Foamy Soft Robotics: How Foams Might Lead to Advanced Wearable Technology

Rice University engineers harness the potential of open-cell foam to perform digital computation and analogue sensing in soft textile-based wearable systems.

When envisioning the future of wearable technology and robotics, the humble foam filling in your couch is not the first material that comes to mind. However, engineers at Rice University have demonstrated that the airflow through the porous structure of open-cell foam can be used for digital computation, analogue sensing, and combined control tasks in next-generation soft textiles.

“In this work, we integrated material intelligence—the ability of materials to sense and respond to their environment—with circuit-driven logic using a surprisingly simple approach based on the flow of fluid through soft foams,” stated Daniel Preston, assistant professor of mechanical engineering and corresponding author of a study recently published in Advanced Functional Materials.

Traditional pneumatic logic circuits in soft robotics and wearables emulate electronic circuits by connecting components like resistors, capacitors, diodes, and gates. These conventional designs depend on interconnected logic gates, fundamental in digital systems, to produce a single output from multiple inputs. However, this architecture typically increases the complexity, weight, cost, and potential failure points of the devices.

Previously, the Preston Innovation Laboratory pioneered an electronics-free method for controlling textile wearables using pneumatic logic circuits. However, this initial approach did not fully exploit the intrinsic properties of soft materials to optimise circuit design efficiency. Preston noted, “The more complex a task or operation, the greater the number of logic gates typically required.”

To address this issue, researchers have leveraged the pressure differences created by airflow through the microscopic pores in foam sheets. This innovative approach allows for complex pneumatic computations and control tasks, enhancing circuit design economy. “Here, we show that the properties of soft materials themselves—such as the sponginess or porosity of foam sheets—can be leveraged to achieve fluidic control tasks such as sensing the amount of force applied by a user or converting digital pressure signals to analogue signals, thereby reducing the reliance on fluidic logic gates and simplifying operation,” explained Anoop Rajappan, the study’s lead author.

Unlike liquids, air density varies with pressure, complicating the modelling of airflow through foam sheets. The researchers developed a theoretical framework to analyse gas flow through porous materials, new experimental techniques to measure the fluidic properties of foam, and a model for the change in fluidic resistance of foam under applied force. They designed foam-based fluidic resistors, which restrict airflow in pneumatic circuits, similar to how electronic resistors limit current flow in electronic circuits. These resistors enable the creation of two-dimensional pneumatic logic circuits that can be integrated into textile-based wearable devices.

“By redesigning circuit components such as resistors to leverage the fluidic properties of soft materials like foam, we can build reliable and streamlined soft robots and wearable devices powered by pneumatics that are less dependent on heavy, bulky or rigid components such as motors and batteries,” Rajappan said. This advancement in material utilisation could significantly benefit wearable robotic devices, providing mobility assistance through comfortable, lightweight, low-cost, and unobtrusive designs powered by compressed air.

For more detailed information, you can access the full paper “Embedded Fluidic Sensing and Control with Soft Open‐Cell Foams” published in Advanced Functional Materials.