The differences in measured prostate material properties between probing and unconfined compression testing methods

Mechanical and suture-holding properties of a UV-cured atelocollagen membrane with varied crosslinked architecture

The mechanical competence and suturing ability of collagen-based membranes are paramount in guided bone regeneration (GBR) therapy, to ensure damage-free implantation, fixation and space maintenancein vivo. However, contact with the biological medium can induce swelling of collagen molecules, yielding risks of membrane sinking into the bone defect, early loss of barrier function, and irreversibly compromised clinical outcomes. To address these challenges, this study investigates the effect of the crosslinked network architecture on both mechanical and suture-holding properties of a new atelocollagen (AC) membrane. UV-cured networks were obtained via either single functionalisation of AC with 4-vinylbenzyl chloride (4VBC) or sequential functionalisation of AC with both 4VBC and methacrylic anhydride. The wet-state compression modulus (Ec) and swelling ratio (SR) were significantly affected by the UV-cured network architecture, leading up to a three-fold reduction in SR and about two-fold increase inEcin the sequentially functionalised, compared to the single-functionalised, samples. Electron microscopy, dimensional analysis and compression testing revealed the direct impact of the ethanol series dehydration process on membrane microstructure, yielding densification of the freshly synthesised porous samples and a pore-free microstructure with increasedEc. Nanoindentation tests via spherical bead-probe atomic force microscopy (AFM) confirmed an approximately two-fold increase in median (interquartile range (IQR)) elastic modulus in the sequentially functionalised (EAFM= 40 (13) kPa), with respect to single-functionalised (EAFM= 15 (9) kPa), variants. Noteworthy, the single-functionalised, but not the sequentially functionalised, samples displayed higher suture retention strength (SRS = 28 ± 2-35 ± 10 N∙mm-1) in both the dry state and following 1 h in phosphate buffered saline (PBS), compared to Bio-Gide® (SRS: 6 ± 1-14 ± 2 N∙mm-1), while a significant decrease was measured after 24 h in PBS (SRS= 1 ± 1 N∙mm-1). These structure-property relationships confirm the key role played by the molecular architecture of covalently crosslinked collagen, aimed towards long-lasting resorbable membranes for predictable GBR therapy.

Wave Propagation in a Fractional Viscoelastic Tissue Model: Application to Transluminal Procedures

In this article, a wave propagation model is presented as the first step in the development of a new type of transluminal procedure for performing elastography. Elastography is a medical imaging modality for mapping the elastic properties of soft tissue. The wave propagation model is based on a Kelvin Voigt Fractional Derivative (KVFD) viscoelastic wave equation, and is numerically solved using a Finite Difference Time Domain (FDTD) method. Fractional rheological models, such as the KVFD, are particularly well suited to model the viscoelastic response of soft tissue in elastography. The transluminal procedure is based on the transmission and detection of shear waves through the luminal wall. Shear waves travelling through the tissue are perturbed after encountering areas of altered elasticity. These perturbations carry information of medical interest that can be extracted by solving the inverse problem. Scattering from prostate tumours is used as an example application to test the model. In silico results demonstrate that shear waves are satisfactorily transmitted through the luminal wall and that echoes, coming from reflected energy at the edges of an area of altered elasticity, which are feasibly detectable by using the transluminal approach. The model here presented provides a useful tool to establish the feasibility of transluminal procedures based on wave propagation and its interaction with the mechanical properties of the tissue outside the lumen.

Experimental Evidence of Generation and Reception by a Transluminal Axisymmetric Shear Wave Elastography Prototype

Experimental evidence on testing a non-ultrasonic-based probe for a new approach in transluminal elastography was presented. The proposed modality generated shear waves by inducing oscillatory rotation on the lumen wall. Detection of the propagated waves was achieved at a set of receivers in mechanical contact with the lumen wall. The excitation element of the probe was an electromagnetic rotational actuator whilst the sensing element was comprised by a uniform anglewise arrangement of four piezoelectric receivers. The prototype was tested in two soft-tissue-mimicking phantoms that contained lumenlike conduits and stiffer inclusions. The shear wave speed of the different components of the phantoms was characterized using shear wave elastography. These values were used to estimate the time-of-flight of the expected reflections. Ultrafast ultrasound imaging, based on Loupas’ algorithm, was used to estimate the displacement field in transversal planes to the lumenlike conduit and to compare against the readouts from the transluminal transmission–reception tests. Experimental observations between ultrafast imaging and the transluminal probe were in good agreement, and reflections due to the stiffer inclusions were detected by the transluminal probe. The obtained experimental evidence provided proof-of-concept for the transluminal elastography probe and encouraged further exploration of clinical applications.

Biomechanical properties of abdominal organs under tension with special reference to increasing strain rate

Currently, abdominal finite element models overlook the organs such as gallbladder, bladder, and intestines, which instead are modeled as a simple bag that is not included in the analysis. Further characterization of the material properties is required for researchers to include these organs into models. This study characterized the mechanical properties of human and porcine gallbladder, bladder, and intestines using uniaxial tension loading from the rates of 25%/s to 500%/s. Small differences were observed between human and porcine gallbladder elastic modulus, failure stress, and failure strain. Strain rate was determined to be a significant factor for predicting porcine gallbladder elastic modulus and failure stress which were found to be 9.03 MPa and 1.83 MPa at 500%/s. Human bladder was observed to be slightly stiffer with a slightly lower failure stress than porcine specimens. Both hosts, however, demonstrated a strain rate dependency with the elastic modulus and failure stress increasing as the rate increased with the highest elastic modulus (2.16 MPa) and failure stress (0.65 MPa) occurring at 500%/s. Both human and porcine intestines were observed to be affected by the strain rate. Failure stress was found to be 1.6 MPa and 1.42 MPa at 500%/s for the human and porcine intestines respectively. For all properties found to be strain rate dependent, a numerical model was created to quantify the impact. These results will enable researchers to create more detailed finite element models that include the gallbladder, bladder, and intestines.