Crimping-induced structural gradients explain the lasting strength of poly L-lactide bioresorbable vascular scaffolds during hydrolysis

Biodegradable polymers open the way to treatment of heart disease using transient implants (bioresorbable vascular scaffolds, BVSs) that overcome the most serious complication associated with permanent metal stents—late stent thrombosis. Here, we address the long-standing paradox that the clinically approved BVS maintains its radial strength even after 9 mo of hydrolysis, which induces a ∼40% decrease in the poly L-lactide molecular weight (Mn). X-ray microdiffraction evidence of nonuniform hydrolysis in the scaffold reveals that regions subjected to tensile stress during crimping develop a microstructure that provides strength and resists hydrolysis. These beneficial morphological changes occur where they are needed most—where stress is localized when a radial load is placed on the scaffold. We hypothesize that the observed decrease in Mn reflects the majority of the material, which is undeformed during crimping. Thus, the global measures of degradation may be decoupled from the localized, degradation-resistant regions that confer the ability to support the artery for the first several months after implantation

Crimping-induced structural gradients explain the lasting strength of poly L-lactide bioresorbable vascular scaffolds during hydrolysis

Biodegradable polymers open the way to treatment of heart disease using transient implants (bioresorbable vascular scaffolds, BVSs) that overcome the most serious complication associated with permanent metal stents—late stent thrombosis. Here, we address the long-standing paradox that the clinically approved BVS maintains its radial strength even after 9 mo of hydrolysis, which induces a ∼40% decrease in the poly L-lactide molecular weight (Mn). X-ray microdiffraction evidence of nonuniform hydrolysis in the scaffold reveals that regions subjected to tensile stress during crimping develop a microstructure that provides strength and resists hydrolysis. These beneficial morphological changes occur where they are needed most—where stress is localized when a radial load is placed on the scaffold. We hypothesize that the observed decrease in Mn reflects the majority of the material, which is undeformed during crimping. Thus, the global measures of degradation may be decoupled from the localized, degradation-resistant regions that confer the ability to support the artery for the first several months after implantation

The Critical Care Research Network: A Partnership in Community Based Research and Research Transfer

The objectives of this study were to present a short history of the Critical Care Research Network (CCR-Net), describe its approach to health ser- vices research and to summarize completed and current research projects. In doing this, we explored the question is this research network accom- plishing its goals? We reviewed the medical literature to identify studies on similar types of Networks and also the evidence supporting the metho- dology used by CCR-Net to conduct research using MEDLINE, HEALTHSTAR, CINAHL and the keywords network and health care or healthcare, benchmarking and health care or healthcare, and research transfer or research utilization. We also reviewed the bibliographies of retrieved articles and our personal files. In addition, we summarized the results of studies conducted by CCR-Net and outlined those currently in progress. A review of the literature identified studies on two similar net- works that appeared to be succeeding. In addition, the literature was also supportive of the general process used by CCR-Net, although the level of evidence varied. Finally, the studies conducted to date within CCR-Net follow the suggested methodology. At the time of this preliminary com- munication CCR-Net appears to have adopted a valid approach to health services research within the area of Critical Care Medicine. Further direct evidence is required and appropriate studies are planned

The O-52 network by molecular design: CECD tetrablock terpolymers

Varying the length of poly(dimethylsiloxane) in poly(cyclohexylethylene-b-ethylene-b-cyclohexylethylene-b-dimethylsiloxane) (CECD) block terpolymers between 0 and 20% produces the sequence of ordered phases: cylindrical-to-network-to-cylindrical. Small-angle X-ray scattering and transmission electron microscopy demonstrate Pnna space group symmetry and a unique network morphology stabilized by the asymmetric molecular architecture and block interactions. These results establish a new design principle for the generation of triply periodic and multiply continuous nano-structured soft materials

The Effects of Ultraviolet-B Radiation on Plant Competition in Terrestrial Ecosystems

Evidence regarding the interaction of ultraviolet-B radiation and plant competition in terrestrial ecosystems is examined. The competitive interactions of some species pairs were affected even by ambient solar UV-B radiation when compared to control pairs grown without UV-B. Also, the total shoot biomass of these species pairs was depressed under ambient UV-B. Relatively large increases in UV-B radiation altered the competitive interactions of some species pairs grown in pots under field conditions, but did not affect the total shoot biomass production of those pairs. Recent field experiments have examined the competitive interactions of wheat and wild oat under a simulated increased UV-B regime resulting from a 16% ozone layer reduction when weighted with the generalized plant action spectrum. This increase in UV-B altered the competitive interactions of these two species without affecting the total shoot biomass production for the species pair. The manner in which increased UV-B affected the relative competitive abilities of the two species was highly dependent upon the environmental conditions during the early life stages of the plants. The implications of these results for both agricultural and natural plant communities are discusses