Table 1.

Properties of Thermo-Active Actuators for Desired Applications, Compared with Human Skeletal Muscles

Material	Energy density	Deformation	Bandwidth (Hz)	Power	Efficiency
Human skeletal muscles71,72	$40\frac{J}{kg}$ 47	20%–40%48	1–1047	$50-300\frac{kW}{m^3}$ 47	20%47
Fiber-based artificial muscles	2–2.573	49%73	1–7.573	$27.1\frac{kW}{kg}$ 73	20%73
Shape memory polymers	$17.9\frac{J}{g}$ 23,24	24–6043,44	—	$2\frac{kJ}{kg}$ 23,24	40%22
Thermally responsive hydrogels	$0.35\frac{J}{c{m}^3}$ 74	90%74	—	—	—
Electrothermal films	10 −3 $\frac{J}{c{m}^3}$75	120%76	0.176	$0.1\frac{W}{c{m}^3}$ 76	12%75
Shape memory alloys	${10}^4\frac{J}{kg}$ 47	10%–50%47	0.5–547	103−105$\frac{kW}{m^3}$47	—
Liquid crystal elastomers77–79	$1-50\frac{J}{kg}$ 47	38%–50%79,80	0.19–1079,80	$\mathrm{0.804.5}\frac{W}{c{m}^3}$ 80,81	—
Phase change actuators	$40\frac{kJ}{m^3}$ 36	20%–40%31,33,36,82	0.15–236,41,52,83,84	$50\frac{W}{c{m}^3}$ 39	—

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