Biomedical subjects

Alexander Alexeev

Publications and source records attributed to Alexander Alexeev.

7 recordsLinked to original sources

PubMed2007

Healing substrates with mobile, particle-filled microcapsules: designing a 'repair and go' system.

We model the rolling motion of a fluid-driven, particle-filled microcapsule along a heterogeneous, adhesive substrate to determine how the release of the encapsulated nanoparticles can be harnessed to repair damage on the underlying surface. We integrate the lattice Boltzmann model for hydrodynamics and the lattice spring model for the micromechanics of elastic solids to capture the interactions between the elastic shell of the microcapsule and the surrounding fluids. A Brownian dynamics model is used to simulate the release of nanoparticles from the capsule and their diffusion into the surrounding solution. We focus on a substrate that contains a damaged region (e.g. a crack or eroded surface coating), which prevents the otherwise mobile capsule from rolling along the surface. We isolate conditions where nanoparticles released from the arrested capsule can repair the damage and thereby enable the capsules to again move along the substrate. Through these studies, we establish guidelines for designing particle-filled microcapsules that perform a 'repair and go' function and thus, can be utilized to repair damage in microchannels and microfluidic devices.

Adhesives↗

PubMed2006

Modeling the release of nanoparticles from mobile microcapsules.

The authors present a novel computational approach to simulate both the release of nanoparticles from a microcapsule, which is moving through a microchannel, and the adsorption of the released particles onto the channel walls. By integrating the lattice spring model for the micromechanics of elastic solids and the lattice Boltzmann model for fluid dynamics, they simulate the relevant fluid-structure interactions in the system. In particular, they capture the dynamic interactions among the capsule's elastic shell, the encapsulated fluid, and the external, host solution. The nanoparticles are treated as "tracer particles" and their motion is modeled via a Brownian dynamics simulation. An imposed pressure gradient drives the capsule to move along an adhesive substrate and the particles are released from the surface of this mobile capsule. The authors determine how the elasticity of the capsule, the strength of the capsule-surface adhesion and the diffusion coefficient of the nanoparticles affect the relative amount of particles that are adsorbed onto the substrate. In addition to showing that the compliant nature of the capsule can significantly affect the nanoparticle deposition, they isolate a range of parameters for maximizing the adsorbed amount. The findings yield guidelines for optimizing the efficiency of microcapsule carriers in the targeted delivery of nanoparticles.

Journal Article↗

PubMed2006

Designing a simple ratcheting system to sort microcapsules by mechanical properties.

Using computational modeling, we analyze the fluid-driven motion of compliant particles over a rigid, saw-toothed surface. The particles are modeled as fluid-filled elastic shells and, thus, simulate ex vivo biological cells or polymeric microcapsules. Through the model, we demonstrate how the patterned surface and an oscillatory shear flow can be combined to produce a ratcheting motion, yielding a straightforward method for sorting these capsules by their relative stiffness. Since the approach exploits the capsule's inherent response to the substrate, it does not involve explicit measurement and assessment. Because the process utilizes an oscillatory shear, the sorting can be accomplished over a relatively short portion of the substrate. Due to these factors, this sorting mechanism can prove to be both efficient and relatively low-cost.

Journal Article↗

PubMed2006

Designing compliant substrates to regulate the motion of vesicles.

By integrating mesoscale models for hydrodynamics and micromechanics, we examine fluid-driven motion of vesicles on compliant surfaces. The vesicles, modeled as fluid-filled elastic shells, represent biological cells or polymeric microcapsules. Focusing on nonspecific interactions between these vesicles and synthetic substrates, we isolate mechanically and topographically patterned surfaces that transmit stop and go instructions, causing the vesicles to halt at specific locations, and with an increase in the flow velocity, to resume moving. For surfaces containing arrays of compliant posts, the substrates also affect the vesicles' gait, causing them to "crawl," "walk," or "jump." The latter behavior could promote the intermixing of reactants that are encapsulated within the microcapsules. Such control over vesicle dynamics can facilitate various biological assays and fabrication of arrays of mobile microreactors.

Computer Simulation↗

PubMed2005

Visualization of single-wall carbon nanotube (SWNT) networks in conductive polystyrene nanocomposites by charge contrast imaging.

The morphology of conductive nanocomposites consisting of low concentration of single-wall carbon nanotubes (SWNT) and polystyrene (PS) has been studied using atomic force microscopy (AFM), transmission electron microscopy (TEM) and, in particular, scanning electron microscopy (SEM). Application of charge contrast imaging in SEM allows visualization of the overall SWNT dispersion within the polymer matrix as well as the identification of individual or bundled SWNTs at high resolution. The contrast mechanism involved will be discussed. In conductive nanocomposites the SWNTs are homogeneously dispersed within the polymer matrix and form a network. Beside fairly straight SWNTs, strongly bended SWNTs have been observed. However, for samples with SWNT concentrations below the percolation threshold, the common overall charging behavior of an insulating material is observed preventing the detailed morphological investigation of the sample.

Journal Article↗

PubMed2004

Cylindrical micelles from the aqueous self-assembly of an amphiphilic poly(ethylene oxide)-b-poly(ferrocenylsilane) (PEO-b-PFS) block copolymer with a metallo-supramolecular linker at the block junction.

A supramolecular AB diblock copolymer has been prepared by the sequential self-assembly of terpyridine end-functionalized polymer blocks by using Ru(III)/Ru(II) chemistry. By this synthetic strategy a hydrophobic poly(ferrocenylsilane) (PFS) was attached to a hydrophilic poly(ethylene oxide) (PEO) block to give an amphiphilic metallo-supramolecular diblock copolymer (PEO/PFS block ratio 6:1). This compound was used to form micelles in water that were characterized by a combination of dynamic and static light scattering, transmission electron microscopy, and atomic force microscopy. These complementary techniques showed that the copolymers investigated form rod-like micelles in water; the micelles have a constant diameter but are rather polydisperse in length, and light scattering measurements indicate that they are flexible. Crystallization of the PFS in these micelles was observed by differential scanning calorimetry, and is thought to be the key behind the formation of rod-like structures. The cylindrical micelles can be cleaved into smaller rods whenever the temperature of the solution is increased or they are exposed to ultrasound.

Journal Article↗

PubMedDate not supplied

Optimizing photo-embossed gratings: a gradient library approach.

Methodologies for the rapid screening of coating systems were developed and applied to photopolymer lacquers for photoembossing applications. Continuous and discrete gradient libraries were prepared with a gradient in grating period along the short axis and along the long axis, a gradient in exposure energy, development temperature, film thickness, photoinitiator concentration, or monomer to polymer mass ratio. Discrete gradient libraries consisted of arrays of rectangular films made by pipetting a certain amount of sample onto a chemically patterned substrate consisting of hydrophilic patches surrounded by hydrophobic, fluorinated barriers. The shape and height of the photoembossed gratings were measured using an automated AFM. Optimum grating height was obtained for a 20-microm period at intermediate exposure energies, photoinitiator concentrations, or both. Height improves with development temperature (max 110 degrees C), monomer-to-polymer ratio (max 55 wt % monomer), and film thickness. Surface topography can also be optimized, depending on any specific application.

Calorimetry, Differential Scanning↗