A batch of the ink for the hydrogel with selective transport for cations consisted of 500 mg AM, 200 mg BIS, 2 mL deionized water, 300 uL MeHQ Polymerization inhibitor stock solution, 50 uL of LAP photoinitiator stock solution, 2.5 g AMPS, and 500 mg MC. The ingredients were added in the order listed while stirring, and needed to be stirred with a spatula after the addition of MC due to viscosity.