- by Derniza Cozorici.
From car tiers, houses and even organs, 3D printing has a lot to promise in the near future
Early beginnings
The first recorded variations of 3D printing may be dated back to the early 1980s in Japan, when Hideo Kodama was looking for a technique to create a quick prototyping system in 1981. He devised a layer-by-layer manufacturing method that employed a photosensitive resin that was polymerized by UV light. However, the first patent for 3D printing was granted in 1986 to Chuck Hull of 3D Systems Corporation. Hull described 3D printing as a technique that involves three-dimensional items by developing a cross-sectional pattern of the object to be made. His innovation is a stereolithography fabrication technique in which layers are added by curing photopolymers using ultraviolet light lasers [1].
Today's 3D Printing
Today, three-dimensional (3D) printing is recognized as a really innovative technology, that has emerged as a flexible technological stage, and is extensively employed across the world.
3D printing, often known as an additive manufacturing, is rapidly revolutionizing industrial technology. It is utilized in a wide range of industries, including automotive, aerospace [2], architecture and construction, electronic, fashion, and food [3]. Recent improvements in printing speed, technology, and material choices have had a substantial influence on multitude of areas, including in medical field [4]. Therefore, three-dimensional printing technologies are also having a big contribution in biomedical research. Medical devices, tissue engineering (TE), bioprinting, and drug delivery are just a few biomedical research fields where 3D printing is being used [5], [6].
Thus, a large part of the reason for the current surge in 3D printing utilization is that it is a simple technology that can be employed in a wide range of applications. From industrial to healthcare, the effects of advancing 3D printing technology can be observed in each and every field. While there are endless examples of 3D printing being used for incredible things, Figure 1 illustrates some interesting applications of this technique.
In 2021 a family from Virginia received the keys to the first 3D printed house. The home measures 1,200 square feet, includes three bedrooms, and two full baths (Figure 1a). It was made using concrete, which has several long-term benefits, including the capacity to keep warmth and survive natural calamities such as tornadoes and hurricanes. The technique enabled the home to be completed in only 12 hours, saving around four weeks of building time for a regular home [7]. Michelin, a well-known French tire maker, unveiled its first prototype tire powered by additive printing technology in 2019. These tires, known as Uptis (Unique Puncture-proof Tire System), have been developed to be airless in order to avoid the possibility of flat tires and other air loss failures caused by punctures or road hazards. The design is only feasible due of additive manufacturing (Figure 1b). The Uptis tire is expected to be available on the market in 2024 [8].
Remarkable advances in the use of 3D printing technology are also seen in the biomedical field (Figure 1c). Three-dimensional (3D) in vitro models, such as organ-on-a-chip microdevices, are a novel and efficient technology that allows the reproduction of tissues and organs functions, bridging the gap between conventional models based on cell cultures or animals and the complicated human system [9].
Figure 1. Applications of 3D printing technology in (a) construction [7], (b) automotive [8] and (c) biomedical field [9]
In manufacturing, three-dimensional printing refers to any of various technologies for generating three-dimensional objects by depositing two-dimensional cross sections successively, one on top of the other.
How does 3D Printing Work?
Every 3D printing technique starts with a three-dimensional model, which is a mathematical representation of any three-dimensional surface built with computer-aided design (CAD) software or created from 3D scan data. The resulting design is then exported as an STL or OBJ file that print preparation software can interpret. 3D printers come with software that allows users to choose print parameters and slice the digital model into layers that reflect the part's horizontal cross-sections. Printing options that may be changed include orientation, support structures, layer height, and material. When the setup is finished, the program transmits the instructions to the printer through wireless or cable connection. Based on the 2D slice information, a 3D printing machine then constructs the components one layer at a time, stacking and combining succeeding layers to create the final 3D item [10].
This is the overall representation of the printing process, but each technology differs in the way components are manufactured and can also differ in choice of materials, surface finish, durability, production speed and cost. Over the last 15 years, an amount of new technologies have emerged and changed the concept of rapid prototyping (RP) into additive manufacturing (AM), where components generated by a 3D printer may be immediately utilized for a range of purposes.
According to an American Society for Testing and Materials (ASTM) International committee, known as ASTM Standard F2792, 3D printing technologies are divided into seven categories: binding jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, and vat photopolymerization [11].
Binder jetting is a quick prototyping and 3D printing technique that involves selectively depositing a liquid binding agent to link powder particles. To form the layer, the binder jetting technique jets a chemical binder over the dispersed powder.
Directed energy deposition (DED) is a 3D printing technique in which material is fed and fused by intense heat energy at the same time it is deposited. This technique can be used to layer-by-layer produce a print, but it may also be used to repair items. Electron Beam Additive Manufacturing (EBAM) and Laser Engineered Net Shaping are two examples of this technique (LENS).
Extrusion-based methods are used to create plastic prototypes and low-volume functional components. Fused Deposition Modeling (FDM) is the most extensively used extrusion-based technology. It is an extrusion-based approach for prototype, modeling, and production applications [4].
Material jetting is a 3D printing technique in which droplets of material are selectively placed and cured on a build plate. Objects are constructed one layer at a time using photopolymers or wax droplets that cure when exposed to light. Material Jetting (MJ) and Drop on Demand (DOD) are two types of 3D printing material jetting technology [12].
Powder bed fusion is the process of fusing and melting small powder particles to create 3D objects. This approach employs a variety of materials, including polymers, metals, ceramics, and composites. Some of the techniques used in this process include selective laser sintering (SLS), Selective Laser Melting (SLM), Electron Beam Melting (EBM), Direct Metal Laser Sintering (DMLS), and Multi Jet Fusion (MJF) [4].
Sheet lamination is a type of 3D printing that involves stacking and laminating sheets of very thin material together to create a 3D object. The material layers can be fused together in a variety of ways, the most frequent of which being heat and sound. Sheet lamination uses paper, polymers, and metals, therefore which process is best depending on the material.
Vat polymerization is a 3D printing technology in which a laser, light, or ultraviolet (UV) source cures a photopolymer resin selectively in a vat. Stereolithography (SLA), Digital Light Processing (DLP), and Masked Stereolithography (MSLA) are three prevalent methods of vat polymerization [13].
The most used 3D printing technologies are Fused Deposition Modeling (FDM), Selective Laser Sintering and Selective Laser Sintering (SLS).
Fused Deposition Modeling (FDM) is a fast, versatile, low-cost, and widely used 3D printing technology that easily and quickly fabricates a complex-shaped item. As a result of its low cost, Fused Deposition Modelling, also known as Fused Filament Fabrication (FFF), is considered one of the most popular additive manufacturing processes for prototyping. Due of the large number of printers on the market, Fused Deposition Modeling (FDM) technology is likely the most common printing process.
The main idea behind this 3D approach is to utilize a thermoplastic filament that has been parched to its melting point and then extrud through a nozzle layer upon layer to construct a 3D object. The nozzle precisely extrudes and directs the molten material, layer by layer, to construct a component. To shape each layer, most printers use an extruder that moves along the x and y axes, while the bed moves along the z-axis, decreasing one level each time a new layer is created. Other 3D printers, on the other hand, use an extrusion head that moves along the x, y, and z axes to create the design. This recreate the patterns of a layer added into the FDM working system by the application software [14]. FDM starts with a virtual design of the item to be printed, which is created in a ".stl" file using computer-aided design (CAD) software. AutoCAD, FreeCAD, and Autodesk Inventor are some examples of software packages used to create this sort of file. Another exemple of modeling software that is often use is Autodesk Fusion 360, offered by Autodesk. Fusion 360 is a cloud-based 3D modeling, Computer-Aided Design (CAD), Computer-Aided Manufacture (CAM), Computer Assisted Engineering (CAE), and Printed Circuit Board (PCB) software platform for product design and manufacturing. It is easy to use, and it is also an affordable and capable option to the industry's other big competitors [15]. The ".stl" file is processed by a slicing program, which turns the design into printer-specific instructions so that the printer can read the design. This ".stl" file is converted into a ".gcode" file. A slicing application is used to choose the parameters needed to print the item, such as print speed, print thread size, temperature, and layer height. These programs generate a file in ".gcode" format that may be directly read by the machine to print the prototype.
FDM printers require filament materials made of thermoplastic polymers, which indicates they can be melted and softened by heating and then regained their properties once they are cooled. Polylactic acid (PLA), polyvinyl alcohol (PVA), acrylonitrile butadiene styrene (ABS), thermoplastic elastomer (TPE), and polycarbonate (PC) are some of the filament materials utilized in FDM printers [16].
Stereolithography, like any other 3D printing technology, begins with a standard tessellation language (STL) file. The foundation of stereolithography is the curing reaction of resins, which is an exothermic polymerization process involving a laser source that triggers the polymerization reaction in photocurable materials [17]. The 3D model is produced layer by layer using a mobile platform. The laser makes contact with the container, hardening the elements needed to create the SLA prototype. When a layer is completed, the movable platform on which the solid layers are placed is lowered by a distance corresponding to the thickness of each layer of material utilized. These stages are repeated until the item is entirely printed. In most situations, the object will subsequently need to be washed with a solvent to remove any remaining resin. The item can also be baked in a UV oven to guarantee that it is fully hardened. [18].
Selective Laser Sintering is another popular 3D printing process that employs a high-powered laser to sinter microscopic particles of powder into a solid structure based on a 3D model. Layers are solidified using CO 2 / Nitrogen lasers, depending on the type of surface end and fusion required. During this procedure, the chemical compound powder is used to create the item. The powder might be made of thermoplastics, ceramics, glasses, or other materials. The powder is heated to a temperature lower than that of the analogous substance's melting point. Following that, the construction platform is lowered by one layer height to make way for the following layer. A sweeper or recoater roller travels over the surface, collecting surplus material from the reservoir and depositing new, cooler powder on top of the build platform to make the next layer. Finishing processes are necessary once production is done [19].
The discovery of printing biomaterials, referred as bioinks, has resulted in the introduction of 3D bioprinting, which has led to significant improvements in the medical field, particularly in regenerative medicine, because it allows on-demand printing of cells, tissues, and organs. Therefore, 3D bioprinting is a novel and promising biofabrication approach that enables the deposition of biomaterial-encapsulated live cells in the fabrication of complex 3D structures with great precision. Current bioprinting technologies are still new to many researchers. As scientists continue to make discoveries in this field, bioprinting seems to have a tremendous impact on a variety of biomedical application areas, such as tissue engineering and regenerative medicine [20], drug development [21].
Some general advantages of 3D printing include less material waste, ease of manufacturing, less human involvement, very little post-processing, and energy efficiency.
At the same time, there are a number of drawbacks to the use of 3D printing technology in the manufacturing sector. For example, the use of 3D printing technology may minimize the utilization of manufacturing workers, which will have a significant impact on the economies of nations that rely on a big number of low-skilled employment. Furthermore, 3D printing technology allows users to produce a wide range of things, including knives, firearms, and dangerous objects. As a result, the usage of 3D printing should be restricted to a small number of people in order to avoid the production of dangerous products. The fact that anyone who obtains a blueprint will be able to easily counterfeit things could also be a disadvantage [11], [19].
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