Recent cell printing systems for tissue engineering

Abstract

Three-dimensional (3D) printing in tissue engineering has been studied for the bio mimicry of the structures of human tissues and organs. Now, it is being applied to 3D cell printing, which can position cells and biomaterials, such as growth factors, at desired positions in the 3D space. However, there are some challenges of 3D cell printing, such as cell damage during the printing process and the inability to produce a porous 3D shape owing to the embedding of cells in the hydrogel-based printing ink, which should be biocompatible, biodegradable, and non-toxic, etc. Therefore, researchers have been studying ways to balance or enhance the post-print cell viability and the print-ability of 3D cell printing technologies by accommodating several mechanical, electrical, and chemical based systems. In this mini-review, several common 3D cell printing methods and their modified applications are introduced for overcoming deficiencies of the cell printing process.

Keywords: bioink; cell-printing; tissue engineering.

Figure 1

Basic techniques of 3D cell printing, (a) laser-assisted 3D cell printing techniques with and without an absorbing layer,[17,22] (b) thermal, piezoelectric, and acoustic inkjet 3D cell printing systems,[22,28] and (c) microextrusion 3D cell printing systems and products[14,35].

Figure 2

3D cell printing with modified crosslinking processes, (a) aerosol crosslinking process with calcium chloride using an alginate-based bioink[36-38] (b) drop-on-demand (submerged) crosslinking with a laser-assisted printing process[41], (c) submerged printing with a core (MSC-laden collagen) /shell (2-5 wt% alginate) nozzle[44], and (d) cell printing process with a crosslinked solution and absorbing stage using a core (3 wt% alginate-based cell-laden bioink)/shell (1.2 wt% CaCl₂)[46].

Figure 3

Temperature-controlled 3D cell printing process, (a) increasing temperature-controlled (from 4 to 37°C) printing using ECM-based bioinks [48, 49] and (b) low-temperature (-10°C) cell printing process [50].

Figure 4

(a) Electrically operated cell printing modification supplemented with the aerosol crosslinking process[51] and (b) extrusion-based cell printing with an electric field (1 to 3 kV in 0.33 to 0.99 mm)[52].

Figure 5

Hybrid modifications of the 3D cell printing process with (a, b) a multi-nozzle system using natural and synthetic polymers ((a) Shim et al.[53], (b) Lee et al.[54]) and (c) an additional electrospinning process for surface alignment (Yeo et al.[56]).