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RESEARCH ARTICLE

Multi-material bioprinting using a helical mixer for fabricating fibers with controlled composition

Reza Gharraei1 ,  Donald J. Bergstrom2 ,  Xiongbiao Chen1,2*
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1 Division of Biomedical Engineering, College of Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
2 Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
IJB, 025140119 https://doi.org/10.36922/IJB025140119
Received: 2 April 2025 | Accepted: 1 July 2025 | Published online: 2 July 2025
(This article belongs to the Special Issue Bioprinting for Tissue Engineering and Modeling)
© 2025 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ )
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Abstract

Multi-material bioprinting is a promising technique for fabricating complex, heterogeneous constructs with tailored mechanical and biological properties for tissue engineering applications. Recently, the use of a helical static mixer in bioprinting has shown feasibility for producing fibers from multiple biomaterials. However, the underlying mechanisms of transient stream mixing and the control of composition gradients during the printing process remain insufficiently understood. This study investigates biomaterial mixing with the objective of improving the spatial resolution of composition gradients along the longitudinal axis of printed fibers. Computational fluid dynamics (CFD) simulations were utilized to investigate the flow and mixing behavior of precursor streams, and the insights obtained were used to redesign the bioprinting head for improved performance. Rheological studies were performed to characterize the flow behavior of the biomaterials. The results were used, in conjunction with CFD, to examine the mixing performance and to estimate the transition time—defined as the delay between flow rate changes at the inlets and the corresponding change in fiber composition. Our results demonstrate that the redesigned bioprinting head achieved complete mixing of biomaterials and that transition time can be effectively regulated or reduced by preemptively adjusting inlet flow rates. This advancement enhanced the spatial resolution of composition gradients by 17–30%, as confirmed through a case study presented in this article. Additionally, adjustments to the toolpath further improved gradient resolution. Overall, this study elucidates key principles underlying multi-material bioprinting and provides strategies for improving bioprinting head design to achieve finer spatial control of composition gradients.

Graphical abstract
Keywords
3D bioprinting
Computational fluid dynamics
Flow behavior
Multi-material bioprinting
Tissue engineering
Funding
This work was supported by the University of Saskatchewan Dean’s Scholarship and the Devolved Scholarship from the Department of Mechanical Engineering for the first author, and by the Natural Sciences and Engineering Research Council (NSERC) funds (Grant numbers: RGPIN 06396- 2019, RGPIN 04981-2022) for the co-authors.
Conflict of interest
Xiongbiao Chen serves as the Editorial Board Member of the journal, but did not in any way involve in the editorial and peer-review process conducted for this paper, directly or indirectly. Other authors declare they have no competing interests.
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International Journal of Bioprinting, Electronic ISSN: 2424-8002 Print ISSN: 2424-7723, Published by AccScience Publishing
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