Characterization and testing of periodic mesoporous organosilicas as potential selective benzene adsorbents.

The effects of surface imprinting on the adsorption and desorption properties of benzene- and diethylbenzene-bridged periodic mesoporous organosilicas (PMOs) acting as GC stationary-phase preconcentration sorbents for benzene and xylene were examined. Surface-imprinted and nonimprinted PMOs with diethylbenzene (DEB), benzene (BENZ), and ethane (BTSE) bridges and nonimprinted mesoporous silica (MCM-41) were prepared via well-established surfactant templating synthetic methods. The imprinted materials were synthesized using a surfactant demonstrated to produce trinitrotoluene (TNT) selective sorbents with increased adsorption capacity for cresol and 4-nitrophenol as well as TNT. Powder XRD and nitrogen sorption measurements revealed that all of the materials were mesoporous with the DEB materials having a random pore structure and lower surface area than the other materials which had ordered pore structures. Results for maximum uptake of benzene and p-xylene indicate a small but consistent positive effect on the adsorption of benzene and p-xylene due to surface imprinting. Comparing the surface area normalized uptakes (mg/m(2)) for materials having the same organic bridge with and without imprinting (DEB vs TDMI-DEB and BENZ vs TDMI-BENZ) shows that in seven of eight comparisons the imprinted analogue had a higher aromatic uptake. The imprinted samples showed higher weight normalized uptakes (mg/g) in five of eight cases. When used as a GC stationary phase, the organosilica materials yield more symmetrical chromatographic peaks and better separation than MCM-41, indicating superior trapping of BTX analytes, particularly at low concentrations. Additionally, these materials rapidly desorb the preconcentrated compounds.

Cost-effectiveness model of adjunctive lamotrigine for the treatment of epilepsy.

OBJECTIVE: To predict the cost-effectiveness of lamotrigine by evaluating the costs and health outcomes in treated patients. BACKGROUND: Lamotrigine adjunctive therapy has been found to be associated with decreased seizure frequency and severity in patients who are refractory to treatment with the older antiepileptic drugs (AEDs). METHODS: We used a cost-effectiveness clinical decision analysis framework to assess the impact of these clinical benefits on patient health care use. The measure of effectiveness was seizure-free days gained. The measures of health care resource use included hospitalizations, outpatient and emergency department visits, surgery, and AEDs. Medical care use and cost estimates were derived from clinical trial data and published sources. Costs and effectiveness (incremental costs per seizure-free days gained) of lamotrigine adjunctive therapy versus older AEDs were compared in patients refractory to previous treatment during three time periods: the start-up year, the second year when decisions about surgery were made, and all subsequent years. RESULTS AND CONCLUSIONS: The model predicts that use of lamotrigine would be associated with an overall reduction in use of other direct medical care resources (hospitalizations, outpatient visits, diagnostic and laboratory tests, and surgery). For a 10-year time horizon, the estimated cost-effectiveness ratio is $6.9 per seizure-free day gained. The model provides a flexible framework to analyze the effect of new antiepileptic drugs.

Diffusion and transfer of antibody proteins from a sugar-based hydrogel.

Diffusion of antibody protein from hydrogel films and hydrogel encapsulated in a microcapillary was studied. Thin hydrogel films were formed by crosslinking 6-acryloyl-B-O-methylgalactoside with N,N'-methylene-bis-acrylamide and the diffusive transport of monoclonal antimouse IgG-FITC into and out of the hydrate films was measured. Diffusion coefficients in 2 and 4% crosslinked hydrogel films were measured. The measured diffusion constants determined for IgG in both the 2 and 4% hydrogel films were comparable to the free diffusion of IgG in bulk water (Dmean approximately 10(-7) cm2/s). In addition, 2% crosslinked hydrogels were prepared in a capillary tube and the transport of antimouse IgG-FITC into and out of the hydrated hydrogel was measured. Kinetic analysis indicated that the protein transport through the capillary hydrogel was faster than would be expected for a simple diffusion process. Finally, by utilizing the diffusion of antibody from the capillary hydrogel, transfer of antibody to a silica surface was demonstrated. A capillary hydrogel loaded with antimouse IgG-FITC was used to transfer the protein to a silica surface forming a 30-micron spot of antibody, which was imaged using fluorescence microscopy. These results may lead to the development of a nonlithographic method of patterning antibodies on surfaces for use in integrated microimmunosensors.

Monolayer study of mixtures of diacetylenic phosphatidylcholine and phospholipids containing metal-chelating iminodiacetic acid headgroup.

The mixing behavior of polymerizable diacetylenic phosphatidylcholine (1) with two diacetylenic phospholipids containing the iminodiacetic acid (IDA) functionality in the headgroup region was studied at the air-water interface. All three phospholipids contained tricosa-10,12-diynoyl acyl chains. In phospholipid 2, the choline group (-CH2-CH2-NMe3) was replaced by an -CH2-CH2-N-(CH2-COOH)2 functionality. In phospholipid 3, the IDA unit was linked to the phosphate headgroup via a sulfonate linker, -CH2-CH2-OS(O2)-O-CH2-CH2-. Monolayers were prepared by mixing polymerizable 1,2 bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (1) with metal-chelating IDA phospholipids (2, 3) on a 10 mM CuCl2 subphase. Studies of monolayer properties of mixtures of 2 and 3 with 1 demonstrated that mixtures of 2 with 1 had better mixing behavior than mixtures of phospholipids 1 and 3.

Formation and properties of a network gel formed from mixtures of diacetylenic and short-chain phosphocholine lipids.

A polymerizable gel superaggregate has been formed from low concentrations (6 mM) of phospholipid mixtures of polymerizable 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine and 1,2-bis(dinonoyl)-sn-glycero-3-phosphocholine. Transmission electron microscopy (TEM) revealed that the superaggregate structure consisted of a network of twisted, braided fibers and that the pore size of the gel ranged from 0.1 to 1.0 micron. TEM of gel plated with Ni revealed that the width of the fibers was 280 A. Optical microscopy demonstrated that the onset of the gel phase occurred at mole fraction 0.43 DNPC in the absence of salt and 0.36 in the presence of 0.25 M NaCl. Polymerization did not affect the morphology of the gel but did increase its temperature stability.

Modulation of bilayer structures derived from diacetylenic phosphocholines containing oxygen linker beta to diacetylene.

Phospholipids with diacetylenes present in the acyl chains form tubules and helices in aqueous dispersions. In order to modulate the morphology of bilayer structures and to understand the role of diacetylene in lipid-bilayer assembly, two diacetylenic phosphocholines, 1,2-bis(9,16-dioxa-hexacosa-11,13-diynoyl)-sn-3-phosph ocholine and 1,2-bis(15-oxa-pentacosa-10,12-diynoyl)-sn-3-phosphocholine, in which the diacetylene is linked to the acyl chain by an oxygen spacer have been synthesized. Lipid dispersions were characterized by calorimetric, film balance and microscopic techniques. Placement of oxygen spacer influences the morphology of the bilayer assemblies formed in aqueous solution. When both ends of the diacetylene were linked to the acyl chain by oxygen atoms, liposomes (diameters ranging from 0.3-3.4 microns) were observed by optical microscopy. Linking only the terminal portion of the acyl chain to the diacetylene with an oxygen atom resulted in a lipid which formed tubular microstructures as well as vesicles. Diameter of the tubular structures ranged from 0.4-4.7 microns. Transmission electron microscopic (TEM) analysis of replicas of a freeze fractured sample of the dispersion revealed that the tubular structures were hollow cylinders consisting of an aqueous core surrounded by a wall of lipid.

Transcatheter stenting of the ductus arteriosus: evaluation as an alternative to surgical shunts.

Implantation of 3.5 mm Gianturco-Roubin coronary artery stents into the ductus arteriosus was evaluated as an alternative to surgical systemic to pulmonary arterial shunts in 3 weanling piglets. Thrombosis of the ductus occurred in all 3 animals (95% confidence limits 29-100%) within 1 hour, despite pretreatment with heparin. In each case, thrombus filled the ductus arteriosus but did not extend to any extraductal portion of the stents. Rapid, heparin-resistant thrombus formation precludes use of this stent procedure as an alternative to surgical shunts.

Determinants of health insurance status among young adults.

This study evaluates the determinants of insurance coverage in the 18-24-year-old population using the National Medical Care Utilization and Expenditure Survey. Three specific issues are addressed: 1) the characteristics of the insured versus uninsured, 2) the reason given by the uninsured for not having coverage, and 3) the role of employment status and other variables in determining insurance status. An important consideration is whether age or usual activity is more important in its effect on insurance status. The results show that employment is the strongest predictor of insurance status in all age and usual activity subgroups. Generally, permanent/full-time workers are most likely to be insured. An exception to this trend is found for those attending school who are also permanent/part-time workers. These individuals are more likely to be insured than permanent full-time workers who are in school. Furthermore, young adults with lower incomes, less education, rural residence, not married, hispanic ethnicity, and Western geography are the least likely to be insured. The findings of this analysis can be used by policymakers to identify the mechanisms that can best enhance insurance coverage among young adults.

The expense of testing in a teaching hospital: the predominant role of high-cost tests.

We analyzed all 32,206 tests ordered in a random sample of 1,000 patients admitted to a teaching hospital. The analysis examined costs instead of charges, included professional costs in addition to hospital costs, and considered the effect of combining tests that are ordered as a panel (e.g., cardiac enzymes) or as part of a procedure (e.g., bronchoscopy). High-cost tests (costing more than $100) accounted for only 4 percent of the total number of tests ordered, but for nearly 50 percent of total test costs. The pattern varied by clinical service: high-cost tests accounted for 31, 47, and 51 percents of total test costs on the obstetrics, medicine, and surgery services, respectively. It would seem to be efficient to concentrate on the use of high-cost tests in attempting to foster cost-effective use of diagnostic technologies.