Microfluidic Systems for Neural Cell Studies

Whereas the axons of the peripheral nervous system (PNS) spontaneously regenerate after an injury, the occurring regeneration is rarely successful because axons are usually directed by inappropriate cues. Therefore, finding successful ways to guide neurite outgrowth, in vitro, is essential for neurogenesis. Microfluidic systems reflect more appropriately the in vivo environment of cells in tissues such as the normal fluid flow within the body, consistent nutrient delivery, effective waste removal, and mechanical stimulation due to fluid shear forces. At the same time, it has been well reported that topography affects neuronal outgrowth, orientation, and differentiation. In this review, we demonstrate how topography and microfluidic flow affect neuronal behavior, either separately or in synergy, and highlight the efficacy of microfluidic systems in promoting neuronal outgrowth.

Wettability Control in Tree Structure-Based 1D Fiber Assemblies for Moisture Wicking Functionality

One of the fundamental properties of natural systems is their water transport ability, and living systems have efficient moisture management features. Here, a unique structure, inspired by the water transfer behavior in trees, was designed for one-dimensional (1D) fiber assemblies. In this 1D fiber assembly structure, a differential capillary effect enabling rapid water transfer at the interface between traditional cotton fibers and electrospun nanofibers was explored. A tree-like structure yarn was constructed successfully by novel electrospinning technology, and the effect was quantitatively controlled by precisely regulating the fibers' wettability. Fabrics based on these tree-like core-spun yarns possessed advanced moisture-wicking performance, a high one-way transport index (R) of 1034.5%, and a desirable overall moisture management capability of 0.88, which are over two times higher than those of conventional fabrics. This moisture-wicking regime endowed these 1D fiber assemblies with unique water transfer channels, providing a new strategy for moisture-heat transmission, microfluidics, and biosensor applications.

Manipulation of Magnetic Beads with Thin Film Microelectromagnet Traps

Integration of point-of-care assays can be facilitated with the use of actuated magnetic beads (MB) to perform testing in less expensive settings to enable the delivery of cost-effective care. In this paper we present six different designs of planar microelectromagnets traps (MEMT) with four external coils in series and one central coil connected for an opposite direction of manipulation of MB in microfluidic flows. The development of a simulation tool facilitated the rapid and efficient optimization of designs by presenting the influence of system variables on real time concentrations of MB. Real time experiments are in good agreement with the simulations and showed that the design enabled synchronous concentration and dispersion of MB on the same MEMT. The yield of local concentration is seen to be highly dependent on coil design. Additional coil turns between the central and external coils (inter-windings) doubled magnetic concentration and repulsion with no significant electrical resistance increase. The assemblage of a copper microchannel closed loop cooling system to the coils successfully eliminated the thermal drift promoted by joule heating generated by applied current.

Characterization of shear stress preventing red blood cells aggregation at the individual cell level: The temperature dependence

BACKGROUND

The novel measure of the red blood cells (RBC) aggregation (RBC-A) - the critical (minimum) shear stress (CSS) to prevent the cells from aggregation was found to be a promising clinically significant parameter. However, the absolute values of this parameter were found to change significantly depending on the shearing geometry (cup-and-bob, cone-plate or microchannel-flow) and have different temperature dependences along with it. The direct confirmation of these dependences aimed to find out the correct values is still pending.

OBJECTIVE

In this work, we aim to assess the absolute values of CSS at different temperatures.

METHODS

The single cell level measurements of CSS were performed using optical tweezers. The measurements were carried out in heavily diluted suspensions of RBCs in plasma.

RESULTS

The temperature dependent changes in CSS were measured at the points (22 and 38°C), in which the cup-and-bob and cone-plate systems yielded about 1.5-fold different values, while the microchannel-flow system yielded a constant value. The single cell CSS were found to be 362±157 mPa (22°C) and 312±57 mPa (38°C).

CONCLUSIONS

Our results prove that the microfluidic-flow approach is reflecting the RBC-A correctly. While the CSS values measured with other systems show the temperature dependent effect of the shearing geometry.

Potentialities of laser trapping and manipulation of blood cells in hemorheologic research

Laser trapping and manipulation of blood cells without mechanical contact have become feasible with implication of laser tweezers. They open up new horizons for the hemorheologic researches, offer new possibilities for studying live cells interactions on individual cell level under the influence of different endogenous and exogenous factors. The operation principle of laser tweezers is based on the property of strongly focused laser beam to act on a dielectric microparticle located in the vicinity of the beam waist with a force that drives the particle to the equilibrium location and holds it there. If the beam waist position is manipulated, so is the position of the particle. The displacement of the particle from the equilibrium position by external forces can be calibrated so that these forces can be precisely measured in the range ca. 0.1-100 pN. This is the range of forces of elastic deformation of blood cells and of their interaction with each other and with vessel walls. Being able to measure these forces without mechanical contact allows for studying on single cell level the mechanisms of interactions that was impossible earlier. Here we discuss the basic features of these techniques and give some examples of challenging hemorheologic studies.

Modulation of Matrix Softness and Interstitial Flow for 3D Cell Culture Using a Cell-Microenvironment-on-a-Chip System

In the past several decades, significant efforts have been devoted to recapitulating the in vivo tissue microenvironment within an in vitro platform. However, it is still challenging to recreate de novo tissue with physiologically relevant matrix properties and fluid flow. To this end, this study demonstrates a method to independently tailor matrix stiffness and interstitial fluid flow using a cell-microenvironment-on-a-chip (C-MOC) platform. Collagen-polyethylene glycol gels tailored to present controlled stiffness and hydraulic conductivity were fabricated in a microfluidic chip. The chip was assembled to continuously create a steady flow of media through the gel. In the C-MOC platform, interstitial flow mitigated the effects of matrix softness on breast cancer cell behavior, according to an immunostaining-based analysis of estrogen receptor-α (ER-α), integrin β1, and E-cadherin. This advanced cell culture platform serves to engineer tissue similar to in vitro tissue and contribute to better understanding and regulating of the biological roles of extracellular microenvironments.

Microscale imaging of cilia-driven fluid flow

Cilia-driven fluid flow is important for multiple processes in the body, including respiratory mucus clearance, gamete transport in the oviduct, right-left patterning in the embryonic node, and cerebrospinal fluid circulation. Multiple imaging techniques have been applied toward quantifying ciliary flow. Here, we review common velocimetry methods of quantifying fluid flow. We then discuss four important optical modalities, including light microscopy, epifluorescence, confocal microscopy, and optical coherence tomography, that have been used to investigate cilia-driven flow.