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Description
Introduction
Two main technologies of Biofabrication are bioprinting and scaffold generation. [1] Bioprinting can be used with cells in the matrix, while scaffold generation is cell-free and cells are attached afterwards. Both have their distinct advantages, e.g. bioprinting enables the generation of complex tissue hierarchies in one step, while scaffolds can guide cell elongation via topographical cues.
In this regard, we previously established Melt-Electro-Fibrillation, which generates microfibrillar polycaprolactone (PCL) via Melt-Electro-Writing (MEW). These support cell orientation, and it was previously shown that macrophages express anti-inflammatory markers caused by the topology alone. [2]
To exploit the advantages of bioprinting and scaffold generation, this study aims to converge these methods by utilizing fragmented fibrillar scaffolds as filler material for bioinks. The orientation of fibers after bioprinting with the orientation of the microfibrils led to the generation of a large anisotropic system, while maintaining the ease of application of bioprinting.
Materials and methods
The blend of polyvinyl acetate (PVAc) and polycaprolactone (PCL) was processed via melt electrowriting (MEW) and printed on a polyvinyl alcohol (PVA) coated grid. Subsequently the grid was transferred to the laser cutter, where the fibers were cut into bundles of equal length with fused microfibrillar fibers at both ends. Afterwards the grids with the fibers were immersed in 70% ethanol to dissolve the PVA and PVAc. The pure PCL microfibrillar fibers detached from the grid without damage and were further washed in 70% ethanol. Finally, they were transferred to pure water, lyophilized, and weighed. Then the hydrogel was added to create different fiber-to-hydrogel mixtures.
Results and discussion
Single microfibrillar fibers were laser cut into bundles and after the removal of the PVAc, the microfibrillar PCL structure was uncovered (Figure 1, A). The general form of the bundles consisted of two dome-like caps, which are caused by melting during the laser cut, and straight microfibrillar fibers. The obtained fibers were treated with NaOH to improve the dispersion of single bundles in a variety of hydrogels. Upon incorporation of the fiber bundles into the hydrogel, they were extruded into single lines, and aligned fiber bundles within the hydrogel were obtained (Figure 1, B). As anticipated, seeded cells aligned to the microfibrils of the ribbon (Figure 1, C).
Conclusion
We present a microfibrillar additive for bioinks that is capable to align cells in fiber direction and themselves in printing direction. Therefore, achieving an anisotropy from the cellular level to the macroscopic level, while maintaining the scalability of bioprinting.
References:
[1] J Groll et al A definition of bioinks and their distinction from biomaterial inks Biofabrication 2019 11 013001
[2] Ryma, et.al., Translation of Collagen Ultrastructure to Biomaterial Fabrication for Material-Independent but Highly Efficient Topographic Immunomodulation. Adv. Mater. 2021, 33, 2101228.
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