The 3D bioprinting technology is a unique platform that can promote the development of pre-designed volumetric objects, with a spatially defined distribution of embedded cells, enzymes and biomolecules, for diverse applications. Organ transplantation and accurate tissue models are factors that drive the development of organ and tissue bioprinting. Because fully functional organs are so complex, it is essential to figure out which is the best combination of parameters that allow different types of bioprinting [1,2].
Choosing the right needle is very important for the accuracy of bioprinting. The geometry and length of the needle determine the shear stress and duration of the printing process, influencing the cell viability. Some studies have discussed this topic in recent years, and researchers are seeking to understand the relation to the applied pressure and printing needle geometry with the viability and physiology of different cells. Depending on the pressure and the needle’s diameter, cell viability can vary from as low as 40%, to near 90% [1,2].
Cell viability can be increased as the needle diameter also increases since a larger diameter requires less bioprinting pressure. Also, larger diameters provide greater speed in the printing process. Inversely, a smaller diameter requires more pressure and decreases the bioprinting speed but can promote a higher resolution at the end of the process. [3].
There are two main types of needles, cylindrical and tapered, and their geometries significantly impact their performance. Tapered needles have larger diameters at their entrance and a small diameter at their exit, resulting in a greater flow rate than cylindrical needles. Thus, tapered needles can facilitate dispensing highly viscous materials, for example. Controlling the flow rate is important as it affects the pore size and porosity of the bioprinted construct [4, 5].
The composition of a needle is also an influential factor in the printing process. It can be metal-based or plastic-based. Metallic needles are required in situations that need very high temperatures and present useful properties, such as high electrical and thermal conductivity [6].
Figure 1: Stainless steel blunt needles from TissueLabs.
In addition to the needle’s diameter, profile, and material, the length can also influence bioprinting and must be taken into account when choosing your needle. Needle length has a significant effect on the printing process’s total pressure; longer needles require more pressure applied so that the material can travel its entire length, consequently resulting in higher cell stress and lower cell viability [7].
REFERENCES
1. Gu, Z., Fu, J., Lin, H. & He, Y. Development of 3D bioprinting: From printing methods to biomedical applications. Asian J. Pharm. Sci. 15, 529–557 (2020).
2. Emmermacher, J. et al. Engineering considerations on extrusion-based bioprinting: interactions of material behavior, mechanical forces and cells in the printing needle. Biofabrication 12, 025022 (2020).
3. Chang, R., Nam, J. & Sun, W. Effects of Dispensing Pressure and Nozzle Diameter on Cell Survival from Solid Freeform Fabrication–Based Direct Cell Writing. Tissue Eng. Part A 14, 41–48 (2008).
4. Li, M., Tian, X., Schreyer, D. J. & Chen, X. Effect of needle geometry on flow rate and cell damage in the dispensing-based biofabrication process. Biotechnol. Prog. 27, 1777–1784 (2011).
5. Vozzi, G., Previti, A., De Rossi, D. & Ahluwalia, A. Microsyringe-based deposition of two-dimensional and three-dimensional polymer scaffolds with a well-defined geometry for application to tissue engineering. Tissue Eng. 8, 1089–1098 (2002).
6. Neumann, T. V. & Dickey, M. D. Liquid metal direct write and 3D printing: A review. Adv. Mater. Technol. 2000070 (2020).
7. Reid, J. A. et al. Accessible bioprinting: adaptation of a low-cost 3D-printer for precise cell placement and stem cell differentiation. Biofabrication 8, 025017 (2016).