Accurate risk assessment in drug development is crucial, as conventional in vitro and in vivo models often fail to predict human-specific responses. Organs on chips offer a promising alternative, but widespread use of polydimethylsiloxane introduces challenges due to its sorption of small lipophilic molecules, distorting pharmacokinetic and pharmacodynamic data. Cyclic olefin copolymer, a chemically stable alternative with minimal sorption, has emerged as a potential solution. This study investigates the sorption behavior of seven pharmaceutically active compounds in microfluidic devices and washout of these compounds, using high-performance liquid chromatography-mass spectrometry to evaluate recovery of compounds. Lipophilic molecules exhibited substantial sorption in polydimethylsiloxane and lower retention in cyclic olefin copolymer. Imipramine (logP = 4.80) decreased from 100 µM to 0.0384 µM for polydimethylsiloxane and 31.5 µM for cyclic olefin copolymer after 24 h incubation. Sorption was governed by multiple factors – lipophilicity and rotatable bond count were critical for both materials, hydrogen bond acceptors and molecular weight played a larger role in cyclic olefin copolymer, whereas topological polar surface area was critical for polydimethylsiloxane. Washout studies revealed that polydimethylsiloxane retains lipophilic compounds through bulk absorption, causing slow release, while cyclic olefin copolymer facilitated easier desorption. The cumulative sum of the first 5 h washout of loperamide (logP = 5.13) is 37.8% for polydimethylsiloxane and 71.5% for cyclic olefin copolymer. These findings highlight the importance of material selection and molecular properties in minimizing sorption and ensuring reliable experimental outcomes especially in microfluidic systems with distinctly different surface to volume ratios to other models.

The ability to isolate specific, viable cell populations from mixed ensembles with minimal manipulation and within intra-operative time would provide significant advantages for autologous, cell-based therapies in regenerative medicine. Current cell-enrichment technologies are either slow, lack specificity and/or require labelling. Thus a rapid, label-free separation technology that does not affect cell functionality, viability or phenotype is highly desirable. Here, we demonstrate separation of viable from non-viable human stromal cells using remote dielectrophoresis, in which an electric field is coupled into a microfluidic channel using shear-horizontal surface acoustic waves, producing an array of virtual electrodes within the channel. This allows high-throughput dielectrophoretic cell separation in high conductivity, physiological-like fluids, overcoming the limitations of conventional dielectrophoresis. We demonstrate viable/non-viable separation efficacy of >98% in pre-purified mesenchymal stromal cells, extracted from human dental pulp, with no adverse effects on cell viability, or on their subsequent osteogenic capabilities.

Extracellular vesicles are small membrane-bound structures that are released by cells and play important roles in intercellular communication garnering significant attention in scientific society recently due to their potential as diagnostic and therapeutic tools. However, separating EVs from large-volume samples remains a challenge due to their small size and low concentration. In this manuscript, we presented a novel method for separating polystyrene beads as control and extracellular vesicles from large sample volumes using bifurcated asymmetric field flow fractionation in PDMS-free microfluidic devices. Separation characteristics were evaluated using the control system of polystyrene bead mix, which offers up to 3.7X enrichment of EV-sized beads. Furthermore, in the EV-sample from bioreactor culture media, we observed a notable population distribution shift of extracellular vesicles. Herein presented novel PDMS-free microfluidic device fabrication protocol resulted in devices with reduced EV-loss compared to size-exclusion columns. This method represented an improvement over the current state of the art in terms of EV separation from large sample volumes through the use of novel field flow fractionation design.

Extracellular vesicles (EV) have many attributes important for biomedicine; however, current EV isolation methods require long multi-step protocols that generally involve bulky equipment that cannot be easily translated to clinics. Our aim was to design a new cyclic olefin copolymer–off-stoichiometry thiol-ene (COC–OSTE) asymmetric flow field fractionation microfluidic device that could isolate EV from high-volume samples in a simple and efficient manner. We tested the device with large volumes of urine and conditioned cell media samples, and compared it with the two most commonly used EV isolation methods. Our device was able to separate particles by size and buoyancy, and the attained size distribution was significantly smaller than other methods. This would allow for targeting EV size fractions of interest in the future. However, the results were sample dependent, with some samples showing significant improvement over the current EV separation methods. We present a novel design for a COC–OSTE microfluidic device, based on bifurcating asymmetric flow field-flow fractionation (A4F) technology, which is able to isolate EV from large volume samples in a simple, continuous-flow manner. Its potential to be mass-manufactured increases the chances of implementing EV isolation in a clinical or industry-friendly setting, which requires high repeatability and throughput.

Current in vitro models have significant limitations for new respiratory disease research and rapid drug repurposing. Lung on a chip (LOAC) technology offers a potential solution to these problems. However, these devices typically are fabricated from polydimethylsiloxane (PDMS), which has small hydrophobic molecule absorption, which hinders the application of this technology in drug repurposing for respiratory diseases. Off-stoichiometry thiol–ene (OSTE) is a promising alternative material class to PDMS. Therefore, this study aimed to test OSTE as an alternative material for LOAC prototype development and compare it to PDMS. We tested OSTE material for light transmission, small molecule absorption, inhibition of enzymatic reactions, membrane particle, and fluorescent dye absorption. Next, we microfabricated LOAC devices from PDMS and OSTE, functionalized with human umbilical vein endothelial cell (HUVEC) and A549 cell lines, and analyzed them with immunofluorescence. We demonstrated that compared to PDMS, OSTE has similar absorption of membrane particles and effect on enzymatic reactions, significantly lower small molecule absorption, and lower light transmission. Consequently, the immunofluorescence of OSTE LOAC was significantly impaired by OSTE optical properties. In conclusion, OSTE is a promising material for LOAC, but optical issues should be addressed in future LOAC prototypes to benefit from the material properties.

We have designed and characterized a simple Rayleigh-surface acoustic wave-based micropump, integrated directly with a fully enclosed 3D microfluidic system, which improves significantly the pumping efficiency within a coupled fluid whilst maintaining planar integration of the micropump and microfluidics. We achieve this by exploiting the Rayleigh-scattering angle of surface acoustic waves into pressure waves on contact with overlaid fluids, by designing a microfluidic channel aligned almost co-linearly with the launched pressure waves and by minimizing energy losses by reflections from, or absorption within, the channel walls. This allows the microfluidic system to remain fully enclosed—a pre-requisite for point-of-care applications—removing sources of possible contamination, whilst achieving pump efficiencies up to several orders of magnitude higher than previously reported, at low operating powers of 0.5 W.