title: Heterogeneous films of ionotropic hydrogels fabricated from delivery templates of patterned paper.
abstract: The use of delivery templates makes it possible to fabricate shaped, millimeter-thick heterogeneously patterned films of ionotropic hydrogels. These structures include two-dimensional (2-D) patterns of a polymer cross-linked by different ions (e.g., alginic acid cross-linked with Ca2+ and Fe3+) and patterns of step gradients in the concentration of a single cross-linking ion. The delivery templates consist of stacked sheets of chromatography paper patterned with hydrophobic barriers (waterproof tape, transparency film, or toner deposited by a color laser printer). Each layer of paper serves as a reservoir for a different solution of cross-linking ions, while the hydrophobic barriers prevent solutions on adjacent sheets from mixing. Holes cut through the sheets expose different solutions of cross-linking ions to the surface of the templates. Films with shaped regions of hydrogels cross-linked by paramagnetic ions can be oriented with a bar magnet. Variations in the concentrations of cations used to cross-link the gel can control the mechanical properties of the film: for single alginate films composed of areas cross-linked with different concentrations of Fe3+, the regions cross-linked with high concentrations of Fe3+ are more rigid than regions cross-linked with low concentrations of Fe3+. The heterogeneous hydrogel films can be used to culture bacteria in various 2-D designs. The pattern of toxic and nontoxic ions used to cross-link the polymer determines the pattern of viable colonies of Escherichia coli within the film.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Bracher
authors.forename: Malancha
authors.initials: M
authors.lastname: Gupta
authors.forename: Eric T
authors.initials: ET
authors.lastname: Mack
authors.forename: George M
authors.initials: GM
authors.lastname: Whitesides
mesh_terms: D000464:Alginates / Q000737:chemistry*; D001419:Bacteria / Q000378:metabolism; D002118:Calcium / Q000737:chemistry; D002351:Carrageenan / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry; D004867:Equipment Design; D004926:Escherichia coli / Q000378:metabolism; D005782:Gels; D020100:Hydrogels / Q000737:chemistry; D007477:Ions; D007501:Iron / Q000737:chemistry; D008670:Metals / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature
chemical_list: D000464:Alginates; D003432:Cross-Linking Reagents; D005782:Gels; D020100:Hydrogels; D007477:Ions; D008670:Metals; D002351:Carrageenan; D007501:Iron; D002118:Calcium