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.