Table 1.

Comparison of representative activation mechanisms as building blocks for responsive architected materials

Activation mechanism		Typical materials	Fabrication methods	Response speeda	Advantages	Limitations
Mechanical actuation		Elastomers, polymers, papers, metals	DIW, SLA, PolyJet, DLP, TPL, SLS, machining	Fast	Mature fabrication and advanced design methods; easy mechanical control; marginal sensitivity to surrounding environment; stable reconfigurability	Difficult to deploy or modulate remotely; response depends on specific loading conditions (such as uniaxial loading)
Heat transfer	Phase change	Polymers, metals, polymer-filler composites, LCEs, SMPs, hydrogels	DIW, DLP, TPL, microfabrication, machining	Slow to medium	Remote activation by temperature; thermal expansion is universal and can be modelled systematically; phase-changing materials have substantial thermal expandability and programmable anisotropy; SMPs can be willfully deformed after fabrication and achieve nearly full shape recovery	Limited to specific temperatures and environments (for example, cannot operate when temperature cannot be changed); may require large temperature change and long heating or cooling time
	Shape memory
Chemomechanical transformation	Swelling	Hydrogels, hydrogel-filler composites, polymers, multi-material composites	DIW, DLP, microfabrication, machining	Slow to medium	Large, programmable structural changes; easy activation by wetting	Transformation speed limited by mass transport; require large environmental changes
	Chemistry	Hydrogels	DLP, TPL, microfabrication, machining	Medium to fast	Chemical activation is useful for biomedical applications; autonomous feedback can be achieved via chemical reactions	Require specific reactions and relevant materials synthesis to respond to different chemical cues
	Electrochemistry	Electrochemically active materials (such as conjugated polymers, battery electrode materials)	Machining, microfabrication, TPL	Slow to medium	Structure and property retention upon stimulus removal; continuous control of transformation; potential to simultaneously store energy	Typically require two electrodes, a liquid or gel electrolyte, and a power source; 3D structuring methods are not fully developed
Electromagnetic interactions	Magnetic field	Polymers with embedded magnetic particles	DIW, DLP, microfabrication	Fast	Fast, remote activation (typically <1 s); complex, reversible, and programmable structural changes	Require strong magnetic fields (typically >0.1 T); mostly soft materials
	Electric field	Ionic hydrogels, dielectric elastomers, piezoelectric composites	DLP, moulding, machining, microfabrication	Medium to fast	Dielectric elastomers integrate into electronic control circuits for autonomous devices; piezoelectric materials can measure strain	Require additional electrodes and electronic control
	Light	Polymers with light-absorbing nanoparticles, azobenzene-containing liquid crystal polymers	DIW, microfabrication, machining	Medium to fast	Fast, remote activation and active manipulation; independent control of shape changes by different polarizations and wavelengths	Limited 3D patterning methods; cannot function without a light source and sufficient transmission

DIW, direct ink writing; DLP, digital light processing; LCE, liquid crystal elastomer; SLS, selective laser sintering; SMP, shape memory polymer; TPL, two-photon lithography. ^aResponse speed is compared in relative terms between representative responsive materials with similar dimensions; the demonstrated response speed of specific responsive architected materials examples depends on both the activation mechanism and the architecture’s geometry and feature sizes. Illustration in row 1 adapted with permission from ref.²⁴, Wiley. Illustration in row 5 adapted from ref.⁹⁶, Springer Nature Limited. Illustration in row 7 adapted from ref.¹⁴, Springer Nature Limited. Illustration in row 9 adapted from ref.¹⁴⁷, Springer Nature Limited.