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Spatially resolved fluid-flow modulation and its corresponding integration becomes a crucial aspect to consider when designing high-performing paper-based analytical devices. As such, high demand exists for cost-effective techniques able to selectively control flow in patternable regions of the device. In this regard, a solution composed of potassium alum and animal glue; sizing materials used in the fabrication of calligraphy Xuan paper, is successfully adapted for the first time in a revolutionary approach to efficiently modulate the capillary flow in paper microfluidic channels. Flow delays are achieved by coating the substrate systematically through the variation of parameters such as the ratio of alum to glue, the concentration of alum-glue in the solution, and the number of subsequent coating layers of alum-glue. Moreover, digitized patterning with alum-glue is developed to achieve programmable wicking profiles of accelerating, decelerating, and quasi-linear flow displacement by alternating coated and uncoated zones in the channel. Additionally, the influence of alum-glue when performing biometric assays is investigated by performing a horseradish peroxidase activity colorimetric assay and found to have negligible effects on reading, where a negligible difference of 5.2% was observed in an assay performed in a coated paper substrate, compared to an uncoated one.

The cell membrane permeability of a cell type to water (Lp) and cryoprotective agents (Ps), is the key factor that determines the optimal cooling and mass transportation during cryopreservation. The human lung adenocarcinoma cell line, CL1, has been widely used to study the invasive capabilities or drug resistance of lung cancer cells. Therefore, providing accurate databases of the mass transport properties of this specific cell line can be crucial for facilitating either flexible and optimal preservation, or supply. In this study, utilizing our previously proposed noncontact-based micro-vortex system, we focused on comparing the permeability phenomenon between CL1-0 and its more invasive subline, CL1-5, under several different ambient temperatures. Through the assay procedure, the cells of favor were virtually trapped in a hydrodynamic circulation to provide direct inspection using a high-speed camera, and the images were then processed to achieve the observation of a cell’s volume change with respect to time, and in turn, the permeability. Based on the noncontact nature of our system, we were able to manifest more accurate results than their contact-based counterparts, excluding errors involved in estimating the cell geometry. As the results in this experiment showed, the transport phenomena in the CL1-0 and CL1-5 cell lines are mainly composed of simple diffusion through the lipid bilayer, except for the case where CL1-5 were suspended in the cryoprotective agent (CPA) solution, which also demonstrated higher Ps values. The deviated behavior of CL1-5 might be a consequence of the altered expression of aquaporins and the coupling of a cryoprotective agent and water, and has given a vision on possible studies over these properties, and their potential relationship to invasiveness and metastatic stability of the CL1 cell line.

Cell-membrane permeability to water (Lp) and cryoprotective agents (Ps) of a cell type is a crucial cellular information for achieving optimal cryopreservation in the biobanking industry. In this work, a new micro-vortex system was developed to virtually trap cells of interest in a flow-driven hydrodynamic circulation passively formed at the expansion region in a microfluidic channel. Trapped cells remain in suspension and flow along with the streamline of the localized vortex, thus, featuring no physical contact with the device structure, and furthermore supporting a pragmatic assumption of 100% sphericity and active surface area of cell membrane for estimating actual cell volume from two-dimensional images. Cell membrane permeability was therefore able to be accurately determined by directly visualizing, with automatic cell recognition from high-speed videos, the transient profile of cell-volume change in response to a sudden osmotic gradient instantaneously (within 2 seconds) applied between the intracellular and extracellular environments. An acute T-cell lymphoma cell line (Jurkat) was used as a model to examine the newly-adopted micro-vortex technology in this research, and our results indicate a moderately higher values (Lp = 0.34 μm min-1 atm-1 for the binary system, Lp = 0.16 μm min-1 atm-1 and Ps = 0.55 × 10-3 cm min-1 for the ternary system) than those in prior arts utilizing contact-based cell-trapping techniques, manifesting an significant influence of active surface area on the determination of cell-membrane permeability.