3D Printing of Functional\nHydrogel Devices for Screenings\nof Membrane Permeability and Selectivity

Developing a fundamental understanding\nof the effects\nof varying\nligand chemistries on mass transport rates is key to designing membranes\nwith solute-specific selectivity. While permeation cells offer a robust\nmethod to characterize membrane performance, they are limited to assessing\na single membrane chemistry or salt solution per test. As a result,\ninvestigating the effects of varying ligand chemistries on membrane\nperformance can be a tedious process, involving both the preparation\nof multiple samples and numerous, time-consuming permeation tests.\nThis study uses digital light processing (DLP) 3D printing to fabricate\na millifluidic flow-based permeation device made from a hydrogel active\nester network that can be easily functionalized with ion-selective\nligands. Without the need for bonding or assembly steps, ligands can\nbe introduced and tested in the permeation device by simply injecting\na small volume of a ligand solution. Various salt concentrations and\nmolecular species can be cycled through a single device by switching\nthe solution feeding into the salt reservoir, thereby reducing the\nnumber of samples needed for permeability and selectivity screenings.\nThis research sets the groundwork for formulation development and\npostprocessing methods to 3D-print functional millifluidic devices\ncapable of assessing solute selectivity in membranes and polymer adsorbents\nfor aqueous separations. In this work, comparable salt permeability\ntrends were observed with both 3D-printed devices and traditional\nassays. Devices were functionalized with an imidazole ligand to investigate\nsalt permeability and selectivity of monovalent and divalent salts.\nMeasurements showed increasing permeability for monovalent salts (NaCl)\nrelative to divalent salts (MgCl<sub>2</sub>, CuCl<sub>2</sub>) in\nfunctionalized membranes, with higher monovalent/divalent selectivity\nat increasing imidazole grafting densities. The methods and findings\ndescribed here represent a step toward developing higher-throughput\nmethods with 3D-printed devices for screening the effects of ligand\nchemistry on mass transport rates in membrane materials.