Force-clamp rheometry for characterizing protein-based hydrogels

Luai R. Khoury, Joel Nowitzke, Narayan Dahal, Kirill Shmilovich, Annie Eis, Ionel Popa

Research output: Contribution to journalArticlepeer-review


Here, we describe a force-clamp rheometry method to characterize the biomechanical properties of protein-based hydrogels. This method uses an analog proportional-integral-derivative (PID) system to apply controlled-force protocols on cylindrical protein-based hydrogel samples, which are tethered between a linear voice-coil motor and a force transducer. During operation, the PID system adjusts the extension of the hydrogel sample to follow a predefined force protocol by minimizing the difference between the measured and set-point forces. This unique approach to protein-based hydrogels enables the tethering of extremely low-volume hydrogel samples (< 5 µL) with different protein concentrations. Under force-ramp protocols, where the applied stress increases and decreases linearly with time, the system enables the study of the elasticity and hysteresis behaviors associated with the (un)folding of proteins and the measurement of standard elastic and viscoelastic parameters. Under constant-force, where the force pulse has a step-like shape, the elastic response, due to the change in force, is decoupled from the viscoelastic response, which comes from protein domain unfolding and refolding. Due to its low-volume sample and versatility in applying various mechanical perturbations, force-clamp rheometry is optimized to investigate the mechanical response of proteins under force using a bulk approach.

Original languageEnglish
Article numbere58280
JournalJournal of Visualized Experiments
Issue number138
StatePublished - 21 Aug 2018
Externally publishedYes


  • Biomaterials elasticity
  • Engineering
  • Force spectroscopy
  • Force-clamp rheometry
  • Issue 138
  • Protein unfolding under force
  • Protein-based hydrogels
  • Smart materials

All Science Journal Classification (ASJC) codes

  • General Chemical Engineering
  • General Immunology and Microbiology
  • General Biochemistry,Genetics and Molecular Biology
  • General Neuroscience


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