Constrained Window Design in Projection Stereolithography for Continuous Three-Dimensional Printing.

Although continuous projection Stereolithography (SL) printing is one of the next-generation ultra-fast additive manufacturing (AM) processes, its current constrained window design of the resin vat is suffering from many challenges, such as the complex control mechanism and limited hardware lifetime. In this article, we investigate a novel constrained window design, namely Island Window (IW), for the continuous three-dimensional (3D) printing by using the projection SL process. The proposed IW window has a highly oxygen-permeable polydimethylsiloxane membrane onto the laser-machined acrylic vat frame, which allows the formation of an effective liquid interface (>200 µm oxygen inhibition layer) to enable the continuous projection SL process. Experimental results verified the feasibility of the window design for extending the maximum printing time (increased by up to 73%) due to the enhanced oxygen concentration. It was also found that the maximum printing speed for producing parts with a smooth surface (Rz <30 µm) can be as high as 90 mm/h, which is comparable to the speeds in recently reported continuous SL processes. In addition, a variety of parts were successfully fabricated through continuous 3D printing by using the proposed IW design, implying tremendous promise for future low-cost, high-resolution, easy-controlled, and ultra-fast AM processes.

Medium-retaining Petri dish insert to grow and image cultured cells.

BACKGROUND: Microscope chambers that accept glass coverslips with cultured cells are often used to monitor intracellular Ca2+ concentration ([Ca2+]i) during cell superfusion. Unfortunately, the experimental maneuvers associated with the coverslip installation in these chambers (medium removal and re-application) trigger unintended [Ca2+]i elevations. NEW METHOD: To prevent these [Ca2+]i elevations, a Petri dish insert has been constructed. The insert features a superfusion-optimized well to grow cell cultures. After this insert is removed from the Petri dish, the well retains the medium. This feature allows the inserts to be installed in microscope chambers while keeping the cells submerged at all times. RESULTS: These inserts were used to test the impact of a transient medium removal from the well (an equivalent of a coverslip removal from the medium) on [Ca2+]i in primary murine cortical neurons and astrocytes, and in HEK-293 cells. In all of these models, the medium removal/re-application caused a micromolar [Ca2+]i spike. While in neurons this spike was caused by a Ca2+ influx, in astrocytes and HEK-293 cells, it was caused by a Ca2+ release from intracellular stores. After the spike, a subpopulation of neurons failed to restore low [Ca2+]i; in 24% of the astrocytes, the spike triggered [Ca2+]i oscillations. However, prior to the spike, [Ca2+]i was low and uniform in all these cells. COMPARISON WITH EXISTING METHOD(S): The new method avoids the artificially-induced [Ca2+]i elevations that take place during the handling of glass coverslips with cultured cells. CONCLUSIONS: The new method allows monitoring [Ca2+]i without disturbing the basal [Ca2+]i levels.

Comparisons between membrane, bridge and cantilever miniaturized resistive vacuum gauges.

Using bulk micromachining, meander-shaped resistor elements consisting of 20 nm Cr and 200 nm Au were fabricated on 1 µm thick silicon nitride membranes, bridges, and cantilevers. The resistance change as a function of pressure depends strongly on the thermal resistance of the two metal lines connecting the heated resistor to the silicon bulk (cold junction) and on the thermal resistance of the silicon nitride. Relative resistance changes ranging from about 3% (small membrane) to 20% (bridge) per mW of input power were obtained when operating the devices in constant voltage mode. The pressure where maximum sensitivity of these gauges occurs depends on the distance 'd' between the periphery of the heated resistor element and the silicon cold junction. Devices with 'd' ranging from 50 µm to 1,200 µm were fabricated. Assuming that pressures can be reliably measured above the 10% and below the 90% points of the resistance versus pressure curve, the range of these devices is about two orders of magnitude. By integrating two devices, one with d = 65 µm and one with d = 1,200 µm on the same chip and connecting them in series, the range can be increased by about a factor of three. By fabricating the cantilever devices so that they curl upon release, it will be shown that these devices also exhibit larger range due to varying 'd'.

Assessing graduate student progress in engineering ethics.

Under a grant from the National Science Foundation, the authors (and others) undertook to integrate ethics into graduate engineering classes at three universities-and to assess success in a way allowing comparison across classes (and institutions). This paper describes the attempt to carry out that assessment. Standard methods of assessment turned out to demand too much class time. Under pressure from instructors, the authors developed an alternative method that is both specific in content to individual classes and allows comparison across classes. Results are statistically significant for ethical sensitivity and knowledge. They show measurable improvement in a single semester.