anti-fouling materials on the target surface is the most widely used method to achieve anti-fouling properties of underwater substations in the marine environment. The anti-fouling properties of the hydrogel coating are attributed to its highly hydrated surface.
oil-water separation: oil pollution is becoming a icing threat to the oceans and aquatic ecosystems due to the increase in industrial oil-containing wastewater and frequent oil spills. The need for efficient, low-cost, reusable oil-water separation materials is becoming increasingly urgent. Ultra-hydrophobic and underwater ultra-hydrophobic hydrogel-coated oil-water mixture separation membrane has the advantages of non-polluting and recycling, and has broad application prospects in industrial oily wastewater treatment and oil spill cleaning.
functional hydrogel coating application
hydrogel coating method
surface bridge: due to the abundance of water at the interface, hydrogel adhesion to other substitities through simple attachment is essentially low. Strong hydrogel adhesion is the result of strong interaction between the polymer network and the substitin of hydrogel. The principle of strong adhesion of the surface bridge is that the ends of the bridge molecules interact with the hydrogel and substrate respectively, and form a strong bond at the substrate-coating interface.
: Surface triggering is in principle suitable for the formation of hydrogel coatings on most substrates. For polymers, hydrophobic triggers can spread to their surfaces with the help of appropriate solvents such as ethanol and acetone. For other substrates, such as metals and ceramics, a trigger containing a trigger, such as ethylene poly acetate, can be applied to the target surface to introduce the trigger. Compared with water, the surface energy of most polymers is lower, which prevents the hydrogel pre-drive from wetting on the target substate. In order to achieve the stable spread of paste hydrogel preludes on the substation or to allow the hydrogel monosome to better spread to the target surface, it is best to choose a substation with higher surface energy for better wetting. To meet this requirement, the target surface can be surfaced for higher surface energy, or additives can be added to the hydrogel preludes to reduce surface stress.
Hydrogel paint: Hydrogel coatings are adjustable in viscosity, using water content or fluid modifiers, so they can be applied and branched to substrates with complex structures, and the oxygen insensitivity of hydrogel coatings is solidified and bonded to the substrates, for example through silane shrinkage, ensuring the successful formation of hydrogel coatings in the environment. All these advantages make hydrogel coating method an attractive method of hydrogel coating formation in practical application. The application and effectiveness of the hydrogel coating is determined by the hydrogenic group or joint agent. For example, silicone groups can be condensed with hydroxyl on the target substrate to enhance bonding and to shrink to cure hydrogel coatings.
Hydrogel Coating Method
Adhesion between the hydrogel coating
The adhesion between the gel coating and the substrate is the energy required to peel off the hydrogel coating per unit area and has J/m2 units, which quantifies the deadhesion resistance of the coating. Hydrogel coating adhesion varies with thickness. At present, the main test methods are peeling test, simple stretch test, scratch test, probe pull test, double cantilever beam test.
Hydration gel adhesion test method
Summary
This paper summarizes the latest progress of functional hydrogel coating, focusing on the function and application of functional hydrogel coating, coating method and adhesion strength test method. Functional hydrogel coatings are expected to play a key role in a wide range of applications. Hydrogel coating methods have begun to achieve tough adhesion in the laboratory, but there are still some gaps in the process of conversion to mass production. Tough hydrogel coatings need to be developed, and it is doubtful whether the adhesion of the hydrogel coating under loading is the same as static loading. Long-term stable adhesion of functional hydrogel coatings in harsh environments such as seawater and biological conditions, including body fluids and blood, is important for their application. The interface between the hydrogel coating and the substation and the functional hydrogel coating itself degrade after prolonged immersion in these environments, resulting in layering or fracture failure of the coating. Finally, there is a lack of a common test method for measuring the adhesion of hydrogel coatings, especially when the coating is very thin, and the fundamental difficulty is how to quantitatively peel off the coating.
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