Shaped Films of Ionotropic Hydrogels Fabricated Using Templates of Patterned Paper

This article describes the use of paper—patterned either by hand or with a color laser printer—to fabricate films of ionotropic hydrogels structured into regular shapes with lateral dimensions from 2 mm to several centimeters, and with thicknesses from 0.3 mm to 1 mm. Water-soluble polymers such as alginic acid (AA) and carboxymethyl cellulose (CMC) form hydrogel films with defined shapes when solutions of these polymers are brought into contact with patterned templates of paper wetted with aqueous solutions of multivalent cations. The hydrogel films are sufficiently strong mechanically to be handled with tweezers; they retain their shapes when stored in water for weeks. When multivalent cations of high magnetic susceptibility (χ) cross-link the polymers (for example, with holmium- or gadolinium-cross-linked alginic acid, Ho3+–AA and Gd3+–AA), the films can be manipulated using rare-earth bar magnets.