MMV-Net: A Multiple Measurement Vector Network for Multifrequency Electrical Impedance Tomography.

Multifrequency electrical impedance tomography (mfEIT) is an emerging biomedical imaging modality to reveal frequency-dependent conductivity distributions in biomedical applications. Conventional model-based image reconstruction methods suffer from low spatial resolution, unconstrained frequency correlation, and high computational cost. Deep learning has been extensively applied in solving the EIT inverse problem in biomedical and industrial process imaging. However, most existing learning-based approaches deal with the single-frequency setup, which is inefficient and ineffective when extended to the multifrequency setup. This article presents a multiple measurement vector (MMV) model-based learning algorithm named MMV-Net to solve the mfEIT image reconstruction problem. MMV-Net considers the correlations between mfEIT images and unfolds the update steps of the Alternating Direction Method of Multipliers for the MMV problem (MMV-ADMM). The nonlinear shrinkage operator associated with the weighted l2,1 regularization term of MMV-ADMM is generalized in MMV-Net with a cascade of a Spatial Self-Attention module and a Convolutional Long Short-Term Memory (ConvLSTM) module to better capture intrafrequency and interfrequency dependencies. The proposed MMV-Net was validated on our Edinburgh mfEIT Dataset and a series of comprehensive experiments. The results show superior image quality, convergence performance, noise robustness, and computational efficiency against the conventional MMV-ADMM and the state-of-the-art deep learning methods.

Blue-light induced breakdown of barrier function on human retinal epithelial cells is mediated by PKC-ζ over-activation and oxidative stress.

We aimed to study the time course decrease of human retinal pigment epithelium (RPE) barrier function when exposed to blue light. To this end, we cultured ARPE-19 cells on Electrical Cell-substrate Impedance Sensing (ECIS) multi-well arrays. Using an ad hoc light emitting diode (LED) array illumination system together with a set of neutral density filters and a 3-dimensional (3D) printed filter holder, cells were exposed to a gradient of irradiances of blue-light with a measured peak at 468 nm. The electrical resistance between 4 kHz and 64 kHz was recorded during the exposure. Blue light exposure induced a dose-dependent decrease in the resistances at 4 kHz, however the time course resistance at 64 kHz did not show any decrease before t = 52 h. Quantification of the barrier function using mathematical model integrated in the ECIS software showed that blue-light exposure induced a dose-dependent decrease in the barrier function associated with tight junction formation (P < 0.05). This was confirmed by the immunostaining of the tight-junction associated structural protein, Zonula occludens-1 (ZO-1). The detection of reactive oxygen species by carboxy-H2DCFDA confirmed that the blue light induced dose-dependent decrease in the barrier function is mediated by oxidative stress. On a separate experiment, blue-light exposed ARPE-19 cells were treated with 100 nM Protein Kinase C zeta (PKC-ζ) pseudo substrate inhibitor to identify underlying pathway for blue-light induced damage on the barrier function. The treatment with 100 nM PKC-ζ pseudo substrate inhibitor induced faster recovery of the barrier function compared to no treatment. Altogether our results document that blue LED light exposure decreased RPE barrier function in-vitro in a dose-dependent manner, before any cell death occurred. This damage induced by blue-light on tight junctions is mediated by oxidative stress through PKC-ζ activation. The quantification of the healing effect observed by inhibition of PKC-ζ might lead to development of high throughput wound healing assays through ECIS in the future.

Low-dose acetaminophen induces early disruption of cell-cell tight junctions in human hepatic cells and mouse liver.

Dysfunction of cell-cell tight junction (TJ) adhesions is a major feature in the pathogenesis of various diseases. Liver TJs preserve cellular polarity by delimiting functional bile-canalicular structures, forming the blood-biliary barrier. In acetaminophen-hepatotoxicity, the mechanism by which tissue cohesion and polarity are affected remains unclear. Here, we demonstrate that acetaminophen, even at low-dose, disrupts the integrity of TJ and cell-matrix adhesions, with indicators of cellular stress with liver injury in the human hepatic HepaRG cell line, and primary hepatocytes. In mouse liver, at human-equivalence (therapeutic) doses, dose-dependent loss of intercellular hepatic TJ-associated ZO-1 protein expression was evident with progressive clinical signs of liver injury. Temporal, dose-dependent and specific disruption of the TJ-associated ZO-1 and cytoskeletal-F-actin proteins, correlated with modulation of hepatic ultrastructure. Real-time impedance biosensing verified in vitro early, dose-dependent quantitative decreases in TJ and cell-substrate adhesions. Whereas treatment with NAPQI, the reactive metabolite of acetaminophen, or the PKCα-activator and TJ-disruptor phorbol-12-myristate-13-acetate, similarly reduced TJ integrity, which may implicate oxidative stress and the PKC pathway in TJ destabilization. These findings are relevant to the clinical presentation of acetaminophen-hepatotoxicity and may inform future mechanistic studies to identify specific molecular targets and pathways that may be altered in acetaminophen-induced hepatic depolarization.

Tissue engineering for tendon repair.

Tissue engineering aims to induce tissue self-regeneration in vivo or to produce a functional tissue replacement in vitro to be then implanted in the body. To produce a viable and functional tendon, a uniaxially orientated collagen type I matrix has to be generated. Biochemical and physical factors can potentially alter both the production and the organisation of this matrix, and their combination in a dose- and time-dependent manner is probably the key to in vitro engineered tendons. This review discusses the role of these different factors affecting tenocyte growth in a three-dimensional environment in vivo and in vitro, and underlines the future challenge of tendon tissue engineering.

Complex permittivity measurement as a new noninvasive tool for monitoring in vitro tissue engineering and cell signature through the detection of cell proliferation, differentiation, and pretissue formation.

In in vitro tissue engineering, microporous scaffolds are commonly used to promote cell proliferation and differentiation in three-dimensional structures. Classic measurement methods are particularly time consuming, difficult to handle, and destructive. In this study, a new nondestructive method based on complex permittivity measurement (CPM) is proposed to monitor and track the osteoblast and macrophage differentiation through their morphological variation upon cell attachment and proliferation inside the microporous scaffolds. CPM is performed using a vector network analyzer and a dielectric probe under sterile conditions in a laminar-flow hood. A suitable effective medium approximation (EMA) is applied to fit the data in order to extract the parameters of the different constituents. Our data show that the EMA depolarization factor can be monitored to assess the variation of cell morphology characterizing cell attachment. Discrimination between two batches of scaffolds seeded, respectively, with 2 million and 1 million osteoblast cells is possible; the ratio of their CPM-derived cell volume fractions is in agreement with the ratio of their cell seeding numbers. In addition, cell proliferation inside scaffolds seeded with osteoblasts cultured in alpha minimum essential medium and inside scaffolds seeded with osteoblasts cultured in alpha minimum essential medium supplemented to induce the formation of extracellular matrix is monitored via CPM over several days. CPM-determined cell volume fraction is compared to DNA assay cell counts. Extracellular matrix formation and cell presence was confirmed by scanning electron microscopy. A set of three signature parameters (epsilon'mem, epsilon'cyt, kappa'cyt) characteristic of cell line is extracted from CPM. Distinct signatures are recorded for osteoblasts and macrophages, thus confirming the ability of CPM to discriminate between different cell types. This study demonstrates the potential of CPM as a diagnostic tool to monitor quickly and noninvasively cell growth and differentiation inside microporous scaffolds. Our findings suggest that the use of CPM could be extended to many biomedical applications, such as drug detection and automation of tissue and bacterial cultures in bioreactors.

Towards on-line monitoring of cell growth in microporous scaffolds: Utilization and interpretation of complex permittivity measurements.

Here we demonstrate the ability to characterize microporous scaffolds and evaluate cell concentration variation via the utilization and interpretation of complex permittivity measurements (CP), a direct and nondestructive method. Polymer-based microporous scaffolds are of importance to tissue engineering, particularly in the promotion of cell adhesion, proliferation, and differentiation in predefined shapes. Chitosan gel scaffolds were seeded with increasing concentrations of macrophages to simulate cell growth. Complex permittivity measurements were performed using a dielectric probe and a vector network analyzer over a frequency ranging from 200 MHz to 2 GHz. An effective medium theory was applied to interpret the data obtained; respectively, Looyenga and Maxwell-Wagner-Hanai functions were used to retrieve the porosity and the variation of the cell concentration from the CP measurements. Calculated porosities were in agreement with experimental evaluation-porosity ranged from 81-96%. Changes in cell concentration inside the scaffolds upon injection of differing cell concentrations into the scaffold were detected distinguishably. Variations resulting from the cumulative injection of 400-1800 microL of 10(6) cells/mL solution into the scaffold were monitored. Results suggest that CP measurements in combination with an appropriate effective medium approximation can enable on-line monitoring of cell growth within scaffolds.