Subsurface pressure profiling: a novel mathematical paradigm for computing colony pressures on substrate during fungal infections

Three-dimensional acoustic impedance mapping of cultured biological cells

The acoustic microscope is a powerful tool for the observation of biological matters. Non-invasive in-situ observation can be performed without any staining process. Acoustic microscopy is contrasted by elastic parameters like sound speed and acoustic impedance. We have proposed an acoustic microscope that can acquire three-dimensional acoustic impedance profile. The technique was applied to cell-size observation. Glial cells were cultured on a 70 μm-thick polypropylene film substrate. A highly focused ultrasound beam was transmitted from the rear side of the substrate, and the reflection was received by the same transducer. An acoustic pulse, its spectrum spreading briefly 100 through 450 MHz, was transmitted. By analyzing the internal reflections in the cell, the distribution of characteristic acoustic impedance along the beam direction was determined. Three-dimensional acoustic impedance mapping was realized by scanning the transducer, exhibiting the intra-cellular structure including nucleus and cytoskeleton.

Material State Awareness for Composites Part II: Precursor Damage Analysis and Quantification of Degraded Material Properties Using Quantitative Ultrasonic Image Correlation (QUIC)

Material state awareness of composites using conventional Nondestructive Evaluation (NDE) method is limited by finding the size and the locations of the cracks and the delamination in a composite structure. To aid the progressive failure models using the slow growth criteria, the awareness of the precursor damage state and quantification of the degraded material properties is necessary, which is challenging using the current NDE methods. To quantify the material state, a new offline NDE method is reported herein. The new method named Quantitative Ultrasonic Image Correlation (QUIC) is devised, where the concept of microcontinuum mechanics is hybrid with the experimentally measured Ultrasonic wave parameters. This unique combination resulted in a parameter called Nonlocal Damage Entropy for the precursor awareness. High frequency (more than 25 MHz) scanning acoustic microscopy is employed for the proposed QUIC. Eight woven carbon-fiber-reinforced-plastic composite specimens were tested under fatigue up to 70% of their remaining useful life. During the first 30% of the life, the proposed nonlocal damage entropy is plotted to demonstrate the degradation of the material properties via awareness of the precursor damage state. Visual proofs for the precursor damage states are provided with the digital images obtained from the micro-optical microscopy, the scanning acoustic microscopy and the scanning electron microscopy.

Citrate-Coated Silver Nanoparticles Growth-Independently Inhibit Aflatoxin Synthesis in Aspergillus parasiticus

Manufactured silver nanoparticles (Ag NPs) have long been used as antimicrobials. However, little is known about how these NPs affect fungal cell functions. While multiple previous studies reveal that Ag NPs inhibit secondary metabolite syntheses in several mycotoxin producing filamentous fungi, these effects are associated with growth repression and hence need sublethal to lethal NP doses, which besides stopping fungal growth, can potentially accumulate in the environment. Here we demonstrate that citrate-coated Ag NPs of size 20 nm, when applied at a selected nonlethal dose, can result in a >2 fold inhibition of biosynthesis of the carcinogenic mycotoxin and secondary metabolite, aflatoxin B₁ in the filamentous fungus and an important plant pathogen, Aspergillus parasiticus, without inhibiting fungal growth. We also show that the observed inhibition was not due to Ag ions, but was specifically associated with the mycelial uptake of Ag NPs. The NP exposure resulted in a significant decrease in transcript levels of five aflatoxin genes and at least two key global regulators of secondary metabolism, laeA and veA, with a concomitant reduction of total reactive oxygen species (ROS). Finally, the depletion of Ag NPs in the growth medium allowed the fungus to regain completely its ability of aflatoxin biosynthesis. Our results therefore demonstrate the feasibility of Ag NPs to inhibit fungal secondary metabolism at nonlethal concentrations, hence providing a novel starting point for discovery of custom designed engineered nanoparticles that can efficiently prevent mycotoxins with minimal risk to health and environment.