Table 2.
Characteristics of some SRG applications in actuators and microfluidics.
| Material | Type of control | Shape | Application | Notes | Ref. |
|---|---|---|---|---|---|
| PEDOT, PSS, PAAm, PAAc | Electroactive | Bulk | Macroscopic actuator | Compressive fracture stress of 1.2 MPa and a fracture strain of 90%. | [178] |
| Layers of PAAm and PAAc gels | Electroactive | Multilayered | Macroscopic actuator | When AAc layer expels water, AAm layer takes water, and vice versa. Thickness changes by 10–15% in response to 3 V. | [165] |
| Poly(AAc-co-vinylsulfonic acid) | Electroactive | Bulk | Macroscopic actuator | Contraction by 15–40% in response to 4.5 V in ~60 min. | [179] |
| P(Aac-co-Aam) blended with conductive polypyrrole/carbon black composite | Electroactive | 400×400×2500 μm | Bending actuator | Bending up to 30 degree. 5 s response time. | [171] |
| Saponified PAN | Electroactive | Yarns of roughly 2000 fibrils of 7 μm diameter | Artificial muscle | Response time: 10–15 min. Linear response ratio: 2 times. Contracted: 1 MPa modulus, 5 MPa strength, 2.4 elongation. Elongated: 4 MPa modulus, 1.5 MPa strength, 0.4 elongation. | [180] |
| PNIPAM | Temperature | Microparticles (~500 μm) and photopatterned microactuator (250×250×50 μm) | Control valve for microfluidics | Explored optimal particle size and optimal particles volume/chamber volume ratio. 0.3–10 s response time. Up to 840 kPa pressure resistance. | [181] |
| PNIPAM | Temperature | Photopatterned microactuator (2000×200×100 μm) | Control valve for microfluidics | 3–5 s response time. 1400 kPa pressure resistance in closed state. 300 kPa back pressure in open state at flow velocity 5 cm/s. | [182] |
| PNIPAM | Temperature | Photopatterned microactuator | Control valve for microfluidics | Applied in polymerase chain reaction device. 5 s response time. Pressure resistance 200 kPa. | [174] |
| P(NIPAM-co-NEAAm) | Temperature | Photopatterned microactuator (5000×100×40 μm) | Control valve for microfluidics | Copolymers with NEAAm enabled higher switch temperature than PNIPAM along. 1–4 s response time. Pressure resistance more than 15 MPa in closed state. | [183] |
| P(NIPAM-co-sodium acrylate) | Temperature | Microactuator | Control valve for microfluidics | 5–10 min response time. | [184] |
| PNIPAAm | Temperature | Photopatterned microactuator (5000×100×100 μm) | Control valve for microfluidics | 4–6 s response time. 9 MPa pressure resistance. | [185] |
| PNIPAAm | Temperature | Microgels | Control valve for microfluidics | Pressure resistance up to 9 MPa; opening time as low as 0.3 s; 2 s closing time. | [186] |
| PNIPAAm | Temperature and alcohol concentration | Microgels | Electronically adjustable automatic control of concentration of alcohols | Pressure resistance up to 600 kPa. Flow rate changes more than 30 times. | [187] |
| PNIPAAm | Temperature | Microactuator | Control valve for microchannel concentrator | 50–240 s valve switching time. | [188] |
| PNIPAAm | Temperature | Photopatterned microactuator | Diffusion micropump | 0.54 μl/min in peristaltic mode and 2.8 μl/min in pulsating mode at 0.43 kPa pumping pressure. 1.28 kPa maximum pumping pressure. | [189] |
| PNIPAAm | Temperature | Packed microgels | Displacement micropump | Higher performance can be achieved by increasing actuator thickness and pump chamber volume. 4.5 μl/min at 0.5 kPa and 0.2 μl/min at 7.5 kPa. | [189] |
| Composite of poly(NIPAAm-co-AAm) and light absorbing particles | Light | Microvalves | Microfluidic control of flow by light of specific wavelength | Gold colloid nanocomposite collapses in response to green light. Gold nanoshells composite collapses in response to near-IR light | [190] |
| PNIPAM functionalized with spirobenzopyran | Light | Microvalves | Microfluidic control of flow by light | 18–30 s to open; more than 1 h to close. | [191] |
| PAN | pH and electroactive | Fibers | Macroscopic actuator | 2.2 times change in length. 0.1 MPa contraction stress. | [192] |
| Poly(HEMA-co-AAc) | pH | Microvalve ~200 μm | “Self-regulated” pH control valve in microfluidic | Several minutes response time. | [193] |
| Poly(HEMA-co-AAc) or poly(HEMA-co-DMAEM) | pH | Microvalves | Switching between channels | 8–12 s response time. More than 300 kPa differential pressure. | [194,195] |
| poly(4-hydroxybutylacrylate–co-AAc) | pH | Microsphere | Microfluidic valve | Flow rate changes 10 times. Valve opens/closes in 4–8 min. | [196] |
| Poly(HEMA-co-AAc) | pH | Cylindrical microactuators | Microvalve and micropump | 35 kPa pressure of micropump. 1.5 MPa pressure resistance of microvalve. 2 μl/min flow rate by the pump along. For a fast bolus release the micropump is used in combination with the valve. The valve is opened after full swelling of the pump actuator, releasing the content of the pump chamber within a few seconds at an average flow rate of 540 μl/min. | [197] |
| Poly (AAm-co-3-methacrylamidophenylboronic acid) | Glucose | 70 μm thick film | Microfluidics; artificial pancreas. | More than 5.4 kPa pressure resistance. 17–18 min response time. 1.5 linear response ratio for 0–100 mM glucose shift. | [198] |
| Poly(NIPAM-co-AMPS-co-Ru(bpy)3) | Cyclic BZ reaction | 0.5 mm thick film | Self-oscilating | Self-waking on ratchet surface. ~100 s per cycle. Walking speed 170 μm/min. | [199] |
| Poly(NIPAM-co-AMPS-co-Ru(bpy)3) | Cyclic BZ reaction | 0.5 mm thick free-standing membrane | Self-oscilating | Cyclic pendulum motion. ~300 s per cycle. | [200] |
| Poly(NIPAM-co-AMPS-co-Ru(bpy)3) | Cyclic BZ reaction | Film | Transport of particles on surface | 1–4 mm/min particle speed. | [201] |