{
    "protocol": "1. Prepare a primer layer by pretreating the solid surface with a solution containing poly(vinyl acetate) (PVAc) and a radical initiator. 2. Allow the primer layer to dry, forming a strong physical coating with the embedded initiator. 3. Prepare a pre-gel solution that contains brittle first network gel particles and second network monomer, acrylamide (AAm), and poly(2-acrylamido-2-methylpropane sulfonic acid sodium salt) (PNaAMPS). 4. Apply the pre-gel solution to the surface covered with a glass plate and spacer to prevent drying and control thickness. 5. Initiate polymerization of the second network from the initiator embedded in the primer layer. 6. The second network will strongly bond to the surface via covalent bonding to the primer layer, forming a tough hydrogel coating.P-DN gel films were synthesized using a two-step sequential free-radical polymerization method. In the first step, for the first network particle preparation, MBAA (0.5-6 mol%) and α-keto (0.1 mol%) were added to a 1 M NaAMPS solution. The mixture was poured into reaction cells consisting of a pair of glass plates with a 1 mm silicone spacer. Photoinduced free radical polymerization was conducted under argon atmosphere with a UV lamp for 10 h (UV light intensity was 3.9 mW/cm²). The resulting PNaAMPS gels were ground into particles, dried in a vacuum oven for 24 h, and then finely ground with a multibead shocker to achieve particles ranging from 10 to 200 μm. For the second network, the dried PNaAMPS particles were added into a 4 M AAm aqueous solution containing MBAA (0.01 mol%) and α-keto (0.01 mol%), with the concentration of PNaAMPS particles to AAm solution varied from 0.005 to 0.030 mg/mL. This precursor mixture was poured into reaction cells and the AAm monomers were photopolymerized with a UV lamp for 8 h to obtain P-DN gel sheets. The P-DN gels exhibited an equilibrium thickness of 1.5 mm when swollen in pure water."
}