Atomic oxygen effects on boron nitride and silicon nitride: A comparison of ground based and space flight data
The effects of atomic oxygen on boron nitride (BN) and silicon nitride (Si3N4) were evaluated in a low Earth orbit (LEO) flight experiment and in a ground based simulation facility. In both the inflight and ground based experiments, these materials were coated on thin (approx. 250A) silver films, and the electrical resistance of the silver was measured in situ to detect any penetration of atomic oxygen through the BN and Si3N4 materials. In the presence of atomic oxygen, silver oxidizes to form silver oxide, which has a much higher electrical resistance than pure silver. Permeation of atomic oxygen through BN, as indicated by an increase in the electrical resistance of the silver underneath, was observed in both the inflight and ground based experiments. In contrast, no permeation of atomic oxygen through Si3N4 was observed in either the inflight or ground based experiments. The ground based results show good qualitative correlation with the LEO flight results, indicating that ground based facilities such as the one at Los Alamos National Lab can reproduce space flight data from LEO.
Evaluation of atomic oxygen interaction with thin-film aluminum oxide
Effects of atomic oxygen on thin-film (750/angstrom/) sputtered aluminum oxide (Al/sub 2/O/sub 3/) have been characterized. Experiments were conducted using the Los Alamos National Laboratory (LANL) O-atom facility. Diffusion of O-atoms through the Al/sub 2/O/sub 3/ thin films was observed, having an activation energy of 5.2 kcal/mole at an O-atom kinetic energy of 2 eV. Silver oxidation was used as the technique to detect penetration of O-atoms through thin-films. The Al/sub 2/O/sub 3/ films were deposited on silver (250/angstrom/), and the electrical resistance of the silver was measured in-situ during exposure. The thin films provided better protection of the substrate when deposited on smooth sapphire surfaces than when deposited on rougher alumina surfaces. The Al/sub 2/O/sub 3/ was amorphous before and after exposure, with less than 2% variation in oxygen atomic concentration and total Al/sub 2/O/sub 3/ thickness before and after exposure. 14 refs., 10 figs., 1 tab.
Optimized Delivery System Achieves Enhanced Endomyocardial Stem Cell Retention
Background—Regenerative cell-based therapies are associated with limited myocardial retention of delivered stem cells. The objective of this study is to develop an endocardial delivery system for enhanced cell retention. Methods and Results—Stem cell retention was simulated in silico using 1- and 3-dimensional models of tissue distortion and compliance associated with delivery. Needle designs, predicted to be optimal, were accordingly engineered using nitinol, a nickel and titanium alloy displaying shape memory and superelasticity. Biocompatibility was tested with human mesenchymal stem cells. Experimental validation was performed with species-matched cells directly delivered into Langendorff-perfused porcine hearts or administered percutaneously into the endocardium of infarcted pigs. Cell retention was quantified by flow cytometry and real-time quantitative polymerase chain reaction methodology. Models, computing optimal distribution of distortion calibrated to favor tissue compliance, predicted that a 75°-curved needle featuring small-to-large graded side holes would ensure the highest cell retention profile. In isolated hearts, the nitinol curved needle catheter (C-Cath) design ensured 3-fold superior stem cell retention compared with a standard needle. In the setting of chronic infarction, percutaneous delivery of stem cells with C-Cath yielded a 37.7±7.1% versus 10.0±2.8% retention achieved with a traditional needle without effect on biocompatibility or safety. Conclusions—Modeling-guided development of a nitinol-based curved needle delivery system with incremental side holes achieved enhanced myocardial stem cell retention.