Electrospinning of Aqueous Solutions of Atactic Poly(N-isopropylacrylamide) with Physical Gelation.

The phase diagram of a given polymer solution is used to determine the solution's electrospinnability. We constructed a phase diagram of an aqueous solution of atactic poly(N-isopropylacrylamide) (a-PNIPAM) based on turbidity measurements and the rheological properties derived from linear viscoelasticity. Several important transition temperatures were obtained and discussed, including the onset temperature for concentration fluctuations T1, gel temperature Tgel, and binodal temperature Tb. On heating from 15 °C, the one-phase a-PNIPAM solution underwent pronounced concentration fluctuations at temperatures above T1. At higher temperatures, the thermal concentration fluctuations subsequently triggered the physical gelation process to develop a macroscopic-scale gel network at Tgel before the phase separation at Tb. Thus, the temperature sequence for the transition is: T1 < Tgel < Tb~31 °C for a given a-PNIPAM aqueous solution. Based on the phase diagram, a low-temperature electrospinning process was designed to successfully obtain uniform a-PNIPAM nanofibers by controlling the solution temperature below T1. In addition, the electrospinning of an a-PNIPAM hydrogel at Tgel < T < Tb was found to be feasible considering that the elastic modulus of the gel was shown to be very low (ca. 10−20 Pa); however, at the jet end, jet whipping was not seen, though the spitting out of the internal structures was observed with high-speed video. In this case, not only dried nanofibers but also some by-products were produced. At T > Tb, electrospinning became problematic for the phase-separated gel because the enhanced gel elasticity dramatically resisted the stretching forces induced by the electric field.

An unusual cause of atrial fibrillation in a young active duty soldier.

Coronary artery fistula (CAF) is an abnormality in which the coronary artery has an anomalous connection with a venous structure such as the coronary sinus or atrium. CAF is usually congenital, but may be acquired. The prevalence in the general population is low with many asymptomatic and discovered incidentally. When symptomatic, CAF may present with dyspnea, decreasing functional capacity, and/or arrhythmia. We report a case of a young otherwise healthy active duty male with progressive symptoms of dizziness and exertional fatigue with paroxysmal atrial fibrillation. An electrically negative, but symptomatically positive stress test led to further workup with coronary computed tomography angiogram, which unexpectedly revealed large coronary fistulas between the aneurysmal right coronary artery and coronary sinus and the dilated left circumflex artery with probable collateralization to the coronary sinus. Cardiac magnetic resonance imaging and cardiac catheterization supported these findings and demonstrated no evidence of significant shunting.

Self-assembled hemispherical nanowell arrays for superhydrophobic antireflection coatings.

The present study reports an inexpensive and simple bottom-up technology for fabricating superhydrophobic antireflection coatings with highly ordered hemispherical nanowell structures, which are assembled by a scalable Langmuir-Blodgett technology. The subwavelength gratings lead to a gradual change in the effective refractive index, substantially suppressing specular reflection over the entire visible wavelength range. After surface modification with fluorinated silane, the resulting nanowell arrays exhibit superhydrophobic surface with high static water contact angle (154°) and low water contact angle hysteresis (7°). The experimental results on the wettability can be qualitatively interpreted by adopting the Cassie's dewetting model. Moreover, the effect of the nanowell shape on the antireflective and superhydrophobic properties has also been investigated in the study.