3D/4D Printing Technologies

Product Manager

Sandra Forbes

Advancements in 3D Printing Technology

Three-dimensional (3D) printing, also referred to as additive manufacturing (AM), has garnered significant attention in recent years due to its transformative potential across diverse applications, from personal tools to aerospace components. Although 3D printing has recently gained prominence, its origins date back to 1983 when Charles W. Hull, co-founder of 3D Systems, developed the first 3D printer.

Expanded Accessibility to 3D Printers

Over time, the applications and markets for 3D printers have expanded rapidly, particularly following the expiration of key patents held by Stratasys Inc. and 3D Systems Inc. This has enabled users to either construct or modify 3D printers independently or take advantage of the growing availability of affordable 3D printing devices. The rise of advanced 3D design software and platforms like Shapeway and Thingiverse has facilitated the sharing of user-generated 3D digital models, further democratizing access to this technology. Compared to traditional manufacturing methods such as casting, machining, and drilling, 3D printing is recognized for its efficiency in material utilization (up to 90%) and energy savings (up to 50%).

As 3D printing evolves beyond a simple production tool, it has become a convergence point for various technologies and applications, including sports equipment, food packaging, jewelry, and high-tech fields like aerospace, medicine, architecture, education, automotive, and military support.

Notable Applications

Fashion: During the 2016 New York Fashion Week, two innovative 3D-printed dresses were showcased, resulting from a collaboration between fashion designers and Stratasys. These designs featured intricate patterns, such as interlocking weaves and biomimetic textures, and utilized advanced materials like nano-enhanced elastomers, offering both durability and flexibility.

Regenerative medicine: Significant strides have been made in regenerative medicine using 3D printing. Dr. Anthony Atala’s team at the Wake Forest Institute for Regenerative Medicine has successfully fabricated living tissues and organs, including muscle, bone, and ear structures, capable of functioning as replacement tissue.

Aerospace: NASA has employed 3D printing to develop materials for repairing or replacing essential components in space. A notable achievement includes the creation of a moon rock replica using lunar regolith simulant and 3D laser printing technology, in collaboration with Washington State University.

Construction: The use of large-scale 3D printers for modular construction has gained traction, particularly in addressing housing needs in developing countries or during emergencies. Several companies have successfully constructed houses and bridges using cement, sand, or concrete materials.

4D Printing

The declining costs, improved software, and expanding range of printable materials have paved the way for four-dimensional (4D) printing. This technology enables printed objects to alter their form or function over time in response to stimuli such as heat, water, electricity, or light. The key distinction between 4D and 3D printing lies in the integration of smart materials that enable time-dependent transformations.

This review explores both 3D and 4D printing processes, highlighting the materials associated with each.

Figure 1. A) Schematic of 1-, 2-, 3-, and 4D concepts. B) The process of 3D and 4D printing technology involves three general stages: (1–2) modeling; (3–4) printing; and (5) finishing.

The 3D and 4D Printing Process

3D printing is the process of fabricating objects by building up materials layer by layer. Figure 1B shows the 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 (Figure 1B1, 1B2). Then, it is sliced into a series of digital cross-sectional layers in accordance with the layer thickness setting (Figure 1B3). 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 (Figure 1B4, 1B5). 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 timedependent material deformations. Figure 2A–C show 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. 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 as shown in Figure 2D–F. For example, the temperature-responsive artificial hand shown in Figure 2F 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. 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.

Figure 2. A–B) The design of the folding box with different materials assigned at different hinges. C) Upon heating, the programmed 3D printed sheet folds into a box with a self-locking mechanism. Copyright 2015, rights managed by Nature Publishing Group. D–E) The resulting swollen flower structures were generated by biomimetic 4D printing with composite hydrogel and cellulose fibrils. Copyright 2016, rights managed by Nature Publishing Group. F) The temperature-responsive artificial hand was made with temperature-responsive TPU filament.

Classification of 3D and 4D Printing Technologies

3D and 4D printing technologies are categorized based on the materials and processes used. The choice of materials directly impacts the mechanical, thermal, and transformative properties of the final product.

Fused-deposition Modeling (FDM)

The FDM technique works by extruding thermoplastic materials and depositing them in a semi-molten state onto a platform to build a 3D object layer by layer. Specifically, the thermoplastic filament is fed into an extruder, which precisely controls the amount of filament fed and retracted. The filament is then melted by a heater block adjusted to the melting temperature and pushed through an extrusion nozzle by two rollers. As the print head traces the design of each predefined cross-sectional layer of the intended structure, the melted filament is deposited. Subsequently, the platform moves to the next Z position according to the specified layer thickness. These steps are iterated until the entire 3D object is completed.

One of the benefits of FDM is the diverse range of filament materials available, as illustrated in Figure 3. Various FDM filaments with different strength and temperature properties are commercially available, including ABS, nylon, PET, TPU, POM, PC, HIPS, and PVA, among others. Some of these materials can be mixed with other functional materials to enhance specific properties. PLA filament is particularly popular due to its numerous advantageous properties. Additionally, many FDM filaments can function as 4D materials when subjected to heat changes due to their thermoplastic nature.

Figure 3. Thermoplastic filaments for Fused-deposition Modeling (FDM). The FDM-printed flower was made with a color changed filament under UV exposure.

Powder Bed and Inkjet Head 3D Printing (PBP)

The PBP process is an inkjet printing adaptation for 3D printing. In this method, a layer of powder is evenly deposited and rolled to ensure consistency. The inkjet print head then dispenses binder in a predefined pattern as it moves, forming a single layer of the printed object. The next powder layer is applied over the deposited binder, and this process is repeated, with each layer adhering to the previous one. Unlike some other methods, PBP does not require support structures because unbound powder can be easily removed using an air gun after the object solidifies. Printing in full color is possible using multiple print heads with colored binder.

Calcium sulfate (CaSO4) is one of the most commonly used powders in PBP due to its ability to rapidly react with water-based binders, transforming into gypsum (CaSO4 ∙ 2H2O) in a solid state. The binding strength is crucial in determining the physical and chemical properties of the printed object, so careful consideration of the powder and binder combination is necessary.

Recently, Voxeljet developed the VX4000, the world's largest industrial PBP system for sand molds, with a cohesive build space of 4,000 × 2,000 × 1,000 mm (L × W × H) and a layer thickness of 300 μM per cycle.

Stereolithography (SLA)

SLA combines ultraviolet (UV) or visible laser light with curable liquid photopolymer resins to create 3D objects. A laser beam illuminates a 2D cross-section of the object in a vat of resin, causing the resin to solidify. The object is then raised by the layer thickness, and more resin is added to maintain contact with the bottom of the object. This process is repeated until the entire object is complete. Afterward, the platform is lifted out of the vat, excess resin is drained, and the object is finished by washing and curing under UV light. SLA produces smoother surfaces than other 3D printing methods due to the use of liquid photopolymers. However, it has drawbacks such as significant resin waste, extensive post-fabrication cleaning, and limited resin options, primarily epoxy or acrylic bases, which can shrink during polymerization.

Recently, Carbon 3D Inc. introduced a groundbreaking advancement in SLA, known as Continuous Liquid Interface Production (CLIP), which reduces printing time by 100 times compared to traditional methods. CLIP creates an oxygen depletion zone (dead zone) in liquid resins, as shown in Figure 4. A unique oxygen-permeable window in the resin reservoir forms a thin liquid interface of uncured resin between the window and the printing part. This dead zone allows for continuous translation and curing of the resin above it, resulting in a consistent solid object.

Figure 4. A) Schematic of a CLIP printer. B) The resulting parts via CLIP at print speeds of 500 mm/hour. Copyright 2015, The American Association for the Advancement of Science.

Future Prospects

3D printing’s versatility and efficiency make it a cornerstone of modern manufacturing. Meanwhile, 4D printing holds immense potential to revolutionize industries by enabling dynamic, self-transforming objects. However, further refinement of these technologies is necessary to fully replace conventional methods. Continued research and investment in materials, printer systems, and market applications are essential to unlocking their full potential.

References

1. Matthew C. May 2013. Pangaea Blog. [Internet]. Available from: http://www.pangaeaventures.com/blog/additive-manufacturing-printing-a-better-and-cleaner-world

2. July 2014. 3-D printer to aid the visually impaired students in their educational endeavors. [Internet]. ScienceDaily . Available from: http://www.sciencedaily.com/releases/2014/07/140702102601

3. Wonjin J, Jang HI, Harianto RA, So JH, Lee H, Lee HJ, Moon M. 2016. Introduction of 3D Printing Technology in the Classroom for Visually Impaired Students. Journal of Visual Impairment & Blindness. 110(2):115-121. https://doi.org/10.1177/0145482x1611000205

4. Tess. 2016. threeASFOUR unveils two spectacular 3D printed dresses at New York Fashion Week. [Internet]. Available from: https://www.3ders.org/articles/20160216-threeasfour-unveils-two-spectacular-3d-printed-dresses-at-new-york-fashion-week.html

5. Kang H, Lee SJ, Ko IK, Kengla C, Yoo JJ, Atala A. 2016. A 3D bioprinting system to produce human-scale tissue constructs with structural integrity. Nat Biotechnol. 34(3):312-319. https://doi.org/10.1038/nbt.3413

6. Shafiee A, Atala A. 2016. Printing Technologies for Medical Applications. Trends in Molecular Medicine. 22(3):254-265. https://doi.org/10.1016/j.molmed.2016.01.003

7. Feb 2016. Bioprinter' creates bespoke lab-grown body parts for transplant. [Internet]. Tim Radford. Available from: https://www.theguardian.com/science/2016/feb/15/bioprinter-creates-bespoke-lab-grown-body-parts-for-transplant

8. Megan G. 2012. 3D Printer Could Transform Moon Dirt Into Lunar Base. [Internet]. SPACE.com. Available from: https://www.space.com/18694-moon-dirt-3d-printing-lunar-base.html

9. Krishna Balla V, Roberson LB, O'Connor GW, Trigwell S, Bose S, Bandyopadhyay A. 2012. First demonstration on direct laser fabrication of lunar regolith parts. Rapid Prototyping Journal. 18(6):451-457. https://doi.org/10.1108/13552541211271992

10. Mar 2015. WASP. Available from: http://www.wasproject.it/w/en/new-extruder-wasp-can-trulyrealize-house-dream/

11. Eddie K. Aug 2014. World’s First 3D Printed Castle is Complete – Andrey Rudenko Now to Print a Full-size House. [Internet]. 3DPrint.com. Available from: http://3dprint.com/12933/3dprinted-castle-complete/

12. Kira. 2015. 3Ders.org. Available from: http://www.3ders.org/articles/20150118-winsunbuilds-world-first-3d-printed-villa-and-tallest-3d-printed-building-in-china.html

13. Choi J, Kwon O, Jo W, Lee HJ, Moon M. 2015. 4D Printing Technology: A Review. 3D Printing and Additive Manufacturing. 2(4):159-167. https://doi.org/10.1089/3dp.2015.0039

14. Mao Y, Yu K, Isakov MS, Wu J, Dunn ML, Jerry Qi H. 2015. Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers. Sci Rep. 5(1): https://doi.org/10.1038/srep13616

15. Sydney Gladman A, Matsumoto EA, Nuzzo RG, Mahadevan L, Lewis JA. 2016. Biomimetic 4D printing. Nature Mater. 15(4):413-418. https://doi.org/10.1038/nmat4544

16. Tibbits S. 2014. 4D Printing: Multi-Material Shape Change. Archit Design. 84(1):116-121. https://doi.org/10.1002/ad.1710

17. Raviv D, Zhao W, McKnelly C, Papadopoulou A, Kadambi A, Shi B, Hirsch S, Dikovsky D, Zyracki M, Olguin C, et al. 2015. Active Printed Materials for Complex Self-Evolving Deformations. Sci Rep. 4(1): https://doi.org/10.1038/srep07422

18. Jo W, Kim DH, Lee JS, Lee HJ, Moon M. 3D printed tactile pattern formation on paper with thermal reflow method. RSC Adv.. 4(60):31764-31770. https://doi.org/10.1039/c4ra02822h

19. Liu W, Wu C, Liu W, Zhai W, Chang J. 2013. The effect of plaster (CaSO4·1/2H2O) on the compressive strength, self-setting property, and in vitro bioactivity of silicate-based bone cement. J. Biomed. Mater. Res.. 101B(2):279-286. https://doi.org/10.1002/jbm.b.32837

20. INDUSTRIAL 3D PRINTING SYSTEMS: EFFICIENT AND ECONOMICAL. [Internet]. Available from: http://www.voxeljet.de/en/systems/vx4000/

21. Tumbleston JR, Shirvanyants D, Ermoshkin N, Janusziewicz R, Johnson AR, Kelly D, Chen K, Pinschmidt R, Rolland JP, Ermoshkin A, et al. 2015. Continuous liquid interface production of 3D objects. Science. 347(6228):1349-1352. https://doi.org/10.1126/science.aaa2397

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