July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 0 2 0 *Member of ASM International 3D BIOPRINTING: A STATE-OF-THE-ART REVIEW ON PRINTING TECHNIQUES 3D printing of organic and inorganic materials requires special consideration in both material selection and the process used. Haripriya Ramesh, Roger J. Narayan,* North Carolina State University, Raleigh Dmitry M. Zuev, Lomonosov Moscow State University 3 D printing is a well-known con- cept. It converts digital directives to real-time molds in the form of polymers, metals, alloys, plastics, ce- ramics, and textiles. Bioprinting is a form of 3D printing involving process- ing of organic and inorganic materi- als, even live cells to produce new hard and soft tissues. The main technologi- cal challenges of 3D bioprinting are the 3D positioning process, formulation of a bio-ink, and the dispensing technique. 3D bioprinting offers the potential to create a construct by blending the prin- ciples of life sciences, engineering, and regenerative medicine with sizes ap- propriate to replace tissue defects. Its potential applications range from struc- tural health monitoring to tissue en- gineering, and from implants to drug delivery [1] . Current research includes an emphasis on developing cellular con- structs for biomedical applications, such as organ transplantation or re- generative medicine [2] . The advantages of 3D printing are personalization/cus- tomization, increased cost efficiency, rapid product development, democrati- zation of design process, micropattern- ing and organization, and biomimetic and biological recapitulation. The con- siderations for materials are wheth- er they can be sterilized, whether they are biocompatibile, biodegradable, me- chanically appropriate, and compati- bile with the printing process. The effect of printing on cell viabil- ity and vascularization is an important consideration. Organs can be printed within a given space (printing cham- ber) during the process of printing. There are six major printing processes including extrusion bioprinting [3] , ink- jet printing [4] , selective laser sintering and selective laser melting [5] , stereo- lithography [6] , laser-induced forward transfer bioprinting [7] or laser-assisted bioprinting, [8] and two-photon polymer- ization [9] . These techniques involve preadjustment, printing, and postpro- cessing. The preadjustment process is similar in all six methods and consists of computer-aided design (CAD), in which the pattern is drawn using the accurate placement along X, Y, and Z axes. Each printing technique has its own advan- tages and disadvantages in terms of printing speed, precision, and specific substrate properties. Selection of the appropriate technique should be based on the final biomedical application [10,11] . As the field of bioprinting has evolved into its current state, several types of bioprinters have been created by research groups around the globe. In addition, commercial bioprinters are being sold by a number of companies. According to recent work [11] , the ideal bioprinter should possess certain ca- pabilities, such as a high degree of freedom in motion, which allows de- positing the bio-ink on non-planar sur- faces, and the bioprinter should be compact enough to fit under a biosafety cabinet or a laminar flow hood to bio- print under sterile conditions [11] . EXTRUSION BIOPRINTING Extrusion bioprinting is one of the most adopted and inexpensive print- ing techniques. These printers consist of a mechanical (i.e., piston or screw) or pneumatic mechanism to eject the bio-ink via the nozzle and print the computer-generated design. Extrusion bioprinters are distinctive from inkjet printers in that they can print high vis- cosity bio-inks and very high cell den- sities for tissue formation. There is a prominent difference between pis- ton-driven and screw-driven systems due to the fact that viscosities of bio- inks can be delivered by regulating the pressure and gating time of the valve. In this approach, the extrusion pressure is inversely proportional to the cellular growth and its feasibility. In fused deposition modeling (FDM), the entire process revolves around the concept of melting the fil- ament of the feedstock material, there is no solvent involved in the entire process. Many structures laid by this method are considered to have good CURRENT RESEARCH INCLUDES AN EMPHASIS ON DEVELOPING CELLULAR CONSTRUCTS FOR BIOMEDICAL APPLICATIONS, SUCH AS ORGAN TRANSPLANTATION OR REGENERATIVE MEDICINE [2] .