[A multifrequency time-difference electrical impedance tomography algorithm using spectral constraints].

This study aims to propose a multifrequency time-difference algorithm using spectral constraints. Based on the knowledge of tissue spectrum in the imaging domain, the fraction model was used in conjunction with the finite element method (FEM) to approximate a conductivity distribution. Then a frequency independent parameter (volume or area fraction change) was reconstructed which made it possible to simultaneously employ multifrequency time-difference boundary voltage data and then reduce the degrees of freedom of the reconstruction problem. Furthermore, this will alleviate the illness of the EIT inverse problem and lead to a better reconstruction result. The numerical validation results suggested that the proposed time-difference fraction reconstruction algorithm behaved better than traditional damped least squares algorithm (DLS) especially in the noise suppression capability. Moreover, under the condition of low signal-to-noise ratio, the proposed algorithm had a more obvious advantage in reconstructions of targets shape and position. This algorithm provides an efficient way to simultaneously utilize multifrequency measurement data for time-difference EIT, and leads to a more accurate reconstruction result. It may show us a new direction for the development of time-difference EIT algorithms in the case that the tissue spectrums are known.

Multitype Perception Method for Drug-Target Interaction Prediction.

With the growing popularity of artificial intelligence in drug discovery, many deep-learning technologies have been used to automatically predict unknown drug-target interactions (DTIs). A unique challenge in using these technologies to predict DTI is fully exploiting the knowledge diversity across different interaction types, such as drug-drug, drug-target, drug-enzyme, drug-path, and drug-structure types. Unfortunately, existing methods tend to learn the specifical knowledge on each interaction type and they usually ignore the knowledge diversity across different interaction types. Therefore, we propose a multitype perception method (MPM) for DTI prediction by exploiting knowledge diversity across different link types. The method consists of two main components: a type perceptor and a multitype predictor. The type perceptor learns distinguished edge representations by retaining the specifical features across different interaction types; this maximizes the prediction performance for each interaction type. The multitype predictor calculates the type similarity between the type perceptor and predicted interactions, and the domain gate module is reconstructed to assign an adaptive weight to each type perceptor. Extensive experiments demonstrate that our proposed MPM outperforms the state-of-the-art methods in DTI prediction.

Real-time imaging of traumatic brain injury using magnetic induction tomography.

Objective. Early diagnosis of traumatic brain injury (TBI) is crucial for its prognosis; however, traditional computed tomography diagnostic methods rely on large medical devices with an associated lag time to receive results. Therefore, an imaging modality is needed that provides real-time monitoring, can easily be carried out to assess the extent of TBI damage, and thus guides treatment.Approach. In the present study, an improved magnetic induction tomography (MIT) data acquisition system was used to monitor TBI in an animal model and distinguish the injury level. A pneumatically controlled cortical impactor was used to strike the parietal lobe of anesthetized rabbits two or three times under the same parameter mode to establish two different rabbit models of TBI. The MIT data acquisition system was used to record data and continuously monitor the brain for one hour without intervention.Main results. A target with increased conductivity was clearly observed in the reconstructed image. The position was relatively fixed and accurate, and the average positioning error of the image was 0.013 72 m. The normalized mean reconstruction value of all images increased with time. The slope of the regression line of the normalized mean reconstruction value differed significantly between the two models (p< 0.0001).Significance. This indicates that in the animal model, the unique features of MIT may facilitate the early monitoring of TBI and distinguish different degrees of injuries, thereby reducing the risk and mortality of associated complications.

Advances of deep learning in electrical impedance tomography image reconstruction.

Electrical impedance tomography (EIT) has been widely used in biomedical research because of its advantages of real-time imaging and nature of being non-invasive and radiation-free. Additionally, it can reconstruct the distribution or changes in electrical properties in the sensing area. Recently, with the significant advancements in the use of deep learning in intelligent medical imaging, EIT image reconstruction based on deep learning has received considerable attention. This study introduces the basic principles of EIT and summarizes the application progress of deep learning in EIT image reconstruction with regards to three aspects: a single network reconstruction, deep learning combined with traditional algorithm reconstruction, and multiple network hybrid reconstruction. In future, optimizing the datasets may be the main challenge in applying deep learning for EIT image reconstruction. Adopting a better network structure, focusing on the joint reconstruction of EIT and traditional algorithms, and using multimodal deep learning-based EIT may be the solution to existing problems. In general, deep learning offers a fresh approach for improving the performance of EIT image reconstruction and could be the foundation for building an intelligent integrated EIT diagnostic system in the future.

Synthesis, characterization, and in vivo biodistribution of 125I-labeled Dex-g-PMAGGCONHTyr.

Dextran graft poly (N-methacryloylglycylglycine) copolymer-tyrosine conjugates (dextran-g-PMAGGCONHTyr) were synthesized and characterized. Dynamic light scattering (DLS) results indicated that the graft copolymers are soluble in pH 7.4 PBS and 0.9% saline solutions. The graft copolymers were labeled with (125)I, and the labeling stability in 0.9% saline solution was investigated. Pharmacokinetics studies showed a rapid clearance of (125)I-labeled graft copolymers from the blood pool. Biodistribution images confirmed the preferable liver and spleen accumulation within 1 h after injection and rapid clearance from all the organs over time. The graft copolymer with molecular weight of 9.8 kDa was eliminated from the kidney significantly faster than those with higher molecular weight. The effect of the numbers of -COOH groups on the graft copolymers on the biodistribution was also investigated. It was found that the graft copolymers with the average number of -COOH groups per glucopyranose unit (DS(-COOH)) of 0.57 and 0.18 are mainly distributed in liver and spleen at 1 h after injection, whereas the graft copolymer with DS(-COOH) of 0.07 is mainly accumulated in kidney.

Adaptive threshold split Bregman algorithm based on magnetic induction tomography for brain injury monitoring imaging.

Objective. Traditional magnetic induction tomography (MIT) algorithms have problems in reconstruction, such as large area error (AE), blurred boundaries of reconstructed targets, and considerable image noise (IN). As the size and boundary of a lesion greatly affect the treatment plan, more accurate algorithms are necessary to meet clinical needs.Approach. In this study, adaptive threshold split Bregman (ATSB) is proposed for brain injury monitoring imaging in MIT. We established a 3D brain MIT simulation model with the actual anatomical structure and a phantom model and obtained the reconstructed images of single targets in different positions and multiple targets, using the Tikhonov, eigenvalue threshold regularisation (ETR), split Bregman (SB), and ATSB algorithms.Main results. Compared with the Tikhonov and ETR algorithms, the ATSB algorithm reduced the AE by 95% and the IN by 17% in a simulation and reduced the AE by 87% and IN by 6% in phantom experiments. Compared with the SB algorithm, the ATSB algorithm can reduce the difficulty of adjusting parameters and is easier to use in clinical practice. The simulation and phantom experiments results showed that the ATSB algorithm could reconstruct the target size more accurately and could distinguish multiple targets more effectively than the other three algorithms.Significance. The ATSB algorithm could improve the image quality of MIT and better meet the needs of clinical applications and is expected to promote brain injury monitoring imaging via MIT.

Smart assembly behaviors of hydroxypropylcellulose-graft-poly(4-vinyl pyridine) copolymers in aqueous solution by thermo and pH stimuli.

Thermo- and pH-sensitive graft copolymers, hydroxypropylcellulose-graft-poly(4-vinyl pyridine) (HPC-g-P4VP), were synthesized via atom transfer radical polymerization (ATRP) and characterized. The thermo- and pH-induced micellization and stimuli-responsive properties of HPC-g-P4VP graft copolymers in aqueous solution were investigated by transmittance, (1)H NMR, dynamic light scattering (DLS), and so on. For the pH-induced micellization, the P4VP side chains collapse to form the core of the micelles, and the HPC backbones stay in the shell to stabilize the micelles. In the case of thermoinduced micellization, the HPC backbones collapse to form the core of the micelles that was stabilized by the P4VP side chains in the shell upon heating. What's more, the cloud point of the HPC-g-P4VP copolymers in the aqueous solution could be finely tuned by changing the length of P4VP side chains or the pH values. In acidic water, the longer the side chains, the higher the cloud point. For those HPC-g-P4VP copolymers with short side chains, for example, HPC0.05-g-P4VP(3), the lower pH correlates a higher cloud point. The thermo- or pH-induced micelles also have the pH- or thermosensitivity due to their P4VP or HPC shells.

Controllable aggregation and reversible pH sensitivity of AuNPs regulated by carboxymethyl cellulose.

A pH-sensitive gold nanoparticle-cysteamine/carboxymethyl cellulose (Au-CA/CMC) dispersion system was prepared by a simple approach. Gold nanoparticles (AuNPs) were first synthesized by directly reducing chloroauric acid (HAuCl(4)) with sodium carboxymethyl cellulose (CMC). Then the AuNPs were decorated by an electrostatic compound of cysteamine hydrochloride (CA) and sodium carboxymethyl cellulose (CMC) through ligand exchange to get the assembly of Au-CA/CMC. The Au-CA/CMC dispersion system exhibits strongly reversible pH-responsive behavior with the aggregation of AuNPs caused by the combined action of the chain conformation change of CMC and electrostatic interactions between CA and CMC at different pH values. Finally, the reversible aggregation mechanism of AuNPs in the Au-CA/CMC dispersion system has been investigated by transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV-vis spectroscopy). This study provides a new method to fabricate a stimuli-responsive system free from complicated organic synthesis without using a toxic reducing agent.

Self-assembly and dual-stimuli sensitivities of hydroxypropylcellulose-graft-poly(N,N-dimethyl aminoethyl methacrylate) copolymers in aqueous solution.

The self-assembly and pH- and thermo-sensitivities properties of hydroxypropyl cellulose-graft-poly(N,N-dimethyl aminoethyl methacrylate) (HPC-g-PDMAEMA) copolymers in aqueous solutions were investigated by transmittance, dynamic light scattering (DLS), and (1)H NMR spectroscopy. Micelles with different structure can be formed by varying either pH value or temperature. At low pH, e.g., 3.0, the HPC backbone of the copolymer collapse to form the core of micelles stabilized with protonated PDMAEMA side chains on the surface of the micelles upon heating. At the medium pH, e.g., 8.1, both HPC backbone and PDMAEMA side chains collapse upon heating to form unstable aggregates. At high pH, e.g., 12.3, PDMAEMA side chains collapse first to form the core of micelles stabilized with HPC chains upon heating. Further heating the copolymer solution at this pH leads to the aggregation of the micelles due to the collapse of the shell HPC chains. The thermal sensitivity of the HPC-g-PDMAEMA copolymers is reversible.

Preparation and characterization of reinforced starch-based composites with compatibilizer by simple extrusion.

Because of the poor performance of starch-based composites, we prepared the starch-based composites with good mechanical properties by a simple two-step melt-blending extrusion. Glycerol and nano-SiO2 were firstly introduced into starch to prepare the TPS/nano-SiO2 composite by the first extrusion, and poly(butylene adipate-co-terephthalate) (PBAT) and the compatibilizers were then incorporated to obtain the improved composites by the second extrusion. The mechanical properties, thermal properties, morphology, and structure of the composites were characterized. The results showed that the strength dramatically increased after the addition of nano-SiO2 into starch, and the elongation at break was significantly improved by the incorporation of PBAT. The tensile strength was increased distinctly after the addition of the compatibilizers. All the composites exhibited good mechanical properties. The melting transition, the thermal stability, and the crystalline structure did not change with the additives, whereas the glass transition of the starch-rich phase shifted to a lower temperature. The results indicated that the combined compatibilizers had better compatibilization than each one alone.

A quantitative method based on total relative change for dynamic electrical impedance tomography.

We proposed a new method based on total relative change (TRC) from measured boundary voltages to quantify the volume changes of fluid during electrical impedance tomography (EIT) monitoring. The results showed that TRC linearly correlated with the volume of infused saline solution into a phantom, and the slope of TRC changes was approximately linear with the infusion speed. A inserted copper tube at different positions did not affect TRC significantly. The linear relationship between TRC and volume change indicates that TRC could be a good quantitative index for dynamic EIT.

Long-term protection effects of National Reserve to forest vegetation in 4 decades: biodiversity change analysis of major forest types in Changbai Mountain Nature Reserve, China.

The Changbai Mountain Nature Reserve (CNR) was established in 1960 to protect the virgin Korean pine mixed hardwood forest, a typical temperate forest of northeast China. We conducted systematic studies of vascular diversity patterns on the north slope of the CNR mountainside forests (800-1700 m a.s.l.) in 1963 and 2006 respectively. The aim of this comparison is to assess the long-term effects of the protection on plant biodiversity of CNR during the interval 43 years. The research was carried out in three types of forests: mixed coniferous and broad-leaved forest (MCBF), mixed coniferous forest (MCF), and sub-alpine coniferous forest (SCF), characterized by different dominant species. The alpha diversity indicted by species richness and the Shannon-Wiener index were found different in the same elevations and forest types during the 43-year interval. The floral composition and the diversity of vascular species were generally similar along altitudinal gradients before and after the 43-year interval, but some substantial changes were evident with the altitude gradient. In the tree layers, the dominant species in 2006 were similar to those of 1963, though diversity declined with altitude. The indices in the three forest types did not differ significantly between 1963 and 2006, and these values even increased in the MCBF and MCF from 1963 to 2006. However, originally dominant species, P. koraiensis for example, tended to decline, while the proportion of broad-leaved trees increased, and the species turnover in the succession layers trended to shift to higher altitudes. The diversity pattern of the under canopy fluctuated along the altitudinal gradient due to micro-environmental variations. Comparison of the alpha diversity in the three forests shows that the diversity of the shrub and herb layer decreased with time. During the process of survey, we also found some rare and medicinal species disappeared. Analysis indicates that the changes of the diversity pattern in this region are caused by both nature and human factors. Meteorological records revealed that climate has changed significantly in the past 43 years. We also found the most severe human disturbance to the CNR forests in the process of another field survey that is the exploitation of herb medicines and Korean pine nuts. We hope this research would give some guidance to the future reserve management in Changbai Mountain area.

Super-strong and tough poly(vinyl alcohol)/poly(acrylic acid) hydrogels reinforced by hydrogen bonding.

Synthetic hydrogels or water-containing polymeric materials are much inferior to biological tissues and solid plastics in many aspects of mechanical properties; it is a great challenge to develop hydrogels with mechanical properties comparable with or even superior to those of biological tissues and plastics. Here, we report a type of super-strong and tough hydrogen-bonded poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) hydrogel by immersing as-prepared PVA hydrogels in aqueous PAA solutions and then cold-drawing the hydrogels to different strains. The immersing process introduces PAA chains into the PVA hydrogels, which increases the cross-linking density by hydrogen bonding and hence, much improved mechanical properties and low water contents (35.9-40.2 wt%) are observed. The cold-drawing orients the polymer chains, which enables the formation of more and stronger hydrogen bonds. The mechanical properties of cold-drawn gels are dramatically enhanced, with tensile strength and elastic modulus up to 140 and 100 MPa, respectively; also, super-high toughness (117 MJ m-3) and fracture energy (101 kJ m-2) are obtained. Very impressively, the ultra-high tensile strengths of the cold-drawn hydrogels are superior to those of biological tissues and most solid engineered plastics. Characterizations and comparative studies prove that the enhancement of mechanical properties is mainly due to the formation of more hydrogen bonding rather than the loss of water or the change in crystallinity. This study provides a new strategy for preparing super-strong physically cross-linked hydrogels and other polymeric materials. This super-strong and tough hydrogel may find potential applications in biomedical and load-bearing fields.

Multi-frequency parameter mapping of electrical impedance scanning using two kinds of circuit model.

Electrical impedance scanning (EIS) is a kind of potential bio-impedance measurement technology, especially aiding the diagnosis of breast cancer in women. By changing the frequency of the driving signal in turn while keeping the other conditions stable, multi-frequency measurement results on the object can be obtained. According to the least square method and circuit theory, the parameters in two models are deduced when measured with data at multiple driving frequencies. The arcs, in the real and imaginary parts of a trans-admittance coordinate, made by the evaluated parameters fit well the realistic data measured by our EIS device on female subjects. The Cole-Cole model in the form of admittance is closer to the measured data than the three-element model. Based on the evaluation of the multi-frequency parameters, we presented parameter mapping of EIS using two kinds of circuit model: one is the three-element model in the form of admittance and the other is the Cole-Cole model in the form of admittance. Comparing with classical admittance mapping at a single frequency, the multi-frequency parameter mapping will provide a novel vision to study EIS. The multi-frequency approach can provide the mappings of four parameters, which is helpful to identify different diseases with a similar characteristic in classical EIS mapping. From plots of the real and imaginary parts of the admittance, it is easy to make sure whether there exists abnormal tissue.

Gelation of Na-alginate aqueous solution: A study of sodium ion dynamics via NMR relaxometry.

Sodium alginate (SA) hydrogels have a wide range of applications including tissue engineering, drug delivery and formulations for preventing gastric reflux. The dynamics of sodium ions during the gelation process of SA solution is critical for clarification of the gelation procedure. In this work, nuclear magnetic resonance (NMR) relaxometry and pulsed-field-gradient (PFG) NMR diffusometry were used to investigate the dynamics of the sodium ions during the gelation of SA alginate. We find that sodium ions are in two different states with the addition of divalent calcium ions, corresponding to Ca2+ crosslinked and un-crosslinked regions in the hydrogels. The sodium ions within the un-crosslinked regions are those released from the alginate chains without Ca2+ crosslinking. The relative content of sodium ions within the Ca2+ crosslinked regions decreased with the increase in the content of calcium ions in the system. The relaxation time T2 of sodium ions within the Ca2+ crosslinked and un-crosslinked regions shift to shorter and longer relaxation time with the increase in concentration of calcium ion, which indicates the closer package of SA chains and the larger space for the diffusion of free sodium ions. This work clarifies the dynamics of 23Na+ in a calcium alginate gel at the equilibrium state.

Thermal sensitivity and protein anti-adsorption of hydroxypropyl cellulose-g- poly(2-(methacryloyloxy) ethyl phosphorylcholine).

Zwitterionic graft copolymers, hydroxypropyl cellulose graft poly(2-(methacryloyloxy) ethyl phosphorylcholine) (HPC-g-PMPC) with well-defined architecture were synthesized by atom transfer radical polymerization (ATRP). The self-assembly behaviors and thermal sensitivity of HPC-g-PMPC copolymers and their correlations with graft density and side chain length were investigated in details. HPC-g-PMPC copolymers can self-assemble into spherical aggregate structure above the critical aggregation concentration (CAC) at room temperature. Meanwhile, the size of the aggregates mainly depended on the graft density. The obtained aggregates were thermal sensitive and their low critical solution temperature (LCST) was efficiently regulated by varying the graft density. Above the LCST, the aggregates were transferred into aggregates with core-shell structure, in which the HPC rich core was stabilized by the PMPC rich shell. The interaction between the HPC-g-PMPC aggregates and BSA was investigated. The results indicated that the anti-adsorption of BSA on the aggregates surface depended on the length and graft density of the PMPC zwitterionic side chains.

Dissolution and Metastable Solution of Cellulose in NaOH/Thiourea at 8 °C for Construction of Nanofibers.

To develop a facile approach for the dissolution of cellulose, a novel solvent (9.3 wt % NaOH/7.4 wt % thiourea aqueous solution) was used, for the first time, to dissolve cellulose within 5 min at 8 °C. The results of NMR and Raman spectra demonstrated that stable thiourea···OH- complexes were formed through strong hydrogen bonds in NaOH/thiourea at room temperature. Moreover, the strength of the hydrogen bonds in thiourea···OH- complexes was much higher than that in urea···OH- complexes, and the number of thiourea···OH- complexes increased significantly in 9.3 wt % NaOH/7.4 wt % thiourea compared to that in 9.5 wt % NaOH/4.5 wt % thiourea, which dissolved cellulose at -5 °C, leading to the dissolution of cellulose at a relatively high temperature (8 °C). The cellulose that dissolved at such a high temperature was metastable. The results of dynamic light scattering and transmission electron microscope experiments confirmed that the extended cellulose chains and their aggregates coexisted in the dilute cellulose solution. Interestingly, stiff cellulose chains could be self-assembled in parallel to form nanofibers in the metastable cellulose solution, from which cellulose microspheres consisting of nanofibers could be easily produced by inducing heating. This work not only proposed a novel method for the dissolution of cellulose in aqueous system at temperatures over 0 °C but also opened up a new pathway for the construction of nanofibrous cellulose materials.

Pseudo-polar drive patterns for brain electrical impedance tomography.

Brain electrical impedance tomography (EIT) is a difficult task as brain tissues are enclosed by the skull of high resistance and cerebrospinal fluid (CSF) of low resistance, which makes internal resistivity information more difficult to extract. In order to seek a single source drive pattern that is more suitable for brain EIT, we built a more realistic experimental setting that simulates a head with the resistivity of the scalp, skull, CSF and brain, and compared the performance of adjacent, cross, polar and pseudo-polar drive patterns in terms of the boundary voltage dynamic range, independent measurement number, total boundary voltage changes and anti-noise performance based on it. The results demonstrate that the pseudo-polar drive pattern is optimal in all the aspects except for the dynamic range. The polar and cross drive patterns come next, and the adjacent drive pattern is the worst. Therefore, the pseudo-polar drive pattern should be chosen for brain EIT.

Reversible redox activity of ferrocene functionalized hydroxypropyl cellulose and its application to detect H2O2.

Novel ferrocene functionalized hydroxypropyl cellulose (HPC-Fc) were prepared by azide-alkyne cycloaddition and characterized. HPC-Fc exhibits an excellent reversible redox activity and could establish amazing electron transfer ability between enzyme and electrode. HPC-Fc and horseradish peroxidase (HRP) were coated on a platinized carbon electrode to prepare an amperometric biosensor for hydrogen peroxide (H2O2) detection. The amperometric response was measured as a function of H2O2 concentration at a fixed potential of 0.35V in 100mM phosphate buffer solution (pH 7.0). The novel biosensor exhibits a fast linear response toward H2O2 in the range of 0.1-8µM with sensitivity of 4.21nA/µM. Moreover, the enzyme assays measured by the spectrophotometer method confirm that abundant hydroxyl groups of HPC backbones are conductive for HRP to maintaining or even enhancing their activity. The redox active HPC-Fc with the unique properties of both ferrocene and cellulose is a good candidate for biosensor applications.

[A bipolar optocoupler isolation amplifier with high precision and wide bandwidth].

To fit the technological requirements in electrical impedance tomography system, an improved bipolar optocoupler isolation amplifier based on single analog optocoupler was realized. The experimental results illustrates that the full power -3dB bandwidth of this circuit is greater than 800 KHz, the equivalent output noise is lower than 50 uV(RMS), and the linearity at +/- 4 V inputs is lower than 0.01%. In addition to these features, the circuit also have the advantages of simple structure and no distortion caused by mismatch between analog optocouplers.