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