Fig. 11. A comparison of hydrogel printability. A: Post printing
spreading ratio’s (filament diameter/needle diameter) determined for
various flow rates using 6% (w/v) alginate. B: Post printing
photographs of printed constructs for each flow rate (i) 100%, (ii)
125%, (iii) 150% and (iv) 200%. Data points are means; error bars
represent SEM for n = 3. Asterix represents statistical significance (p
= 0.0363; p < 0.05), no Asterisk shows no statistical
significance (p > 0.05). Scale bars represent 5 mm.
Figure 11 shows a positive correlation between flow percentage and
spreading ratios obtained. The spreading ratios obtained for 100 % and
200 % flow percentage groups showed a statistically significant
difference; p = 0.0363; p < 0.05, whereas no other statistical
significance was found between groups. Similarly, Kahl et al.(2019) shows the higher the extrusion rate, at a constant nozzle
diameter, results in lower shape fidelity of the printed construct.
Images in Fig. 11 show the inconsistency in filament structure produced
when printing at a 100 % flow percentage, even though a low spreading
ratio was noted. Due to the complex nature of bioprinting and the
necessity to print complex geometries at extremely high resolutions, the
final printed construct must be highly precise and accurate. A high
spreading ratio is, therefore, an undesirable characteristic and further
optimizing must take place in order to accommodate for this [24].
Conclusions
The overall aim to create a low-cost bioprinter from a commercially
available thermoplastic 3D delta printer was achieved. The final
bioprinter designed and manufactured consists of an already established
syringe-based extruder, incorporated with minor alterations to fit the
delta style 3D printer, and an easily built commercially available Delta
printer with added enclosure and easily modifiable firmware. Converting
the thermoplastic Delta 3d printer into a bioprinter cost a total of $
1,007.52, making it affordable to most research laboratories. This
system allows for the printing of geometrically complex structures using
cell-free hydrogel based bioinks and can be easily modified (i.e.,
firmware parameters) for other paste extrusion materials and future
cell-laden hydrogel bioprinting. There is, however, much room for
improvement where this study only aims to provide the much needed and
promising foundation work for what could be a fully functional low-cost
bioprinter with multiple applications. The modifications made to the
hardware during the conversion from 3D printer to bioprinter were
successful and allowed for an increased sterile environment for the
sensitive nature of bioprinting, as set out as a priority criterion. To
further increase sterility, one improvement would include the addition
of HEPA-filtered laminar air flow to the system. Smaller
sterility-related improvements may include the addition of UV lights to
the system and re-designing of the internal hardware components (i.e.,
extruder carriage) into fully enclosed and easily cleaned singular
components.
Securing the extruder carriage to the frame of the printer had the
desired effect of removing the excessive weight from the effector plate
which then allowed for smoother printing movements and higher printed
construct quality. Another important design criterion stipulated was
that of producing highly complex shapes with precise geometry. This
criterion was partially met but remains an area that requires much
improvement. Lowering the extruder carriage closer to the nozzle would
aid in reducing the distance between the syringe feedstock and the
nozzle which in turn allows for more control over the extrusion of the
bioinks. More control over the extrusion means less possibility of under
or overextrusion; gaps forming within the construct versus leakage of
bioink during travel moves, respectively.
Overall, the results achieved with the final bioprinter prototype model
were satisfactory and provide the much-needed foundation work for future
optimization studies. Incorporating the use of cell-laden bioinks and
assessing the different modes of cell-based bioprinting will be employed
in future work, along with the assessment of various bioink formulations
and cross-linking methods. While Delta style bioprinters are
commercially available (Pensees Vitarix and VitarixW) the systems are
registered design closed-source premium systems. The leading goal of the
SV1 was toward the development of an open-source system.. Relative to
commercial systems the substantial cost reduction presented may prove to
be impactful to research laboratories in lower resourced economies as
well as in developed countries.
Acknowledgements
The authors acknowledge the South African Medical Research Council for a
Self-Initiated Research grant, National Research Foundation of South
Africa (NRF) for a Competitive Support for Unrated Researchers (UID:
129400) and Rhodes University for research and student funding.
Conflict of interest
Authors have no conflict of interest relevant to this article.
Human and animal rights
Not applicable.