Exploitation of Cationic Silica Nanoparticles for Bioprinting of Large-Scale Constructs with High Printing Fidelity.

Three-dimensional (3D) bioprinting allows the fabrication of 3D structures containing living cells whose 3D shape and architecture are matched to a patient. The feature is desirable to achieve personalized treatment of trauma or diseases. However, realization of this promising technique in the clinic is greatly hindered by inferior mechanical properties of most biocompatible bioink materials. Here, we report a novel strategy to achieve printing large constructs with high printing quality and fidelity using an extrusion-based printer. We incorporate cationic nanoparticles in an anionic polymer mixture, which significantly improves mechanical properties, printability, and printing fidelity of the polymeric bioink due to electrostatic interactions between the nanoparticles and polymers. Addition of cationic-modified silica nanoparticles to an anionic polymer mixture composed of alginate and gellan gum results in significantly increased zero-shear viscosity (1062%) as well as storage modulus (486%). As a result, it is possible to print a large (centimeter-scale) porous structure with high printing quality, whereas the use of the polymeric ink without the nanoparticles leads to collapse of the printed structure during printing. We demonstrate such a mechanical enhancement is achieved by adding nanoparticles within a certain size range (<100 nm) and depends on concentration and surface chemistry of the nanoparticles as well as the length of polymers. Furthermore, shrinkage and swelling of the printed constructs during cross-linking are significantly suppressed by addition of nanoparticles compared with the ink without nanoparticles, which leads to high printing fidelity after cross-linking. The incorporated nanoparticles do not compromise biocompatibility of the polymeric ink, where high cell viability (>90%) and extracellular matrix secretion are observed for cells printed with nanocomposite inks. The design principle demonstrated can be applied for various anionic polymer-based systems, which could lead to achievement of 3D bioprinting-based personalized treatment.

Acoustic analysis of the directional information captured by five different hearing aid styles.

This study compared the head-related transfer functions (HRTFs) recorded from the bare ear of a mannequin for 393 spatial locations and for five different hearing aid styles: Invisible-in-the-canal (IIC), completely-in-the-canal (CIC), in-the-canal (ITC), in-the-ear (ITE), and behind-the-ear (BTE). The spectral distortions of each style compared to the bare ear were described qualitatively in terms of the gain and frequency characteristics of the prominent spectral notch and two peaks in the HRTFs. Two quantitative measures of the differences between the HRTF sets and a measure of the dissimilarity of the HRTFs within each set were also computed. In general, the IIC style was most similar and the BTE most dissimilar to the bare ear recordings. The relative similarities among the CIC, ITC, and ITE styles depended on the metric employed. The within-style spectral dissimilarities were comparable for the bare ear, IIC, CIC, and ITC with increasing ambiguity for the ITE and BTE styles. When the analysis bandwidth was limited to 8 kHz, the HRTFs within each set became much more similar.

Gene maps linearization using genomic rearrangement distances.

A preliminary step to most comparative genomics studies is the annotation of chromosomes as ordered sequences of genes. Different genetic mapping techniques often give rise to different maps with unequal gene content and sets of unordered neighboring genes. Only partial orders can thus be obtained from combining such maps. However, once a total order O is known for a given genome, it can be used as a reference to order genes of a closely related species characterized by a partial order P. Our goal is to find a linearization of P that is as close as possible to O, in term of a given genomic distance. We first prove NP-completeness complexity results considering the breakpoint and the common interval distances. We then focus on the breakpoint distance and give a dynamic programming algorithm whose running time is exponential for general partial orders, but polynomial when the partial order is derived from a bounded number of genetic maps. A time-efficient greedy heuristic is then given for the general case and is empirically shown to produce solutions within 10% of the optimal solution, on simulated data. Applications to the analysis of grass genomes are presented.

Effects of blood pressure lowering on cerebral white matter hyperintensities in patients with stroke: the PROGRESS (Perindopril Protection Against Recurrent Stroke Study) Magnetic Resonance Imaging Substudy.

BACKGROUND: The prevalence of white matter hyperintensities (WMHs) detected on cerebral MRI is associated with hypertension, but it is not known whether blood pressure lowering can arrest their progression. We report here the results of an MRI substudy of PROGRESS (Perindopril Protection Against Recurrent Stroke Study), a randomized trial of blood pressure lowering in subjects with cerebrovascular disease. METHODS AND RESULTS: The substudy comprised 192 participants who had a cerebral MRI both at baseline and after a mean follow-up time of 36 months (SD=6.0 months). At the first MRI, WMHs were graded with a visual rating scale from A (no WMH) to D (severe WMH). Participants were assigned to a combination of perindopril plus indapamide (or their placebos; 58%) or to single therapy with perindopril (or placebo). At the time of the second MRI, the blood pressure reduction in the active arm compared with the placebo arm was 11.2 mm Hg for systolic blood pressure and 4.3 mm Hg for diastolic blood pressure. Twenty-four subjects (12.5%) developed new WMHs at follow-up. The risk of new WMH was reduced by 43% (95% CI -7% to 89%) in the active treatment group compared with the placebo group (P=0.17). The mean total volume of new WMHs was significantly reduced in the active treatment group (0.4 mm3 [SE=0.8]) compared with the placebo group (2.0 mm3 [SE=0.7]; P=0.012). This difference was greatest for patients with severe WMH at entry, 0.0 mm3 (SE=0) in the active treatment group versus 7.6 mm3 (SE=1.0) in the placebo group (P<0.0001). CONCLUSIONS: These results indicate that an active blood pressure-lowering regimen stopped or delayed the progression of WMHs in patients with cerebrovascular disease.

Simple design rules for optimal design of dielectric temperature-compensated sapphire resonators.

It has been shown that the use of two dielectric crystals with opposite temperature coefficient of permittivity allows the realization of a resonator with a zero temperature coefficient of frequency. By using sapphire and rutile materials, which have low-loss tangents, some compensated resonators with very high Q-factors have been realized. In this work we develop rules that greatly simplify the design of a dielectric-compensated resonator. We show that the optimum design for compensation at a specific temperature may be determined by simply selecting the aspect ratio of the sapphire resonator.

High Q-factor Bragg-reflection sapphire-loaded cavity TE01delta mode resonators.

An innovative method of enhancing the quality factor of TE01delta cavity resonators with a dielectric tube made of monolithic sapphire is presented. Very high Q-factor is achieved by employing a Bragg reflection technique. A TE01delta mode in a copper cavity was measured to have a Q-factor of 1 x 10(5) at 8.78 GHz and 290 K. This is only 30% less than the limit due to the loss tangent of the dielectric material. The technique confines electromagnetic energy in the sapphire dielectric and in the vacuum well away from the cavity walls, thus reducing the surface losses in the copper shield. The technique offers some significant advantages over other methods. One advantage is the very low spurious mode density, which can improve filter and resonator design capabilities. Another is the small compact design, with a single sapphire piece, as compared to previously published Bragg reflection techniques. Finite element simulations and experimental data for this method were compared and found to be in very good agreement. The cavity dimensions were optimized to achieve maximum quality factor.