logo
ResearchBunny Logo
Programmable adhesion and morphing of protein hydrogels for underwater robots

Engineering and Technology

Programmable adhesion and morphing of protein hydrogels for underwater robots

S. Huang, Y. Zhu, et al.

Discover the innovation in soft robotics driven by Sheng-Chen Huang, Ya-Jiao Zhu, Xiao-Ying Huang, Xiao-Xia Xia, and Zhi-Gang Qian. Their research reveals how dynamic underwater robots, constructed from designer protein materials, can seamlessly switch between adhesive and non-adhesive states, leveraging temperature changes for complex tasks in aquatic environments.

00:00
00:00
Playback language: English
Introduction
Underwater soft robots offer significant potential across various applications, from miniaturized medical instruments and sensors to ocean exploration. Their ability to navigate and operate in fluid-immersed environments is particularly advantageous. The development of soft robots often involves the use of smart materials as actuators and sensors, including liquid crystal polymers, dielectric elastomers, and stimuli-responsive hydrogels. However, several challenges hinder their performance and widespread application. A major obstacle is achieving strong and controllable adhesion to diverse surfaces underwater. This adhesive capability is crucial for tasks such as remotely collecting biological samples, transmitting bio-signals, and adhering to tissue damage for repair and healing. Underwater adhesion presents a significant challenge because the formation of a hydration layer interferes with the interaction between the substrate and the adhesive material. Marine organisms provide inspiration, utilizing adhesive proteins and polypeptides to bond dissimilar materials in aquatic environments. Biomimetic approaches have led to the development of various underwater adhesives, frequently incorporating L-3,4-dihydroxyphenylalanine into material designs. However, these adhesives often lack dynamic responsiveness and are susceptible to losing adhesiveness due to catechol group oxidation. Another approach involves complex coacervation of oppositely charged polyelectrolytes through liquid-liquid phase separation, offering tunable adhesion in response to stimuli. Yet, these adhesives typically exhibit poor mechanical properties and lack controllable attachment/detachment behaviors across different substrates, limiting their use in complex robotic tasks.
Literature Review
Existing research on underwater adhesives has primarily focused on two strategies: incorporating L-3,4-dihydroxyphenylalanine (DOPA) and utilizing complex coacervation of polyelectrolytes. DOPA-based adhesives, inspired by mussels, offer strong adhesion but suffer from limitations in dynamic control and susceptibility to oxidation. Polyelectrolyte complex coacervation provides tunable adhesion but often lacks the necessary mechanical strength and control for sophisticated robotic applications. The lack of materials exhibiting both strong, controllable underwater adhesion and suitable mechanical properties for complex robotic manipulation has motivated this research. This study builds upon previous work on resilin-like proteins and polyoxometalates, aiming to create a novel bio-inspired adhesive hydrogel.
Methodology
This study developed a novel gel-type underwater adhesive through the controlled complexation of intrinsically disordered resilin-like proteins (RLPs) and Keggin-type polyoxometalates. Resilin-like protein R32, composed of 32 repeats of a resilin-like block, was chosen for its positive charge and crosslinkable tyrosine residues. The protein was recombinantly produced and purified. The complexation process involved two steps: first, pre-crosslinked R32 protein solution was dropped into a silicotungstic acid (SiW) bath, forming coacervate droplets; second, gentle stirring fused these droplets into aligned fibrils, creating a soft hydrogel. Fourier transform infrared (FTIR) spectroscopy and 183W nuclear magnetic resonance (NMR) spectroscopy confirmed SiW incorporation into the hydrogels. The resulting hydrogels exhibited shape-moldability and aligned microfibrillar structures. Mechanical properties were characterized using dynamic mechanical analysis (DMA) and uniaxial tensile tests across a range of temperatures, revealing a temperature-dependent reversible switch between rigid (high modulus, low strain) and soft (low modulus, high strain) states. Underwater adhesion was evaluated using probe-tack tests on various substrates, demonstrating adhesion to both hydrophilic and hydrophobic surfaces and biological tissues. The temperature at which maximum adhesion occurred was tunable by controlling the degree of di-tyrosine crosslinking in the R32 protein. A warm-attaching and cooling method was developed to enhance underwater adhesion. To enable remote control, magnetic Fe3O4 nanoparticles were integrated into the hydrogels, creating photothermally and magnetically responsive soft robots. The photothermal properties were characterized by measuring the temperature increase upon infrared (IR) light illumination. The performance of the resulting robots was demonstrated through complex tasks, including multi-cargo capture and delivery and artificial blood vessel repair.
Key Findings
The key findings of this study demonstrate the successful creation of a novel protein hydrogel with programmable adhesion and morphing capabilities for underwater robotics. The hydrogel, formed by complexing resilin-like protein R32 with silicotungstic acid (SiW), exhibits a reversible transition between a rigid, non-adhesive state and a soft, adhesive state within a narrow temperature range. The transition temperature is tunable by varying the degree of di-tyrosine crosslinking in the R32 protein. The hydrogels exhibit strong underwater adhesion (30-40 kPa), comparable to many reported bioadhesive hydrogels. A novel warm-attaching and cooling method was developed to significantly enhance underwater adhesion. The incorporation of magnetic Fe3O4 nanoparticles enables remote control of the hydrogel's properties through IR light irradiation and magnetic fields. The resulting soft robots successfully performed complex tasks: (1) capturing and delivering multiple cargoes in water; (2) repairing a simulated blood vessel leak. The thermo-responsive properties of the hydrogel allow for rapid switching between adhesive and non-adhesive states (within 9 seconds for a 10°C temperature change), highlighting the dynamic nature of the electrostatic interactions between the protein and polyoxometalate. The combination of mechanical strength, reversible adhesion, and remote actuation makes this a promising material for advanced underwater robots.
Discussion
This research addresses the critical need for materials with both strong, controllable underwater adhesion and suitable mechanical properties for complex robotic manipulations. The findings demonstrate that the designed protein hydrogel successfully achieves this goal. The tunable temperature-dependent switch between adhesive and non-adhesive states, coupled with remote control via IR light and magnetic fields, opens up new possibilities for underwater robotics. The biocompatibility of the protein-based hydrogel also suggests potential biomedical applications, such as minimally invasive surgery and targeted drug delivery. The success of the multi-cargo capture and blood vessel repair experiments showcases the potential of these soft robots for realistic applications. The study's findings advance the field of soft robotics by providing a new bio-inspired material platform with superior performance characteristics compared to existing underwater adhesives.
Conclusion
This study successfully designed and constructed a protein hydrogel-based adhesive for biomimetic underwater robots. The hydrogel's programmable adhesion and morphing capabilities, enabled by dynamic electrostatic interactions and remote control via IR light and magnetic fields, demonstrate significant advancements in soft robotics. The successful completion of complex tasks highlights the potential of this material for diverse applications. Future research could focus on optimizing the robot design for enhanced speed and efficiency, exploring new functionalities through the integration of additional sensors, and expanding applications to more complex underwater environments.
Limitations
While the developed hydrogel robots demonstrate impressive capabilities, some limitations exist. The response time for shape morphing using magnetic actuation is relatively slow (3-8 minutes), primarily due to the relatively weak magnetic field strength and the low content of Fe3O4 nanoparticles. The shape recovery after elongation is not complete. However, the hydrogel's dynamic nature allows for thermal remolding, suggesting good reusability. Further investigation is needed to optimize the nanoparticle concentration and magnetic field strength to improve response times and shape recovery.
Listen, Learn & Level Up
Over 10,000 hours of research content in 25+ fields, available in 12+ languages.
No more digging through PDFs, just hit play and absorb the world's latest research in your language, on your time.
listen to research audio papers with researchbunny