Mechanical Properties of DNA-Crosslinked Polyacrylamide Hydrogels with Increasing Crosslinker Density.

DNA-cross-linked polyacrylamide hydrogels (DNA gels) are dynamic mechanical substrates. The addition of DNA oligomers can either increase or decrease the crosslinker density to modulate mechanical properties. These DNA-responsive gels show promise as substrates for cell culture and tissue-engineering applications, since the gels allow time-dependent mechanical modulation.

Fibroblast morphology on dynamic softening of hydrogels.

Despite cellular environments having dynamic characteristics, many laboratories utilized static polyacrylamide hydrogels to study the ECM-cell relationship. To attain a more in vivo like environment, we have developed a dynamic, DNA-crosslinked hydrogel (DNA gel). Through the controlled delivery of DNA, we can temporally decrease or increase gel stiffness while expanding or contracting the gel, respectively.

Neural lineage differentiation of embryonic stem cells within alginate microbeads.

Cell replacement therapies, using renewable stem cell sources, hold tremendous potential to treat a wide range of degenerative diseases. Although many studies have established techniques to successfully differentiate stem cells into different mature cell lineages using growth factors or extracellular matrix protein supplementation in both two and three-dimensional configurations, they are often limited by lack of control and low yields of differentiated cells. Previously, we developed a scalable murine embryonic stem cell differentiation environment which maintained cell viability and supported ES cell differentiation to hepatocyte lineage cells.

Complete mechanical characterization of soft media using nonspherical rods.

Hydrogels have been used as substrates for studying the cellular processes by many researchers. The stiffness of such gels was also characterized previously. However, in most of the cases, these soft Poisson's ratio was assumed incompressible and Poisson's ratio is assumed to be one-half.

A nonintrusive method of measuring the local mechanical properties of soft hydrogels using magnetic microneedles.

Soft hydrogels serving as substrates for cell attachment are used to culture many types of cells. The mechanical properties of these gels influence cell morphology, growth, and differentiation. For studies of cell growth on inhomogeneous gels, techniques by which the mechanical properties of the substrate can be measured within the proximity of a given cell are of interest.

Functional modulation of ES-derived hepatocyte lineage cells via substrate compliance alteration.

Pluripotent embryonic stem cells represent a promising renewable cell source to generate a variety of differentiated cell types including hepatocyte lineage cells, and may ultimately be incorporated into extracorporeal bioartificial liver devices and cell replacement therapies. Recently, we and others have utilized sodium butyrate to directly differentiate hepatocyte-like cells from murine embryonic stem cells cultured in a monolayer configuration. However, to incorporate stem cell technology into clinical and pharmaceutical applications, and hopefully increase the therapeutic potential of these differentiated cells for liver disease treatment, a major challenge remains in sustaining differentiated functions for an extended period of time in their secondary culture environment.

Effect of the structural water on the mechanical properties of collagen-like microfibrils: a molecular dynamics Study.

The objective of this paper is to investigate the role played by the structural water on the intermolecular sliding between collagen-like 1QSU peptides in a microfibril under deformation. Three modes of deformation are used to generate intermolecular sliding: forced axial stretching (case I) or sliding (case II) of a central peptide monomer (while other surrounding monomers are fixed); and cantilever bending (case III) under a terminal lateral load. The force-displacement curve of each deformation mode is derived using a module called Steered Molecular Dynamics (SMD) in a molecular dynamics package NAMD under the CHARMM22 force field.