Collagen-based scaffolds are gaining more prominence in the field of tissue engineering. However, readily available collagen scaffolds either lack the rigid structure (hydrogels) and/or the organization (biopapers) seen in many organ tissues, such as the cornea and meniscus. Direct-write electrospinning is a promising potential additive manufacturing technique for constructing highly ordered fibrous scaffolds for tissue engineering and foundational studies in cellular behavior, but requires specific process parameters (voltage, relative humidity, solvent) in order to produce organized structures depending on the polymer chosen. To date, no work has been done to optimize direct-write electrospinning parameters for use with pure collagen. In this work, a custom electrospinning 3D printer was constructed to derive optimal direct write electrospinning parameters (voltage, relative humidity and acetic acid concentrations) for pure collagen. A LabVIEW program was built to automate control of the print stage. Relative humidity and electrospinning current were monitored in real-time to determine the impact on fiber morphology. Fiber orientation was analyzed via a newly defined parameter (spin quality ratio (SQR)). Finally, tensile tests were performed on electrospun fibrous mats as a proof of concept.

We have recently made advancements in a linear electrodynamic quadrupole (LEQ) device for capturing and levitating either single or multiple micro-particles that provides significant improvements in capture efficiency, reliability, and optical measurement access. We have used our LEQ to trap particles ranging from 30 to less than 0.5 μm in size and provide a controlled environment to study particle physical/chemical dependencies on temperature, relative humidity, and gas constituents. To demonstrate this approach, we present data and analysis of liquid-droplet evaporation rates for two materials: glycerol and dibutyl sebacate. Droplet size was monitored as a function of time by two independent optical methods: direct imaging and fixed-angle light scattering. This new approach provides a means to rapidly characterize a wide range of aerosol particle properties and a platform for development of new aerosol optical-diagnostic measurements.

We compared response patterns and electrical receptive fields (ERF) of retinal ganglion cells (RGCs) during epiretinal and subretinal electrical stimulation of isolated mouse retina. Retinas were stimulated with an array of 3200 independently controllable electrodes. Four response patterns were observed: a burst of activity immediately after stimulation (Type I cells, Vision Research (2008), 48, 1562–1568), delayed bursts beginning >25 ms after stimulation (Type II), a combination of both (Type III), and inhibition of ongoing spike activity. Type I responses were produced more often by epiretinal than subretinal stimulation whereas delayed and inhibitory responses were evoked more frequently by subretinal stimulation. Response latencies were significantly shorter with epiretinal than subretinal stimulation. These data suggest that subretinal stimulation is more effective at activating intraretinal circuits than epiretinal stimulation. There was no significant difference in charge threshold between subretinal and epiretinal configurations. ERFs were defined by the stimulating array surface area that successfully stimulated spikes in an RGC. ERFs were complex in shape, similar to receptive fields mapped with light. ERF areas were significantly smaller with subretinal than epiretinal stimulation. This may reflect the greater distance between stimulating electrodes and RGCs in the subretinal configuration. ERFs for immediate and delayed responses mapped within the same Type III cells differed in shape and size, consistent with different sites and mechanisms for generating these two response types.

No abstract

No abstract

On discharge, the Li-O 2 battery can form a Li 2 O 2 film on the cathode surface, leading to low capacities, low rates and early cell death, or it can form Li 2 O 2 particles in solution, leading to high capacities at relatively high rates and avoiding early cell death. Achieving discharge in solution is important and may be encouraged by the use of high donor or acceptor number solvents or salts that dissolve the T he high theoretical specific energy of the rechargeable Li-O 2 battery has generated intense interest in the possibility of a practical device that could deliver energy storage significantly in excess of today's lithium-ion batteries 1-9 . However, major challenges hinder the development of such a technology 1-6,10-14 . Typically a Li-O 2 battery is composed of a lithium metal anode separated by an aprotic electrolyte solution from a porous O 2 cathode. The reaction at the cathode involves, on discharge, the reduction of O 2 to form Li 2 O 2 , with oxidation of the latter on charge. Growth of Li 2 O 2 on the cathode surface leads to low capacities, poor rates and early cell death [15][16][17] . In contrast, if Li 2 O 2 can be induced to grow in the electrolyte solution then high discharge capacities at relatively high rates and avoiding early cell death is possible 15 . It is clearly important to operate a Li-O 2 battery in which Li 2 O 2 grows in solution.A number of groups have elucidated the mechanism of O 2 reduction to Li 2 O 2 on discharge 15,16,[18][19][20][21] . The reduction proceeds through the following general steps: 22,[27][28][29][30] . High donor number salts have been shown to increase the capacity fourfold and reduce the discharge overpotential by ∼30-50 mV over low donor number salts 22 . Viologens 27,28 , phthalocyanines 29 and quinones 30 have been investigated as possible soluble reduction catalysts. Although the studies of such catalysts are important, in most cases there is little or no direct evidence demonstrating that they promote formation of Li 2 O 2 in solution and not on the electrode surface because they rely on electrochemical measurements alone. Yet past work on Li-O 2 batteries has shown how essential it is to provide more than electrochemical evidence in this field 31 . In some cases, soluble catalysts show an increase in discharge voltage (lower overpotential) as small as, for example, 40 mV (refs 28,29), which is very unlikely to be sufficient to shut off the direct reduction of O 2 to Li 2 O 2 , essential to stop detrimental Li 2 O 2 film formation. Also, none of the previous studies in low donor number solvents exhibited a significant increase in capacity on discharge at a relatively high rate, which is important for a successful Li-O 2 battery.Here we demonstrate that addition of DBBQ (2,5-di-tert-butyl-1,4-benzoquinone) to a weakly solvating (low donor number) electrolyte solution, LiTFSI in ether 22 , promotes O 2 reduction to Li 2 O 2 in solution while halving the discharge overpotential (increasing the discharge potential), suppressing the growth of a Li 2...

No abstract

A very large format neural stimulator device, to be used in future retinal prosthesis experiments, has been designed, fabricated, and tested. The device was designed to be positioned against a human retina for short periods in an operating room environment. Demonstrating a very large format, parallel interface between a 2-D microelectronic stimulator array and neural tissue would be an important step in proving the feasibility of high resolution retinal prosthesis for the blind. The architecture of the test device combines several novel components, including microwire glass, a microelectronic multiplexer, and a microcable connector. The array format is 80 times 40 array pixels with approximately 20 microwire electrodes per pixel. The custom assembly techniques involve indium bump bonding, ribbon bonding, and encapsulation. The design, fabrication, and testing of the device has resolved several important issues regarding the feasibility of high-resolution retinal prosthesis, namely, that the combination of conventional CMOS electronics and microwire glass provides a viable approach for a high resolution retinal prosthesis device. Temperature change from power dissipation within the device and maximum electrical output current levels suggest that the device is acceptable for acute human tests.