A guest post by Italian Institute of Technology (IIT) researchers Dr. Mike Geven, Dr. Roberto Donno, and Prof. Nicola Tirelli
Microfluidic-assisted processes for the reproducible and upscalable preparation of drug-loaded colloidal materials
By Dr. Mike Geven, Dr. Roberto Donno, and Prof. Nicola Tirelli on September 27th, 2019 in Flow chemistry, The Flow Chemistry Collection
Dr. Mike Geven (The Good), Prof. Nicola Tirelli (The Bad), and Dr. Roberto Donno (The Ugly) from the Group of Polymers and Biomaterials of the Italian Institute of Technology in Genoa, Italy.
The group of Polymers and Biomaterials at the Italian Institute of Technology focuses on applications in the field of drug delivery/nanomedicine and in regenerative medicine, with an expertise in polymer synthesis, nanomanufacturing, and colloidal characterization.
In our recent study published in ACS Applied Materials & Interfaces we tackle a central point in the use of the disulfides for the nanoparticles bioconjugation; that is, the efficiency and stability of the surface functionalization, focusing also on the nanomanufacturing and characterization.
We have employed an amphiphilic and biocompatible poly(ethylene glycol)-b-poly(ɛ-caprolactone) (PEG-PCL) bearing or not a 2-pyridyl group (PDS) terminal group, as the material and an operator-independent, microfluidic-based nanoprecipitation as the nanomanufacturing process.
Such microfluidic-assisted processes allow for the reproducible and upscalable preparation of a variety of drug-loaded colloidal materials (PEGylated emulsifiers, PEGylated lipids). The advantage of microfluidics is in the provision of a well-defined fluid-dynamic environment where a polymer solution mixes with a nonsolvent; because the speed of nanoprecipitation is a critical parameter, we have employed a chip based on enhanced laminar mixing as the Syrris Asia Micromixer Chip to accelerate it.
Using PEG-PCL, we have investigated the effect of the Flow Rate Ratio (organic/aqueous ratio in the final dispersion) over particle size and polydispersity index (PDI): the highest FRR corresponded to the lowest PDI at any value of the Total Flow Rate (TFR) tested. We have then recorded the effect of TFR showing that the nanoparticle size decreased with increasing flow rate. We have also paid specific attention to size characterization, thereby also demonstrating limitations of dynamic light scattering (DLS) as a stand-alone technique.
By using asymmetric flow field fractionation coupled with DLS, static light scattering (SLS), and refractive index detectors, we show that relatively small amount of >100 nm aggregates dominated the stand-alone results, whereas the “real” size distribution picked <50 nm. Our key result is that the kinetics of the conjugation based on PDS-thiol exchange was controlled by the pKa, and this also determined the rate of the exchange between the resulting disulfides and glutathione. In particular, more acidic thiols react faster with PDS, but their disulfides hardly exchange with the glutathione; the reverse applies to thiols with a higher pKa.
Finally, experiments of both thiol release and nanoparticles uptake in human colon cancer cell line show that also the disulfides formed from less-acidic and, therefore, less-reactive, and more exchangeable thiols were stable for at least a few hours even in the glutathione-rich environment. This suggests a sufficiently long stability of surface groups to achieve, for example, a cell targeting effect.
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About the authors
The guest authors all conduct their ground-breaking research at the Polymers and Biomaterials arm of the Italian Institute of Technology’s Central Research Labs (Genova).
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