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Penetrating microjets in soft substrates: towards controlled needle-free injections

Periodic Reporting for period 2 - BuBble Gun (Penetrating microjets in soft substrates: towards controlled needle-free injections)

Reporting period: 2021-07-01 to 2022-12-31

The needle-free delivery of liquid jets into soft and heterogeneous substrates, e.g. human tissue, is hindered by the need to reach specific penetration depths with energy efficient means, the break-up of jets that impedes control over liquid splash-back after impacting the substrate that cause cross-contamination between injections, and the dose delivery. These issues are faced by many applications, particularly the delivery of drugs or cosmetic products.

We are generating new knowledge in the fields of microfluidics, physics, and bioengineering. These, combined, will open new ways to improve injection phenomena, e.g. in the delivery of drugs, dermatologic applications and other industries. We aim at developing a portable energy-efficient injection platform that could help quantifying injections with experimental resolutions below the microsecond and micrometer scales. As an added result, we will probe the rheological properties of jets made of biocompatible additives.

This project is concerned with studying the energy partition between the creation of bubbles, the formation of liquid jets, and the penetration of these jets into soft substrates. We are achieving new ways to control cavitation within microfluidic confinement, tune the rheology of jets emerging from confined cavitation. As a result, we are unveiling the relationships between fluid dynamics and material properties governing jet injection into soft substrates.
The three work packages (WP) are led by motivated and independent researchers with complimentary experiences and skills. In WP1 we have characterized different laser (light sources) equipment to understand the differences of using additives for improved energy absorption that lead to bubble formation (cavitation, boiling). In WP2 the focus is on understanding how to predict the break-up or fragmentation of fast traveling liquid jets generated by the bubble growing inside the microfluidic channels studied in WP1. Finally, WP3 has covered the impact and penetration of the liquid jets onto different materials with increased complexity level: droplets of liquids with known physicochemical properties, gelatins (translucent and fair reproducibility of preparation), ex vivo skin samples (animal and human). All combined, the team has published a review paper and a series of original articles and a book in different scientific platforms. We have also applied for Intellectual Property protection (patent) on one idea, and currently prepare a second application.
As evidenced in our review paper and the original articles (some under review), we are opening a new area at the intersection of engineering, physics, chemistry, and biomedical applications. The ultrafast generation of droplets with accurate control is a feat. With the modeling and characterization experiments we are carrying out and planned for the remaining period, we can convincingly say that we will advance the state-of-the-art in microfluidics generation of fast liquid jets for needle-free injections.