Applications of four-dimensional printing in emerging directions: Review and prospects

doi:10.1016/j.jmst.2021.02.040

Abstract

Abstract:

Four-dimensional (4D) printing technology is an extension of three-dimensional (3D) printing technology that enables a 3D-printed static structure to dynamically change its shape with time. Therefore, the resulting structure can undergo self-folding/unfolding assisted by some stimuli. This technology has made much initial progress in many industrial fields. Aiming to investigate the in-depth application value of 4D printing, this study reviews the recent research and application breakthroughs of 4D printing in several emerging directions, including the simulation of plant and animal behaviors, smart tissue scaffolds and biomedical devices, food printing, digitalization of industrial art design, renewable energy, intelligent communication, soft electronics and robots, vehicle optimization, textile customization, and flexible machinery and mechanical structure. Based on the analyses of specific cases and processes, we present the current obstacles to large-scale applications and the future prospects.

Key words: 4D printing, Smart materials, Product design, Emerging directions

Jinjian Huang, Shaojun Xia, Zongan Li, Xiuwen Wu, Jianan Ren. Applications of four-dimensional printing in emerging directions: Review and prospects[J]. J. Mater. Sci. Technol., 2021, 91: 105-120.

Figures/Tables 17

Fig. 1. Mechanisms for shape-morphing materials. (A) shape-memory polymers (SMPs), Tg: glass transition temperature. (B) shape-memory alloys (SMAs), Ms: martensite start temperature. (C) liquid crystal elastomers (LCEs) with shape change effect, Tc: clearing point temperature. (D) hydrogels with shape change effect.

Table 1 A summary of stimuli-responsive four-dimensional (4D) printing materials.

Stimuli	Ink composition	Fabrication methods	Deformation principles	References
Direct heating
Temperature	Methacrylate-conjugated polycaprolactone (SMP)	SLA	Thermoinducive deformation of polymer chains	Zarek et al. [30]
	NiTi alloy (SMA)	SLS	Thermoelastic martensitic transformation	Clare et al. [31]
	LCE + base inks (Tangoblack and Verowhite) + silver ink	Inkjet printing	Thermoinducive rearrangement of elastomer chains	Yuan et al. [32]
	Poly(N-propylacrylamide) hydrogel-based acrylamide matrix	Ultraviolet (UV) curing in a specific inkjet printing mask	Thermoinducive hydrogel dehydration leading to deformation	Wu et al. [33]
Indirect heating
Magnetic field	Poly(lactic acid) (SMP) + Fe₃O₄ magnetic particles	FDM	Magnetic particles act as inductive heaters in alternating magnetic fields to heat the SMP	Lin et al. [34]
Light	Carbon black-reinforced polyurethane (SMP)	FDM	Deformation of SMP by photothermal effects	Yang et al. [35]
Voltage	Poly(lactic acid) (SMP) + Ag + carbon nanofibers	Solvent-cast printing	Deformation of SMP by electrothermal effects	Wei et al. [36]
Chemical stimuli
Humidity	Cellulose fibers embedded in a soft acrylamide matrix (hydrogel)	DIW	Deformation driven by differences in swelling ratio of hydrogel	Gladman et al. [37]
Volatilization	Butyl acrylate+ photosensitive resin	DLP	Deformation by the volatilization of unreacted butyl acrylate with spatial heterogeneity caused by grayscale light	Zhang et al. [38]
Others
Strain	Silicone + wax microparticles	Extrusion-based printing	The retained strain in wax drove the deformation	Deng et al. [39]
Voltage	Ionic polymer-metal composite (IPMC) (SMP)	Modeling by a 3D printing mold	Deformation by voltage-induced ion migration [40]	Liu et al. [41]

Fig. 2. An illustration showing the similarity of a tree growth process with the development of four-dimensional (4D) printing in emerging directions; the printing technology and stimulus-responsive inks are the basis, and the diverse applications make this technology attractive to scientists and enterprises. The number of publications sorted by time was from Web of Science Core Collection by searching “4D printing” in all fields.

Fig. 3. Examples of water-driven 4D-printed bionic plants. (A) 4D-printed orchids with different movement paths driven by anisotropic swelling in water. Reproduced with permission from Nature Publishing Group. (B) Mathematical model prediction of the real deformation process of 4D-printed calla lily flowers. Reproduced with permission from Nature Publishing Group. (C) The mechanism of the hydration-induced deformation of pine cones. Reproduced with permission from Elsevier. (D) 4D-printed flowers with the cellulose-based hydrogel at the base of petals for driving the deforming force. Reproduced with permission from Elsevier. (E) Industrial 4D-printed aquatic plants. Reproduced with permission from Nicole Hone.

Fig. 4. Light-driven and heat-driven 4D-printed bionic plants. (A) 4D-printed UV-responsive maple leaves with a high manufacturing resolution. Reproduced with permission from the Royal Society of Chemistry. (B) 4D-printed tulip flowers with self-opening induced by different swelling ratios because of differential light exposure time. Reproduced with permission from Wiley. (C) 4D-printed multimaterial heat-driving flowers. Reproduced with permission from Nature Publishing Group. (D) 4D-printed sunflowers with photothermal effects. Reproduced with permission from Wiley. (E) 4D-printed heat-driven flowers with a permanent shape developed by adding elastomers with built-in compressive strain. Reproduced with permission from AAAS. (F) Formation of a flower-like 3D structure from a 3D-printed planar sheet induced by heat. Reproduced with permission from Nature Publishing Group.

Fig. 5. 4D-printed bionic animals. (A) 4D-printed heat-responsive movable insects. Reproduced with permission from the Nature Publishing Group. (B) 4D-printed laser-driven flying birds based on the differential distribution of graphene nanoparticles. Reproduced with permission from Wiley. (C) 4D-printed magnetically responsive butterfly. Reproduced with permission from the American Chemical Society. (D) 4D-printed magnetically controllable clamping jaw. Reproduced with permission from the American Chemical Society.

Fig. 6. 4D-printed cell and drug carriers. (A) 4D-printed water-driven bending of cell-laden hydrogels; and (B) the applications on the tracheal defect treatment. Reproduced with permission from Elsevier. (C) Printed tissue spheroids fused into hollow (left), long (middle) or branched (right) vascular structures based on tissue self-assembly. Reproduced with permission from Elsevier. (D) Two droplets of different osmolarities joined by a lipid bilayer tended to swell or shrink in the presence of water; and (E) a droplet network that comprised two strips with different osmolarities could form a closed space for drug encapsulation and delivery. Reproduced with permission from AAAS.

Fig. 7. 4D-printed medical devices and equipment. (A) 4D-printed heat-driven self-rolling stents. Reproduced with permission from Elsevier. (B) 4D-printed heat-driven self-tightening substrates. Reproduced with permission from Elsevier. (C) 4D-printed heat-driven self-expanding stents. Reproduced with permission from the Nature Publishing Group. (D) 4D-printed heat-driven self-expanding embolization devices. Reproduced with permission from Elsevier. (E) 4D-printed magnetism-driven vascular stents for blood vessel recanalization. Reproduced with permission from the American Chemical Society. (F) 4D-printed magnetism-driven occluders for the repair of congenital heart diseases. Reproduced with permission from Wiley. (G) 4D-printed voltage-driven surgical robotic actuators. Reproduced with permission from SPIE Digital Library.

Fig. 8. 4D food printing. (A) Schematic diagram of microcapsule rapture and content release by microwave heating (left), and the color changes of printed buckwheat dough (right). Reproduced with permission from Elsevier. (B) Anthocyanins enabled the multi-material printing of mashed potatoes in different colors by using different pH environments. Reproduced with permission from Elsevier. (C) Microwave heating-induced dehydration led to the deformation of bilayered 3D printed purple sweet potato purees in various shapes. Reproduced with permission from the American Chemical Society.

Fig. 9. 4D printing enhancement of the digital programming of artworks. (A) 4D-printed programmable honeycomb structures for inducing shape deformation of the ETH university logo. Reproduced with permission from Mary Ann Liebert, Inc. (B) 4D-printed programmable structures (honeycomb, zigzag, and square) causing different bending angles of polymer substrates. Reproduced with permission from Elsevier. (C) 4D-printed continuous carbon fibers embedded in the soft matrix allowing the deformation of composite products. Reproduced with permission from Elsevier. (D) 4D-printed linear filaments with different segment compositions characterized by all-direction deformation capacity and the ability to be made into diverse structures. Reproduced with permission from ACM. (E) 4D-printed ceramic origami structures with complex curvatures. Reproduced with permission from AAAS.

Fig. 10. 4D-printed equipment for renewable energy. (A) 4D-printed smart wind turbine blades. Reproduced with permission from Elsevier. (B) 4D-printed smart solar concentrators improving optical efficiency. Case 1: non-smart compound parabolic concentrator (CPC); case 2: non-smart compound hyperbolic concentrator (CHC); and case 3: 4D-printed smart concentrator that can reversibly change its shape from CPC to CHC. Reproduced with permission from Elsevier.

Fig. 11. 4D printing technology applications in optic communication. (A) Traditional deployable antenna composed of truss and metal wire mesh (left); 4D-printed mesh antenna without truss (right). Reproduced with permission from Space Electronic Technology. (B) 4D-printed packages enclosed with RF electronics as an antenna system. Reproduced with permission from IEEE. (C) Magnetically responsive 3D-TPCs with a periodic woodpile structure (upper). Regardless of the rod spacing (middle), the THz photonic band-gap peaks for these 3D-TPC devices all shifted to a lower frequency (~0.1 THz lower) in the presence of magnetic stimuli (down). Reproduced with permission from the American Chemical Society. (D) 4D printing web-based service sequence diagram. Reproduced with permission from Transactions of the Society of CAD/CAM Engineers.

Fig. 12. 4D-printed electronics. (A) 4D-printed heat-responsive switches. Reproduced with permission from Wiley. (B) 4D-printed swelling-driven electric relays. Reproduced with permission from the Royal Society of Chemistry. (C) The design of a self-folding electronic composite based on a new ink with residual stress. Reproduced with permission from the American Chemical Society. (D) Examples of soft robotic grippers that can detect multiple somatosensory feelings. Reproduced with permission from Wiley. (E) A printed hand model with electronic sensors for contact sensory feedback. Reproduced with permission from the American Chemical Society.

Fig. 13. 4D-printed vehicle components. (A) Heat-driven active origami airplanes. Reproduced with permission from IOP Publishing Ltd. (B) Compaction and self-deployment of a UAV Model. Reproduced with permission from Research Publishing Services. (C) Heat-driven layered tensegrity structure. Reproduced with permission from Nature Publishing Group. (D) Superelastic tire made of SMA. Reproduced with permission from Wonderful Engineering.

Fig. 14. 4D printing textile approaches and products. (A) Heat-driven braided tubes (left) and the tube/silicone elastomer composite (right). Reproduced with permission from Elsevier. (B) Design and production of 4D-printed shoes. Reproduced with permission from ACM. (C) Force-driven midsole of running shoes based on CLIP. Reproduced with permission from Adidas. (D) Design of a force-driven self-adaptive dress (left) and its internal hinge structure showed by X-ray (right). Reproduced with permission from Nervous System.

Fig. 15. 4D-printed flexible structures. (A) Example of a heat-triggered simple self-folding joint. Reproduced with permission from Elsevier. (B) The design of a single actuator. Reproduced with permission from the Nature Publishing Group. (C) Design hierarchy of a single actuator. Reproduced with permission from the Nature Publishing Group. (D) Design of a self-expandable/shrinkable stent from single actuators. Reproduced with permission from IOP Publishing Ltd. (E) Production of a morphing wing flap and a deployable structure using multiple active hinges. Reproduced with permission from IOP Publishing Ltd.

Table 2 The frontier states of 4D printing in different areas.

Areas	Market entry requirement	State	TRL*
Bionics in robot	High	Proof-of-concept	3
In vitro cell models	High	Prototype	4
Drug carriers for controlled release	High	Prototype	4
Biomedical devices	High	Prototype	5
Energy harvesting equipment	High	Proof-of-concept	3
Smart antenna	Middle	Prototype	4
Vehicle accessories	Middle	Prototype	5
Textile	Low	Market	6
Artwork	Low	Market	6

References 143

[1]	E. MacDonald, R. Wicker, Science 353 (6307) (2016) aaf2093.
[2]	X. Kuang, D.J. Roach, J. Wu, et al., Adv.Funct. Mater. 29(2019) 1805290.
[3]	A. Haleem, M. Javaid, R. Vaishya, J. Clin. Orthop. Trauma 9 (2018) 275-276.
[4]	H. Kim, M.N. Park, J. Kim, et al., J. Tissue Eng. 10 (2019) 1544414506.
[5]	L. Tang, S. Cheng, L. Zhang, et al., Science 4 (2018) 302-311.
[6]	A.P. Piedade. J. Funct. Biomater. 10(2019) 9.
[7]	Z. Zhang, N. Corrigan, A. Bagheri, et al., Angew.Chem. Int. Ed. Engl. 58(2019) 17954-17963.
[8]	X. Li, J. Shang, Z. Wang, Assem. Autom. 37(2017) 170-185.
[9]	H. Shinoda, S. Azukizawa, K. Maeda, F. Tsumori. J. Electrochem. Soc. 166(2019) B3235-B3239.
[10]	J. Huang, Y. Liu, X. Chi, et al., J. Mater. Chem. A 9 (2021) 963-973.
[11]	Q. Peng, H. Wei, Y. Qin, et al., Nanoscale 8 (2016) 18042-18049.
[12]	M. Shie, Y. Shen, S. Astuti, et al., Polymers 11 (2019) 1864 BASEL.
[13]	W.M. Huang, Y. Zhao, C.C. Wang, et al., J.Polym. Res. 19(2012) 9952.
[14]	L. Wu, C. Jin, X. Sun, Biomacromolecules 12(2011) 235-241.
[15]	M.R. Pfau, K.G. McKinzey, A.A. Roth, M.A. Grunlan, Biomacromolecules 21 (2020) 2493-2501.
[16]	B. Zhang, W. Zhang, Z. Zhang, et al., ACS Appl. Mater. Interfaces 11 (2019) 10328-10336.
[17]	Z.X. Khoo, Y. Liu, J. An, et al., Materials 11 (2018) 519 (Basel).
[18]	H.Z. Lu, C. Yang, X. Luo, et al., Mater. Sci. Eng. A 763 (2019) 138166.
[19]	L. Sun, W.M. Huang, Z. Ding, et al., Mater.Des. 33(2012) 577-640.
[20]	L.T. de Haan, J.M. Verjans, D.J. Broer, et al., J. Am. Chem. Soc. 136(2014) 10585-10588.
[21]	J. Lv, Y. Liu, J. Wei, et al., Nature 537 (2016) 179-184.
[22]	Y. Wang, K.A. Burke, Soft Matter 14(2018) 9885-9900.
[23]	C. Zhang, X. Lu, G. Fei, et al., ACS Appl. Mater. Interfaces 11 (2019) 44774-44782.
[24]	L. Yin, L. Han, F. Ge, et al., Angew.Chem. Int. Ed. 59(2020) 15129-15134.
[25]	S.E. Bakarich, I.II.R. Gorkin, M.I.H. Panhuis, G.M. Spinks, Macromol. Rapid Commun. 36(2015) 1211-1217.
[26]	P. Rastogi, B. Kandasubramanian, Biofabrication 11 (2019) 42001.
[27]	N. Chen, H. Wang, C. Ling, et al., Carbohydr.Polym. 225(2019) 115207.
[28]	H. Peng, X. Ning, G. Wei, et al., Carbohydr.Polym. 195(2018) 349-355.
[29]	H. Ko, M.C. Ratri, K. Kim, et al., Sci.Rep. 10(2020) 7527.
[30]	M. Zarek, M. Layani, I. Cooperstein, et al., Adv.Mater. 28(2016) 4166.
[31]	A.T. Clare, P.R. Chalker, S. Davies, et al., Int.J. Mech. Mater. Des. 4(2008) 181-187.
[32]	C. Yuan, D.J. Roach, C.K. Dunn, et al., Soft Matter 13 (2017) 5558-5568.
[33]	Z.L. Wu, M. Moshe, J. Greener, et al., Nat.Commun. 4(2013) 1586.
[34]	C. Lin, J. Lv, Y. Li, et al., Adv.Funct. Mater. 29(2019) 1906569.
[35]	H. Yang, W.R. Leow, T. Wang, et al., Adv.Mater. 29(2017) 1701627.
[36]	H. Wei, X. Cauchy, I.O. Navas, et al., ACS Appl. Mater. Interfaces 11 (2019) 24523-24532.
[37]	A.S. Gladman, E.A. Matsumoto, R.G. Nuzzo, et al., Biomimetic 4D printing, Nat. Mater. 15(2016) 413-418.
[38]	Q. Zhang, X. Kuang, S. Weng, et al., ACS Appl. Mater. Interfaces 12 (2020) 17979-17987.
[39]	H. Deng, C. Zhang, K. Sattari, et al., ACS Appl. Mater. Interfaces (2020) Article In Press.
[40]	H. Kim, S. Ahn, D.M. Mackie, et al., Mater. Today 41 (2020) 243-269.
[41]	L. Jiayu, W. Yanjie, Z. Dongxu, et al., in: Proceedings of the SPIE, 2014 2014-03-08; 2014.
[42]	A. Mitchell, U. Lafont, M. Hoły ´nska, C. Semprimoschnig, Addit. Manuf. 24(2018) 606-626.
[43]	A. Walther, Adv. Mater. 32(2020) e1905111.
[44]	D. Khorsandi, A. Fahimipour, P. Abasian, et al., Acta Biomater. 122(2021) 26-49.
[45]	R. Xiao, W.M. Huang, Macromol. Biosci. 20 (2020) e2000108.
[46]	G. Liu, Y. Zhao, G. Wu, J. Lu, Sci. Adv. 4(2018) t641.
[47]	X. Lu, C.P. Ambulo, S. Wang, et al., Angew.Chem. Int. Ed. Engl. 60(2021) 5536-5543.
[48]	C. Han, Q. Fang, Y. Shi, et al., Adv.Mater. 32(2020) e1903855.
[49]	L. Sun, W.M. Huang, T.X. Wang, et al., Mater.Des. 136(2017) 238-248.
[50]	X. Wang, X. Guo, J. Ye, et al., Adv.Mater. 31(2019) e1805615.
[51]	M.C. Mulakkal, R.S. Trask, V.P. Ting, A.M. Seddon, Mater Des. 160(2018) 108-118.
[52]	https://www.thisiscolossal.com/2018/09/hydrophytes-by-nicole-hone/.
[53]	A.S. Mathews, S. Abraham, S.K. Kumaran, et al., RSC Adv. 7(2017) 41429-41434.
[54]	L. Huang, R. Jiang, J. Wu, et al., Adv.Mater. 29(2017) 1605390.
[55]	Q. Ge, A.H. Sakhaei, H. Lee, et al., Sci. Rep. UK 6 (2016) 31110.
[56]	Z. Ding, C. Yuan, X. Peng, et al., Sci.Adv. 3(2017) e1602890.
[57]	Q. Zhang, K. Zhang, G. Hu, Sci. Rep. UK 6 (2016) 22431.
[58]	J. Wu, C. Yuan, Z. Ding, et al., Sci. Rep. UK 6(2016) 24224.
[59]	S. Miao, H. Cui, M. Nowicki, et al., Adv.Biosyst. 2(2018) 1800101.
[60]	P. Zhu, W. Yang, R. Wang, et al., ACS Appl. Mater. Interfaces 10 (2018) 36435-36442.
[61]	C. Wang, W. Huang, Y. Zhou, et al., Bioact.Mater. 5(2020) 82-91.
[62]	Y. Xu, C. Chen, P.B. Hellwarth, X. Bao, Bioact. Mater. 4(2019) 366-379.
[63]	M. Chadwick, C. Yang, L. Liu, et al., Science 23 (2020) 101365.
[64]	B. Gao, Q. Yang, X. Zhao, et al., Trends Biotechnol. 34(2016) 746-756.
[65]	S.H. Kim, Y.B. Seo, Y.K. Yeon, et al., Biomaterials 260 (2020) 120281.
[66]	V. Mironov, R.P. Visconti, V. Kasyanov, et al., Biomaterials 30 (2009) 2164-2174.
[67]	G. Villar, A.D. Graham, H. Bayley, Science 340 (2013) 48.
[68]	Z.Y. Xu, H.J. Ren, J.J. Huang, et al., World J.Gastroenterol. 25(2019) 1775-1782.
[69]	V. Matter-Parrat, P. Liverneaux, Hand Surg. Rehabil. 38(2019) 338-347.
[70]	J. Maier, M. Weiherer, M. Huber, C. Palm, Quant. Imaging Med. Surg. 9(2019) 30-42.
[71]	M. Javaid, A. Haleem, Clin. Epidemiol. Glob. Health 7 (2019) 317-321.
[72]	W.J. Hendrikson, J. Rouwkema, F. Clementi, et al., Biofabrication 9(2017) 31001.
[73]	M. Bodaghi, A.R. Damanpack, W.H. Liao, Mater. Des. 135(2017) 26-36.
[74]	C. Cheng, H. Xie, Z. Xu, et al., Chem.Eng. J. 396(2020) 125242.
[75]	S. Miao, H. Cui, T. Esworthy, et al., Adv. Sci.(Weinh) 7(2020) 1902403.
[76]	M. Miotto, R.M. Gouveia, A.M. Ionescu, et al., Adv.Funct. Mater. 29(2019) 1807334.
[77]	A. Zolfagharian, M. Denk, M. Bodaghi, et al., Acta Mech.Solida Sin. 33(2020) 418-430.
[78]	W.M. Huang, C.L. Song, Y.Q. Fu, et al., Adv.Drug Deliv. Rev. 65(2013) 515-535.
[79]	Lancet 390 (2017) 1151-1210.
[80]	S. Miao, W. Zhu, N.J. Castro, et al., Sci.Rep. 6(2016) 27226.
[81]	D. Kashyap, P. Kishore Kumar, S Kanagaraj, Addit. Manuf. 24(2018) 687-695.
[82]	Y.S. Wong, A.V. Salvekar, K.D. Zhuang, et al., Biomaterials 102 (2016) 98-106.
[83]	H. Wei, Q. Zhang, Y. Yao, et al., ACS Appl. Mater. Interfaces 9 (2017) 876-883.
[84]	M.A . Biomed. Res. Int. 2015(2015) 729076.
[85]	T.C. Boire, M.K. Gupta, A.L. Zachman, et al., Acta Biomater. 24(2015) 53-63.
[86]	G. Lee, J. Choi, M. Kim, S. Ahn, Smart Mater. Struct. 20(2011) 105026.
[87]	L. Zhao, M. Zhang, B. Chitrakar, B. Adhikari, Crit. Rev. Food Sci. Nutr. (2020) 1-15.
[88]	C. Guo, M. Zhang, S. Devahastin, Food Hydrocoll. 112(2021) 106358.
[89]	C. He, M. Zhang, C. Guo, Innov. Food Sci. Emerg. Technol. 59(2020) 102250.
[90]	C. He, M. Zhang, S. Devahastin, ACS Appl. Mater. Interfaces 12 (2020) 37896-37905.
[91]	P. Phuhongsung, M. Zhang, B. Bhandari, Food Res. Int. 137(2020) 109605.
[92]	D. Deng, Y. Chen. J. Mech. Des. 137(2015) 21701.
[93]	J.W. Boley, W.M. van Rees, C. Lissandrello, et al., in: Proceedings of the Na- tional Academy of Sciences, 116, 2019, p. 20856.
[94]	M. Wagner, T. Chen, K. Shea, 3D Print. Addit. Manuf. 4(2017) 133-142.
[95]	A. Zolfagharian, A. Kaynak, S.Y. Khoo, A. Kouzani , Sens. Actuators A Phys. 274(2018) 231-243.
[96]	Q. Wang, X. Tian, L. Huang, et al., Mater.Des. 155(2018) 404-413.
[97]	G. Wang, Y. Tao, O.B. Capunaman, et al., in: A-line: 4D Printing Morphing Lin- ear Composite Structures, ACM, 2019, pp. 1-12. 2019 2019-01-01.
[98]	T. Huang, W. Wu, J. Mater. Chem. A 7(2019) 23280-23300.
[99]	M. Zeng, Y. Zhang, J. Mater. Chem. A 7 (2019) 23301-23336.
[100]	F. Momeni, S. Sabzpoushan, R. Valizadeh, et al., Renew. Energy 130 (2019) 329-351.
[101]	F. Momeni, J. Ni, Renew. Energy 122 (2018) 35-44.
[102]	X. Liu, Science 22 (2019) 489-506.
[103]	Y. Yang, F. He, Q. Guo, et al., Appl.Opt. 58(2019) 9808-9814.
[104]	X. Wang, Z. Shao, Space Electron. Technol. 13(2016) 96-100 104.
[105]	J. Kimionis, M. Isakov, B.S. Koh, A. Georgiadis, M.M. Tentzeris, et al., IEEE Trans. Microw. Theory 63(2015) 4521-4532.
[106]	B. Jo, B. Ryan, H. Jimmy, et al., in: Proceedings of the SPIE, 2017 2017 2017-05-18.
[107]	H.J. Song, K. Ajito, A. Hirata, A. Wakatsuki, Y. Muramoto, T. Furuta, N. Kukutsu, T. Nagatsuma, Y. Kado, Electronics Lett. 45(2009) 1121-1122.
[108]	M. Tonouchi, Nat. Photonics 1 (2007) 97-105.
[109]	G.Y. Yun, Y.G. Lee, Korean J. Comput. Des. Eng. 21(2016) 122-129.
[110]	L. Ren, B. Li, Y. He, et al., ACS Appl. Mater. Interfaces 12 (2020) 15562-15572.
[111]	L. Min, H. Zhang, H. Pan, et al., Science 19 (2019) 93-100.
[112]	R. Suriano, R. Bernasconi, L. Magagnin, M. Levi. J. Electrochem. Soc. 166(2019) B3274-B3281.
[113]	J. Li, C. Wu, P.K. Chu, M. Gelinsky, Mater. Sci. Eng. R Rep. 140(2020) 100543.
[114]	J. Su, X. Tao, H. Deng, et al., Soft Matter 14 (2018) 765-772.
[115]	S. Sundaram, D.S. Kim, M.A. Baldo, et al., ACS Appl. Mater. Interfaces 9 (2017) 32290-32298.
[116]	D.J. Glugla, M.D. Alim, K.D. Byars, et al., ACS Appl. Mater. Interfaces 8 (2016) 29658-29667.
[117]	G. Scalet, Actuators 9(2020) 10.
[118]	A. Zolfagharian, A. Kaynak, A. Kouzani, Mater. Des. 188(2020) 108411.
[119]	T.J. Wallin, J. Pikul, R.F. Shepherd, Nat. Rev. Mater. 3(2018) 84-100.
[120]	R.L. Truby, M. Wehner, A.K. Grosskopf, et al., Adv.Mater. 30(2018) 1706383.
[121]	P.A. Lopes, H. Paisana, A.T. De Almeida, et al., ACS Appl. Mater. Interfaces 10(2018) 38760-38768.
[122]	Q. Ge, C.K. Dunn, H.J. Qi, M.L. Dunn, Smart Mater. Struct. 23(2014) 94007.
[123]	J. Teoh, C. Chua, Y. Liu, et al., in: Proceedings of the 2nd International Confer- ence on Progress in Additive Manufacturing, 2016, pp. 288-293.
[124]	K. Liu, J. Wu, G.H. Paulino, H.J. Qi, Sci. Rep. 7(2017) 3511.
[125]	https://wonderfulengineering.com/nasa-designs-new-super-elastic-tire-for-mars-terrain/.
[126]	M.C. Mulakkal, A.M. Seddon, G. Whittell, et al., Smart Mater.Struct. 25(2016) 95052.
[127]	W. Zhang, F. Zhang, X. Lan, et al., Compos.Sci. Technol. 160(2018) 224-230.
[128]	T.R. Nachtigall, O. Tomico, R. Wakkary, et al., 2018, p. 2018.
[129]	https://n-e-r-v-o-u-s.com/projects/albums/kinematics-cloth/.
[130]	J. Teoh, J. An, X. Feng, et al., Materials 11 (2018) 376(Basel).
[131]	Y. Liu, W. Zhang, F. Zhang, et al., Compos.Part B Eng. 153(2018) 233-242.
[132]	T. Chen, J. Mueller, K. Shea, Sci. Rep. 7(2017) 45671.
[133]	M. Bodaghi, A.R. Damanpack, W.H. Liao, Smart Mater. Struct. 25(2016) 105034.
[134]	S. Akbari, A.H. Sakhaei, K. Kowsari, et al., Smart Mater.Struct. 27(2018) 65027.
[135]	https://www.marketsandmarkets.com/Market-Reports/4d-printing-market-3084180.html.
[136]	https://www.nasa.gov/directorates/heo/scan/engineering/technology/txt_accordion1.html.
[137]	A.Y. Lee, J. An, C.K. Chua, Eng. PRC 3 (2017) 663-674.
[138]	A. Le Duigou, G. Chabaud, F. Scarpa, M Castro, Adv. Funct. Mater. 29(2019) 1903280.
[139]	A.Y. Lee, A. Zhou, J. An, et al., Virtual Phys.Prototyp. 15(2020) 481-495.
[140]	E. Sachyani Keneth, R. Lieberman, M. Rednor, et al., Polymers 12 (2020) 710 BASEL.
[141]	Z.X. Khoo, J.E.M. Teoh, Y. Liu, et al., Virtual Phys. Prototyp. 10(2015) 103-122.
[142]	Y. Yu, H. Liu, K. Qian, et al., Comput.Aided Des. 122(2020) 102817.
[143]	S. Chung, S.E. Song, Y.T. Cho, Int. J. Precis. Eng. Manuf. Green Technol. 4(2017) 359-371.