Mechanical & Materials Engineering, Department of


Date of this Version

Spring 4-25-2014


Rahman, Md Mahmudur, "Application of limited mixing in the Hele-Shaw geometry in fabrication of Janus hydrogels" MS thesis, Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, 2014


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering and Applied Mechanics, Under the Supervision of Professor Sangjin Ryu. Lincoln, Nebraska: May 2014

Copyright (c) 2014 Md Mahmudur Rahman


It is widely accepted that cells behave differently responding to the stiffness of their extracellular matrix (ECM). Such observations were made by culturing cells on hydrogel substrates of tunable stiffness. However, it was recently proposed that cells may sense how strongly they are tethered to ECM, not the local stiffness of ECM. To investigate both hypotheses, we developed a method to fabricate Janus polyacrylamide (PAAM) gels. We squeeze two drops of different concentrations in the Hele-Shaw geometry to generate radial Stokes flow. When the drops coalesce, limited mixing occurs at the interface due to the narrow confinement, and diffusion normal to the interface generates a gradient of the concentration. To test the first hypothesis, we fabricated Janus gel substrates with varying stiffness by coalescing two acrylamide solution drops of different concentrations and then polymerizing them. Based on the indentation test, we confirmed that the fabricated gel had the zone of varying stiffness. To test the second hypothesis, we mimicked protein-gel tethering variation by varying the degree of functionalization of amine and an amine-reactive-dye. We fabricated PAAM gel of uniform stiffness with varying concentration of primary amines by coalescing two drops of same hydrogel solution with different concentrations of primary amines in the same manner. The gel, containing variable primary amines, was submerged in the solution of a fluorescent dye having amine functional groups. Based on fluorescence imaging, we confirmed that the fabricated gel was functionalized to different degrees depending on the concentration distribution of the primary amines. We expect that cells cultured on the Janus gel substrates will behave differently responding to changes in the stiffness and matrix tethering density.

Advisor: Sangjin Ryu