A batch of the ink for the hydrogel with selective transport for anions consisted of 700 mg AM, 200 mg BIS, 3 mL deionized water, 100 uL of MeHQ polymerization inhibitor stock solution, 50 uL of LAP photoinitiator stock solution, 525 mg MC, and 2 mL of APTAC. The ingredients were added in the order listed while stirring. The MC was allowed to completely dissolve by stirring for at least 15 minutes before adding APTAC, which was then stirred in gently with a spatula.