Effects of hydrogel properties and extrusion parameters on 3D bioprinting
Nathan Tessema Ersumo, Kara L. Spiller
School of Biomedical Engineering, Science and Health Systems, Drexel University
TRAVEL FEED RATE
AND RESOLUTION
INTRODUCTION
The recent rise of 3D bioprinting as a prominent biofabrication method
We next investigated the role of travel feed rate, i.e. printing speed, on
has seen widespread investigation into extrusion/deposition techniques
resolution of the printed structures. The effects of increasing the travel
and hydrogels to optimize cytocompatibility and printability [1-3].
feed rate from 4 mm/sec to 8 mm/sec and 12 mm/sec were tested by
Using various methods, efforts have also been made to assess the
extruding a series of lines (Fig. 2) at 10%, 15% and 20% GelMA. Line
fidelity of 3D printed structures [4-7], though no accurate standardized
thicknesses were measured (Fig. 4) from images obtained using an
method has been developed for 3D bioprinting. Despite these studies,
the effects of hydrogel properties and bioprinting parameters on
extruded constructs have yet to be systematically and accurately
evaluated. Using a Biobots 3D bioprinter, gelatin methacrylate
hydrogels and various evaluation methods, including finite element
Fig. 1. Young’s moduli at various GelMA concentrations with 0.25%
and 0.5% w/v LAP. Data shown as mean ±SEM (n=6). For each LAP
concentration, Young’s moduli at all GelMA concentrations are
significantly different from each other (***p≤0.001, ANOVA with posthoc Tukey analysis). There is no significant difference between 0.25%
and 0.5% LAP.
EVOS microscope (transmitted light, phase contrast, 4x magnification)
(Fig. 5). A decrease in printed line thickness was observed with
increasing GelMA concentration and travel feed rate.
Fig. 6. HUVEC viability for both ‘Extrusion Only’ and ‘Extrusion + 15 min
Photocrosslinking’ conditions. Data shown as mean ±SEM (n=5). No significant
difference between the two groups (ANOVA with post-hoc Tukey analysis).
analysis and micro-computed tomography, we characterize the impact
of biomaterial composition, CAD structure and printing speed on the
rigidity, stress distribution, resolution and fidelity of extruded
constructs. Such a characterization will be instrumental in developing a
versatile and modular biofabrication platform.
CONCLUSIONS
EXTRUSION PRESSURE
Interactions between hydrogel properties, extrusion pressure, and
Subsequently, the impact of extruding pressure on extrusion quality
printing speed affect the resolution of 3D-bioprinted structures. Current
was determined by extruding a series of lines (Fig. 2) at various
studies include extending these results to multiple layers and 3D
concentrations and pressures. Qualitative characterization of the
assessment of printing fidelity using micro-computed tomography.
extruded lines using an EVOS microscope (transmitted light, phase
contrast, 4x magnification) revealed the existence of optimal extruding
BIOMATERIAL COMPOSITION
AND ELASTIC MODULUS
A. Biomaterial Selection
Given its abundance, low cost and biocompatibility [8], gelatin
pressures for every GelMA concentration (Table 1). Indeed, for each
GelMA concentration, beading is observed at pressures below the
optimal range whereas irregular, excessive outpour is observed above
that range. Representative images are shown in Fig. 3.
Fig. 4. Line thickness at travel feed rates of 4, 8 and 12 mm/sec for various
concentrations of GelMA (10%, 15% and 20%). Data shown as mean ±SEM
(n=8 per group). Increase in travel feed rate from 4 mm/sec to 8 mm/sec and 12
mm/sec caused a significant decrease in line thickness at each GelMA
concentration (***p≤0.001, ANOVA with post-hoc Tukey analysis). Increase in
GelMA concentration from 10% to 15% and 20% also caused a significant
decrease in line thickness at each travel feed rate (***p≤0.001, ANOVA with
post-hoc Tukey analysis).
ACKNOWLEDGMENTS
The authors gratefully acknowledge the Cell Imaging Center at Drexel
University as well as technical assistance from Daniel Cabrera and
Ricardo Solorzano (BioBots, Philadelphia, PA).
methacrylate (GelMA) was synthesized using previously reported
methods [8, 9] and dissolved in PBS at concentrations of 10%, 15%
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Fig. 5. Representative images of line extrusions at 4 mm/sec (left), 8 mm/sec
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