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Fabrication of Hydrogels with a Stiffness Gradient Using Limited Mixing in the Hele-Shaw Geometry

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Abstract

Hydrogel substrates with a stiffness gradient have been used as a surrogate of the extracellular matrix (ECM) to investigate how cells respond to the stiffness of their surrounding matrix. Various fabrication methods have been proposed to create a stiffness gradient in the hydrogel substrate, and some of them rely on generating a concentration gradient in a prepolymer solution before photo-polymerization. One easy way to do so is to coalesce two prepolymer solution drops of different stiffness values in a narrow confinement formed by two glass surfaces and then to induce polymerization using ultraviolet (UV) light irradiation, as proposed by Lo et al. [Biophys. J. 2000, 79:144–152]. We have improved their method to enable modulating the obtained stiffness gradient and characterized fabricated polyacrylamide (PAAM) gels. We controlled the coalescence and mixing duration of two prepolymer drops using the lab-built Hele-Shaw cell device and glass surfaces with a superhydrophobic barrier. Limited mixing between the drops created a concentration gradient of the gel ingredient, which was converted to a stiffness gradient by UV-based photo-polymerization. Atomic force microscopy (AFM) indentation showed that the fabricated gels had the stiffness gradient zone at the center and that the width of the zone increased with the mixing duration.

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Acknowledgements

This study was supported by Bioengineering for Human Health grant from the University of Nebraska-Lincoln (UNL) and the University of Nebraska Medical Centre (UNMC). KG appreciates UNL Undergraduate Creative Activities and Research Experiences (UCARE) program, and AM and BG appreciate UNL Summer Research Program and NSF Research Experiences for Undergraduates (REU) grant. AFM measurements were performed at the NanoEngineering Research Core Facility of UNL (part of the Nebraska Nanoscale Facility), which is partially funded from Nebraska Research Initiative Funds.

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Author notes

  1. D. Lee

    Present address: Department of Genetics, Cell Biology and Anatomy, University of Nebraska Medical Center, Omaha, NE, 68198, USA

  2. Md. M. Rahman

    Present address: Department of Mechanical Engineering, University of Louisville, Louisville, KY, 40292, USA

  3. A. Moran

    Present address: Department of Biomedical Engineering, University of Florida, Gainesville, FL, 32611, USA

  4. B. Gonzalez

    Present address: Department of Biomedical Engineering, Florida International University, Miami, FL, 33174, USA

Authors and Affiliations

  1. Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA

    D. Lee, Md. M. Rahman & S. Ryu

  2. School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA

    K. Golden

  3. Department of Agricultural and Biological Engineering, University of Florida, Gainesville, FL, 32611, USA

    A. Moran

  4. Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA

    B. Gonzalez

  5. Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA

    S. Ryu

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  1. D. Lee
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Lee, D., Golden, K., Rahman, M.M. et al. Fabrication of Hydrogels with a Stiffness Gradient Using Limited Mixing in the Hele-Shaw Geometry. Exp Mech 59, 1249–1259 (2019). https://doi.org/10.1007/s11340-018-0416-1

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