Multiscale assembly for tissue engineering and regenerative medicine

Abstract

Our understanding of cell biology and its integration with materials science has led to technological innovations in the bioengineering of tissue-mimicking grafts that can be utilized in clinical and pharmaceutical applications. Bioengineering of native-like multiscale building blocks provides refined control over the cellular microenvironment, thus enabling functional tissues. In this review, we focus on assembling building blocks from the biomolecular level to the millimeter scale. We also provide an overview of techniques for assembling molecules, cells, spheroids, and microgels and achieving bottom-up tissue engineering. Additionally, we discuss driving mechanisms for self- and guided assembly to create micro-to-macro scale tissue structures.

Figure 1

(A) Corresponding technologies for assembling building blocks at different scales. The size of each biological entity is shown above the scale axis, while the sample size that each assembly technology can manipulate is shown below the scale axis. (B) Schematic of multiscale assembly strategies from bottom to top for engineering 3D tissue constructs. The assembly strategies can follow paths starting with biomolecules or cells and can be integrated in the engineering of the final 3D tissue constructs.

Figure 2

Cell assembly technologies. (A) Liquid-based template assembly (LBTA). Left: Schematics of reconfigurable assembly by LBTA. Right: Assembled cell pattern. The region marked with red dashed lines indicates the magnified region. Cells were stained with cell tracker (green). Reproduced, with permission, from [49]. (B) Molecular recognition-assisted cell assembly. Left: Schematic demonstration. Right: Images of assembled cells and enlarged heterogeneous cell arrangement. Green- and red-stained Jurkat cells marked with the complementary DNA sequences. Adapted from [53]. (C) Sketch showing laser-guided direct writing (LGDW). Left: LGDW. The laser is focused into a cell suspension and the radiation force due to the difference in refractive index moves cells onto a receiving substrate. Right: Phase contrast and immunofluorescence of human hepatocytes and endothelial structure engineered by LGDW. Reproduced, with permission, from [56].

Figure 3

Illustration of mechanisms for assembly technologies. (A) Self-assembly explores intrinsic interactions among building blocks to generate ordered structures. (B) Guided self-assembly explores interactions between building blocks and external forces to generate controlled global structures. (C) Guided assembly with a pick-and-place strategy builds complex structures with controlled global geometry and arrangement of cell carriers piece by piece.

Figure 4

Digital patterning. (A) Schematic of digital patterning of heterogeneous structures. (B) Patterning of three cell types [ESCs in green, 3T3 cells in blue, human umbilical vein endothelial cells (HUVECs) in red] in a single tissue structure. (C,D) Digital patterning of a 100-μm hydrogel next to a 500-μm hydrogel, where only the 100-μm hydrogel includes a single neuron. Reproduced, with permission, from [94]. (E–J) 3D patterning of living units via magnetic microrobots. (E,F) Microrobotic assembly of heterogeneous objects. (G–J) Heterogeneous assembly of soft hydrogels and rigid objects. Reproduced, with permission, from [95].