Alginate Composition Effects on a Neural Stem Cell-Seeded Scaffold

The purpose of this study was to evaluate the effects of alginate composition on the neurotrophic factor release, viability, and proliferation of encapsulated neural stem cells (NSCs), as well as on the mechanical stability of the scaffold itself. Four compositions were tested: a high guluronic acid (68%) and a high mannuronic acid (54%) content alginate, with or without a poly-L-lysine (PLL) coating layer. Enzyme-linked immunosorbent assay was used to quantify the release of brain-derived neurotrophic factor, glial-derived neurotrophic factor, and nerve growth factor from the encapsulated cells. All three factors were detected from encapsulated cells only when a high L-guluronic acid alginate without PLL was used. Additionally, capsules with this composition remained intact more frequently when exposed to solutions of low osmolarity, potentially indicating superior mechanical stability. Alginate beads with a PLL-coated, high D-mannuronic acid composition were the most prone to breakage in the osmotic pressure test, and were too fragile for histology and proliferation assays after 1 week in vitro. NSCs survived and proliferated in the three remaining alginate compositions similarly over the 21-day study course irrespective of scaffold condition. NSC-seeded alginate beads with a high L-guluronic acid, non-PLL-coated composition may be useful in the repair of injured nervous tissue, where the mechanism is the secretion of neuroprotective factors. We verify the neuroprotective effects of medium conditioned by NSC-seeded alginate beads on the serum withdrawal-mediated death of PC-12 cells here.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78133/1/ten.tec.2008.0302.pd

Effects of microstructure and shock loading conditions on the damage behavior of polycrystalline copper

A suite of plate-impact experiments have been conducted to determine the dominant factors in dynamic damage evolution in uniaxial strain tensile (spall) experiments. The first group of experiments addresses the effect of microstructure by using copper samples with varying grain sizes while maintaining similar loading conditions (peak compressive stress ∼ 1.5GPa). In a second set, the density of grain boundaries in copper samples and the compressive stress (∼ 1.6GPa) were held constant while the tensile loading characteristics were tailored by controlling the geometry of flyers and targets. For similar loading conditions, the damage fields were observed to depend on the grain size: void growth and coalescence were observed to dominate the damage behavior in samples with either small (30μm) or large grain size (200μm); whereas in samples with intermediate grain size (60 and 100μm), most of the damage was restricted to individual voids. For the second portion of the study the characteristics of the damage fields were observed to strongly depend on the characteristics of the tensile pulse. In this case, an increasing large plastic dissipation, in the form of grain misorientation, and more advanced stages of damage were observed in the samples deformed at lower tensile stress rates