Page 96 - IJB-9-2

International Journal of Bioprinting Holistic charge-based MEW scaffold model

post-seeding strategy ). Although the former strategy has critical stage speeds, thereby introducing sinusoidal fibers
[5]
prevailed for many in vitro applications for engineered into the scaffold structure . Furthermore, Saidy et al.
[17]
tissue fabrication, the latter also possesses several distinct printed scaffolds with bidirectional crimped fibers to
attributes. First, the post-seeding strategy prevents the mimic the wavy nature of collagen . Onur et al. fabricated
[5]
in-process damage to the living cells due to the shear anisotropic scaffolds with linear and crimped fibers in
stress in the cell-laden bioink flow in the nozzle and the different directions, thus mimicking the microstructure
downstream filament deposition process, which is a of biological soft tissues . In addition, MEW has
[18]
[6]
common challenge in bioprinting . Second, the post- found its applications in bone , cardiac , nerve ,
[20]
[21]
[19]
seeding strategy offers additional freedom with respect muscle tissue engineering, etc. Compared to other
[22]
to the selection of the scaffold fabrication processes, 3D biomaterial scaffold fabrication methods (e.g., fused
allowing the adoption of printing conditions that would deposition modeling, stereolithography, and selective laser
be deleterious for cell viability and phenotypic outcomes sintering), MEW is able to produce scaffolds with facile
in the context of direct bioprinting. These may include implementation, wide range of fiber diameter (800 nm –
[23]
printing at high operating temperatures, high voltage, high 150 μm ), and high tunability in terms of microstructure.
[24]
viscosities, and high pressures . By availing the materials
[7]
processing approach to a wide dynamic range of processing However, due to the semiconductive nature of polymer
conditions, the quality of the scaffolds can be improved material, substantial amounts of charges are entrapped
[25]
in terms of printing accuracy, resolution, structural within the deposited fibers . Depending on parameter
complexity, and mechanical property. Third, sterility is a settings, the net polarity of deposited fibers in the scaffold
main concern in the direct bioprinting strategy, wherein can be either negative or positive. In either case, the electric
long-term biological studies necessitate that the bioink field exerted on the jet deviate it from its prescribed path,
be maintained under sterile conditions throughout the resulting in the structural disorder in the scaffold in two
printing process. This constraint may inevitably limit the ways. First, when the deposited fiber is negatively charged,
selection of bioink formulation, as well as the overall system it remains challenging to print fibers of a specific diameter
configuration of the bioprinters used. In contrast, with the (d) over a small interfiber distance (S ). The smallest
f
f
post-seeding strategy, the sterility challenge is not an issue achievable value of S /d is approximately 6 in current
f
f
[26]
since a post-desterilization process can be implemented study . Closer interfiber proximity will cause obvious
before cell seeding. Finally, compared to the direct fiber deviation or overlapping due to the net negative
[27]
bioprinting strategy in which the cells are encapsulated in charges and charge polarization within the fibers .
the bioink, the tailored design and fabrication of scaffolds Second, when the deposited fiber is positively charged,
provides for not only the sites for cell attachment but also the jet is exposed to the jet-scaffold repulsion, resulting
the necessary geometrical and mechanical cues to guide in jet’s deviation from the locations prescribed by the
cell differentiation , which helps to drive the formation of toolpath. Attempts have been made to alleviate this effect
[8]
[28]
the desired tissue constructs. by increasing the voltage and utilizing an in situ charge
elimination module, by which a highly ordered scaffold as
As an emerging 3D-structured materials processing high as 1 cm has been fabricated. All these phenomena
[29]
approach that adopts the aforementioned post-print need further explanation, and it is imperative to find ways
cell seeding strategy as part of the fabrication workflow, to improve the charge dissipation process.
the additive polymer melt-based electrohydrodynamic
printing process, or melt electrowriting (MEW), has In a previous study, the residual charge amount in
the unique capability of manufacturing 3D-structured MEW-enabled scaffold was successfully measured using
[30]
biomaterial scaffolds composed of intersecting microscale a nanocoulomb meter . While investigating the effect of
polymer fibers [9,10] . Due to its multiparametric nature , it different design and process parameters on the residual
[11]
is highly controllable and designable in terms of the fiber charge amount, the effect of fiber morphologies on the
diameter , pore shape , pore size, and macroscopic residual charge amount is noteworthy. The residual
[12]
[13]
geometry , which determine its versatility in tissue charges entrapped within a fibrous wall composed of
[14]
engineering . Heterogeneous scaffolds, with varying discretely deposited fibers are usually more than those in
[15]
fiber diameters , pore features and even curly fiber a fibrous wall composed of compactly deposited fibers ,
[16]
[30]
patterns , have been successfully fabricated. Moreover, in which “fiber sagging” occurs, and as a result, contact
[5]
[31]
MEW-enabled scaffolds with distinctive mechanical discharge happens more easily. The effects of different
properties have also been attempted to simulate the natural process parameters on the residual charge amount can be
biological tissues. To mimic the non-linear extension of either dependent or independent of fiber morphologies
ligaments and tendons, Hochleitner et al. printed at sub- (MDE and MIE). Moreover, MDE and MIE can be either
Volume 9 Issue 2 (2022) 88 https://doi.org/10.18063/ijb.v9i2.656