(Image: uwaterloo.ca)

These tiny robots have the potential to conduct medical procedures — such as biopsy and cell and tissue transport — in a minimally invasive fashion. They can move through confined and flooded environments like the human body and deliver delicate and light cargo, such as cells or tissues, to a target position.

The tiny soft robots are a maximum of one centimeter long and are bio-compatible and non-toxic. The robots are made of advanced hydrogel composites that include sustainable cellulose nanoparticles derived from plants.

The research — published in Nature Communications — portrays a holistic approach to the design, synthesis, fabrication, and manipulation of microrobots. The hydrogel used in this work changes its shape when exposed to external chemical stimulation. The ability to orient cellulose nanoparticles at will enables researchers to program such shape-change, which is crucial for the fabrication of functional soft robots.

"In my research group, we are bridging the old and new," said Shahsavan, who is a Professor in the Department of Chemical Engineering. "We introduce emerging microrobots by leveraging traditional soft matter like hydrogels, liquid crystals, and colloids."

The other unique component of this advanced smart material is that it is self-healing, which allows for programming a wide range in the shape of the robots. Researchers can cut the material and paste it back together without using glue or other adhesives to form different shapes for different procedures.

The material can be further modified with a magnetism that facilitates the movement of soft robots through the human body. As proof of concept of how the robot would maneuver through the body, the tiny robot was moved through a maze by researchers controlling its movement using a magnetic field.

The next step in this research is to scale the robot down to submillimeter scales.

“We are still trying to scale these materials down and this road is very bumpy,” Shahsavan told Tech Briefs in an exclusive interview, the entirety of which can be read below. “The bottleneck is access to equipment, such as microscale 3D printers. Unfortunately, we do not have access to such necessary equipment to make microrobots throughout Canada. We are behind other players of the field, and it’s very hard to catchup without government’s investment or attention. For now, I am working with my collaborators across the ocean to make this happen. They have numerous pieces of equipment for the fabrication of microrobots.”

Here is the interview — edited for length and clarity — with Shahsavan.

Tech Briefs: What was the catalyst for developing these soft robots?

Shahsavan: Small-scale soft robotics is a field of research that focuses on the development of tiny machines that could perform different tasks inside tiny and confined environments, while controlled remotely. One main area of application for such robots is medicine. These robots indeed have potential to be used as miniature surgeons and doctors, in the future, to carry out medical procedures, such as biopsy and tissue transport, none-invasively.

One of the main challenges in the field of small-scale soft robotics is developing a material that has integrated sensing and actuation. Such materials ought to be biocompatible, scalable, and programmable, too. In this work, we introduced a new material that is non-toxic, scalable, programmable, and responsive to external cues such as changes in environmental alkalinity, salinity, and temperature. These materials are programmable, and their stimuli-responsive shape-change can be elicited for robotic functions, such as cargo containment and transport.

Tech Briefs: What were the biggest technical challenges you faced while developing them?

Shahsavan: Aside from the optimization of chemical formulation, the main technical challenge we had was the programming of these materials. For programming, we used shear-force alignment of plant-based rod-like nanoparticles — cellulose nanoparticles. But it was challenging to program our shape-change in a consistent manner, as our method is still manual and naturally carries human-based errors.

Tech Briefs: Can you explain in simple terms how everything works?

Shahsavan: We want to make a hydrogel change its shape the way we want it and the time we want it. For this we synthesized hydrogels that change their shape to change in environmental conditions such as pH and salinity, which is usually simple and uniform expansion/shrinkage in all directions. The shape-change can be programmed, though, to complex profiles.

The first stage of programming was done by the introduction and alignment of cellulose nanoparticles to the hydrogel. Hydrogels containing aligned nanoparticles change their shape non-uniformly. We can use such non-uniformity and engineer complex shape-change.

The second stage of crosslinking was using the adhesive properties of hydrogels to make multi-piece constructs by cutting and pasting already programmed hydrogels. Once a construct with predictable shape-change profile was made, we can use them as robots.

Tech Briefs: Do you have any advice for engineers/researchers aiming to bring their ideas to fruition?

Shahsavan: Never give up on your futuristic ideas, even if they sound crazy, hard, or unimaginable. With small steps at a time, many such ideas can be materialized over time. Of course, it takes time and effort. The secret is to be consistent but persistent.