Enhancing Fenton-like Degradation of Organic Pollutants at Neutral pH by Multivalent Cu NCs/HAp Nanocatalysts.

Heterogeneous Fenton-like catalysis is a widely used method for the degradation of organic pollutants. However, it still has some limitations such as low activity in the neutral condition, low conversion rates of metals with different valence states, and potential secondary metal pollution. In this study, a Fenton-like nanocatalyst was first created by generating ultrasmall copper nanoclusters (Cu NCs) on the surface of hydroxyapatite (HAp) through a process of doping followed by modification. This resulted in the formation of a composite nanocatalyst known as Cu NCs/HAp. With the help of hydrogen peroxide (H2O2), Cu NCs/HAp exhibits an outstanding Fenton-like catalytic performance by efficiently degrading organic dyes such as methylene blue under mild neutral conditions. The removal rate can reach over 83% within just 30 min, demonstrating ideal catalytic universality and stability. The improved Fenton-like catalytic performance of Cu NCs/HAp can be ascribed to the synergistic effect of the multivalent Cu species through two simultaneous reaction pathways. During route I, the embedded Cu NCs with a core-shell Cu0/Cu+ structure can undergo sequential oxidation to form Cu2+, which continuously activates H2O2 to generate hydroxyl radicals (•OH) and singlet oxygen (1O2). In route II, Cu2+ produced from route I and initially adsorbed on the surface of HAp can be reduced by H2O2, thus regenerating Cu+ species for route I and achieving a closed-loop reaction. This work has confirmed that Cu NCs loaded on HAp may be an alternative Fenton-like catalyst for degradation of organic pollutants and environmental remediation, opening up new avenues for potential applications of other Cu NCs in future water pollution control.

Electrical performance of monolayer MoS2transistor with MoS2nanobelt metallic edges as electrodes.

The contact electrodes have great influence on the performance of monolayer MoS2devices. In this paper, monolayer MoS2and MoS2nanobelts were synthesized on SiO2/Si substrates via the chemical vapor deposition method. By using wet and dry transfer process, MoS2nanobelt metallic edges were designed as the source/drain contact electrodes of monolayer MoS2field effect transistor. The 'nanobelt metallic edges' refers to the top surface of the nanobelt being metallic. Because the base planes of MoS2nanobelt vertically stand on the substrate, which makes the layer edges form the top surface of the nanobelt. The nonlinearIds-Vdscharacteristics of the device indicates that the contact between the monolayer MoS2and MoS2metallic edges displays a Schottky-like behavior. The back-gated transfer characteristics indicate that monolayer MoS2device with MoS2nanobelt metallic edges as electrodes shows an n-type behavior with a mobility of ∼0.44 cm2V-1·s-1, a carrier concentration of ∼7.31 × 1011cm-2, and an on/off ratio of ∼103. The results enrich the electrode materials of two-dimensional material devices and exhibit potential for future application of MoS2metallic edges in electronic devices.

Robust Control Based on Adaptive Neural Network for the Process of Steady Formation of Continuous Contact Force in Unmanned Aerial Manipulator.

Contact force control for Unmanned Aerial Manipulators (UAMs) is a challenging issue today. This paper designs a new method to stabilize the UAM system during the formation of contact force with the target. Firstly, the dynamic model of the contact process between the UAM and the target is derived. Then, a non-singular global fast terminal sliding mode controller (NGFTSMC) is proposed to guarantee that the contact process is completed within a finite time. Moreover, to compensate for system uncertainties and external disturbances, the equivalent part of the controller is estimated by an adaptive radial basis function neural network (RBFNN). Finally, the Lyapunov theory is applied to validate the global stability of the closed-loop system and derive the adaptive law for the neural network weight matrix online updating. Simulation and experimental results demonstrate that the proposed method can stably form a continuous contact force and reduce the chattering with good robustness.

Influence on the physicochemical properties of fish collagen gels using self-assembly and simultaneous cross-linking with the N-hydroxysuccinimide adipic acid derivative.

Collagen gels from Southern catfish (Silurus meridionalis Chen) skins were prepared via the self-assembly of collagen molecules and simultaneous cross-linking with the N-hydroxysuccinimide adipic acid derivative (NHS-AA). The doses of NHS-AA were converted to [NHS-AA]/[NH2] ratios (0.025-1.6, calculated by the [active ester group] of NHS-AA and [ε-NH2] of lysine and hydroxylysine residues of collagen). When the ratio < 0.05, collagen gels were formed by collagen molecule self-assembly, resulting in the opalescent appearance of collagen gels and the characteristic D-periodicity of partial collagen fibrils, the collagen gel ([NHS-AA]/[NH2] = 0.05) displayed a small increase in denaturation temperature (Td, 42.8 °C), remaining weight (12.59%), specific water content (SWC 233.7) and elastic modulus (G' 128.4 Pa) compared with uncross-linked collagen gel (39.1 °C, 9.12%, 222.4 and 85.4 Pa, respectively). As the ratio > 0.05, disappearance of D-periodicity and a gradual change in appearance from opalescent to transparent suggested that the inhibition of NHS-AA in the self-assembly of collagen molecules was more obvious. As a result, the collagen gel ([NHS-AA]/[NH2] = 0.2) had the lowest Td (35.8 °C), remaining weight (7.96%), SWC (130.9) and G' (31.9 Pa). When the ratio was 1.6, the collagen molecule self-assembly was markedly suppressed and the formation of collagen gel was predominantly via the covalent cross-linking bonds which led to the transparent appearance, and the maximum values of Td (47.0 °C), remaining weight (45.92%) and G' (420.7 Pa) of collagen gel. These results indicated that collagen gels with different properties can be prepared using different NHS-AA doses.

Construction of collagen gel with high viscoelasticity and thermal stability via combining cross-linking and dehydration.

Collagen gel is widely used in tissue engineering due to excellent biological properties and swollen three-dimensional network structure. To improve viscoelasticity and thermal stability, collagen gels consisting of fibrils were cross-linked with glutaraldehyde and sequentially dehydrated via ethanol or heating (named as EGC or HGC, respectively). For EGC, ethanol replaced free and loosely bound water and then combined with tightly bound water, inducing the increase in hydrogen bonds and molecular interactions. Therefore, the thermal transition temperature (Tt ) and storage modulus (G') obviously increased from 47.3 ± 0.5°C and 0.1 kPa to 92.7 ± 0.8°C and 7.8 kPa, respectively. Unfortunately, the high deformation (γ > 60%) and low recovery percentage (R < 15%) reflected the poor anti-deformation of gels due to the volatility of ethanol. For HGC, the entanglement and rigidity of fibrils increased owing to the contraction of cross-linked fibrils and cohesive action of denatured collagen. As a result, HGC were more resistant to deformation and exhibited more elasticity than native collagen gel, accompanied by the fact that G' and R increased to 28.8 kPa and 90.0% ± 0.7%. Additionally, HGC exhibited higher Tt (121.4 ± 0.5°C) due to lower water content and higher collagen concentration.

Glutamic acid concentration dependent collagen mineralization in aqueous solution.

The aim of this research is to evaluate the effects of glutamic acid (Glu) on the process of collagen mineralization, the structure and property of mineralized composites. Collagen mineralization was initiated by introducing PBS to blended solutions containing 1 mg/mL collagen, 6 mmol/L calcium and Glu ranged from 0 to 550 mmol/L. The kinetic curves and quantitation analyses showed that Glu could delay the collagen mineralization, and reduce the crystalline size and the amount of hydroxyapatite. With the Glu concentration increased from 50 to 200 mmol/L, the collagen self-assembly was promoted, resulting in the improvement of hardness and thermal stability of mineralized composites. However, further increase in the Glu concentration to 400 mmol/L or above would significantly inhibit the self-assembly of collagen and reduce the hardness and thermal stability of mineralized composites. Scanning electron microscopy revealed that the diameter of collagen became thicker as the Glu concentration increased. Moreover, hydroxyapatite with spherical morphology was uniformly dispersed and well combined with collagen fibril at Glu concentration of 200 mmol/L. These results may provide a broader understanding of the potential mechanism of biomineralization and be critical in the design of biomimetic scaffolds for bone tissue engineering.

Stable and biocompatible hydrogel composites based on collagen and dialdehyde carboxymethyl cellulose in a biphasic solvent system.

Stable hydrogels with a mechanically strong matrix microenvironment are favorable biomaterials for three-dimensional cell culture. Acidic collagen solution is commonly combined with chemical crosslinkers for rapid network formation. Herein, dialdehyde carboxymethyl cellulose (DCMC) was selected as an optimal crosslinking reagent for its excellent biocompatibility and suitable chemical reactivity. Both shielding of electrostatic attractions between these two oppositely charged biomaterials and obtaining concentrated collagen solution were achieved using a novel biphasic acetic acid /1-ethyl-3-methylimidazolim acetate (AA/[EMIM][Ac]) solvent system. Hydrogel composites containing more crosslinks were obtained by increasing collagen concentrations (5-25 mg/mL), as confirmed by the improved mechanical properties, thermal denaturation temperature, anti-enzymatic ability and compact microstructure. Moreover, cell proliferation assay demonstrated that all the obtained DCMC-crosslinked collagen hydrogel composites ensures commendable biocompatibility. This study provides a promising strategy for manipulating stable and biocompatible hydrogel composites by blending concentrated collagen solution with DCMC in a biphasic solvent system.

Investigation on the behavior of collagen self-assembly in vitro via adding sodium silicate.

Silicon, a trace element found in human body, plays a critical role in the process of collagen self-assembly. In this study, the intermolecular interaction and fibrillogenesis process were investigated to understand the effects of various concentrations of sodium silicate (SS) on collagen self-assembly in vitro. Fourier transform infrared spectroscopy analysis indicated that the triple helical structure of collagen was not significantly affected by SS. Hydrophobic interactions and particle sizes of collagen aggregates, which were measured using pyrene fluorescence and dynamic light scanning, enhanced via adding 2 mM SS whereas decreased with further increasing concentrations (4-8 mM). Kinetic analysis revealed that an increase in hydrophobic interactions boosted collagen self-assembly in the presence of 2 mM SS. The inhibition of self-assembly with the addition of 4-8 mM SS, as illustrated by a reduction in the fibrillogenesis rate and turbidity, was potentially attributed to weak hydrophobic interactions and strong electrostatic repulsion. The observation of microscopy demonstrated that the fibrils exhibited the characteristic D-periodicity at 2 mM SS. The inhibitory effect of 4 mM SS was slight and the fibrils still formed, while the microstructure was consisted of clustered collagen aggregates as SS ≥ 6 mM owing to serious inhibition on collagen self-assembly.

Rheological properties of glutaraldehyde-crosslinked collagen solutions analyzed quantitatively using mechanical models.

Understanding the rheological behavior of collagen solutions crosslinked by various amounts of glutaraldehyde (GTA) [GTA/collagen (w/w)=0-0.1] is fundamental either to design optimized products or to ensure stable flow. Under steady shear, all the samples exhibited pseudoplasticity with shear-thinning behavior, and the flow curves were well described by Ostwald-de Waele model and Carreau model. With increased amounts of GTA, the viscosity increased from 6.15 to 168.54 Pa·s at 0.1s(-1), and the pseudoplasticity strengthened (the flow index decreased from 0.549 to 0.117). Additionally, hysteresis loops were evaluated to analyze the thixotropy of the native and crosslinked collagen solutions, and indicated that stronger thixotropic behavior was associated with higher amount of GTA. Furthermore, the values of apparent yield stress were negative, and a flow index <1 for all the systems obtained via Herschel-Bulkley model confirmed that the native and crosslinked collagen solutions belonged to pseudoplastic fluid without apparent yield stress. However, the increment of dynamic denaturation temperature determined by dynamic temperature sweep was not obvious. The viscoelastic properties were examined based on creep-recovery measurements and then simulated using Burger model and a semi-empirical model. The increase in the proportion of recoverable compliance (instantaneous and retardant compliance) reflected that the crosslinked collagen solutions were more resistant to the deformation and exhibited more elastic behavior than the native collagen solution, accompanied by the fact that the compliance value decreased from 39.317 to 0.152 Pa(-1) and the recovery percentage increased from 1.128% to 87.604%. These data indicated that adjusting the amount of GTA could be a suitable mean for manipulating mechanical properties of collagen-based biomaterials.

Changes in aggregation behavior of collagen molecules in solution with varying concentrations of acetic acid.

A critical aggregation concentration of 0.30-0.50mg/mL was previously obtained for type I collagen at 0.1M acetic acid (AA). In the present study, the aggregation behavior of collagen in solution (0.5mg/mL) in the presence of 0.1-2.0M AA was investigated. Circular dichroism showed that the three helix structure was maintained across the whole AA concentration range. However, the ratio of positive peak intensity over negative peak intensity varied depending on the conformational state of collagen aggregates. Ultra-sensitive differential scanning calorimetry revealed that transition temperatures Tm1 and Tm2 decreased by 8.35°C and 7.80°C, respectively, between 0.1M and 2.0M, indicating a possible relationship between the aggregation state and the thermal effect. The surrounding polarity of collagen molecules in solution containing pyrene was investigated by fluorescence spectroscopy, which demonstrated that disaggregation of collagen aggregates was enhanced with increasing AA concentration. This observation was correlated with changes in collagen fiber size observed by atomic force microscopy. Furthermore, collagen tyrosine residues were blue-shifted in an intrinsic fluorescence spectra, further indicating changes in aggregation behavior with increasing AA concentration. Finally, the dynamic response of collagen molecules to AA was analyzed by two-dimensional correlation fluorescence spectra.

Two-dimensional infrared spectroscopic study on the thermally induced structural changes of glutaraldehyde-crosslinked collagen.

The thermal stability of collagen solution (5 mg/mL) crosslinked by glutaraldehyde (GTA) [GTA/collagen (w/w)=0.5] was measured by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR), and the thermally induced structural changes were analyzed using two-dimensional (2D) correlation spectra. The denaturation temperature (Td) and enthalpy change (ΔH) of crosslinked collagen were respectively about 27°C and 88 J/g higher than those of native collagen, illuminating the thermal stability increased. With the increase of temperature, the red-shift of absorption bands and the decreased AIII/A1455 value obtained from FTIR spectra indicated that hydrogen bonds were weakened and the unwinding of triple helix occurred for both native and crosslinked collagens; whereas the less changes in red-shifting and AIII/A1455 values for crosslinked collagen also confirmed the increase in thermal stability. Additionally, the 2D correlation analysis provided information about the thermally induced structural changes. In the 2D synchronous spectra, the intensities of auto-peaks at 1655 and 1555 cm(-1), respectively assigned to amide I band (CO stretching vibration) and amide II band (combination of NH bending and CN stretching vibrations) in helical conformation were weaker for crosslinked collagen than those for native collagen, indicating that the helical structure of crosslinked collagen was less sensitive to temperature. Moreover, the sequence of the band intensity variations showed that the band at 1555 cm(-1) moved backwards owing to the addition of GTA, demonstrating that the response of helical structure of crosslinked collagen to the increased temperature lagged. It was speculated that the stabilization of collagen by GTA was due to the reinforcement of triple helical structure.