Introdução ao funcionamento da impressão 4-D

Em outras palavras, e se pudéssemos imprimir objetos quadridimensionais?

Ok, claro, tecnicamente tudo é quadridimensional – na verdade, 10 ou mais dimensões , de acordo com os físicos – mas pensamos principalmente no mundo construído em termos de comprimento, largura e altura. A quarta dimensão, o tempo, vemos como o inimigo, cujos efeitos fazemos o nosso melhor para resistir (os especialistas permanecem divididos sobre se a quinta dimensão é "The Twilight Zone" ou a banda que cantou "The Age of Aquarius") .

E assim construímos paredes e tubos tão fortes quanto podemos – e continuamos consertando-os à medida que envelhecem – porque a construção leva tempo, dinheiro e esforço, e não queremos fazê-lo repetidamente. Mas e se o tempo não fosse o inimigo? Suponha que uma estrutura pudesse se desdobrar, como o origami. Imagine se suas paredes pudessem flexionar ou endurecer em resposta a cargas em movimento, ou se um cano enterrado pudesse mudar de forma para acomodar fluxos de água variados – ou para bombear água via peristaltismo, como seu sistema digestivo. Através da impressão 4-D, nada é imutável, a menos que você queira.

Se pesquisadores e fabricantes conseguirem fazê-lo funcionar, a impressão 4-D pode mudar toda a nossa ideia de fabricação. As empresas podem imprimir abrigos, máquinas e ferramentas, depois embalá-los e enviá-los para onde for necessário – áreas de desastre, talvez, ou prepará-los para ambientes hostis, como o espaço ou o fundo do oceano. Lá, as condições ambientais prejudiciais aos humanos podem realmente impulsionar as mudanças na forma e nas propriedades do objeto – não apenas uma vez, mas repetidamente.

No centro de tudo está a física básica, química e geometria por trás dos processos naturais mais mundanos. Considere como seu cabelo muda de forma quando uma tempestade se aproxima, uma simples questão de água transportada pelo ar fazendo com que as proteínas de queratina formem uma proporção incomumente alta de ligações de hidrogênio, o que as faz dobrar para trás em vez de esticar [fonte: Stromberg ]. Ou pense em como uma cadeira inflável plana assume uma forma previsível à medida que absorve ar porque suas seções têm propriedades diferentes.

Dispositivos quadridimensionais não requerem humanos para construí-los, nem são robôs que requerem microchips, servos e armaduras para funcionar. Sua única "programação" envolve a geometria, a física e a química embutidas em suas estruturas.

1. Adicionando Dimensão
2. Matéria Programável: Geometria é Destino
3. Origami dobrável
4. Desvendando o futuro do 4-D

Em sua essência, a impressão 4D é uma combinação de impressão 3D e outro campo de ponta, a automontagem .

A automontagem é exatamente o que parece – a ordenação espontânea de peças em um todo maior e funcional. O campo é popular nos círculos de nanotecnologia por duas razões muito boas. Primeiro, a automontagem já acontece em nanoescala e fornece a força motriz por trás de processos que vão desde o dobramento de proteínas até a formação de cristais [fonte: Boncheva and Whitesides ]. Em segundo lugar, não temos martelos, chaves inglesas e chaves de fenda que possam construir uma máquina do tamanho de uma molécula. Ele precisa se virar sozinho.

Mas se pudéssemos aumentar a automontagem para proporções humanas, isso poderia nos permitir tornar os produtos atuais mais baratos e mais simples, ou criar novas tecnologias impossíveis [fonte: Boncheva e Whitesides ]. É um trabalho meticuloso e muitas vezes frustrante. Mesmo em circunstâncias ideais, é necessário quebrar uma sequência de montagem, desenvolver peças programáveis ​​e criar uma fonte de energia que fará com que sua engenhoca funcione. Construir alguma correção de erros também não é uma má ideia [fonte: Tibbits ]. Principalmente, porém, você precisa das ferramentas e materiais certos para o trabalho.

Insira a impressão 3D . Embora novas abordagens continuem a surgir, tradicionalmente, a impressão 3-D implicou a colocação repetida de camadas de polímero cuidadosamente definidas em uma mesa de impressão. À medida que cada nova camada endurece e se funde com as de baixo, surge uma forma tridimensional. Os primeiros modelos podiam imprimir com apenas um material por vez, mas as impressoras 3-D mais recentes permitem uma ampla variedade de mídias de impressão e impressão com mais de um material por vez. Esse é um avanço importante para a impressão 4-D, porque materiais variados permitem que os desenvolvedores construam em áreas que endurecem, flexionam ou incham, ou que "querem" dobrar de certas maneiras. Eles podem ter zonas que absorvem água como uma esponja ou que geram corrente elétrica quando expostas à luz. O céu é o limite, contanto que você '

Isso é o que o Self-Assembly Lab do MIT chama de matéria programável – uma abordagem da ciência, engenharia e materiais que se concentra na matéria que pode ser codificada para se remodelar ou alterar sua função. Uma aplicação da matéria programável é a impressão 4-D [fonte: MIT ].

O mercado para a mutabilidade

A 2015 report by market research firm Marketsandmarkets projected that 4-D printing would constitute a $555.6 million sector annually by 2025. The report assumes that 4-D tech will see commercialization in the short term, but only moderate initial progress (the switchover carries a high initial cost). As for early adopters, the report singled out the aerospace, defense and military sectors, but it saw industries such as automotive, textiles, health care, construction and utilities as potential early adopters as well [source: Halterman].

MIT researchers are not the only ones working on 4-D printing, but the school's Self-Assembly Lab is the one that made the earliest splash, largely thanks to the TED talks of its director, architect Skylar Tibbits.

The lab's researchers first entered the world of self-assembly by creating simple, large-scale, self-building robots. When they found the labor and expense unworkable, they turned to making shapes and materials with logic built into them.

In 2010, they created Logic Matter, a set of interlocking shapes that could solve computational problems using only their geometry.

Reduced to its most basic, a computer operates using electronic gates that combine 1s and 0s and return a true or false answer. These gates use Boolean algebra, which asks questions like "are both inputs 1s?" or "is either input a 1?" The Tibbits lab asked the same questions, but using complex polyhedrons instead of the usual electrical on/off states representing 1s and 0s. Input involved clicking shapes into place. This created a new configuration that would allow the next shape — the output — to attach only in an upward (true) or downward (false) orientation, providing the answer.

Logic Matter did not rise to the level of self-assembly — the pieces required human hands to snap them together — but it did constitute an important first step in that direction by showing that matter could have instructions built into it [source: Tibbits]. Over the years that followed, researchers from the Self-Assembly Lab moved increasingly to items more in keeping with their name: geometric shapes that would combine if rolled or shaken in a container, chains that assumed particular shapes when shaken, and so on.

This marked the next important step: combining a built-in geometric tendency with an input of energy (or some other environmental factor) to kick it into gear.

But what is this geometric tendency? Well, if you've ever tried to make something out of cardboard (or wood, or metal), you know that it folds more readily if you score it first. Scoring, then, is a kind of programming, a way to make the material more likely to behave the way you want it to. Now instead of cardboard, imagine a combination of materials, some of which can absorb water and grow while others remain stiff. Toss it in water, and watch its shape change. Get clever enough with your foldings and scorings and, before you know it, you have something truly special.

But first, you need a lot of precise control over the materials you use and the pattern in which your machinery lays them down. And this approach will work better on smaller scales, where energy inputs and material differences can have a greater effect. Multi-material 3-D printing helped provide the control researchers needed, but they also needed the right materials.

When Tibbits mentioned his idea to the folks at Stratasys, a Minnesota-based 3-D printing company, they showed him a material that could grow 150 percent when submerged in water. Water offers a promising means by which to manipulate 4-D objects, since nature provides numerous working models of objects that change shape in response to moisture. We call them plants.

Plants exhibit tropisms, tendencies to grow in certain ways based on environmental factors, such as sunlight (phototropism), water (hydrotropism), gravity (gravitropism), chemicals (chemotropism) and even physical contact (thigmotropism). For example, plants tend to bend toward sunlight because sunlight kills hormones called auxins that encourage growth. Consequently, the side of a plant facing away from the sun grows faster than the side facing it, causing the plant to bend toward the light. With a little imagination, it's easy to see how we might similarly bend the physics that link materials, environments and energy to do our bidding.

Given the inspiration that plants have provided 4-D printing researchers, it's perhaps not surprising that a Harvard team made news in 2016 by creating a 4-D-printed "orchid" that assumed its namesake's shape when placed in water. The flower was printed using a hydrogel composite, which was piped, layer after layer, like icing from a pastry bag, onto the print bed [source: McAlpine].

Two aspects of the printing process explain the flower's behavior. First is the use of hydrogel, which can absorb large amounts of water. The second is the fact that the composite also contained cellulose fibrils — small, strong fibers essential to plant structure. Because the cellulose always flowed in a known direction, the team could carefully pattern it to control which parts of the flower could swell up and which parts would remain stiff once exposed to water [source: McAlpine].

No doubt, as time goes by we'll see many more experiments using a variety of other materials, such as conductors for flexible and dynamic electric circuits . But we'll also likely see the term 4-D printing, like most buzzwords, take on a life of its own, expanding to comprise a wider array of topics. For example, one company, Nervous System, describes its novel technique for 3-D printing clothing — which creates clothes from cleverly arranged nylon petals connected by joints— as "4-D printing" [source: Rosencranz].

Let's look at a few other potential 4-D futures.

I Don't Know If It's Art, But I'd Wear It

Nervous System's dress was designed using kinematics, sometimes referred to as the geometry of motion. Through a lot of computation and some clever design, the company could build flexible garments out of tens of thousands of rigid, interlocking pieces. The Museum of Modern Art has since acquired the dress and the software used to create it for its permanent collection [source: Rosencranz].

The world of nanomachines has a head start on the road of self-assembly, in part because it can draw from nature for examples of efficient, complex designs that self-assemble, rarely make mistakes and self-repair as needed. Moving these principles into the human scale has proven challenging but, if it works, the possibilities are impressive — a fact that is not lost on the U.S. Army, which has already split $855,000 among Harvard University, University of Pittsburgh and University of Illinois to fund research into military applications such as self-building bridges and shelters [source: Campbell-Dollaghan].

We've already mentioned how fashion and furnishings can provide a fun, profitable way to introduce a novel technology, and given the fact that one size very clearly does not fit all, it's a sector ripe for such applications. We could soon see patterns — or hemlines — that change on command.

The point is, much of 3-D and 4-D printing's appeal lies in its flexibility. Via 3-D computer modeling, a company could customize a dress or shoe to fit any body, right out of the gate, without any cutting or sewing — and print it as a one-off [source: Rosencranz]. Using 4-D materials and geometry, the garment could self-adjust in response to forces of stretch and strain. A running shoe could stiffen to provide lateral support and stability while sensing the stresses of a tennis match, for example.

BMW has already shown a concept car that would incorporate 4-D designs in what they call "Alive Geometry." Picture interior or exterior components that could change shape to handle shifting driving conditions. Outside the car, 4-D panels could adjust to temperature, airflow, steering or sensor input to maximize aerodynamic efficiency. Tires and brakes could also change in response to road conditions [source: Vijayenthiran].

In the future, as biomimetics and 4-D printing come together, we could see medical devices tailored to our bodies and even body augmentations that respond to their environments [source: Grunewald]. Now that's what we call personalized medicine.

Of course, 4-D printing will have to overcome numerous limitations before it can reach its full potential. First, the process remains, for now anyway, very, very slow. And its dependence on geometry limits it somewhat in terms of what it can do, but that's likely a temporary impediment. Potentially more serious are the stresses that act on any material that is forced to bend, or the failure points possibly introduced by such geometry. Moreover, in some cases, 4-D materials have trouble un-changing — they stay in their new form rather than reverting back to the old, or fail to switch among states as designed [source: Wassmer].

As to whether 4-D printing constitutes a fad, a curiosity or the next big thing, only time — appropriately enough — will tell.

3-D Printing Picks up Speed

One of the main problems with 3-D printers is that they are s-l-o-w. But a new technology launched by Carbon3D at the 2015 TED conference might just have kicked the technology into higher gear. Instead of the additive approach used by most of its cousin printers, it uses oxygen and light to grow objects as it pulls them from a resin bath, in a process resembling high-speed crystal growth [source: DelViscio].

Author's Note: How 4-D Printing Works

4-D printing remains in its early stages — certainly too early to know whether it's anything more than a clever way to market a collection of related ideas, let alone if it can be made practical. But a few of the sorts of people who bet on these kinds of things are betting on it, and why not? If it can do a fraction of what it's touted to be able to do, it'll go places. Just look how far 3-D printing has come in just a few decades.

Still, one has to wonder if there's not a limit to how fast these macroscale self-assembling technologies can operate. There's only so fast a material can grow, curl, bend or just plain slam together without having to alter the material in some radical ways. Then again, perhaps enough energy jammed into a given system can overcome any such problem, assuming the materials can take the stresses.

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