Three-dimensional bioprinting of stem-cell derived tissues for human regenerative medicine

Abstract

Stem cell technology in regenerative medicine has the potential to provide an unlimited supply of cells for drug testing, medical transplantation and academic research. In order to engineer a realistic tissue model using stem cells as an alternative to human tissue, it is essential to create artificial stem cell microenvironment or niches. Three-dimensional (3D) bioprinting is a promising tissue engineering field that offers new opportunities to precisely place stem cells within their niches layer-by-layer. This review covers bioprinting technologies, the current development of 'bio-inks' and how bioprinting has already been applied to stem-cell culture, as well as their applications for human regenerative medicine. The key considerations for bioink properties such as stiffness, stability and biodegradation, biocompatibility and printability are highlighted. Bioprinting of both adult and pluriopotent stem cells for various types of artificial tissues from liver to brain has been reviewed. 3D bioprinting of stem-cell derived tissues for human regenerative medicine is an exciting emerging area that represents opportunities for new research, industries and products as well as future challenges in clinical translation.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Keywords: bioprinting; regenerative medicine; stem cells; three dimensional.

Figure 1.

The three primary bioprinting methods. (a) Drop-on-demand (DoD) bioprinting, comprising: ink-jet and valve-jet bioprinting. (b) Micro-extrusion bioprinting: pressure, spring or piston forces the bio-ink to extrude through a nozzle. (c) Laser-assisted bioprinting: stereolithography and laser-induced forward transfer (LIFT). (Online version in colour.)

Figure 2.

The primary properties of bio-ink material have biological and mechanical effects in the engineered tissue. (Online version in colour.)

Figure 3.

Different endogenous tissue types display varying rigidity. Brain, lung, liver and muscle, for example, all reside in relatively soft tissues, whereas common tissue culture plastic (TCP) is several orders of magnitude more rigid. This can lead to changes in cell viability, function and phenotype when culturing cells in vitro. However, the characteristics of bio-inks can be tuned for the bespoke need of the desired tissue. (Online version in colour.)

Figure 4.

Examples of 3D bioprinting. (a) Workflow of bioprinting large-scale human tissue from Kang et al. [24]. Medical imaging is first used to generate a computer-aided design (CAD) file that the bioprinter can then optimize for printing. The tissue was then printed in the integrated tissue-organ printer (ITOP) bioprinter to form the artificial tissue. (b) Biomimetic patterning of stem-cell derived hepatocytes from Ma et al. [54]. The hexagonal lobule of the liver was used as a template for printing iPSC-derived hepatocytes and supporting endothelial and mesenchymal cells. (c) Fine-tuning of bio-ink characteristics. By adding varying levels of carboxymethylcellulose, Gu et al. [66] were able to control porosity in their bio-ink, optimizing encapsulation of human neural stem cells. (d) Post-implantation, anatomically designed bioprinted bone tissue from Daly et al. [67]. A soft bio-ink with MSCs was reinforced with PCL fibres for mechanical stiffness prior to implantation. Twelve weeks following implantation, the structure was shown to be vascularized. (e) Bioprinting full-scale nose using hybrid bio-ink to optimize printability and porosity for cell viability [68]. This ink was used to encapsulate mesenchymal stem cells and differentiate them to functional chondrogenic and osteogenic cells. (Online version in colour.)