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International Journal of Bioprinting New fibrillar collagen for 3D printing and bioprinting

Figure 4. 3D-printed collagen scaffolds at different concentrations together with their printing conditions (pressure and speed) for each case. Scale bars:
10 mm. (B) Scaffold printed with ColA ink (acidic ink, 5% w/w) with 27 layers. As it can be seen, the consistency of this ink is appropriate to produce
complex structures without collapsing.

conditions and despite their higher dimensions, the number agreement with the rheology studies (Figure 2); the acidic
of “free independent” fibers within the network reduces and, inks have higher consistency compared to the neutral ones
therefore, there is more “space” available between them and (see tan δ values). This great consistency allows for the
less cohesiveness. This can be translated into lesser interactions printing of tall, complex scaffolds as shown in Figure 4B.
during stress application (rheology measurements) and When it comes to cell-laden scaffolds produced by
therefore, lower viscosity values. Similar results were observed pneumatic extrusion 3D bioprinting, it is desirable to
for viscosity values of type I collagen in the presence of salts, obtain the highest resolution and shape retention with
thus supporting the present hypothesis . the lowest pressure to guarantee cellular viability. In fact,
[27]
3.1.3. 3D printing a recent systematic review confirmed that cell viability is
The resolution, shape fidelity, and cell viability are inversely proportional to printing pressure and directly
important factors determining the suitability of the proportional to printing nozzle diameter [35,36] . Bearing in
resultant scaffold for TE. As previously mentioned, high- mind that the nozzle used to obtain all the scaffolds was
viscosity bioinks usually led to high-quality structures the same, the 3D printing performance of the neutral
with remarkable shape fidelity, while lower viscosities are inks (Figure 4) is more desirable since they provide good
related to higher cell viability and softer structures, which resolution with low printing pressures together with an
are unable to maintain their shape after printing. optimal pH for the cells to be laden.
The ColA mass was bioprinted at different 3.1.4. In vitro cytotoxicity
concentrations in order to obtain a continuous, self- None of the in vitro studies have revealed evidence of cell
standing scaffold with the maximum shape fidelity and toxicity by acid or neutral collagen formulations toward
resolution. The pressure and speed were adjusted to L929 cells, as demonstrated by the cellular viability
guarantee a continuous flow. Higher concentrations of percentages provided by the WST-1 test, as presented
collagen require higher printing pressures (Figure 4). in Figure 5A and B. In fact, the cellular viability was
The necessity of higher printing pressures for the acidic systematically equivalent or even superior to the positive
formulation with respect to the neutral ink (ColN) is in control. Although no statistically significant differences

Volume 9 Issue 3 (2023) 320 https://doi.org/10.18063/ijb.712