Enhanced mixing in polyacrylamide gels containing embedded silica nanoparticles as internal electroosmotic pumps

New design of hydrogels with tuned electro-osmosis: a potential model system to understand electro-kinetic transport in biological tissues

A series of charged polymer gels with precisely controlled magnitude and direction of electro-osmotic flow was prepared and opens up the possibility for understanding the contribution of electro-osmosis to transport phenomenon in native biological tissues.

Real-time discrimination between proliferation and neuronal and astroglial differentiation of human neural stem cells

Neural stem cells (NSCs) are characterized by a capacity for self-renewal, differentiation into multiple neural lineages, all of which are considered to be promising components for neural regeneration. However, for cell-replacement therapies, it is essential to monitor the process of in vitro NSC differentiation and identify differentiated cell phenotypes. We report a real-time and label-free method that uses a capacitance sensor array to monitor the differentiation of human fetal brain-derived NSCs (hNSCs) and to identify the fates of differentiated cells. When hNSCs were placed under proliferation or differentiation conditions in five media, proliferating and differentiating hNSCs exhibited different frequency and time dependences of capacitance, indicating that the proliferation and differentiation status of hNSCs may be discriminated in real-time using our capacitance sensor. In addition, comparison between real-time capacitance and time-lapse optical images revealed that neuronal and astroglial differentiation of hNSCs may be identified in real-time without cell labeling.

Synthesis and characterization of a hydrogel with controllable electroosmosis: a potential brain tissue surrogate for electrokinetic transport

Electroosmosis is the bulk fluid flow initiated by application of an electric field to an electrolyte solution in contact with immobile objects with a nonzero ζ-potential such as the surface of a porous medium. Electroosmosis may be used to assist analytical separations. Several gel-based systems with varying electroosmotic mobilities have been made in this context. A method was recently developed to determine the ζ-potential of organotypic hippocampal slice cultures (OHSC) as a representative model for normal brain tissue. The ζ-potential of the tissue is significant. However, determining the role of the ζ-potential in solute transport in tissue in an electric field is difficult because the tissue's ζ-potential cannot be altered. We hypothesized that mass transport properties, namely the ζ-potential and tortuosity, could be modulated by controlling the composition of a set of hydrogels. Thus, poly(acrylamide-co-acrylic acid) gels were prepared with three compositions (by monomer weight percent): acrylamide/acrylic acid 100/0, 90/10, and 75/25. The ζ-potentials of these gels at pH 7.4 are distinctly different, and in fact vary approximately linearly with the weight percent of acrylic acid. We discovered that the 25% acrylic acid gel is a respectable model for brain tissue, as its ζ-potential is comparable to the OHSC. This series of gels permits the experimental determination of the importance of electrokinetic properties in a particular experiment or protocol. Additionally, tortuosities were measured electrokinetically and by evaluating diffusion coefficients. Hydrogels with well-defined ζ-potential and tortuosity may find utility in biomaterials and analytical separations, and as a surrogate model for OHSC and living biological tissues.

Electroacoustics of particles dispersed in polymer gel

This study examines the electroacoustics of particles dispersed in polymer hydrogels, with the particle size either less than or greater than the gel mesh size. When the particles are smaller than the gel mesh size, their acoustic vibration is resisted by only the background water medium, and the measured dynamic electrophoretic mobility, μ(d) (obtained in terms of colloid vibration current, CVI), is the same as that in water. For the case of particles larger than the gel mesh size, μ(d) is decreased due to trapping, and the net decrease depends on the viscoelastic properties of the gel. The gel mesh size was varied by varying its cross-link density, with the latter being characterized as the storage modulus, G'. The dependence of mobility on G', for systems of a given particle size, and on particle size, for gels of a given G', are investigated. The measured mobility remains constant as G' is increased (i.e., mesh size is decreased) up to a value of approximately 300 Pa, beyond which it decreases. In the second set of measurements, the trapped particle size was increased in a gel medium of constant mesh size, with G' being approximately 100 Pa. In this case, the measured μ(d) is found to be effectively constant over the particle size range studied (14-120 nm); that is, it is independent of the degree of trapping as expressed by the ratio of the particle size to the mesh size.