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Hybrid polycaprolactone/hydrogel scaffold fabrication and in-process plasma treatment using PABS
structure with a uniform pore distribution and pore size 3.4. Biological Assessment of Full-layer Plasma
in the range of ~500 µm (Figure 4C). The N plasma Modified Scaffold
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treatment was conducted at a pressure of 0.689 bar and a The adhesion and proliferation of hADSCs cells on
flow rate of 5 L/mm. The deposition speed of the plasma plasma full-layer modified PCL scaffolds were studied
jet was 3 mm/s, and each layer was subjected to the and compared with untreated ones. The biological
plasma treatment for 1 min. The distance from the bottom characterization was assessed using Alamar Blue Assay.
of the jet to the surface of the PCL filaments was 10 mm. The fluorescence intensity of cell-seeded scaffolds
Figure 4D presents the filament surface after N plasma measured at four different culture time points (Days 1,
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modification, where lines in the direction of plasma 3, 7, and 14) is shown in Figure 5A. Higher fluorescence
movement can be observed making the surface roughness intensity corresponds to more metabolically active cells.
increased. As observed, cell proliferation increases with time in
all types of scaffolds, suggesting that they are suitable
3.3. Wettability Assessment of Full-layer Plasma structures for cell attachment and proliferation. However,
Modified Scaffold a fast proliferation rate is observed in the case of plasma-
WCA measurements were performed on untreated treated scaffolds. The different performance is statistically
and fully treated plasma PCL scaffold surfaces to significant after day 3.
Confocal microscopy images (Figure 5B) present the
determine the effect of plasma modification on the cell attachment and distribution after cell seeding (day 1)
surface wettability. Table 1 highlights the WCA and proliferation (day 14). It can be observed that plasma-
results at different time points after the droplet was treated scaffolds presented higher numbers of cells
dropped on the surface of the scaffolds. The results than untreated scaffolds. In addition, it is also possible
show that in the case of an untreated PCL scaffold, to observe that the plasma surface-treated scaffolds
there are no significant changes in the WCA values presented best cell attachment and dispersion.
with time with values varying between 83.2±2.0° and
80.9±2.7°. For treated scaffolds, the WCA value, at 4. Discussion
0 s, was lower (63.0±3.1°), leading to a fully wetting The printed hybrid PCL scaffolds filled with hydrogel
value of 26.7±0.9° at 0.5 s. At 3 s, the droplet was present the printability of PBAS, enabling the soft hard
fully absorbed material integration. The photo and SEM images of
the whole printed structure indicate that the plasma
A B C modification process does not affect the physical
appearance of the structure and potentially no effect on
the mechanical performances . Moreover, the SEM
[31]
image of the filament surface confirms the increased
surface roughness is due to the etching process , which
[32]
D E F results in the stripping off the topmost layer of the polymer
filament. From this study, the increase surface roughness
is also resulted from the linear scratches attributed to
the gas flow by the plasma jetting directly after the PCL
deposition when the material is still in the molten status.
Figure 4. (A) Hybrid polycaprolactone (PCL)/hydrogel scaffold; As the printed material is not totally cooled down, when
(B) Scanning electron microscopy (SEM) image of top view of the plasma modification occurs, the gas flow effect is
PCL/hydrogel scaffold; (C) SEM image of side view of PCL/
hydrogel scaffold; (D) photo of a full-layer N plasma-treated PCL stronger, significantly influencing the surface topography.
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scaffold; (E) SEM image of top view of full-layer N plasma treated Moreover, the increase of surface roughness is beneficial
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[33]
PCL scaffold; (F) SEM image of filament surface of full-layer N for cell colonization in the scaffolds .
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plasma-treated PCL scaffold. The wettability results reveal that the hydrophilicity of
the surface is dramatically improved due to the ionizable
Table 1. Temporal variation of WCAs for treated and untreated groups introduced on the surface by the N plasma, which
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scaffolds enhances the hydrogel bonding with water. Compared
with the results published in [28,34] , the absorption speed is
Time PCL scaffolds N plasma fully treated
2 dramatically increased, due to chemical heterogeneity on
0s 83.2±2.0° 63.0±3.1°
0.5s 82.9±1.2° 26.7±0.9° the surface of each layer due to the plasma modification
3s 80.9±2.7° Fully absorbed layer on layer. However, the effect of plasma modification
PCL: Polycaprolactone, WCAs: Water contact angles can last within a certain period of time depending
6 International Journal of Bioprinting (2019)–Volume 5, Issue 1