Dynamically Tunable Friction via Subsurface Stiffness Modulation

Siavash Sharifi, Caleb Rux, Nathaniel Sparling, Guangchao Wan, Amir Mohammadi Nasab, Arpith Siddaiah, Pradeep Menezes, Teng Zhang, Wanliang Shan

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Currently soft robots primarily rely on pneumatics and geometrical asymmetry to achieve locomotion, which limits their working range, versatility, and other untethered functionalities. In this paper, we introduce a novel approach to achieve locomotion for soft robots through dynamically tunable friction to address these challenges, which is achieved by subsurface stiffness modulation (SSM) of a stimuli-responsive component within composite structures. To demonstrate this, we design and fabricate an elastomeric pad made of polydimethylsiloxane (PDMS), which is embedded with a spiral channel filled with a low melting point alloy (LMPA). Once the LMPA strip is melted upon Joule heating, the compliance of the composite structure increases and the friction between the composite surface and the opposing surface increases. A series of experiments and finite element analysis (FEA) have been performed to characterize the frictional behavior of these composite pads and elucidate the underlying physics dominating the tunable friction. We also demonstrate that when these composite structures are properly integrated into soft crawling robots inspired by inchworms and earthworms, the differences in friction of the two ends of these robots through SSM can potentially be used to generate translational locomotion for untethered crawling robots.

Original languageEnglish (US)
Article number691789
JournalFrontiers in Robotics and AI
StatePublished - Jul 1 2021


  • dynamically tunable friction
  • low melting point alloy
  • soft robots
  • subsurface stiffness modulation
  • untethered crawling robots

ASJC Scopus subject areas

  • Computer Science Applications
  • Artificial Intelligence


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