Quantitative Analysis of Stress-Stretch Curves in Canine Lumbar Vertebrae Using Modified Logistic Functions.

BACKGROUND: The mechanical characteristics of bone are crucial for comprehending its functionality and response to different load conditions, which are essential for advancing medical treatments, implants, and prosthetics. By employing mathematical modeling to analyze the mechanical properties of bone, we can assess stress and deformation under both normal and abnormal conditions. This analysis offers valuable perspectives on potential fracture risks, the effects of diseases, and the effectiveness of various treatments. Therefore, researchers are attempting to find an adequate mathematical description of the mechanical properties of bone. METHODS: Experimental stress-stretch external loading curves were obtained through investigations of canine vertebrae. The obtained experimental curves were fitted using the SciPy Python library with a slightly modified logistic function (logistic function plus additional const). RESULTS: The resulting coefficient of determination R2 (R squared) for most curves was near 0.999, indicating that an appropriate fitting function was selected for the description of the experimental stress-stretch curves. CONCLUSIONS: The stress-stretch behavior of canine vertebrae can be described using a logistic function modified by adding additional parameters for the most accurate fitting results.

Modeling the Effect of Annulus Fibrosus Stiffness on the Stressed State of a Vertebral L1 Body and Nucleus Pulposus.

The investigation examines the transference of stiffness from intervertebral discs (IVDs) to the lumbar body of the L1 vertebra and the interactions among adjacent tissues. A computational model of the vertebra was developed, considering parameters such as cortical bone thickness, trabecular bone elasticity, and the nonlinear response of the nucleus pulposus to external loading. A nonlinear dynamic analysis was performed, revealing certain trends: a heightened stiffness of the annulus fibrosus correlates with a significant reduction in the vertebral body's ability to withstand external loading. At a supplied displacement of 6 mm, the vertebra with a degenerative disc reached its yielding point, whereas the vertebrae with a healthy annulus fibrosus exhibited a strength capacity exceeding 20%. The obtained findings and proposed methodology are potentially useful for biomedical engineers and clinical specialists in evaluating the condition of the annulus fibrosus and predicting its influence on the bone components of the spinal system.

Experimental and theoretical investigation of aortic wall tissue in tensile tests.

BACKGROUND: Understanding the mechanical properties of aortic tissue is essential for developing numerical computation tools and assessing the risk of aortic aneurysm fractures. Tensile tests using aortic wall specimens allow for the determination of stress and strain depending on the location and direction of the sample. OBJECTIVE: The aim of this study was to perform a mechanical tensile test using canine aorta samples and create a numerical model of aortic tissue tension from the processed data. METHODS: Dogbone-shaped samples were dissected from canine aortic segments. The initial measurements were made at zero tension and the tensile tests were conducted at 10 mm/min until rupture. Force and stretch data were used to obtain engineering and true stress-strain curves. The true stress-strain curves were taken until the maximum strength was obtained, after which they were smoothed and fitted using a logistic function with three coefficients. These curves were then used as material mechanical properties for a numerical model of the aortic tissue tension. A simplified rectangle form was used to mimic the middle of the dogbone-shaped portion of the tissue specimen. Experimental displacement data were collected for the boundary conditions of the finite element 3D model. RESULTS: The experimental data processing revealed that the logistic function described the nonlinear behaviour of the aorta soft tissue with an accuracy of 95% from the start of the tension to the media layer rupture. By applying numerical simulations, we obtained a correspondence of the load curve with an RMSE = 0.069 for the theoretical and experimental external tension data. CONCLUSION: The numerical investigation confirmed that the non-linear soft tissue was validated by applying a logistic function approach to the mechanical properties of the aortic wall.

Modeling the Impact of Meniscal Tears on von Mises Stress of Knee Cartilage Tissue.

The present study aims to explore the stressed state of cartilage using various meniscal tear models. To perform this research, the anatomical model of the knee joint was developed and the nonlinear mechanical properties of the cartilage and meniscus were verified. The stress-strain curve of the meniscus was obtained by testing fresh tissue specimens of the human meniscus using a compression machine. The results showed that the more deteriorated meniscus had greater stiffness, but its integrity had the greatest impact on the growth of cartilage stresses. To confirm this, cases of radial, longitudinal, and complex tears were examined. The methodology and results of the study can assist in medical diagnostics for meniscus treatment and replacement.

Histomorphometry and µCT scan analysis of osteoporosis in spayed female dogs.

Background: Both humans and small animals suffer from similar metabolic and structural diseases that impact the musculoskeletal system; however, instead of studying animal disease in its own right, animals are more often used as models for research into various human ailments, such as osteoporosis. There are few studies indicating that animals may suffer from osteoporosis, which raises the question of why small animals, which we believe to be equally susceptible, receive so little attention. With this research, we hope to draw the attention of researchers to the fact that the examination of animals for this disease is just as important as the examination of humans; human osteoporosis research receives a great deal of attention, while animals and their health are neglected. Aims: We aimed to analyze the bone volume fraction (BV/TV) and thickness of first (L1) and second (L2) lumbar vertebrae samples from five cadavers using histomorphometric analysis. In addition, we aimed to investigate one cadaver using microcomputed tomography (µCT) imaging. Methods: The L1 and L2 vertebrae from five dog carcasses were used to evaluate the BV/TV and the trabecular thicknesses. We used precise sampling criteria, and also developed a methodological approach to the study of the vertebrae. Using semi-automated methods, we performed histomorphometric analysis and µCT data analysis. Results: We used five dog cadavers in this research. During the histomorphometry study, we observed that the lowest L1 BV/TV ratio was 7.88% and the highest was 23.08%. The L2 vertebrae BV/TV ranged from 11.58% to 23.7%. The L1 and L2 lumbar trabeculae thicknesses were also measured. L1's smallest trabecula was 17.34 microns and its largest was 31.88. The L2 vertebrae trabecula thickness was 18.76-30.75 microns. BV/TV and trabecular thickness were positively correlated (and vice versa). The two-tailed p value was less than 0.00001. This difference is statistically significant. After µCT analysis, we discovered regions in the vertebral body with low porosity; these cavities are usually filled with connective tissue. The bone tissue in these areas is more vulnerable, meaning fracture risk has increased. Conclusions: Animals should not just be considered as models for osteoporosis in humans, but also as potential patients. A single test, such as histomorphometry, may not be sufficient; more advanced technology, such as µCT, is required, since it reveals the pores that make the vertebral column more brittle and susceptible to fracture.

Empirical case report of the mechanical properties of three spayed canine lumbar vertebrae.

Background: Today, animals, like humans, suffer from spinal illnesses, which are aggravated in old age. Much emphasis is placed on diagnosis and treatment, but little focus is given to the spine's mechanical properties. Degenerative spine diseases are a major problem throughout the world. According to the World Health Organization, osteoporosis is a world-class public problem that reduces bone mass, resulting in bone fracturing and increased risk of bone fracturing. Therefore, the mechanical investigation of vertebrae can provide more information about the development of osteoporosis.s. Case Description: For our case report, we used spayed mongrel lumbar vertebrae samples obtained from a canine which was about 8 years old and weighed 28 kg. The dog was diagnosed with a mammary tumor, and its owners decided to euthanize the dog. All consent forms were filled. Conclusion: Mechanical tests were performed on three vertebrae, and a notable difference was observed in the first cycle of the first vertebra (L1). Second-order polynomials for displacement and seventh-order polynomials for pressure were proposed for describing the stress-strain relationship of the vertebrae under the cyclical loads. Our research protocol has been broken down into several parts. After measuring the area of the loaded surface, the largest area was in the L2 vertebra (176 ± 16 mm; 177 ± 3 mm) and the smallest was in the L7 vertebra (156 ± 4 mm; 151 ± 33 mm). The smallest distance was recorded between the first (L1) and seventh (L7) lumbar vertebrae (L1) (15.17 ± 0.93 mm), and the largest distance was recorded between the L3 and L4 vertebrae of the lumbar (19.8 ± 3.7 mm).

Computational analysis of aortic haemodynamics in the presence of ascending aortic aneurysm.

BACKGROUND: The usefulness of numerical modelling of a patient's cardiovascular system is growing in clinical treatment. Understanding blood flow mechanics can be crucial in identifying connections between haemodynamic factors and aortic wall pathologies. OBJECTIVE: This work investigates the haemodynamic parameters of an ascending aorta and ascending aortic aneurysm in humans. METHODS: Two aortic models were constructed from medical images using the SimVascular software. FEM blood flow modelling of cardiac cycle was performed using CFD and CMM-FSI at different vascular wall parameters. RESULTS: The results showed that highest blood velocity was 1.18 m/s in aorta with the aneurysm and 1.9 m/s in healthy aorta model. The largest displacements ware in the aorta with the aneurysm (0.73 mm). In the aorta with the aneurysm, time averaged WSS values throughout the artery range from 0 Pa to 1 Pa. In the healthy aorta, distribution of WSS values changes from 0.3 Pa to 0.6 Pa. CONCLUSIONS: In the case of an ascending aortic aneurysm, the maximum blood velocity was found to be 1.6 times lower than in the healthy aorta. The aneurysm-based model demonstrates a 45% greater wall displacement, while the oscillatory shear index decreased by 30% compared to healthy aortic results.

Investigation of the backflows and outlet boundary conditions for computations of the patient-specific aortic valve flows.

BACKGROUND: Simulation divergence due to the backflow through the outlet boundary is a common, but not fully addressed challenge in patient-specific simulations of the aortic valve flows. OBJECTIVE: The purpose of this study is to develop the outlet boundary conditions aiming to improve convergence of the patient-specific aortic valve computations and to control the backflow in the case of partial reversal of the flow through the outlet. METHODS: Haemodynamic analysis of the aortic valve flows governed by the Navier-Stokes equations is performed by using the finite volume method. The pressure distribution, obtained from the convergent computations driven by the outflow boundary condition, is approximated by the parabolic surface of revolution and prescribed on the outlet as the novel pressure boundary condition. RESULTS: Various types of outlet boundary conditions are investigated to evaluate their influence on the resulting backflows. The outflow boundary condition produces a smaller backflow than other investigated boundary conditions, but it causes the solution divergence. The proposed outlet boundary condition allows for continuing the solution and preserving the expected backflow. CONCLUSIONS: The proposed outlet boundary condition helps to achieve a convergent solution and to conserve the observed backflow by varying the convexity of the specified pressure surface.

Modelling of silk-reinforced PDMS properties for soft tissue engineering applications.

BACKGROUND: Polydimethylsiloxane (PDMS) is widely used in biomedical research and technology, but its mechanical properties should be tuned according to the desired product specifications. Mixing ratio of base polymer to curing agent or additives enables its mechanical properties to be manipulated and fit to mechanical properties of biological tissues. OBJECTIVE: In this paper, we analysed the effect of mechanical load on silk-reinforced PDMS depending on silk concentration. METHODS: We prepared cylinder-type PDMS samples with different silk concentrations and performed cyclic uniaxial compression tests with a fixed magnitude of applied strain. Next, we analysed the mechanical charascteristics of PDMS using computational modelling. RESULTS: The stress-strain data within the large-strain region of different PDMS cylinders without silk and with 1%, 5% and 10% silk concentrations was fitted to non-linear second order Mooney-Rivlin, and third-order Ogden models. The results show the equivalence of both models for investigated strain region of PDMS. On the other hand, PDMS cylinders with 10% silk concentration allowed the successful fitting of experimental data just for the second-order Mooney-Rivlin model, while all numerical probes to find an appropriate fitting parameters for third-order Ogden models were unsuccessful. CONCLUSIONS: The second-order Mooney-Rivlin model is preferable for analysing the properties of silk-reinforced PDMS over the entire measurement range.

Recognition of normal-abnormal phonocardiographic signals using deep convolutional neural networks and mel-frequency spectral coefficients.

Intensive care unit patients are heavily monitored, and several clinically-relevant parameters are routinely extracted from high resolution signals. OBJECTIVE: The goal of the 2016 PhysioNet/CinC Challenge was to encourage the creation of an intelligent system that fused information from different phonocardiographic signals to create a robust set of normal/abnormal signal detections. APPROACH: Deep convolutional neural networks and mel-frequency spectral coefficients were used for recognition of normal-abnormal phonocardiographic signals of the human heart. This technique was developed using the PhysioNet.org Heart Sound database and was submitted for scoring on the challenge test set. MAIN RESULTS: The current entry for the proposed approach obtained an overall score of 84.15% in the last phase of the challenge, which provided the sixth official score and differs from the best score of 86.02% by just 1.87%.