Convective flow reversal in self-powered enzyme micropumps.

Surface-bound enzymes can act as pumps that drive large-scale fluid flows in the presence of their substrates or promoters. Thus, enzymatic catalysis can be harnessed for "on demand" pumping in nano- and microfluidic devices powered by an intrinsic energy source. The mechanisms controlling the pumping have not, however, been completely elucidated. Herein, we combine theory and experiments to demonstrate a previously unreported spatiotemporal variation in pumping behavior in urease-based pumps and uncover the mechanisms behind these dynamics. We developed a theoretical model for the transduction of chemical energy into mechanical fluid flow in these systems, capturing buoyancy effects due to the solution containing nonuniform concentrations of substrate and product. We find that the qualitative features of the flow depend on the ratios of diffusivities δ=D(P)/D(S) and expansion coefficients ß=ß(P)/ß(S) of the reaction substrate (S) and product (P). If δ>1 and δ>ß (or if δ<1 and δ<ß ), an unexpected phenomenon arises: the flow direction reverses with time and distance from the pump. Our experimental results are in qualitative agreement with the model and show that both the speed and direction of fluid pumping (i) depend on the enzyme activity and coverage, (ii) vary with the distance from the pump, and (iii) evolve with time. These findings permit the rational design of enzymatic pumps that accurately control the direction and speed of fluid flow without external power sources, enabling effective, self-powered fluidic devices.

Factors affecting patients' functional status and their impact on outcomes of ruptured abdominal aortic aneurysms.

OBJECTIVE: Despite advances in surgical techniques, ruptured abdominal aortic aneurysm (rAAA) remains associated with extremely high mortality. Several preoperative risk factors have been shown to predict poor prognosis after rAAA repair. Notably, a preoperative dependent functional status has previously been shown to be associated with poor outcomes after several vascular surgery procedures. The purpose of this study was to examine the effect of preoperative functional status on postoperative outcomes for patients undergoing repair of rAAA. METHODS: Patients with rAAA were identified in the American College of Surgeons National Surgical Quality Improvement Program database for the year 2013. The patients' demographics, procedural data, and postoperative outcomes were analyzed. Patients were then divided into two groups: dependent functional status and independent functional status. Preoperative variables and outcomes were compared between these two groups. A multivariate logistic regression analysis was then conducted to assess independent risk factors that predispose to dependent functional status. RESULTS: A total of 1239 patients underwent repair of rAAAs. Of these, 34 patients did not have a recorded functional status. The total number of patients analyzed was therefore 1205 (male, 78%; female; 22%; group I, dependent functional status, n = 62 [5%]; group II, independent functional status, n = 1143 [95%]). Bivariate analysis identified the following variables as having a significant association with dependent functional status: age >80 years (odds ratio [OR], 8.70; confidence interval [CI] 1.18-64.43; P = .002), female sex (OR, 2.89; CI, 1.71-4.87; P < .001), dyspnea (OR, 3.77; CI, 2.0-7.13; P < .001), dialysis (OR, 7.55; CI, 3.21-17.73; P < .001), insulin-dependent diabetes mellitus (vs nondiabetic: OR, 3.76; CI, 1.39-10.21; P = .033), current smoker (OR, 0.41; CI, 0.22-0.77; P = .005), and hypertension (OR, 2.86; CI, 1.4-5.87; P = .004). Preoperative functional status had no effect on the following postoperative outcomes: surgical site infection, cardiac arrest, unplanned intubation, readmission, return to the operating room, and death. Dependent functional status was associated with increased length of hospital stay (group I, median of 10 days; group II, median of 7 days). CONCLUSIONS: Dependent functional status is considered to be strongly associated with poor outcomes after surgical operations. Our study shows that functional status has little or no bearing on the outcomes of operations for rAAA and that preoperative dialysis, female sex, advanced age, and dyspnea are strong predictors of dependent functional status. Dependent functional status should not be used to exclude patients with rAAA from being offered surgical treatment.

Normalcy in Post-operative Period After Bilateral IJV Ligation: A Rare Case Report.

Ligation of bilateral IJV causes interruption of major part of venous drainage from Dural venous sinuses that causes complications such as gross facial edema, increased intracranial pressure, brain compression, coma and even death increasing the morbidity and mortality post-operatively. This case report illustrates a case of normalcy noted in post-operative period in a patient after ligation of bilateral IJV in left lower alveolus cancer.

Neurofibroma at unusual locations: report of two cases in teenage girls.

Solitary neurofibromas are rare occurrence in salivary gland region as well as mons pubis of females. We present two cases of teenage girls with swelling in parotid region and mons pubis. Fine needle aspiration cytology was inconclusive in both cases. They were both managed surgically and a diagnosis of neurofibroma was ascertained histopathologically and also confirmed with S-100 immunohistochemistry. The patients were followed up for a period of six months, however, no recurrence was noted. Though, one patient had a previous history of recurrence. We report these cases in view of their rarity of site and age as well as no correlation with neurofibromatosis and clitoromegaly.

Self-powered enzyme micropumps.

Non-mechanical nano- and microscale pumps that function without the aid of an external power source and provide precise control over the flow rate in response to specific signals are needed for the development of new autonomous nano- and microscale systems. Here we show that surface-immobilized enzymes that are independent of adenosine triphosphate function as self-powered micropumps in the presence of their respective substrates. In the four cases studied (catalase, lipase, urease and glucose oxidase), the flow is driven by a gradient in fluid density generated by the enzymatic reaction. The pumping velocity increases with increasing substrate concentration and reaction rate. These rechargeable pumps can be triggered by the presence of specific analytes, which enables the design of enzyme-based devices that act both as sensor and pump. Finally, we show proof-of-concept enzyme-powered devices that autonomously deliver small molecules and proteins in response to specific chemical stimuli, including the release of insulin in response to glucose.