Common 3D Printing Materials

Polylactic Acid (PLA)

Polylactic acid (PLA) is one of the most commonly used plastics for 3D printing. It is a biodegradable polymer which is produced from the bacterial fermentation of plants such as corn, potato, or cassava. It is approved by the USDA for food contact, so it is potentially food safe. In reality, there are other aspects inherent to the 3D printing process, such as the metal nozzle (which may or may not be food safe and could contain metal contaminants such as lead) or small crevices which are difficult to clean both creating complications for 3D printing with food products. Another beneficial aspect of this polymer is the fact that it can be created into complex shapes; this is the reason it is commonly used for bone fixation and reconstruction. It is a great source for medical implants, orthopedic devices, and tissue engineering due to its strong durability and cheap cost. The fact that it is thermoplastic and biodegradable is also a plus because it has mechanical strength and good biocompatibility; in addition, fibers can be spun from it which is then turned into implants or other medical applications.

Acrylonitrile Butadiene Styrene (ABS)

ABS is usually a relatively difficult material to print with, but its application outside of 3D printing have made it desirable to work through the troubles and make it work. ABS is a thermoplastic copolymer, and one main advantage is that it can be heated and cooled to change from liquid to solid and vice verse without causing significant material degradation. ABS is known for its impact, chemical and heat resistance, with a high structural strength and great stiffness (Figure 1). This makes it very desirable to work with in additive manufacturing to reduce waste and form parts from the ground up.

Figure 1: The various 3D printing filaments tested for strength, stiffness and elongation.

Examples of ABS used in products are kitchen appliances, auto dashboards, protective equipment, toys, musical instruments and electrical equipment. The wide range of applications of the material, mated with this excellent strength and resistance to weathering make it a sensible material to 3D print.

There are hurdles to 3D printing with ABS however. It is infamously subject to warping, curling and they have a tendency to shrink up to 2% on cooling after the extrusion process. Often times, users will have to exercise trial and error fighting the setup parameters to get the material extrusion to behave as needed. A build chamber will be required for extrusion efficiency and for health and safety purposes. The chamber stops cooler air from cooling the material from all around increasing the warping. The chamber will also need a fume extractor, because even though the fumes are not considered toxic, they could cause physical discomfort including eye irritation, nausea and headaches.

Polydimethylsiloxane (PDMS)

Figure 2: This figure depicts the mechanical characterization of PDMS samples. (A) The dogbone-shaped samples which were 3D printed in both the transverse direction along with the longitudinal direction. (B) The ultimate strength of the 3D printed and cast inks are compared while (C) compares the Young’s modulus for the 3D printed and cast inks. (D) The failure strain is compared. Reprinted figure with permission from Ozbolat V, Dey M, Ayan B et al. 3D Printing of PDMS Improves Its Mechanical and Cell Adhesion Properties. ACS Biomater. Sci. Eng. 2018 4(2), 682–693. Copyright 2018 American Chemical Society.

3D printing is widely used to print polydimethylsiloxane (PDMS) based microfluidic devices. 3D rapid prototyping fabrication technique maintains the desirable permeability and bio-compatibility of PDMS. The ink for 3D printing PDMS can be prepared by blending a shear thinning PDMS material, and a low-viscosity PDMS material. After desired mixing, the final PDMS inks were loaded into a syringe barrel at room temperature. Using a 3D bioprinter, different nozzle pressures, extrusion pressures, and printing speed can be controlled.

Using this 3D printing technique, the PDMS object has higher mechanical properties in comparison to casting due to its decreased porosity and bubble entrapment (Figure 2).

Bioprinting

Bioprinting is a 3D printing technique which allows for tissue-like structures to be created using biomaterials which could be cells or growth factors. Bioink is the material used to create the desired structure, and the structures are created layer by layer just as in other methods of 3D printing. The difference with this is live cell suspension is used rather than a thermoplastic or PDMS. This means bioink is composed of living cells along with a compatible base which allows the cells to grow and have nutrients. The amount of bioink deposited for each layer depends on the type of tissue that is being printed along with the number of nozzles. As the layers are added, the layer starts to solidify which is defined as crosslinking. This type of 3D printing is used to imitate natural tissues, so it is most often in bioengineering and medical needs. It has also recently been used in reconstruction and regeneration of cartilage tissue. In general, this method is extremely important when it comes to mimicking the environments of micro and macro tissues and organs which is used in clinical trials along with drug testing. In the future, this could be use to create artificial organs used as organ transplants or for tissue repair; bioink allows for the product to be patient-specific since their cells are being used which is why this method is so promising for tissue repair and organ transplants.