Hydrogel Engineering and Imaging Group

Combining expertise in order to


Thomas J. Pence, Professor, Mechanical Engineering

Neil T. Wright, Associate Professor, Mechanical Engineering

Seungik Baek, Assistant Professor, Mechanical Engineering

L. Guy Raguin, Assistant Professor, Mechanical Engineering & Adjunct Assistant Professor, Radiology


Hydrogel Research

Hydrogels are mixtures of cross-linked long chain polymers in an aqueous solvent.  The cross-links prevent the polymer from going into solution.  The thermal, physical and chemical properties of the solvent (i.e. temperature, pH, concentration of other chemical species, etc.) determine the extent to which the solvent interpenetrates the polymer network, and hence determines the concentration of solvent in the hydrogel.   This solvent concentration determines the natural free volume of the hydrogel.  Thus placing an initially dry polymer in an aqueous solution will lead to swelling as the solvent diffuses into the polymer, giving rise to the gel.   Changing the thermal, physical or chemical properties of the solvent will generally lead to a change in the solvent concentration and, in turn, a change in the amount of swelling.  Mechanical loads applied directly to the hydrogel can also drive solvent in and out of the hydrogel, leading to additional volume change.  To the extent that the loading leads to non-uniform stress, such additional volume change can also be non-uniform.  Since these processes involve large deformation, the proper framework for describing the associated macro-scale strain and displacement is that of large (a.k.a. finite) deformation continuum mechanics.  The modern treatment of the associated equilibrium states of solvent penetration and deformation traces back to Flory, Rehner, Treloar, Rivlin and Biot, although the general thermodynamic framework harks back to Gibbs

Recent presentations:

Tom Pence at the IMA, July 2008

These interests can be grouped broadly into

Theoretical Modeling

  1. Modeling gel microstructure: entropic chains, bound & free ions, varied chemical species
  2. Microfluidics, flow, & multi-species diffusion
  3. Chemomechanical coupling, chemical reaction, & phase transformation
  4. Continuum modeling based on finite strain & large deformation
  5. Constitutive relation development: gel elasticity, swelling, viscosity, & dissipation
  6. Self-assembly, growth, remodeling, & allied biomechanics

Experimental Mechanics and Gel System Prototyping

  1. Multiaxial & uniaxial finite deformation
  2. Viscoelastic behavior
  3. Measurement of multiaxial thermal diffusivity
  4. Swelling characterization: thermal & electrochemical activation
  5. Inverse problem algorithms for experimental design, diagnostics, & data analysis
  6. Tissue engineering, optimal scaffolding, & cell-hydrogel interaction

Numerical Simulation

  1. Microstructural representation & response statistics to external stimuli
  2. Continuum representation, finite deformation, large stress: FEA, BE, FD
  3. Environmentally sensitive hydrogels (pH, temperature, glucose, etc)
  4. Continuum numerics with internal variables for microstructural change
  5. Growth & remodeling of cell-seeded hydrogels
  6. Validation of theoretical models

Imaging and Diagnostics

  1. Magnetic resonance: MRI (including microscopic & molecular MRI, flow & diffusion imaging) & NMR spectroscopy at 9.4T, using 1H, 13C, 19F, 23Na, 31P nuclei
  2. Micro-CT
  3. Fluorescence & polarizing light microscopy, immunohistology
  4. 3D visual tracking for time-dependent deformation
  5. TEM, SEM
  6. Inverse problem algorithms for mechanics-based image reconstruction, microstructural information, & functional diagnostics