Impact of large scale, multicomponent intervention to reduce proton pump inhibitor overuse in integrated healthcare system: difference-in-difference study

OBJECTIVE

To determine how a large scale, multicomponent, pharmacy based intervention to reduce proton pump inhibitor (PPI) overuse affected prescribing patterns, healthcare utilization, and clinical outcomes.

DESIGN

Difference-in-difference study.

SETTING

US Veterans Affairs Healthcare System, in which one regional network implemented the overuse intervention and all 17 others served as controls.

PARTICIPANTS

All individuals receiving primary care from 2009 to 2019.

INTERVENTION

Limits on PPI refills for patients without a documented indication for long term use, voiding of PPI prescriptions not recently filled, facilitated electronic prescribing of H2 receptor antagonists, and education for patients and clinicians.

MAIN OUTCOME MEASURES

The primary outcome was the percentage of patients who filled a PPI prescription per 6 months. Secondary outcomes included percentage of days PPI gastroprotection was prescribed in patients at high risk for upper gastrointestinal bleeding, percentage of patients who filled either a PPI or H2 receptor antagonist prescription, hospital admission for acid peptic disease in older adults appropriate for PPI gastroprotection, primary care visits for an upper gastrointestinal diagnosis, upper endoscopies, and PPI associated clinical conditions.

RESULTS

The number of patients analyzed per interval ranged from 192 607 to 250 349 in intervention sites and from 3 775 953 to 4 360 868 in control sites, with 26% of patients receiving PPIs before the intervention. The intervention was associated with an absolute reduction of 7.3% (95% confidence interval -7.6% to -7.0%) in patients who filled PPI prescriptions, an absolute reduction of 11.3% (-12.0% to -10.5%) in PPI use among patients appropriate for gastroprotection, and an absolute reduction of 5.72% (-6.08% to -5.36%) in patients who filled a PPI or H2 receptor antagonist prescription. No increases were seen in primary care visits for upper gastrointestinal diagnoses, upper endoscopies, or hospital admissions for acid peptic disease in older patients appropriate for gastroprotection. No clinically significant changes were seen in any PPI associated clinical conditions.

CONCLUSIONS

The multicomponent intervention was associated with reduced PPI use overall but also in patients appropriate for gastroprotection, with minimal evidence of either clinical benefits or harms.

Intravenous dantrolene in hypermetabolic syndromes: a survey of the U.S. Veterans Health Administration database

BACKGROUND

Intravenous dantrolene is often prescribed for hypermetabolic syndromes other than the approved indication of malignant hyperthermia (MH). To clarify the extent of and indications for dantrolene use in conditions other than MH, we sought to document current practices in the frequency, diagnoses, clinical characteristics and outcomes associated with dantrolene treatment in critical care settings.

METHODS

Inpatients receiving intravenous dantrolene from October 1, 2004 to September 30, 2014 were identified retrospectively in the U.S. Veterans Health Administration national database. Extracted data included; diagnoses of hypermetabolic syndromes; triggering drugs; dantrolene dosages; demographics; vital signs; laboratory values; in-hospital mortality; complications; and lengths of stay. Frequency and mortality of patients who did not receive dantrolene were obtained in selected diagnoses for exploratory comparisons.

RESULTS

Dantrolene was administered to 304 inpatients. The most frequent diagnoses associated with dantrolene treatment were neuroleptic malignant syndrome (NMS; N = 108, 35.53%) and sepsis (N = 47, 15.46%), with MH accounting for only 13 (4.28%) cases. Over half the patients had psychiatric comorbidities and received psychotropic drugs before dantrolene treatment. Common clinical findings in patients receiving dantrolene included elevated temperature (mean ± SD; 38.7 ± 1.3 °C), pulse (116.33 ± 22.80/bpm), respirations (27.75 ± 9.58/min), creatine kinase levels (2,859.37 ± 6,646.88 IU/L) and low pO₂ (74.93 ± 40.16 mmHg). Respiratory, renal or cardiac failure were common complications. Mortality rates in-hospital were 24.01% overall, 7.69% in MH, 20.37% in NMS and 42.55% in sepsis, compared with mortality rates in larger and possibly less severe groups of unmatched patients with MH (5.26%), NMS (6.66%), or sepsis (41.91%) who did not receive dantrolene.

CONCLUSIONS

In over 95% of cases, dantrolene administration was associated with diagnoses other than MH in critically-ill patients with hypermetabolic symptoms and medical and psychiatric comorbidities. Exploratory survey data suggested that the efficacy and safety of dantrolene in preventing mortality in hypermetabolic syndromes other than MH remain uncertain. However, randomized and controlled studies using standardized criteria between groups matched for severity are essential to guide practice in using dantrolene.

Suicidal ideation and behaviors among women veterans with recent exposure to intimate partner violence

OBJECTIVE

Women veterans have disproportionately high risk for both suicide and intimate partner violence compared to women non-veterans. The objective of this study was to assess the relationship between intimate partner violence (IPV) and suicidal ideation and suicidal or self-harm behaviors among women veterans.

METHOD

Veterans Health Administration (VHA) electronic medical records were extracted for 8427 women veterans who completed screening for past-year IPV between April 2014 and 2016. Risk for suicidal ideation and self-harm behaviors were estimated as function of screening results using logistic regression.

RESULTS

Overall, 8.4% screened positive for IPV. Suicidal ideation or self-harm behaviors were recorded for 3.2%. Positive IPV screen was associated with double the odds for suicidal ideation (AOR = 2.04; 95% CI = 1.47-2.86) and self-harm behaviors (AOR = 2.05, 95% CI = 1.10-3.83). Risks did not significantly differ by IPV type. Suicide-related ICD codes were most often recorded prior to IPV screening.

CONCLUSIONS

There is a strong association between positive IPV screen and suicidal ideation and self-harm behaviors among VHA-engaged women veterans. Documentation of either event is an important marker for the other. Integration of suicide prevention with IPV services may enhance identification of women at risk and speed service uptake. Suicidal ideation and behaviors should be assessed among women with positive IPV screens, and identification of suicide risk should trigger IPV assessment.

Women's Healthcare Utilization Following Routine Screening for Past-Year Intimate Partner Violence in the Veterans Health Administration

BACKGROUND

Experience of intimate partner violence (IPV) can have adverse health impacts and has been associated with elevated rates of healthcare service utilization. Healthcare encounters present opportunities to identify IPV-related concerns and connect patients with services. The Veterans Health Administration (VHA) conducts IPV screening within an integrated healthcare system.

OBJECTIVE

The objectives of this study were to compare service utilization in the 6 months following IPV screening between those screening positive and negative for past-year IPV (IPV+, IPV-) and to examine the timing and types of healthcare services accessed among women screening IPV+.

DESIGN

A retrospective chart review was conducted for 8888 female VHA patients across 13 VHA facilities who were screened for past-year IPV between April 2014 and April 2016.

MAIN MEASURES

Demographic characteristics (age, race, ethnicity, marital status, veteran status), IPV screening response, and healthcare encounters (based on visit identification codes).

KEY RESULTS

In the 6 months following routine screening for past-year IPV, patients screening IPV+ were more likely to utilize outpatient care (aOR = 1.85 [CI 1.26, 2.70]), including primary care or psychosocial care, and to have an inpatient stay (aOR = 2.09 [CI 1.23, 3.57]), compared with patients screening IPV-. Among those with any utilization, frequency of outpatient encounters within the 6-month period following screening was higher among those screening IPV+ compared with those screening IPV-. The majority of patients screening positive for past-year IPV returned for an outpatient visit within a brief time frame following the screening visit (> 70% within 14 days, >95% within 6 months). More than one in four patients screening IPV+ had an emergency department visit within the 6 months following screening.

CONCLUSIONS

Women who screen positive for past-year IPV have high rates of return to outpatient visits following screening, presenting opportunities for follow-up support. Higher rates of emergency department utilization and inpatient stays among women screening IPV+ may indicate adverse health outcomes related to IPV experience.

Recent Intimate Partner Violence and Housing Instability Among Women Veterans

INTRODUCTION

Women Veterans are at increased risk of both housing instability and intimate partner violence compared with their non-Veteran counterparts. The objectives of the present study were (1) to assess the relationship between women Veterans' experience of intimate partner violence and various indicators of housing instability, and (2) to assess what correlates help to explain experiences of housing instability among women Veterans who experienced past-year intimate partner violence.

METHODS

Data were collected from U.S. Department of Veterans Affairs electronic medical records for 8,427 women Veterans who were screened for past-year intimate partner violence between April 2014 and April 2016 at 13 Veterans Affairs' facilities. Logistic regressions performed during 2017 assessed the relationship between past-year intimate partner violence and housing instability.

RESULTS

A total of 8.4% of the sample screened positive for intimate partner violence and 11.3% for housing instability. Controlling for age and race, a positive intimate partner violence screen increased odds of housing instability by a factor of 3. Women Veterans with past-year intimate partner violence were more likely to have an indicator of housing instability if they identified as African American, had screened positive for military sexual trauma, or had a substance use disorder; receiving compensation for a disability incurred during military service and being married were protective.

CONCLUSIONS

For women Veterans, intimate partner violence interventions should assess for both physical and psychological housing needs, and housing interventions should coordinate with intimate partner violence programs to address common barriers to resources.

Adoption, penetration, and effectiveness of a secondary risk screener for intimate partner violence: Evidence to inform screening practices in integrated care settings

OBJECTIVE

Veterans Health Administration (VHA) has implemented screening for past-year intimate partner violence (IPV) in some healthcare facilities along with secondary screening of risk for severe violence among those screening positive in order to facilitate follow-up care for high-risk patients. We evaluated the adoption, penetration, and effectiveness of secondary screening as a tool to facilitate timely follow-up services.

METHODS

Retrospective review of medical records (screening and healthcare use) of 774 women screening positive for past-year IPV (IPV+) at 11 facilities nationwide from April 2014-April 2016. Chi-square and t-tests examined factors related to secondary screening.

RESULTS

Three of eleven (27.3%) facilities that implemented primary IPV screening adopted secondary screening. At adopting sites, 56.4% eligible (i.e., IPV+) women received secondary screening. Among 185 IPV+ women who completed secondary screening, 33.0% screened positive for severe IPV. Screening positive during secondary screening was associated with higher rate of psychosocial care within 60 days (73.8% vs. 54.0% of IPV+ patients screening negative; p < .05), posttraumatic stress disorder diagnosis (31.1% vs. 15.3%; p < .05), and being physically threatened or harmed (>50% vs. <15%; p < .001).

CONCLUSIONS

Secondary risk assessment following IPV screening may expedite access to psychosocial follow-up care in integrated healthcare settings. However, program uptake needs to be enhanced.

Disproportionate Mental Health Burden Associated With Past-Year Intimate Partner Violence Among Women Receiving Care in the Veterans Health Administration

Experience of intimate partner violence (IPV) can lead to mental health conditions, including anxiety, depression, and unhealthy substance use. Women seen in the Veterans Health Administration (VHA) face high rates of both IPV and mental health morbidity. This study aimed to identify associations between recent IPV experience and mental health diagnoses among women VHA patients. We examined medical records data for 8,888 female veteran and nonveteran VHA patients across 13 VHA facilities who were screened for past-year IPV between April, 2014 and April, 2016. Compared with women who screened negative for past-year IPV (IPV-), those who screened positive (IPV+; 8.7%) were more than twice as likely to have a mental health diagnosis, adjusted odds ratio (AOR) = 2.27, 95% confidence interval (CI) [1.95, 2.64]; or more than two mental health diagnoses, AOR = 2.29, 95% CI [1.93, 2.72]). Screening IPV+ was also associated with significantly higher odds of each type of mental health morbidity (AOR range = 1.85-3.19) except psychoses. Over half (53.5%) of the women who screened IPV+ had a mental health diagnosis, compared with fewer than one-third (32.6%) of those who screened IPV-. Each subtype of IPV (psychological, physical, and sexual violence) was significantly associated with having a mental health diagnosis (AOR range = 2.25-2.37) or comorbidity (AOR range = 2.17-2.78). Associations remained when adjusting for military sexual trauma and combat trauma among the veteran subsample. These findings highlight the mental health burden associated with past-year IPV among female VHA patients and underscore the need to address psychological and sexual IPV, in addition to physical violence.

Screening for Food Insecurity in Six Veterans Administration Clinics for the Homeless, June-December 2015

OBJECTIVE

We assessed findings from a food-insecurity screening of a national sample of Veterans Administration clinics for homeless and formerly homeless veterans.

METHODS

We reviewed results from initial screenings administered at 6 Veterans Administration primary care clinics for the homeless and responses from clinic staff members interviewed about the screening program.

RESULTS

A total of 270 patients were screened. The average age was 53 years, and most were male (93.1%). Screening showed a high prevalence of food insecurity. Of the 270, 48.5% reported they experienced food insecurity in the previous 3 months, 55.0% reported averaging 2 meals a day, and 27.3% averaged 1 meal a day. Eighty-seven percent prepared their own meals, relying on food they bought (54.2%), help from friends and family (19.1%), and soup kitchens and food pantries (22%); 47.3% received Supplemental Nutrition Assistance Program benefits (food stamps). Additionally, of those who screened positive for food insecurity 19.8% had diabetes or prediabetes, and 43.5% reported hypoglycemia symptoms when without food. Clinic staff members responded positively to the screening program and described it as a good rapport builder with patients.

CONCLUSIONS

Integrating screening for food insecurity among patients in clinical settings was well received by both patients and health care providers. Addressing these positive findings of food insecurity requires a multidisciplinary health care approach.

Screening for Homelessness in the Veterans Health Administration: Monitoring Housing Stability through Repeat Screening

OBJECTIVE

This study examined veterans' responses to the Veterans Health Administration's (VHA's) universal screen for homelessness and risk of homelessness during the first 12 months of implementation.

METHODS

We calculated the baseline annual frequency of homelessness and risk of homelessness among all veterans who completed an initial screen during the study period. We measured changes in housing status among veterans who initially screened positive and then completed a follow-up screen, assessed factors associated with such changes, and identified distinct risk profiles of veterans who completed a follow-up screen.

RESULTS

More than 4 million veterans completed an initial screen; 1.8% (n=77,621) screened positive for homelessness or risk of homelessness. Of those who initially screened positive for either homelessness or risk of homelessness and who completed a second screen during the study period, 85.0% (n=15,060) resolved their housing instability prior to their second screen. Age, sex, race, VHA eligibility, and screening location were all associated with changes in housing stability. We identified four distinct risk profiles for veterans with ongoing housing instability.

CONCLUSION

To address homelessness among veterans, efforts should include increased and targeted engagement of veterans experiencing persistent housing instability.

Screening for homelessness among individuals initiating medication-assisted treatment for opioid use disorder in the Veterans Health Administration

OBJECTIVE

To determine the prevalence of homelessness and risk for homelessness among veterans with opioid use disorder initiating treatment.

SETTING

Addiction treatment programs operated by the US Department of Veterans Affairs (VA).

PARTICIPANTS

All veterans initiating treatment with methadone or buprenorphine for opioid use disorder between October 1, 2013 and September 30, 2014 (n = 2,699) who were administered the VA's national homelessness screener.

MAIN OUTCOME MEASURES

Self-reported homelessness or imminent risk of homelessness.

RESULTS

The prevalence of homelessness was 10.2 percent and 5.3 percent were at risk for homelessness. Compared to male veterans, women veterans were less likely to report homelessness (8.9 percent vs 10.3 percent) but more likely to be at risk (11.8 percent vs 4.9 percent). By age group, veterans aged 18-34 and 45-54 years most frequently reported homelessness (12.0 and 11.7 percent, respectively) and veterans aged 45-54 and 55-64 years most frequently reported risk for homelessness (6.5 and 6.8 percent, respectively).

CONCLUSIONS

The prevalence of homelessness in this population is approximately 10 times that of the general veteran population accessing care at VA. Screening identified a substantial number of veterans who could benefit from VA housing assistance and had not received it recently. Programs to address veteran homelessness should engage with veterans seeking addiction treatment. Integration of homelessness services into addiction treatment settings may, in turn, improve outcomes.

Comparative effectiveness of high-dose versus standard-dose influenza vaccination in community-dwelling veterans

BACKGROUND

Influenza is a significant cause of morbidity and mortality in older adults. High-dose (HD) trivalent inactivated vaccine has increased immunogenicity in older adults compared with standard-dose (SD) vaccine. We assessed the relative effectiveness of HD influenza vaccination (vs SD influenza vaccination).

METHODS

We conducted a retrospective cohort study among patients who receive primary care at Veteran Health Administration (VHA) medical centers, and who received influenza vaccine in the 2010-2011 influenza season. The primary outcome was hospitalization for influenza or pneumonia. We also conducted an analysis in subgroups defined by age.

RESULTS

We evaluated 25 714 patients who received HD vaccine and 139 511 who received SD vaccine in 23 VHA medical centers. The rate of hospitalization for influenza or pneumonia was 0.3% in both groups in the influenza season. After accounting for patient characteristics in propensity-adjusted analyses, the risk of hospitalization for influenza or pneumonia was not significantly lower among patients receiving HD vaccine vs those receiving SD vaccine (risk ratio, 0.98; 95% confidence interval, .68-1.40). In the subgroup of patients ≥85 years of age, receiving HD (compared with SD) vaccine was associated with lower rates of hospitalization for influenza or pneumonia.

CONCLUSIONS

HD vaccine was not found to be more effective than SD vaccine in protecting against hospitalization for influenza or pneumonia; however, we found a protective effect in the oldest subgroup of patients. Additional studies are needed to evaluate the effectiveness of HD vaccine.

Catalytic hydrodechlorination of trichloroethylene in water with supported CMC-stabilized palladium nanoparticles

In this work, we developed and tested a new class of supported Pd catalysts by immobilizing CMC (carboxymethyl cellulose) stabilized Pd nanoparticles onto alumina support. The alumina supported Pd nanoparticles were able to facilitate rapid and complete hydrodechlorination of TCE (trichloroethylene) without intermediate by-products detected. With a Pd mass loading of 0.33 wt% of the alumina mass, the observed pseudo first order reaction rate constant, k(obs), for the catalyst was increased from 28 to 109 L/min/g when CMC concentration was raised from 0.005 to 0.15 wt%. The activity increase was in accord with an increase of the Pd dispersion (measured via CO chemisorption) from 30.4% to 45.1%. Compared to the commercial alumina supported Pd, which has a lower Pd dispersion of 21%, our CMC-stabilized Pd nanoparticles offered more than 7 times greater activity. Pre-calcination treatment of the supported catalyst resulted in minor drop in activity, yet greatly reduced bleeding (<6%) of the Pd nanoparticles from the support during multiple cycles of applications. The presence of DOM (dissolved organic matter) at up to 10 mg/L as TOC had negligible effect on the catalytic activity. The alumina supported CMC-stabilized Pd nanoparticles may serve as a class of more effective catalysts for water treatment uses.

Synthesis and characterization of supported polysugar-stabilized palladium nanoparticle catalysts for enhanced hydrodechlorination of trichloroethylene

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer-Emmett-Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al(2)O(3) support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.

Supercritical Activity Restoration for Fischer Tropsch Synthesis

Previous research has demonstrated that supercritical phase Fischer Tropsch Synthesis (SC-FTS) using hexanes as the solvent medium offers superior activity maintenance to traditional fixed-bed (gas phase) Fischer Tropsch Synthesis (GP-FTS) (Elbashir et al., 2005). This has prompted an investigation into whether supercritical media can reactivate a catalyst used in GP-FTS. To that end, a study was conducted in which a series of GP-FTS experiments of approximately 2 days each were performed, separated by in situ periods of catalyst reactivation using supercritical hexanes as well as SC-FTS.It was found that the supercritical hexanes media and SC-FTS reactivation periods were effective in partially restoring lost catalyst activity and selectivity. GP-FTS was demonstrated to have detrimental effects on subsequent SC-FTS operation while SC-FTS operation showed beneficial effects on subsequent GP-FTS operation. Specifically, SC-FTS reactivations reduced the methane selectivity in subsequent GP-FTS periods. The CO2 selectivity in SC-FTS is consistently lower than that in GP-FTS, while the olefin selectivity into the diesel range is higher in SC-FTS. While the propagation probability was initially higher in SC-FTS than GP-FTS, the propagation probability values converged as the experiment progressed.

Characterization of gas-expanded liquid-deposited gold nanoparticle films on substrates of varying surface energy

Dodecanethiol-stabilized gold nanoparticles (AuNPs) were deposited via a gas-expanded liquid (GXL) technique utilizing CO(2)-expanded hexane onto substrates of different surface energy. The different surface energies were achieved by coating silicon (100) substrates with various organic self-assembled monolayers (SAMs). Following the deposition of AuNP films, the films were characterized to determine the effect of substrate surface energy on nanoparticle film deposition and growth. Interestingly, the critical surface tension of a given substrate does not directly describe nanoparticle film morphology. However, the results in this study indicate a shift between layer-by-layer and island film growth based on the critical surface tension of the capping ligand. Additionally, the fraction of surface area covered by the AuNP film decreases as the oleophobic nature of the surfaces increases. On the basis of this information, the potential exists to engineer nanoparticle films with desired morphologies and characteristics.

Size-selective fractionation of nanoparticles at an application scale using CO2 gas-expanded liquids

Size-based fractionation of nanoparticles remains a non-trivial task for the preparation of well-defined nanomaterials for certain applications and fundamental studies. Typical fractionation techniques prove to be inefficient for large nanoparticle quantities due to several factors including the expense of equipment, throughput constraints, and the amount of organic solvent waste produced. Through the use of the pressure-tunable physico-chemical properties of CO2-expanded liquids, a rapid, precise, and environmentally sustainable size-selective fractionation of ligand-stabilized nanoparticles is possible through simple variations in applied CO2 pressure. An apparatus capable of fractionating large quantities of nanoparticles into distinct fractions with the ability to control mean diameters and size distributions has been developed. This apparatus consists of three vertically mounted pressure vessels connected in series with needle valves. This process, at current design scales, operated at room temperature, and CO2 pressures between 0 and 50 bar, results in a batch size-selective fractionation of a concentrated nanoparticle dispersion. This paper presents this new apparatus and the separation results of various single pass fractionations as well as recursive fractionations.

Precise seed-mediated growth and size-controlled synthesis of palladium nanoparticles using a green chemistry approach

In this paper, we present a "green" and size-controlled seed-mediated growth method by which differently sized palladium (Pd) nanoparticles, spanning from 3.4 to 7.6 nm, with an increment of 1.4 nm, were synthesized. Monodisperse Pd nanoparticles (ca. 3.4 nm, standard deviation = 0.7 nm) were first synthesized and stabilized in an aqueous solution at 95 degrees C using nontoxic ascorbic acid and sodium carboxymethyl cellulose (CMC) as reducing agent and capping agent, respectively. These Pd nanoparticles were subsequently employed as seeds on the surface of which fresh Pd (2+) ions were reduced by the weak reducing agent ascorbic acid. Optimal conditions were determined that favored the homogeneous and sequential accumulation of Pd atoms on the surface of the Pd seeds, rather than the formation of new nucleation sites in the bulk growth solution, thereby achieving atomic-level control over particle sizes. The adsorbed CMC molecules did not inhibit the addition of Pd atoms onto the seeds during the growth but provided stabilization of the Pd nanoparticles in aqueous solution after the growth. Potential mechanisms that underpin this seed-mediated growth process are provided and discussed. One advantage of this seed growth process is that it provides stoichiometric control over the size of the Pd nanoparticles by simply varying Pd(2+) added during the growth stage. Furthermore, the use of ecologically friendly reagents, such as water (solvent), CMC (capping agent), and ascorbic acid (reducing agent), in both the seed synthesis and subsequent seed-mediated growth provides both "green" and economic attributes to this process.

A gas-expanded liquid nanoparticle deposition technique for reducing the adhesion of silicon microstructures

A gas-expanded liquid-based nanoparticle deposition technique was integrated with a critical point drying process to modify the surface of polysilicon microstructures in order to reduce the adhesion that ordinarily occurs due to dominant interfacial surface forces. Dodecanethiol-capped gold nanoparticles (AuNPs) were deposited onto arrays of cantilever beams using gas-expanded liquid technology in an effort to increase the surface roughness, thereby reducing the real contact surface area as well as changing the chemical constituents of the contacting areas. Both AuNP-coated and uncoated (native oxide surface) arrays were actuated electrostatically in order to determine the work of adhesion. The results of this study indicate that while cantilever beams with only their native oxide exhibit apparent adhesion energies of about 700 +/- 100 microJ m(-2), cantilever beam arrays coated with AuNPs exhibit an apparent adhesion energy of about 8 microJ m(-2) or less. These results indicate that metallic nanoparticle coatings can be successfully applied to micromachines and provide a drastic reduction in apparent adhesion energy.

Synaptic integration in hypothalamic gonadotropin releasing hormone (GnRH) neurons

The impact of the A-type GABA (GABA-A) receptor in gonadotropin releasing hormone (GnRH) neurons is controversial. In adult GnRH neurons, the GABA-A receptor conductance has been reported to either hyperpolarize or depolarize GnRH neurons. Regardless of whether GABA is inhibitory or excitatory in GnRH neurons, GABAergic input would be integrated with post-synaptic potentials generated by other synaptic inputs. We used dynamic current clamping and compartmental computer modeling to examine the integration of AMPA-type glutamatergic input and GABA-mediated input in both the hyperpolarizing (inhibitory) and depolarizing (excitatory) modes in GnRH neurons from transgenic mice (Mus Musculus) generated on a C57BL6 background. In both living and model neurons, action potentials were most likely a few ms after a maximum in AMPA conductance coincided with a minimum in inhibitory GABA. Excitatory GABA interacted differently with AMPA, with spikes most likely, in both dynamic clamping of living neurons and in model neurons, when a maximum in AMPA coincided with the decay from peak of a maximum in GABA. Distributing synapses along the dendrite maximized the temporal relationship between AMPA and GABA conductances and therefore, the potential for spiking. Thus, these two dominant neurotransmitters could interact in multiple frames to generate action potentials in GnRH neurons.

Dendrites determine the contribution of after depolarization potentials (ADPs) to generation of repetitive action potentials in hypothalamic gonadotropin releasing-hormone (GnRH) neurons

The impact of structure in modulating synaptic signals originating in dendrites is widely recognized. In this study, we focused on the impact of dendrite morphology on a local spike generating mechanism which has been implicated in hormone secretion, the after depolarization potential (ADP). Using multi-compartmental models of hypothalamic GnRH neurons, we systematically truncated dendrite length and determined the consequence on ADP amplitude and repetitive firing. Decreasing the length of the dendrite significantly increased the amplitude of the ADP and increased repetitive firing. These effects were observed in dendrites both with and without active conductances suggesting they largely reflect passive characteristics of the dendrite. In order to test the findings of the model, we performed whole-cell recordings in GnRH neurons and elicited ADPs using current injection. During recordings, neurons were filled with biocytin so that we could determine dendritic and total projection (dendrite plus axon) length. Neurons exhibited ADPs and increasing ADP amplitude was associated with decreasing dendrite length, in keeping with the predictions of the models. Thus, despite the relatively simple morphology of the GnRH neuron's dendrite, it can still exert a substantial impact on the final neuronal output.

Polysugar-stabilized Pd nanoparticles exhibiting high catalytic activities for hydrodechlorination of environmentally deleterious trichloroethylene

In this paper, we present a straightforward and environmentally friendly aqueous-phase synthesis of small Pd nanoparticles (approximately 2.4 nm under the best stabilization) by employing a "green", inexpensive, and biodegradable/biocompatible polysugar, sodium carboxymethylcellulose (CMC), as a capping agent. The Pd nanoparticles exhibited rather high catalytic activity (observed pseudo-first-order reaction kinetic rate constant, k(obs), is up to 828 L g(-1) min(-1)) for the hydrodechlorination of environmentally deleterious trichloroethene (TCE) in water. Fourier transform IR (FT-IR) spectra indicate that CMC molecules interact with the Pd nanoparticles via both carboxyl (-COO-) and hydroxyl (-OH) groups, thereby functioning to passivate the surface and suppress the growth of the Pd nanoparticles. Hydrodechlorination of TCE using differently sized CMC-capped Pd nanoparticles as catalyst was systematically investigated in this work. Both the catalytic activity (k(obs)) and the surface catalytic activity (turnover frequency, TOF) of these CMC-capped Pd nanoparticles for TCE degradation are highly size-dependent. This point was further verified by a comparison of the catalytic activities and surface catalytic activities of CMC-capped Pd nanoparticles with those of beta-D-glucose-capped Pd and neat Pd nanoparticles for TCE degradation.

Finely controlled size-selective precipitation and separation of CdSe/ZnS semiconductor nanocrystals using CO2-gas-expanded liquids

A technique was developed to size-selectively separate polydisperse dispersions of CdSe/ZnS nanocrystals into distinct color fractions using only the tunable solvent properties of CO2-expanded hexane. This size-selective precipitation of semiconductor nanoparticles is achieved by finely tuning the solvent strength of the CO2/hexane medium by simply adjusting the applied CO2 pressure. These subtle changes affect the balance between osmotic repulsive and van der Waals attractive forces, thereby allowing fractionation of the nanocrystals into multiple narrow size populations.

Solvent Effects on AOT Reverse Micelles in Liquid and Compressed Alkanes Investigated by Neutron Spin−Echo Spectroscopy

Neutron Spin-Echo (NSE) spectroscopy has been employed to study the interfacial properties of reverse micelles formed with the common surfactant sodium bis-2-ethylhexyl-sulfosuccinate (AOT) in liquid alkane solvents and compressed propane. NSE spectroscopy provides a means to measure small energy transfers for incident neutrons that correspond to thermal fluctuations on the nanosecond time scale and has been applied to the study of colloidal systems. NSE offers the unique ability to perform dynamic measurements of thermally induced shape fluctuation in the AOT surfactant monolayer. This study investigates the effects of the bulk solvent properties, water content, and the addition of octanol cosurfactant on the bending elasticity of AOT reverse micelles and the reverse micelle dynamics. By altering these solvent properties, specific trends in the bending elasticity constant, k, are observed where increasing k corresponds to an increase in micelle rigidity and a decrease in intermicellar exchange rate, k(ex). The observed corresponding trends in k and k(ex) are significant in relating the dynamics of microemulsions and their application as a reaction media. Compressed propane was also examined for the first time with a high-pressure, compressible bulk solvent where variations in temperature and pressure are used to tune the properties of the bulk phase. A decrease in the bending elasticity is observed for the d-propane/AOT/W = 8 reverse micelle system by simultaneously increasing the temperature and pressure, maintaining constant density. With isopycnic conditions, a constant translational diffusion of the reverse micelles through the bulk phase is observed, conforming to the Stokes-Einstein relationship.

Synthesis and Steric Stabilization of Silver Nanoparticles in Neat Carbon Dioxide Solvent Using Fluorine-Free Compounds

The adjustable solvent properties, vanishingly low surface tensions, and environmentally green characteristics of supercritical carbon dioxide present certain advantages in nanoparticles synthesis and processing. Unfortunately, most current techniques employed to synthesize and disperse nanoparticles in carbon dioxide use environmentally persistent fluorinated compounds as metal precursors and/or stabilizing ligands. This paper illustrates a one-step process for synthesis and stabilization of silver nanoparticles in carbon dioxide using only fluorine-free compounds. Isostearic acid coated silver nanoaparticles were formed and stably dispersed through arrested precipitation. Silver bis(3,5,5-trimethyl-1-hexyl)sulfosuccinate (Ag-AOT-TMH) was reduced in the presence of isostearic acid as a capping ligand in carbon dioxide solvent to form silver nanoparticles. The addition of cyclohexane as cosolvent or an increase in carbon dioxide solvent density enhances the dispersibility of the particles due to an increase in solvent strength. The dispersibility of the isostearic acid capped silver nanoparticles diminished with time until a stable dispersion was achieved due to the precipitation of a fraction of particle sizes too large to be stabilized by the solvent medium, thereby leaving a smaller size fraction of nanoparticles stably dispersed in the CO2 mixtures. This paper presents the one-step synthesis and stabilization of metallic nanoparticles in neat carbon dioxide without the aid of any fluorinated compounds.

Synthesis and extraction of beta-D-glucose-stabilized Au nanoparticles processed into low-defect, wide-area thin films and ordered arrays using CO2-expanded liquids

This letter presents a straightforward and economic strategy to create aqueous Au nanoparticle dispersions using small amounts of beta-D-glucose as a "green" alternative to the conventional phase-transfer catalyst approach. Furthermore, this new process provides for efficient extraction of these monodisperse Au nanoparticles into an organic phase that was successfully processed into wide-area, locally ordered nanoparticle arrays and thin films using a precisely controlled CO2-expanded liquid particle deposition technique. This CO2-based technique allows for pressure-tunable particle deposition while eliminating the detrimental surface tension and dewetting effects common to normal solvent-evaporation techniques.

Dendritic processing of excitatory synaptic input in hypothalamic gonadotropin releasing-hormone neurons

The activity of hypothalamic GnRH neurons results in the intermittent release of GnRH required for reproductive function. This intermittent neurosecretory activity has been proposed to reflect integration of intrinsic properties of and synaptic input to GnRH neurons. Determining the relative impact of synaptic inputs at different locations on the GnRH neuron is difficult, if not impossible, using only experimental approaches. Thus, we used electrophysiological recordings and neuronal reconstructions to generate computer models of GnRH neurons to examine the effects of synaptic inputs at varying distances from the soma along dendrites. The parameters of the models were adjusted to duplicate measured passive and active electrophysiology of cells from mouse brain slices. Our morphological findings reinforce the emerging picture of a complex dendritic structure of GnRH neurons. Furthermore, analysis of reduced morphology models indicated that this population of cells is unlikely to exhibit low-frequency tonic spiking in the absence of synaptic input. Finally, applying realistic patterns of synaptic input to modeled GnRH neurons indicates that synapses located more than about 30% of the average dendrite length from the soma cannot drive firing at frequencies consistent with neuropeptide release. Thus, processing of synaptic input to dendrites of GnRH neurons is probably more complex than simple summation.

Stable dispersions of silver nanoparticles in carbon dioxide with fluorine-free ligands

Iso-stearic acid, a short, stubby compound with branched, methylated tails has been shown to have high solubility in carbon dioxide. Tail solvation by carbon dioxide makes iso-stearic acid a good choice for use as a ligand to sterically stabilize metallic nanoparticles. Iso-stearic acid coated silver nanoparticles have been stably dispersed in carbon dioxide with hexane cosolvent. Neat carbon dioxide has successfully dispersed iso-stearic acid coated silver nanoparticles that had been deposited on either quartz or polystyrene surfaces. These results are the first reports of sterically stabilized nanoparticles in carbon dioxide without the use of any fluorinated compounds.

Tunable Solvation Effects on the Size-Selective Fractionation of Metal Nanoparticles in CO2 Gas-Expanded Solvents

This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process.

Oxygenated Hydrocarbon Ionic Surfactants Exhibit CO2 Solubility

Several oxygenated hydrocarbons, including acetylated sugars, poly(propylene glycol), and oligo(vinyl acetate), have been used to generate CO2-soluble ionic surfactants. Surfactants with vinyl acetate tails yielded the most promising results, exhibiting levels of CO2 solubility comparable to those associated with fluorinated ionic surfactants. For example, a sodium sulfate with single, oligomeric vinyl acetate (VAc) tails consisting of 10 VAc repeat units was 7 wt % soluble in CO2 at 25 degrees C and 48 MPa. Upon introduction of water to these systems, only surfactants with the oligomeric vinyl acetate tails exhibited spectroscopic evidence of a polar environment that was capable of solubilizing the methyl orange into the CO2-rich phase. For example, a single-phase solution of CO2, 0.15 wt % sodium bis(vinyl acetate)8 sulfosuccinate, and water, at water loading (W) values ranging from 10 to 40 at 25 degrees C and 34.5 MPa, exhibited a methyl orange peak at 423 nm. This result indicated that the core of a reverse micelle provided a microenvironment with a polarity similar to that of methanol. Quantum chemical calculations indicate that the acetylated sugars may be too hydrophilic to readily form reverse micelles, whereas the VAc-based surfactants appear to have the correct balance of hydrophilic and hydrophobic forces necessary to form reverse micelles.

Chloride ion effects on synthesis and directed assembly of copper nanoparticles in liquid and compressed alkane microemulsions

Microemulsions are effective media for solution-based synthesis of metallic nanoparticles where surfactants and other ionic species influence the directed assembly of the nanomaterials with specific sizes, geometries, and compositions. This study demonstrates the effects of chloride ion on the synthesis of copper nanoparticles within the sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelle system utilizing both liquid isooctane and compressed propane as the bulk solvent. Copper nanoparticle synthesis can be achieved in the presence of HCl in the micelle core, taking advantage of the buffering action of the AOT surfactant. The concentration of chloride ions influence the particle growth rate and dispersion in liquid isooctane. The presence of chloride ions during particle synthesis in compressed propane has a significant effect on the geometry and structure of the copper nanomaterials produced. Chloride ion addition to the compressed propane/Cu(AOT)(2)-AOT/water reverse micelle system at 20 degrees C and 310 bar results in the formation of diamond-shaped copper nanoparticle assemblies. The copper nanoparticle assemblies exhibit unique structure and retain this structure through repeated solvent processing steps, allowing separation and recovery of the assembled diamond-shaped copper nanoparticle structures.

CO2-expanded liquid deposition of ligand-stabilized nanoparticles as uniform, wide-area nanoparticle films

Deposition of nanoparticles into uniform, wide-area thin films using CO(2) as an antisolvent is presented. Ligand-stabilized silver particles are controllably precipitated from organic solvents by pressurizing and expanding the solution with carbon dioxide. Subsequent addition of carbon dioxide as a dense supercritical fluid provides for removal of the organic solvent while avoiding the surface tensions common to evaporating solvents that are detrimental to nanoscale assemblies and structures. This brand new CO(2)-expanded liquid particle deposition technique allows for the targeted deposition of particles and results in more uniform and lower defect metal nanoparticle thin films than are provided by conventional solvent evaporation techniques.