The Fourth Dimension – The Next Big Thing In 3D Printing

3D Printing has been around for almost 30 years, yet the Additive Manufacturing industry is discovering new applications, materials, and 3D printers to push the boundaries of what is possible. As 3D printing advancements continue to explore different materials, shapes, and objects, 4D Printing is emerging. Like 3D Printing, 4D objects are built layer by layer but morph into other forms over time, changing the objects' function.

So far, researchers have created devices actuated by water or heat. The significance of this process is that the structures are ready when you pick them up from the printer. Unfortunately, the prototypes are slow and limited in the number of times they can be used.

What Is 4D Printing?

4D Printing is a process where a 3D printed object changes itself into another structure over the influence of external energy like temperature, light, or other stimuli used as a catalyst of change. It is part of the MIT Self-Assembly Lab project, and the primary purpose of this project is to combine technology and design to create self-assembly and programmable material techniques. It aims to reimagine construction, manufacturing, product assembly, and performance with real-world implications.

This blog post will take you through 4D Printing technology and explore its potential and future applications.

3D Printing vs. 4D Printing - What Is The Difference?

The apparent difference is that 4D Printing has one more "D" than 3D Printing. Why is it creating so much added value to dimensional printing technology? 3D Printing is repeating a 2D structure, layer by layer, in a path from the bottom to the top until a 3D object is created. 4D Printing is seen as 3D Printing that transforms over time, and any object created with 4D technology changes shape over time. 

How 4D Printing Works

4D Printing uses commercial 3D printers like Polyjet. Using hydrogel or a shape memory polymer (smart materials) as the input, shape change attributes differ from common 3D printing materials because of their thermomechanical and other material properties, whereas 3D printed objects keep their 3D shape once printed.

4D Materials & Technologies

Many materials, designs, and modeling are used in 4D printing technology. Each produces a different result and is researched both individually and together to understand how external stimuli affect the materials and the change process.

Smart Material is one of the highly focused research areas in 4D Printing, wherein various materials' deformation mechanisms are synthesized as per their responses to various external stimuli.

Equipment Design is the process of developing advanced printer technology and printing multiple materials simultaneously. Currently, researchers use inkjet cure, fused deposition modeling, stereolithography, laser-assisted bioprinting, and selective laser melting methods for 4D Printing.

Mathematical Modeling research is critical to understanding the functional structures of 4D-printed objects. This modeling predicts an object's deformation (forward) and formation (backward) processes when external stimuli trigger.

Material Selection

4d printing materials are classified based on the environment or external stimuli they contact and create a reaction. The current classes of smart materials are classified into three categories:

Thermo Responsive:

Thermo-responsive materials work on the Shape Memory Effect (SME) mechanism. Each type of material is classified into different Shape Memory types:

  • Shape Memory Alloys (SMA)
  • Shape Memory Polymers (SMP)
  • Shape Memory Hybrids (SMH)
  • Shape Memory Ceramics (SMC)
  • Shape Memory Gels (SMG)

Most researchers prefer using SMPs because it's easy to print with these materials. SMPs also form and deform when heat or thermal energy is used as a stimulus.

Moisture-Responsive Materials:

These materials react when they come into contact with water or moisture. Researchers prefer moisture-responsive materials because they can be used in various applications. Hydrogel reacts actively with water. They can increase their size by up to 200% of their volume when they come into contact with water. 

Photo/Electro/Magneto-Responsive Materials:

These materials react to light, electrical currents, and magnetic fields. For example, when photo-responsive chromophores are combined with polymer gels in specific locations, they swell, absorbing light when exposed. Similarly, when an electric current is applied to an object that contains ethanol, it evaporates, increasing its volume and expanding the overall matrix. Magnetic-responsive materials are nanoparticles embedded into the printed object and gain magnetic control of the object.

Real-World Applications

3D Printing has revolutionized multiple industries ranging from fashion to manufacturing. As technology advances and 4D Printing becomes more accessible, it shows real-world applications that will impact technological advancement for years to come. Look at some currently used applications and upcoming research for additional applications.

3D Applications

Fashion – Two unique 3D-printed dresses were unveiled at New York Fashion Week in 2016, announcing an entirely new material used in clothing. The dresses were created through a collaboration between fashion designers and Stratasys, a 3D printing company. The complex designs of interlocking weaves, biomimicking of animal textures, and using cutting-edge material like nano-enhanced elastomeric 3D printing material gave the dresses durability, and flexibility, creating a new way of producing textiles.

Regenerative Medicine – Regenerative medicine has experienced impressive applications within the 3D printing field. For example, the Wake Forest Institute for Regenerative Medicine successfully used 3D printing technology to fabricate living organs and tissue capable of generating functional replacement tissues. 

Aerospace – NASA is implementing 3D-printing techniques to develop materials allowing astronauts to repair or replace parts and build structures in space. In fact, NASA collaborated with researchers at Washington State University to fabricate a replica of a moon rock by using raw lunar regolith stimulant and 3D laser printing.

Construction – Assembling modular construction materials using giant 3D printers for the housing industry has attracted significant interest recently. This is incredibly impactful for poorer countries, natural disasters, or sudden emergencies. Some 3D companies have successfully built houses and bridges with cement, sand, and concrete materials, pushing the boundaries of the materials e used with 3D Printing.

4D Printing

As technology for 3D Printing continually grows, 4D Printing is keeping pace and expanding on the technology. With 4D Printing, several other real-world applications benefit individuals and societies. But first, let's look at the recent advances in 4D Printing. 

3D Working Heart Models Using 4D flow MRI Images

Researchers, technicians, and doctors combine 4D magnetic resonance images (MRIs) of blood flow with 3D printers to create functional heart models. The 4D flow scans enable doctors to visualize where problems are located as blood is pumped through each section of the heart. As a result, doctors can pinpoint specific problems and plan the surgery using multiple colors of the heart parts and liquids. This research attempts to replicate native tissue and evolve it into a fully functioning model for surgical planning. Additional implications for this technology are for medical education and research.

Drug Delivery

Building a 4D printed device from magneto-restrictive materials driven by an external magnetic field can be used and aid with specific drugs and appropriate dosing. For example, a micro-robot was created to use a standard lithographic approach, and when a layer changes shape when exposed to certain pH levels, it helps the drug released into the body. An Iron Oxide coating on the device allows it to be magnetically directed and ensures site-specific drug delivery. This is especially useful for providing anti-cancer medications targeted to a specific area. These drug delivery devices administer the maximum beneficial drug therapy and minimize unwanted side effects. Research is ongoing about the practical application of this form of 4D Printing.

Bioprinting

Artificial hard tissues like bone grafts are created using 4D Printing. For example, scientists have printed grid-patterned polymeric bone grafts and coated them with MSCs (Mesenchymal stem cells) derived from human tissue. Once the culture is complete, the bone graft shows post-printing maturation. However, it lacks the mechanical strength of natural bones. While mini tissues can be prepared with 4D bioprinting and integrated to develop larger tissue over time, the technology is still emerging, but additional research is necessary for public use.

4D Printing Healthcare

4D Printing in the healthcare market is forecasted to grow to 32 million USD in 2026. This growth is primarily due to the development of smart, programmable materials and 3D technology advancements. However, 4D Printing in the medical industry is constrained by high development and production costs and regulatory and performance standards. It will slow product launches and be affected by potential safety hazards.

4D Printing in the medical field will be dominated by FDM (Fused Deposition Modeling) during 2021. However, the PolyJet segment is expected to grow the most. Using FDM helps create complex shapes with intricate details and delicate features. They combine products in various colors and materials into a single model. The two main advantages of the FDM process are using multiple materials and colors and reducing material waste.

3D & 4D Technology Classification

There are three technology classifications for 3D and 3D Printing. These classifications identify the type of materials (thermal, smart, etc.) and their uses.

FDM - Fused-Deposition Modeling

As referenced above, FDM extrudes thermoplastic materials and places the semi-molten materials to fabricate a 3D structure layer by layer. This material is a thermoplastic filament that is first fed to an extruder and then feeds and retracts the filament into precise amounts. It is then melted and moved through the extrusion nozzle tip by two rollers. The last step is to deposit the extruded filament as the print head traces the design of each defined cross-sectional layer of the structure with a digitally positioned mechanism. Then, the stage moved into the "Z" position according to the setting value of layer thickness and repeated to complete the fabrication of the 3D structure. One of the advantages of FDM is the variety of filament materials available with different strength and temperature properties. 

Powder Bed & Inkjet Head 3D Printing (PBP)

The PBP process is an adaptation of inkjet printing. During this process, a layer of powder is deposited and rolled to a uniform thickness. Next, the inkjet print head drops a binder in a specific pattern as it moves, forming a single layer of a printed object across the powder. Next, another powder layer is deposited over the liquid binder, and the process is repeated, with each layer sticking to the last. PBP doesn't require support structures because it's easy to remove the excess powder using an air gun after the object is solidified. In addition, PBP allows full-color Printing because of the use of multiple print heads combined with a colored binder.

Stereolithography (SLA)

SLA combines UV or visible laser light with photopolymer resins. The laser beam illuminates a 2D cross-section of the object in resin, allowing it to solidify. Then, the object is raised by equal distances of layer thickness to fill resin under the object and maintain contact with the bottom of the object. Resins used are either epoxy or acrylic based because they shrink on polymerization. The process is repeated until the model is completed and the resin is drained. SLA objects are finished by washing and curing under UV or visible laser light. 

SLA produces a smooth surface on the final product compared to other 3D Printing.

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