Solvent-based Extrusion 3D Printing for the Fabrication of Tissue Engineering Scaffolds

Abstract

Three-dimensional (3D) printing has been emerging as a new technology for scaffold fabrication to overcome the problems associated with the undesirable microstructure associated with the use of traditional methods. Solvent-based extrusion (SBE) 3D printing is a popular 3D printing method, which enables incorporation of cells during the scaffold printing process. The scaffold can be customized by optimizing the scaffold structure, biomaterial, and cells to mimic the properties of natural tissue. However, several technical challenges prevent SBE 3D printing from translation to clinical use, such as the properties of current biomaterials, the difficulties associated with simultaneous control of multiple biomaterials and cells, and the scaffold-to-scaffold variability of current 3D printed scaffolds. In this review paper, a summary of SBE 3D printing for tissue engineering (TE) is provided. The influences of parameters such as ink biomaterials, ink rheological behavior, cross-linking mechanisms, and printing parameters on scaffold fabrication are considered. The printed scaffold structure, mechanical properties, degradation, and biocompatibility of the scaffolds are summarized. It is believed that a better understanding of the scaffold fabrication process and assessment methods can improve the functionality of SBE-manufactured 3D printed scaffolds.

Keywords: Fabrication process parameters; Ink materials; Ink rheology; Solvent-based extrusion 3D printing; Tissue scaffolds.

Figure 1

SBE 3D printing types, pneumatic-driven based 3D printing (A); piston-driven based 3D printing (B); screw-driven based 3D printing (C); a schematic showing the factors that influence SBE 3D printing.

Figure 2

The relationship between viscosity (η) and shear rate (γ̇) for the inks with 1 wt% alginate and a laponite concentration (cL) between 0 and 6 wt% (A); storage modulus (G’) (elastic modulus) and loss modulus (G’’) (viscous modulus) as a function of strain (γ) (B); viscosity as a function of the time (t) for the ink recovery test (C); microscopy images of the extrusion of alginate/laponite inks with the laponite between 0 and 6 wt%. The scale bar is 1 mm (D)[39].

Figure 3

The schematic of ink flow inside the printing needle (A); the first layer of filament formation on the substrate (B); the fusion process of two filament layers in the vertical direction within the printed woodpile structure (C).

Figure 4

The schematic of overlap area in acute angle printing (A); the ink diffusion and fusion on the same layer when the D_L was at 1-4 mm (B); the comparison of lattice area from theory and experiment as well as the relationship among line distance, line width, and diffusion rate (C)[19].