Shape Memory Polyurethane-Based Smart Polymer Substrates for Physiologically Responsive, Dynamic Pressure (Re)Distribution.

Shape memory polymers (SMPs) are an exciting class of stimuli-responsive smart materials that demonstrate reactive and reversible changes in mechanical property, usually by switching between different states due to external stimuli. We report on the development of a polyurethane-based SMP foam for effective pressure redistribution that demonstrates controllable changes in dynamic pressure redistribution capability at a low transition temperature (∼24 °C)-ideally suited to matching modulations in body contact pressure for dynamic pressure relief (e.g., for alleviation or pressure ulcer effects). The resultant SMP material has been extensively characterized by a series of tests including stress-strain testing, compression testing, dynamic mechanical analysis, optical microscopy, UV-visible absorbance spectroscopy, variable-temperature areal pressure distribution, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, dynamic thermogravimetric analysis, and 1H nuclear magnetic resonance spectroscopy. The foam system exhibits high responsivity when tested for plantar pressure modulation with significant potential in pressure ulcers treatment. Efficient pressure redistribution (∼80% reduction in interface pressure), high stress response (∼30% applied stress is stored in fixity and released on recovery), and excellent deformation recovery (∼100%) are demonstrated in addition to significant cycling ability without performance loss. By providing highly effective pressure redistribution and modulation when in contact with the body's surface, this SMP foam offers novel mechanisms for alleviating the risk of pressure ulcers

Enabling New Functionally Embedded Mechanical Systems Via Cutting, Folding, and 3D Printing

Traditional design tools and fabrication methods implicitly prevent mechanical engineers from encapsulating full functionalities such as mobility, transformation, sensing and actuation in the early design concept prototyping stage. Therefore, designers are forced to design, fabricate and assemble individual parts similar to conventional manufacturing, and iteratively create additional functionalities. This results in relatively high design iteration times and complex assembly strategies

A survey of DA techniques for PLD and FPGA based systems

Programmable logic devices (PLDs) are gaining in acceptance, of late, for designing systems of all complexities ranging from glue logic to special purpose parallel machines. Higher densities and integration levels are made possible by the new breed of complex PLDs and FPGAs. The added complexities of these devices make automatic computer aided tools indispensable for achieving good performance and a high usable gate-count. In this article, we attempt to present in an unified manner, the different tools and their underlying algorithms using an example of a vending machine controller as an illustrative example. Topics covered include logic synthesis for PLDs and FPGAs along with an in-depth survey of important technology mapping, partitioning and place and route algorithms for different FPGA architectures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31206/1/0000108.pd

3D structures based on carbón materials and conducting polymers for electroresponsive cell cultures

149 p.El campo de la ingeniería de tejidos (TE) requiere la generación de nuevas plataformas tridimensionales como implantes o materiales tridimensionales para estudios de modelos. Dentro de todos los tejidos, nosotros nos hemos enfocado en aquellos que se ven favorecidos cuando están crecidos sobre un entorno electroactivo, tales como el tejido neuronal o cardíaco. Para que estas estructuras cumplan todos los requisitos y mimeticen el tejido nativo se requieren propiedades mecánicas blandas, conductividad, porosidad controlada y biocompatibilidad.Esta tesis doctoral ha abordado el desafío de fabricar estructuras 3D con el polímero conductor PEDOT, que carece de posibilidad de formar estructuras 3D por él mismo, usando otros materiales auxiliares para conseguirlo. De esta manera, en el primer y segundo capítulo de la tesis se han desarrollado estructuras tidimensionales de PEDOT y nanotubos de carbono (CNT) usando metodologías comúnmente utilizadas para formar estructuras bidimensionales tipo films. Estas estructuras han sido caracterizadas mostrando excelente conductividad, propiedades mecánicas ideales para cultivo neuronal, porosidad y buena biocompatibilidad. Por último, se ha diseñado un material conductor e imprimible por impresión 3D, formado por un poliéster común (PLA) y PEDOT. Ambos en conjunto poseen buena biocompatibilidad y la posibilidad de madurar tejido cardíaco, generando durante su co-cultivo estructuras de la matriz extracelular que permiten al cardiomiocito latir y por lo tanto mantener su funcionalidad.Polymat CICbiomaGUN

Stretching the limits of dynamic range, shielding effectiveness, and multiband frequency response

In this dissertation, an RF MEMS variable capacitor suitable for applications requiring ultrawide capacitive tuning ranges is reported. The device uses an electrostatically tunable liquid dielectric interface to continuously vary the capacitance without the use of any moving parts. As compared to existing MEMS varactors in literature, this device has an extremely simple design that can be implemented using simple fabrication methods that do not necessitate the use of clean room equipment. In addition, this varactor is particularly suited for incorporating a wide range of liquid dielectric materials for specific tuning ratio requirements. Additionally, the shielding effectiveness performance of graphene-doped ABS thin films is investigated. The use of graphene as a replacement for metal fillers in composite EMI shielding materials is quickly becoming a widely-investigated field in the electromagnetic compatibility community. By replacing conventional metal-based shielding methods with graphene-doped polymers, low-weight, field-use temporary shielding enclosures can be implemented that do not suffer from mechanical unreliability and corrosion/oxidation like a traditional metal enclosure. While the performance of composite EMI shielding materials has not yet surpassed metals, the advantages of polymer-based shielding methods could find usage in a variety of applications. Finally, mutliband pre-fractal antennas fabricated via 3D printing are reported. These devices are the first to incorporate the advantages of 3D printing (rapid prototyping, fabrication of complex geometries otherwise unobtainable) with the advantages of self-similar antennas (increased gain and multiband performance) in a single device. The Sierpinski tetrahedron-based antenna design was both computationally modeled and physically realized to illustrate its potential as a solution to enable true multiband communication platforms

Development & Characterisation of Nanocomposites for Bone Tissue Engineering

The aim of this thesis was to develop a bioactive and resorbable nanoscale composite that mimics the properties of bone and will have the potential to regenerate bone. In conventional composites, the polymer phase can mask the bioactive phase and often degrades faster than the ceramic phase due to the weak interfacial bonding between the polymer and ceramic. Here in this thesis an organic/inorganic nanocomposite with stronger interfacial bonding between the two phases has been produced using the sol-gel route. Glasses containing SiO2 and CaO were used as the inorganic while the amino acid poly-γ−glutamic acid (γ−PGA) was used as the organic. This is the first time an inorganic/organic hybrid with enzymatically degradable polymer covalently crosslinked to the inorganic has been produced. Several factors contributed to the homogeneity of the nanocomposites; most important of all was the extent of integration (homogeneity and phase miscibility) of the organic into the inorganic sol. The main focus of this thesis was to synthesise this new material and to develop an understanding of the nanoscale interactions of the two phases. The chemical structure of the nanocomposites were characterised with Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR) and the nanostructure was characterised with scanning and transmission electron microscopy (SEM and TEM). Bioactivity studies of the nanocomposites in simulated body fluid (SBF) showed that the nanocomposites containing calcium were bioactive. Initial in vitro cell response studies also showed that the nanocomposites were not toxic to cells. Nanocomposites were also foamed to create the first porous bioactive inorganic/organic scaffolds with covalent bonding between the organic and inorganic. Micro-computed tomography (μCT) was used to non-destructively image and quantify the internal pore structure of the bioactive nanocomposite scaffolds. The three-dimensional images of the scaffolds show that the nanocomposites have large macropores with multiple connections between them giving a suitable pore structure for tissue engineering

Segmented hydrogels: process development of a reproducible 3D tissue engineered interface system and its use as a muscle–tendon model

Prior to commercialisation, all drugs and medical devices must undergo testing to ensure safety to the end user. Part of this process is the pre-clinical trials stage in which high-throughput testing of the product is performed on cells in monolayer followed by testing in animal models. Monolayer cultures are generally basic, containing one cell type, which leads to minimal testing parameters. The more complex animal tests are often misleading as they do not adequately represent the human physiology and their ethics are also often contested. 3D Tissue engineered models, an evolution of the monolayer model more accurately mimic the structure and biochemistry of specific native tissues. To observe effects on the musculoskeletal system, a model representing these tissues is necessary. This thesis focuses on attempting to create an in vitro myotendinous junction (MTJ) for such purposes. Firstly, the most suitable published process for making a 3D tissue engineered skeletal muscle model was identified based on an analysis of requirements. A model using the C2C12 cell line in a collagen hydrogel between two anchor points was chosen and the process was optimised using a Quality-by-Design framework. This was essential to make a system that would lend itself to high-throughput testing in the long run. Following this, a simple process for creating an MTJ, termed ‘segmentation’ of the gel, was tested and showed a reduction in surface area consistent with cell attachment as previously reported. This involved physically blocking regions of the gel during manufacture. Multiple design iterations were tested to enable reproducibility. Of the tested configurations, a 3D printed PLA mould adhered to a 6-well plate with sliding dividers for segmentation and posts for gel anchor points was found to be optimal. Finally, standardising the use of ice in the gel fabrication process to prevent premature polymerisation of the hydrogel led to the success rate of fabrication to increase to up to 100%. Comparisons with the initial system showed multiple indicators of more consistent gels with reduced failure rates, a reduction in the resources required due to scaling down, and versatility in the design allowing for segmentation and simple adaptation to testing apparatus for future experiments. This system was then tested by only seeding the central region of a gel with C2C12 muscle-precursor cells to create “segmented gels”. Compared to homogenously seeded constructs, the ‘muscle’ region in segmented gels was found to have no difference in macroscopic behaviour and only a slight decrease in myotube width measurements, still within published parameters. These models exhibited a unique ‘bow-tie’ shape from the seeding discrepancies in the different regions. During the 14-day culture period, the cells became equally distributed throughout the gel, indicating that they may be migrating over the culture period. These regions also exhibited myotube formation and although less densely populated, a greater incidence of striated myotubes were found in these regions as demonstrated by staining with rhodamine phalloidin. Finally, the end regions were seeded with human dermal fibroblasts (hDFs) to represent a tendon to create a tendon-muscle-tendon model. Immunostaining showed that the majority of cells in the resulting construct were desmin-positive, a muscle-specific marker. This is in agreement with previous research that shows that dermal fibroblasts can be driven down a myogenic lineage by secreted factors in culture. However, transitional interdigitation between the two morphologically different cell types were observed in some models. This represents the first report of the successful formation of a myotendinous junction in a collagen-based potentially high-throughput system

Development of scaffolds by thermally-induced phase separation from biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(butylene succinate)

Aplicat embargament des de la data de defensa fins el 31 de juliol de 2022TIPS process followed by freeze-dtying was used to prepare blodegradable and biocompatible matrices from poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5 and 12 wt% of 3-hydroxyvalerate (HV) and poly(butylene succinate) (PBS). 1,4 dioxane (DXN) and tetrahydofuran (THF) were used as solvents. The cloud points of the polymer solutions were determíned by turbidimetry method, to predict the locus of binodal curve in the binary phase diagrams. A multidirectional cooling from ~70ºC to 25ºC, and then to -5 ºC or -25 ºC was applied to PHBV solutions in the TIPS process. The effect of the applied thermal gradients and HV molar ratio of PHBV copolymer on phase separation mechanism, morphology and mechanical properties of the scaffolds was studied. Upon high HV contents and fast cooling, the solid-liquid phase separation through crystallization of DXN was the controlling mechanism and generated large pores with well-distinguished walls and great structural continuity. The morphologies ascribed to polymer crystallizatíon, mostly with low structural consistency were further discernible upon slow cooling. An improvement in scaffolds rigidity were observed in low HV and fast cooling conditions, due to the increased polymer crystallinity and the greater structural consistency, respectively. PHBV scaffolds showed a complete biocompatibility towards MDCK and NRK cell adhesion and proliferation. A multidirectional cooling from ~70 ºC to -20 or -74 ºC were applied to PBS-DXN and PBS-THF solutions and a uniaxial cooling from ~70ºC to -74 or -196 ºC to PBS-DXN. 5 and 100 wt% ofcurcumin (CUR) and piperine (PIP) natural drugs were loaded into PBS matrices via a one-step TIPS fabrication/drug loadlng protocot. Utílizing DXN and THF solvents, solid-liquid and liquid-liquid phase separation were respectívely detected as the main mechanisms responsible for creating the porous structures, while the subregions composed of crysta llized PBS were also obse rved . The applied uniaxial thermal gradient enabled DXN solvent to crystallize along the heat transfer direction and form an oriented pare structure. Although the low drug values did not significantly influence the morphology, the high-level drug loading gave rise to the decreased porosity and superficial roughness ofthe scaffolds . A uniform distribution ofprismatic PIP crystals and matrix-integrated CUR aggregation was observed all overthe structure. The integration of CUR which was confirmed by the physicochemical analyses attributed to a possible interaction with the PBS matrix, as it also showed a slower release profile compared to PIP. Oriented matrices showed greater biocompatibility and also retarded drug release from their·dense spherulitic pore walls. Biobased highly rigid polycarbonate and polyesters with terpene oxide units were blended with PBS at different ratios to increase the biocontents and modify the properties. Ali the terpene-derived polymers exhibi ted high Tg, thermal stability biocompatibility and mechanical strength. Their rigid nature and stiff chains led to insignificant hydrolytic and enzymatic biodegradation, while an accelerated degradation in oxidative media was observed. Their blends with PBS were also biocom patible and to sorne extent biodegradable . 30 wt% of poly (PA-LO) the copolyester derived from phthalic anhydride and limonene oxide, was blended with PBS and porous matrices were prepared by a one-step TIPS fabrication/blending protocol. Multidirectional cooling to -20 ºC or-74 ºC and uniaxial cooling to -74 ºC or-196 ºC was applied to PBS-Poly (PA-LO)-DX N system. Although the blending did not affect the morphology and pore structure of the random/oriented matrices, could somewhat restrict the crystallization of PBS from the solution during the TIPS process. Accordin gly, thinner polymer leaves upon multídirectional and lower thermal gradient, and smaller, less planar and less integrated spherulites were formed upon high uniaxial gradient.El proceso TIPS seguido de liofilización fue usado para preparar matrices porosas ("scaffolds") biodegradables y biocompatibles a partir del poliéster poli (3-hidroxibutirato-co-3-hidroxivalerato) (PHBV) que contiene 5 y 12 wto/o de 3- hidroxivalerato (HV) y del poliéster poli(butilensuccinato) (PBS). El 1.4 dioxano (DXN) yel tetrahidofurano (THF) fueron los disolventes. En el TIPS para las disoluciones de PHBV se aplicó un enfriamiento multidireccional de 70 a 25ºC y luego a -5 ó -25ºC. Se estudiaron los efectos del gradiente térmico y contenido de HV del copolímero sobre el mecanismo de separación de fases, la morfología y propiedades mecánicas de los scaffolds. La separación de fase sólido-líquido en la cristalización del DXN durante el enfriamiento rápido fue el mecanismo que controla la formación de los scaffolds del copolímero con alto contenido de HV. Los scaffolds mostraron grandes poros con paredes bien formadas y gran integridad estructural. Las morfologías atribuidas a la cristalización del polímero. en su mayoría con poca integridad estructural. fueron obtenidas con el enfriamiento lento. Se observó una mejora en la rigidez y mayor integridad estructural de los scaffolds con bajo HV y enfriamiento rápido. debido al aumento de la cristalinidad del polímero. Los scaffolds de PHBV mostraron gran biocompatibilidad determinada por la adhesión y proliferación de células MDCK y NRK. Las disoluciones de PBS-DXN y PBS-THF fueron enfriadas multidireccionalmente de 70ºC a -20 ó -74ºC. y de manera uniaxial para PBS-DXN de 70ºC a -74 ó -196ºC. Los scaffolds de PBS durante su preparación por TIPS fueron cargados con 5 y 100 wt% de curcumina (CUR) o piperina (PIP). La separación de fases sólido-líquido y líquido-líquido (con los disolventes DXN y THF respectivamente) fueron los principales mecanismos responsables para formar las estructuras porosas y subregiones compuestas por PBS cristalizada. El gradiente térmico uniaxial permitió la cristalización del DXN a lo largo de la dirección de transferencia de calor y la formación de poros orientados. La presencia de los fármacos no influyo significativamente en la morfología de los scaffolds. La gran cantidad del fármaco disminuye la porosidad y la rugosidad superficial en los scaffolds. En los scaffolds se observó una distribución uniforme de cristales de PIP y agregación de CUR. La integración de CUR indico una posible interacción con la matriz de PBS y mostró un perfil de liberación más lento en comparación con PIP. Los scaffolds orientados mostraron una mayor biocompatibilidad y una liberación lenta del fármaco debido a sus densas paredes formadas por esferulitas policarbonatos y poliésteres biobasados altamente rígidos y formados por unidades de óxido de terpeno fueron mezclados con PBS en diferentes proporciones para aumentar su biocontenido y modificar sus propiedades. La Tg. estabilidad térmica, biocompatibilidad y resistencia mecánica son elevadas en los polímeros derivados del terpeno. La biodegradación hidrolítica y enzimática de estos polímeros fue insignificante debido a la rigidez de sus cadenas. mientras una degradación acelerada fue lograda en medios oxidativos. Las mezclas con PBS fueron biocompatibles y algo biodegradables. La mezcla del copoliéster derivado de anhídrido phtalico y óxido de limoneno (poli(PA-LO)) con PBS (30:70 wo/o, respectivamente) fue usada para preparar scaffolds con la metodología TIPS. El enfriamiento multidireccional a -20ºC ó -74ºC y el enfriamiento uniaxial a -74ºC ó -196ºC fue aplicado al sistema PBS-Poly(PA-LO)-DXN. Esta mezcla no influye en la morfología y estructura de los poros de los scaffolds con porosidad orientada o al azar. Durante el proceso TIPS, la cristalización del PBS fue afectada. En consecuencia, el PBS en el menor gradiente térmico multidireccional forma estructuras en hojas más delgadas y con el mayor gradiente uniaxial se formaron esferolitas más pequeñas, menos planas y menos integradas.Postprint (published version