New hydrogel film robot skin will solve three major problems of soft robots

Researchers at the University of Cambridge's Bionic Robotics Laboratory have created a new hydrogel-based skin that uses a series of electrodes and algorithms to allow robots to detect the tactile properties of objects, replicating the human sense of touch and potentially facilitating the development of soft robotics.

According to relevant data, the global market value of soft robots was US$1.049 billion in 2020, and is expected to reach US$6.3 billion in 2026. China's soft robot market will account for 1/4, and the future prospects are very broad.

The skin material of current soft robots is mainly made of silicone, and some also use polyurethane, fluororubber and other materials. The body is composed of multiple connected airbags, which can move through compressed air or liquid, and sensors that detect information such as pressure, deformation and posture are usually embedded in the airbags to control the movement and interaction of the robot.

Although the future market for soft robots is promising, it is still necessary to break through the bottleneck of commercial promotion before soft robots can truly open up the market. Currently, issues such as material properties, control performance, and overall machine cost have become obstacles in the development of soft robots.

Although soft robots have the characteristics of safety and deformability, they still have some shortcomings. First, the elastic materials of soft robots usually have lower stiffness and precision than hard materials, and may not be able to achieve high-precision movement and control; second, the materials currently used, such as silicone, are prone to fatigue and aging during long-term use, which may affect the stability and life of the robot.

The emergence of hydrogel skin can solve the current difficulties. Hydrogel is a polymer material that can simulate the flexibility and light transmittance of human tissue. Compared with traditional materials such as silicone, hydrogel materials have better durability and stability, and are not prone to aging and fatigue. In addition, hydrogel can be more easily embedded with sensors and circuits, allowing robots to have a sense of touch similar to that of humans, greatly enhancing the robot's perception ability.

The use of soft robots is a rigid demand in many scenarios in real life, but the biggest obstacle to the commercialization of soft robots is the insufficient perception and control capabilities, which results in the robot's performance failing to meet expectations, causing customers to be unwilling to use robots to perform certain tasks. However, with the emergence of hydrogel membrane skin, these scenarios may be better compatible with robots.

For example, in the most common medical industry , soft robots can be used in surgery, ward care, rehabilitation treatment, etc. If the surgical robot is equipped with a flexible hydrogel membrane skin that can sense force, the robot can better adapt to the human body and reduce surgical trauma; the nursing robot's hands are equipped with a hydrogel membrane skin that can sense force, which can maximize the effect of simulating human medication, and even control the force more accurately than humans, so that patients can use nursing robots with more confidence, so that nursing robots can be popularized in this usage scenario.

The emergence of hydrogel skin can not only help soft robots obtain information about the external environment such as the position, shape, force and pressure of objects, allowing robots to have the ability to perceive changes in the surrounding environment in real time, but also help robots improve their control capabilities. Through the information transmitted by the skin sensors, the robot can control its own movement and shape more accurately, and learn movement postures through AI technology to complete complex operations and tasks.

The hydrogel skin used by the researchers is biodegradable and very elastic. Combining it with an electrical impedance tomography hard sensor, which uses electrodes at the edge of the skin to apply current and measure voltage, can provide information about the state of the skin, thereby inferring where the artificial skin was touched and whether it was damaged.

According to the researchers, they also tested the potential of the new hydrogel skin in three key real-world applications: injury detection or location, monitoring the environment, and identifying different tactile stimuli. They found that it performed well in all three tasks, indicating that it can be used to enhance the capabilities of soft robotic systems to perform different tasks. The research team is currently working to improve the shape and size of the skin so that it can sense more complex stimuli. For example, when the skin is applied to a robotic hand, it can not only sense the location and force of the skin being touched, but also the position of each finger of the robotic hand and whether the hand is damaged.

The manufacture of this hydrogel membrane is not particularly difficult, and the cost of mass production can be better controlled in the future. It is reported that the hydrogel membrane robot skin is made of gelatin, glycerol, water, citric acid monohydrate, and table salt. After homogenization at 50°C in a ratio of 1:1.5:2.5:0.2:0.1 wt%, the mixture is manually poured into a laser-cut circular polymethyl methacrylate mold with a diameter of 180 mm and a depth of 3 mm. It is left at room temperature for two days to ensure equilibrium with the ambient humidity, and the hydrogel membrane is manufactured.

Low-cost materials and easy-to-achieve processes mean that the difficulty of promoting this technology will be greatly reduced, solving another difficult problem in the commercial application of soft robots.