by Aadi Biswas
3D Printing technology has existed for many decades now. While the Additive Manufacturing industry is still discovering new applications, new materials, and new 3D printers, we see yet another futuristic technology arising. It is called 4D Printing. 4D printing is nothing more than a digital manufacturing technology -3D printing- but now it includes a new dimension: the temporal. By integrating the dimension of time, printed objects change their shape dynamically based on the needs and demands of the situation, without any electromechanical parts or moving parts. This shape-changing phenomenon of 3D printed objects is based on the material’s ability to transform over time in response to specific stimuli, such as light, heat, electricity, magnetic field, etc. and it does not require human intervention to aid the process. Skylar Tibbits, an American designer and computer scientist, also a co-director and founder of Self-Assembly lab at MIT coined the term of 4D printing and popularised it in his 2013 TED Talk. 4D Printing was developed as a collaboration between the Self-Assembly Lab, Stratasys and Autodesk.
How does 4D printing work?
4D printing makes it possible for an object, to bend, repair, assemble or even disintegrate itself. It acquires a new shape or functionality on its own by reacting with the environment. 4D printing directly depends on the so-called smart materials used to create the objects. According to researcher Anna Ploszajski the four-dimensional structures are made from active, animated, intelligent materials which move autonomously – swelling, shrinking or bending in reaction to a stimulus – combined with passive materials. That allows them to move and change shape without robotics, electronics or engines. Are there any intelligent materials found in the nature? Anna cites the example of the pine cone. It has two layers of rigid fibers that run in different directions, which allow the cone to open and close, so that the seeds are only released when the time is favorable for germination in the soil. When humidity is high, the cone remains closed, protecting the seeds. Materials engineers seek to understand and replicate this complex processes of adaptability, resilience and efficiency. 4D printing will make it possible to program the material, making it react according to environmental parameters. According to Self-Assembly lab, the pioneers of 4D printing, this technique offers a streamlined path from idea to full functionality built directly into the materials, including; actuation, sensing and material logic. With a single multi-material print, a product or mechanism can transform from any 1D strand into 3D shape, 2D surface into 3D shape or morph from one 3D shape into another. Using only water, heat, light or other simple energy input, this technique offers adaptability and dynamic response for structures and systems of all sizes.
What are the possible smart/intelligent materials?
Smart material is one of the highly focused research areas in 4D printing, wherein the deformation mechanism of various materials is synthesized as per their responses to various external stimuli. Materials for 4D printing are classified based on their environment or the external stimuli they react with.
Thermo Responsive Materials
Materials that exhibit conformational changes in response to temperature stimuli, especially near body temperature are called Thermo Responsive Materials. These materials work on the mechanism of the Shape Memory Effect (SME). They are classified into Shape Memory Alloys (SMA), Shape Memory Polymers (SMP), Shape Memory Hybrids (SMH), Shape Memory Ceramics (SMC), and Shape Memory Gels (SMG). The most popular ones are SMPs as it becomes easy to print on these materials. They form and deform when heat or thermal energy is applied as a stimulus.
Moisture Responsive Materials
Materials that react when in contact with water or moisture are classified as moisture responsive materials. Hydrogel falls under this category as it can increase its size by up to 200% of its original volume, when it comes in contact with water.
Photo/Electro/Magneto Responsive Materials
These materials react with light, current, and magnetic fields. When photo responsive chromophores are infused with polymer gels at specific locations, they swell up absorbing light when exposed to natural light. Similarly, when current is applied to an object containing ethanol, it evaporates, thereby increasing its volume and expanding the overall matrix. Magnetic nanoparticles are embedded into the printed object to gain magnetic control of the object.
4D printing applications
When we look closely into the 4D printed structures, we find that their ability to self-assemble and self-repair adds to their potential for various applications. It has the potential and is destined to revolutionise the industry. In 2015, a medical team from the University of Michigan saved the lives of three babies with respiratory problems by inserting a 4D printed implant. This polycaprolactone device, designed to fit each patient, was designed to adapt its size to the child's growth and to dissolve itself when no longer necessary. The use of 4D printing in ultrasound scans allows to know more precisely the structural and functional development of the nervous system of the foetus. Recently, a Korean research team announced amazing results in regenerating animal muscles and bones using 4D printable technology. Customizable clothes also does not seem far fetched with the first 4D printed dress - Kinematics dress - by MIT’s 3D printing design studio Nervous System. Made up of 2,279 unique triangular panel pieces connected with over 3,316 hinges, the Kinematics Dress is the world’s first 4D printed dress, capable of shape-changing to fit the human body. Since the patterns of the pieces are interconnected, they are modified to fit the body shape of each person.The U.S. military is testing uniforms that change colour depending on the environment, or that regulate perspiration depending on the soldier's pulse or environment temperature. 4D printed shoes will also be able to adapt to movement, impact, temperature and atmospheric pressure. Nasa, Airbus and car manufacturers are all using 4D printing for their astronaut suits, materials to cool its engines and for intelligent airbags. With this the Fourth Industrial Revolution is already underway.
Like with all technology 4D printing comes with its own risks. Hackers could sabotage 4D printed objects to cause malicious failures. By gaining access to printers and manipulating designs of parts such as medical devices, aircraft propellers in ways which are difficult to detect, attackers could pose a great risk. Strict security measures with stringent quality control measures might be the answer to mitigate these risks.
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