Search

Electrically conductive 3D periodic microscaffolds are fabricated using a particle-free direct ink writing approach for use as neuronal growth and electrophysiological recording platforms. A poly (2-hydroxyethyl methacrylate)/pyrrole ink, followed by chemical in situ polymerization of pyrrole, enables hydrogel printing through nozzles as small as 1 µm. These conductive hydrogels can pattern complex 2D and 3D structures and have good biocompatibility with test cell cultures (≈94.5% viability after 7 days). Hydrogel arrays promote extensive neurite outgrowth of cultured Aplysia californica pedal ganglion neurons. This platform allows extracellular electrophysiological recording of steady-state and stimulated electrical neuronal activities. In summation, this 3D conductive ink printing process enables the preparation of biocompatible and micron-sized structures to create customized in vitro electrophysiological recording platforms., QC 20211115

Genetic determinants of antibiotic resistance (AR) have been extensively investigated. High-throughput sequencing allows for the assessment of the relationship between genotype and phenotype. A panel of 672 Pseudomonas aeruginosa strains was analysed, including representatives of globally disseminated multidrug-resistant and extensively drug-resistant clones; genomes and multiple antibiograms were available. This panel was annotated for AR gene presence and polymorphism, defining a resistome in which integrons were included. Integrons were present in >70 distinct cassettes, with In5 being the most prevalent. Some cassettes closely associated with clonal complexes, whereas others spread across the phylogenetic diversity, highlighting the importance of horizontal transfer. A resistome-wide association study (RWAS) was performed for clinically relevant antibiotics by correlating the variability in minimum inhibitory concentration (MIC) values with resistome data. Resistome annotation identified 147 loci associated with AR. These loci consisted mainly of acquired genomic elements and intrinsic genes. The RWAS allowed for correct identification of resistance mechanisms for meropenem, amikacin, levofloxacin and cefepime, and added 46 novel mutations. Among these, 29 were variants of the oprD gene associated with variation in meropenem MIC. Using genomic and MIC data, phenotypic AR was successfully correlated with molecular determinants at the whole-genome sequence level.

Biofilms are major causes of impairment of wound healing and patient morbidity. One of the most common and aggressive wound pathogens is Staphylococcus aureus, displaying a large repertoire of virulence factors and commonly reduced susceptibility to antibiotics, such as the spread of methicillin-resistant S. aureus (MRSA). Bacteriophages are obligate parasites of bacteria. They multiply intracellularly and lyse their bacterial host, releasing their progeny. We isolated a novel phage, DRA88, which has a broad host range among S. aureus bacteria. Morphologically, the phage belongs to the Myoviridae family and comprises a large double-stranded DNA (dsDNA) genome of 141,907 bp. DRA88 was mixed with phage K to produce a high-titer mixture that showed strong lytic activity against a wide range of S. aureus isolates, including representatives of the major international MRSA clones and coagulase-negative Staphylococcus. Its efficacy was assessed both in planktonic cultures and when treating established biofilms produced by three different biofilm-producing S. aureus isolates. A significant reduction of biofilm biomass over 48 h of treatment was recorded in all cases. The phage mixture may form the basis of an effective treatment for infections caused by S. aureus biofilms.

The widespread use of antibiotics in association with high-density clinical care has driven the emergence of drugresistant bacteria that are adapted to thrive in hospitalized patients. Of particular concern are globally disseminated methicillin-resistant Staphylococcus aureus (MRSA) clones that cause outbreaks and epidemics associated with health care. The most rapidly spreading and tenacious health-care-associated clone in Europe currently is EMRSA-15, which was first detected in the UK in the early 1990s and subsequently spread throughout Europe and beyond. Using phylogenomic methods to analyze the genome sequences for 193 S. aureus isolates, we were able to show that the current pandemic population of EMRSA-15 descends from a health-care-associatedMRSA epidemic that spread throughout England in the 1980s, which had itself previously emerged froma primarily community-associated methicillin-sensitive population. The emergence of fluoroquinolone resistance in this EMRSA-15 subclone in the English Midlands during the mid-1980s appears to have played a key role in triggering pandemic spread, and occurred shortly after the first clinical trials of this drug. Genome-based coalescence analysis estimated that the population of this subclone over the last 20 yr has grown four times faster than its progenitor. Using comparative genomic analysis we identified the molecular genetic basis of 99.8% of the antimicrobial resistance phenotypes of the isolates, highlighting the potential of pathogen genome sequencing as a diagnostic tool.We document the genetic changes associated with adaptation to the hospital environment and with increasing drug resistance over time, and how MRSA evolution likely has been influenced by country-specific drug use regimens

On-board sensors that can detect and size a crack in a structural component are being developed and will be deployed to enhance structural health monitoring and prognosis. This research examines the simulation of recurring automated inspection resulting from simulated on-board "crack" sensors, and their potential effect on reducing the probability-of-fracture of structural components. The concept of a probability of detection (POD) curve is used to characterize the performance of the sensor, as done for traditional inspections. However, we assert that recurring inspections for an automated system should be modeled as dependent with respect to the first inspection due to the largely repeatable aspects of the sensor and data collection system. This assertion has a large effect on the computed probability of detecting a crack and alleviates the substantial over prediction of sensor efficacy generated using the assumption of independent inspections for automated systems. Furthermore, it is demonstrated that the fundamental feature that determines the efficacy of a recurring automated on-board sensor is the probability of detecting a crack of critical size, i.e., the size that will cause fracture, and this feature is by and large separate from the shape of the POD curve. This information can be used to determine the required accuracy of an on-board automated inspection to achieve a specified reliability of a structural component. The methodology is demonstrated using fatigue and fracture of a representative titanium compressor disk from a gas turbine aircraft engine but is applicable to any structural system with recurring automated inspections., Prepared in cooperation with Southwest Research Institute San Antonio, TX. Submitted for publication to Structural Health Monitoring, 22 Mar 2006.

Premium grade titanium alloys are used for fan and compressor rotors and disks in aircraft turbine engines. Occasional upsets during processing can result in the formation of metallurgical anomalies referred to as hard alpha (HA). Although rare, low-cycle fatigue cracks initiated by HA have led to uncontained engine failures that resulted in fatal accidents such as the incident at Sioux City, Iowa, in 1989. In a report issued by the Federal Aviation Administration (FAA) after the accident at Sioux City, it was recommended that a damage tolerance approach be implemented to explicitly address HA anomalies, with the objective of enhancing conventional rotor life management methodology. The probabilistic, damage tolerance code developed in this program for low-cycle fatigue of titanium rotors/disks is intended to supplement, not replace, the current safe-life design. The code is called Design Assessment of Reliability With INspection (DARWIN) and was developed in collaboration with AlliedSignal Engines, General Electric Aircraft Engines, Pratt & Whitney, and Rolls-Royce Allison. DARWIN integrates finite element stress analysis, fracture mechanics analysis, nondestructive inspection simulation, and probabilistic analysis to assess the risk of rotor fracture. Supplementary tasks performed in this program in support of code implementation included the generation of fatigue crack growth data for Ti-64, Ti-6242, and Ti-17beta in high vacuum; determination of the crack initiation behavior of artificial and natural HA defects embedded in plates of Ti-64; and development of a forging microcode to predict the movement, shape and orientation of HA anomalies during processing from ingot to billet, and from billet to a disk forging., Original contains color plates: All DTIC reproductions will be in black and white. Prepared in cooperation with AlliedSignal, Phoenix, AZ; General Electric, Cincinnati, OH; Scientific Forming Technologies, Corp, Columbus, OH; Pratt and Whitney, East Hartford, CT; Rolls-Royce Allison, Indianapolis, IN.