{
    "protocol": "The renatured hydrogel painting (RHP) method involves a two-step technology for synthesizing hydrophilic polymers with functional groups. First, dehydrated xerogel particles are adhered to solid surfaces using a special adhesive. Next, these xerogel particles are rehydrated in an aqueous medium, resulting in a uniform hydrogel coating layer on the intended surface.First, spread or spray an uncured fluidic adhesive (e.g., diluted epoxy resin with acetone) on the surface of the substrate. Next, immediately cover the adhesive layer with xerogel particles made from a polyacrylamide-alginate-Ca2+ double-network hydrogel. Allow the adhesive to cure, bonding the xerogel particles to the substrate. Subsequently, rehydrate the xerogel particles in the presence of water to initiate the renaturation process, forming a hydrogel layer.The synthesis of hydrophilic polymers involved the use of sodium alginate (SA) as the primary material, which is extracted from brown algae. Acrylamide (AM) and N,N'-methylenebisacrylamide (MBAM) were incorporated as crosslinking agents to modify the polymer network. The process also utilized calcium chloride (CaCl2) and N,N,N',N'-tetramethyl-ethylenediamine (TEMED) as catalysts to facilitate the polymerization reaction. The precise mixing ratios and conditions such as temperature and time were not specified in the provided text.The epoxy resin components A and B were added to acetone with a ratio of 1:1, and they were fully stirred to form a uniform solution. The linker solution was freshly prepared just before use, but the component A or B solution could be stored separately for the long term. The viscosity of epoxy resin solution was measured by a rheometer (MCR 302, Anton Paar). The shear rate varied from 10^{-1} to 10^{3} s^{-1}. A steel parallel rotor with a diameter of 20 mm was used. The gap was kept at 50 µm, and the temperature was fixed at 25°C.PAM-alginate-${\\mathrm{Ca}}^{2+}$ hydrogel was prepared by curing a precursor solution containing 20 wt % AM, 0.05 wt % MBAM, 2 wt % SA, 0.05 wt % $(\\mathrm{NH}_{4})_{2}\\mathrm{S}_{2}\\mathrm{O}_{8}$, 0.34 wt % $\\mathrm{CaSO}_{4}{\\cdot}2\\mathrm{H}_{2}\\mathrm{O}$, and 0.1 wt % TEMED for 12 hours at room temperature. The double-network xerogel was made by vacuum freeze-drying and then triturated into multisize xerogel microparticles by ball milling. The multisize xerogel microparticles were filtered by size using ethanol as the solution. After evaporation of the ethanol, SP (30 to 40 μm), MP (60 to 80 μm), and LP (100 to 150 μm) were obtained. The substrates were cleaned with deionized water and ethanol, followed by drying at room temperature. The linker solution was coated on the surface of dry substrates, and then the xerogel powder was sprayed on the intermediate layer prepolymer. After polymerization of the linker, a uniform hydrogel coating was obtained, which was then immersed in deionized water for 24 hours.The PAM-Alginate hydrogel labeled with Rhodamine B was prepared by curing a pregel solution, containing 20 wt % AM, 0.05 wt % MBAM, 2 wt % SA, 0.05 wt % (NH4)2S2O8, 0.34 wt % CaSO4·2H2O, 0.1 wt % TEMED, and Rhodamine B (10^-5 g/ml) for 12 hours at room temperature. The xerogel containing Rhodamine B was punched into xerogel microparticles by ball milling. The microparticles with size approximately at 30 μm were screened out via rational filtration. The glass substrates were cleaned with deionized water and ethanol followed by drying under room temperature. A linker solution containing epoxy resin prepolymer (1.0 g/ml) and petroleum fluorescent tracing dye (10^-5 g/ml) in acetone was coated on the surface of cleaned glass slide. Afterward, the xerogel powder was sprayed on the adhesive layer after its precuring for 15 min at 75°C. The sandwich-like sample was further placed in an oven with a temperature of 75°C for another 3 hours and then immersed in Rhodamine B solution (10^-5 g/ml) for 24 hours to allow the rehydration of xerogel particles.The RHP coated on a metal panel was immersed in silicone oil for full impregnation. Upon placement into deionized water, the oil skin in the hydrogel coating was gradually removed. This demonstrated the completeness and continuity of the hydrogel coating. The RHP coated panel was then subjected to a high-pressure water jet impingement test. Finally, the panel that endured the impact went through an oil skin delamination experiment to verify the hydrogel coating's completeness.Spraying the epoxy solution on the PVC substrate for about 5 minutes. Allowing the epoxy resin to precure for 30 minutes at room temperature. Spraying xerogel powders on the surface of the partially cured epoxy resin for about 15 minutes. Further curing the epoxy resin for 3 hours at room temperature. Rinsing the xerogel layer with water to form the RHP coating."
}