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How new materials are transforming industry

4D printing: intelligent materials of the future?

with Giancarlo Rizza, Researcher at CEA specialised in 4D additive manufacturing
On February 16th, 2022 |
4min reading time
Giancarlo rizza
Giancarlo Rizza
Researcher at CEA specialised in 4D additive manufacturing
Key takeaways
  • 4D printing is the functional form of 3D printing, capable of creating dynamic objects that respond to external stimuli.
  • The term "4D printing" to produce programmable objects was proposed by Skylab Tibias during a TedX Talk.
  • One use is to push the limits of design by allowing “self-assembly” of smart materials.
  • Other applications of 4D printing include for prosthetics in medicine, or in energy to maximise photovoltaic structures.
  • It could be said that 4D printing is already contributing to a profound transformation in design and production of industrial objects, initiated by 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​nit​ivemedi​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://​sel​fassemblylab​.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://​roboti​cart​.org/​i​c​r​a2021

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