Validation of Ultrasound Elastography Imaging for Nondestructive Characterization of Stiffer Biomaterials

Abstract

Ultrasound elastography (UE) has been widely used as a “digital palpation” tool to characterize tissue mechanical properties in the clinic. UE benefits from the capability of noninvasively generating 2-D elasticity encoded maps. This spatial distribution of elasticity can be especially useful in the in vivo assessment of tissue engineering scaffolds and implantable drug delivery platforms. However, the detection limitations have not been fully characterized and thus its true potential has not been completely discovered. Characterization studies have focused primarily on the range of moduli corresponding to soft tissues, 20kPa–600kPa. However, polymeric biomaterials used in biomedical applications such as tissue scaffolds, stents, and implantable drug delivery devices can be much stiffer. In order to explore UE’s potential to assess mechanical properties of biomaterials in a broader range of applications, this work investigated the detection limit of UE strain imaging beyond soft tissue range. To determine the detection limit, measurements using standard mechanical testing and UE on the same polydimethylsiloxane samples were compared and statistically evaluated. The broadest detection range found based on the current optimized setup is between 47kPa and 4MPa which exceeds the modulus of normal soft tissue suggesting the possibility of using this technique for stiffer materials’ mechanical characterization. The detectable difference was found to be as low as 157 kPa depending on sample stiffness and experimental setup.

Nondestructive Characterization of Biodegradable Polymer Erosion in Vivo Using Ultrasound Elastography Imaging

“…A laboratory-designed stage and a linear actuator were used to induce uniform compression for all samples. The USE scans were carried out as described previously . Briefly, the ultrasound transducer was fixed to the laboratory designed stage, and the programmable linear actuator was used to provide uniform displacement.…”

“…In our previous study, we characterized USE for its application in imaging stiffer materials by comparing it to the gold standard mechanical test using polydimethylsiloxane (PDMS). The detection range was found to be between 47 kPa and 4 MPa, with a detectable difference as low as 157 kPa based on the optimized scan setup during experimentation …”

“…The detection range was found to be between 47 kPa and 4 MPa, with a detectable difference as low as 157 kPa based on the optimized scan setup during experimentation. 30 For this study, USE technique was applied to a PLGA based in situ forming implant (ISFI) drug delivery system for characterization of implant erosion in vitro and in vivo. Implant solutions prepared with three different molecular weights of PLGA were examined.…”

Quantitative Ultrasound for Nondestructive Characterization of Engineered Tissues and Biomaterials

“…Compression elastography has been demonstrated capable of visualizing differences in elastic properties of polymer samples with moduli ranging from 47 kPa to 4 MPa. 77 Other ultrasound techniques, have been employed to characterize the properties of porous baghdadite scaffolds 78 or bioglass-based scaffolds 79 used for bone tissue engineering. In these studies, pulse-echo ultrasound was used to measure the time-of-flight, estimate the longitudinal wave velocity, and then calculate the normal component of the stiffness tensor.…”

In Vitro-In Vivo Correlation for the Degradation of Tetra-PEG Hydrogel Microspheres with Tunable β-Eliminative Crosslink Cleavage Rates

“…Such studies have usually been performed by analysis of one implant per animal after euthanasia, necessitating multiple animals for each profile. Recently, efforts have shifted to the use of biomedical imaging to noninvasively monitor in vivo changes accompanying degradation of implants-notably MRI and various ultrasound (US) methodologies that can be translated across species [7]. However, these approaches measure several concurrent changes, including mass loss and gel swelling or shrinkage.…”