Excessive Shear Rate, Not Shear Stress, Influences Cell Mechanical Damage in Small-Bore Needle Injections.

Area of Science:

• Biotechnology
• Biomedical Engineering
• Cell Biology

Background:

• Cell therapies and 3D bioprinting necessitate cell suspension delivery through small-gauge needles.
• Cell damage during needle injection impacts short- and long-term viability.
• Previous assumptions attributed cell damage to viscous stresses, but experimental data suggests otherwise.

Purpose of the Study:

• To identify the critical fluid flow parameter responsible for mechanical damage to cells during needle injection.
• To challenge the prevailing hypothesis linking cell damage solely to viscous stress.

Main Methods:

• Analysis of existing published data on cell injection.
• Conducting cell injection experiments using human umbilical vein endothelial cells.
• Suspending cells in Newtonian fluids of varying viscosities and injecting through 30-gauge needles under controlled shear stress and shear rate conditions.

Main Results:

• Cell viability demonstrated a stronger correlation with shear rate (a kinematic property) compared to shear stress.
• Experimental evidence contradicts the hypothesis that higher viscosity fluids inherently protect cells at the same flow rate.

Conclusions:

• Shear rate is identified as the primary fluid mechanical parameter influencing cell damage during injection.
• This finding provides a scientific basis for optimizing injection protocols and suspension fluid properties to enhance cell viability in bioprinting and cell therapies.