Programmable Matter Research Solidifies

The Defense Advanced Research Projects Agency (DARPA) is developing a technology that will allow future military equipment to change shape on command. Several university teams are working on different approaches to create "programmable matter"—made of individual pieces that can self-assemble into tools or spare parts. One of the approaches being examined uses sheets of self-folding material that can form three-dimensional shapes on command.

A revolutionary new technology may allow future warfighters to command their equipment to physically change itself to meet new operational needs or to form spare parts or tools. Researchers are developing techniques to order materials to self-assemble or alter their shape, perform a function and then disassemble themselves. These capabilities offer the possibility for morphing aircraft and ground vehicles, uniforms that can alter themselves to be comfortable in any climate, and “soft” robots that flow like mercury through small openings to enter caves and bunker complexes.

The goal of the Defense Advanced Research Projects Agency’s (DARPA’s) Programmable Matter program is to create a new type of matter that can assemble itself into complex three-dimensional objects on command, explains program manager Dr. Mitchell R. Zakin. The program originated to meet warfighters’ needs in rapidly changing battlefield environments. Citing the example of commercial software, Zakin notes that users are limited to the capabilities of a product’s latest version. He explains that this idea can be extended to hardware as well. “Can we have materials that are fluid enough, plastic enough—they can change—in terms of their capabilities, so that they can be used in any environment? And can they also take on the characteristics to solve many different problems with the same material?” he asks.

Zakin envisions programmable matter in this way: In the future a soldier will have something that looks like a paint can in the back of his vehicle. The can is filled with particles of varying sizes, shapes and capabilities. These individual bits can be small computers, ceramics, biological systems—potentially anything the user wants them to be. The soldier needs a wrench of a specific size. He broadcasts a message to the container, which causes the particles to automatically form the wrench. After the wrench has been used, the soldier realizes that he needs a hammer. He puts the wrench back into the can where it disassembles itself back into its components and re-forms into a hammer. “That is the essence of programmable matter,” he says.

Although the concept of self-forming matter smacks of science fiction, Zakin says that considerable progress has been made in proving the technology’s underlying science. Developing programmable matter is also its own new field of study: infochemistry, which blends several different sciences such as chemistry, information theory and control engineering to build information directly into materials.

Zakin explains that materials are “dumb,” in that they do not have much fluidity or plasticity in their properties. There are shape memory alloys that can slightly alter their shape when heated by an electric current, but he notes that their range of motion and capabilities are limited. To build truly changeable, plastic materials, the information to do so must be directly integrated into the material itself. The exact composition of the material can vary—it can be a chemical or a microchip, or a larger structure with computers embedded in it. The goal is to distribute processing capabilities throughout the material. “You’re blurring the distinction between materials and machines. Materials act like computers and communications systems, and communications systems and computers act like materials,” he says.

An important part of infochemistry is what Zakin describes as mesomatter, the particles needed to build structures. Ranging in size from 100 microns to a centimeter, these pieces are large enough to have machinery built into them. A key function behind mesomatter is separability. Zakin notes that a particular particle’s shape determines how it fits together with other particles, but its internal structure carries its function and data sharing capabilities. Not only does this combination of data and material allow for dynamic flexibility in creating structures, but he says that it can potentially create new states of matter. Conventional materials can transition from liquids to solids, but these new “infomaterials” can have infosolids, where the matter is solid and its information is localized; “infoliquids” where both the material and information are flowing, and any number of combinations in between.

Besides battlefield uses, programmable matter has potential applications ranging from aerospace to medicine. Morphing materials can be used to change an aircraft’s wings in flight or in clothing that alters its characteristics to keep users cool in the day and warm at night. Zakin says that another use would be to create a “universal spare part” capable of morphing to fit and repair a number of parts for forces on the move.

The Programmable Matter program is now approximately five months into its second phase, which is scheduled to last about 15 months. The first phase of the effort involved five teams, two from Harvard University, two from the Massachusetts Institute of Technology (MIT) and one from Cornell University. Zakin notes that all of the teams successfully met their goals and are all now working on phase two. The teams are made up of experts from a range of disciplines such as computer scientists, roboticists, biologists, chemical engineers, mechanical engineers, physicists and artists. Zakin describes the research on programmable matter as “the ultimate interdisciplinary endeavor.” Another important part of the program is that the five teams are collaborating with each other, not competing. This is because each team has its own strengths and weaknesses and they share information. The teams meet on a regular basis and present their results to each other to help facilitate the information sharing.

Zakin says that during the first phase of the Programmable Matter program, the teams immediately went from modeling to building prototypes. “They were so excited, we couldn’t stop them,” he says. He adds that the scientists realized that they had to begin building components to make sure that their models worked and to prove the harder technological aspects of their approaches.

Each of the teams has its own approach to developing programmable matter. These methods range from developing two-dimensional objects that fold into three-dimensional shapes to particles that build up to larger structures. One group is building what Zakin describes as “self-folding origami” machines that use specialized sheets of material with built-in actuators and data. These machines use cutting-edge mathematical theorems to fold themselves into virtually any three-dimensional object.

Programming the mesoscale components to take shape is a core part of the program. One Harvard team is using a DNA-based approach. Zakin notes that these researchers are manipulating large strands of DNA, not individual nanocomponents. The team has developed a programming language to manipulate the DNA. Researchers can command the binding interactions between long synthesized strands of DNA, something which he says has never been done before.

Another method uses a type of enzyme reaction that can take place in air or liquid. These “flow streams” are used as director functions. For example, to achieve a desired shape the flow captures a certain particle and then gathers other specific particles in the flow to form the object. By using selective attraction and repulsion, the various building blocks can be drawn together and formed into a shape. Once the framework is built, additional particles are added to provide structural strength.

One of the key challenges of DARPA’s Programmable Matter program is to get the individual pieces, ranging in size from 100 micrometers to one centimeter, to stick together to form an effective tool. One of the program’s research teams has developed a way to both program and coat objects with DNA. The DNA strands act as a "molecular Velcro" to hold small objects together to assemble into a tool. After it is used, the DNA can be commanded to release and disassemble the object.

A team at MIT is using tiny servo motors to assemble objects into desired shapes. But the advantage of creating strings is that all of the parts can be programmed. Zakin describes it as a tendon, which must react to varying forces placed on it through the skeletal structure it is attached to. He explains that by using a fixed set of building blocks and putting specific stresses on individual particles, they will combine to build different shapes.

One potential application for this approach would be the ability to open or unfold large, complex structures in space or under water, regions where it is difficult to place and assemble large structures. For space launches, launch weight limitations can be severe. This would allow complex structures such as antenna arrays to be built or stored in very small spaces because their components are very small.

Another Harvard team is building a device that Zakin calls “a generalized Rubik’s Cube” consisting of a central organizing mechanism. Zakin adds that the device itself does not resemble a Rubik’s Cube, but its mechanism is inspired by the toy and it allows scientists to build a variety of shapes that can alter their exteriors to perform different tasks.

Programming particles is one challenge, but an equally important goal is making them stick together to create a useful tool. This process, known as adhesion, is difficult because the particles must self-assemble and then undergo torque or other stresses without failing. Zakin maintains that this is one of the major basic science questions of the program.

Some of the approaches that use sheets or strings of material already have some strength built into them. But for the particle approaches, the objects must stick together as if they were glued. Zakin shares that the team working with DNA is planning to use it as a “molecular Velcro.” He explains that the team’s scientists believe that it is necessary to get enough DNA on a surface to achieve adhesion. “DNA strands stick together. Each pair that sticks together is an adhesive. The trick is getting enough, and that means getting a density of DNA on a certain area,” he says. In the program’s first phase, the researchers demonstrated the highest density of DNA coverage on a surface ever achieved. Zakin says that this approach has potential applications in biological sciences and medicine.

At the end of phase two, the teams must be able to assemble four or five three-dimensional solids of a specific size and shape from a set of building blocks. Zakin notes that not all of the building blocks have to be used to create a specific shape, but they must demonstrate the ability to build objects the size and shape of a tool. The teams must also demonstrate that when the building blocks form a shape, they can adhere with the strength of a standard industrial/engineering plastic.

Once programmable matter’s capabilities have been proven, phase three will begin looking at the different applications for the technology. This phase will focus on using the science for specific applications, either through this program or other DARPA efforts.

Zakin observes that much more can be done with the science of programmable matter. One possible direction for the technology is programming adaptability into the material itself. The Programmable Matter program is a first step, he explains. Adaptability, for example, could produce electronics that can cope with heat and dust in the desert and then shift to resist humidity and moisture in a jungle environment. “It [matter] can now begin to adapt to the environment that it is put in. When you buy a tool or a radio, you’re not limited to the installed version of what you bought. Within limits, it will be able to adapt to the environment and what you need it to do,” he says.

WEB RESOURCES
DARPA Programmable Matter program: www.darpa.mil/dso/thrusts/physci/newphys/program_matter/index.htm
DARPA Chemical Robots program: www.darpa.mil/dso/thrusts/materials/multfunmat/chembots/index.htm
DARPA Chemical Communications program: www.darpa.mil/dso/thrusts/physci/newphys/chemcom/index.htm