In a recent article published in the journal Nature Communications, researchers introduced an innovative design strategy for soft robots that mimic the integration of skeletal muscles and sensory skins in living organisms. They demonstrated examples of robotic implants capable of sensing various stimuli and responding with on-demand actuation inside the body.
Schematic illustration showing bio-inspired sensory robots as minimally invasive smart implants for diagnosis, stimulation, and drug delivery. Image Credit: https://www.nature.com/articles/s41467-024-48903-z
Background
Soft robotics is a field of engineering focused on developing robots that are flexible, adaptable, and biocompatible, drawing inspiration from natural systems like animals and plants. These robots hold promise for various applications, including medical technology, wearable devices, and human-robot interaction. However, a significant challenge in soft robotics is seamlessly and robustly integrating sensing and actuation capabilities, particularly for implantable devices operating in complex and dynamic environments.
About the Research
In this paper, the authors proposed a new design strategy for skin-inspired sensory robots that integrate actuators, sensors, and stimulators through biomimicry. The primary components of these soft robots were an electronic skin (e-skin) layer and an artificial muscle layer made of thermally responsive poly(N-Isopropylacrylamide) polymer (PNIPAM) hydrogel to generate adaptive motion.
The e-skin layer comprised diverse sensing materials, such as silver nanowires, reduced graphene oxide, MXene, and conductive polymers, embedded within a polymer matrix like polyimide. It could sense various stimuli, including pressure, temperature, potential hydrogen (pH), and electrical signals, and transmit them to the artificial muscle layer for on-demand actuation, such as bending, expanding, twisting, and drug delivery.
The flexible multi-modal e-skin was fabricated using an in-situ solution-based approach, allowing the incorporation of a wide range of functional materials into a polymeric matrix to form various types of sensors (e.g., temperature, pressure, and strain) with high spatiotemporal resolution. Biomimetic designs inspired by starfish and chiral seedpods were used to enable various motions with tissues. Additionally, a battery-free wireless module was integrated into the soft robots to allow untethered operation and communication with external devices.
The study demonstrated four examples of robotic implants using the e-skin and artificial muscle layers: a robotic cuff for monitoring blood pressure, an ingestible robot for pH sensing and drug delivery, a robotic gripper for measuring bladder volume, and a robotic patch for assessing cardiac function and delivering electrotherapy. Furthermore, the performance and biocompatibility of these robotic implants were tested both in vitro and in vivo, using animal models and human subjects.
Research Findings
The outcomes showcased that the newly designed robot achieved high sensitivity, accuracy, and stability in sensing various stimuli and responding with on-demand actuation. This actuation was triggered by electrothermal stimulation from electrical heaters embedded in the e-skin layer. The authors also explored the bioadhesive behavior of their devices on targeted tissues and organs, observing that the hydrogel's inherent adhesiveness was significantly related to its water content and temperature.
Additionally, the robotic cuff effectively measured the blood pressure of a rat and triggered a drug delivery system when the pressure exceeded a threshold. The robotic gripper tracked the bladder volume of a pig and released the bladder when it was full. The ingestible robot sensed the pH of a pig's stomach and delivered an antacid drug when the pH was low. Furthermore, the robotic patch quantified the cardiac function of a human and delivered electrotherapy when the heart rate was abnormal.
Finally, the study confirmed that the presented robots were biocompatible and wireless, causing no adverse effects or inflammation in the tissues. It claimed that the design strategy was universal and scalable, applicable to a wide range of responsive and sensing materials, forming integrated soft robots for biomedical technology and beyond.
Applications
The newly designed sensory robot has significant potential in the field of medical technology. These robotic implants offer tailored and accurate healthcare solutions, catering to individual patient needs. For example, they can regulate blood pressure levels dynamically, ensuring optimal cardiovascular health. Additionally, the ability of robotic grippers to track bladder volume and release contents as needed presents a groundbreaking approach to managing urinary issues, enhancing patient comfort and quality of life.
Moreover, the ingestible robot's capability to sense gastric pH levels and administer targeted medication represents a significant advancement in gastrointestinal health management. Delivering antacid drugs precisely when needed can help prevent gastric ulcers and alleviate associated discomfort.
Furthermore, the robotic patch's capacity to assess cardiac function and provide electrotherapy interventions offers a proactive approach to addressing cardiovascular conditions, potentially reducing the risk of adverse cardiac events. Beyond medical technology, these soft robots could be used in other fields, such as environmental monitoring, where their ability to adapt and respond to various stimuli could be invaluable.
Conclusion
In summary, the development of skin-inspired, sensory soft robots represented a significant advancement in the field of biomedical robotics. By closely mimicking the combination of motor and sensor functions found in biological systems, these soft robots offered a promising solution for safely interacting with dynamic, unstructured environments and interfacing with biological tissues and organs.
Moving forward, the researchers suggested directions for future work. They recommended improving the biodegradability, biostability, and biointegration of the soft robots, as well as exploring new applications and functionalities. Additionally, they highlighted the importance of enhancing the long-term performance and reliability of these robots in various physiological conditions.
Journal Reference
Zhang, L., Xing, S., Yin, H. et al. Skin-inspired, sensory robots for electronic implants. Nat Commun 15, 4777 (2024). https://doi.org/10.1038/s41467-024-48903-z, https://www.nature.com/articles/s41467-024-48903-z.
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