Particle Detection in Free-Falling Nanoliter Droplets

Area of Science:

• Bioprinting and Tissue Engineering
• Microfluidics and Droplet Technology
• 3D In Vitro Model Development

Background:

• Accurate dispensing of multicellular spheroids (MCSs) is essential for creating functional 3D in vitro tissue models.
• Existing Drop-on-Demand (DoD) systems face challenges with spheroid adhesion to nozzles, impacting dispensing accuracy.
• Pre-dispensing detection methods are unreliable due to surface effects causing spheroid adherence.

Purpose of the Study:

• To develop and evaluate a post-ejection detection system for micrometer-sized particles within free-falling droplets.
• To improve the accuracy and reliability of particle counting in DoD bioprinting applications.
• To address limitations of current pre-dispensing detection methods in DoD systems.

Main Methods:

• Development of a system to detect particles in ~30 nanoliter droplets after ejection.
• Testing of different illumination modalities (glare point projection, diffuse white light) and detection algorithms.
• Evaluation of detection accuracy for synthetic particles and MCF-7 spheroids of varying sizes.

Main Results:

• Glare point projection achieved 95% accuracy for particles >75 μm and 70% for smaller particles.
• Diffuse white light illumination improved detection of small opaque particles, reaching up to 96% accuracy.
• The developed methods demonstrate suitability for enhancing quality control in DoD bioprinting.

Conclusions:

• Post-ejection detection of particles in droplets offers a robust alternative to pre-ejection methods.
• The presented illumination and detection strategies significantly improve particle detection accuracy in DoD systems.
• This technology is vital for advancing the precision and reliability of 3D bioprinting and in vitro model creation.