[1] [1] Layani M, Wang X F and Magdassi S 2018 Novel materials for 3D printing by photopolymerization Adv. Mater. 30 1706344

[2] [2] Bikas H, Stavropoulos P and Chryssolouris G 2016 Additive manufacturing methods and modelling approaches: a critical review Int. J. Adv. Manuf. Technol. 83 389–405

[3] [3] UPS 2019 3D printing: the next revolution in industrial manufacturing (https://www.ups.com/media/ en/3D_Printing_executive_summary.pdf)

[4] [4] Macdonald N P, Cabot J M, Smejkal P, Guijt R M, Paull B and Breadmore M C 2017 Comparing microfluidic performance of three-dimensional (3D) printing platforms Anal. Chem. 89 3858–66

[5] [5] Stratasys Inc 2019 Connex3 objet500 and objet350 (https://www.stratasys.com/3d-printers/objet-350-500- connex3)

[6] [6] BigRep GmbH 2019 Large-scale 3D printer BigRep ONE (https://bigrep.com/bigrep-one/)

[7] [7] Kuang X, Chen K J, Dunn C K, Wu J T, Li V C F and Qi H J 2018 3D printing of highly stretchable, shape-memory, and self-healing elastomer toward novel 4D printing ACS Appl. Mater. Interfaces 10 7381–8

[8] [8] Sydney Gladman A, Matsumoto E A, Nuzzo R G, Mahadevan L and Lewis J A 2016 Biomimetic 4D printing Nat. Mater. 15 413–8

[9] [9] Chen B L, Jiang Y Z, Tang X H, Pan Y Y and Hu S 2017 Fully packaged carbon nanotube supercapacitors by direct ink writing on flexible substrates ACS Appl. Mater. Interfaces 9 28433–40

[10] [10] Le T T, Austin S A, Lim S, Buswell R A, Gibb A G F and Thorpe T 2012 Mix design and fresh properties for high-performance printing concrete Mater. Struct. 45 1221–32

[11] [11] Gosselin C, Duballet R, Roux P, Gaudilli`ere N, Dirrenberger J and Morel P 2016 Large-scale 3D printing of ultra-high performance concrete—a new processing route for architects and builders Mater. Des. 100 102–9

[12] [12] 3D Concrete House Printer 2019 (http://www. totalkustom.com/3d-concrete-printers.html)

[13] [13] Skylar-Scott M A, Mueller J, Visser C W and Lewis J A 2019 Voxelated soft matter via multimaterial multinozzle 3D printing Nature 575 330–5

[14] [14] SLM-Solutions Inc 2019 (www.slm-solutions. com/products/machines/selectivelasermeltingmachine)

[15] [15] TRUMPF Inc 2019 Additive production systems (https://www.trumpf.com/en_US/products/machinessystems/ additive-production-systems/)

[16] [16] 3D Systems Inc. 3D printers, 3D scanning, software, manufacturing and healthcare services (https://www.3dsystems.com/)

[17] [17] EOS Inc 2019 Systems and materials for additive manufacturing with metals (www.eos.info/systems_solutions/ metal/systems_equipment?_scrivito_display_mode= view&_scrivito_workspace_id=published)

[18] [18] Nanoscribe GmbH 2019 Photonic Professional GT2: world's highest resolution 3D printer (https://www.nanoscribe. com/en/solutions/photonic-professional-gt2)

[19] [19] Kawata S, Sun H B, Tanaka T and Takada K 2001 Finer features for functional microdevices Nature 412 697–8

[20] [20] Takada K, Sun H B and Kawata S 2005 Improved spatial resolution and surface roughness in photopolymerizationbased laser nanowriting Appl. Phys. Lett. 86 071122

[21] [21] Xing J F, Dong X Z, Chen W Q, Duan X M, Takeyasu N, Tanaka T and Kawata S 2007 Improving spatial resolution of two-photon microfabrication by using photoinitiator with high initiating efficiency Appl. Phys. Lett. 90 131106

[22] [22] Saha S K, Wang D E, Nguyen V H, Chang Y N, Oakdale J S and Chen S-C 2019 Scalable submicrometer additive manufacturing Science 366 105–9

[23] [23] Zhang X, Jiang X N and Sun C 1999 Micro-stereolithography of polymeric and ceramic microstructures Sensors Actuators A 77 149–56

[24] [24] Wang J, Goyanes A, Gaisford S and Basit A W 2016 Stereolithographic (SLA) 3D printing of oral modified-release dosage forms Int. J. Pharm. 503 207–12

[25] [25] UnionTech Inc. 2019 3D stereolithography printing solutions (http://en.union-tek.com/)

[26] [26] Materialise Inc. 2019 Stereolithography (https://www.materialise.com/en/manufacturing/ 3d-printing-technology/stereolithography)

[27] [27] Formlabs 2019 Resin library and 3D printing materials (https://formlabs.com/3d-printers/form-3/ tech-specs/)

[28] [28] Sun C, Fang N, Wu D M and Zhang X 2005 Projection micro-stereolithography using digital micro-mirror dynamic mask Sensors Actuators A 121 113–20

[29] [29] Zheng X Y, Deotte J, Alonso M P, Farquar G R, Weisgraber T H, Gemberling S, Lee H, Fang N and Spadaccini C M 2012 Design and optimization of a light-emitting diode projection micro-stereolithography three-dimensional manufacturing system Rev. Sci. Instrum. 83 125001

[30] [30] Zheng X Y et al 2014 Ultralight, ultrastiff mechanical metamaterials Science 344 1373–7

[31] [31] Zheng X Y et al 2016 Multiscale metallic metamaterials Nat. Mater. 15 1100–6

[32] [32] BMF Materials Inc. 2019 Micro 3D printing, industrial micro precision 3D printing (http://www.bmftec. com/)

[33] [33] Gong H, Bickham B P, Woolley A T and Nordin G P 2017 Custom 3D printer and resin for 18 μm × 20 μm microfluidic flow channels Lab Chip 17 2899–909

[34] [34] Zhang R J and Larsen N B 2017 Stereolithographic hydrogel printing of 3D culture chips with biofunctionalized complex 3D perfusion networks Lab Chip 17 4273–82

[35] [35] Shallan A I, Smejkal P, Corban M, Guijt R M and Breadmore M C 2014 Cost-effective three-dimensional printing of visibly transparent microchips within minutes Anal. Chem. 86 3124–30

[36] [36] Ge Q, Sakhaei A H, Lee H, Dunn C K, Fang N X and Dunn M L 2016 Multimaterial 4D printing with tailorable shape memory polymers Sci. Rep. 6 31110

[37] [37] EnvisionTEC, Inc. 2019 Desktop, professional and industrial 3D printers (https://envisiontec.com/)

[38] [38] Tumbleston J R et al 2015 Continuous liquid interface production of 3D objects Science 347 1349–52

[39] [39] Walker D A, Hedrick J L and Mirkin C A 2019 Rapid, large-volume, thermally controlled 3D printing using a mobile liquid interface Science 366 360–4

[40] [40] Wu S H, Serbin J and Gu M 2006 Two-photon polymerisation for three-dimensional micro-fabrication J. Photochem. Photobiol. A 181 1–11

[41] [41] Hull C W 1986 Apparatus for production of three-dimensional objects by stereolithography US Patent US4575330A

[42] [42] Reiser A, Lind′en M, Rohner P, Marchand A, Galinski H, Sologubenko A S, Wheeler J M, Zenobi R, Poulikakos D and Spolenak R 2019 Multi-metal electrohydrodynamic redox 3D printing at the submicron scale Nat. Commun. 10 1853

[43] [43] Liashenko I, Rosell-Llompart J and Cabot A 2020 Ultrafast 3D printing with submicrometer features using electrostatic jet deflection Nat. Commun. 11 753

[44] [44] Kelly B E, Bhattacharya I, Heidari H, Shusteff M, Spadaccini C M and Taylor H K 2019 Volumetric additive manufacturing via tomographic reconstruction Science 363 1075–9

[45] [45] Loterie D, Delrot P and Moser C 2020 High-resolution tomographic volumetric additive manufacturing Nat. Commun. 11 852

[46] [46] Kowsari K, Akbari S, Wang D, Fang N X and Ge Q 2018 High-efficiency high-resolution multimaterial fabrication for digital light processing-based three-dimensional printing 3D Print. Addit. Manuf. 5 185–93

[47] [47] Han D, Yang C, Fang N X and Lee H 2019 Rapid multi-material 3D printing with projection micro-stereolithography using dynamic fluidic control Addit. Manuf. 27 606–15

[48] [48] Xiang Y L, Huang S L, Huang T Y, Dong A, Cao D, Li H, Xue Y, Lv P and Duan H 2020 Superrepellency of underwater hierarchical structures on Salvinia leaf Proc. Natl Acad. Sci. USA 117 2282–7

[49] [49] Han D, Morde R S, Mariani S, La Mattina A A, Vignali E, Yang C, Barillaro G and Lee H 2020 4D printing of a bioinspired microneedle array with backward-facing barbs for enhanced tissue adhesion Adv. Funct. Mater. 30 1909197

[50] [50] Wang Y J, Gao L B, Fan S F, Zhou W Z, Li X and Lu Y 2019 3D printed micro-mechanical device (MMD) for in situ tensile testing of micro/nanowires Extreme Mech. Lett. 33 100575

[51] [51] Yang Y, Li X J, Zheng X, Chen Z Y, Zhou Q F and Chen Y 2018 3D-printed biomimetic super-hydrophobic structure for microdroplet manipulation and oil/water separation Adv. Mater. 30 1704912

[52] [52] Ge Q, Qi H J and Dunn M L 2013 Active materials by four-dimension printing Appl. Phys. Lett. 103 131901

[53] [53] Ge Q, Dunn C K, Qi H J and Dunn M L 2014 Active origami by 4D printing Smart Mater. Struct. 23 094007

[54] [54] Wang Q M, Jackson J A, Ge Q, Hopkins J B, Spadaccini C M and Fang N X 2016 Lightweight mechanical metamaterials with tunable negative thermal expansion Phys. Rev. Lett. 117 175901

[55] [55] Liu W J et al 2017 Rapid continuous multimaterial extrusion bioprinting Adv. Mater. 29 1604630

[56] [56] Zhang B et al 2018 Highly stretchable hydrogels for UV curing based high-resolution multimaterial 3D printing J. Mater. Chem. B 6 3246–53

[57] [57] Zhang Y F, Zhang N B, Hingorani H, Ding N Y, Wang D, Yuan C, Zhang B, Gu G and Ge Q 2019 Fast-response, stiffness-tunable soft actuator by hybrid multimaterial 3D printing Adv. Funct. Mater. 29 1806698

[58] [58] Zhang Y F, Ng C J X, Chen Z, Zhang W, Panjwani S, Kowsari K, Yang H Y and Ge Q 2019 Miniature pneumatic actuators for soft robots by high-resolution multimaterial 3D printing Adv. Mater. Technol. 4 1900427

[59] [59] Martin J J, Fiore B E and Erb R M 2015 Designing bioinspired composite reinforcement architectures via 3D magnetic printing Nat. Commun. 6 8641

[60] [60] Yang Y, Chen Z Y, Song X, Zhang Z F, Zhang J, Shung K K, Zhou Q and Chen Y 2017 Biomimetic anisotropic reinforcement architectures by electrically assisted nanocomposite 3D printing Adv. Mater. 29 1605750

[61] [61] Yang Y, Li X J, Chu M, Sun H F, Jin J, Yu K, Wang Q, Zhou Q and Chen Y 2019 Electrically assisted 3D printing of nacre-inspired structures with self-sensing capability Sci. Adv. 5 eaau9490

[62] [62] Bagheri A and Jin J Y 2019 Photopolymerization in 3D printing ACS Appl. Polym. Mater. 1 593–611

[63] [63] Wu J T, Zhao Z A, Hamel C M, Mu X M, Kuang X, Guo Z and Qi H J 2018 Evolution of material properties during free radical photopolymerization J. Mech. Phys. Solids 112 25–49

[64] [64] Mu Q Y, Wang L, Dunn C K, Kuang X, Duan F, Zhang Z, Qi H J and Wang T 2017 Digital light processing 3D printing of conductive complex structures Addit. Manuf. 18 74–83

[65] [65] Zhang B, Zhang W, Zhang Z Q, Zhang Y F, Hingorani H, Liu Z, Liu J and Ge Q 2019 Self-healing four-dimensional printing with an ultraviolet curable double-network shape memory polymer system ACS Appl. Mater. Interfaces 11 10328–36

[66] [66] Patel D K, Sakhaei A H, Layani M, Zhang B, Ge Q and Magdassi S 2017 Highly stretchable and UV curable elastomers for digital light processing based 3D printing Adv. Mater. 29 1606000

[67] [67] Zhang B, Kowsari K, Serjouei A, Dunn M L and Ge Q 2018 Reprocessable thermosets for sustainable three-dimensional printing Nat. Commun. 9 1831

[68] [68] Yu K H, Xin A, Du H X, Li Y and Wang Q M 2019 Additive manufacturing of self-healing elastomers NPG Asia Mater. 11 7

[69] [69] Li X P, Yu R, He Y Y, Zhang Y, Yang X, Zhao X and Huang W 2019 Self-healing polyurethane elastomers based on a disulfide bond by digital light processing 3D printing ACS Macro Lett. 8 1511–6

[70] [70] Shelby R A, Smith D R and Schultz S 2001 Experimental verification of a negative index of refraction Science 292 77–9

[71] [71] Parimi P V, Lu W T, Vodo P and Sridhar S 2003 Imaging by flat lens using negative refraction Nature 426 404

[72] [72] Yen T J, Padilla W J, Fang N, Vier D C and Smith D R et al 2004 Terahertz magnetic response from artificial materials Science 303 1494–6

[73] [73] Fang N, Xi D J, Xu J Y, Ambati M, Srituravanich W, Sun C and Zhang X 2006 Ultrasonic metamaterials with negative modulus Nat. Mater. 5 452–6

[74] [74] Zhang S, Xia C G and Fang N 2011 Broadband acoustic cloak for ultrasound waves Phys. Rev. Lett. 106 024301

[75] [75] Zhang S, Yin L L and Fang N 2009 Focusing ultrasound with an acoustic metamaterial network Phys. Rev. Lett. 102 194301

[76] [76] Chen X F, Liu W Z, Dong B Q, Lee J, Ware H O T, Zhang H F and Sun C 2018 High-speed 3D printing of millimeter-size customized aspheric imaging lenses with sub 7 nm surface roughness Adv. Mater. 30 1705683

[77] [77] Gissibl T, Thiele S, Herkommer A and Giessen H 2016 Two-photon direct laser writing of ultracompact multi-lens objectives Nat. Photonics 10 554–60

[78] [78] Yuan C, Kowsari K, Panjwani S, Chen Z C, Wang D, Zhang B, Ng C J-X, Alvarado P V Y and Ge Q 2019 Ultrafast three-dimensional printing of optically smooth microlens arrays by oscillation-assisted digital light processing ACS Appl. Mater. Interfaces 11 40662–8

[79] [79] Tibbits S 2013 The emergence of ‘4D printing' (https://www.ted.com/talks/skylar_tibbits_the_ emergence_of_4d_printing)

[80] [80] Mao Y Q, Yu K, Isakov M S, Wu J T, Dunn M L and Jerry Qi H 2015 Sequential self-folding structures by 3D printed digital shape memory polymers Sci. Rep. 5 13616

[81] [81] Wu J T, Yuan C, Ding Z, Isakov M, Mao Y Q, Wang T, Dunn M L and Qi H J 2016 Multi-shape active composites by 3D printing of digital shape memory polymers Sci. Rep. 6 24224

[82] [82] Zarek M, Layani M, Cooperstein I, Sachyani E, Cohn D and Magdassi S 2016 3D printing of shape memory polymers for flexible electronic devices Adv. Mater. 28 4449–54

[83] [83] Yang C, Boorugu M, Dopp A, Ren J, Martin R, Han D, Choi W and Lee H 2019 4D printing reconfigurable, deployable and mechanically tunable metamaterials Mater. Horiz. 6 1244–50

[84] [84] Raviv D et al 2015 Active printed materials for complex self-evolving deformations Sci. Rep. 4 7422

[85] [85] Wu D, Song J Q, Zhai Z R, Hua M T, Kim C, Frenkel I, Jiang H and He X 2019 Visualizing morphogenesis through instability formation in 4-D printing ACS Appl. Mater. Interfaces 11 47468–75

[86] [86] Yuan C, Roach D J, Dunn C K, Mu Q Y, Kuang X, Yakacki C M, Wang T J, Yu K and Qi H J 2017 3D printed reversible shape changing soft actuators assisted by liquid crystal elastomers Soft Matter 13 5558–68

[87] [87] Davidson E C, Kotikian A, Li S C, Aizenberg J and Lewis J A 2020 3D printable and reconfigurable liquid crystal elastomers with light-induced shape memory via dynamic bond exchange Adv. Mater. 32 1905682

[88] [88] Zhang C, Lu X L, Fei G X, Wang Z H, Xia H S and Zhao Y 2019 4D printing of a liquid crystal elastomer with a controllable orientation gradient ACS Appl. Mater. Interfaces 11 44774–82

[89] [89] Kotikian A, McMahan C, Davidson E C, Muhammad J M, Weeks R D, Daraio C and Lewis J A 2019 Untethered soft robotic matter with passive control of shape morphing and propulsion Sci. Robot. 4 eaax7044

[90] [90] Kuang X, Roach D J, Wu J T, Hamel C M, Ding Z, Wang T, Dunn M L and Qi H J 2019 Advances in 4D printing: materials and applications Adv. Funct. Mater. 29 1805290

[91] [91] Han D, Farino C, Yang C, Scott T, Browe D, Choi W, Freeman J W and Lee H 2018 Soft robotic manipulation and locomotion with a 3D printed electroactive hydrogel ACS Appl. Mater. Interfaces 10 17512–8

[92] [92] Han D, Lu Z C, Chester S A and Lee H 2018 Micro 3D printing of a temperature-responsive hydrogel using projection micro-stereolithography Sci. Rep. 8 1963

[93] [93] Xu T Q, Zhang J C, Salehizadeh M, Onaizah O and Diller E 2019 Millimeter-scale flexible robots with programmable three-dimensional magnetization and motions Sci. Robot. 4 eaav4494

[94] [94] Ma X Y et al 2016 Deterministically patterned biomimetic human iPSC-derived hepatic model via rapid 3D bioprinting Proc. Natl Acad. Sci. USA 113 2206–11

[95] [95] Kim S H et al 2018 Precisely printable and biocompatible silk fibroin bioink for digital light processing 3D printing Nat. Commun. 9 1620

[96] [96] Grigoryan B et al 2019 Multivascular networks and functional intravascular topologies within biocompatible hydrogels Science 364 458–64

[97] [97] Koffler J et al 2019 Biomimetic 3D-printed scaffolds for spinal cord injury repair Nat. Med. 25 263–9