Rheological and printing behaviour of inks and matrix materials. Courtesy of An integrated design and fabrication strategy for entirely soft, autonomous robots.
Unlike traditional rigid robots, soft robots made from compliant materials such as hydrogels and shape memory polymers closely mimic human tissue properties. As a result, they can operate within the human body with minimal disruption, reducing injury risk and improving therapeutic precision. Furthermore, material science and microfabrication advances have significantly expanded their capabilities and clinical relevance.
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Hydrogel-based continuum soft robots demonstrated in vitro and in vivo include: (a) magnetically controlled microrobots for targeted drug delivery; (b) micro- and nano-scale robots designed for precise therapeutic delivery; (c) skin-inspired hydrogel sensors for real-time monitoring; and (d) spinning-designed, weaveable hydrogel fiber robots for wearable applications. Courtesy of Hydrogel-Based Continuum Soft Robots.
Among soft materials, hydrogels stand out due to their high water content, softness, and excellent biocompatibility. They are particularly valuable in soft robotics because they can respond to external stimuli like temperature, pH, light, and magnetic fields. Consequently, they enable programmable deformation, eliminating the need for motors or mechanical joints. Moreover, hydrogel systems can be designed to react autonomously, which enhances their functionality in dynamic biological environments. For example, researchers developed a biodegradable magnetic hydrogel robot that delivers chemotherapy drugs by shifting between locomotion modes. Likewise, ultrasound-responsive hydrogels promote bone healing by stabilizing stem cells and countering oxidative stress through acoustic stimulation. These innovations highlight the versatility of hydrogel actuators and their therapeutic potential in precision medicine.
In addition to their actuation properties, hydrogels play a central role in bio-inspired soft devices. Specifically, soft microrobots composed of gelatin-based hydrogels have demonstrated the ability to cross the blood–brain barrier, a feat rarely achieved by conventional drug carriers. This enables localized delivery of chemotherapy for glioma treatment, which increases efficacy while minimizing systemic toxicity. Furthermore, hydrogel-based wearables now monitor motion and pressure, aiding patients during physical therapy and rehabilitation. These systems not only detect strain and deformation but also provide feedback for controlled movement. Therefore, hydrogel-integrated wearables contribute to both diagnosis and recovery in clinical settings.
Fabrication techniques for manufacturing soft robots.Courtesy of Emerging soft medical robots for clinical translations from diagnosis through therapy to rehabilitation.
To support complex medical tasks, researchers are increasingly turning to 3D and 4D printing technologies. These allow the fabrication of sophisticated hydrogel architectures that change shape or function in response to environmental triggers. Notably, 4D-printed hydrogels expand or contract post-implantation, making them useful for applications such as wound sealing or tissue scaffolding. In terms of actuation, various control mechanisms are in use. For instance, magnetic fields allow remote control, while light and heat enable precise spatial activation. Chemical stimuli, including pH shifts, also drive targeted behaviors, particularly in microenvironments like tumors. By integrating multiple types of control, engineers are creating highly tunable systems with enhanced responsiveness.
| Feature | Description | Application Example |
|---|---|---|
| Stimuli-responsive behavior | Reacts to pH, light, temperature, solvent, or magnetic fields | Controlled drug delivery (glioma, retina) |
| Biocompatibility | Compatible with tissue; minimizes immune response and damage | Implantable soft actuators and sensors |
| Multi-modal actuation | Enables bending, swelling, twisting, or rolling via external/internal stimuli | Rehabilitation aids and tumor navigation |
| Programmable shape-shifting | 4D printing allows shape transformation post-implantation | Wound sealing and tissue scaffolding |
| Integrated sensing capabilities | Monitors pressure, strain, temperature, or environment changes | Wearable medical sensors and robotic skins |
Notably, the field has grown rapidly in both academic and commercial sectors.
For instance, soft robotics publications have increased from just 20 in 2005 to nearly 600 in 2024, reflecting an explosion of research activity. At the same time, patent filings reached nearly 10,000 by 2016, driven by innovations such as the Da Vinci robotic system and emerging soft robotic tools. As a result, soft robots are expanding beyond operating rooms into diagnostics, therapeutics, and home-based rehabilitation systems.
In summary, hydrogel-based soft robots are redefining how medicine approaches diagnosis, treatment, and rehabilitation. Their softness, adaptability, and responsiveness allow them to operate safely and effectively within the human body. As fabrication methods improve and regulatory pathways clarify, these robots are poised to become indispensable tools in personalized and minimally invasive care. Ultimately, the convergence of soft materials and intelligent actuation is not just a trend—it is a paradigm shift in medical robotics.
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