| Summary: | Hydrogels have been used as scaffolds and structural supports for cell growth. However, injecting these hydrogels requires substantial forces which also lead to high shear in the cell and ultimately cell death. Current methods to mitigate this problem suffer from limited applicability, poor durability, lack of stability and no significant enhancement in injectability. Here, we propose a viscoplastic lubricated gel co-flow, where the flow of the cell-laden payload through needles is facilitated by coaxial lubrication from a lower yield stress gel, to mitigate shear death, enhance injectability and enable stable flow. In this study, we optimize fluidic and flow parameters to minimize drag and shear on the payload gel. We establish regime maps of stable coaxial lubrication using both simulations and experiments. The velocity profile inside the needle is plotted using PTV to visualize the shear-free transport of the inner payload. Experimentally, we were able to achieve a 4x reduction in injection force and 5x increase in plug region (zero-shear region). Finally, we propose a theoretical model to explain the simulations and experimental results.
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