Developments in 3D Printing Technology
Three-dimensional (3D) printing technology, also called additive manufacturing (AM), has recently come into the spotlight because of its potential high-impact implementation in applications ranging from personal tools to aerospace equipment. Even though 3D printing technology has only recently emerged as a hot topic, its history can be traced back to 1983 when the first 3D printer was created by Charles W. Hull, co-founder of 3D Systems.
3D Printing Techniques Using Polymers
• Fused Deposition Modeling (FDM)
• Selective Laser Sintering (SLS)
• Stereolithography (SLA)
• Near-Field Electrospinning (NFES)
Fashion: At the 2016 New York Fashion Week, two unique 3D printed dresses were unveiled. These masterpieces were produced through a collaboration between fashion designers and the 3D printing company, Stratasys.4 The complex designs (e.g., mixing a variety of interlocking weaves, biomimicking natural animal textures) and cutting-edge material (e.g., nano-enhanced elastomeric 3D printing material) gave the dresses durability and flexibility.
Regenerative medicine: The area of regenerative medicine has also achieved impressive applications within the 3D printing field. Dr. Anthony Atala’s team from the Wake Forest Institute for Regenerative Medicine has successfully used 3D printing technology to fabricate living organs and tissue (including muscle structures, and bone and ear tissue).5,6 These bioprinted body parts are capable of generating functional replacement tissue.
Aerospace: NASA has also been implementing 3D printing techniques and 3D printers to develop materials that allow astronauts to repair or replace essential parts and build structures in space. NASA recently collaborated with researchers at Washington State University to fabricate a replica of a moon rock using raw lunar regolith simulant and 3D laser printing technology.
Construction: The assembly of modular construction materials using giant 3D printers for use in the housing industry has gained significant interest, especially for poorer countries, during natural disasters, or sudden emergencies. Some 3D companies have succeeded in building houses or bridges with cement, sand, or concrete materials.10–12
The rapidly decreasing cost, improved software design, and increasing range of printable materials have helped to bring about a new technology called four-dimensional (4D) printing. 4D printing provides printed objects with the ability to change form or function with time according to various stimuli such as heat, water, current, or light (Figure 1A).13 The essential difference between 4D printing and 3D printing is the addition of smart design, or responsive materials that cause time-dependent deformations of objects.
This review covers both 3D and 4D printing processes and shows the materials related to different printing types.
The process of 3D & 4D Printing Technology
3D printing is the process of fabricating objects by building up materials layer by layer. he 3D printing process from modeling to final printing. Based on the use of computer-aided design (CAD) describing the geometry and the size of the objects to be printed, a complicated 3D model is created in a printable standard tessellation language (STL) file format. Then, it is sliced into a series of digital cross-sectional layers in accordance with the layer thickness setting.
Upon completion of the model, the object is fabricated by a 3D printer through the layer-by-layer fabrication process based on a series of 2D layers to create a static 3D object. 3D printing can involve different types of materials such as thermoplastic polymer, powder, metal, UV curable resin, etc.
Four-dimensional printing incorporates a time component to the 3D printed objects, making the design process more important. 4D-printed structures must be preprogrammed in detail based on the transforming mechanism of controllable smart materials that incorporate time dependent material deformations. 3D structures that self-fold based on the thermal activation of spatially variable patterns printed with a variety of shape memory polymers. Each polymer has a different thermal-dependent behavior that can make the box self-fold in a time-sequential manner based on smart design and thermomechanical mechanisms.14 The choice of materials for 4D printing is significant, however, because most 3D printing materials are designed only to produce rigid, static objects. Recently, some smart shape alloy/polymer memory materials have been developed to utilize their self-assembled behaviors driven by heat, UV, or water absorption-driven. For example, the temperature-responsive artificial hand was printed with a temperature-responsive TPU (thermal polyurethane) filament. It has the ability to contract or expand in response to specific temperatures. In addition, multi-materials having different environmental behaviors are also useful in 4D printing. A research group at the Massachusetts Institute of Technology used two different materials with different porosities and water-absorption abilities to print transformable structures.16,17 It was composed of a porous water-absorbing material on one side and a rigid waterproof material on the opposite side. When exposed to water, the water-absorbing side increased in volume while the other side remained unchanged, resulting in shape deformation.
Three-dimensional printing technology is highly versatile and efficient with respect to design, fabrication, and applications. 4D printing may be of great importance in the future due to its potential to redefine manufacturing-related industries. However, the technology must be further refined before it can replace conventional manufacturing methods. Therefore, future research and investment in 3D and 4D printing technologies are imperative to bring about improvements in essential areas including materials, printer systems, and product markets.