In a recent study published in Cell Reports Physical Science, researchers introduced a new method called perforation-type anchors to attach living skin to robots. They used a technique inspired by nature to securely connect skin to robotic structures. The main goal was to achieve a strong and seamless integration of living skin with robot parts, which is crucial for developing advanced biohybrid robots with self-healing and human-like features.
Study: Biohybrid Robots: Seamlessly Integrating Living Skin. Image Credit: Jounn/Shutterstock.com
Background
In recent years, the development of robotic skin materials has progressed significantly to help humanoid robots work better in complex and unpredictable environments. Traditional robotic skins include features like touch sensitivity, self-repair, sweating or perspiration, and a human-like look. However, these materials still lack the full biological functions of real skin.
Cultured skin, made of living cells and extracellular matrix, offers a promising alternative because it can mimic human skin’s biological functions and capabilities, including self-healing. This progress is particularly important for keeping robots functional in changing environments.
About the Research
In this paper, the authors focused on developing and characterizing a perforation-type anchor system inspired by the structure of human skin ligaments to effectively adhere skin equivalents to robotic surfaces. Traditional methods of attaching cultured skin to robots face challenges like deformation and risk of damage due to the lack of effective fixation mechanisms.
The novel anchors, designed to mimic the skin ligaments, offer a solution by providing secure attachment without compromising the robot's aesthetic integrity. Skin ligaments, composed primarily of collagen and elastin, are tiny connecting tissues that anchor the skin to underlying tissues, enabling fluid facial expressions and bodily motions.
The system involves creating V-shaped holes in the robot's structure, which are filled with a gel containing skin-forming cells. This gel, made of collagen and fibroblasts, solidifies within the holes to form a secure anchor point for the skin equivalent.
To improve the gel's penetration, the researchers used a water-vapor-based plasma treatment. This treatment makes the robot's surface more hydrophilic, facilitating the gel's entry and ensuring a strong bond between the skin and the robotic surface.
Furthermore, tensile tests and contraction tests were performed to validate the perforation-type anchor system. The authors also conducted computer simulations to evaluate the impact of anchor number and arrangement on anchoring performance.
Research Findings
The plasma treatment significantly improved the wettability of the device surface, enhancing collagen gel penetration into the perforation-type anchors. This improvement showed a reduction in the collagen contact angle from 37.9° to 15.6° and an increase in the collagen spreading area from 18.0 mm² to 38.2 mm² on plasma-treated surfaces compared to normal ones.
The contraction tests demonstrated that the new anchors effectively prevented the contraction of dermis equivalents. Devices without anchors experienced up to 84.5 % contraction, while those with 3-mm anchors limited contraction to 26.3 %. Even small-diameter anchors restrained tissue contraction, with 3-mm anchors showing the highest resistance to shrinkage.
The tensile tests revealed that anchoring strength increased with the diameter of the perforation-type anchors. Devices without anchors had a maximum tensile strength of approximately 0.03 N, while those with 5-mm anchors exhibited a tensile strength of 0.51 N, showing superior ability to withstand external forces without detaching the skin equivalent.
Additionally, the simulations showed that increasing the number of anchors enhances the skin equivalent's resistance to tensile stress, distributing the applied force more evenly across multiple anchor points.
Furthermore, the versatility of the perforation-type anchors was demonstrated through two applications. First, a facial mold was constructed and covered with a skin equivalent. The skin equivalent was tightly secured to the device, preventing detachment even when pulled with force.
A robotic face was also developed, covered with a dermis equivalent and a silicone layer, connected to a slider via the perforation-type anchors. The sliding motion of the actuator deformed the silicone layer, selectively actuating the dermis equivalent to generate a smiling expression.
Applications
The developed anchor has significant implications in the field of biohybrid robotics. It can be applied to humanoid robots designed for social interactions, healthcare, and service industries, where a human-like presence is essential.
Additionally, the ability of robots to self-heal minor damages improves their longevity and reduces maintenance costs. Furthermore, the outcomes from this paper can contribute to the broader field of tissue engineering, offering insights into effective tissue fixation techniques that can be applied in medical and biotechnological applications.
Conclusion
In summary, the novel approach effectively attached skin to the robot's surface without causing contraction. This method offers a secure, aesthetically pleasing, and biocompatible solution for integrating living skin into robotic designs. Furthermore, this research opens directions for exploring biomimetic design in robotics, aiming to mimic human body structures and functionalities. This approach can lead to robots that are more adaptable, resilient, and capable of complex tasks.
Moving forward, the researchers acknowledged the need for further optimization of the perforation-type anchor system and its exploration for other applications. They also emphasized the importance of studying the long-term effects of this system on the health and functionality of living skin.
Journal Reference
Kawai, M., Nie, M., Oda, H, Takeuchi, S. Perforation-type anchors inspired by skin ligament for robotic face covered with living skin. Cell Reports Physical Science, 2024, 102066. DOI: 10.1016/j.xcrp.2024.102066, https://www.cell.com/cell-reports-physical-science/fulltext/S2666-3864%2824%2900335-7
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