Stabilized Production of Lipid Nanoparticles of Tunable Size in Taylor Flow Glass Devices with High-Surface-Quality 3D Microchannels

PhagoScreener: A novel phagogram platform based on a capillary-wave microbioreactor

Due to the overuse of antibiotics, the number of multidrug-resistant pathogen bacteria is rising in recent years posing a serious threat to human health. One promising alternative for treatment is the application of phage therapy using highly selective bacteriophages. Because of their selectivity, individual screens called phagograms for each patient are required to select phages from a phage library. Phagograms are mostly performed via bacterial cultivation on double layer agar plates and phage addition causing bacterial lysis. However, these assays are work-intensive and have a low ability for parallelization and automation. Hence, highly parallelizable and automatable microbioreactors in the lowest microliter scale could offer an economic solution increasing the throughput of phagograms. This paper demonstrates the applicability of a novel capillary-wave microbioreactor (cwMBR) to perform phagograms. Due to its small volume of only 7 µL and the open-droplet design, it can be easily automated and parallelized in future. Furthermore, the ability of online biomass measurement makes the cwMBR a perfect phagogram platform in the future. Herein, phagograms with E. coli and different concentrations of the phages MM02 and EASG3 were performed as proof of concept for phagograms in the cwMBR. Thereby, the cwMBR was able to measure differences in lysis kinetics of different phages. Furthermore, the phagograms were compared to those in conventional microtiter plate readers revealing the cwMBR as ideal alternative for phagograms as it combines favorable mixing conditions and a phage repellent hydrophilic glass surface with online biomass measurement in an open-droplet design for future parallelization and automation.

Diffusive micromixing combined with dynamic in situ laser scattering allows shedding light on lipid nanoparticle precipitation

Pharmaceutical formulations are increasingly based on drug nanoparticles or carrier nanoparticles encapsulating drugs or mRNA molecules. Sizes and monodispersity of the nanoparticles regulate bioavailability, pharmacokinetics and pharmacology. Microfluidic mixers promise unique conditions for their continuous preparation. A novel microfluidic antisolvent precipitation device was realized by two-photon-polymerization with a mixing channel in which the organic phase formed a sheet with a homogeneous thickness of down to 7 μm completely wrapped in the aqueous phase. Homogeneous diffusion through the sheet accelerates mixing. Optical access was implemented to allow in-situ dynamic light scattering. By centering the thin sheet in the microchannel cross-section, two important requirements are met. On the one hand, the organic phase never reaches the channel walls, avoiding fouling and unstable flow conditions. On the other hand, in the sheet positioned at the maximum of the parabolic flow profile the nanoparticle velocities are homogenized which enables flow-compensated Dynamic Light Scattering (flowDLS). These unique features allowed in-situ particle size determination for the first time. Monitoring of lipid nanoparticle precipitation was demonstrated for different rates of solvent and antisolvent flows. This breakthrough innovation will not only enable feedback control of nanoparticle production but also will provide new insights into the dynamics of nanoparticle precipitation.

2PP-Hydrogel Covered Electrodes to Compensate for Media Effects in the Determination of Biomass in a Capillary Wave Micro Bioreactor

Microbioreactors increase information output in biopharmaceutical screening applications because they can be operated in parallel without consuming large quantities of the pharmaceutical formulations being tested. A capillary wave microbioreactor (cwMBR) has recently been reported, allowing cost-efficient parallelization in an array that can be activated for mixing as a whole. Although impedance spectroscopy can directly distinguish between dead and viable cells, the monitoring of cells in suspension within bioreactors is challenging because the signal is influenced by the potentially varying properties of the culture medium. In order to address this challenge, an impedance sensor consisting of two sets of microelectrodes in a cwMBR is presented. Only one set of electrodes was covered by a two-photon cross-linked hydrogel to become insensitive to the influence of cells while remaining sensitive to the culture medium. With this impedance sensor, the biomass of Saccharomyces cerevisiae could be measured in a range from 1 to 20 g L-1. In addition, the sensor can compensate for a change in the conductivity of the suspension of 5 to 15 mS cm-1. Moreover, the two-photon cross-linking of hydroxyethyl starch methacrylate hydrogel, which has been studied in detail, recommends itself for even much broader sensing applications in miniaturized bioreactors and biosensors.

Toward the Scalable, Rapid, Reproducible, and Cost-Effective Synthesis of Personalized Nanomedicines at the Point of Care

Organic nanoparticles are used in nanomedicine, including for cancer treatment and some types of COVID-19 vaccines. Here, we demonstrate the scalable, rapid, reproducible, and cost-effective synthesis of three model organic nanoparticle formulations relevant to nanomedicine applications. We employed a custom-made, low-cost fluid mixer device constructed from a commercially available three-dimensional printer. We investigated how systematically changing aqueous and organic volumetric flow rate ratios determined liposome, polymer nanoparticle, and solid lipid nanoparticle sizes, size distributions, and payload encapsulation efficiencies. By manipulating inlet volumes, we synthesized organic nanoparticles with encapsulation efficiencies approaching 100% for RNA-based payloads. The synthesized organic nanoparticles were safe and effective at the cell culture level, as demonstrated by various assays. Such cost-effective synthesis approaches could potentially increase the accessibility to clinically relevant organic nanoparticle formulations for personalized nanomedicine applications at the point of care, especially in nonhospital and low-resource settings.

A review on microfluidic-assisted nanoparticle synthesis, and their applications using multiscale simulation methods

Recent years have witnessed an increased interest in the development of nanoparticles (NPs) owing to their potential use in a wide variety of biomedical applications, including drug delivery, imaging agents, gene therapy, and vaccines, where recently, lipid nanoparticle mRNA-based vaccines were developed to prevent SARS-CoV-2 causing COVID-19. NPs typically fall into two broad categories: organic and inorganic. Organic NPs mainly include lipid-based and polymer-based nanoparticles, such as liposomes, solid lipid nanoparticles, polymersomes, dendrimers, and polymer micelles. Gold and silver NPs, iron oxide NPs, quantum dots, and carbon and silica-based nanomaterials make up the bulk of the inorganic NPs. These NPs are prepared using a variety of top-down and bottom-up approaches. Microfluidics provide an attractive synthesis alternative and is advantageous compared to the conventional bulk methods. The microfluidic mixing-based production methods offer better control in achieving the desired size, morphology, shape, size distribution, and surface properties of the synthesized NPs. The technology also exhibits excellent process repeatability, fast handling, less sample usage, and yields greater encapsulation efficiencies. In this article, we provide a comprehensive review of the microfluidic-based passive and active mixing techniques for NP synthesis, and their latest developments. Additionally, a summary of microfluidic devices used for NP production is presented. Nonetheless, despite significant advancements in the experimental procedures, complete details of a nanoparticle-based system cannot be deduced from the experiments alone, and thus, multiscale computer simulations are utilized to perform systematic investigations. The work also details the most common multiscale simulation methods and their advancements in unveiling critical mechanisms involved in nanoparticle synthesis and the interaction of nanoparticles with other entities, especially in biomedical and therapeutic systems. Finally, an analysis is provided on the challenges in microfluidics related to nanoparticle synthesis and applications, and the future perspectives, such as large-scale NP synthesis, and hybrid formulations and devices.

A Digital Twin of the Coaxial Lamination Mixer for the Systematic Study of Mixing Performance and the Prediction of Precipitated Nanoparticle Properties

The synthesis of nanoparticles in microchannels promises the advantages of small size, uniform shape and narrow size distribution. However, only with insights into the mixing processes can the most suitable designs and operating conditions be systematically determined. Coaxial lamination mixers (CLM) built by 2-photon polymerization can operate long-term stable nanoparticle precipitation without fouling issues. Contact of the organic phase with the microchannel walls is prevented while mixing with the aqueous phase is intensified. A coaxial nozzle allows 3D hydrodynamic focusing followed by a sequence of stretch-and-fold units. By means of a digital twin based on computational fluid dynamics (CFD) and numerical evaluation of mixing progression, the influences of operation conditions are now studied in detail. As a measure for homogenization, the mixing index (MI) was extracted as a function of microchannel position for different operating parameters such as the total flow rate and the share of solvent flow. As an exemplary result, behind a third stretch-and-fold unit, practically perfect mixing (MI>0.9) is predicted at total flow rates between 50 µL/min and 400 µL/min and up to 20% solvent flow share. Based on MI values, the mixing time, which is decisive for the size and dispersity of the nanoparticles, can be determined. Under the conditions considered, it ranges from 5 ms to 54 ms. A good correlation between the predicted mixing time and nanoparticle properties, as experimentally observed in earlier work, could be confirmed. The digital twin combining CFD with the MI methodology can in the future be used to adjust the design of a CLM or other micromixers to the desired total flow rates and flow rate ratios and to provide valuable predictions for the mixing time and even the properties of nanoparticles produced by microfluidic antisolvent precipitation.

Review on the Scale-Up Methods for the Preparation of Solid Lipid Nanoparticles

Solid lipid nanoparticles (SLNs) are an alternate carrier system to liposomes, polymeric nanoparticles, and inorganic carriers. SLNs have attracted increasing attention in recent years for delivering drugs, nucleic acids, proteins, peptides, nutraceuticals, and cosmetics. These nanocarriers have attracted industrial attention due to their ease of preparation, physicochemical stability, and scalability. These characteristics make SLNs attractive for manufacture on a large scale. Currently, several products with SLNs are in clinical trials, and there is a high possibility that SLN carriers will quickly increase their presence in the market. A large-scale manufacturing unit is required for commercial applications to prepare enough formulations for clinical studies. Furthermore, continuous processing is becoming more popular in the pharmaceutical sector to reduce product batch-to-batch differences. This review paper discusses some conventional methods and the rationale for large-scale production. It further covers recent progress in scale-up methods for the synthesis of SLNs, including high-pressure homogenization (HPH), hot melt extrusion coupled with HPH, microchannels, nanoprecipitation using static mixers, and microemulsion-based methods. These scale-up technologies enable the possibility of commercialization of SLNs. Furthermore, ongoing studies indicate that these technologies will eventually reach the pharmaceutical market.

Horseshoe lamination mixer (HLM) sets new standards in the production of monodisperse lipid nanoparticles

Microfluidic mixers promise unique conditions for the controlled and continuous preparation of nanoparticles by antisolvent precipitation. Nanoparticles may enable encapsulation of drug or mRNA molecules in the form of carrier nanoparticles or can provide higher bioavailability in the form of drug nanoparticles. The ultimate goal in microfluidic approaches is the production of nanoparticles with narrow size distributions while avoiding contaminations and achieving sufficiently high throughput. To achieve this, a novel microfluidic precipitation device was developed and realized by two-photon polymerization: mixing elements were designed in such a way that the liquids undergo a repeated Smale horseshoe transformation resulting in an increased interfacial area and mixing times of less than 10 ms. These elements and an additional 3D flow focusing ensure that no organic phase is exposed to the channel walls. The integration of a fluidic shield layer in the flow focusing proved to be useful to delay the precipitation process until reaching a sufficient distance to the injection nozzle. Lipid nanoparticle preparation with different concentrations of castor oil or the hard fat Softisan® 100 were performed at different flow rates and mixing ratios with and without a shield layer. Flow rates of up to 800 μl min^-1 and organic phase mixing ratios of up to 20% resulted in particle sizes ranging from 42 nm to 166 nm with polydispersity indices from 0.04 to 0.11, indicating very narrowly distributed, and in most cases even monodisperse, nanoparticles. The occurrence of fouling can be completely suppressed with this new type of mixing elements, as long as Dean vortices are prevented. Moreover, this parameter range in the horseshoe lamination mixer provided a stable and continuous process, which enables a scalable production.

Tissue Barrier-on-Chip: A Technology for Reproducible Practice in Drug Testing

One key application of organ-on-chip systems is the examination of drug transport and absorption through native cell barriers such the blood–brain barrier. To overcome previous hurdles related to the transferability of existing static cell cultivation protocols and polydimethylsiloxane (PDMS) as the construction material, a chip platform with key innovations for practical use in drug-permeation testing is presented. First, the design allows for the transfer of barrier-forming tissue into the microfluidic system after cells have been seeded on porous polymer or Si3N4 membranes. From this, we can follow highly reproducible models and cultivation protocols established for static drug testing, from coating the membrane to seeding the cells and cell analysis. Second, the perfusion system is a microscopable glass chip with two fluid compartments with transparent embedded electrodes separated by the membrane. The reversible closure in a clamping adapter requires only a very thin PDMS sealing with negligible liquid contact, thereby eliminating well-known disadvantages of PDMS, such as its limited usability in the quantitative measurements of hydrophobic drug molecule concentrations. Equipped with tissue transfer capabilities, perfusion chamber inertness and air bubble trapping, and supplemented with automated fluid control, the presented system is a promising platform for studying established in vitro models of tissue barriers under reproducible microfluidic perfusion conditions.

Merits and advances of microfluidics in the pharmaceutical field: design technologies and future prospects

Microfluidics is used to manipulate fluid flow in micro-channels to fabricate drug delivery vesicles in a uniform tunable size. Thanks to their designs, microfluidic technology provides an alternative and versatile platform over traditional formulation methods of nanoparticles. Understanding the factors that affect the formulation of nanoparticles can guide the proper selection of microfluidic design and the operating parameters aiming at producing nanoparticles with reproducible properties. This review introduces the microfluidic systems' continuous flow (single-phase) and segmented flow (multiphase) and their different mixing parameters and mechanisms. Furthermore, microfluidic approaches for efficient production of nanoparticles as surface modification, anti-fouling, and post-microfluidic treatment are summarized. The review sheds light on the used microfluidic systems and operation parameters applied to prepare and fine-tune nanoparticles like lipid, poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles as well as cross-linked nanoparticles. The approaches for scale-up production using microfluidics for clinical or industrial use are also highlighted. Furthermore, the use of microfluidics in preparing novel micro/nanofluidic drug delivery systems is presented. In conclusion, the characteristic vital features of microfluidics offer the ability to develop precise and efficient drug delivery nanoparticles.

Microbes, Clinical trials, Drug Discovery, and Vaccine Development: The Current Perspectives

Because of the frequent emergence of novel microbial species and the re-emergence of genetic variants of hitherto known microbes, the global healthcare system, and human health has been thrown into jeopardy. Also, certain microbes that possess the ability to develop multi-drug resistance (MDR) have limited the treatment options in cases of serious infections, and increased hospital and treatment costs, and associated morbidity and mortality. The recent discovery of the novel Coronavirus (n-CoV), the Severe Acute Respiratory Syndrome CoV-2 (SARS-CoV-2) that is causing the CoV Disease-19 (COVID-19) has resulted in severe morbidity and mortality throughout the world affecting normal human lives. The major concern with the current pandemic is the non-availability of specific drugs and an incomplete understanding of the pathobiology of the virus. It is therefore important for pharmaceutical establishments to envisage the discovery of therapeutic interventions and potential vaccines against the novel and MDR microbes. Therefore, this review is attempted to update and explore the current perspectives in microbes, clinical research, drug discovery, and vaccine development to effectively combat the emerging novel and re-emerging genetic variants of microbes.

Goodbye fouling: a unique coaxial lamination mixer (CLM) enabled by two-photon polymerization for the stable production of monodisperse drug carrier nanoparticles

Poorly soluble drugs can be incorporated in lipid carrier nanoparticles to achieve sufficient bioavailability and open up diverse routes of administration. Preparation by antisolvent precipitation in microfluidic systems enables excellent control of lipid nanoparticle size. However, particle-containing flows bear the risk of material deposition on microchannel surfaces, limiting reproducibility, prolonged continuous processing and scale-up by parallelization as required for practical use. The coaxial lamination mixer (CLM) introduced in this study can fully eliminate contact of the organic phase with the channel walls while efficiently mixing organic and aqueous phases. This unique micromixer, including a nozzle for coaxial injection, a sequence of stretch-and-fold elements and inlet filters, cannot be realized by conventional 2.5D microfabrication but only by 3D two-photon polymerization. Hydrodynamic focusing of the organic phase and fast coaxial lamination were studied in simulations and flow visualization experiments. Different concentrations of castor oil or a hard fat and polysorbate 80 dissolved in ethanol were injected and combined with purified water. Total flow rates of 100 and 200 μL min-1 and flow rate ratios of 15% or less resulted in particle sizes between 67 and 153 nm and polydispersity indices of 0.04 to 0.10. Extended preparation time revealed stable particle sizes and displayed no fouling, indicating that CLMs will even allow high throughput parallelization. Stable castor oil nanoemulsions loaded with the poorly soluble drugs fenofibrate or cannabidiol were prepared. In conclusion, the unique 3D design of the CLM enables prolonged, stable and scalable production of small as well as very narrowly distributed, in most cases even monodisperse drug-loaded lipid nanoparticles.

Microextraction of lanthanum using a rotating microchannel extractor

This work introduced a novel microchannel extractor. The extraction system was to extract lanthanum nitrate aqueous solution with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA). Different feeding methods and inner rotors were explored first. The results showed that parallel feeding and inner rotors engraved with spiral stripes were more favorable for extraction. Next, the effect of various factors on the extraction was explored, including the pH of the aqueous phase, rotational inner rotor speed (R) and the fluid volumetric flow rate (Q). The results showed that these factors are closely related to the extraction. Finally, the experiment was verified by CFD numerical simulation, the simulation result was consistent with the experiment. In this device, active mixing was introduced into the microchannel extraction, which significantly improved the extraction efficiency. Under certain conditions, the extraction efficiency of this device exceeded stirring extraction equilibrium. Moreover, the extraction in this device is faster than conventional stirring extraction. These advantages provide a possibility for highly efficient extraction and use of rare earth elements.

Microfluidics for pharmaceutical nanoparticle fabrication: The truth and the myth

Using micro-sized channels to manipulate fluids is the essence of microfluidics which has wide applications from analytical chemistry to material science and cell biology research. Recently, using microfluidic-based devices for pharmaceutical research, in particular for the fabrication of micro- and nano-particles, has emerged as a new area of interest. The particles that can be prepared by microfluidic devices can range from micron size droplet-based emulsions to nano-sized drug loaded polymeric particles. Microfluidic technology poses unique advantages in terms of the high precision of the mixing regimes and control of fluids involved in formulation preparation. As a result of this, monodispersity of the particles prepared by microfluidics is often recognised as being a particularly advantageous feature in comparison to those prepared by conventional large-scale mixing methods. However, there is a range of practical drawbacks and challenges of using microfluidics as a direct micron- and nano-particle manufacturing method. Technological advances are still required before this type of processing can be translated for application by the pharmaceutical industry. This review focuses specifically on the application of microfluidics for pharmaceutical solid nanoparticle preparation and discusses the theoretical foundation of using the nanoprecipitation principle to generate particles and how this is translated into microfluidic design and operation.

High-Efficiency Small Sample Microparticle Fractionation on a Femtosecond Laser-Machined Microfluidic Disc

The fabrication and testing of microfluidic spinning compact discs with embedded trapezoidal microchambers for the purpose of inertial microparticle focusing is reported in this article. Microparticle focusing channels require small features that cannot be easily fabricated in acrylic sheets and are complicated to realize in glass by traditional lithography techniques; therefore, the fabrication of microfluidic discs with femtosecond laser ablation is reported for the first time in this paper. It could be demonstrated that high-efficiency inertial focusing of 5 and 10 µm particles is achieved in a channel with trapezoidal microchambers regardless of the direction of disc rotation, which correlates to the dominance of inertial forces over Coriolis forces. To achieve the highest throughput possible, the suspension concentration was increased from 0.001% (w/v) to 0.005% (w/v). The focusing efficiency was 98.7% for the 10 µm particles and 93.75% for the 5 µm particles.

A Primer on Microfluidics: From Basic Principles to Microfabrication

Microfluidic systems enable manipulating fluids in different functional units which are integrated on a microchip. This chapter describes the basics of microfluidics, where physical effects have a different impact compared to macroscopic systems. Furthermore, an overwiew is given on the microfabrication of these systems. The focus lies on clean-room fabrication methods based on photolithography and soft lithography. Finally, an outlook on advanced maskless micro- and nanofabrication methods is given. Special attention is paid to laser structuring processes.

Sheath-less high throughput inertial separation of small microparticles in spiral microchannels with trapezoidal cross-section

Various mechanisms of different designs have emerged for the purpose of microparticle separation and cell sorting. The main goals behind such designs are to create high throughput and high purity sample isolation. In this study, high efficiency, high throughput and precise separation of microparticles under inertial lift and drag forces induced by trapezoidal curvilinear channels are reported. This work is the first to focus and recover 2 from 5 μm and 2 from 10 μm particles in spiral channels in a sheath-less flow device, which reduces the overall complexity of the system and allows for higher throughput. The new microfluidic chip design is fabricated in glass using femtosecond laser ablation. In addition, mathematical force calculations were conducted during the design phase of the microfluidic channels and compared with experiments. The results show a close prediction of the equilibrium position of the tested microparticles.

Enhanced inertial focusing of microparticles and cells by integrating trapezoidal microchambers in spiral microfluidic channels

In this work, manipulating width and equilibrium position of fluorescent microparticles in spiral microchannel fractionation devices by embedding microchambers along the last turn of a spiral is reported. Microchambers with different shapes and sizes were tested at Reynolds numbers between 15.7 and 156.6 (100-1000 μL min-1) to observe focusing of 2, 5 and 10 μm fluorescent microparticles. This paper also discusses the fabrication process of the microfluidic chips with femtosecond laser ablation on glass wafers, as well as a particle imaging velocimetry (μPIV) study of microparticle trajectories inside a microchamber. It could be demonstrated with an improved final design with inclined microchamber side walls, that the 2 μm particle equilibrium position is shifted towards the inner wall by ∼27 μm and the focusing line's width is reduced by ∼18 μm. Finally, Saccharomyces cerevisiae yeast cells were tested in the final chip and a cell focusing efficiency of 99.1% is achieved.