Hydrogel Paint

2022101017220432.pdf (sustech.edu.cn)

Adv. Mater. 2019, 31, 1903062

For a hydrogel coating on a substrate to be stable, covalent bonds polymerize monomer units into polymer chains, crosslink the polymer chains into a polymer network, and interlink the polymer network to the substrate.
The three processes—polymerization, crosslinking, and interlinking—usually concur. This concurrency hinders widespread applications of hydrogel coatings.

The paint maker formulates the hydrogel paint by copolymerizing monomer units and coupling agents into polymer chains, but does not crosslink them.
The paint user applies the paint on various materials (elastomer, plastic, glass, ceramic, or metal), and by various operations (brush, cast, dip, spin, or spray).

During cure, the coupling agents crosslink the polymer chains into a network and interlink the polymer network to the substrate.
As an example, hydrogels with thickness in the range of 2–20 µm are dip coated on medical nitinol wires.

Preparing Hydrogel Paint p(AAm-co-TMSPMA) on Nitinol Guidewire: For 1 mL solution of AAm (2 moles per a liter of DI water, 2 mol L−1), 1 µL of CTA (10% volume ratio in THF), 10 µL of acetic acid (0.1 moles per a liter of DI water, 0.1 mol L−1), and 5.7 µL of TMSPMA are added, followed by vortex mixing for 60 s.
Here acetic acid is added to tune the pH value of the precursor, such that the condensation of silane is minimized during the hydrogel paint formulation.
After preparation of the hydrogel coating, acetic acid can be removed, if needed, either by distillation or dialysis.
Then, 2 µL of I-2959 (0.1 moles per a liter of ethanol, 0.1 mol L−1)
is added followed by vortex mixing for 10 s.
The resulting transparent solution is drawn into a plastic syringe and subject to UV irradiation (15W 365 nm; UVP XX-15L, 5 cm distance between sample and bulb.
For the following mentioned UV curing procedure, the type of the UV lamp and the distance between sample and bulb are kept the same).
After 30 min, the p(AAm-co-TMSPMA) hydrogel paint is obtained. Nitinol guidewire with diameter of ≈310 µm and length of 17 cm is washed with IPA, acetone, and DI water in sequence twice and then dried by air.
The treated guidewire is fixed to Instron (Instron 5966) load cell and immersed in the p(AAm-co-TMSPMA) hydrogel paint.
During the dip coating, the guidewire is pulled out of the hydrogel paint vertically with a constant velocity of 10 mm min−1.
Finally, the coated wire is sealed in a bottle with saturated humidity and stored in oven at 65 °C for 24 h.

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