3D Bioprinting of complex channels—Effects of material, orientation, geometry, and cell embedding

Abstract

Creating filled or hollow channels within 3D tissues has become increasingly important in tissue engineering. Channels can serve as vasculature enhancing medium perfusion or as conduits for nerve regeneration. The 3D biofabrication seems to be a promising method to generate these structures within 3D constructs layer-by-layer. In this study, geometry and interface of bioprinted channels were investigated with micro-computed tomography and fluorescent imaging. In filament printing, size and shape of printed channels are influenced by their orientation, which was analyzed by printing horizontally and vertically aligned channels, and by the ink, which was evaluated by comparing channels printed with an alginate-gelatin hydrogel or with an emulsion. The influence of geometry and cell-embedding in the hydrogel on feature size and shape was investigated by printing more complex channels. The generation of hollow channels, induced through leaching of a support phase, was monitored over time. Horizontally aligned channels provided 163 smaller cross-sectional areas than channels in vertical orientation. The smallest feature size of hydrogel filaments was twice as large compared to emulsion filaments. Feature size and shape depended on the geometry but did not alter when living cells were embedded. With that knowledge, channels can be consciously tailored to the particular needs.

Structured Macroporous Hydrogels: Progress, Challenges, and Opportunities

“…[178] The use of in situ gelation chemistries in 3D printing is still in its infancy, aside from the ionotropic alginate-calcium gelation mechanism that forms the basis of most existing hydrogel 3D printers. [139,179,180] Thermogelation by printing on a heated platform (e.g., methacrylamide-PEG-based triblock copolymer hydrogels [181] ) or a cooled platform (e.g., sodium alginate/ gelatin [92] ) has also been demonstrated, although suffers from drawbacks associated with the stability of the resulting structures outside of the controlled temperature environment, the capacity to print thicker structures further away from the temperature-controlled base, and a lack of flexibility regarding the hydrogel components in order to facilitate the required thermogelation. Combinations of physical gelation with UV photopolymerization have also been demonstrated.…”

Photo-patterning PEG-based hydrogels for neuronal engineering

“…It may be similarly possible to control cellular behavior through the fabrication of three-dimensional (3D) patterns in biomimetic materials. In this context, microfabrication techniques have been used extensively with 3D biomaterials to study which specific cell-matrix interactions can be associated with morphogenesis, development and tissue regeneration [7][8][9][10][11][12][13].…”

X-ray computed tomography for additive manufacturing: a review

“…This is most notably the case with AM parts due to the aforementioned complex geometries that are now commonly present. Further to older studies discussed earlier in this review, the past year has seen many publications exploring the use of XCT for direct measurements of part features and a number of these will be discussed in the following section [5,86,[92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111].…”

“…Wüst et al [92], for example, used XCT to examine the geometry of bioprinted channels through comparison of cross-sectional area measurements to theoretical values. In another application, Huang et al [96] used XCT to plan appropriate plate and screw trajectories for complex bone surgery, and then used an AM surgical guide to achieve these trajectories.…”