Freeze-Dried Microfluidic Monodisperse Microbubbles as a New Generation of Ultrasound Contrast Agents.

We succeeded in freeze-drying monodisperse microbubbles without degrading their performance, that is, their monodispersity in size and echogenicity. We used microfluidic technology to generate cryoprotected highly monodisperse microbubbles (coefficient of variation [CV] <5%). By using a novel retrieval technique, we were able to freeze-dry the microbubbles and resuspend them without degradation, that is, keeping their size distribution narrow (CV <6%). Acoustic characterization performed in two geometries (a centimetric cell and a millichannel) revealed that the resuspended bubbles conserved the sharpness of the backscattered resonance peak, leading to CVs ranging between 5% and 10%, depending on the geometry. As currently observed with monodisperse bubbles, the peak amplitudes are one order of magnitude higher than those of commercial ultrasound contrast agents. Our work thus solves the question of storage and transportation of highly monodisperse bubbles. This work might open pathways toward novel clinical non-invasive measurements, such as local pressure, impossible to carry out with the existing commercial ultrasound contrast agents.

Ionic strength for tailoring the synthesis of monomodal stealth cationic liposomes in microfluidic devices.

In this work, we describe a hydrodynamic flow-focusing microfluidic process to produce stealth cationic liposomes (SCL), stabilized with poly(ethylene glycol) (PEG), with uniform and reproducible features. Through cryogenic transmission electron microscopy (cryo-TEM) characterization and real-time monitoring, we verified the formation of multi-sized lipid self-aggregates, which can be attributed to micelles formation. These structures tend to undergo deposition within the PDMS/glass microchannels through intermolecular interactions with the glass walls, hindering not only the process reproducibility but also the final biological application of the SCL products. In view of this, we propose the modulation of ionic strength of the side streams aiming to ionically shield the glass surface, decrease the intermolecular interactions of the lipid polar heads, and, essentially, to promote the bilayer-driven self-assembly of SCL with 1% of DSPE-PEG2000 lipid. Herein, we applied phosphate-buffered saline (PBS) from 10 to 50 mM concentration as side streams, and evaluated its effects on SCL final physicochemical properties in terms of size distribution, mean diameter, zeta potential and polydispersity index (PDI). We present evidences indicating that the ionic strength can be used as a microfluidic process parameter to modulate the lipids self-assembly kinetics whilst preventing micelles formation. Finally, the proposed diffusion-based microfluidic system with high ionic strength enables the formation of monodisperse (PDI < 0.2) SCL of around 140 nm with monomodal size distributions and enhanced properties when compared to usual bulk mixing.

Fibrin-Targeted Polymerized Shell Microbubbles as Potential Theranostic Agents for Surgical Adhesions.

The development of new therapies for surgical adhesions has proven to be difficult as there is no consistently effective way to assess treatment efficacy in clinical trials without performing a second surgery, which can result in additional adhesions. We have developed lipid microbubble formulations that use a short peptide sequence, CREKA, to target fibrin, the molecule that forms nascent adhesions. These targeted polymerized shell microbubbles (PSMs) are designed to allow ultrasound imaging of early adhesions for diagnostic purposes and for evaluating the success of potential treatments in clinical trials while acting as a possible treatment. In this study, we show that CREKA-targeted microbubbles preferentially bind fibrin over fibrinogen and are stable for long periods of time (∼48 h), that these bound microbubbles can be visualized by ultrasound, and that neither these lipid-based bubbles nor their diagnostic-ultrasound-induced vibrations damage mesothelial cells in vitro. Moreover, these bubbles show the potential to identify adhesionlike fibrin formations and may hold promise in blocking or breaking up fibrin formations in vivo.

Effects of diffusion and mixing pattern on microfluidic-assisted synthesis of chitosan/ATP nanoparticles.

Chitosan (CHI) nanoparticles present promising applications in pharmaceutical and biomedical fields, including drug and gene delivery. Among different approaches, microfluidics emerges as a resourceful tool for nanoparticle production in low-cost, reproducible processes with predictable fluid dynamics. However, microfluidic-assisted synthesis of CHI nanoparticles has not been widely explored in the literature. In this context, we systematically investigated different process parameters that influence the synthesis of CHI/ATP nanoparticles. We highlight the effects and limitations of diffusion and distinct mixing patterns developed through the microchannels on the final physicochemical characteristics of CHI/ATP nanoparticles produced. To address these hurdles, here we describe a simple, feasible, and reproducible method for the production of CHI/ATP nanoparticles. This strategy enables the development of a continuous and homogeneous production process for CHI nanoparticles to be applied in the most varied fields of research.

Microfluidic tools toward industrial biotechnology.

Microfluidics is a technology that operates with small amounts of fluids and makes possible the investigation of cells, enzymes, and biomolecules and encapsulation of biocatalysts in a greater variety of conditions than permitted using conventional methods. This review discusses technological possibilities that can be applied in the field of industrial biotechnology, presenting the principal definitions and fundamental aspects of microfluidic parameters to better understand advanced approaches. Specifically, concentration gradient generators, droplet-based microfluidics, and microbioreactors are explored as useful tools that can contribute to industrial biotechnology. These tools present potential applications, inclusive as commercial platforms to optimizing in bioprocesses development as screening cells, encapsulating biocatalysts, and determining critical kinetic parameters. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1372-1389, 2016.