Intense acoustic bursts as a signal-enhancement mechanism in ultrasound-modulated optical tomography

Biophotonic imaging with ultrasound-modulated optical tomography (UOT) promises ultrasonically resolved imaging in biological tissues. A key challenge in this imaging technique is a low signal-to-noise ratio (SNR). We show significant UOT signal enhancement by using intense time-gated acoustic bursts. A CCD camera captured the speckle pattern from a laser-illuminated tissue phantom. Differences in speckle contrast were observed when ultrasonic bursts were applied, compared with when no ultrasound was applied. When CCD triggering was synchronized with burst initiation, acoustic-radiation-force-induced displacements were detected. To avoid mechanical contrast in UOT images, the CCD camera acquisition was delayed several milliseconds until transient effects of acoustic radiation force attenuated to a satisfactory level. The SNR of our system was sufficiently high to provide an image pixel per acoustic burst without signal averaging. Because of the substantially improved SNR, the use of intense acoustic bursts is a promising signal enhancement strategy for UOT.

Macrophage Serum-Based Adhesion to Plasma-Processed Surface Chemistry is Distinct from That Exhibited by Fibroblasts

Plasma-polymerized films deposited from AlAm, HxAm, NVP, NVFA, AA and FC were compared to TCPS and PS surfaces in supporting cellular attachment, viability, and proliferation in serum-based culture in vitro for extended periods of time (>7 d). Surface patterns were created using multi-step depositions with physical masks. Cell adhesion in the presence of serum was compared for (monocyte-) macrophage and fibroblast cell lines. Cellular response was tracked over time, reporting adhesive behavior, proliferative rates, and morphological changes as a function of surface chemistry. Micropatterned surfaces containing different surface chemistries and functional groups (e.g. -NH(2), -COOH, -CF(3)) produced differential cell adhesive patterns for NIH 3T3 fibroblasts compared to J774A.1, RAW 264.7 or IC-21 (monocyte-) macrophage cell types. Significantly, macrophage adhesion is substantial on surfaces where fibroblasts do not adhere under identical culture conditions.

Antagonistic forces generated by cytoplasmic dynein and myosin-II during growth cone turning and axonal retraction

Cytoplasmic dynein transports short microtubules down the axon in part by pushing against the actin cytoskeleton. Recent studies have suggested that comparable dynein-driven forces may impinge upon the longer microtubules within the axon. Here, we examined a potential role for these forces on axonal retraction and growth cone turning in neurons partially depleted of dynein heavy chain (DHC) by small interfering RNA. While DHC-depleted axons grew at normal rates, they retracted far more robustly in response to donors of nitric oxide than control axons, and their growth cones failed to efficiently turn in response to substrate borders. Live cell imaging of dynamic microtubule tips showed that microtubules in DHC-depleted growth cones were largely confined to the central zone, with very few extending into filopodia. Even under conditions of suppressed microtubule dynamics, DHC depletion impaired the capacity of microtubules to advance into the peripheral zone of the growth cone, indicating a direct role for dynein-driven forces on the distribution of the microtubules. These effects were all reversed by inhibition of myosin-II forces, which are known to underlie the retrograde flow of actin in the growth cone and the contractility of the cortical actin during axonal retraction. Our results are consistent with a model whereby dynein-driven forces enable microtubules to overcome myosin-II-driven forces, both in the axonal shaft and within the growth cone. These dynein-driven forces oppose the tendency of the axon to retract and permit microtubules to advance into the peripheral zone of the growth cone so that they can invade filopodia.

Silica-shelled single quantum dot micelles as imaging probes with dual or multimodality

The present study describes a stabilization of single quantum dot (QD) micelles by a "hydrophobic" silica precursor and an extension of a silica layer to form a silica shell around the micelle using "amphiphilic" and "hydrophilic" silica precursors. The obtained product consists of approximately 92% single nanocrystals (CdSe, CdSe/ZnS, or CdSe/ZnSe/ZnS QDs) into the silica micelles, coated with a silica shell. The thickness of the silica shell varies, starting from 3-4 nm. Increasing the shell thickness increases the photoluminescence characteristics of QDs in an aqueous solution. The silica-shelled single CdSe/ZnS QD micelles possess a comparatively high quantum yield in an aqueous solution, a controlled small size, sharp photoluminescence spectra (fwhm approximately 30 nm), an absence of aggregation, and a high transparency. The surface of the nanoparticles is amino-functionalized and ready for conjugation. A comparatively good biocompatibility is demonstrated. The nanoparticles show ability for intracellular delivery and are noncytotoxic during long-term incubation with viable cells in the absence of light exposure, which makes them appropriate for cell tracing and drug delivery. The presence of the hydrophobic layer between the QD and silica-shell ensures an incorporation of other hydrophobic molecules with interesting properties (e.g., hydrophobic paramagnetic substances, hydrophobic photosensitizers, membrane stabilizers, lipid-soluble antioxidants or prooxidants, other hydrophobic organic dyes, etc.) in the close proximity of the nanocrystal. Thus, it is possible to combine the characteristics of hybrid materials with the priority of small size. The silica-shelled single QD micelles are considered as a basis for fabrication of novel hybrid nanomaterials for industrial and life science applications, for example, nanobioprobes with dual modality for simultaneous application in different imaging techniques (e.g., fluorescent imaging and functional magnetic resonance imaging).

Development of a rapid method to generate multiple oncolytic HSV vectors and their in vivo evaluation using syngeneic mouse tumor models

Replication-conditional herpes simplex virus (HSV)-based vectors have great potential in the treatment of various types of cancers including brain tumors. HSV mutants lacking the U(L)39 gene and both copies of the gamma(1)34.5 gene (e.g. MGH1, G207) have been demonstrated to possess oncolytic effects as well as potent anticancer vaccination effects without compromising safety. Such mutants thus provide optimal templates to produce novel oncolytic HSV vectors for cancer gene therapy applications. In order to accomplish quick and efficient construction of oncolytic HSV vectors, a novel BAC-based method designated as 'HSVQuik system' was developed. This system sequentially utilizes two different site-specific recombination systems to introduce virtually any transgene cassettes of interest into the deleted U(L)39 locus (Flp-FRT in Escherichia coli) and to release the vector genome sequence from the procaryotic plasmid backbone (Cre-loxP in Vero cells). Taking advantage of the HSVQuik system, we constructed three oncolytic HSV vectors that express mouse IL4, CD40 ligand and 6CK, respectively. In vivo therapeutic experiments using two luciferase-labeled syngeneic mouse brain tumor models revealed that expression of these immunomodulators significantly enhanced antitumor efficacy of oncolytic HSV. The HSVQuik system, together with luciferase-labeled tumor models, should expedite the process of generating and evaluating oncolytic HSV vectors for cancer gene therapy applications.

Preliminary comparative study of small amplitude helical and conventional ePTFE arteriovenous shunts in pigs

Intimal hyperplasia (IH), which causes occlusion of arterial bypass grafts and arteriovenous (A-V) shunts, develops preferentially in low wall shear, or stagnation, regions. Arterial geometry is commonly three-dimensional, generating swirling flows, the characteristics of which include in-plane mixing and inhibition of stagnation. Clinical arterial bypass grafts are commonly two-dimensional, favouring extremes of wall shear. We have developed small amplitude helical technology (SwirlGraft) devices and shown them to generate physiological-type swirling flows. Expanded polytetrafluorethylene (ePTFE) grafts, although widely used as A-V shunts for renal dialysis access, are prone to thrombosis and IH. In a small preliminary study in pigs, we have implanted SwirlGraft ePTFE carotid artery-to-jugular vein shunts on one side and conventional ePTFE carotid artery-to-jugular vein shunts contralaterally. There was consistently less thrombosis and IH in the SwirlGraft than conventional shunts. At eight weeks (two animals), the differences were marked, with virtually no disease in the SwirlGraft devices and occlusion of the conventional grafts by thrombosis and IH. The study had limitations, but the lesser pathology in the SwirlGraft devices is likely to have resulted from their geometry and the associated swirling flow. The results could have implications for vascular biology and prolongation of the patency of arterial bypass grafts and A-V shunts.

Editing-defective tRNA synthetase causes protein misfolding and neurodegeneration

Misfolded proteins are associated with several pathological conditions including neurodegeneration. Although some of these abnormally folded proteins result from mutations in genes encoding disease-associated proteins (for example, repeat-expansion diseases), more general mechanisms that lead to misfolded proteins in neurons remain largely unknown. Here we demonstrate that low levels of mischarged transfer RNAs (tRNAs) can lead to an intracellular accumulation of misfolded proteins in neurons. These accumulations are accompanied by upregulation of cytoplasmic protein chaperones and by induction of the unfolded protein response. We report that the mouse sticky mutation, which causes cerebellar Purkinje cell loss and ataxia, is a missense mutation in the editing domain of the alanyl-tRNA synthetase gene that compromises the proofreading activity of this enzyme during aminoacylation of tRNAs. These findings demonstrate that disruption of translational fidelity in terminally differentiated neurons leads to the accumulation of misfolded proteins and cell death, and provide a novel mechanism underlying neurodegeneration.

Purinergic junctional transmission and propagation of calcium waves in spinal cord astrocyte networks

Micro-photolithographic methods have been employed to form discrete patterns of spinal cord astrocytes that allow quantitative measurements of Ca(2+) wave propagation. Astrocytes were confined to lanes 20-100 microm wide and Ca(2+) waves propagated from a point of mechanical stimulation or of application of adenosine triphosphate; all Ca(2+) wave propagation was blocked by simultaneous application of purinergic P2Y(1) and P2Y(2) antagonists. Stimulation of an astrocyte at one end of a lane, followed by further stimulation of this astrocyte, gave rise to Ca(2+) transients in the same astrocytes; however, if the second stimulation was applied to an astrocyte at the other end of the lane, then this gave rise to a different but overlapping set of astrocytes generating a Ca(2+) signal. Both the amplitude and velocity of the Ca(2+) wave decreased over 270 microm from the point of initiation, and thereafter remained, on average, constant with random variations for at least a further 350 microm. Also, the percentage of astrocytes that gave a Ca(2+) transient decreased with distance along lanes. All the above observations were quantitatively predicted by our recent theoretical model of purinergic junctional transmission, as was the Ca(2+) wave propagation along and between parallel lanes of astrocytes different distances apart. These observations show that a model in which the main determinants are the diffusion of adenosine triphosphates regeneratively released from a stimulated astrocyte, together with differences in the properties and density of the purinergic P2Y receptors on astrocytes, is adequate to predict a wide range of Ca(2+) wave transmission and propagation phenomena.

Matrix protein microarrays for spatially and compositionally controlled microspot thrombosis under laminar flow

Microarraying allows the spatial and compositional control of surfaces, typically for the purpose of binding reactions. Collagen and/or von Willebrand Factor (vWF) in 5% glycerol was contact printed onto glass slides to create defined microspots (176-microm diameter) of adsorbed protein without sample dehydration. The arrays were mounted on flow chambers allowing video microscopy during perfusion (wall shear rate of 100-500 s(-1)) of recalcified corn trypsin inhibitor-treated whole blood or platelet rich plasma and subsequent array scanning via anti-GPIbalpha and anti-fibrin(ogen) immunofluorescence. To mimic the subendothelial matrix, vWF was microarrayed over sonicated type I collagen microspots. For whole blood perfusion (500 s(-1), 10 min) over collagen, vWF, and collagen/vWF microspots, the amount of platelet deposition on the collagen/vWF spots was approximately 2 times greater in comparison to the collagen spots and approximately 18 times greater in comparison to the vWF spots. The amount of fibrin(ogen) deposition on the collagen/vWF spots was approximately 2 times greater in comparison to the collagen spots and approximately 4 times greater in comparison to the vWF spots. This protocol allowed for highly uniform (CV = 18%) and precisely located thrombus formation at a density of >or=400 spots/cm(2). Microarrays are ideal for the combinatorial assembly of adhesive and procoagulant proteins to study thrombosis as well as to study axial and lateral transport effects between discrete microspots of distinct composition.

Spatially resolved non-invasive chemical stimulation for modulation of signalling in reconstructed neuronal networks

Functional coupling of reconstructed neuronal networks with microelectronic circuits has potential for the development of bioelectronic devices, pharmacological assays and medical engineering. Modulation of the signal processing properties of on-chip reconstructed neuronal networks is an important aspect in such applications. It may be achieved by controlling the biochemical environment, preferably with cellular resolution. In this work, we attempt to design cell-cell and cell-medium interactions in confined geometries with the aim to manipulate non-invasively the activity pattern of an individual neuron in neuronal networks for long-term modulation. Therefore, we have developed a biohybrid system in which neuronal networks are reconstructed on microstructured silicon chips and interfaced to a microfluidic system. A high degree of geometrical control over the network architecture and alignment of the network with the substrate features has been achieved by means of aligned microcontact printing. Localized non-invasive on-chip chemical stimulation of micropatterned rat cortical neurons within a network has been demonstrated with an excitatory neurotransmitter glutamate. Our system will be useful for the investigation of the influence of localized chemical gradients on network formation and long-term modulation.

Impaired integrin-dependent function in Wiskott-Aldrich syndrome protein-deficient murine and human neutrophils

Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency that manifests as increased susceptibility to many pathogens. Although the spectrum of infections suffered by WAS patients is consistent with defects in neutrophil (PMN) function, the consequences of WAS protein (WASp) deficiency on this innate immune cell have been unclear. We report that deficiency of WASp in both human and murine PMNs resulted in profound defects in clustering of beta2 integrins, leading to defective adhesion and transendothelial migration under conditions of physiologic shear flow. Wild-type PMNs redistributed clustered beta2 integrins to the uropod of the cell during active migration, whereas WASp-deficient cells remain unpolarized. The WASp-deficient PMNs also showed reduced integrin-dependent activation of degranulation and respiratory burst. PMNs from a WAS patient manifested similar defects in integrin clustering and signaling. These results suggest that impaired beta2 integrin function in WASp-deficient PMNs may contribute substantially to the clinical immunodeficiency suffered by WAS patients.

Co-culture of human embryonic stem cells with murine embryonic fibroblasts on microwell-patterned substrates

Human embryonic stem (hES) cells are generally cultured as cell clusters on top of a feeder layer formed by mitotically inactivated murine embryonic fibroblasts (MEFs) to maintain their undifferentiated state. This co-culture system, which is typically used to expand the population of undifferentiated hES cells, presents several challenges since it is difficult to control cell cluster size. Large cell clusters tend to differentiate at the borders, and clusters with different sizes may lead to heterogeneous differentiation patterns within embryoid bodies. In this work, we develop a new approach to culture hES cells with controlled cluster size and number through merging microfabrication, and biomaterials technologies. Polymeric microwells were fabricated and used to control the size and uniformity of hES cell clusters in co-culture with MEFs. The results show that it is possible to culture hES cells homogeneously while keeping their undifferentiated state as confirmed by the expression of stem cell markers octamer binding protein 4 (Oct-4) and alkaline phosphatase (ALP). In addition, these clusters can be recovered from the microwells to generate nearly homogeneous cell aggregates for differentiation experiments.

Wireless technologies and patient safety in hospitals

In the development of policies for wireless technologies, it is important for healthcare organizations to reduce risks to patients from use of wireless devices. Policy should be devised for instructing hospital staff, visitors, and patients, avoiding unwarranted restrictions but not ignoring evidence regarding potential interference problems, and allowing comparison with other clinical facilities of benefits of policy. To inform policy developers and a general audience of hospital personnel, a review was conducted on the safety of wireless devices for communication within hospitals. This review targeted electromagnetic interference effects of devices on medical devices and summarises key recommendations from published reports and international standards. There is consensus that the highest risk of interference occurs with two-way radios used by emergency crews, followed by mobile phones, while radio local area networks produce negligible interference. Wireless technologies are deemed suitable for use throughout hospital areas including intensive care units and operating rooms, given that recommended separation distances from medical equipment are observed.

The pericellular matrix as a transducer of biomechanical and biochemical signals in articular cartilage

The pericellular matrix (PCM) is a narrow tissue region surrounding chondrocytes in articular cartilage, which together with the enclosed cell(s) has been termed the "chondron." While the function of this region is not fully understood, it is hypothesized to have important biological and biomechanical functions. In this article, we review a number of studies that have investigated the structure, composition, mechanical properties, and biomechanical role of the chondrocyte PCM. This region has been shown to be rich in proteoglycans (e.g., aggrecan, hyaluronan, and decorin), collagen (types II, VI, and IX), and fibronectin, but is defined primarily by the presence of type VI collagen as compared to the extracellular matrix (ECM). Direct measures of PCM properties via micropipette aspiration of isolated chondrons have shown that the PCM has distinct mechanical properties as compared to the cell or ECM. A number of theoretical and experimental studies suggest that the PCM plays an important role in regulating the microenvironment of the chondrocyte. Parametric studies of cell-matrix interactions suggest that the presence of the PCM significantly affects the micromechanical environment of the chondrocyte in a zone-dependent manner. These findings provide support for a potential biomechanical function of the chondrocyte PCM, and furthermore, suggest that changes in the PCM and ECM properties that occur with osteoarthritis may significantly alter the stress-strain and fluid environments of the chondrocytes. An improved understanding of the structure and function of the PCM may provide new insights into the mechanisms that regulate chondrocyte physiology in health and disease.

Optimization of a spherical mechanism for a minimally invasive surgical robot: theoretical and experimental approaches

With a focus on design methodology for developing a compact and lightweight minimally invasive surgery (MIS) robot manipulator, the goal of this study is progress toward a next-generation surgical robot system that will help surgeons deliver healthcare more effectively. Based on an extensive database of in-vivo surgical measurements, the workspace requirements were clearly defined. The pivot point constraint in MIS makes the spherical manipulator a natural candidate. An experimental evaluation process helped to more clearly understand the application and limitations of the spherical mechanism as an MIS robot manipulator. The best configuration consists of two serial manipulators in order to avoid collision problems. A complete kinematic analysis and optimization incorporating the requirements for MIS was performed to find the optimal link lengths of the manipulator. The results show that for the serial spherical 2-link manipulator used to guide the surgical tool, the optimal link lengths (angles) are (60 degrees, 50 degrees). A prototype 6-DOF surgical robot has been developed and will be the subject of further study.

Investigating the Interactions of Hyaluronan Derivatives with Biomolecules. The Use of Diffusional NMR Techniques

[Chemical structure: see text] The interactions between a biomaterial and biomolecules present in body fluids often determine the fate of the biomaterial. This paper presents a study on hyaluronan (HA)-containing materials (in soluble or colloidal form) that focuses on their interactions with lipids and proteins and for the first time uses PFG NMR as an analytical technique for probing these events. The interactions of HA-based polymers with phospholipids (DPPC and DPPG liposomes) are shown to depend both on charge and hydrophobicity factors. Despite the difference in behavior between albumin (substantially non-adhesive) and fibrinogen (adhesive), the interactions of the polymers with proteins do not seem to be based on hydrophobic effects but on surface polar interactions.

Regulation of the Neurofibromatosis 2 gene promoter expression during embryonic development

Mutations in the Neurofibromatosis 2 (NF2) gene are associated with predisposition to vestibular schwannomas, spinal schwannomas, meningiomas, and ependymomas. Presently, how NF2 is expressed during embryonic development and in the tissues affected by neurofibromatosis type 2 (NF2) has not been well defined. To examine NF2 expression in vivo, we generated transgenic mice carrying a 2.4-kb NF2 promoter driving beta-galactosidase (beta-gal) with a nuclear localization signal. Whole-mount embryo staining revealed that the NF2 promoter directed beta-gal expression as early as embryonic day E5.5. Strong expression was detected at E6.5 in the embryonic ectoderm containing many mitotic cells. beta-gal staining was also found in parts of embryonic endoderm and mesoderm. The beta-gal staining pattern in the embryonic tissues was corroborated by in situ hybridization analysis of endogenous Nf2 RNA expression. Importantly, we observed strong NF2 promoter activity in the developing brain and in sites containing migrating cells including the neural tube closure, branchial arches, dorsal aorta, and paraaortic splanchnopleura. Furthermore, we noted a transient change of NF2 promoter activity during neural crest cell migration. While little beta-gal activity was detected in premigratory neural crest cells at the dorsal ridge region of the neural fold, significant activity was seen in the neural crest cells already migrating away from the dorsal neural tube. In addition, we detected considerable NF2 promoter activity in various NF2-affected tissues such as acoustic ganglion, trigeminal ganglion, spinal ganglia, optic chiasma, the ependymal cell-containing tela choroidea, and the pigmented epithelium of the retina. The NF2 promoter expression pattern during embryogenesis suggests a specific regulation of the NF2 gene during neural crest cell migration and further supports the role of merlin in cell adhesion, motility, and proliferation during development.

Methods and mechanisms for contact feedback in a robot-assisted minimally invasive environment

Providing a surgeon with information regarding contacts made between instruments and tissue during robot-assisted interventions can improve task efficiency and reliability. In this report, different methods for feedback of such information to the surgeon are discussed. It is hypothesized that various methods of contact feedback have the potential to enhance performance in a robot-assisted minimally invasive environment. To verify the hypothesis, novel mechanisms needed for incorporating contact feedback were designed, including a surgeon-robot interface with full force feedback capabilities and a surgical end-effector with full force sensing capabilities, that are suitable for minimally invasive applications. These two mechanisms were used to form a robotic "master-slave" test bed for studying the effect of contact feedback on the system and user performance. Using the master-slave system, experiments for surgical tasks involving soft tissue palpation were conducted. The performance of the master-slave system was validated in terms of criteria that assess the accurate transmission of task-related information to the surgeon, which is critical in the context of soft tissue surgical applications. Moreover, using a set of experiments involving human subjects, the performance of several users in carrying out the task was compared among different methods of contact feedback.

Exogenous control of mammalian gene expression via modulation of translational termination

Here, we describe a system for the exogenous control of gene expression in mammalian cells that relies on the control of translational termination. To achieve gene regulation, we modified protein-coding sequences by introduction of a translational termination codon just downstream from the initiator AUG codon. Translation of the resulting mRNA leads to potent reduction in expression of the desired gene product. Expression of the gene product can be controlled by treating cells that express the mRNA with either aminoglycoside antibiotics or several nonantibiotic compounds. We show that the extent of regulation of gene expression can be substantial (60-fold) and that regulation can be achieved in the case of a variety of different genes, in different cultured cell lines and in primary cells in vivo. This gene regulation strategy offers significant advantages over existing methods for controlling gene expression and should have both immediate experimental application and possible clinical application.

Identification and characterization of a human monoclonal antagonistic antibody AL-57 that preferentially binds the high-affinity form of lymphocyte function-associated antigen-1

LFA-1 (alpha(L)beta(2)) mediates cell-cell and cell-extracellular matrix adhesions essential for immune and inflammatory responses. One critical mechanism regulating LFA-1 activity is the conformational change of the ligand-binding alpha(L) I domain from low-affinity (LA), closed form, to the high-affinity (HA), open form. Most known integrin antagonists bind both forms. Antagonists specific for the HA alpha(L) I domain have not been described. Here, we report the identification and characterization of a human antibody AL-57, which binds to the alpha(L) I domain in a HA but not LA conformation. AL-57 was discovered by selection from a human Fab-displaying library using a locked-open HA I domain as target. AL-57 Fab-phage bound HA I domain-expressing K562 cells (HA cells) in a Mg(2+)-dependent manner. AL-57 IgG also bound HA cells and PBMCs, activated by Mg(2+)/EGTA, PMA, or DTT. The binding profile of AL-57 IgG on PBMCs was the same as that of ICAM-1, the main ligand of LFA-1. In contrast, an anti-alpha(L) murine mAb MHM24 did not distinguish between the HA and LA forms. Moreover, AL-57 IgG blocked ICAM-1 binding to HA cells with a potency greater than MHM24. It also inhibited ICAM-1 binding to PBMCs, blocked adhesion of HA cells to keratinocytes, and inhibited PHA-induced lymphocyte proliferation with potencies comparable with MHM24. These results indicate that specifically targeting the HA I domain is sufficient to inhibit LFA-1-mediated, adhesive functions. AL-57 represents a therapeutic candidate for treatment of inflammatory and autoimmune diseases.

Antisense-based cancer therapeutics: are we there yet?

Despite significant advances that have been made in recent years, there is still an urgent need for novel, more effective and less toxic therapeutics for human cancer. Among many new molecular therapeutics being explored for cancer therapy, antisense oligonucleotides are a promising nucleic acid-based approach, with numerous antisense agents being evaluated in preclinical studies and several anticancer antisense drugs in clinical trials. Although there are still a few problems facing the development of antisense strategies for cancer therapy, with progress made in chemical modifications, target selection and drug delivery systems, antisense oligonucleotides are emerging as a novel approach to cancer therapy used alone or in combination with conventional treatments such as chemotherapy and radiation therapy.

Building the power house: recent advances in mitochondrial studies through proteomics and systems biology

The emerging field of systems biology seeks to develop novel approaches to integrate heterogeneous data sources for effective analysis of complex living systems. Systemic studies of mitochondria have generated a large number of proteomic data sets in numerous species, including yeast, plant, mouse, rat, and human. Beyond component identification, mitochondrial proteomics is recognized as a powerful tool for diagnosing and characterizing complex diseases associated with these organelles. Various proteomic techniques for isolation and purification of proteins have been developed; each tailored to preserve protein properties relevant to study of a particular disease type. Examples of such techniques include immunocapture, which minimizes loss of posttranslational modification, 4-iodobutyltriphenylphosphonium labeling, which quantifies protein redox states, and surface-enhanced laser desorption ionization-time-of-flight mass spectrometry, which allows sequence-specific binding. With the rapidly increasing number of discovered molecular components, computational models are also being developed to facilitate the organization and analysis of such data. Computational models of mitochondria have been accomplished with top-down and bottom-up approaches and have been steadily improved in size and scope. Results from top-down methods tend to be more qualitative but are unbiased by prior knowledge about the system. Bottom-up methods often require the incorporation of a large amount of existing data but provide more rigorous and quantitative information, which can be used as hypotheses for subsequent experimental studies. Successes and limitations of the studies reviewed here provide opportunities and challenges that must be addressed to facilitate the application of systems biology to larger systems.

Brain development in children and adolescents: insights from anatomical magnetic resonance imaging

Advances in neuroimaging have ushered in a new era of developmental neuroscience. Magnetic resonance imaging (MRI) is particularly well suited for pediatric studies because it does not use ionizing radiation which enables safe longitudinal scans of healthy children. Key findings related to brain anatomical changes during childhood and adolescent are increases in white matter volumes throughout the brain and regionally specific inverted U-shaped trajectories of gray matter volumes. Brain morphometric measures are highly variable across individuals and there is considerable overlap amongst groups of boys versus girls, typically developing versus neuropsychiatric populations, and young versus old. Studies are ongoing to explore the influences of genetic and environmental factors on developmental trajectories.

Pumpless, selective docking of yeast cells inside a microfluidic channel induced by receding meniscus

We present a simple cell docking method induced by receding meniscus to capture non-adherent yeast cells onto microwells inside a microfluidic channel. Microwells were fabricated either by capillary moulding of UV curable polyurethane acrylate (PUA) onto glass substrate or direct replica moulding of poly(dimethyl siloxane) (PDMS). A cell suspension of the budding yeast, Saccharomyces cerevisiae, was introduced into the microfluidic channel by surface tension driven capillary flow and a receding meniscus was subsequently generated by evaporation. As the meniscus progressed, one to multiple yeast cells were spontaneously captured onto microwells by lateral capillary force created at the bottom of the meniscus. Using this cell-based platform, we observed the response of yeast cells upon stimulation by a mating pheromone (alpha-factor) by monitoring the expression of green fluorescent protein (GFP) with time. It was observed that alpha-factor triggered the expression of GFP at 60 min after stimulation and the fluorescence intensity was sustained for an additional 60 min without changes.

Nuclear Localization Signal Receptor Affinity Correlates with in Vivo Localization in Saccharomyces cerevisiae

Nuclear localization signals (NLSs) target proteins into the nucleus through mediating interactions with nuclear import receptors. Here, we perform a quantitative analysis of the correlation between NLS receptor affinity and the steady-state distribution of NLS-bearing cargo proteins between the cytoplasm and the nucleus of live yeast, which reflects the relative import rates of various NLS sequences. We find that there is a complicated, but monotonic quantitative relationship between the affinity of an NLS for the import receptor, importin alpha, and the steady-state accumulation of the cargo in the nucleus. This analysis takes into consideration the impact of protein size. In addition, the hypothetical upper limit to an NLS affinity for the receptors is explored through genetic approaches. Overall, our results indicate that there is a correlation between the binding affinity of an NLS cargo for the NLS receptor, importin alpha, and the import rate for this cargo. This correlation, however, is not maintained for cargoes that bind to the NLS receptor with very weak or very strong affinity.

Anatomy and flow in normal and ischemic microvasculature based on a novel temporal fractal dimension analysis algorithm using contrast enhanced ultrasound

Strategies for improvement of blood flow by promoting new vessel growth in ischemic tissue are being developed. Recently, contrast-enhanced ultrasound (CEU) imaging has been used to assess tissue perfusion in models of ischemia-related angiogenesis, growth-factor mediated angiogenesis, and tumor angiogenesis. In these studies, microvascular flow is measured in order to assess the total impact of adaptations at different vascular levels. High-resolution methods for imaging larger vessels have been developed in order to derive "angiograms" of arteries, veins, and medium to large microvessels. We describe a novel method of vascular bed (microvessel and arterial) characterization of vessel anatomy and flow simultaneously, using serial measurement of the fractal dimension (FD) of a temporal sequence of CEU images. This method is proposed as an experimental methodology to distinguish ischemic from nonischemic tissue. Moreover, an improved approach for extracting the FD unique to this application is introduced.

Glow discharge plasma treatment of polyethylene tubing with tetraglyme results in ultralow fibrinogen adsorption and greatly reduced platelet adhesion

Previous studies from our lab have shown that fibrinogen adsorption (Gamma(Fg)) must be reduced below 10 ng/cm(2) to significantly reduce platelet adhesion, and that radio frequency glow discharge (RFGD) treatment of polymeric films in the presence of tetraethylene glycol dimethyl ether (tetraglyme) can reduce Gamma(Fg) to the desired ultralow value. In this report, the effects of RFGD coatings of tetraglyme on the lumenal surface of PE tubing on Gamma(Fg) and on blood interactions both in vitro and ex vivo are described. Gamma(Fg) on the tetraglyme-coated PE tubing was reduced to the desired ultralow level (<10 ng/cm(2)), and we also observed a significant decrease in adsorption of von Willebrand's factor. In vitro platelet adhesion from washed platelet suspensions, platelet rich plasma, or whole blood to tetraglyme-coated PE tubing was decreased compared to PE, polyurethane, or silicone rubber tubes. In addition, thrombin generation by platelets adherent to tetraglyme-coated PE was also much less than by platelets adherent to PE. When inserted in an ex vivo carotid artery-carotid artery shunt in sheep, the RFGD tetraglyme-coated PE exhibited a very low number of adherent platelets compared to heparin-coated, chromic acid-etched, or plain PE. The RFGD tetraglyme-coated PE tubes exhibited high protein and platelet resistance in vitro, and high platelet resistance ex vivo. The improved hemocompatibility is attributed to the unique chemical structure of RFGD tetraglyme that makes it highly protein resistant.

Cellular and genetic basis of primary immune deficiencies

Knowledge of the genetic mutations of primary immune deficiency syndromes has grown significantly over the last 30 years. In this article the authors present an overview of the clinical aspects, laboratory evaluation, and genetic defects of primary immunodeficiencies, with an emphasis on the pathophysiology of the known molecular defects. This article is designed to give the primary pediatrician a general knowledge of this rapidly expanding field.

MICROVASCULAR PERSPECTIVE OF OXYGEN-CARRYING AND -NONCARRYING BLOOD SUBSTITUTES

The development of an alternative to natural blood has evolved from the initial goal of replicating blood properties to the current objective of formulating a fluid that can be used to replace blood while preserving microvascular function and delivering oxygen. The properties of this fluid are counterintuitive and different from blood because it has high viscosity, oxygen affinity, and a low oxygen carrier concentration when compared with blood. The optimal oxygen carrier devised presently is poly-ethylene-conjugated human hemoglobin, a material demonstrated to be vasoinactive and void of the toxicities present in previous hemoglobin formulations. A feature of this material is that it is effective in small quantities, and therefore amplifies the equivalent supply of blood derived from blood donations.

Bioreactors for Tissue Engineering: Focus on Mechanical Constraints. A Comparative Review

Considering the current techniques in cell culture, the stimulation of cellular proliferation and the formation of bidimensional tissues such as skin are widely performed in academic and industrial research laboratories. However, the formation of cohesive, organized, and functional tissues by three-dimensional (3D) cell culture is complex. A suitable environment is required, which is achieved and maintained in a specific bioreactor, a device that reproduces the physiological environment (including biochemical and mechanical functions) specific to the tissue that is to be regenerated. Bioreactors can also be used to apply mechanical constraints during maturation of the regenerating tissue for studying and understanding the mechanical factors influencing tissue regeneration. In this work, the main types of bioreactors used for tissue engineering and regeneration, as well as their most common applications, were reviewed and compared. The importance of the mechanical properties applied to the scaffolds and the regenerating constructs has been often neglected. This review focused on the influence of mechanical stresses and strains during the culture period that leads to the final mechanical properties of the construct.

An integrated telemedicine platform for the assessment of affective physiological states

AUBADE is an integrated platform built for the affective assessment of individuals. The system performs evaluation of the emotional state by classifying vectors of features extracted from: facial Electromyogram, Respiration, Electrodermal Activity and Electrocardiogram. The AUBADE system consists of: (a) a multisensorial wearable, (b) a data acquisition and wireless communication module, (c) a feature extraction module, (d) a 3D facial animation module which is used for the projection of the obtained data through a generic 3D face model; whereas the end-user will be able to view the facial expression of the subject in real time, (e) an intelligent emotion recognition module, and (f) the AUBADE databases where the acquired signals along with the subject's animation videos are saved. The system is designed to be applied to human subjects operating under extreme stress conditions, in particular car racing drivers, and also to patients suffering from neurological and psychological disorders. AUBADE's classification accuracy into five predefined emotional classes (high stress, low stress, disappointment, euphoria and neutral face) is 86.0%. The pilot system applications and components are being tested and evaluated on Maserati's car. racing drivers.

3-D microwell culture of human embryonic stem cells

Human embryonic stem cells (hESCs) have the ability to proliferate indefinitely and differentiate into each of the embryonic cell lineages. Great care is required to maintain undifferentiated hESC cultures since spontaneous differentiation often occurs in culture, presumably resulting from soluble factors, cell-cell contact, and/or cell-matrix signaling. hESC differentiation is typically stimulated via generation of embryoid bodies (EBs) and lineage commitment of individual cells depends upon numerous cues throughout the EB environment, including EB shape and size. Common EB formation protocols, however, produce a very heterogeneous size distribution, perhaps reducing efficiency of directed differentiation. We have developed a 3-D microwell-based method to maintain undifferentiated hESC cultures for weeks without passaging using physical and extracellular matrix patterning constraints to limit colony growth. Over 90% of hESCs cultured in microwells for 2-3 weeks were viable and expressed the hESC transcription marker Oct-4. Upon passaging to Matrigel-coated tissue culture-treated polystyrene dishes (TCPS), microwell cultured hESCs maintained undifferentiated proliferation. Microwell culture also permits formation of hESC colonies with a defined size, which can then be used to form monodisperse EBs. When cultured in this system, hESCs retained pluripotency and self-renewal, and were able to be passaged to standard unconstrained culture conditions.

A stereotaxic MRI template set for the rat brain with tissue class distribution maps and co-registered anatomical atlas: Application to pharmacological MRI

We describe a stereotaxic rat brain MRI template set with a co-registered digital anatomical atlas and illustrate its application to the analysis of a pharmacological MRI (phMRI) study of apomorphine. The template set includes anatomical images and tissue class probability maps for brain parenchyma and cerebrospinal fluid (CSF). These facilitate the use of standard fMRI software for spatial normalisation and tissue segmentation of rat brain data. A volumetric reconstruction of the Paxinos and Watson rat brain atlas is also co-localised with the template, enabling the atlas structure and stereotaxic coordinates corresponding to a feature within a statistical map to be interactively reported, facilitating the localisation of functional effects. Moreover, voxels falling within selected brain structures can be combined to define anatomically based 3D volumes of interest (VOIs), free of operator bias. As many atlas structures are small relative to the typical resolution of phMRI studies, a mechanism for defining composite structures as agglomerations of individual atlas structures is also described. This provides a simple and robust means of interrogating structures that are otherwise difficult to delineate and an objective framework for comparing and classifying compounds based on an anatomical profile of their activity. These developments allow a closer alignment of pre-clinical and clinical analysis techniques.

Photopolymerized check valve and its integration into a pneumatic pumping system for biocompatible sample delivery

In this paper, we present a simple check valve whose operation mimics that of venous valves. Our check valve has a mono-leaflet and is constructed via an in situ fabrication method inside the PDMS platform. For the smooth operation of the valve's leaflet, the elasticity and the shape of the leaflet and the lubrication between the leaflet and the channel surface are important. We used 4-hydroxybutyl acrylate (4-HBA) as an elastic and photopolymerizable leaflet material. We mixed the triton X-100 with the 4-HBA pre-polymer solution for the adequate lubrication of the leaflet. We constructed the micro-pumping system by combining two venous-like check valves with an oscillating polymeric diaphragm driven by pneumatic force, and measured the flow rate according to the change of pumping frequency. We also investigated the pump's feasibility as a delivery system of biocompatible materials by using mouse embryo fibroblast cells.

Development of a nonrigid, durable calcium phosphate cement for use in periodontal bone repair

BACKGROUND

Calcium phosphate cement (CPC) hardens in situ to form hydroxyapatite and has been used in dental and craniofacial restorative applications. However, when CPC was used in periodontal osseous repair, tooth mobility resulted in the fracture and exfoliation of the brittle CPC implant. The objective of the authors' study was to develop a strong and nonrigid CPC to provide compliance for tooth mobility without fracturing the implant.

METHODS

The authors used tetracalcium phosphate, dicalcium phosphate anhydrous and biopolymer chitosan to develop a strong and nonrigid CPC. They used a powder:liquid ratio of 2:1, compared with the 1:1 ratio of a previously developed nonrigid CPC control. Specimens were characterized using a flexural test, scanning electron microscopy and powder X-ray diffraction.

RESULTS

After 28 days of immersion, the new cement had a flexural strength (mean +/- standard deviation; n = 6) of 5.2 +/- 1.0 megapascals, higher than 1.8 +/- 1.5 MPa for the control (P < .05) and overlapping the reported strengths of sintered hydroxyapatite implants and cancellous bone. This cement showed a high ductility with a strain at peak load of 6.5 +/- 1.3 percent, compared with 4.4 +/- 1.9 percent for the control; both were 20-fold higher than the 0.2 percent of the conventional CPC. Nanosized hydroxyapatite crystals, similar to those in teeth and bones, were formed in the cements.

CONCLUSIONS

The new nonrigid cement, containing nanohydroxyapatite crystals, possessed a high ductility and superior fracture resistance. This strong, tough and nonrigid CPC may be useful in periodontal repair to provide compliance for tooth mobility without fracture.

CLINICAL IMPLICATIONS

The results of this study may yield the first self-hardening and nonrigid hydroxyapatite composite with high strength and durability and large deformation capability to be useful in the regeneration of periodontal osseous defects.

Multifractal analysis of human retinal vessels

In this paper, it is shown that vascular structures of the human retina represent geometrical multifractals, characterized by a hierarchy of exponents rather then a single fractal dimension. A number of retinal images from the STARE database are analyzed, corresponding to both normal and pathological states of the retina. In all studied cases, a clearly multifractal behavior is observed, where capacity dimension is always found to be larger then the information dimension, which is in turn always larger then the correlation dimension, all the three being significantly lower then the diffusion limited aggregation (DLA) fractal dimension. We also observe a tendency of images corresponding to the pathological states of the retina to have lower generalized dimensions and a shifted spectrum range, in comparison with the normal cases.

Anatomy and biomechanics of the back muscles in the lumbar spine with reference to biomechanical modeling

STUDY DESIGN

This article describes the development of a musculoskeletal model of the human lumbar spine with focus on back muscles. It includes data from literature in a structured form.

OBJECTIVE

To review the anatomy and biomechanics of the back muscles related to the lumbar spine with relevance for biomechanical modeling.

SUMMARY OF BACKGROUND DATA

To reduce complexity, muscle units have been incorporated in an abridged manner, reducing their actions more or less to a single force equivalent. In early models of the lumbar spine, this may have been a necessary step to reduce complexity and, thereby, calculation time. The muscles of the spine are well described in the literature, but mainly qualitatively. Most of the literature provides a description of the structures without precise data of fiber length, muscle length, cross-sectional areas, moment arms, forces, etc. The predicted output of musculoskeletal models is very much dependent on the input parameters. The information needed to improve models consists of better approximations of the attachments to the vertebrae, and more precise data.

METHOD

Review of literature.

RESULTS

The predicted output of musculoskeletal models is very much dependent on the input parameters. Moderate changes in the assumed muscle line-of-action (i.e., moment arm) could substantially alter the magnitudes of predicted muscle and spinal forces, while the choice of optimization formulation is less sensitive.

CONCLUSIONS

Input parameters, moment arms, as well as physiologic cross-sectional areas have a profound effect on the predicted muscle forces. Therefore, it is important to choose the values for moment arm and physiologic cross-sectional area carefully because they are essential input parameters to biomechanical models.

Corneal structure and biomechanics: impact on the diagnosis and management of glaucoma

PURPOSE OF REVIEW

Highlights recent studies relating to the impact of corneal structure and biomechanical properties on glaucoma evaluation and management.

RECENT FINDINGS

Central corneal thickness has been shown to play a role in the interpretation of intraocular pressure. Central corneal thickness has also been suggested as a glaucoma risk factor. The potential role of other corneal factors, such as stromal makeup, in the accurate measurement of intraocular pressure and the assessment of glaucoma risk remains to be determined.

SUMMARY

Improved understanding of central corneal thickness and corneal biomechanical properties may someday lead to a better understanding of glaucoma risk and its assessment.

Shear and Compression Differentially Regulate Clusters of Functionally Related Temporal Transcription Patterns in Cartilage Tissue

Chondrocytes are subjected to a variety of biophysical forces and flows during physiological joint loading, including mechanical deformation, fluid flow, hydrostatic pressure, and streaming potentials; however, the role of these physical stimuli in regulating chondrocyte behavior is still being elucidated. To isolate the effects of these forces, we subjected intact cartilage explants to 1-24 h of continuous dynamic compression or dynamic shear loading at 0.1 Hz. We then measured the transcription levels of 25 genes known to be involved in cartilage homeostasis using real-time PCR and compared the gene expression profiles obtained from dynamic compression, dynamic shear, and our recent results on static compression amplitude and duration. Using clustering analysis, we determined that transcripts for proteins with similar function had correlated responses to loading. However, the temporal expression patterns were strongly dependent on the type of loading applied. Most matrix proteins were up-regulated by 24 h of dynamic compression or dynamic shear, but down-regulated by 24 h of 50% static compression, suggesting that cyclic matrix deformation is a key stimulator of matrix protein expression. Most matrix proteases were up-regulated by 24 h under all loading types. Transcription factors c-Fos and c-Jun maximally responded within 1 h to all loading types. Pre-incubating cartilage explants with either a chelator of intracellular calcium or an inhibitor of the cyclic AMP pathway demonstrated the involvement of both pathways in transcription induced by dynamic loading.

Three-Dimensional Microchannels in Biodegradable Polymeric Films for Control Orientation and Phenotype of Vascular Smooth Muscle Cells

The poor mechanical strength and vasoactivity of current small-diameter tissue engineered blood vessels (TEBVs) remain unsolved problems. Given the plasticity of smooth muscle cells (SMCs), 1 of the main limitations of current scaffolding techniques is the difficulty in controlling SMC phenotype shifts in vitro. A synthetic phenotype allows the cells to rapidly proliferate and produce extracellular matrix (ECM), whereas a shift to contractile phenotype with organized ECM ultimately provides a functional blood vessel. In this study, 3D deep (65 microm) and wide microchannels separated by high-aspect ratio (8) microwalls were successfully ultraviolet (UV) microembossed using a liquid UV polymerizable biodegradable macromer (poly(epsilon-caprolactone-r-L-lactide-r-glycolide) diacrylate) and the in vitro guidance effects of varying channel width (40-160 microm) on SMCs were verified. The results show that SMCs cultured in the wider microchannels (80-160 microm wide) switch from fibroblast morphology and random orientation to spindle-shaped morphology, and align along the direction of the microchannel nearing confluence achieved with similar cell density to unpatterned film. Further, an enhanced expression of smooth muscle alpha-actin of SMCs grown on micropatterns was found nearing confluence, which demonstrates a phenotype shift to a more contractile phenotype. These films are flexible and can be folded into tubular and lamellar structures for tissue engineering of small-diameter TEBVs as well as other organs such as esophagus or intestine. These results suggest that these micropatterned synthetic biodegradable scaffolds may be useful for guiding SMCs to grow into functional, small-diameter vascular grafts.

The fundamental operating principles of electronic root canal length measurement devices

It is generally accepted that root canal treatment procedures should be confined within the root canal system. To achieve this objective the canal terminus must be detected accurately during canal preparation and precise control of working length during the process must be maintained. Several techniques have been used for determining the apical canal terminus including electronic methods. However, the fundamental electronic operating principles and classification of the electronic devices used in this method are often unknown and a matter of controversy. The basic assumption with all electronic length measuring devices is that human tissues have certain characteristics that can be modelled by a combination of electrical components. Therefore, by measuring the electrical properties of the model, such as resistance and impedance, it should be possible to detect the canal terminus. The root canal system is surrounded by dentine and cementum that are insulators to electrical current. At the minor apical foramen, however, there is a small hole in which conductive materials within the canal space (tissue, fluid) are electrically connected to the periodontal ligament that is itself a conductor of electric current. Thus, dentine, along with tissue and fluid inside the canal, forms a resistor, the value of which depends on their dimensions, and their inherent resistivity. When an endodontic file penetrates inside the canal and approaches the minor apical foramen, the resistance between the endodontic file and the foramen decreases, because the effective length of the resistive material (dentine, tissue, fluid) decreases. As well as resistive properties, the structure of the tooth root has capacitive characteristics. Therefore, various electronic methods have been developed that use a variety of other principles to detect the canal terminus. Whilst the simplest devices measure resistance, other devices measure impedance using either high frequency, two frequencies, or multiple frequencies. In addition, some systems use low frequency oscillation and/or a voltage gradient method to detect the canal terminus. The aim of this review was to clarify the fundamental operating principles of the different types of electronic systems that claim to measure canal length.

Angiogenesis in Tissue Engineering: Breathing Life into Constructed Tissue Substitutes

Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ.

Anatomical and Functional Imaging of Tumors in Animal Models: Focus on Pheochromocytoma

This review focuses on anatomical (computed tomography, magnetic resonance imaging) and functional (positron emission tomography) imaging methods for tumor localization and identification of experimentally induced tumors in animal models, especially pheochromocytoma. Although anatomical imaging can precisely locate primary and metastatic tumors, functional imaging has high specificity for some tumors, especially those of endocrine origin. This is due to the fact that endocrine tumor cells take up hormone precursors, express hormone receptors and transporters, and synthesize, store, and release hormones. These characteristic properties of endocrine tumors enable investigators to create highly specific radiopharmaceuticals, particularly for positron emission tomography. For example, localization of pheochromocytoma involves [18F]-6F-dopamine. It is a highly specific radiopharmaceutical since it uses the norepinephrine transporter system expressed in most pheochromocytoma cells. Here we review both anatomical and functional imaging methods that are used conjointly in order to localize and identify specific characteristics of tumors.

Nanoliter-scale reactor arrays for biochemical sensing

A general approach is described for array-based biochemical sensing that uses contact-free dispersal of compounds into addressable microfabricated reactors. The arrays are composed of 1 to 100 nL volume open reactors that have been microfabricated on quartz substrates using lithography. The open architecture of these reactors allows them to be addressed in parallel or individually with an ink-jet arrayer that is capable of distributing 0.004 to 1 nL volumes of reagents. A seven-step biochemical assay has been conducted on a small array of reactors to demonstrate how they can be integrated with an ink-jet arrayer and optical detector. This nanoreactor assay format appears to overcome several limitations that chip-based microarray technology currently imposes on protein assays: the arrays can be created in a manner that does not expose the biochemical reagents to osmotic stress, independent reactions can be conducted in individual reactors, and the conditions in all of the reactors (e.g., concentration and pH) can be rapidly scanned. We believe that these nanoreactor arrays will be useful for biochemical sensing that involves delicate proteins and protein assemblies.

Flow Effects on Coagulation and Thrombosis

Thrombosis occurs in a dynamic rheological field that constantly changes as the thrombus grows to occlusive dimensions. In the initiation of thrombosis, flow conditions near the vessel wall regulate how quickly reactive components are delivered to the injured site and how rapidly the reaction products are disseminated. Whereas the delivery and removal of soluble coagulation factors to the vessel is thought to occur via classic convection-diffusion phenomena, the movement of cells and platelets to the injured wall is strongly augmented by flow-dependent cell-cell collisions that enhance their ability to interact with the wall. In addition, increased shear conditions have been shown to activate platelets, alter the cellular localization of proteins such as tissue factor (TF) and TF pathway inhibitor, and regulate gene production. In the absence of high shearing forces, red cells, leukocytes, and platelets can form stable aggregates with each other or cells lining the vessel wall, which, in addition to altering the biochemical makeup of the aggregate or vessel wall, effectively increases the local blood viscosity. Thus, hemodynamic forces not only regulate the predilection of specific anatomic sites to thrombosis, but they strongly influence the biochemical makeup of thrombi and the reaction pathways involved in thrombus formation.

In vitro and in vivo evaluation of ultrananocrystalline diamond for coating of implantable retinal microchips

In this work, ultrananocrystalline diamond (UNCD) thin films were evaluated for use as hermetic and bioinert coatings for a retinal microchip. These films were deposited on highly conductive Si substrates at different temperatures (from 400 to 800 degrees C), using microwave plasma enhanced chemical vapor deposition with argon-rich Ar/CH4 gas mixtures and different relative amounts of hydrogen (0-20%). Scanning electron microscopy studies showed that all the films are dense and continuous. Results of cyclic voltammetry test revealed that when there was <2% of hydrogen in the plasma, the film obtained renders the surface electrochemically inactive, with very low leakage currents ( approximately 4 x 10(-7) A/cm2 at +/-5 V). In addition, in vivo tests of the UNCD-coated Si samples were performed by implanting them in the eyes of rabbits for 4-6 months within the eye physiological environment. According to all these results, it was concluded that UNCD is a promising candidate for use as the encapsulating coatings for implantable retinal microelectronic devices.

Microscopic calculations of local lipid membrane permittivities and diffusion coefficients for application to electroporation analyses

Interaction of electric fields with biological systems has begun to receive considerable attention for applications that include field-assisted drug delivery, medical interventions, and genetic engineering. External fields induce the strongest effects at membranes with electroporation being a common feature. Membrane transport in this context of poration is often based on continuum approaches utilizing macroscopic parameters such as the permittivity, diffusion coefficients, and mobilities. In such modeling, field dependences, local inhomogeneities, and microscopic details are usually ignored. Here, a molecular dynamics (MD) scheme is used for a more rigorous and physically realistic evaluation of such parameters for potential application to electroporative transport model development. A suitable membrane structure containing a nanopore derived from MD analysis is used as the initial geometric configuration. Both static and frequency dependent diffusion coefficients have been evaluated. Permittivities are also calculated and shown to be dramatically non-uniform in the vicinity of membranes under high external fields. A positive feedback mechanism leading to enhanced membrane fields is discussed.

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Oxygen Mass Transport in a Compliant Carotid Bifurcation Model

The purpose of the present study was to investigate oxygen mass transfer in the human carotid bifurcation, focusing on the effects of the wall compliance and flow field on the temporal variation and spatial distribution of the oxygen wall flux. Details of unsteady convective-diffusive oxygen transport were examined numerically using a compliant model of the human carotid bifurcation and realistic blood flow waveforms. Results reveal that axial flow separation at the outer common-internal carotid wall can significantly alter the flow field, oxygen tension field, and oxygen wall flux distribution. At the outer wall of the sinus, the Sherwood number, Sh (non-dimensional oxygen wall flux), takes on significantly lower values than at other sites due to the attenuation of transport rates by convective flow away from wall. More specifically, the lowest value of Sh was Sh approximately 6 (in the sinus), which is much lower than the value of the non-dimensional oxygen consumption rate (Damkohler number, Da) in the reactive wall tissue (Da=29-39). At the inner wall of the sinus, Sh approximately 170 is far above the expected value of Da. This implies that flow separation on the outer wall of the sinus provides a very strong fluid mechanical barrier to oxygen transport; whereas at the inner wall of the sinus, the mechanism of transport is controlled by the wall consumption rate.