ELECTROKINETIC PARTICLE MANIPULATIONS IN SPIRAL MICROCHANNELS

Recent developments in the field of microfluidics have created a multitude of new useful techniques for practical particle and cellular assays. Among them is the use of dielectrophoretic forces in \u27lab-on-a-chip\u27 devices. This sub-domain of electrokinetic flow is particularly popular due to its advantages in simplicity and versatility. This thesis makes use of dielectrophoretic particle manipulations in three distinct spiral microchannels. In the first of these experiments, we demonstrate the utility of a novel single-spiral curved microchannel with a single inlet reservoir and a single outlet reservoir for the continuous focusing and filtration of particles. The insulator-based negative-dielectrophoretic (repulsive) force is used in a parametric study of the effects of electric field strength, particle size, and solution concentration on particle focusing abilities. It was summarily determined that all three factors are positively correlated with increased particle focusing ability. From these results, a partial filtration of 10 μm particles from a binary solution of 3 and 10 μm particles was demonstrated. Also observed was a balance between dielectrophoretic and repulsive particle-wall interactions; thus yielding a novel approach for particle manipulation. Following the results of the first, we demonstrate in the second experiment a continuous-flow electrokinetic separation of both a binary mixture and a ternary mixture of colloidal particles based on size in a single-spiral microchannel with a single inlet reservoir and triple outlet reservoirs. This method also utilizes both curvature-induced dielectrophoresis to focus particles to a tight stream and the previously observed wall-induced electric lift to manipulate the aligned particles to size-dependent equilibrium positions. Due to the continuous nature of the flow through concentric spiral loops, both focusing forces influence particles simultaneously. This novel technique is useful for its compact geometry, robust structure, ease of manufacture, and ease of use in the manipulation of independent particle species. A theoretical model is also developed to understand this separation, and the obtained analytical formula predicts the experimentally measured particle center-wall distance in the spiral with a close agreement. We demonstrate in the third experiment a continuous-flow electrical sorting of spherical and peanut-shaped particles of similar volumes in an asymmetric double-spiral microchannel with a single inlet reservoir and triple outlet reservoirs. This experiment, unlike the first two, differentiates particle species based principally on shape. Shape is an intrinsic marker of cell cycle, an important factor for identifying a bio-particle, and also a useful indicator of cell state for disease diagnostics; therefore, shape can be a specific marker in label-free particle and cell separation for various chemical and biological applications. The double-spiral geometry exploits curvature-induced dielectrophoresis to initially focus particles to a tight stream in the first spiral without any sheath flow. Particles are subsequently displaced to shape-dependent flow paths in the second spiral without any external force. We also develop a numerical model to simulate and understand this shape-based particle sorting in spiral microchannels. The predicted particle trajectories agree qualitatively with the experimental observation

Viscoelastic effects on electrokinetic particle focusing in a constricted microchannel

Focusing suspended particles in a fluid into a single file is often necessary prior to continuous-flow detection, analysis, and separation. Electrokinetic particle focusing has been demonstrated in constricted microchannels by the use of the constriction-induced dielectrophoresis. However, previous studies on this subject have been limited to Newtonian fluids only. We report in this paper an experimental investigation of the viscoelastic effects on electrokinetic particle focusing in non-Newtonian polyethylene oxide solutions through a constricted microchannel. The width of the focused particle stream is found NOT to decrease with the increase in DC electric field, which is different from that in Newtonian fluids. Moreover, particle aggregations are observed at relatively high electric fields to first form inside the constriction. They can then either move forward and exit the constriction in an explosive mode or roll back to the constriction entrance for further accumulations. These unexpected phenomena are distinct from the findings in our earlier paper [Lu et al., Biomicrofluidics 8, 021802 (2014)], where particles are observed to oscillate inside the constriction and not to pass through until a chain of sufficient length is formed. They are speculated to be a consequence of the fluid viscoelasticity effects. (c) 2015 AIP Publishing LLC

Microfluidic Electrical Sorting of Particles Based on Shape in a Spiral Microchannel

Shape is an intrinsic marker of cell cycle, an important factor for identifying a bioparticle, and also a useful indicator of cell state for disease diagnostics. Therefore, shape can be a specific marker in label-free particle and cell separation for various chemical and biological applications. We demonstrate in this work a continuous-flow electrical sorting of spherical and peanut-shaped particles of similar volumes in an asymmetric double-spiral microchannel. It exploits curvature-induced dielectrophoresis to focus particles to a tight stream in the first spiral without any sheath flow and subsequently displace them to shape-dependent flow paths in the second spiral without any external force. We also develop a numerical model to simulate and understand this shape-based particle sorting in spiral microchannels. The predicted particle trajectories agree qualitatively with the experimental observation. (C) 2014 AIP Publishing LLC

Systemic anticoagulation in the setting of vascular extremity trauma

Introduction There is conflicting data regarding if patients with vascular extremity trauma who undergo surgical treatment need to be systematically anticoagulated. We hypothesized that intraoperative systemic anticoagulation (ISA) decreased the risk of repair thrombosis or limb amputation after traumatic vascular injury of the extremities. Methods We analyzed a composite risk of repair thrombosis and/or limb amputation (RTLA) between patients who did and did not undergo ISA during arterial injury repair. Patient data was collected in the American Association for the Surgery of Trauma PROspective Vascular Injury Treatment (PROOVIT) registry. This registry contains demographic, diagnostic, treatment, and outcome data. Results Between February 2013 and August 2015, 193 patients with upper or lower extremity arterial injuries who underwent open operative repair were entered into the PROOVIT registry. The majority were male (87%) with a mean age of 32.6 years (range 4–91) and 74% injured by penetrating mechanism. 63% of the injuries were described as arterial transection and 37% had concomitant venous injury. 62% of patients underwent ISA. RTLA occurred in 22 patients (11%) overall, with no significant difference in these outcomes between patients who received ISA and those that did not (10% vs. 14%, p = 0.6). There was, however, significantly higher total blood product use noted among patients treated with ISA versus those that did not receive ISA (median 3 units vs. 1 unit, p = 0.002). Patients treated with ISA also stayed longer in the ICU (median 3 days vs. 1 day, p = 0.001) and hospital (median 9.5 days vs. 6 days, p = 0.01). Discussion In this multicenter prospective cohort, intraoperative systemic anticoagulation was not associated with a difference in rate of repair thrombosis or limb loss; but was associated with an increase in blood product requirements and prolonged hospital stay. Our data suggest there is no significant difference in outcome to support use of ISA for repair of traumatic arterial injuries

Risk Factors Associated With Severe Hypoglycemia in Older Adults With Type 1 Diabetes

OBJECTIVE Severe hypoglycemia is common in older adults with long-standing type 1 diabetes, but little is known about factors associated with its occurrence

Prospective Study Examining Clinical Outcomes Associated with a Negative Pressure Wound Therapy System and Barker’s Vacuum Packing Technique

Background The open abdomen has become a common procedure in the management of complex abdominal problems and has improved patient survival. The method of temporary abdominal closure (TAC) may play a role in patient outcome. Methods A prospective, observational, open-label study was performed to evaluate two TAC techniques in surgical and trauma patients requiring open abdomen management: Barker’s vacuum-packing technique (BVPT) and the ABTheraTM open abdomen negative pressure therapy system (NPWT). Study endpoints were days to and rate of 30-day primary fascial closure (PFC) and 30-day all-cause mortality. Results Altogether, 280 patients were enrolled from 20 study sites. Among them, 168 patients underwent at least 48 hours of consistent TAC therapy (111 NPWT, 57 BVPT). The two study groups were well matched demographically. Median days to PFC were 9 days for NPWT versus 12 days for BVPT (p = 0.12). The 30-day PFC rate was 69 % for NPWT and 51 % for BVPT (p = 0.03). The 30-day all-cause mortality was 14 % for NPWT and 30 % for BVPT (p = 0.01). Multivariate logistic regression analysis identified that patients treated with NPWT were significantly more likely to survive than the BVPT patients [odds ratio 3.17 (95 % confidence interval 1.22–8.26); p = 0.02] after controlling for age, severity of illness, and cumulative fluid administration. Conclusions Active NPWT is associated with significantly higher 30-day PFC rates and lower 30-day all-cause mortality among patients who require an open abdomen for at least 48 h during treatment for critical illness

Proceedings of the 3rd Biennial Conference of the Society for Implementation Research Collaboration (SIRC) 2015: advancing efficient methodologies through community partnerships and team science

It is well documented that the majority of adults, children and families in need of evidence-based behavioral health interventionsi do not receive them [1, 2] and that few robust empirically supported methods for implementing evidence-based practices (EBPs) exist. The Society for Implementation Research Collaboration (SIRC) represents a burgeoning effort to advance the innovation and rigor of implementation research and is uniquely focused on bringing together researchers and stakeholders committed to evaluating the implementation of complex evidence-based behavioral health interventions. Through its diverse activities and membership, SIRC aims to foster the promise of implementation research to better serve the behavioral health needs of the population by identifying rigorous, relevant, and efficient strategies that successfully transfer scientific evidence to clinical knowledge for use in real world settings [3]. SIRC began as a National Institute of Mental Health (NIMH)-funded conference series in 2010 (previously titled the “Seattle Implementation Research Conference”; $150,000 USD for 3 conferences in 2011, 2013, and 2015) with the recognition that there were multiple researchers and stakeholdersi working in parallel on innovative implementation science projects in behavioral health, but that formal channels for communicating and collaborating with one another were relatively unavailable. There was a significant need for a forum within which implementation researchers and stakeholders could learn from one another, refine approaches to science and practice, and develop an implementation research agenda using common measures, methods, and research principles to improve both the frequency and quality with which behavioral health treatment implementation is evaluated. SIRC’s membership growth is a testament to this identified need with more than 1000 members from 2011 to the present.ii SIRC’s primary objectives are to: (1) foster communication and collaboration across diverse groups, including implementation researchers, intermediariesi, as well as community stakeholders (SIRC uses the term “EBP champions” for these groups) – and to do so across multiple career levels (e.g., students, early career faculty, established investigators); and (2) enhance and disseminate rigorous measures and methodologies for implementing EBPs and evaluating EBP implementation efforts. These objectives are well aligned with Glasgow and colleagues’ [4] five core tenets deemed critical for advancing implementation science: collaboration, efficiency and speed, rigor and relevance, improved capacity, and cumulative knowledge. SIRC advances these objectives and tenets through in-person conferences, which bring together multidisciplinary implementation researchers and those implementing evidence-based behavioral health interventions in the community to share their work and create professional connections and collaborations

A calorimetric study of the magnetic ordering of microcrystalline nickelous oxide

Vita.A calorimetric study of a finely divided NiO powder sample was carried out in order to investigate its magnetic ordering. Two different adiabatic calorimeters were built and test on calorimetric standard samples. The heat capacities of bulk-like NiO and a fine powder sample which exhibits an anomalously large paramagnetic susceptibility in the temperature range of interest were then measured. The magnetic heat capacity of the fine powder sample was obtained by analysis of the difference in their heat capacities and the magnetic entropy computed. The size of this magnetic entropy is consistent with the view that some of the nickel atoms on the surface of the particles undergo a magnetic order-disorder phase transition. The possibility of superparamagnetic ordering in this sample is not excluded but the magnetic entropy is too small to be the result of an order-disorder transition of a significant portion of the whole particles in the sample