Toward an efficient inverse characterization of the viscoelastic properties of anisotropic media based on the ultrasonic polar scan

Composite materials (e.g., carbon fiber reinforced plastics (CFRP)) are increasingly used for critical components in several industrial sectors (e.g. aerospace, automotive). Their anisotropic nature makes it difficult to accurately determine material properties or to assess internal damages. To resolve these challenges, the Ultrasonic Polar Scan (UPS) technique has been introduced. In a UPS experiment, a fixed material spot is insonified at a multitude of incidence angles Psi(theta,phi) for which the transmission amplitude as well as the associated arrival time (time-of-flight) are measured. Mapping these quantities on a polar diagram represents a fingerprint of the local viscoelasticity of the investigated material. In the present study, we propose a novel two-stage inversion scheme that is able to infer both the elastic and the viscous properties. In the first step, we solve the inverse problem of determining the elastic constants from time-of-flight UPS recordings. The second stage handles a similar inverse problem, but now operates on the amplitude landscape of a UPS experiment for determining the viscous part of the viscoelastic tensor. This two-stage procedure thus yields the viscoelastic tensor of the insonified material spot. The developed characterization scheme has been employed on both virtual (numerical) UPS recordings, to test the effectiveness of the method, and experimental UPS recordings of unidirectional C/E plates

Damage signature of fatigued fabric reinforced plastics in the pulsed ultrasonic polar scan

This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fiber reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of -12.8% along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics

The use of thermographic imaging to evaluate therapeutic response in human tumour xenograft models

YesNon-invasive methods to monitor tumour growth are an important goal in cancer drug development. Thermographic imaging systems offer potential in this area, since a change in temperature is known to be induced due to changes within the tumour microenvironment. This study demonstrates that this imaging modality can be applied to a broad range of tumour xenografts and also, for the first time, the methodology’s suitability to assess anti-cancer agent efficacy. Mice bearing subcutaneously implanted H460 lung cancer xenografts were treated with a novel vascular disrupting agent, ICT-2552, and the cytotoxin doxorubicin. The effects on tumour temperature were assessed using thermographic imaging over the first 6 hours post-administration and subsequently a further 7 days. For ICT-2552 a significant initial temperature drop was observed, whilst for both agents a significant temperature drop was seen compared to controls over the longer time period. Thus thermographic imaging can detect functional differences (manifesting as temperature reductions) in the tumour response to these anti-cancer agents compared to controls. Importantly, these effects can be detected in the first few hours following treatment and therefore the tumour is observable non-invasively. As discussed, this technique will have considerable 3Rs benefits in terms of reduction and refinement of animal use.University of Bradfor

Cell penetrating peptides for in vivo molecular imaging applications.

Cell penetrating peptides (CPPs) are a relatively new class of peptides that have the promising capability to cross cell membranes. While details remain to be resolved, various non-receptor-mediated endocytic pathways likely contribute most to the cell penetrating properties of these peptides. CPPs have been used to deliver many different cargos - ranging from radionuclides and other peptides to antibodies and nanoparticles - into cells. Besides many different drug delivery applications, CPPs have also seen a limited use in molecular imaging. Molecular imaging of intracellular and intranuclear targets, by techniques such as SPECT, PET, optical imaging, and MRI, relies heavily on the delivery of contrast agents to the cytoplasm and/or nuclei of the target tissue. Therefore, the number of applications in molecular imaging of intracellular targets has remained relatively low, because of the effective barrier presented by the cell membrane. One of the key strategies to overcome this challenge is the introduction of membrane-transducing peptides in the design of new contrast agents. This review presents an overview of the literature on CPPs, focusing on their use for molecular imaging. Applications using proteins and peptides, DNA/RNA, and CPP-loaded cells as the imaging agents will be looked at. Moreover, the difficulties and pitfalls regarding the use of CPPs in molecular imaging will be discussed