Polymer solutions are useful precursors to synthesize microparticles with microfluidic devices, but most polymer solutions are incompatible with microfluidic emulsification due to their non-Newtonian flow characteristics. A technique is presented to form monodisperse particles from such solutions by surrounding them with a chaperoning Newtonian fluid and forcing both to pinch into preparticle drops.
We study the micromechanics of collagen-I gel with the goal of bridging the gap between theory and experiment in the study of biopolymer networks. Three-dimensional images of fluorescently labeled collagen are obtained by confocal microscopy, and the network geometry is extracted using a 3D network skeletonization algorithm. Each fiber is modeled as an elastic beam that resists stretching and bending, and each crosslink is modeled as torsional spring. The stress-strain curves of networks at three different densities are compared with rheology measurements. The model shows good agreement with experiment, confirming that strain stiffening of collagen can be explained entirely by geometric realignment of the network, as opposed to entropic stiffening of individual fibers. The model also suggests that at small strains, crosslink deformation is the main contributer to network stiffness, whereas at large strains, fiber stretching dominates. As this modeling effort uses networks with realistic geometries, this analysis can ultimately serve as a tool for understanding how the mechanics of fibers and crosslinks at the microscopic level produce the macroscopic properties of the network. (C) 2010Wiley Periodicals, Inc. Complexity 16: 22-28, 2011
We introduce an approach that combines the concepts of emulsion-templating and dewetting for fabricating polymersomes with a large number of compartments. The resultant polymersome gel behaves as a gel-like solid, but is a true vesicle suspended in an aqueous environment. Due to the thin membranes that separate the compartments, the polymersome gels have a high volume fraction of internal phase for encapsulation of hydrophilic actives; they also provide a large surface area of diblock copolymer membrane for encapsulation of lipophilic actives. Multiple actives can also be encapsulated in the gel without cross-contamination. Our technique represents a simple and versatile bulk approach for fabricating polymersome gels; it does not require the use of any specialized equipment or subsequent polymerization steps to solidify the gel. The resultant polymersome gel is promising as an encapsulating structure as well as a scaffold for tissue engineering.