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International Journal of Bioprinting Nozzle geometry for enhanced cell viability

technology with cell biology and biomaterial science. function. 13,14 These mechanical forces can disrupt cell
This technology has revolutionized regenerative medicine membranes, causing damage that adversely affects cell
by enabling the fabrication of complex, patient-specific viability and, consequently, the functionality of the printed
tissues and organoids through the precise deposition of structures. Indeed, these stresses ultimately reduce cell
living cells, bioactive molecules, and extracellular matrix viability to as low as 45%, depending on bioink viscosity,
components. The bioprinting technique is driven by cell concentration, and nozzle diameter. During the
2,3
the critical need to address significant challenges in printing process, shear stress primarily affects cells at the
regenerative medicine, particularly organ transplantation narrow tip of the needle. In contrast, extensional stress
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and tissue engineering. Therefore, this approach not only occurs as cells pass through the constriction in the nozzle,
offers a potential alternative to alleviate the organ shortage where the channel narrows from the larger diameter of the
crisis but also advances fields such as personalized syringe to the smaller diameter of the needle. 16
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medicine, in vitro disease modeling, and high-throughput Recent studies suggest that the extensional stress
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drug screening, offering sophisticated models that can experienced by cells during the bioprinting process plays
better mimic human tissue architecture and function a significant role in cell membrane rupture, affecting
compared to conventional 2D cultures. 7
their post-printing viability. 17,18 It is well-established
Cell manipulation and deposition are fundamental that extensional flow is more effective than simple shear
to tissue engineering, prompting the development of flow in deforming and disrupting droplets, bubbles, or
various advanced methodologies to overcome associated vesicles. Compared to shear stress, extensional stress is
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challenges. Human tissues exhibit a wide range of more likely to cause severe cell damage. 20,21 Despite this,
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cellular densities, reflecting their diverse structures and most existing models of cell damage during bioprinting
functions. For example, native human tissues typically primarily focus on shear stress and do not adequately
have a cell density of 1–3 billion cells per milliliter. This address the effects of extensional stress. To fill this gap,
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high cell density is essential for maintaining the complex Ning et al. explored how both shear and extensional
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architecture and functionality of various tissues. 9 stresses generated during extrusion-based bioprinting
Several bioprinting techniques have been developed contribute to cell damage. However, the role of nozzle
to process high-density cell-based bioinks. These design in influencing cell damage remains unexamined.
include inkjet-based, laser-assisted, and extrusion- Nozzle geometry, particularly contraction angle and
based bioprinting. Inkjet-based bioprinting, which relies final diameter, has the potential to modulate the relative
on precise droplet deposition, is advantageous for its contribution of shear and extensional stresses, thereby
high resolution and ability to print multiple cell types impacting cell viability.
simultaneously. However, it is limited by low cell density This study hypothesizes that optimized nozzle design,
and potential nozzle clogging. Meanwhile, laser-assisted specifically focusing on the contraction angle and final
bioprinting offers superior resolution and cell viability diameter, significantly enhances cell viability by reducing
by using laser pulses to transfer bioink onto a substrate; extensional stress during bioprinting. This work aims to
however, it requires complex setups and expensive investigate the feasibility of producing in-house nozzles
materials. Among these, extrusion-based bioprinting that improve cell viability during the extrusion-based
remains the most scalable and adaptable method for bioprinting process. Starting from the identification of
fabricating large-scale tissue constructs with high cell a gap in bioprinting, represented by the lack of specific
density and structural integrity. 10 nozzles for different processes, tests were conducted to
Extrusion-based bioprinting operates by dispensing demonstrate the feasibility of performing a bioprinting
bioink—typically composed of living cells embedded in process with custom-designed nozzles. Through a
hydrogels—through a nozzle under applied pressure to combination of simple analytical relationships and a
create 3D constructs. Common biomaterials used in computational cell damage model, a practical tool for
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this method include hydrogel-based inks, such as gelatin optimizing nozzle design to minimize cell damage during
methacryloyl (GelMA), which is widely used due to its the bioprinting process was proposed.
biocompatibility, tunable physicochemical properties, 2. Materials and methods
and ability to form stable hydrogels upon photo-cross-
linking. However, this technique requires highly viscous 2.1. Nozzle design and manufacturing
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bioinks, which expose cells to significant mechanical The 3D-printed nozzles for the bioprinter were produced
stresses, particularly shear stress and extensional stress, using a stereolithography 3D printer (Anycubic Photon
that critically impact cell viability and post-printing Mono X 6Ks, Anycubic, China) based on a digitally

Volume 11 Issue 4 (2025) 316 doi: 10.36922/IJB025190182