The effect of sulfur on structure and conversion of bioactive borate glasses

The effect of sulfur on glass structure and the conversion process of bioactive CaO-LI2O-B2O3 glasses were studied. One glass without and two glasses with different amounts of sulfur were made using conventional melting and dry quenching techniques. These glasses reacted with a phosphate solution and converted to hydroxyapatite. Particles (150-355µm) were reacted in 0.25 and 0.5 molar K2HPO4 solutions at 37⁰C for 2 to 96 hours. The weight loss of the particles and the final pH of the solution were measured. The weight loss measurements indicated that the reaction rate increases with increasing the sulfur content. Sulfur was released from the glass, causing the pH of the solution to decrease, but was absent in the reacted layer. In the in-vivo studies, the effect of sulfur and phosphorus on the conversion of two different bioactive borate glasses was studied, in-vivo. Discs made from two sulfur-free glasses (CaLB-0 and 93B3-0) and two sulfur-containing glasses (CaLB-12 and 93B3-6) were implanted in a subcutaneous site in rats for 2, 4, and 12 weeks. Each rat remained healthy during the experiment and there were no sign of infection or necrosis at the implantation site. The CaLB glass discs reacted with the body fluids and formed a thin calcium phosphate reacted layer on their surface, but the 93B3 glass discs reacted to form a thicker calcium phosphate reacted layer with an onion-skin structure. Compared the phosphorus-free CaLB implants to phosphorus-containing 93B3 implants the CaLB implants absorbed 2 times more phosphorus from the body fluids to form the calcium phosphate reacted layer. Compared to the CaLB implants, the connective tissue attached to the 93B3 implants was ~3 times thicker, and contained more blood vessels and collagen. For all of the sulfur-containing implants sulfur released to the body fluids and was not presented in the reacted materials --Abstract, page iv

Biodegradable Composite Scaffold for Repairing Defects in Load-Bearing Bones

A tissue scaffold for repair and regeneration of bone hard tissue or muscle, skin, or organ soft tissue, including load-bearing bone tissue, the scaffold comprising a core of biocompatible, biodegradable inorganic glass fibers; and a biocompatible, biodegradable, flexible polymer film surrounding the core and adhered to the core

A continuum model for tension-compression asymmetry in skeletal muscle

[EN] Experiments on passive skeletal muscle on different species show a strong asymmetry in the observed tension-compression mechanical behavior. This asymmetry shows that the tension modulus is two orders of magnitude higher than the compression modulus. Until now, traditional analytical constitutive models have been unable to capture that strong asymmetry in anisotropic solids using the same material parameters. In this work we present a model which is able to accurately capture five experimental tests in chicken pectoralis muscle, including the observed tension-compression asymmetry. However, aspects of the anisotropy of the tissue are not captured by the model.Partial financial support for this work has been given by grant DPI2015-69801-R from the Direccion General de Proyectos de Investigacion of the Ministerio de Economia y Competitividad of Spain. FJM also acknowledges the support of the Department of Mechanical and Aerospace Engineering of University of Florida during the sabbatical period in which this paper was completed and Ministerio de Educacion, Cultura y Deporte of Spain for the financial support for that stay under grant PRX15/00065Latorre, M.; Mohammadkhah, M.; Simms, CK.; Montáns, FJ. (2018). A continuum model for tension-compression asymmetry in skeletal muscle. Journal of the Mechanical Behavior of Biomedical Materials. 77:455-460. https://doi.org/10.1016/j.jmbbm.2017.09.0124554607

A review on computer modeling of bone piezoelectricity and its application to bone adaptation and regeneration

Bone is a hierarchical, multiphasic and anisotropic structure which in addition possess piezoelectric properties. The generation of piezoelectricity in bone is a complex process which has been shown to play a key role both in bone adaptation and regeneration. In order to understand the complex biological, mechanical and electrical interactions that take place during these processes, several computer models have been developed and used to test hypothesis on potential mechanisms behind experimental observations. This paper aims to review the available literature on computer modeling of bone piezoelectricity and its application to bone adaptation and healing. We first provide a brief overview of the fundamentals of piezoelectricity and bone piezoelectric effects. We then review how these properties have been used in computational models of bone adaptation and electromechanical behaviour of bone. In addition, in the last section, we summarize current limitations and potential directions for future work

Evaluation of the Learning Environment based on the Dundee Ready Education Environment Measure Model from the Perspective of Primary School Students in Roudsar City

Educational environment plays a vital role on effectiveness of learning and educational activity. The DREEM questionnaire is a tool for assessing educational environment. We estimated the dental students’ perceptions of their educational environment. This was a descriptive study using a convenience sampling in addition to DREEM questionnaire which was carried out on 23 female students of Roudsar city in 2015. The mean and standard diversion scores of perception. Students in the five areas including: the area of learning 34/2±5/66 of 60 score, teachers area 34/62±5/23 of 55 score, areas of academic ability 25/94±4/36 of 40 score, educational environment 33/33±5/05 of 50 score and the perception of students in the social condition 24±1/40 of 35 score. Total score was 168 of 200 score. Educational environment of learning is important, so improving this situation should be responsible priority

Risk-taking behaviors of the Tehran city; Iranian college students in 2018

Background and aims: High-risk behaviors among different strata are one of the most severe health threats in recent years. This study aimed to investigate the frequency of high-risk behaviors among college students in Iran. Methods: This study was a cross-sectional study with 144 new students in Tehran City, Iran, performed in 2018 using random sampling. The data collection tools included questions on demographic variables and Youth Risk Behavior Survey (YRBS) questionnaire. Students completed the questionnaire. The data were analyzed using SPSS 24 and descriptive tests. Results: In this study, all students were in their first year of university. The results showed that 66% of students were girls and 34% were boys. 6.9% and 9% of students did not wear helmets when riding motorcycles or sitting in the driver’s seat, respectively. Also, threatened and beaten once with a weapon such as a knife or a stick and physically assaulted or beaten once were seen in 9% and 3.6% of students, respectively.9.7% had taken money from their parents or others once without permission. Conclusion: Based on the findings, many participants engage in high-risk behaviors that endanger their health; Therefore, designing and improving health programs and strategies is essential to reduce the risks and factors that cause high-risk behaviors

The Energy of Muscle Contraction. II. Transverse Compression and Work

In this study we examined how the strain energies within a muscle are related to changes in longitudinal force when the muscle is exposed to an external transverse load. We implemented a three-dimensional (3D) finite element model of contracting muscle using the principle of minimum total energy and allowing the redistribution of energy through different strain energy-densities. This allowed us to determine the importance of the strain energy-densities to the transverse forces developed by the muscle. We ran a series of in silica experiments on muscle blocks varying in initial pennation angle, muscle length, and external transverse load. As muscle contracts it maintains a near constant volume. As such, any changes in muscle length are balanced by deformations in the transverse directions such as muscle thickness or muscle width. Muscle develops transverse forces as it expands. In many situations external forces act to counteract these transverse forces and the muscle responds to external transverse loads while both passive and active. The muscle blocks used in our simulations decreased in thickness and pennation angle when passively compressed and pushed back on the load when they were activated. Activation of the compressed muscle blocks led either to an increase or decrease in muscle thickness depending on whether the initial pennation angle was less than or greater than 15°, respectively. Furthermore, the strain energy increased and redistributed across the different strain-energy potentials during contraction. The volumetric strain energy-density varied with muscle length and pennation angle and was reduced with greater transverse load for most initial muscle lengths and pennation angles. External transverse load reduced the longitudinal muscle force for initial pennation angles of β0 = 0°. Whereas for pennate muscle (β0 > 0°) longitudinal force changed (increase or decrease) depending on the muscle length, pennation angle and the direction of the external load relative to the muscle fibres. For muscle blocks with initial pennation angles β0 ≤ 20° the reduction in longitudinal muscle force coincided with a reduction in volumetric strain energy-density

The Energy of Muscle Contraction. I. Tissue Force and Deformation During Fixed-End Contractions

During contraction the energy of muscle tissue increases due to energy from the hydrolysis of ATP. This energy is distributed across the tissue as strain-energy potentials in the contractile elements, strain-energy potential from the 3D deformation of the base-material tissue (containing cellular and extracellular matrix effects), energy related to changes in the muscle\u27s nearly incompressible volume and external work done at the muscle surface. Thus, energy is redistributed through the muscle\u27s tissue as it contracts, with only a component of this energy being used to do mechanical work and develop forces in the muscle\u27s longitudinal direction. Understanding how the strain-energy potentials are redistributed through the muscle tissue will help enlighten why the mechanical performance of whole muscle in its longitudinal direction does not match the performance that would be expected from the contractile elements alone. Here we demonstrate these physical effects using a 3D muscle model based on the finite element method. The tissue deformations within contracting muscle are large, and so the mechanics of contraction were explained using the principles of continuum mechanics for large deformations. We present simulations of a contracting medial gastrocnemius muscle, showing tissue deformations that mirror observations from magnetic resonance imaging. This paper tracks the redistribution of strain-energy potentials through the muscle tissue during fixed-end contractions, and shows how fibre shortening, pennation angle, transverse bulging and anisotropy in the stress and strain of the muscle tissue are all related to the interaction between the material properties of the muscle and the action of the contractile elements

Tension and compression stress-strain asymmetry in passive skeletal muscle

THESIS 11341The general aim of this study is to advance the knowledge of the relationship between the skeletal muscle passive compressive and tensile behaviour, and the microstructure of the muscle through combined experimental, microstructural and theoretical approaches. The mechanics of passive skeletal muscle are important in many biomechanical applications. Existing data from porcine tissue has shown a significant tension/compression asymmetry, which is not captured by current constitutive modelling approaches using a single set of material parameters, and an adequate explanation for this effect remains elusive. In this thesis, the passive elastic deformation properties of chicken pectoralis muscle are assessed for the first time, to provide deformation data on a skeletal muscle which is very different to porcine tissue. Uniaxial, quasi-static compression and tensile tests were performed on fresh chicken pectoralis muscle in the fibre and cross-fibre directions, and at 45? to the fibre direction. Results show that chicken muscle elastic behaviour is nonlinear and anisotropic. The tensile stress?stretch response is two orders of magnitude larger than in compression for all directions tested, which reflects the tension/compression asymmetry previously observed in porcine tissue. In compression the tissue is stiffest in the cross-fibre direction. However, tensile deformation applied at 45? gives the stiffest response, and this is different to previous findings relating to porcine tissue. Chicken muscle tissue is most compliant in the fibre direction for both tensile and compressive applied deformation. Generally, a small percentage of fluid exudation was observed in the compressive samples. Since collagen is the main structural protein in animal connective tissues, it is believed to be primarily responsible for their passive load-bearing properties. The direct detection and visualisation of collagen using fluorescently tagged CNA35 binding protein (fused to EGFP or tdTomato) is also reported for the first time on fixed skeletal muscle tissue. A working protocol is then established by examining tissue preparation, dilution factor, exposure time etc. for sensitivity and specificity. Penetration of the binding protein into intact mature skeletal muscle was found to be very limited, but detection works well on tissue sections with higher sensitivity on wax embedded sections compared to frozen sections. CNA35 fused to tdTomato has a higher sensitivity than CNA35 fused to EGFP but both show specific detection. Best results were obtained with 15 ?m wax embedded sections, with blocking of non-specific binding in 1% BSA and antigen retrieval in Sodium Citrate. There was a play-off between dilution of the binding protein and time of incubation but both CNA35-tdTomato and CNA35-EGFP worked well with approximately 100 ?g/ml of purified protein with overnight incubation, while CNA35- tdTomato could be utilized at 5 fold less concentration. The tension/compression asymmetry observed in the stress-strain response of skeletal muscle is not well understood. The optimised protocol is then applied to report qualitatively on skeletal muscle ECM reorganization during applied deformation using a combination of CNA35 binding protein and confocal imaging of tensile and compressive deformation of porcine and chicken muscle samples applied in both the fibre and cross-fibre directions. Results show the overall three-dimensional structure of collagen in perimysium visible in planes perpendicular (w1) and parallel (w2) to the muscle fibres in both porcine and chicken skeletal muscle. Furthermore, there is clear evidence of the reorganization of these structures under compression and tension applied in both the muscle fibre and cross-fibre directions, which generally explains anisotropy observed in the stress-strain response of skeletal muscle both in tension and compression for chicken and porcine tissues. These observations improve our understanding of how perimysium responds to three-dimensional deformations. The proposed three-dimensional illustration of perimysium structure is then used as a basis to create a microstructural-geometrical model to predict the passive mechanical stress-strain response observed in skeletal muscle. The current model represents the whole muscle response as a combination of both a group of muscle fibres (fascicle) response and the perimysium (ECM) response. It shows that although perimysium was believed to be a key element in the muscle stress response, the muscle fibres (in Tension-Fibre and Compression-XFibre deformations) also contribute to stress-stretch response since the order of magnitude for the stress in muscle fibres is similar to that of perimysium. The model shows more asymmetric response than previously published micromechanical model (Gindre et al., 2013). The model yields a good prediction of the whole muscle behaviour in Tension-Fibre and Compression-Fibre deformations using the optimum values for the model parameters obtained from the conducted sensitivity studies; connective tissue percentage of pc=1.75 , Elast modulus of Ec=300 MPa, and perimysium sheet waviness of w=1.25. However, the model overestimates the Compression-XFibre deformation and underestimates the Tension-XFibre deformations even by using the optimum parameters. The current model attempts to relate the mechanical stress-stretch response observed in muscle to the collagen reorganization in the muscle microstructure under load application, which further help develop better constitutive models for finite element modelling purposes. The general aim of this study is to advance the knowledge of the relationship between the skeletal muscle passive compressive and tensile behaviour, and the microstructure of the muscle through combined experimental, microstructural and theoretical approaches. The mechanics of passive skeletal muscle are important in many biomechanical applications. Existing data from porcine tissue has shown a significant tension/compression asymmetry, which is not captured by current constitutive modelling approaches using a single set of material parameters, and an adequate explanation for this effect remains elusive. In this thesis, the passive elastic deformation properties of chicken pectoralis muscle are assessed for the first time, to provide deformation data on a skeletal muscle which is very different to porcine tissue. Uniaxial, quasi-static compression and tensile tests were performed on fresh chicken pectoralis muscle in the fibre and cross-fibre directions, and at 45? to the fibre direction. Results show that chicken muscle elastic behaviour is nonlinear and anisotropic. The tensile stress?stretch response is two orders of magnitude larger than in compression for all directions tested, which reflects the tension/compression asymmetry previously observed in porcine tissue. In compression the tissue is stiffest in the cross-fibre direction. However, tensile deformation applied at 45? gives the stiffest response, and this is different to previous findings relating to porcine tissue. Chicken muscle tissue is most compliant in the fibre direction for both tensile and compressive applied deformation. Generally, a small percentage of fluid exudation was observed in the compressive samples. Since collagen is the main structural protein in animal connective tissues, it is believed to be primarily responsible for their passive load-bearing properties. The direct detection and visualisation of collagen using fluorescently tagged CNA35 binding protein (fused to EGFP or tdTomato) is also reported for the first time on fixed skeletal muscle tissue. A working protocol is then established by examining tissue preparation, dilution factor, exposure time etc. for sensitivity and specificity. Penetration of the binding protein into intact mature skeletal muscle was found to be very limited, but detection works well on tissue sections with higher sensitivity on wax embedded sections compared to frozen sections. CNA35 fused to tdTomato has a higher sensitivity than CNA35 fused to EGFP but both show specific detection. Best results were obtained with 15 ?m wax embedded sections, with blocking of non-specific binding in 1% BSA and antigen retrieval in Sodium Citrate. There was a play-off between dilution of the binding protein and time of incubation but both CNA35-tdTomato and CNA35-EGFP worked well with approximately 100 ?g/ml of purified protein with overnight incubation, while CNA35- tdTomato could be utilized at 5 fold less concentration. The tension/compression asymmetry observed in the stress-strain response of skeletal muscle is not well understood. The optimised protocol is then applied to report qualitatively on skeletal muscle ECM reorganization during applied deformation using a combination of CNA35 binding protein and confocal imaging of tensile and compressive deformation of porcine and chicken muscle samples applied in both the fibre and cross-fibre directions. Results show the overall three-dimensional structure of collagen in perimysium visible in planes perpendicular (w1) and parallel (w2) to the muscle fibres in both porcine and chicken skeletal muscle. Furthermore, there is clear evidence of the reorganization of these structures under compression and tension applied in both the muscle fibre and cross-fibre directions, which generally explains anisotropy observed in the stress-strain response of skeletal muscle both in tension and compression for chicken and porcine tissues. These observations improve our understanding of how perimysium responds to three-dimensional deformations. The proposed three-dimensional illustration of perimysium structure is then used as a basis to create a microstructural-geometrical model to predict the passive mechanical stress-strain response observed in skeletal muscle. The current model represents the whole muscle response as a combination of both a group of muscle fibres (fascicle) response and the perimysium (ECM) response. It shows that although perimysium was believed to be a key element in the muscle stress response, the muscle fibres (in Tension-Fibre and Compression-XFibre deformations) also contribute to stress-stretch response since the order of magnitude for the stress in muscle fibres is similar to that of perimysium. The model shows more asymmetric response than previously published micromechanical model (Gindre et al., 2013). The model yields a good prediction of the whole muscle behaviour in Tension-Fibre and Compression-Fibre deformations using the optimum values for the model parameters obtained from the conducted sensitivity studies; connective tissue percentage of pc=1.75 , Elast modulus of Ec=300 MPa, and perimysium sheet waviness of w=1.25. However, the model overestimates the Compression-XFibre deformation and underestimates the Tension-XFibre deformations even by using the optimum parameters. The current model attempts to relate the mechanical stress-stretch response observed in muscle to the collagen reorganization in the muscle microstructure under load application, which further help develop better constitutive models for finite element modelling purposes

Bioactive glass/polymer composites for bone and nerve repair and regeneration

Bioactive glasses have several attractive properties in hard and soft tissue repair but their brittleness limited their use, as scaffolding materials, for applications in load- bearing hard tissue repair. At the same time, because of their bioactive properties, they are being studied more often for soft tissue repair. In the present work, a new glass/polymer composite scaffold was developed for the repair of load-bearing bones with high flexural strength and without brittle behavior. The new composites have 2.5 times higher flexural strength and ~100 times higher work of fracture (without catastrophic failure) compared to a similar bare glass scaffold. Also the use of two known bioactive glasses (13-93-B3 and 45S5) was investigated in developing glass/Poly(ε -caprolactone) (PCL) composite films for peripheral nerve repair. It was found that a layer of globular hydroxyapatite (HA) formed on both sides of the composites. The borate glass in the composites was fully reacted in SBF and different ions were released into the solution. The addition of bioactive glass particles to the PCL lowered its elastic modulus and yield strength, but the composites remained intact after the 14 day period in SBF at 37°C. Finally, in an effort to design a better bioactive glass, new borosilicate glass compositions were developed that possess advantages of borate and silicate bioactive glasses at the same time. It was found that replacing small amounts of B2O3 with SiO2 improved glass formation, resistance to nucleation and crystallization, and increased the release rate of boron and silicon in vitro. This new borosilicate glass could be a good alternative to existing silicate and borate bioactive glasses --Abstract, page iv