Springer Science and Business Media LLC

Polymeric vascular stents must employ other strategies than malleable deformation, as generally practiced with metal stents, to expand and withstand compressive stresses in situ. The stent expansion strategy must further consider induced flow perturbations and wall stresses that may injure the vessel wall and promote thrombogenesis. Analyzing the stresses furled stents undergo during balloon-assisted expansion is an important first step in achieving a better understanding of stent–wall mechanical interactions, thereby to improve stent function. To this end, we performed finite element (FE) analysis of the balloon-induced unfurling of an internally coiled, bioresorbable polymeric stent employing a 3D FE solid model of a 120° symmetric stent segment and a large deformation finite strain formulation. Uni-axial tensile testing of stent fiber elastic to plastic yielding provided the mechanical property information, and the von Mises criterion was employed to establish the elastic–plastic transition in the FE model. The model was validated with pressure and deformation measurements obtained during stent expansion tests. The internal coils of this inner coil–outer coil design twisted as the stent expanded, leading to plastic yielding at the point of tangency of the inner and outer coils. The remaining stent fiber portions underwent elastic bending. Cross-sections revealed only the outside surface layer of the coiled fiber underwent plastic yielding. The interior elastic fiber was supported by this plastic shell. The analysis suggests that during balloon-induced expansion, local plastic yielding in torsion “sets” the stent fibers, imparting high radial collapse resistance. The results further suggest that the stent exerts non-uniform mechanical forces on the vessel wall during expansion.

Magnetic resonance imaging (MRI) provides high-quality soft-tissue images of anatomical structures and radiation free imaging. The research community has focused on establishing new workflows, developing new technology, and creating robotic devices to change an MRI room from a solely diagnostic room to an interventional suite, where diagnosis and intervention can both be done in the same room. Closed bore MRI scanners provide limited access for interventional procedures using intraoperative imaging. MRI robots could improve access and procedure accuracy. Different research groups have focused on different technology aspects and anatomical structures. This paper presents the results of a systematic search of MRI robots for needle-based interventions. We report the most recent advances in the field, present relevant technologies, and discuss possible future advances. This survey shows that robotic-assisted MRI-guided prostate biopsy has received the most interest from the research community to date. Multiple successful clinical experiments have been reported in recent years that show great promise. However, in general the field of MRI robotic systems is still in the early stage. The continued development of these systems, along with partnerships with commercial vendors to bring this technology to market, is encouraged to create new and improved treatment opportunities for future patients.

Ophthalmic biomarkers have long played a critical role in diagnosing and managing ocular diseases. Oculomics has emerged as a field that utilizes ocular imaging biomarkers to provide insights into systemic diseases. Advances in diagnostic and imaging technologies including electroretinography, optical coherence tomography (OCT), confocal scanning laser ophthalmoscopy, fluorescence lifetime imaging ophthalmoscopy, and OCT angiography have revolutionized the ability to understand systemic diseases and even detect them earlier than clinical manifestations for earlier intervention. With the advent of increasingly large ophthalmic imaging datasets, machine learning models can be integrated into these ocular imaging biomarkers to provide further insights and prognostic predictions of neurodegenerative disease. In this manuscript, we review the use of ophthalmic imaging to provide insights into neurodegenerative diseases including Alzheimer Disease, Parkinson Disease, Amyotrophic Lateral Sclerosis, and Huntington Disease. We discuss recent advances in ophthalmic technology including eye-tracking technology and integration of artificial intelligence techniques to further provide insights into these neurodegenerative diseases. Ultimately, oculomics opens the opportunity to detect and monitor systemic diseases at a higher acuity. Thus, earlier detection of systemic diseases may allow for timely intervention for improving the quality of life in patients with neurodegenerative disease.

Biomechanical testing of human musculoskeletal joints not only requires qualified testing machines and devices, but also needs an excellent control method to obtain better experimental results. In this paper, we take the human functional spinal unit (FSU) as an example to study how to improve the performance of the robotic testing system. First, the mechanical characteristics of FSU are described and the simplified model (rigid body–spring system) for the specimen is given. Because the location of the center of rotation (COR) of the specimen affects the performance of the system, a comprehensive analysis on the location of COR is carried out. The performance of the robotic testing system can also be improved through the improvement of the control method. Two control methods have been proposed in this paper: one is the improved hybrid control, the other is fuzzy logic control.

This study relates to our earlier study which predicts the transmural distribution as well as the global left ventricular (LV) function and oxygen demand, based on the LV structure, geometry and sarcomere function. Here, we test the predicted global oxygen demand against experimental data in anesthetized, open chest dogs under changing working conditions. The experimental oxygen demand was calculated from the arterio-venous difference in oxygen content times the measured coronary flow. LV load was manipulated by a combination of a pressurized chamber connected to the femoral artery, phenylephrine infusion and an adjustable arteriovenous shunt. The heart was paced in two preset heart rates. The study demonstrates that the global predictions, based on the local distributed oxygen demand model, are comparable to those obtained by other methods of global metabolic predictions. However, unlike other global methods, the distributed model gives spatial information and predicts an endo/epi ratio of oxygen demand ranging between 1.05 to 1.14, depending on the loading conditions, which is comparable to available experimental data. For the experimental conditions studied here (stroke volume, heart rate, aortic pressure), the theoretical analysis shows that only the end diastolic volume is significantly correlated to the endo/epi ratio of the transmural oxygen demand.

Biocompatibility of artificial lungs can be improved by endothelialization of hollow fibers. Bioavailability of growth-inducing and anti-thrombotic agents on the hollow fiber–blood interface inhibits thrombosis. We investigated if nanoliposomal growth-inducing growth hormone (nGH) and anti-thrombotic sodium nitrite (nNitrite) incorporation into collagen-coating on silicone hollow fibers improves blood biocompatibility by increasing endothelial cell growth and nitrite bioavailability under flow. Nitrite production rate was assessed under varying flow conditions. Finite element (FE) modeling was used to simulate nitrite transport within the parallel-plate flow chamber, and nitrite bioavailability on the fiber–blood interface at 1–30 dyn/cm2 shear stress. Endothelial cell number on fibers coated with nNitrite-nGH-collagen conjugate was 1.5-fold higher than on collagen-coated fibers. For collagen-coated fibers, nitrite production reached a maximum at 18 dyn/cm2 shear stress. When fibers were coated with nNitrite-nGH-collagen conjugate, nitrite production increased continuously by increasing shear stress. FE modeling revealed that nitrite concentrations at the fiber–blood interface were affected by shear stress-induced nitrite production, and diffusion/convection-induced nitrite removal. Highest nitrite concentrations and lowest thrombus deposition were observed on fibers coated with nNitrite-nGH-collagen conjugate exposed to 6–12 dyn/cm2 shear stress. In conclusion, our results suggest that nNitrite-nGH-Col conjugate coatings promote endothelialization of silicone hollow fibers in biohybrid artificial lungs.

This work was aimed at providing a local mechanical characterisation of tissues from the healthy human atria. Thirty-two tissue specimens were harvested from nine adult subjects whose death was not directly related to cardiovascular diseases. Tissues were kept in Tyrode’s solution and tested using a planar biaxial device. Results showed that tissues from healthy human atria undergo large deformations under in-plane distributed tensions roughly corresponding to an in vivo pressure of 15 mmHg. The material was modelled as hyperelastic and a Fung-type elastic strain energy potential was chosen. This class of potentials is based on a function of a quadratic form in the components of the Green–Lagrange strain tensor, and it has been previously proved that the fourth-order tensor of this quadratic form is proportional to the linear elasticity tensor of the linearised theory. This has three important consequences: (i) the coefficients in Fung-type potentials have a precise physical meaning; (ii) whenever a microstructural description for the linear elasticity tensor is available, this is automatically inherited by the Fung-type potential; (iii) because of the presence of the linear elasticity tensor in the definition of a Fung-type potential, each of the three normal stresses is coupled with all three normal strains.We propose to include information on the microstructure of the atrium by writing the linear elasticity tensor as the volumetric-fraction-weighed sum of the linear elasticity tensors of the three constituents of the tissue: the ground matrix, the main fibre family and the secondary fibre family. To the best of our knowledge, this is the first time that a Fung-type potential is given a precise structural meaning, based on the directions and the material properties of the fibres. Because of the coupling between normal strains and normal stresses, this structurally-based Fung-type potential allows for discriminating among all testing protocols in planar biaxial stretch.