4D printing: Producing programmable materials that transform over time
18 Apr 2016
3D Printing is booming. The capabilities are expanding and new applications emerge everyday.
The field of 3D Printing includes processes such as Fused Deposition Modeling (FDM), Stereolithography (SLA), Selective Laser Sintering (SLS), Polyjet, powder-based printing and various forms of metal printing. Printing processes cross scales from nano-scale printers to printed houses with concrete. New materials are being used, such as glass, wood filaments, printed composites (eg carbon fiber, fiberglass, Kevlar) and many more. It is now possible to produce electrospun printed clothing. The applications span a number of domains including at-home and desktop printing, academic research and finally, industrial printing for products and manufacturing.
Advantages of 3D printing in industry
Industrially, there are a number of reasons for the interest in printing. The first reason is performance structures. Printing offers a unique opportunity to produce geometries and complex structures that would have been otherwise impossible with traditional industrial processes. Given this, products may have structures that were designed for specific conditions with maximum performance, yet they minimise materials and maximise efficiency. Fasteners may be eliminated to save cost or weight, pathways or internal cavities can be infinitely complex and highly tuned and multiple functional components can now be combined into one element.
The second aspect of 3D printing that is important for many industries is the ability to produce smaller quantities of customized products. Traditional manufacturing processes often require expensive and complex tooling, which usually is amortised over hundreds or thousands of products produced. Thus, products cannot change without an enormous increase in production cost. However, since printing eliminates tooling - and the complexity of an object is essentially free given that printing time is nearly the same for a complex object as it is for a simple object - unique and customised products can be produced for the same cost or production time as standardised products. This can be passed on to the consumer whereby products can be customised by or for the customer directly, making each version uniquely suited for their interests and applications without additional time or expense.
The third aspect of printing that is useful for industry is the material properties themselves. The possibility to print complex micro and macro architectures can give products new “metamaterial” properties whereby the pattern and geometry can augment the material’s natural properties. For example, a plastic block may have a certain tensile or compression characteristic, yet if the material is printed in an intricate lattice pattern, the macro-scale component may now have a much better performance as compared to the original material. This can enhance and specifically tune product and structural performance through new manufacturing capabilities.
3D printing success stories and challenges
There are a number of amazing success stories around 3D printing that have recently emerged like e-NABEL’s printed prosthetic hand for children, GE’s engine component, Local Motors’ printed car and many others. Yet, the questions still remain, “why is 3D printing the future of manufacturing”, or “why should a certain industry adopt 3D printing”, or “when will 3D printing have a ‘real’ impact”. These questions are important. Yet, the most important aspect of printing seems to be the future of the technology, not just today’s capabilities.
The success stories are truly incredible and unquestionably important. Yet, we need to look realistically at the challenges that industry faces today and how the frontiers of research can open up possibilities that printing (or other industrial processes) have yet to realise. I believe that some of the main challenges that printing faces today are not necessarily downsides (in the long run), rather they paint an incredible picture of the next possibilities for printing as well as opportunities for research. Such challenges include: bed-size and limitations on scale, print speed, software tools and material properties.
Bed-Size: Most of today’s 3D printers focus on mid-size components from millimeter to centimeters, which is limiting. This constrains the industries and applications that may utilise printing, given they must have products or components that fit within the bed-size. There are certainly printers that fall outside of this range and these developments are extremely interesting. One of the main challenges, however, is what I call the “skyscraper” problem. Whereby, you don’t want to build a skyscraper size machine to build a skyscraper, because you might as well stop at the machine. This challenge calls for more distributed and scalable processes. One of the most interesting developments in this area is the “unfolding” scenario. Nervous System’s 4D Printed dress demonstrates this quite well, whereby an object that is larger than any print volume may be digitally “folded” or crumpled into a smaller volume, then physically printed and pulled out of the printer. Thus, making large objects on small machines. This is obviously fascinating and has applications for in-space manufacturing or printing for human-scale objects like furniture, dresses and other products.
Print speed: Printers are still quite slow. Many complain that they are slower than other industrial processes like injection molding. Carbon3D recently received a lot of attention for their faster SLA printing process with an intelligent oxygenated layer; this certainly contributes to the next generation of print speeds. However, one of the most interesting scenarios in my mind is to print flat structures with minimal material, reduced supports, minimal print time and then allow them to fold or even better, self-fold into much larger structures afterwards!
Software: Today’s software tools are behind our hardware capabilities. Bioprinting, multi-material printing, printed electronics and 4D Printing, are all processes that require new types of software tools with capabilities that go beyond computer aided design (CAD), computer aided manufacturing (CAM) or even voxel modeling. New capabilities like Monolith multi-material voxel software and new file formats are emerging, but the complexities are growing with the need to simulate complex deposition of active matter, or living biomaterial. This is a moment where we may be able to rethink our design tools and look beyond the screen to determine the right design tool when we are able to print and program nearly all type of physical material.
Materials: Most companies today compare 3D printed materials to traditional materials and argue that we need better properties. This is certainly true. We also need better methods for insuring and analysing printed parts compared to other industrial processes. However, I think it is the wrong question. Rather, than trying to make the same type of part, or create the same material property that we could already produce in other ways, we should be looking to produce properties, capabilities and components we have never seen before. We should not settle for what we know today and try to fit printing into that paradigm. I like to think of printing as a “materials science chamber” whereby we can mix and match different materials, properties, as well as micro and macro architectures to produce material behaviors and capabilities like actuation, sensing and logic, which would have been impossible with other industrial processes.
At MIT’s Self-Assembly Lab, I direct a series of research projects investigating the frontier of assembly techniques, material performance and printing capabilities. We have introduced a topic called, Programmable Materials, whereby we program physical materials to change shape, property or other characteristics. We do this by utilising a few main ingredients: materials & geometry, energy and transformation. First, we identify a material pallet that has specific material properties and related fabrication processes. In relationship to the material properties, we then look at the activation energy that we may utilise. Any one application may require a specific environment or energy source (heat, light, moisture etc), or alternatively, require a specific material (metal, wood, plastic etc). If we select wood, we then might want to utilise moisture to activate the material. Or if we select heat as the energy source, we may then look at metals or thermoplastics. Finally, we identify the type of transformation that we are interested in and how we can develop a series of geometric and material compositions to achieve that transformation. For example, we may want to create a folding mechanism for a joint. Therefore, we could create a geometry and composition of wood that would fold to a specific angle when subjected to moisture. These ingredients give us full control of the material program and the resultant self-transformation when subjected to external energy.
The emergence of 4D printing
Our most notable work, to date, is a technology called 4D Printing. 4D Printing grew out of the idea that we wanted to take 3D printing further by adding the 4th dimension, time. Through this technique, we are able to print materials that have the capability to self-transform from any one shape to any other. This enables the production of customised “smart materials” that can transform in precise ways based on a variety of activation energies. Going beyond the robot, we are also able to print robot-like materials that do not have motors, sensors or computers, yet they can move, sense and make logical actions with materials alone.
4D printing is made possible through multi-material printers like Stratasys’ Connex 500. A variety of materials can be deposited simultaneously with custom geometries and material properties. In this work, we often utilise two materials. One is a rigid plastic that encodes the geometric information to create precise transformations (fold, curl, twist, stretch, shrink etc.). The second material is a hydrogel that can swell 150% when submerged in water. This gives the information and the activation energy to go from one shape to another. Throughout the past three years of development, we have been able to print many structures that demonstrate 1D to 2D, 1D to 3D, 2D to 2D, 2D to 3D and 3D to 3D transformations. We have printed small structures that fold into precise shapes, like the letters “MIT” as well as enormous structures that fold 75x their length, spanning across an Olympic swimming pool. 4D printing proposes a new capability for multi-material printers to go beyond the production of static components and into a world of highly active self-transforming material systems for the future of products and environments.
3D and 4D printing offer unquestionable advantages, yet face realistic constraints today. These constraints are truly opportunities that are emerging for new frontiers of the technology. I believe the breakthroughs in the coming years will unquestionably surpass the advantages that printing offers today over industrial manufacturing. I am optimistic about this future “material science chamber” and the reality that is emerging for the convergence of our physical and digital world.
Today we program computers and machines and I believe tomorrow we will program matter itself.
See also the event "Expert Forum on 3-D printing", which took place at the Centre for Global Dialogue in September 2015.
See also the summary of the event.