Origami and kirigami in the service of science

Have you ever tried to make an A4 sheet of paper stand up? Flex­i­ble as it is, no mat­ter how hard you try, it will keep col­laps­ing in on itself. But if you fold the same sheet length­wise, it gains a new prop­er­ty: more rigid, this time it stands on the table! How­ev­er, the mate­r­i­al of the sheet does not change, only a dif­fer­ent aspect of its struc­ture has been added. How can this change in prop­er­ties be explained?

This phe­nom­e­non can be observed in nature, in var­i­ous forms – such as the leaf of a tree, which has a spe­cif­ic fold­ing for its unfold­ing out of the bud and which rein­forces, at the same time, its struc­ture. Origa­mi, the art of fold­ing, and kiriga­mi, the art of cut­ting, work in a sim­i­lar way. Sophie Ramana­nari­vo, a researcher at the Hydro­dy­nam­ics Lab­o­ra­to­ry (Lad­HyX*¹), is cur­rent­ly work­ing on these arts and their con­tri­bu­tion to science.

One of the main advan­tages of origa­mi and kiriga­mi is it’s the flex­i­bil­i­ty they bring to the mod­i­fied object. What is more, this flex­i­bil­i­ty becomes con­trol­lable. A flex­i­ble object can, through this char­ac­ter­is­tic, acquire new prop­er­ties. “One of my pre­vi­ous projects con­sist­ed of observ­ing and under­stand­ing the use­ful­ness of the flex­i­bil­i­ty of the wings of cer­tain insects,” explains Sophie Ramana­nari­vo. “In fact, this char­ac­ter­is­tic was a pas­sive way of lim­it­ing the effort of flap­ping these wings for bet­ter per­for­mance².” Anoth­er study looked at the folds that made up the wings of cer­tain insects³. Instead of hav­ing mus­cles that would allow a stronger flap­ping action, the folds struc­tur­ing their wings give a greater ampli­tude to the flap­ping action, while facil­i­tat­ing their deploy­ment. “It would be inter­est­ing to observe the role of these folds in flight per­for­mance,” admits the researcher. “This is some­thing I would like to study in the future.”

In this phe­nom­e­non, it is not the mate­r­i­al of the wing that gives it this prop­er­ty, but the folds that it is com­posed of. This struc­ture can be repro­duced on a sheet of paper, using origa­mi. “Origa­mi and kiriga­mi are used as meta­ma­te­ri­als,” she explains. “The prop­er­ties of the object do not come from its mate­r­i­al, but from the struc­ture we give it.”

These tech­niques soon became of inter­est to the field of ‘soft robot­ics’⁴⁵. “Pre­vi­ous­ly, in robot­ics, we tend­ed to favour rigid com­po­nents,” explains the researcher, “so that each of the robot’s parts that had to move in rela­tion to each oth­er was robust. But there is a real ben­e­fit in mak­ing com­po­nents that are more flex­i­ble: this field of research makes it pos­si­ble.” Like an octo­pus ten­ta­cle, which is much more flex­i­ble than the arm of a tra­di­tion­al robot and has greater free­dom of move­ment. How­ev­er, the dis­ad­van­tage of a weak ten­ta­cle, which pre­vents it from car­ry­ing heavy loads, must be tak­en into account. 

The tech­niques spe­cif­ic to these Japan­ese arts are sub­jects of research in full expan­sion, “espe­cial­ly as it is a ‘low-cost’ way of mak­ing mate­ri­als with very impres­sive prop­er­ties”, insists Sophie Ramana­nari­vo. The aim is there­fore to make an object that can ful­fil a func­tion ‘pas­sive­ly’. A good exam­ple of this type of pas­sive func­tion is a valve that can open accord­ing to the inten­si­ty of the water flow it encounters. 

This valve is designed using origa­mi fold­ing tech­niques. These folds give the valve more flex­i­bil­i­ty: if the flow of water reach­es a cer­tain speed – itself set accord­ing to our require­ments – it will open to allow the flow to take place with­out the need to oper­ate it remote­ly. The process is there­fore pas­sive. “Being able to per­form a func­tion pas­sive­ly, with a flex­i­ble object, lim­its the process­es that would have to be put in place if the func­tion in ques­tion were active,” says the researcher. There is no need to install an oper­a­tor to mea­sure the flow rate and final­ly acti­vate the valve at the right moment.

A sig­nif­i­cant advan­tage is that a flex­i­ble object tends to adapt eas­i­ly to its envi­ron­ment, whether it is sta­ble or sub­ject to chang­ing con­di­tions. “It’s like the fable of the Oak and the Reed, the lat­ter being flex­i­ble enough to cope with the wind,” she says. “This phe­nom­e­non can also be observed with sea­weed, which can fol­low the sea cur­rent with­out being uproot­ed. But to design such an object, you need to be able to con­trol how it will deform. Origa­mi and kiriga­mi allow you to do just that: con­trol the defor­ma­tion in a fair­ly com­plex way,” con­cludes Sophie Ramana­nari­vo. “That is why this tech­nique is of such great research interest.”

These Japan­ese arts allow the cre­ation of flex­i­ble objects at a low­er cost, more resis­tant depend­ing on the con­di­tions of use, and whose pas­sive func­tion­ing could almost earn them the qual­i­fi­ca­tion of “intel­li­gent objects”. Thanks to all these advan­tages, origa­mi and kiriga­mi have many appli­ca­tions in many fields. 

“These Japan­ese arts could almost earn flex­i­ble objects the title of intel­li­gent objects.”

In fact, this type of tech­nique is already being used in every­day life, for exam­ple in a deliv­ery box. It con­sists of three lay­ers, one of which is made of cor­ru­gat­ed card­board – in the shape of a wavelet. This is an origa­mi tech­nique to absorb shocks dur­ing trans­port. The same goes for crepe bob­bins, also made of card­board, which use the kiriga­mi tech­nique to pro­tect what they surround.

These assets can also enable tech­no­log­i­cal inno­va­tions. For exam­ple, they allow the solar pan­els of a satel­lite⁷ to unfold and ori­en­tate them­selves accord­ing to the time of day, giv­ing it an ide­al posi­tion in rela­tion to the sun at all times. Once the con­trol of the objec­t’s defor­ma­tion was acquired, researchers were also able to make a kind of shield to pro­tect a drone: the rotariga­mi⁸.   

Pablo Andres