"For the last few decades, cell or tissue sheets have been increasingly used to treat injured or diseased tissues. A crucial aspect of tissue transplantation surgery, such as corneal tissue transplantation surgery, is surgical gripping and safe transplantation of soft tissues. However, handling these living substances remains a grand challenge because they are fragile and easily crumple when picking them up from the culture media," said study leader Hyunjoon Kong, a professor of chemical and biomolecular engineering at Illinois.

Kong's group, along with collaborators at Purdue University, the University of Illinois at Chicago, Chung-Ang University in South Korea, and the Korea Advanced Institute for Science and Technology, published their work in the journal Science Advances.

Current methods of transferring the sheets involve growing them on a temperature-sensitive soft polymer that, once transferred, shrinks and releases the thin film. However, this process takes 30-60 minutes to transfer a single sheet, requires skilled technicians and runs the risk of tearing or wrinkling, Kong said.

"During surgery, surgeons must minimize the risk of damage to soft tissues and transplant quickly, without contamination. Also, transfer of ultrathin materials without wrinkle or damage is another crucial aspect," Kong said.

Seeking a way to quickly pick up and release the thin, delicate sheets of cells or electronics without damaging them, the researchers turned to the animal kingdom for inspiration. Seeing the way an octopus or squid can pick up both wet and dry objects of all shapes with small pressure changes in their muscle-powered suction cups, rather than a sticky chemical adhesive, gave the researchers an idea.

They designed a manipulator made of a temperature-responsive layer of soft hydrogel attached to an electric heater. To pick up a thin sheet, the researchers gently heat the hydrogel to shrink it, then press it to the sheet and turn off the heat. The hydrogel expands slightly, creating suction with the soft tissue or flexible electronic film so it can be lifted and transferred. Then they gently place the thin film on the target and turn the heater back on, shrinking the hydrogel and releasing the sheet.

The entire process takes about 10 seconds. Video: https://www.youtube.com/watch?v=EhMySEk-lRw&feature=emb_logo

Next, the researchers hope to integrate sensors into the manipulator, to further take advantage of their soft, bio-inspired design.

"For example, by integrating pressure sensors with the manipulator, it would be possible to monitor the deformation of target objects during contact and, in turn, adjust the suction force to a level at which materials retain their structural integrity and functionality," Kong said. "By doing so, we can improve the safety and accuracy of handling these materials. In addition, we aim to examine therapeutic efficacy of cells and tissues transferred by the soft manipulator."

Story Source:

Materials provided by University of Illinois at Urbana-Champaign, News Bureau. Original written by Liz Ahlberg Touchstone. Note: Content may be edited for style and length.

Journal Reference:

1. Byoung Soo Kim, Min Ku Kim, Younghak Cho, Eman E. Hamed, Martha U. Gillette, Hyeongyun Cha, Nenad Miljkovic, Vinay K. Aakalu, Kai Kang, Kyung-No Son, Kyle M. Schachtschneider, Lawrence B. Schook, Chenfei Hu, Gabriel Popescu, Yeonsoo Park, William C. Ballance, Seunggun Yu, Sung Gap Im, Jonghwi Lee, Chi Hwan Lee, Hyunjoon Kong. Electrothermal soft manipulator enabling safe transport and handling of thin cell/tissue sheets and bioelectronic devices. Science Advances, 2020; 6 (42): eabc5630 DOI: 10.1126/sciadv.abc5630