Self-folding thermo-magnetically responsive soft microgrippers

ACS Appl Mater Interfaces. 2015 Feb 11;7(5):3398-405. doi: 10.1021/am508621s. Epub 2015 Jan 28.


Hydrogels such as poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-AAc) can be photopatterned to create a wide range of actuatable and self-folding microstructures. Mechanical motion is derived from the large and reversible swelling response of this cross-linked hydrogel in varying thermal or pH environments. This action is facilitated by their network structure and capacity for large strain. However, due to the low modulus of such hydrogels, they have limited gripping ability of relevance to surgical excision or robotic tasks such as pick-and-place. Using experiments and modeling, we design, fabricate, and characterize photopatterned, self-folding functional microgrippers that combine a swellable, photo-cross-linked pNIPAM-AAc soft-hydrogel with a nonswellable and stiff segmented polymer (polypropylene fumarate, PPF). We also show that we can embed iron oxide (Fe2O3) nanoparticles into the porous hydrogel layer, allowing the microgrippers to be responsive and remotely guided using magnetic fields. Using finite element models, we investigate the influence of the thickness and the modulus of both the hydrogel and stiff polymer layers on the self-folding characteristics of the microgrippers. Finally, we illustrate operation and functionality of these polymeric microgrippers for soft robotic and surgical applications.

Keywords: NIPAM; polypropylene fumarate; robotics; smart materials; stimuli responsive materials; surgery.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acrylates / chemistry
  • Acrylates / radiation effects
  • Acrylic Resins / chemistry
  • Acrylic Resins / radiation effects
  • Equipment Design
  • Equipment Failure Analysis
  • Hydrogels / chemistry*
  • Hydrogels / radiation effects
  • Magnetic Fields
  • Magnetics / instrumentation*
  • Magnetite Nanoparticles / chemistry*
  • Magnetite Nanoparticles / radiation effects
  • Micromanipulation / instrumentation*
  • Robotic Surgical Procedures / instrumentation*
  • Temperature


  • Acrylates
  • Acrylic Resins
  • Hydrogels
  • Magnetite Nanoparticles
  • poly-N-isopropylacrylamide
  • acrylic acid