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4D printing: intelligent materials of the future?

Giancarlo rizza
Giancarlo Rizza
Researcher at CEA specialised in 4D additive manufacturing

3D print­ing tech­nol­o­gy, which has been around for near­ly 35 years, has played a major role in rein­vent­ing tra­di­tion­al man­u­fac­tur­ing mod­els. It has enabled the cre­ation of a mar­ket esti­mat­ed at €30 bil­lion euros with a growth rate of 20% per year. How­ev­er, when an inven­tion reach­es matu­ri­ty, there comes a time when a new tech­nol­o­gy arrives on the mar­ket that will replace it. 4D print­ing, where the fourth dimen­sion is time, rep­re­sents this break­through technology.

In a way, 4D print­ing rep­re­sents a func­tion­al form of 3D print­ing and allows the print­ing of dynam­ic objects that active­ly respond to exter­nal stim­uli. This pos­si­bil­i­ty of pro­gram­ming the mate­r­i­al so that arti­fi­cial objects can behave like intel­li­gent organ­isms opens new per­spec­tives for research along­side an infi­nite num­ber of poten­tial applications.

Time, the 4th dimension

Para­dox­i­cal­ly, the fas­ci­nat­ing hypoth­e­sis of being able to pro­gram mat­ter has pre­vi­ous­ly been intro­duced in anoth­er sci­en­tif­ic field. In 1991, Tof­foli and Mar­go­lus, two com­put­er sci­en­tists from MIT, intro­duced the term “pro­gram­ma­ble mat­ter” to describe a set of com­pu­ta­tion­al nodes arranged in a cer­tain space, which can com­mu­ni­cate with each oth­er only via first neigh­bours1.

This idea, by cross-fer­til­i­sa­tion, spread to oth­er dis­ci­plines, until in 2005 the DARPA (Defense Advanced Research Projects Agency) launched a mul­ti-year project with the enti­tled “Real­iz­ing Pro­gram­ma­ble Mat­ter”, focus­ing on mod­u­lar robot­ics, pro­gram­ming assem­blies and nano­ma­te­ri­als2. Now, the sto­ry cross­es paths with that of intel­li­gent mate­ri­als; mean­ing mate­ri­als with prop­er­ties that can be acti­vat­ed or mod­i­fied by exter­nal stim­uli either phys­i­cal (elec­tric field, mag­net­ic field, light, tem­per­a­ture, vibra­tions), chem­i­cal (PH, pho­to­chem­istry) or bio­log­i­cal (glu­cose, enzymes, biomolecules).

Final­ly, in 2013, Sky­lar Tib­bits, founder of the Self-assem­bly lab at MIT, dur­ing his speech at a TedX con­fer­ence, pro­posed using smart mate­ri­als in 3D print­ing process­es to pro­duce pro­gram­ma­ble objects, and pro­posed the name “4D print­ing” for this new tech­nol­o­gy. The con­ver­gence of these three areas of research – 3D print­ing, pro­gram­ma­ble mate­ri­als and smart mate­ri­als – led to the 4D rev­o­lu­tion3.

More complicated than it sounds

Clear­ly, at the heart of this new tech­nol­o­gy are smart mate­ri­als. This is both the great­est asset and the biggest hur­dle to its devel­op­ment, as research in this area is still in its infan­cy and few smart, print­able mate­ri­als are cur­rent­ly avail­able (most­ly poly­mers). This is why part of the research is focused on the pos­si­bil­i­ty of extend­ing the set of print­able mate­ri­als to ceram­ic and metal­lic mate­ri­als, but also to bio­log­i­cal and com­pos­ite materials.

How­ev­er, the mate­r­i­al is not the only cri­te­ri­on to con­sid­er, it is also nec­es­sary to be able to design and cre­ate an object with a desired behav­iour. Hence, such oper­a­tions require work to cor­rect­ly com­bine mate­r­i­al, process­es, and func­tion­al­i­ties. As well as devel­op method­ol­o­gy based on the tri­ad of design-mod­el­ling-sim­u­la­tion so that the print­ed object responds in an appro­pri­ate way to exter­nal stimuli.

In par­al­lel with com­put­er sci­ence, if a “bit” is the basic unit of pro­gram­ming, the vox­el (a con­trac­tion of the words vol­ume and ele­ment) is the ele­men­tary vol­ume that stores the physical/chemical/biological infor­ma­tion of an active mate­r­i­al in 4D print­ing. Pro­gram­ming an object with print­ed behav­iour in 4D there­fore means mod­el­ling and sim­u­lat­ing the opti­mal dis­tri­b­u­tion of vox­els so that the appli­ca­tion of a stim­u­lus cor­re­sponds to a deter­min­is­tic effect. This com­plex prob­lem requires ad hoc solu­tions where the desired behav­iour is treat­ed as an input vari­able, while the action (the vox­el dis­tri­b­u­tion) is treat­ed as an out­put variable.

Final­ly, an object print­ed in 4D can be het­ero­ge­neous. That is to say: com­posed of one or more active mate­ri­als inter­spersed with pas­sive ele­ments. This requires the devel­op­ment of mul­ti-mate­r­i­al print­ers and spe­cif­ic codes to adapt them to the mate­ri­als used and the stim­uli introduced.

What are the applications?

The pos­si­bil­i­ty of com­bin­ing com­plex geome­tries and evolv­ing behav­iours allows 4D print­ing to push the lim­its of object design and to rev­o­lu­tionise the world of man­u­fac­tur­ing as it is under­stood today. It will fos­ter the devel­op­ment of new tech­nolo­gies that are based, for exam­ple, on self-assem­bly, if the print­ed ele­ments can assem­ble them­selves autonomous­ly at a spe­cif­ic time and place with­out human inter­ven­tion. On self-adapt­abil­i­ty if the print­ed struc­tures can com­bine sens­ing and actu­a­tion with­in the same mate­r­i­al. Or on self-repair, if print­ed objects pos­sess the abil­i­ty to detect and repair defects (wear, man­u­fac­tur­ing) by them­selves reduc­ing the need for inva­sive procedures.

Fig­ure 1: a) Self-assem­bly of a trun­cat­ed octa­he­dron print­ed in 4D evap­o­rat­ing in liq­uid medi­um. Cred­its Self-assem­bly Lab4. b) Syn­thet­ic bio-inspired fab­ric formed from a set of 4D print­ed micro­droplets. Cred­its Sci­ence5. c) Ther­moac­tive Eif­fel Tow­er print­ed in 4D with shape mem­o­ry poly­mers. Cred­its Sci­en­tif­ic Reports6.

There are count­less pos­si­bil­i­ties. 4D print­ing is already a dri­ving force in flex­i­ble robot­ics for the fab­ri­ca­tion of ever small­er robots (mil­li-robots, micro-robots, nano-robots) capa­ble of work­ing in haz­ardous envi­ron­ments or mov­ing in con­fined envi­ron­ments, such as in the human body, to deliv­er a drug or to per­form micro-inva­sive oper­a­tions. In the field of bio­med­ical appli­ca­tions, stud­ies are under­way to be able to bio-print stents, organs, and intel­li­gent tis­sues. 4D print­ing will pro­mote the devel­op­ment of flex­i­ble and embed­ded elec­tron­ics as well as intel­li­gent sen­sors adapt­ed to the con­nect­ed city.

In the field of ener­gy, research is under­way to max­i­mize the effi­cien­cy of solar cells by inte­grat­ing microstruc­tures print­ed on flex­i­ble sub­strates. We can imag­ine con­sumer appli­ca­tions in the field of fash­ion and lifestyle, such as self-adapt­ing bio­mimet­ic tex­tiles or intel­li­gent self-fold­ing shoes. In archi­tec­ture, 4D print­ing will allow the devel­op­ment of a new approach focused on sus­tain­able devel­op­ment such as the Hygroskin project, which uses the hygro­met­ric prop­er­ties of wood to close and open a pavil­ion accord­ing to the humid­i­ty with­out any inter­ven­tion or exter­nal ener­gy. 4D print­ing also finds appli­ca­tions in research and cre­ation prac­tices in art and sci­ence around the notion of mat­ter with behav­iour to ques­tion the rela­tion­ship between the liv­ing world and the arti­fi­cial world.

Fig­ure 2. a) Autonomous archi­tec­tur­al sys­tems that adapt to envi­ron­men­tal changes through hygro­scop­ic mate­r­i­al prop­er­ties. Cred­its Mate­r­i­al Research Soci­ety (MRS)7. b) 4D-print­ed space chain mail to pro­tect astro­nauts from fly­ing mete­orites. Cred­its NASA8. c) Use of active mate­r­i­al in research-cre­ation prac­tices. Cred­its Arts&Sciences Chair Ecole poly­tech­nique-ENSAD-Fon­da­tion Caras­so9.

The future of 4D printing

To quote Bernard de Chartres “we are like dwarfs on the shoul­ders of giants”. We can already affirm that 4D print­ing has been added to the process of pro­found trans­for­ma­tion, of design and pro­duc­tion of indus­tri­al objects, ini­ti­at­ed by addi­tive man­u­fac­tur­ing. Although com­pared to the glob­al mar­ket for 3D tech­nol­o­gy (€30bn/year), the mar­ket for 4D print­ing is still mod­est (€30–50m/year), its dis­rup­tive char­ac­ter is obvi­ous. This is not sur­pris­ing because in the life cycle of a prod­uct, 4D print­ing is still in its infan­cy. For this rea­son, and beyond the tech­ni­cal-sci­en­tif­ic devel­op­ments, 4D print­ing still needs to find its eco­nom­ic mod­el and demon­strate the pos­si­bil­i­ty of indus­tri­al pro­duc­tion at an eco­nom­ic cost. Final­ly, in order for 4D print­ing to leave the research lab­o­ra­to­ries, this tech­nol­o­gy must nec­es­sar­i­ly go through the imple­men­ta­tion of a clear and ambi­tious roadmap and cre­ate in par­al­lel a “social desir­abil­i­ty”. This will also require the will­ing­ness of investors and indus­tri­al­ists to sup­port 4D print­ing and to push it towards eco­nom­ic maturity.

1T. Tof­foli and N. Mar­go­lus, Pro­gram­ma­ble mat­ter: con­cepts end real­i­sa­tion, Phys­i­ca D 47 (1991) 263–272
2https://​cog​ni​tivemedi​um​.com/​a​s​s​e​t​s​/​m​a​t​t​e​r​/​D​A​R​P​A​2​0​0​6.pdf
3Active Mat­ter, Edit­ed by Sky­lar Tib­bits, The MIT Press (2017)
4https://​self​assem​bly​lab​.mit​.edu/​4​d​-​p​r​i​nting
5G. Vil­lar et al, A Tis­sue-Like Print­ed Mate­r­i­al, Sci­ence, 5 Apr 2013, Vol 340, Issue 6128, pp. 48–52
6Q Ge et al, Mul­ti­ma­te­r­i­al 4D print­ing with tai­lorable shape mem­o­ry poly­mers, Sci­en­tif­ic reports, 2016, 6(1): 1–11
7Cor­rea Zulu­a­ga et al, 3D Print­ed Hygro­scop­ic Pro­gram­ma­ble Mate­r­i­al Sys­tems, Mater. Res. Soc. Symp. Proc. Vol. 1800 © 2015 Mate­ri­als Research Soci­ety
8https://​www​.nasa​.gov/​f​e​a​t​u​r​e​/​j​p​l​/​s​p​a​c​e​-​f​a​b​r​i​c​-​l​i​n​k​s​-​f​a​s​h​i​o​n​-​a​n​d​-​e​n​g​i​n​e​ering
9Antoine Des­jardins and Gian­car­lo Riz­za, The use of active mat­ter in research-cre­ation prac­tices: Using an artis­tic vocab­u­lary for 4D print­ing of mag­ne­to-active poly­mers deployed in exper­i­men­tal and obser­va­tion devices. https://​robot​i​cart​.org/​i​c​r​a2021

Contributors

Giancarlo rizza

Giancarlo Rizza

Researcher at CEA specialised in 4D additive manufacturing

Giancarlo Rizza is a specialist in 4D additive manufacturing, electron microscopy and nanostructuring. For ten years, he created and directed the interdisciplinary microscopy centre at École Polytechnique (CimeX). In this framework, he coordinated the Nan'eau project (labelled strategic by the Université Paris-Saclay) for the development of a multi-correlative microscopy platform (optical, electronic and X-ray). Giancarlo Rizza has also collaborated with the International Atomic Energy Agency (IAEA). He is a member of the steering committee of the international conference "Radiation Effects in Insulators" (REI), of the Groupement National de Recherche (GdR) NACRE (Nanocrystals in dielectrics for electronics and optics) and of the "Chaire Arts&Sciences" of the Ecole Polytechnique-ENSAD-Fondation Carasso. In this context, he develops the use of intelligent materials in research-creation practices and is interested in their dissemination in scientific conferences as a means of communication with society.