Mechanisms of Extracellular Matrix Scaffold Remodeling

Scaffolds composed of extracellular matrix (ECM) and derived from various species and various organs have been shown to promote constructive, site-specific tissue remodeling in pre-clinical studies and clinical use, including musculoskeletal, urogenital, dermal, cardiovascular, and neural applications. Despite extensive study, the mechanisms of the remodeling process are still not thoroughly understood. The goals of this dissertation were to elucidate the role of mechanical loading in the remodeling of ECM scaffolds and the role of bone marrow derived cells in the remodeling process. To better understand the role of mechanical loading on the remodeling of an ECM scaffold, an ECM scaffold derived from the porcine small intestinal submucosa (SIS-ECM) was seeded with fibroblasts and subjected to a variety of magnitudes and frequencies of cyclic strain using a custom designed Cyclic Stretching Tissue Culture system. The magnitudes of stretch were based on a study of the collagen fiber kinematics of the SIS-ECM under uniaxial and biaxial loading conditions. The cyclic loading experiments showed that mechanical loading led to expression of matrix related genes that was consistent with a constructive remodeling response with increased expression of collagen type I (Col I), á-smooth muscle actin (SMA), and tenascin-C (TN-C), as well as decreased expression of collagen type III (Col III).It was also found that bone marrow cells were recruited to the site of ECM remodeling and that the cells remained at the site of remodeling for 16 weeks after implantation, unlike an autologous tendon repair. Furthermore, it was found that the bone marrow derived cells did not express the hematopoietic marker CD45, but did express Col I, Col III, and SMA. The cells did not show the same expression pattern as normal tendon fibroblast (Col I+, TN-C+), suggesting that the cells differentiated towards a myofibroblastic cell as opposed to a normal fibroblast. The results of this study show that an ECM scaffold recruits a bone marrow derived mesenchymal progenitor to the site of remodeling, and that those cells differentiate into site specific tissue as a result of mechanical and biochemical cues

Desarrollo de nuevas férulas de inmovilización sensorizadas, para la monitorización y generación de información clínica

Es conocido que el origen de las escayolas y férulas para inmovilizar con yeso se atribuye a los persas, en el siglo X. Desde entonces, la evolución ha sido escasa, y se sigue empleando la misma técnica para inmovilizar miembros lesionados. Este tipo de técnica, aunque válida, no permite aplicar ciertos tratamientos o airear la zona de la piel cubierta, entre otras cosas. Es por esto por lo que aprovechando las nuevas técnicas de fabricación y las nuevas tecnologías en sensores y electrónica, que se plantea la reinterpretación de esta técnica del siglo X para traerla a nuestra época actual. Desarrollo de férulas inteligentes diseñadas según la lesión y morfología del paciente, que permitan una monitorización en tiempo real de la evolución y la aplicación de nuevos tratamientos

Translational Models for Advancement of Regenerative Medicine and Tissue Engineering

At the root of each regenerative medicine or tissue engineering breakthrough is a simple goal, to improve quality of healing, thus improving a patient’s quality of life. Each tissue presents its own complexities and limitations to healing, whether it is the scarring nature of tendon healing or the mechanical complexity driving bone regeneration. Preclinical, translational models aim to reflect these complexities and limitations, allowing for effective development and refinement of tissue engineered therapeutics for human use. The following body of work explores several of these translational models, both utilizing them for tissue regenerative therapy development and evaluating the benefits and complications incurred with each model. This work begins with a discussion of the complexity of bone healing and how dysfunction in the mechanical, surgical, and systemic fracture environment can lead to delayed healing and nonunion. A comprehensive review of the advances in preventative and corrective therapeutics for bone nonunion is included next, with specific focuses on mechanical and tissue-engineered technology. Then, this work presents a tissue-engineered application of mesenchymal stem cells in acute tendon injury, highlighting experimentation in cell fate direction in vitro and intralesional mesenchymal stem cell implantation in vivo. Next, this work presents a series of experiments that evaluated and refined a commonly utilized preclinical model of delayed bone healing, the caprine segmental tibial defect stabilized using single locking plate fixation. First, the biomechanical stability of the model was evaluated in vivo using plantar-pressure analysis of gait. Then, the surgical technique was refined through a retrospective analysis of the effects of plate length and position on fixation stability in vitro and in vivo. Finally, the comorbidities of this preclinical model were explored via an analysis of the effect of long-term tibial locking plate fixation on cortical dimensions and density

Desarrollo de nuevas férulas de inmovilización sensorizadas para la generación de información clínica

[ES]El objetivo principal de esta tesis es desarrollar un nuevo sistema de férulas totalmente novedoso, que permita aplicar un tratamiento más efectivo a lesiones principalmente de las extremidades. Este nuevo sistema de férulas inteligentes podría llegar a ser revolucionario en lesiones musculares, óseas, de fibras o de tendones; ya que no hay ningún desarrollo previo de bajo coste que monitorice la evolución de la lesión, especialmente en las primeras horas de producirse. El sistema permitirá detectar cambios de presión, temperatura, humedad y color de la piel en la zona de la lesión. La férula será diseñada exclusivamente para cada individuo, y podría contemplarse el tener férulas preparadas previamente a producirse una lesión, especialmente en deportistas de alto nivel. Esto aplicando la metodología tradicional es totalmente impensable ya que se construyen directamente sobre el paciente. Las tecnologías de sensorizado se presentarán para la adquisición de datos que faciliten información sobre el estado de salud, basándose en el concepto IoT (Internet of Things). Los parámetros que se controlarán son la temperatura, la humedad, la presión y el color de la piel, así como una colocación correcta de la férula. La combinación de estos puede indicar diferentes problemas que pueden estar sufriendo los pacientes, como la inflamación. Para obtener el prototipo de la férula se considerarán las ventanas para el alojamiento de las terapias rehabilitadoras y el tipo de tratamiento. De hecho, la aplicación de tratamientos en la fase de inmovilización tiene una influencia sustancial en la evolución de la lesión y en la rehabilitación de la movilidad del miembro. Además, las férulas contemplarán la aplicación de nuevos tratamientos en la fase de inmovilización por ser sumergibles en medio acuoso, y permitirán el acceso visual a través de ventanas de trabajo y el contacto directo con la piel. Los tratamientos que se plantean son: 1. Cura para el caso de simultaneidad con heridas, patologías dermatológicas o cirugías. 2. Drenaje Linfático 3. Iontoforesis 4. Ultrasonidos 5. Láser 6. Electroestimulació

Ankle-Foot Orthosis Stiffness: Biomechanical Effects, Measurement and Emulation

Ankle-foot orthoses (AFOs) are braces worn by individuals with gait impairments to provide support about the ankle. AFOs come in a variety of designs for clinicians to choose from. However, as the effects of different design parameters on AFO properties and AFO users have not been adequately quantified, it is not clear which design choices are most likely to improve patient outcomes. Recent advances in manufacturing have further expanded the design space, adding urgency and complexity to the challenge of selecting optimal designs. A key AFO property affected by design decisions is sagittal-plane rotational stiffness. To evaluate the effectiveness of different AFO designs, we need: 1) a better understanding of the biomechanical effects of AFO stiffness and 2) more precise and repeatable stiffness measurement methods. This dissertation addresses these needs by accomplishing four aims. First, we conducted a systematic literature review on the influence of AFO stiffness on gait biomechanics. We found that ankle and knee kinematics are affected by increasing stiffness, with minimal effects on hip kinematics and kinetics. However, the lack of effective stiffness measurement techniques made it difficult to determine which specific values or ranges of stiffness influence biomechanics. Therefore, in Aim2, we developed an AFO stiffness measurement apparatus (SMApp). The SMApp is an automated device that non-destructively flexes an AFO to acquire operator- and trial-independent measurements of its torque-angle dynamics. The SMApp was designed to test a variety of AFO types and sizes across a wide range of flexion angles and speeds exceeding current alternatives. Common models of AFO torque-angle dynamics in literature have simplified the relationship to a linear fit whose slope represents stiffness. This linear approximation ignores damping parameters. However, as previous studies were unable to precisely control AFO flexion speed, the presence of speed effects has not been adequately investigated. Thus, in Aim3, we used the SMApp to test whether AFOs exhibit viscoelastic behaviors over the range of speeds typically achieved during walking. This study revealed small but statistically significant effects of flexion speed on AFO stiffness for samples of both traditional AFOs and novel 3-D printed AFOs, suggesting that more complex models that include damping parameters could be more suitable for modeling AFO dynamics. Finally, in Aim 4, we investigated the use of an active exoskeleton, that can haptically-emulate different AFOs, as a potential test bed for studying the effects of AFO parameters on human movement. Prior work has used emulation for rapid prototyping of candidate assistive devices. While emulators can mimic a physical device's torque-angle profile, the physical and emulated devices may have other differences that influence user biomechanics. Current studies have not investigated these differences, which limits translation of findings from emulated to physical devices. To evaluate the efficacy of AFO emulation as a research tool, we conducted a single-subject pilot study with a custom-built AFO emulator device. We compared user kinematics while walking with a physical AFO against those with an emulated AFO and found they elicited similar ankle trajectories. This dissertation resulted in the successful development and evaluation of a framework consisting of two test beds, one to assess AFO mechanical properties and another to assess the effects of these properties on the AFO user. These tools enable innovations in AFO design that can translate to measurable improvements in patient outcomes.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163219/1/deema_1.pd