Microparticle separation using dielectrophoresis-assisted inertial microfluidics: A GPU-accelerated immersed boundary-lattice Boltzmann simulation.

In this study, the migration of microparticles towards the inertial equilibrium positions in a straight microchannel with a square cross section in the presence of an inhomogeneous oscillating electric field was examined. The dynamics of microparticles were simulated using the immersed boundary-lattice Boltzmann method of fluid-structure interaction simulation. Moreover, the lattice Boltzmann Poisson solver was applied to calculate the electric field required for calculation of the dielectrophoretic force using the equivalent dipole moment approximation. These numerical methods were implemented on a single GPU coupled with the AA pattern of storing distribution functions in memory to speed up the computationally demanding simulation of microparticles dynamics. In the absence of an electric field, spherical polystyrene microparticles migrate to four symmetric stable equilibrium positions corresponding to the sidewalls of the square cross-sectional microchannel. The equilibrium distance from the sidewall was increased by increasing the particle size. The equilibrium positions near electrodes disappeared and particles migrated to the other equilibrium positions far from the electrodes by the application of the high-frequency oscillatory electric field at voltages beyond a threshold value. Finally, a two-step dielectrophoresis-assisted inertial microfluidics methodology was introduced for particle separation based on the crossover frequencies and the observed threshold voltages of different particles. The proposed method exploited the synergistic effect of dielectrophoresis and inertial microfluidics methods to remove their limitations, allowing the separation of a broad range of polydisperse particle mixtures with a single device in a short time.

Adsorption Dynamics of Surface-Modified Silica Nanoparticles at Solid-Liquid Interfaces.

Understanding the adsorption dynamics of nanoparticles at solid-liquid interfaces is of paramount importance to engineer nanoparticles for a variety of applications. The nanoparticle surface chemistry is significant for controlling the adsorption dynamics. This study aimed to experimentally examine the adsorption of surface-modified round-shaped silica nanoparticles (with an average diameter of 12 nm), grafted with hydrophobic (propyl chains) and/or hydrophilic (polyethylene glycol chains) agents, at an aqueous solution-silica interface with spherical soda-lime glass beads (diameter of 3 mm) being used as adsorbents. While no measurable adsorption was observed for solely hydrophobic or hydrophilic nanoparticles, a considerable level of adsorption was detected for nanoparticles comprising both hydrophobic and hydrophilic agents. Various kinetic models were employed to model the adsorption dynamics of the responsive nanoparticles. The results demonstrated that the mixed diffusion-kinetics models could predict the dynamics better than the adsorption diffusion models, indicating that the dynamics is controlled by a combination of liquid film diffusion, intra-particle diffusion, and mass action. Additionally, the adsorption of the surface-modified silica nanoparticles onto a mineral silica surface was examined using molecular dynamics simulations. The interaction energy for nanoparticles comprising both hydrophobic and hydrophilic agents was evaluated to be more favorable than that of solely hydrophobic or hydrophilic nanoparticles.

Nrf2 signaling pathway in cisplatin chemotherapy: Potential involvement in organ protection and chemoresistance.

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a vital transcription factor and its induction is of significant importance for protecting against oxidative damage. Increased levels of Reactive Oxygen Species (ROS) stimulate Nrf2 signaling, enhancing the activity of antioxidant enzymes such as catalase, superoxide dismutase and glutathione peroxidase. These enzymes are associated with retarding oxidative stress. On the other hand, Nrf2 activation in cancer cells is responsible for the development of chemoresistance due to disrupting oxidative mediated-cell death by reducing ROS levels. Cisplatin (CP), cis-diamminedichloroplatinum(II), is a potent anti-tumor agent extensively used in cancer therapy, but its frequent application leads to the development of chemoresistance as well. In the present study, association of Nrf2 signaling with chemoresistance to CP and protection against its deleterious effects is discussed. Anti-tumor compounds, mainly phytochemicals, retard chemoresistance by suppressing Nrf2 signaling. Upstream mediators such as microRNAs can regulate Nrf2 expression during CP chemotherapy regimens. Protection against side effects of CP is mediated via activating Nrf2 signaling and its downstream targets activating antioxidant defense system. Protective agents that activate Nrf2 signaling, can ameliorate CP-mediated ototoxicity, nephrotoxicity and neurotoxicity. Reducing ROS levels and preventing cell death are the most important factors involved in alleviating CP toxicity upon Nrf2 activation. As pre-clinical experiments advocate the role of Nrf2 in chemoprotection and CP resistance, translating these findings to the clinic can provide a significant progress in treatment of cancer patients.

Mechanical Characteristics of SPG-178 Hydrogels: Optimizing Viscoelastic Properties through Microrheology and Response Surface Methodology

Background: Self-assembling peptides (SApeptides) have growing applications in tissue engineering and regenerative medicine. The application of SApeptide-based hydrogels depends strongly on their viscoelastic properties. Optimizing the properties is of importance in tuning the characteristics of the hydrogels for a variety of applications. Methods: In this study, we employed statistical modeling, conducted with the response surface methodology (RSM) and particle tracking microrheology, to investigate the effects of self-assembling SPG-178 peptide and added NaCl salt concentrations and milieu type (deionized water or blood serum) on the viscoelastic properties of SPG-178 hydrogels. A central composite RSM model was employed for finding the optimum value of the parameters to achieve the highest storage modulus and the lowest tan δ. Results: Viscoelastic properties of each sample, including storage modulus, loss modulus, and tan δ, were determined. Storage modulus and tan δ were modeled, accounting for the impact of the SPG-178 peptide and NaCl concentrations and milieu type on the viscoelastic properties. It was found that the SPG-178 hydrogel storage modulus was positively influenced by the SPG-178 peptide concentration and the serum. Conclusion: A combination of microrheology and RSM is a useful test method for statistical modeling and analysis of rheological behavior of solid-like gels, which could be applied in various biomedical applications such as hemostasis.

A continuous flow microfluidic device based on contactless dielectrophoresis for bioparticles enrichment.

In recent years, applications of dielectrophoresis-based platforms have been recognized as effective and dependable approach to separate cells and bioparticles, suspended in different carrier fluids, based on particle size and electrical properties. In this study, a microfluidic device was fabricated by an unprecedented electrode pattern, and several experiments were performed to enrich samples including either of yeast, Escherichia coli, or latex particles. A chemical deposition-based method was employed for fabrication of microelectrodes, inducing nonuniform electric field required for dielectrophoresis-based separation. One major advantage of our employed method is low fabrication cost, in addition to its accuracy and operation at low voltages. The performance of the microfluidic device in enriching either of injected samples was studied using spectrophotometric techniques. The effects of experimentally controllable parameters (applied-voltage amplitude and frequency, and flow rate) were studied by changing a parameter while keeping the others constant. It became evident that all the aforementioned parameters had modulating impact on the performance of the microfluidic device. Furthermore, to investigate binary interactions among the parameters, response surface methodology was exploited, resulting in a second-order polynomial model for the performance of the device as a function of the parameters. The model was employed for finding the optimum values of the parameters at which the performance of the device is the highest. At optimum values for the experimentally controllable parameters, enrichment efficiencies of 87 ± 2, 82 ± 4, and 86 ± 3% for, respectively, yeast, E. coli, and latex particles were obtained experimentally, confirming the ability of the proposed method for biological and polymeric particles enrichment.

Dynamic electrical response of colloidal micro-spheres in compliant micro-channels from optical tweezers velocimetry.

We report the dynamic response of colloidal silica in aqueous electrolytes to oscillatory electric fields at frequencies up to approximately 50 kHz. Particles were optically trapped at various positions across the gap of straight and crossed parallel-plate micro-channels. Using back-focal-plane interferometry, we measured the apparent electrophoretic mobility in NaCl and CaCl(2) electrolytes over a wide range of salt concentrations. The mobility has a strikingly complex dependence on channel position and forcing frequency that cannot be understood on the basis of standard electrokinetic theory for rigid micro-channels. We ascribe the anomalous dynamics to coupling of electro-osmotic flow and elastic modes of the micro-channel and auxiliary hardware. By integrating into the classical theory a complex-valued channel-compliance parameter--that modulates the phase and amplitude of the dynamic electro-osmotic flow--theoretical interpretation of the frequency-dependent mobility furnishes robust measurements of the intrinsic particle electrophoretic mobility and the upper and lower channel-wall zeta-potentials. Together, the single-particle experiments and accompanying theoretical interpretation highlight--for the first time--how spatially and temporally resolved particle dynamics are exquisitely sensitive to channel compliance. Accordingly, specially designed compliant micro-fluidic channels and flexible tube connections might be tailored for dynamic electrical micro-fluidic diagnostic applications.