Three-dimensional Printing of Multilayered Tissue Engineering Scaffolds

Abstract

The field of tissue engineering has produced new therapies for the repair of damaged tissues and organs, utilizing biomimetic scaffolds that mirror the mechanical and biological properties of host tissue. The emergence of three-dimensional printing (3DP) technologies has enabled the fabrication of highly complex scaffolds which offer a more accurate replication of native tissue properties and architecture than previously possible. Of strong interest to tissue engineers is the construction of multilayered scaffolds that target distinct regions of complex tissues. Musculoskeletal and dental tissues in particular, such as the osteochondral unit and periodontal complex, are composed of multiple interfacing tissue types, and thus benefit from the usage of multilayered scaffold fabrication. Traditional 3DP technologies such as extrusion printing and selective laser sintering have been used for the construction of scaffolds with gradient architectures and mixed material compositions. Additionally, emerging bioprinting strategies have been used for the direct printing and spatial patterning of cells and chemical factors, capturing the complex organization found in the body. To better replicate the varied and gradated properties of larger tissues, researchers have created scaffolds composed of multiple materials spanning natural polymers, synthetic polymers, and ceramics. By utilizing high precision 3DP techniques and judicious material selection, scaffolds can thus be designed to address the regeneration of previously challenging musculoskeletal, dental, and other heterogeneous target tissues. These multilayered 3DP strategies show great promise in the future of tissue engineering.

Figure 1

Multilayered scaffold approaches to various complex tissue types. A) Using SLS, PCL and HA/PCL microspheres were used to create heterogeneous scaffolds with mechanical property gradients in order to model the cartilage, interface, and subchondral bone layers of the osteochondral unit. Reproduced with permission from Du et al.(76) B) Multiphasic scaffold design to target the cementum/dentin interface, periodontal ligament, and alveolar bone in phases A, B, C, respectively. Includes differential microchannel diameter across three phases as well as the delivery of amelogenin, connective tissue growth factor, and bone morphogenetic protein-2 to phases A, B, and C, respectively, via encapsulation in poly(lactic-co-glycolic acid) microspheres. Reproduced with permission from Lee et al.(127) C) Homogeneous and heterogeneous tissue constructs can be constructed from the spontaneous fusion of homocellular and heterocellular spheroids, respectively. The goal of whole organ printing is to eventually develop fully vascularized, 3D organs from the printing and subsequent fusion of these spheroids. Reproduced with permission from Mironov et al.(128)

Figure 2

Integrated Tissue-Organ Printing system used by Kang et. al. a) A computer-controlled 3-axis stage and multi-cartridge print head are used to print heterogeneous structures with high fidelity. b) Within a 3DP construct, different cell-laden hydrogels are patterned within a PCL framework. c) Medical images, such as MRIs, can be used to create 3D CAD models that give specific xyz locations and deposition instructions to the stage and print heads respectively to produce a 3DP construct. Reproduced with permission from Kang et al.(94)

Figure 3

Multi-head extrusion system used by Liu et al. a, b) Schematic of the printer and pneumatic controls. The multi-head system contains up to 7 different cartridges, but individual pneumatic control is retained for each cartridge during printing. c, d) Photographs of the cartridges and print head described. e) Sample schematic showing how different bioinks can be mixed through pneumatic control. f,g) Printed microfiber of a multi-bioink extrusion material. Reproduced with permission from Liu et al.(62)