‘One-trick ponies’: Tiny robot ‘claw’ grabs marble balls with vapor power

According to researchers, existing soft actuators are often limited to a single type of movement, but this innovative composite film can contort itself in various ways based on the vapor it encounters.

“We hope our findings will be used to develop advanced soft robotic systems capable of precise and adaptable movements in various environments,” said Niveen M. Khashab, a Chemistry Professor at KAUST and the study’s author, told Cell Press.

Versatile soft actuators

Soft actuators, smart materials that convert chemical or physical stimuli into mechanical motion, are valued for their flexibility, adaptability, and high energy density.

These properties have led to their use in diverse applications, such as precision agriculture, deep-sea exploration, wearable devices, and artificial muscles.

However, current soft actuators are limited to single modes of motion, restricting their use in tasks requiring multiple degrees of freedom. To address this, researchers are developing new materials and designs for versatile actuators.

Recent advancements include incorporating organic macrocycles or cage compounds into smart materials, enhancing their actuation modes.

According to researchers, organic cages, with their three-dimensional structures, solubility, and customizability, show promise due to their host-guest chemistry, allowing for guest-induced actuation. Urea-functionalized organic cages, in particular, offer significant potential.

Despite the challenges in their synthesis, advancements in synthetic techniques are making the robust synthesis of urea cages more feasible.

Molecular motion control

In this study, researchers present a soft actuator based on the host-guest interaction of molecular organic cages capable of complex mechanical motions like bending, stretching, contracting, and expanding.

They prepared a responsive composite film by incorporating a novel urea cage into a polymer matrix, demonstrating significant mechanical actuation when exposed to organic vapor.

According to the team, urea cages serve as responsive fillers due to their ability to form multiple hydrogen bonds. They offer sensitive responses to guest molecules and improved mechanical profiles. The actuation mode varies in different vapor atmospheres, categorized into “curvature-stretching-holding-reverting” and “curvature-holding-reverting.”

The actuation process is driven by the crystal phase transformation of the urea cages, triggered by organic vapor. Host-guest interactions between urea cages and solvent molecules, either occupying extrinsic spaces or being encapsulated in intrinsic cavities, lead to crystalline polymorph transformations.

These urea cages act as smart molecular recognition units within the polymer matrix, enabling precise control of the actuation process through vapor stimuli manipulation.

Flexible electronic devices

The team claims that “by judiciously controlling the type and the concentration of the vapor stimulus,” the material the machine is composed of can be “effectively programmed to achieve complex movements.”

“The most remarkable finding was the unique actuation behavior where the soft actuator performed a complex motion involving ‘curvature, stretching, and reverting,’ which had not been reported previously,” said Khashab.

Researchers believe systems may find application in industrial automation, medical equipment, and instruments for measuring humidity, temperature, and air quality.

The team now intends to investigate the claw machine’s energy density and conversion efficiency to improve its performance. They also plan to test its capability to generate electrical signals when combined with materials that produce an electric charge.

The team’s ultimate goal is to use its designs to develop flexible wearable electronic devices.

The details of the team’s research were published in the journal Chem.