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	$0.80-4.5\frac{W}{c{m}^3}$ 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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