Página 19 dos resultados de 1523 itens digitais encontrados em 0.001 segundos

‣ Born Normalization for Fluorescence Optical Projection Tomography for Whole Heart Imaging

Vinegoni, Claudio; Razansky, Daniel; Figueiredo, Jose-Luiz; Fexon, Lyuba; Pivovarov, Misha; Nahrendorf, Matthias; Ntziachristos, Vasilis; Weissleder, Ralph
Fonte: MyJove Corporation Publicador: MyJove Corporation
Tipo: Artigo de Revista Científica
Publicado em 02/06/2009 Português
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Optical projection tomography is a three-dimensional imaging technique that has been recently introduced as an imaging tool primarily in developmental biology and gene expression studies. The technique renders biological sample optically transparent by first dehydrating them and then placing in a mixture of benzyl alcohol and benzyl benzoate in a 2:1 ratio (BABB or Murray s Clear solution). The technique renders biological samples optically transparent by first dehydrating them in graded ethanol solutions then placing them in a mixture of benzyl alcohol and benzyl benzoate in a 2:1 ratio (BABB or Murray s Clear solution) to clear. After the clearing process the scattering contribution in the sample can be greatly reduced and made almost negligible while the absorption contribution cannot be eliminated completely. When trying to reconstruct the fluorescence distribution within the sample under investigation, this contribution affects the reconstructions and leads, inevitably, to image artifacts and quantification errors.. While absorption could be reduced further with a permanence of weeks or months in the clearing media, this will lead to progressive loss of fluorescence and to an unrealistically long sample processing time. This is true when reconstructing both exogenous contrast agents (molecular contrast agents) as well as endogenous contrast (e.g. reconstructions of genetically expressed fluorescent proteins).

‣ The Microfluidic Probe: Operation and Use for Localized Surface Processing

Perrault, Cecile M.; Qasaimeh, Mohammad A.; Juncker, David
Fonte: MyJove Corporation Publicador: MyJove Corporation
Tipo: Artigo de Revista Científica
Publicado em 04/06/2009 Português
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Microfluidic devices allow assays to be performed using minute amounts of sample and have recently been used to control the microenvironment of cells. Microfluidics is commonly associated with closed microchannels which limit their use to samples that can be introduced, and cultured in the case of cells, within a confined volume. On the other hand, micropipetting system have been used to locally perfuse cells and surfaces, notably using push-pull setups where one pipette acts as source and the other one as sink, but the confinement of the flow is difficult in three dimensions. Furthermore, pipettes are fragile and difficult to position and hence are used in static configuration only.

‣ Glucuronyltransferase Activity of KfiC from Escherichia coli Strain K5 Requires Association of KfiA: KfiC AND KfiA ARE ESSENTIAL ENZYMES FOR PRODUCTION OF K5 POLYSACCHARIDE, N-ACETYLHEPAROSAN*

Sugiura, Nobuo; Baba, Yuichi; Kawaguchi, Yoshirou; Iwatani, Toru; Suzuki, Kiyoshi; Kusakabe, Takahiro; Yamagishi, Kiwamu; Kimata, Koji; Kakuta, Yoshimitsu; Watanabe, Hideto
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Português
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139.0294%
Heparan sulfate is a ubiquitous glycosaminoglycan in the extracellular matrix of most animals. It interacts with various molecules and exhibits important biological functions. K5 antigen produced by Escherichia coli strain K5 is a linear polysaccharide N-acetylheparosan consisting of GlcUA β1–4 and GlcNAc α1–4 repeating disaccharide, which forms the backbone of heparan sulfate. Region 2, located in the center of the K5-specific gene cluster, encodes four proteins, KfiA, KfiB, KfiC, and KfiD, for the biosynthesis of the K5 polysaccharide. Here, we expressed and purified the recombinant KfiA and KfiC proteins and then characterized these enzymes. Whereas the recombinant KfiC alone exhibited no GlcUA transferase activity, it did exhibit GlcUA transferase and polymerization activities in the presence of KfiA. In contrast, KfiA had GlcNAc transferase activity itself, which was unaffected by the presence of KfiC. The GlcNAc and GlcUA transferase activities were analyzed with various truncated and point mutants of KfiA and KfiC. The point mutants replacing aspartic acid of a DXD motif and lysine and glutamic acid of an ionic amino acid cluster, and the truncated mutants deleting the C-terminal and N-terminal sites, revealed the essential regions for GlcNAc and GlcUA transferase activity of KfiC and KfiA...

‣ Next-Generation Optical Technologies for Illuminating Genetically Targeted Brain Circuits

Deisseroth, Karl; Feng, Guoping; Majewska, Ania K.; Miesenböck, Gero; Ting, Alice; Schnitzer, Mark J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/10/2006 Português
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Emerging technologies from optics, genetics, and bioengineering are being combined for studies of intact neural circuits. The rapid progression of such interdisciplinary “optogenetic” approaches has expanded capabilities for optical imaging and genetic targeting of specific cell types. Here we explore key recent advances that unite optical and genetic approaches, focusing on promising techniques that either allow novel studies of neural dynamics and behavior or provide fresh perspectives on classic model systems.

‣ A finite dissipative theory of temporary interfibrillar bridges in the extracellular matrix of ligaments and tendons

Ciarletta, P.; Ben Amar, M.
Fonte: The Royal Society Publicador: The Royal Society
Tipo: Artigo de Revista Científica
Português
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139.0294%
The structural integrity and the biomechanical characteristics of ligaments and tendons result from the interactions between collagenous and non-collagenous proteins (e.g. proteoglycans, PGs) in the extracellular matrix. In this paper, a dissipative theory of temporary interfibrillar bridges in the anisotropic network of collagen type I, embedded in a ground substance, is derived. The glycosaminoglycan chains of decorin are assumed to mediate interactions between fibrils, behaving as viscous structures that transmit deformations outside the collagen molecules. This approach takes into account the dissipative effects of the unfolding preceding fibrillar elongation, together with the slippage of entire fibrils and the strain-rate-dependent damage evolution of the interfibrillar bridges. Thermodynamic consistency is used to derive the constitutive equations, and the transition state theory is applied to model the rearranging properties of the interfibrillar bridges. The constitutive theory is applied to reproduce the hysteretic spectrum of the tissues, demonstrating how PGs determine damage evolution, softening and non-recoverable strains in their cyclic mechanical response. The theoretical predictions are compared with the experimental response of ligaments and tendons from referenced studies. The relevance of the proposed model in mechanobiology research is discussed...

‣ Selective biodegradation of keratin matrix in feather rachis reveals classic bioengineering

Lingham-Soliar, Theagarten; Bonser, Richard H. C.; Wesley-Smith, James
Fonte: The Royal Society Publicador: The Royal Society
Tipo: Artigo de Revista Científica
Português
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139.0294%
Flight necessitates that the feather rachis is extremely tough and light. Yet, the crucial filamentous hierarchy of the rachis is unknown—study hindered by the tight chemical bonding between the filaments and matrix. We used novel microbial biodegradation to delineate the fibres of the rachidial cortex in situ. It revealed the thickest keratin filaments known to date (factor >10), approximately 6 µm thick, extending predominantly axially but with a small outer circumferential component. Near-periodic thickened nodes of the fibres are staggered with those in adjacent fibres in two- and three-dimensional planes, creating a fibre–matrix texture with high attributes for crack stopping and resistance to transverse cutting. Close association of the fibre layer with the underlying ‘spongy’ medulloid pith indicates the potential for higher buckling loads and greater elastic recoil. Strikingly, the fibres are similar in dimensions and form to the free filaments of the feather vane and plumulaceous and embryonic down, the syncitial barbules, but, identified for the first time in 140+ years of study in a new location—as a major structural component of the rachis. Early in feather evolution, syncitial barbules were consolidated in a robust central rachis...

‣ A complex 3D human tissue culture system based on mammary stromal cells and silk scaffolds for modeling breast morphogenesis and function

Wang, Xiuli; Sun, Lin; Maffini, Maricel V.; Soto, Ana; Sonnenschein, Carlos; Kaplan, David L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Epithelial-stromal interactions play a crucial role in normal embryonic development and carcinogenesis of the human breast while the underlying mechanisms of these events remain poorly understood. To address this issue, we constructed a physiologically relevant, three-dimensional (3D) culture surrogate of complex human breast tissue that included a tri-culture system made up of human mammary epithelial cells (MCF10A), human fibroblasts and adipocytes, i.e., the two dominant breast stromal cell types, in a Matrigel™/collagen mixture on porous silk protein scaffolds. The presence of stromal cells inhibited MCF10A cell proliferation and induced both alveolar and ductal morphogenesis and enhanced casein expression. In contrast to the immature polarity exhibited by co-cultures with either fibroblasts or adipocytes, the alveolar structures formed by the tri-cultures exhibited proper polarity similar to that observed in breast tissue in vivo. Only alveolar structures with reverted polarity were observed in MCF10A monocultures. Consistent with their phenotypic appearance, more functional differentiation of epithelial cells was also observed in the tri-cultures, where casein α- and -β mRNA expression was significantly increased. This in vitro tri-culture breast tissue system sustained on silk scaffold effectively represents a more physiologically relevant 3D microenvironment for mammary epithelial cells and stromal cells than either co-cultures or monocultures. This experimental model provides an important first step for bioengineering an informative human breast tissue system...

‣ Protein-assisted self-assembly of multifunctional nanoparticles

Nikitin, Maxim P.; Zdobnova, Tatiana A.; Lukash, Sergey V.; Stremovskiy, Oleg A.; Deyev, Sergey M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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A bioengineering method for self-assembly of multifunctional superstructures with in-advance programmable properties has been proposed. The method employs two unique proteins, barnase and barstar, to rapidly join the structural components together directly in water solutions. The properties of the superstructures can be designed on demand by linking different agents of various sizes and chemical nature, designated for specific goals. As a proof of concept, colloidally stable trifunctional structures have been assembled by binding together magnetic particles, quantum dots, and antibodies using barnase and barstar. The assembly has demonstrated that the bonds between these proteins are strong enough to hold macroscopic (5 nm–3 μm) particles together. Specific interaction of such superstructures with cancer cells resulted in fluorescent labeling of the cells and their responsiveness to magnetic field. The method can be used to join inorganic moieties, organic particles, and single biomolecules for synergistic use in different applications such as biosensors, photonics, and nanomedicine.

‣ Bioelectric controls of cell proliferation: Ion channels, membrane voltage and the cell cycle

Blackiston, Douglas J.; McLaughlin, Kelly A.; Levin, Michael
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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All cells possess long-term, steady-state voltage gradients across the plasma membrane. These transmembrane potentials arise from the combined activity of numerous ion channels, pumps and gap junction complexes. Increasing data from molecular physiology now reveal that the role of changes in membrane voltage controls, and is in turn controlled by, progression through the cell cycle. We review recent functional data on the regulation of mitosis by bioelectric signals, and the function of membrane voltage and specific potassium, sodium and chloride ion channels in the proliferation of embryonic, somatic and neoplastic cells. Its unique properties place this powerful, well-conserved, but still poorly-understood signaling system at the center of the coordinated cellular interactions required for complex pattern formation. Moreover, disregulation of ion channel expression and function is increasingly observed to be not only a useful marker but likely a functional element in oncogenesis. New advances in genomics and the development of in vivo biophysical techniques suggest exciting opportunities for molecular medicine, bioengineering and regenerative approaches to human health.

‣ Biosynthesis of Dictyostelium discoideum differentiation-inducing factor by a hybrid type I fatty acid–type III polyketide synthase

Austin, Michael B; Saito, Tamao; Bowman, Marianne E; Haydock, Stephen; Kato, Atsushi; Moore, Bradley S; Kay, Robert R; Noel, Joseph P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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139.0294%
Differentiation-inducing factors (DIFs) are well known to modulate formation of distinct communal cell types from identical Dictyostelium discoideum amoebas, but DIF biosynthesis remains obscure. We report complimentary in vivo and in vitro experiments identifying one of two ~3,000-residue D. discoideum proteins, termed ‘steely’, as responsible for biosynthesis of the DIF acylphloroglucinol scaffold. Steely proteins possess six catalytic domains homologous to metazoan type I fatty acid synthases (FASs) but feature an iterative type III polyketide synthase (PKS) in place of the expected FAS C-terminal thioesterase used to off load fatty acid products. This new domain arrangement likely facilitates covalent transfer of steely N-terminal acyl products directly to the C-terminal type III PKS active sites, which catalyze both iterative polyketide extension and cyclization. The crystal structure of a steely C-terminal domain confirms conservation of the homodimeric type III PKS fold. These findings suggest new bioengineering strategies for expanding the scope of fatty acid and polyketide biosynthesis.

‣ Multifunctional Micellar Nanomedicine for Cancer Therapy

Blanco, Elvin; Kessinger, Chase W.; Sumer, Baran D.; Gao, Jinming
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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139.0294%
Polymeric micelles are supramolecular, core-shell nanoparticles that offer considerable advantages for cancer diagnosis and therapy. Their relatively small size (10-100 nm), ability to solubilize hydrophobic drugs as well as imaging agents, and improved pharmacokinetics provide a useful bioengineering platform for cancer applications. Several polymeric micelle formulations are currently undergoing phase I/II clinical trials, which have shown improved antitumor efficacy and reduced systemic toxicity. This minireview will focus on recent advancements in the multifunctional design of micellar nanomedicine with tumor targeting, stimulated drug release, and cancer imaging capabilities. Such functionalization strategies result in enhanced micellar accumulation at tumor sites, higher drug bioavailability, as well as improved tumor diagnosis and visualization of therapy. Ultimately, integrated nanotherapeutic systems (e.g., theranostic nanomedicine) may prove essential to address the challenges of tumor heterogeneity and adaptive resistance to achieve efficacious treatment of cancer.

‣ Potential role of stem cells in management of COPD

Hackett, Tillie L; Knight, Darryl A; Sin, Don D
Fonte: Dove Medical Press Publicador: Dove Medical Press
Tipo: Artigo de Revista Científica
Português
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Chronic obstructive pulmonary disease (COPD) is a worldwide epidemic affecting over 200 million people and accounting for more than three million deaths annually. The disease is characterized by chronic inflammation of the airways and progressive destruction of lung parenchyma, a process that in most cases is initiated by cigarette smoking. Unfortunately, there are no interventions that have been unequivocally shown to prolong survival in patients with COPD. Regeneration of lung tissue by stem cells from endogenous and exogenous sources is a promising therapeutic strategy. Herein we review the current literature on the characterization of resident stem and progenitor cell niches within the lung, the contribution of mesenchymal stem cells to lung regeneration, and advances in bioengineering of lung tissue.

‣ Periacetabular osteotomy in adult hip dysplasia – developing a computer aided real-time biomechanical guiding system (BGS)

Lepistö, Jyri; Armand, Mehran; Armiger, Robert S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2008 Português
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139.0294%
Osteotomies around hip acetabulum have become a routine surgical intervention in cases with constant pain without joint degeneration in adult dysplasia. However, it remains a challenge to plan and realign optimally the joint after osteotomy to reach best function and longevity in the clinical outcome. Tool tracking navigation systems have been available for many years but they have not become popular among surgeons because they extend operation time, require preoperative CT scan and, on the other hand, produce only marginal advantage in hands of an experienced surgeon. Real-time biomechanical assessment, based on computer analysis using preoperative CT-scanning, has become an interesting means to adjust the acetabular reorientation during surgery according to the patient’s individual structure and loading conditions. Further, real-time feedback allows the surgeon to foresee radiographic angles while performing fixation of the osteotomized fragment. Assessment of peak pressure and potential weight bearing area in real-time allows prospective and retrospective systematic biomechanical studies of patient outcomes. To conclude, a major development in navigation software is under way and we have so far seen a spectrum of new features like loading condition assessment in real time for osteotomies. This is...

‣ Bioengineering a unique deimmunized bispecific targeted toxin that simultaneously recognizes human CD22 and CD19 receptors in a mouse model of B cell metastases

Vallera, Daniel A.; Oh, Seunguk; Chen, Hua; Shu, Yanqun; Frankel, Arthur E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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139.0294%

‣ Engineering Adipose Tissue for Regenerative and Reparative Therapies

Patrick, Charles W.
Fonte: Thieme Medical Publishers Publicador: Thieme Medical Publishers
Tipo: Artigo de Revista Científica
Publicado em /08/2005 Português
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The correction or augmentation of soft tissue defects caused by trauma, tumor resection, congenital abnormalities, and aging presents a multitude of challenges in reconstructive surgery. Soft tissue defects run the gamut in terms of volume, from restoring the fullness of the face by removing wrinkles to restoring the breast mound after mastectomy. The limitations of current restorative and reparative techniques have served as drivers for the development of adipose tissue as an application area for tissue engineering. Tissue engineering is a multidisciplinary and maturing field that combines bioengineering, the clinical sciences, and the life sciences to repair or regrow tissues. This article discusses the inadequacies of current methods of correcting soft tissue defects and the innovative adipose tissue engineering strategies under pursuit to abrogate these limitations and improve patients’ outcomes and quality of life, and speculates rationally on the future. It does not discuss the applications and technologies involved with adipose-derived stem cells unless directly applied toward adipogenesis.

‣ Fractional dynamics pharmacokinetics–pharmacodynamic models

Verotta, Davide
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Português
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139.0294%
While an increasing number of fractional order integrals and differential equations applications have been reported in the physics, signal processing, engineering and bioengineering literatures, little attention has been paid to this class of models in the pharmacokinetics–pharmacodynamic (PKPD) literature. One of the reasons is computational: while the analytical solution of fractional differential equations is available in special cases, it this turns out that even the simplest PKPD models that can be constructed using fractional calculus do not allow an analytical solution. In this paper, we first introduce new families of PKPD models incorporating fractional order integrals and differential equations, and, second, exemplify and investigate their qualitative behavior. The families represent extensions of frequently used PK link and PD direct and indirect action models, using the tools of fractional calculus. In addition the PD models can be a function of a variable, the active drug, which can smoothly transition from concentration to exposure, to hyper-exposure, according to a fractional integral transformation. To investigate the behavior of the models we propose, we implement numerical algorithms for fractional integration and for the numerical solution of a system of fractional differential equations. For simplicity...

‣ Biocompatibility of Intracortical Microelectrodes: Current Status and Future Prospects

Marin, Cristina; Fernández, Eduardo
Fonte: Frontiers Research Foundation Publicador: Frontiers Research Foundation
Tipo: Artigo de Revista Científica
Publicado em 28/05/2010 Português
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139.0294%
Rehabilitation of sensory and/or motor functions in patients with neurological diseases is more and more dealing with artificial electrical stimulation and recording from populations of neurons using biocompatible chronic implants. As more and more patients have benefited from these approaches, the interest in neural interfaces has grown significantly. However an important problem reported with all available microelectrodes to date is long-term viability and biocompatibility. Therefore it is essential to understand the signals that lead to neuroglial activation and create a targeted intervention to control the response, reduce the adverse nature of the reactions and maintain an ideal environment for the brain-electrode interface. We discuss some of the exciting opportunities and challenges that lie in this intersection of neuroscience research, bioengineering, neurology and biomaterials.

‣ Solute transporters in plant thylakoid membranes: Key players during photosynthesis and light stress

Spetea, Cornelia; Schoefs, Benoît
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
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139.0294%
Plants utilize sunlight to drive photosynthetic energy conversion in the chloroplast thylakoid membrane. Here are located four major photosynthetic complexes, about which we have great knowledge in terms of structure and function. However, much less we know about auxiliary proteins, such as transporters, ensuring an optimum function and turnover of these complexes. The most prominent thylakoid transporter is the proton-translocating ATP-synthase. Recently, four additional transporters have been identified in the thylakoid membrane of Arabidopsis thaliana, namely one copper-transporting P-ATPase, one chloride channel, one phosphate transporter, and one ATP/ADP carrier. Here, we review the current knowledge on the function and physiological role of these transporters during photosynthesis and light stress in plants. Subsequently, we make a survey on the outlook of thylakoid activities awaiting identification of responsible proteins. Such knowledge is necessary to understand the thylakoid network of transporters, and to design strategies for bioengineering crop plants in the future.

‣ Molecular Thermometry

McCabe, Kevin M.; Hernandez, Mark
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/2010 Português
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139.0294%
Conventional temperature measurements rely on material responses to heat, which can be detected visually. When Galileo developed an air expansion based device to detect temperature changes, Santorio, a contemporary physician, added a scale to create the first thermometer. With this instrument, patients’ temperatures could be measured, recorded and related to changing health conditions. Today, advances in materials science and bioengineering provide new ways to report temperature at the molecular level in real time. In this review the scientific foundations and history of thermometry underpin a discussion of the discoveries emerging from the field of molecular thermometry. Intracellular nanogels and heat sensing biomolecules have been shown to accurately report temperature changes at the nano-scale. Various systems will soon provide the ability to accurately measure temperature changes at the tissue, cellular, and even sub-cellular level, allowing for detection and monitoring of very small changes in local temperature. In the clinic this will lead to enhanced detection of tumors and localized infection, and accurate and precise monitoring of hyperthermia based therapies. Some nanomaterial systems have even demonstrated a theranostic capacity for heat-sensitive...

‣ Perturbation of single hematopoietic stem cell fates in artificial niches†

Lutolf, Matthias P.; Doyonnas, Regis; Havenstrite, Karen; Koleckar, Kassie; Blau, Helen M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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139.0294%
Hematopoietic stem cells (HSCs) are capable of extensive self-renewal in vivo and are successfully employed clinically to treat hematopoietic malignancies, yet are in limited supply as in culture this self-renewal capacity is lost. Using an approach at the interface of stem cell biology and bioengineering, here we describe a novel platform of hydrogel microwell arrays for assessing the effects of either secreted or tethered proteins characteristic of the in vivo microenvironment, or niche, on HSC fate in vitro. Time-lapse microscopic analyses of single cells were crucial to overcoming inevitable heterogeneity of FACS-enriched HSCs. A reduction in proliferation kinetics or an increase in asynchronous division of single HSCs in microwells in response to specific proteins (Wnt3a and N-Cadherin) correlated well with subsequent serial long-term blood reconstitution in mice in vivo. Single cells that divided once in the presence of a given protein were capable of in vivo reconstitution, providing evidence of self-renewal divisions of HSCs in vitro. These results validate the hydrogel microwell platform as a broadly applicable paradigm for dissecting the regulatory role of specific signals within a complex stem cell niche.