(Nanowerk Spotlight) Hydrogel is a soft polymer material rich in water and biocompatible. These materials have been around for more than half a century, and today they have many applications in various fields and industries. Recently, environmentally sensitive ("smart") hydrogels have been the subject of much scientific research in various fields including biomedicine, biotechnology, pharmaceuticals, and separation science.
As a coating, a hydrogel brings many advantages to a regular solid surface: the substrate of a hydrogel coating combines the excellent properties of the substrate (such as strength, stiffness, and toughness) with the excellent properties of a hydrogel (such as Hydrophilicity, lubricity, biocompatibility) together and drug release).
In principle, any hydrogel can be coated with any substrate to achieve certain functions through its combination. This tremendous diversity makes possible many existing and emerging applications in the fields of engineering and medicine. Examples include soft robotic components, drug delivery (for example, using nanocomposite hydrogels), implants, artificial skin, plasmon nanosensors and actuators.
However, manufacturing hydrogel coatings outside of a laboratory environment can be difficult. In existing methods for stable hydrogel coatings, three processes are required: polymerizing monomer units into polymer chains by covalent bonds, crosslinking polymer chains into polymer networks, and polymerizing The network is interconnected to the substrate.
Su Zhigang Suo, a professor of mechanics and materials at Harvard University, told Nanowerk: "The concurrency of the three processes of polymerization, cross-linking, and cross-linking is unnecessary and hinders the widespread application of hydrogel coatings." Inspiration from science, we developed a hydrogel coating preparation technology, which is divided into several steps. This step-by-step synthesis mode separates the polymerization reaction from cross-linking and cross-linking, so that the hydrogel coating The manufacturer and its users. "
Suo and his team of researchers from the Krafty Biotechnology Institute detailed their findings in Advanced Materials ("Hydrogel Coatings").
Principles of hydrogel coatings
Principles of hydrogel coatings. a) Formulation: The monomer unit and the coupling agent are copolymerized into a polymer chain, but are not cross-linked into a network to form an aqueous solution. This solution may also contain other compounds with various functions, but is not drawn here. b) Substrate preparation: A functional group complementary to the coupling agent is imparted to the substrate surface. c) Coating: the aqueous solution is applied to the substrate through various operations. d) Curing: The coupling agents react with each other to crosslink. (Reprinted with permission from Wiley-VCH Verlag)
By introducing silane chemistry, scientists have achieved uncoupling of polymerization, cross-linking, and interconnection processes. Silane is a broad compound of silicon and other atoms such as carbon, nitrogen, and hydrogen. They are commonly used as coupling agents in copolymerization processes during hydrogel synthesis.
The step-by-step production of hydrogel coatings in different steps is a new concept in this field, but it is very basic and common in the coatings industry: coatings are made in the factory by any sophisticated chemical processing and processing method, The product then becomes user-friendly and can be stocked at the retailer.
The team‘s hydrogel coatings are aqueous solutions of silane-modified polymer chains that can be crosslinked and crosslinked to the target substrate.
"Our hydrogel coatings can be dried, ground to a powder, and can preserve a long life," Dr. Yao Xi co-authored with Liu Junjie and Dr. Yang Canhui. "After re-dissolving in water, the dry powder turns into a hydrogel coating and can form crosslinks and crosslinks."
"The result is that we are now able to inhibit polymerization (a toxic and laboratory-critical chemical process) in a secure production facility, and to produce hydrogels from the finished product just like ordinary coatings," the researchers noted. Adhesive coatings. "" Hydrogel coatings may one day even become specialty coatings with high-end features and special applications. "
After synthesizing a hydrogel coating, its rheology must be adjusted to suit every operation of the coating. "For example, thick hydrogel coatings can be used for brushes, while thin hydrogel coatings can be used for spraying," Yao explained. "The rheology of hydrogel coatings can be easily adjusted with chain transfer agents (CTA), silane content, water content, and rheology modifiers."
The team‘s uncoupling method allows for more customizable preparations than traditional methods that control all synthetic processes with only one reaction. For example, it is now possible to adjust the chain length and crosslinking rate.
Suo concluded: "The principles established in our work can be adapted to guide the development of other chemical and characteristic hydrogel coatings." "For example, we can further make cross-linking and cross-linking based on tips such as pH changes or exposure to UV light. Coupling and uncoupling to achieve separable hydrogel coatings as needed. Crosslinking can still be covalent bonds to maintain the integrity of the hydrogel, but the links between them can be various non-covalent bonds or Dynamic covalent bonds in response to various clues. "