Hydrogel Actuators and Sensors for Biomedical Soft Robots: Brief Overview with Impending Challenges
Abstract
:1. Introduction
2. Hydrogel-Based Soft Actuators
2.1. Thermo-Sensitive Hydrogel Actuators
2.2. Electro-Responsive Hydrogel Actuators
2.3. Magneto-Responsive Hydrogel Actuators
2.4. Biomimetic Hydrogel Actuators
Key Limitations
2.5. Miscellaneous
3. Hydrogel-Based Biomedical Sensors
3.1. Glucose Sensors
3.2. Touch/Stress/Stretch Sensors
3.3. Ionic Strength Sensing for pH Ions
3.4. Temperature Sensors
3.5. Living Hydrogel Sensors
3.6. Biochemical Sensing Mechanisms
4. Different Hydrogel Structures: An Overview from a Mechanical Standpoint
4.1. Single-Phase Gels
4.2. Multi-Phase Gels
4.3. Double-Network Gels
5. Mechanical Properties: Robust, Tougher, and Stretchable Hydrogels
6. Rapid Prototyping Tools: Hydrogel-Based 3D Printing for Biomedical Soft Robots
7. Self-Healing Hydrogels for Soft Robotics
8. Conclusions and Future Challenges
Author Contributions
Funding
Conflicts of Interest
References
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Hydrogels | Silicone Elastomers |
---|---|
Excellent water-absorbing properties | Excellent elastic properties |
Volume changes with external stimuli | Less responsive to external stimuli |
Preferred as biomaterials, e.g., dressing wounds | Chemically inert and more toxic |
Absorb body fluids; very soft and bendable | Good absorbers of gases |
Excellent transport properties, e.g., controlling drugs and nutrient release | Generally hydrophobic; cannot retain fluids |
Semi-solid/liquid state; better relaxation behavior | Mixed with hydrogels give better hydrophilic properties |
Mostly water; hence better fire-retardant skin-based devices | Better oxygen permeability and transport |
Gelatin is hemostatic; hence faster wound healing | Highly viscous and hydrophobic |
Better mechanical strength in composite, better self-healing time, etc. | Less responsive |
Resist protein adsorption; good wettability; can be used in soft contact lenses | Less likely to be used |
Adaptable to small, delicate structures | Inability to adapt to small scale |
Relatively complex preparation protocol | Ease of preparation |
Actuator | Energy Density (J cm) | Elongation (%) | Pressure (MPa) | Response Time (ms) |
---|---|---|---|---|
Solenoids | 0.025 | 50 | 0.1 | 5 |
Piezo-actuators | 0.05 | 0.2 | 110 | 0.5 |
Magnetostrictive | 0.025 | 0.2 | 70 | 0.4 |
Electrostrictive | 0.17 | 32 | 2 | 2 |
Shape-memory alloy | 10 | 8 | 900 | 300 |
Hydrogels | 0.35 | 90 | 4 | 300 |
Electrochemical | 0.14 | 50 | 25 | 16 |
Electrostatic | 0.0015 | 50 | 0.03 | 0.003 |
Muscle | 0.59 | 70 | 1.18 | 0.03 |
Stimulus | Advantages | Limitations | Reference |
---|---|---|---|
Thermal | Ease of operation | Slow response | [143,144] |
Electrical | Faster response | Electrolyte layer formation | [145,146] |
pH | Faster response, reversible volume change | Complex pH solution formation | [147,148] |
Magnetic | Wireless, remote-controlled | Brittle structure, difficult to print | [147,149] |
Light | Wireless, remote-controlled | Difficult to control and penetrate | [80] |
Hydrogel | Transduction Strategy | Specification | Reference |
---|---|---|---|
Polyaniline | Electrochemical | RT: 3 s; LR: 0.01–8 mM | [179] |
Polyaniline–PEG | Electrochemical | - | [180] |
PEG | Optical | RT: 10 min; LR: 0–600 mg/dL | [166] |
PVA–vinyl pyridine | Electrochemical | RT: 11 s | [181] |
Chitosan | Electrochemical | RT: 7 s; LR: 5 M to 2.5 nM | [182] |
Chitosan–graphene oxide | Electrochemical | LR: 0.02–6.78 mM | [183] |
Polypyrrole | Electrochemical | LR: up to 15 mM | [184] |
PEG (injectable) | Optical | RT: 11 min; LR: up to 370 mg dL | [185] |
Polyvinylpyrrolidone | Optical | - | [186] |
Alginate | Optical | LR: 2.6–350 mg/dL | [187] |
HEMA | Electrochemical | LR: 10 M to 40 mM | [188] |
Chemicals | Stimulus | Reference |
---|---|---|
Alginate/poly(N-isopropylacrylamide) (pNIPAM) Polycaprolactone Alginate/poly(acrylamideionic covalent entanglement) (Alg/PAAmICE) Pluronic F127 Gelatinmethacryloyl (GelMa) | Thermal | [143,147,316,317,318] |
Poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) 4-Hydroxybutyl acrylate (4-HBA) Acrylamide (AAm)/sodium acrylate (NaAc) | Electrical | [52,145,146] |
Poly(methacrylic acid) (PMAA) Collagen Keratin Polyacrylic acid (PAA) | pH | [147,148] |
Magnetic nanoparticles such as FeO, FeO, FePt, and CoFeO in polymers such as poly(2-hydroxyethyl methacrylate) (pHEMA) | Magnetic | [110,147] |
Gellan gum methacrylate (GGMA) Graphene oxide (GO)/pNIPAM | Light | [319,320,321] |
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Banerjee, H.; Suhail, M.; Ren, H. Hydrogel Actuators and Sensors for Biomedical Soft Robots: Brief Overview with Impending Challenges. Biomimetics 2018, 3, 15. https://doi.org/10.3390/biomimetics3030015
Banerjee H, Suhail M, Ren H. Hydrogel Actuators and Sensors for Biomedical Soft Robots: Brief Overview with Impending Challenges. Biomimetics. 2018; 3(3):15. https://doi.org/10.3390/biomimetics3030015
Chicago/Turabian StyleBanerjee, Hritwick, Mohamed Suhail, and Hongliang Ren. 2018. "Hydrogel Actuators and Sensors for Biomedical Soft Robots: Brief Overview with Impending Challenges" Biomimetics 3, no. 3: 15. https://doi.org/10.3390/biomimetics3030015
APA StyleBanerjee, H., Suhail, M., & Ren, H. (2018). Hydrogel Actuators and Sensors for Biomedical Soft Robots: Brief Overview with Impending Challenges. Biomimetics, 3(3), 15. https://doi.org/10.3390/biomimetics3030015