Modeling Bovine Pericardium

Bovine pericardium has been widely used over the last decades as bioprosthetic material due to its excellent biocompatibility. However, the durability of pericardial heart valves is still inadequate and prevents them from being the perfect heart valve substitutes. To increase their short-time performance, studying the tissue mechanical features is of prime importance. Consequently, constitutive relations need to be developed.The purpose of this work was to analyze two different constitutive approaches used to model bovine pericardium: the phenomenological approach and the structural approach.Phenomenological constitutive laws are formulated to fit empirical data, independent of histological considerations. Their main drawback is the variability of material parameters for different protocols for the same specimen. Thus, they do not consent to interpret the tissue's mechanical behavior. In the second chapter, some physically sound restrictions on the parameters, which appear in some forms of the exponential Fung model, are obtained by invoking the Legendre-Hadamard and the Strong Ellipticity conditions. These restrictions can validate the empirical models and can be used in the fitting procedure. Structural constitutive equations are determined by taking into account the tissue's architecture. A structurally based constitutive law describing the tissue's mechanical response through failure behavior has been proposed in the third chapter. The model has been tested by using published experimental data and a sufficiently good fit has been obtained

MODELING BOVINE PERICARDIUM

ABSTRACT MODELING BOVINE PERICARDIUM Raffaella De Vita, M.S. University of Pittsburgh, 2003 Bovine pericardium has been widely used over the last decades as bioprosthetic material due to its excellent biocompatibility. However, the durability of pericardial heart valves is still inadequate and prevents them from being the perfect heart valve substitutes. To increase their short-time performance, studying the tissue mechanical features is of prime importance. Consequently, constitutive relations need to be developed. The purpose of this work was to analyze two different constitutive approaches used to model bovine pericardium: the phenomenological approach and the structural approach. Phenomenological constitutive laws are formulated to fit empirical data, independent of histological considerations. Their main drawback is the variability of material parameters for different protocols for the same specimen. Thus, they do not consent to interpret the tissue's mechanical behavior. In the second chapter, some physically sound restrictions on the parameters, which appear in some forms of the exponential Fung model, are obtained by invoking the Legendre-Hadamard and the Strong Ellipticity conditions. These restrictions can validate the empirical models and can be used in the fitting procedure. iii Structural constitutive equations are determined by taking into account the tissue's architecture. A structurally based constitutive law describing the tissue's mechanical response through failure behavior has been proposed in the third chapter. The model has been tested by using published experimental data and a sufficiently good fit has been obtained. i

Structural Constitutive Models for Knee Ligaments

It has been estimated that approximately 375,000 people experience knee injuries every year in the United States. The majority of the pathologies affect the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL). Thus, a thorough characterization of the mechanical properties of the ligaments is needed to understand the etiology of their injuries and to improve the strategies of their treatment. The first chapter of this dissertation offers a brief overview of the morphology and mechanics of the ligaments.Since injuries are estimated to occur at strain rates that range from 50%/s to 150,000%/s, studying the mechanical behavior of ligaments at various strain rates is imperative. In the second chapter, a structural constitutive model is formulated by taking into account the nonlinearity, anisotropy, incompressibility, and strain rate-related properties of the ligaments. The collagen fibers, which comprise the ligament, are assumed to be the only load-bearing component of the tissue. They are oriented in various directions, undulated in the stress-free configuration, and they gradually become straight upon deformation. Moreover, the collagen fibers are characterized by a Kelvin-Voigt-type viscoelastic behavior. The fiber spatial orientation and gradual recruitment are represented statistically by probability density functions. Published experimental data on the ACLs are used to assess the constitutive model. The most severe of the knee ligament injuries are partial and complete tears. Thus, there is a compelling need to understand the mechanical failure behavior of ligaments. In the third chapter, a structural constitutive model for the description of the ligament tensile properties is proposed. The model reproduces the three-regions of the nonlinear stress-strain relationship of ligaments. The collagen fibers contribute to the overall tissue's response after becoming taut and before failing and they are assumed to behave as a linear elastic material. The fiber recruitment and failure processes are stochastically defined. Available experimental data for the MCLs are employed to validate the constitutive relation. Furthermore, the generalization to a three-dimensional model is also given. Future research directions toward the development of a structural constitutive model for the subfailure behavior of ligaments are indicated in the fourth chapter and conclusions are drawn in the fifth chapter

A NONLINEAR VISCOELASTIC MODEL FOR THE RELAXATION BEHAVIOR OF TENDON

INTRODUCTION Tendons are viscoelastic materials which undergo stress relaxation when held at a constant strain. The most successful model used to describe the viscoelastic behavior of tendons is the quasi-linear viscoelastic (QLV) model In this study, a transversely isotropic nonlinear viscoelastic model for the stress relaxation of rat tail tendon fascicles is presented. The model is formulated within the nonlinear viscoelastic framework set forth by Pipkin and Rogers [3] by considering recent theoretical developments by Rajagopal and Wineman [4] for anisotropic materials. The current model represents a departure from current viscoelastic models widely used in biomechanics for soft biological tissues because it incorporates a nonseparable relaxation which is a function of the strain invariants and time. It is validated using stress relaxation data collected at multiple strain levels from rat tail tendon fascicles and compared to the predictions of the QLV model

Theatre is a valid add-on therapeutic intervention for emotional rehabilitation of parkinson's disease patients

Conventional medical treatments of Parkinson's disease (PD) are effective on motor disturbances but may have little impact on nonmotor symptoms, especially psychiatric ones. Thus, even when motor symptomatology improves, patients might experience deterioration in their quality of life. We have shown that 3 years of active theatre is a valid complementary intervention for PD as it significantly improves the well-being of patients in comparison to patients undergoing conventional physiotherapy. Our aim was to replicate these findings while improving the efficacy of the treatment. We ran a single-blinded pilot study lasting 15 months on 24 subjects with moderate idiopathic PD. 12 were assigned to a theatre program in which patients underwent "emotional" training. The other 12 underwent group physiotherapy. Patients were evaluated at the beginning and at the end of their treatments, using a battery of eight clinical and five neuropsychological scales. We found that the emotional theatre training improved the emotional well-being of patients, whereas physiotherapy did not. Interestingly, neither of the groups showed improvements in either motor symptoms or cognitive abilities tested by the neuropsychological battery. We confirmed that theatre therapy might be helpful in improving emotional well-being in PD

A Unique Case of Bilateral Thalamic High-Grade Glioma in a Pediatric Patient with LI-Fraumeni Syndrome: Case Presentation and Review of the Literature

Li-Fraumeni syndrome (LFS) is a rare high-penetrance and autosomal-dominant pathological condition caused by the germline mutation of the TP53 gene, predisposing to the development of tumors from pediatric age. We conducted a qualitative systematic review following the ENTREQ (Enhancing Transparency in Reporting the Synthesis of Qualitative Research) framework. A search was made in MEDLINE/Pubmed and MeSH Database using the terms “Li-Fraumeni” AND “pediatric high-grade glioma (HGG)”, identifying six cases of HGGs in pediatric patients with LFS. We added a further case with peculiar features such as no familiar history of LFS, association of embryonal rhabdomyosarcoma and bithalamic HGG, whose immunohistochemical profile was accurately defined by Next Generation Sequencing. Knowledge synthesis and case analysis grounded the discussion about challenges in the management of this pathology in pediatric age

A collaborative, semantic and context-aware search engine

Search engines help people to find information in the largest public knowledge system of the world: the Web. Unfortunately its size makes very complex to discover the right information. The users are faced lots of useless results forcing them to select one by one the most suitable. The new generation of search engines evolve from keyword-based indexing and classification to more sophisticated techniques considering the meaning, the context and the usage of information. We argue about the three key aspects: collaboration, geo-referencing and semantics. Collaboration distributes storage, processing and trust on a world-wide network of nodes running on users’ computers, getting rid of bottlenecks and central points of failures. The geo-referencing of catalogued resources allows contextualisation based on user position. Semantic analysis lets to increase the results relevance. In this paper, we expose the studies, the concepts and the solutions of a research project to introduce these three key features in a novel search engine architecture.213-21

Fulvestrant and trastuzumab in patients with luminal HER2-positive advanced breast cancer (ABC): an Italian real-world experience (HERMIONE 9)

Purpose The most appropriate therapy for HR+/HER2-positive (HER2+) advanced breast cancer (ABC) is a matter of debate. Co-targeting of both receptors represents an attractive strategy to overcome the cross-talk between them. Methods The HERMIONE 9 is an observational retrospective multicentric study which aimed to describe the clinical outcome of patients with HR+/HER2+ABC who received the combination of Fulvestrant (F) and Trastuzumab (T) as part of their routine treatment at 10 Italian Institutions. Results Eighty-seven patients were included. Median age was 63 (range, 35–87) years. The median number of previous treatments was 3 (range, 0–10) and F and T were administered as≥3rd line in 67 patients. Among the 86 evaluable patients, 6 (6.9%) achieved CR, 18 (20.7%) PR, and 44 (50.6%) had SD ≥24 weeks with an overall CBR of 78.2%. At a median follow-up of 33.6 months, mPFS of the entire cohort was 12.9 months (range, 2.47–128.67). No diference was observed in mPFS between patients treated after progression or as maintenance therapy (mPFS 12.9 and 13.9 months in 64 and 23 patients, respectively), neither considering the number of previous treatment lines (≤3 or<3). Conclusion The combination of F and T was active in this cohort at poor prognosis and deserves further investigations possibly in combination with pertuzumab in patients with high ER expression

π+\pi^+ photoproduction on the proton for photon energies from 0.725 to 2.875 GeV

Differential cross sections for the reaction $\gamma p \to n \pi^+$ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID and MAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes.Comment: 18 pages, 10 figure