Yolk-shell smart polymer microgels and their hybrids: fundamentals and applications.

Yolk-shell microgels and their hybrids have attained great importance in modern-day research owing to their captivating features and potential uses. This manuscript provides the strategies for preparation, classification, properties and current applications of yolk-shell microgels and their hybrids. Some of the yolk-shell microgels and their hybrids are identified as smart polymer yolk-shell microgels and smart hybrid microgels, respectively, as they react to changes in particular environmental stimuli such as pH, temperature and ionic strength of the medium. This unique behavior makes them a perfect candidate for utilization in drug delivery, selective catalysis, adsorption of metal ions, nanoreactors and many other fields. This review demonstrates the contemporary progress along with suggestions and future perspectives for further research in this specific field.

Recent developments in chitosan based microgels and their hybrids.

Chitosan based microgels have gained great attention because of their chemical stability, biocompatibility, easy functionalization and potential uses in numerous fields. Production, properties, characterization and applications of chitosan based microgels have been systematically reviewed in this article. Some of these systems exhibit responsive behavior towards external stimuli like pH, light, temperature, glucose, etc. in terms of swelling/deswelling in an aqueous medium depending upon the functionalities present in the network which makes them a potential candidate for various applications in the fields of biomedicine, agriculture, catalysis, sensing and nanotechnology. Current research development and critical overview in this field accompanying by future possibilities is presented. The discussion is concluded with recommended possible future works for further progress in this field.

Biocompatible Anisole-Nonlinear PEG Core-Shell Nanogels for High Loading Capacity, Excellent Stability, and Controlled Release of Curcumin.

Curcumin, a nontoxic and cheap natural medicine, has high therapeutic efficacy for many diseases, including diabetes and cancers. Unfortunately, its exceedingly low water-solubility and rapid degradation in the body severely limit its bioavailability. In this work, we prepare a series of biocompatible poly(vinyl anisole)@nonlinear poly(ethylene glycol) (PVAS@PEG) core-shell nanogels with different PEG gel shell thickness to provide high water solubility, good stability, and controllable sustained release of curcumin. The PVAS nanogel core is designed to attract and store curcumin molecules for high drug loading capacity and the hydrophilic nonlinear PEG gel shell is designed to offer water dispersibility and thermo-responsive drug release. The nanogels prepared are monodispersed in a spherical shape with clear core-shell morphology. The size and shell thickness of the nanogels can be easily controlled by changing the core-shell precursor feeding ratios. The optimized PVAS@PEG nanogels display a high curcumin loading capacity of 38.0 wt%. The nanogels can stabilize curcumin from degradation at pH = 7.4 and release it in response to heat within the physiological temperature range. The nanogels can enter cells effectively and exhibit negligible cytotoxicity to both the B16F10 and HL-7702 cells at a concentration up to 2.3 mg/mL. Such designed PVAS@PEG nanogels have great potential to be used for efficient drug delivery.

Fabrication of silver nanoparticles within chitosan based microgels for catalysis.

Chitosan based monodisperse poly[chitosan-N-isopropylmethacrylamide-acrylic acid] [P(CNA)] microgels were produced via precipitation polymerization. Resulting crosslinked P(CNA) micro particles were used as micro-reactors to prepare silver nanoparticles within the polymeric network by chemical reduction of Ag+ ions with sodium borohydride. Various techniques including transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-vis) spectroscopy were used to analyze P(CNA) microgels and Ag-P(CNA) hybrid microgels. Catalytic potential of Ag-P(CNA) hybrid system towards individual and simultaneous reduction of various nitroarenes like p-nitrophenol (pNP), o-nitrophenol (oNP), p-nitroaniline (pNA) and o-nitroaniline (oNA) into corresponding aminoarenes using sodium borohydride as a reductant in aqueous medium was evaluated. The catalytic activity of Ag-P(CNA) system towards both the individual and simultaneous reduction of nitroarenes was examined at various concentrations of catalyst. The values of pseudo first order rate constant (k1) for reduction of individual nitroarene and multiple nitroarenes were determined for comparison. The Ag-P(CNA) hybrid microgel system was found to be stable, economical and efficient catalyst for rapid individual and simultaneous reduction of nitroarenes.

Application of Convolutional Neural Network in Motor Bearing Fault Diagnosis.

In the field of mechanical and electrical equipment, the motor rolling bearing is a workpiece that is extremely prone to damage and failure. However, the traditional fault diagnosis methods cannot keep up with the development pace of the times because they need complex manual pretreatment or the support of specific expert experience and knowledge. As a rising star, the data-driven fault diagnosis methods are increasingly favored by scholars and experts at home and abroad. The convolutional neural network has been widely used because of its powerful feature extraction ability for all kinds of complex information and its outstanding research results in image processing, target tracking, target diagnosis, time-frequency analysis, and other scenes. Therefore, this paper introduces a convolutional neural network and applies it to motor-bearing fault diagnosis. Aiming at the shortcomings of fault signal and convolutional neural network, a large-scale maximum pooling strategy is proposed and optimized by wavelet transform to improve the fault diagnosis efficiency of motor bearing under high-voltage operation. Compared with other machine learning algorithms, the convolution neural network fault diagnosis model constructed in this paper not only has high accuracy (up to 0.9871) and low error (only 0.032) but also is simple to use. It provides a new way for motor bearing fault diagnosis and has very important economic and social value.

Progress and Perspective on Carbon-Based Nanozymes for Peroxidase-like Applications.

Tumor microenvironment-responsive chemodynamic therapy (CDT), an approach based on Fenton/Fenton-like reaction to convert hydrogen peroxide (H2O2) into the highly cytotoxic hydroxyl radical (·OH) in situ to kill cancer cells, represents an important direction for cancer therapy. Different types of nanozymes (nanomaterial-based catalysts that can mimic the activities of natural enzymes) have been developed to mimic peroxidase. This Perspective highlights the latest research progress regarding low-cost and biocompatible carbon-based nanozymes for peroxidase mimics. The effects of structure and surface properties of carbon-based nanozymes on their electronic transfer and peroxidase-like activity are analyzed, including nanospheres, nanotubes, nanosheets, and graphene quantum dots (GQDs) with or without surface functionalization and heteroatom doping. We expand our newly developed carbon nitride (g-C3N4) QD systems to nanozyme application, which are highly efficient in converting the intracellular H2O2 to ·OH species to kill 4T1 cancer cells and demonstrate a great potential for CDT.

Structures and dimensions of micelle-templated nanoporous silicas derived from swollen spherical micelles of temperature-dependent size.

Subambient temperatures are employed in Pluronic-block-copolymer-templated syntheses of many large-pore silicas: SBA-15 (2-D hexagonal with cylindrical mesopores), FDU-12 (face-centered cubic with spherical mesopores), nanotubes and hollow nanospheres. Herein, the origin of a significant temperature dependence of the unit-cell parameter and pore diameter of silicas templated by swollen micelles of Pluronics under subambient conditions was elucidated. The temperature dependence of size of swollen spherical micelles of Pluronic F127 (EO106PO70EO106) in 2 M HCl solution was studied in 12-25 °C range using dynamic light scattering and was correlated with structure types, unit-cell sizes and pore sizes of silicas synthesized at four silica-precursor/Pluronic ratios with a swelling agent (toluene, ethylbenzene). The increase in size of swollen micelles with temperature decrease was paralleled by the increase in the unit-cell size and pore diameter, even if the micelle shape changed in the process of formation of the micelle-templated silica. The decrease in the silica-precursor/Pluronic F127 ratio at constant temperature triggered a succession of phases, including SBA-15 - nanotube sequence that may involve an intermediate nanotube bundle structure, which is uncommon and potentially useful. The temperature decrease also led to a succession of phases, including FDU-12 - SBA-15, hollow nanospheres - nanotube bundles, and nanotubes - SBA-15 sequences.

Carbon-based hybrid nanogels: a synergistic nanoplatform for combined biosensing, bioimaging, and responsive drug delivery.

Nanosized crosslinked polymer networks, named as nanogels, are playing an increasingly important role in a diverse range of applications by virtue of their porous structures, large surface area, good biocompatibility and responsiveness to internal and/or external chemico-physical stimuli. Recently, a variety of carbon nanomaterials, such as carbon quantum dots, graphene/graphene oxide nanosheets, fullerenes, carbon nanotubes, and nanodiamonds, have been embedded into responsive polymer nanogels, in order to integrate the unique electro-optical properties of carbon nanomaterials with the merits of nanogels into a single hybrid nanogel system for improvement of their applications in nanomedicine. A vast number of studies have been pursued to explore the applications of carbon-based hybrid nanogels in biomedical areas for biosensing, bioimaging, and smart drug carriers with combinatorial therapies and/or theranostic ability. New synthetic methods and structures have been developed to prepare carbon-based hybrid nanogels with versatile properties and functions. In this review, we summarize the latest developments and applications and address the future perspectives of these carbon-based hybrid nanogels in the biomedical field.

Liposomal TriCurin, A Synergistic Combination of Curcumin, Epicatechin Gallate and Resveratrol, Repolarizes Tumor-Associated Microglia/Macrophages, and Eliminates Glioblastoma (GBM) and GBM Stem Cells.

Glioblastoma (GBM) is a deadly brain tumor with a current mean survival of 12-15 months. Despite being a potent anti-cancer agent, the turmeric ingredient curcumin (C) has limited anti-tumor efficacy in vivo due to its low bioavailability. We have reported earlier a strategy involving the use two other polyphenols, epicatechin gallate (E) from green tea and resveratrol (R) from red grapes at a unique, synergistic molar ratio with C (C:E:R: 4:1:12.5, termed TriCurin) to achieve superior potency against HPV+ tumors than C alone at C:E:R (µM): 32:8:100 (termed 32 µM+ TriCurin). We have now prepared liposomal TriCurin (TrLp) and demonstrated that TrLp boosts activated p53 in cultured GL261 mouse GBM cells to trigger apoptosis of GBM and GBM stem cells in vitro. TrLp administration into mice yielded a stable plasma concentration of 210 nM C for 60 min, which, though sub-lethal for cultured GL261 cells, was able to cause repolarization of M2-like tumor (GBM)-associated microglia/macrophages to the tumoricidal M1-like phenotype and intra-GBM recruitment of activated natural killer cells. The intratumor presence of such tumoricidal immune cells was associated with concomitant suppression of tumor-load, and apoptosis of GBM and GBM stem cells. Thus, TrLp is a potential onco-immunotherapeutic agent against GBM tumors.

Biocompatible Chitosan-Carbon Dot Hybrid Nanogels for NIR-Imaging-Guided Synergistic Photothermal-Chemo Therapy.

Multifunctional nanocarriers with good biocompatibility, good imaging function, and smart drug delivery ability are crucial for realizing highly efficient imaging-guided chemotherapy in vivo. This paper reports a type of chitosan-carbon dot (CD) hybrid nanogels (CCHNs, ∼65 nm) by integrating pH-sensitive chitosan and fluorescent CDs into a single nanostructure for simultaneous near-infrared (NIR) imaging and NIR/pH dual-responsive drug release to improve therapeutic efficacy. Such CCHNs were synthesized via a nonsolvent-induced colloidal nanoparticle formation of chitosan-CD complexes assisted by ethylenediaminetetraacetic acid (EDTA) molecules in the aqueous phase. The selective cross-linking of chitosan chains in the nanoparticles can immobilize small CDs complexed in the chitosan networks. The resultant CCHNs display high colloidal stability, high loading capacity for doxorubicin (DOX), bright and stable fluorescence from UV to NIR wavelength range, efficient NIR photothermal conversion, and intelligent drug release in response to both NIR light and change in pH. The results from in vitro tests on cell model and in vivo tests on different tissues of animal model indicate that the CCHNs are nontoxic. The DOX-loaded CCHNs can permeate into the implanted tumor on mice and release drug molecules efficiently on site to inhibit tumor growth. The additional photothermal treatments from NIR irradiation can further inhibit the tumor growth, benefited from the effective NIR photothermal conversion of CCHNs. The demonstrated CCHNs manifest a great promise toward multifunctional intelligent nanoplatform for highly efficient imaging-guided cancer therapy with low side effects.

Mesoporous carbon nanoshells for high hydrophobic drug loading, multimodal optical imaging, controlled drug release, and synergistic therapy.

Loading and controlled release of sufficient hydrophobic drugs to tumor cells has been the bottleneck in chemotherapy for decades. Herein we report the development of a fluorescent and mesoporous carbon nanoshell (FMP-CNS) that exhibits a loading capacity for the hydrophobic drug paclitaxel (PTX) as high as ∼80 wt% and releases the drug in a controllable fashion under NIR irradiation (825 nm) at an intensity of 1.5 W cm-2. The high drug loading is primarily attributed to its mesoporous structure and to the supramolecular π-stacking between FMP-CNSs and PTX molecules. The FMP-CNS also exhibits wavelength-tunable and upconverted fluorescence properties and thus can serve as an optical marker for confocal, two-photon, and near infrared (NIR) fluorescence imaging. Furthermore, our in vitro results indicate that FMP-CNSs demonstrate high therapeutic efficacy through the synergistic effect of combined chemo-photothermal treatment. In vivo studies demonstrate marked suppression of tumor growth in mice bearing rat C6 glioblastoma after administration with a single intratumoral injection of PTX-loaded FMP-CNS.

Chitosan-Gated Magnetic-Responsive Nanocarrier for Dual-Modal Optical Imaging, Switchable Drug Release, and Synergistic Therapy.

A dual-layer shell hollow nanostructure as drug carrier that provides instant on/off function for drug release and contrast enhancement for multimodal imaging is reported. The on-demand drug release is triggered by irradiation of an external magnetic field. The nanocarrier also demonstrates a high drug loading capacity and synergistic magnetic-thermal and chemotherapy.

NIR upconversion fluorescence glucose sensing and glucose-responsive insulin release of carbon dot-immobilized hybrid microgels at physiological pH.

This work reports the preparation of multifunctional hybrid microgels based on the one-pot free radical dispersion polymerization of hydrogen-bonding complexes in water, formed from hydroxyl/carboxyl bearing carbon dots with 4-vinylphenylboronic acid and acrylamide comonomers, which can realize the simultaneous optical detection of glucose using near infrared light and glucose-responsive insulin delivery.

Magnetic and fluorescent carbon-based nanohybrids for multi-modal imaging and magnetic field/NIR light responsive drug carriers.

Carbon nanomaterials have gained significant momentum as promising candidate materials for biomedical applications due to their unique structure and properties. After functionalization with magnetic and fluorescent components, the resultant carbon-based nanohybrids can serve not only as magnetic resonance and fluorescence imaging contrast agents, but also as photothermally/magneto-thermally responsive drug carriers for combined photothermo/chemotherapy. This mini-review summarizes the latest developments and applications and addresses the future perspectives of carbon-based magnetic and fluorescent nanohybrids in the biomedical field.

Near-Infrared- and Visible-Light-Enhanced Metal-Free Catalytic Degradation of Organic Pollutants over Carbon-Dot-Based Carbocatalysts Synthesized from Biomass.

Cost-efficient nanoparticle carbocatalysts composed of fluorescent carbon dots (CDs) embedded in carbon matrix were synthesized via one-step acid-assisted hydrothermal treatment (200 °C) of glucose. These as-synthesized CD-based carbocatalysts have excellent photoluminescence (PL) properties over a broad range of wavelengths and the external visible or NIR irradiation on the carbocatalysts could produce electrons to form electron-hole (e(-)-h(+)) pairs on the surface of carbocatalysts. These restant electron-hole pairs will react with the adsorbed oxidants/reducers on the surface of the CD-based carbocatalysts to produce active radicals for reduction of 4-nitrophenol and degradation of dye molecules. Moreover, the local temperature increase over CD-based carbocatalyst under NIR irradiation can enhance the electron transfer rate between the organic molecules and CD-based carbocatalysts, thus obviously increase the catalytic activity of the CD-based carbocatalyst for the reduction of 4-nitrophenol and the degradation of dye molecules. Such a type of CD-based carbocatalysts with excellent properties and highly efficient metal-free photocatalytic activities is an ideal candidate as photocatalysts for the reduction of organic pollutants under visible light and NIR radiation.

Immobilization of Carbon Dots in Molecularly Imprinted Microgels for Optical Sensing of Glucose at Physiological pH.

Nanosized carbon dots (CDs) are emerging as superior fluorophores for biosensing and a bioimaging agent with excellent photostability, chemical inertness, and marginal cytotoxicity. This paper reports a facile one-pot strategy to immobilize the biocompatible and fluorescent CDs (∼6 nm) into the glucose-imprinted poly(N-isopropylacrylamide-acrylamide-vinylphenylboronic acid) [poly(NIPAM-AAm-VPBA)] copolymer microgels for continuous optical glucose detection. The CDs designed with surface hydroxyl/carboxyl groups can form complexes with the AAm comonomers via hydrogen bonds and, thus, can be easily immobilized into the gel network during the polymerization reaction. The resultant glucose-imprinted hybrid microgels can reversibly swell and shrink in response to the variation of surrounding glucose concentration and correspondingly quench and recover the fluorescence signals of the embedded CDs, converting biochemical signals to optical signals. The highly imprinted hybrid microgels demonstrate much higher sensitivity and selectivity for glucose detection than the nonimprinted hybrid microgels over a clinically relevant range of 0-30 mM at physiological pH and benefited from the synergistic effects of the glucose molecular contour and the geometrical constraint of the binding sites dictated by the glucose imprinting process. The highly stable immobilization of CDs in the gel networks provides the hybrid microgels with excellent optical signal reproducibility after five repeated cycles of addition and dialysis removal of glucose in the bathing medium. In addition, the hybrid microgels show no effect on the cell viability in the tested concentration range of 25-100 µg/mL. The glucose-imprinted poly(NIPAM-AAm-VPBA)-CDs hybrid microgels demonstrate a great promise for a new glucose sensor that can continuously monitor glucose level change.

Fluorescent porous carbon nanocapsules for two-photon imaging, NIR/pH dual-responsive drug carrier, and photothermal therapy.

An efficient nanomedical platform that can combine two-photon cell imaging, near infrared (NIR) light and pH dual responsive drug delivery, and photothermal treatment was successfully developed based on fluorescent porous carbon-nanocapsules (FPC-NCs, size ∼100 nm) with carbon dots (CDs) embedded in the shell. The stable, excitation wavelength (λex)-tunable and upconverted fluorescence from the CDs embedded in the porous carbon shell enable the FPC-NCs to serve as an excellent confocal and two-photon imaging contrast agent under the excitation of laser with a broad range of wavelength from ultraviolet (UV) light (405 nm) to NIR light (900 nm). The FPC-NCs demonstrate a very high loading capacity (1335 mg g(-1)) toward doxorubicin drug benefited from the hollow cavity structure, porous carbon shell, as well as the supramolecular π stacking and electrostatic interactions between the doxorubicin molecules and carbon shell. In addition, a responsive release of doxorubicin from the FPC-NCs can be activated by lowering the pH to acidic (from 7.4 to 5.0) due to the presence of pH-sensitive carboxyl groups on the FPC-NCs and amino groups on doxorubicin molecules. Furthermore, the FPC-NCs can absorb and effectively convert the NIR light to heat, thus, manifest the ability of NIR-responsive drug release and combined photothermal/chemo-therapy for high therapeutic efficacy.

Magnetic/NIR-responsive drug carrier, multicolor cell imaging, and enhanced photothermal therapy of gold capped magnetite-fluorescent carbon hybrid nanoparticles.

This paper reports a type of multifunctional hybrid nanoparticle (NP) composed of gold nanocrystals coated on and/or embedded in a magnetite-fluorescent porous carbon core-shell NP template (Fe3O4@PC-CDs-Au) for biomedical applications, including magnetic/NIR-responsive drug release, multicolor cell imaging, and enhanced photothermal therapy. The synthesis of the Fe3O4@PC-CDs-Au NPs firstly involves the preparation of core-shell template NPs with magnetite nanocrystals clustered in the cores and fluorescent carbon dots (CDs) embedded in a porous carbon shell, followed by an in situ reduction of silver ions (Ag(+)) loaded in the porous carbon shell and a subsequent replacement of Ag NPs with Au NPs through a galvanic replacement reaction using HAuCl4 as a precursor. The Fe3O4@PC-CDs-Au NPs can enter the intracellular region and light up mouse melanoma B16F10 cells in multicolor mode. The porous carbon shell, anchored with hydrophilic hydroxyl/carboxyl groups, endows the Fe3O4@PC-CDs-Au NPs with excellent stability in the aqueous phase and a high loading capacity (719 mg g(-1)) for the anti-cancer drug doxorubicin (DOX). The superparamagnetic Fe3O4@PC-CDs-Au NPs with a saturation magnetization of 23.26 emu g(-1) produce localized heat under an alternating magnetic field, which triggers the release of the loaded drug. The combined photothermal effects of the Au nanocrystals and the CDs on/in the carbon shell can not only regulate the release rate of the loaded drug, but also efficiently kill tumor cells under NIR irradiation. Benefitting from their excellent optical properties, their magnetic field and NIR light-responsive drug release capabilities and their enhanced photothermal effect, such nanostructured Fe3O4@PC-CDs-Au hybrid NPs are very promising for simultaneous imaging diagnostics and high efficacy therapy.

Magnetic/NIR-thermally responsive hybrid nanogels for optical temperature sensing, tumor cell imaging and triggered drug release.

The paper demonstrates a class of multifunctional core-shell hybrid nanogels with fluorescent and magnetic properties, which have been successfully developed for simultaneous optical temperature sensing, tumor cell imaging and magnetic/NIR-thermally responsive drug carriers. The as-synthesized hybrid nanogels were designed by coating bifunctional nanoparticles (BFNPs, fluorescent carbon dots embedded in the porous carbon shell and superparamagnetic iron oxide nanocrystals clustered in the core) with a thermo-responsive poly(N-isopropylacrylamide-co-acrylamide) [poly(NIPAM-AAm)]-based hydrogel as the shell. The BFNPs in hybrid nanogels not only demonstrate excellent photoluminescence (PL) and photostability due to the fluorescent carbon dots embedded in the porous carbon shell, but also has targeted drug accumulation potential and a magnetic-thermal conversion ability due to the superparamagnetic iron oxide nanocrystals clustered in the core. The thermo-responsive poly(NIPAM-AAm)-based gel shell can not only modify the physicochemical environment of the BFNPs core to manipulate the fluorescence intensity for sensing the variation of the environmental temperature, but also regulate the release rate of the loaded anticancer drug (curcumin) by varying the local temperature of environmental media. In addition, the carbon layer of BFNPs can adsorb and convert the NIR light to heat, leading to a promoted drug release under NIR irradiation and improving the therapeutic efficacy of drug-loaded hybrid nanogels. Furthermore, the superparamagnetic iron oxide nanocrystals in the core of BFNPs can trigger localized heating using an alternating magnetic field, leading to a phase change in the polymer gel to trigger the release of loaded drugs. Finally, the multifunctional hybrid nanogels can overcome cellular barriers to enter the intracellular region and light up the mouse melanoma B16F10 cells. The demonstrated hybrid nanogels would be an ideal system for the biomedical applications due to their excellent optical properties, magnetic properties, high drug loading capacity and responsive drug release behavior.

Multifunctional 1D magnetic and fluorescent nanoparticle chains for enhanced MRI, fluorescent cell imaging, and combined photothermal/chemotherapy.

While the assembled 1D magnetic nanoparticle (NP) chains have demonstrated synergistic magnetic effects from the individual NPs, it is essential to prepare new 1D NP chains that can combine the magnetism with other important material properties for multifunctional applications. This paper reports the fabrication and multifunctional investigation of a new type of 1D NP chains that combine the magnetic properties with fluorescent properties, photothermal conversion ability, and drug carrier function. The building block NPs are composed of magnetic Fe(3)O(4) nanocrystals clustered in the core and fluorescent carbon dots embedded in the mesoporous carbon shell with hydroxyl/carboxyl groups anchored on their surface. These NPs can assemble under the induction of external magnetic field and form stable 1D NP chains of diameter ∼ 90 nm and length ∼ 3 µm via the hydrogen bonding and π-π stacking linkage of the carbon shell. The resulted 1D hybrid NP chains not only demonstrate much higher magnetic resonance imaging (MRI) contrasting ability than the dispersed building block NPs, but also enter into intracellular region and light up the B16F10 cells under a laser excitation with strong and stable fluorescence. While the mesoporous carbon shell provides high drug loading capacity, the embedded fluorescent carbon dots convert near-infrared (NIR) light to heat, and hence kill the tumor cells efficiently and enhance the drug release rate to further improve the therapeutic efficacy under NIR irradiation. Such designed 1D magnetic-fluorescent hybrid NP chains with enhanced MRI contrast, fluorescent imaging ability, and combined chemo-/photothermal therapeutic ability have great potential for various biomedical applications.