Biomaterials / bioinks and extrusion bioprinting

Abstract

Bioinks are formulations of biomaterials and living cells, sometimes with growth factors or other biomolecules, while extrusion bioprinting is an emerging technique to apply or deposit these bioinks or biomaterial solutions to create three-dimensional (3D) constructs with architectures and mechanical/biological properties that mimic those of native human tissue or organs. Printed constructs have found wide applications in tissue engineering for repairing or treating tissue/organ injuries, as well as in vitro tissue modelling for testing or validating newly developed therapeutics and vaccines prior to their use in humans. Successful printing of constructs and their subsequent applications rely on the properties of the formulated bioinks, including the rheological, mechanical, and biological properties, as well as the printing process. This article critically reviews the latest developments in bioinks and biomaterial solutions for extrusion bioprinting, focusing on bioink synthesis and characterization, as well as the influence of bioink properties on the printing process. Key issues and challenges are also discussed along with recommendations for future research.

Graphical abstract

Highlights

• •

  Bioninks have been formulated from various biomaterials and living cells for bioprinting.

• •

  Important properties of bioinks include their physical, rheological, crosslinking, mechanical, and biological ones.

• •

  Bioprinting parameters, including the flow rate of the printed bioink, must be appreciately designed and regulated.

• •

  Cell viability and printability are two key issues of extrusion bioprinting.

• •

  Extrusion-based bioprinting techniques have been rapidly developed and evolved with various advances.