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Little is known about how metabolites couple tissuespecific stem cell function with physiology. Here we show that, in the mammalian small intestine, the expression of Hmgcs2 (3-hydroxy-3-methylglutarylCoA synthetase 2), the gene encoding the ratelimiting enzyme in the production of ketone bodies, including beta-hydroxybutyrate (beta OHB), distinguishes self-renewing Lgr5(+) stem cells (ISCs) from differentiated cell types. Hmgcs2 loss depletes beta OHB levels in Lgr5(+) ISCs and skews their differentiation toward secretory cell fates, which can be rescued by exogenous beta OHB and class I histone deacetylase (HDAC) inhibitor treatment. Mechanistically, beta OHB acts by inhibiting HDACs to reinforce Notch signaling, instructing ISC self-renewal and lineage decisions. Notably, although a high-fat ketogenic diet elevates ISC function and postinjury regeneration through beta OHB-mediated Notch signaling, a glucose-supplemented diet has the opposite effects. These findings reveal how control of beta OHB-activated signaling in ISCs by diet helps to fine-tune stem cell adaptation in homeostasis and injury.

Cardiovascular disease is a rising epidemic worldwide, and curative therapies remain elusive. Heart and vascular disease remain some of the hardest to cure due to the limited capacity of the heart to repair itself, necessitating a cell or organ based therapy to cure the inevitable descent into heart failure. Tissue engineering is uniquely poised to significantly alter this disease burden though the fabrication of cardiac and vascular tissues in vitro. However, the challenges for achieving these aims are significant - for cardiac tissues, the therapy must adhere to strict requirements of adequate perfusion and functional integration with the damaged heart. Vascular tissues are required to be amenable to surgical anastomosis while at the same time provide nutrient transport on the cellular level. Recently, a new set of technologies based from the semiconductor industry, have enabled micron level control over the cellular environment and cells themselves and may enable novel approaches to fulfill these tissue engineering requirements. In this dissertation, these microtechnologies will be leveraged to address some of the current obstacles that limit the use of tissue engineering approaches for functional therapy. Specifically, microtechnologies were used to screen the effect of electrical stimulation on the function and maturation of human embryonic stem cell derived cardiomyocytes, which resulted in the ability to program specific individual beating frequencies of the cells while improving contractile function and led to the identification of a channel specific effect for frequency modulation. These technologies were also used to distinguish the vasculogenic potential of different mesenchymal stem cell sources for nascent vessel stabilization, and enabled the development of a powerful hydrogel docking platform with the novel capability to spatially pattern any number of cells, cytokines or drugs on the microscale, while permitting scale up for larger tissue generation without the loss of precision. Finally, these technologies were used to create vascular networks with hierarchical branching patterns that could be implanted and used in vivo fulfilling a major criterion of vascular tissue function - surgical compatibility with microscale architecture for tissue perfusion. Therefore, these microtechnologies support novel interrogation of cell function and enable new methods to engineer cardiovascular tissues.

It is becoming increasingly apparent that the architecture and mechanical properties of scaffolds, particularly with respect to mimicking features of natural tissues, are important for tissue engineering applications. Acrylated poly(glycerol sebacate) (Acr-PGS) is a material that can be crosslinked upon exposure to ultraviolet light, leading to networks with tunable mechanical and degradation properties through simple changes during Acr-PGS synthesis. For example, the number of acrylate functional groups on the macromer dictates the concentration of crosslinks formed in the resulting network. Three macromers were synthesized that form networks that vary dramatically with respect to their tensile modulus (~30 kPa to 6.6 MPa) and degradation behavior (~20 to 100% mass loss at 12 weeks) based on the extent of acrylation (~1 to 24%). These macromers were processed into biodegradable fibrous scaffolds using electrospinning, with gelatin as a carrier polymer to facilitate fiber formation and cell adhesion. The resulting scaffolds were also diverse with respect to their mechanics (tensile modulus ranging from ~60 kPa to 1 MPa) and degradation (~45 to 70% mass loss by 12 weeks). Mesenchymal stem cell adhesion and proliferation on all fibrous scaffolds was indistinguishable from controls. The scaffolds showed similar diversity when implanted on the surface of hearts in a rat model of acute myocardial infarction and demonstrated a dependence on scaffold thickness and chemistry in the host response. In summary, these diverse scaffolds with tailorable chemical, structural, mechanical and degradation properties are potentially useful for the engineering of a wide range of soft tissues.

Преобразуването на сигнали от аналогов в цифров вид е основна задача във всички интегрални схеми обработващи смесени сигнали, като интерфейсните и телекомуникационните чипове. Сигналът в цифров вид е лесно податлив на математически манипулации и неговото точно представяне в дискретен вид е от първостепенно значение. Въпросното преобразуване на непрекъснатите във времето сигнали към дискретни, се извършва от аналогово-цифровите преобразуватели. В настоящия дисертационен труд са разгледани в дълбока детайлност аналогово-цифровите преобразуватели от сигма-делта вида. Принципно един преобразувател от този тип се разделя на аналогова част, модулатор и цифрова, цифрови филтри. Обект на разглеждане ще бъде реализацията на модулаторите, които по същество са силно нелинейни системи. Това тяхно качество води до трудности при проектирането на модулатори от висок ред, по-конкретно определяне на тяхната устойчивост и условията за запазване на устойчивостта, което ще е един от акцентите в дисертационната работа. Работата ще е с теоретична и практическа насоченост включваща етапите на математическо описание, проектиране и симулиране на системно и схемно ниво, изследвания на различни влияния върху работата на устройството, като изменения на външни и технологични параметри, проектиране на топология на схемата и верификация. Converting signals from analog to digital form is a fundamental task in all integrated circuits handling mixed signals, such as interface and telecommunication chips. A signal in digital form is easily amenable to mathematical manipulation, and its accurate representation in discrete form is of high importance. The conversion of continuous-time signals to discrete ones is carried out by analog-digital converters. In this thesis, analog-to-digital converters of the sigma-delta type are examined in great detail. In principle, a converter of this type is divided into an analog part, a modulator and a digital part, digital filters. The object of consideration will be the implementation of modulators, which are essentially highly nonlinear systems. This quality leads to difficulties in the design of high-order modulators, determining their stability and the conditions for maintaining stability, which will be one of the highlights of the dissertation work. The work will have a theoretical and practical focus, including the stages of mathematical description, design and simulation at the system and circuit level, studies of various influences on the operation of the device, such as changes in external and technological parameters, design of the circuit topology and verification.

Дисертационния труд е насочен към изследване и оптимизирано характеризиране на тънки слоеве от техен интерференчен спектър на пропускане и на отражение. Спектроскопичното характеризиране на материалите се основава на изследване на взаимодействието между изследвания материал и външно електромагнитно излъчване. Целта на настоящия труд е да се определи и оптимизира алгоритъм за най-точно характеризиране на един тънък полупроводников или диелектричен слой от тънкия слой, нанесен върху светопропускаща подложка, с използване на само един спектър на пропускане на тънък светопропускащ слой, нанесен върху светопропускаща подложка, на базата на съществуващите методи за изследване. В дисертацията е предложен оптимизиран алгоритъм на метода на обвивките за спектъра на пропускане и е показано че използването му води до най-точно характеризиране на тънки аморфни слоеве а-Si от тънкия слой, нанесен върху светопропускаща подложка, в сравнение със съществуващите алгоритми за характеризиране на тънък слой от тънък светопропускащ слой, нанесен върху светопропускаща подложка, въз основа на спектъра на пропускане. Оптимизираният алгоритъм на метода на обвивките за спектъра на пропускане е използван за характеризиране и на тънки аморфни слоеве AsxTe100-x, като е постигнато още по точно характеризиране в сравнение със слоевете а-Si. The dissertation thesis is focused on research and optimized characterization of thin films from their transmission and reflection interference spectrum. The spectroscopic characterization of materials is based on the study of the interaction between the studied material and external electromagnetic radiation. The aim of the dissertation is to define and optimize an algorithm for most accurate characterization of a thin semiconductor or dielectric film from the thin film deposited on a transparent substrate, using only one transmission spectrum of a thin transparent film deposited on a transparent substrate, based on existing research methods. The thesis proposes an optimized algorithm based on the envelope method for the transmission spectrum and shows that its use leads to the most accurate characterization of thin amorphous a-Si films from the thin film deposited on a transparent substrate, compared to existing algorthms for the characterization of thin film of thin transparent film deposited on a transparent substrate, based on the transmission spectrum. The optimized envelope method algorithm for the transmission spectrum was also used to characterize AsxTe100-x thin amorphous film, achieving an even more accurate characterization compared to a-Si films. These results show that an optimized algorithm of the envelopes method for the transmission spectrum can be used to characterize as accurately as possible an arbitrary amorphous film of a transparent thin film deposited

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis, which rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR-Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/ΔKras G12D/+ ;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5 + stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis., National Institutes of Health (U.S.) (Grant K08 CA198002), National Institutes of Health (U.S.) (Grant K99 CA187317), National Institutes of Health (U.S.) (Grant U54-CA163109)