(36c) Design of Modular 3D-Printed Milli-Fluidic Mixers to Enable Sequential Nanoprecipitation (SNaP) for the Tunable Synthesis of Nano- and Micro- Particles

Sequential NanoPrecipitation (SNaP) is an emerging synthesis process for the controlled and robust formation of nanoparticles for drug delivery and bioimaging. SNaP relies on the same rapid mixing and controlled self-assembly principles as traditional one-step Flash NanoPrecipitation (FNP)^1-3. However, it involves a two-step assembly process by decoupling the core formation and stabilization⁴. This provides a novel strategy to better control the final nanoparticle structure.

Given the novelty of this synthesis process, the understanding of the nanoparticle formation mechanism remains incomplete, and the impact of the synthesis parameters on the synthesis outcome is yet to be investigated. In particular, the impact of the delay time separating the core formation and the stabilization is lacking. This is due to technical challenges stemming from a lack of versatility in the available SNaP experimental setups. Indeed, current SNaP experimental mixing set-ups rely on the use of two commercially available mixers connected via tubing in a series arrangement¹. This setup suffers from several drawbacks including significant dead volumes, lack of modularity, and limited mixing geometries. Our goal is to present an approach for rapidly prototyping the SNaP mixers to address the issues currently observed with existing setups. These mixers will be used to study the impact of the synthesis parameters on the synthesis outcome. Specifically, we will investigate the impact of the delay time on the nanoparticle's size.

Method:

In this work, we first presented a 3D-printed mixing platform, that relies on the same rapid mixing principle as the currently used rapid mixers, while offering greater modularity and better control over the synthesis parameter. We later used this platform for the synthesis of drug and fluorophore-loaded polymeric particles. We additionally used this platform to study the impact of the synthesis parameters on the synthesis outcome.

We used Dynamic Light Scattering (DLS) for size measurments, High Performance Liquid Chromatography (HPLC) for measuring the drug loading, and ThermoGravimetric Analyzer (TGA) for determining the total particle solids concentration.

Results:

With our 3D approach for the fabrication of the SNaP mixers, we rapidly prototyped several mixers with diverse designs. We first designed two mixing configurations that differ in the number of the inlets of the first mixer stage. We then changed the distance that separates the first mixing stage and the second mixing stage. Such change resulted in a change in the delay time between the core formation and the stabilizer addition. We later demonstrated that this setup enabled us to synthesize drug-loaded nanoparticles through SNaP with high encapsulation efficiency. We then showed that by changing the mixer configuration we were able to access the micron size range, previously inaccessible with SNaP and traditional FNP. We were able to form drug-loaded microparticles with a size of up to 1.2 µm. Additionally, we investigated the impact of the delay time on the synthesis outcome, and we evidenced that this parameter is crucial for controlling nanoparticle size. We observed that by changing the delay time from 5.8 ms to 10.5 the size of the formed nanoparticle increased from 198 nm to 233 nm. This allowed us to expand the size range of the polymeric particles formed through rapid nanoprecipitation.

Conclusion:

This approach presents a strategy to tune the nanoparticle’s size while keeping the composition constant. This was achieved with the use of our 3D-printed SNaP mixers that provided control over the various synthesis parameters, and most importantly allowed us to tune the delay time with precise control. This also presents a strategy to have a better understanding of the particle formation mechanism, which can present a strategy to enhance drug loading efficiency, and stability and to tackle certain challenges with current methods used to produce drug-loaded nanoparticles.

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