Extrusion bioprinting of soft materials: An emerging technique for biological model fabrication

Abstract

Bioprinting has attracted increasing attention in the tissue engineering field and has been touted to potentially become the leading technology to fabricate, and regenerate, tissues and organs. Bioprinting is derived from well-known additive manufacturing (AM) technology, which features layered deposition of materials into complex three-dimensional geometries that are difficult to fabricate using conventional manufacturing methods. Unlike the conventional thermoplastics used in desktop, AM bioprinting uses cell-laden hydrogel materials, also known as bioinks, to construct complex living biological model systems. Inkjet, stereolithography, laser-induced forward transfer, and extrusion are the four main methods in bioprinting, with extrusion being the most commonly used. In extrusion-based bioprinting, soft materials are loaded into the cartridges and extruded from the nozzle via pneumatic or mechanical actuation. Multiple materials can be printed into the same structure resulting in heterogeneous models. In this focused review, we first review the different methods to describe the physical mechanisms of the extrusion process, followed by the commonly employed bioprintable soft materials with their mechanical and biochemical properties and finally reviewing the up-to-date heterogeneous in vitro models afforded via bioprinting.

Extrusion and Microfluidic‐Based Bioprinting to Fabricate Biomimetic Tissues and Organs

“…Nozzles with larger diameters operated with lower pressure levels were introduced as ways to reduce the shear stress. [237,239,241,242]…”

Multicomponent polysaccharide alginate-based bioinks

“…However, because alginate is easy to gel at room temperature, allowing the encapsulation of living cells before the printing process, it can be readily applied to other bioprinting methods. The reader is, therefore also referred to a number of additional reviews and research articles for a more detailed discussion, 24,[26][27][28][29][30][31][32][33][34] and we will go on to briefly review inkjet and microfluidic bioprinting technologies, for which the properties of this polymer are particularly advantageous, later in this article.…”

Engineered 3D Polymer and Hydrogel Microenvironments for Cell Culture Applications

“…Bioinks loaded with polysaccharides and proteins (e.g., collagen, alginate) can show very different values of viscosity. The technology is mature with available bioprinters on the market at reasonable costs, which allow customization and focus on bioink mixtures [45][46][47][48][49][50][51][52][53].…”