Polymer JournalPub Date : 2024-08-08DOI: 10.1038/s41428-024-00940-7
Ryoyu Hifumi, Kotaro Ochiai, Ikuyoshi Tomita
{"title":"Synthesis of phosphine sulfide group-containing aromatic poly(ether)s with aliphatic substituents on the phosphorus atoms and low dielectric properties","authors":"Ryoyu Hifumi, Kotaro Ochiai, Ikuyoshi Tomita","doi":"10.1038/s41428-024-00940-7","DOIUrl":"10.1038/s41428-024-00940-7","url":null,"abstract":"Recently, materials with low dielectric properties have attracted particular attention because low dielectric properties are key factors in realizing next-generation communication devices with high-speed and low-loss signal transmission and processing and electronic components with high electrical breakdown voltages. In this study, phosphine sulfide (P=S) group-containing aromatic poly(ether)s with aliphatic substituents on the phosphorus atoms were developed for use as low dielectric materials, taking advantage of the low polarity of the P=S groups and the less polarizable nature of the aliphatic moieties. These polymers have moderate to high molecular weights (number-average molecular weights of 8900–35,000 and weight-average molecular weights of 31,900–178,000), good thermal stability (5% weight loss temperatures of 363–423 °C), and high glass transition temperatures (Tg = 210–219 °C). In addition, some of the polymers exhibited low dielectric constants (ε = 2.64–2.68 at 10 GHz and 2.56–2.59 at 20 GHz) and low dielectric dissipation factors (tanδ = 0.0034–0.0035 at 10 GHz and 0.0036–0.0037 at 20 GHz). These results may indicate that P=S group-containing aromatic poly(ether)s with high aliphatic contents are potentially applicable to electrically insulating materials with good dielectric properties in the GHz frequency range and could contribute to high-performance electronic devices. Phosphine sulfide (P=S) group-containing aromatic poly(ether)s with aliphatic substituents on the phosphorus atoms were developed for use as low dielectric materials, taking advantage of the low polarity of the P=S groups and the less polarizable nature of the aliphatic moieties. These polymers exhibited low dielectric constants (ε = 2.64–2.68 at 10 GHz and 2.56–2.59 at 20 GHz) and low dielectric dissipation factors (tanδ = 0.0034–0.0035 at 10 GHz and 0.0036–0.0037 at 20 GHz).","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 11","pages":"997-1004"},"PeriodicalIF":2.3,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00940-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141929623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Changes in amorphous structure and reaction acceleration during bulk polymerization of methacrylates","authors":"Yasuhito Suzuki, Ryutaro Mishima, Shodai Onozato, Jo-chi Tseng, Satoshi Hiroi, Kentaro Kobayashi, Koji Ohara, Akikazu Matsumoto","doi":"10.1038/s41428-024-00943-4","DOIUrl":"10.1038/s41428-024-00943-4","url":null,"abstract":"It has long been known that a sudden reaction acceleration (i.e., the Trommsdorff effect) occurs during bulk polymerization of methacrylates. While this effect has been qualitatively explained by an increased macroscopic viscosity and decreased termination rate, the detailed mechanism is still debated. This is because the effect occurs so suddenly that the change in macroscopic viscosity is not sufficient to explain the effect quantitatively. Less attention has been given to the change in the amorphous structure during bulk polymerization. In this study, we investigate the amorphous structure during bulk polymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA), and butyl methacrylate (BMA) via X-ray scattering. The amorphous structure changes dramatically at some point during bulk polymerization. To obtain detailed microscopic information, we applied pair distribution function (PDF) analysis during the bulk polymerization of MMA. Our results suggest that a change in the amorphous structure influences the reaction kinetics during bulk polymerization. Changes in the amorphous structure during the bulk polymerization of methacrylates were analyzed using X-ray scattering. As the polymerization progresses, the relative concentrations of monomer and polymer change. Traditionally, it has been assumed a priori that the change in the amorphous structure of the polymerization solution is smooth and continuous. In contrast, our results indicate that the amorphous structure undergoes a sudden change in the late stage of bulk polymerization. Furthermore, this sudden change in the amorphous structure coincides with the rapid reaction acceleration known as the Trommsdorff effect.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 11","pages":"1005-1015"},"PeriodicalIF":2.3,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00943-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polymer JournalPub Date : 2024-08-02DOI: 10.1038/s41428-024-00938-1
Yujie Wu, Shenghuan Wang, Yahui Liu, Yanhong Ji, Benqiao He, Mohammad Younas
{"title":"Preparation of small-pore UF membranes with high porosity by modulating the size of nano-CaCO3 in a casting solution","authors":"Yujie Wu, Shenghuan Wang, Yahui Liu, Yanhong Ji, Benqiao He, Mohammad Younas","doi":"10.1038/s41428-024-00938-1","DOIUrl":"https://doi.org/10.1038/s41428-024-00938-1","url":null,"abstract":"<p>High-performance ultrafiltration (UF) membranes show significant potential for high selectivity and permeation. In the present study, small-pore polyethersulfone (PES) UF membranes with narrow size distributions and high surface porosities were successfully prepared from PES casting solutions that contained nano-CaCO<sub>3</sub> particles of different sizes and were coagulated in a HCl solution. The nano-CaCO<sub>3</sub> particles with different sizes (22.8–6.3 nm) were produced by modulating the HCl/nano-CaCO<sub>3</sub> molar ratio in the casting solution. The size of the nano-CaCO<sub>3</sub> particles and the amount of CaCl<sub>2</sub> produced synergistically affected the viscosity of the casting solution; in addition, these factors regulated the structure and performance of the PES UF membranes. The obtained membranes exhibited small pore sizes with narrow pore size distributions and high surface porosities, as well as high water flux and bovine serum albumin (BSA) rejection. The optimized membrane had a surface pore size of 9.8 nm with an FWHM of 5.5 nm and a high surface porosity of 12.8%. The membrane also exhibited a high water permeance of 737.2 L·m<sup>−2</sup>·h<sup>−1</sup>·bar<sup>−1</sup> with a BSA rejection of 99.3%, which surpassed those reported for PES membranes in the literature. This work provided a simple and effective method for preparing high-performance UF membranes.</p>","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"44 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141881677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Coarse-grained molecular dynamics simulation of oxidative aging of polymers -effect of free radical diffusivity -","authors":"Takato Ishida, Yuya Doi, Takashi Uneyama, Yuichi Masubuchi","doi":"10.1038/s41428-024-00942-5","DOIUrl":"10.1038/s41428-024-00942-5","url":null,"abstract":"Recently, we developed an oxidative aging simulation technique that explicitly considers the transport of radicals by combining oxidation kinetics with coarse-grained molecular dynamics [1]. The current study explores the role of the free radical diffusivity of oxidative aging in polymers, with a focus on its effects on the heterogeneity of spatiotemporal structures and reaction kinetics, through coarse-grained simulations. By examining two distinct systems, including a heterosystem with a high reaction rate and a quasi-homosystem with a low reaction rate, we investigated how the diffusivity of free radicals influences the oxidative aging process. We examined three different diffusivity levels of radicals. For the slowest case, the radical diffusivity is slightly faster than that of the single polymer segment, whereas for the fastest case, the radical diffuses infinitely faster than the polymers. The aging simulations revealed that the variations in free radical diffusivity quantitatively change the reaction kinetics and spatiotemporal structures without qualitatively altering the overall aging behavior. Specifically, in a heterosystem, lower radical diffusivity slows the oxidation kinetics by increasing fluctuations in the local conversion ratios. In contrast, in a quasi-homosystem, reduced radical diffusivity slightly amplifies the heterogeneity of structures in the early aging stages; however, in a high-conversion region, the aged state becomes homogeneous regardless of the degree of radical diffusivity. We recently developed an oxidative aging simulation that combines oxidation kinetics with coarse-grained molecular dynamics. This study examines free radical diffusivity in polymer aging, focusing on its impact on spatiotemporal structures and reaction kinetics. We explored two systems with varying reaction rates and three radical diffusivity levels, observing how changes in diffusivity affect aging. Our findings indicate that while radical diffusivity alters reaction kinetics and structures, it does not fundamentally change the aging scenarios.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 11","pages":"1069-1078"},"PeriodicalIF":2.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00942-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141881791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polymer JournalPub Date : 2024-07-25DOI: 10.1038/s41428-024-00937-2
Yuma Morimitsu, Hisao Matsuno, Keiji Tanaka
{"title":"Morphologies of polymer chains spun onto solid substrates","authors":"Yuma Morimitsu, Hisao Matsuno, Keiji Tanaka","doi":"10.1038/s41428-024-00937-2","DOIUrl":"10.1038/s41428-024-00937-2","url":null,"abstract":"External fields are often present when polymers contact solids, potentially affecting chain adsorption onto a substrate. The adsorbed chains, which are difficult to relax thermally, could semipermanently influence the dynamics of the surrounding chains and bulk chains. In this study, we examined the effect of a force field induced by spin coating on the adsorption of a model polymer chain, DNA. Observations using atomic force microscopy indicated that the morphologies of adsorbed chains were affected not only by the force field but also by the incubation time (tinc) after deposition and before spinning. A longer tinc caused a greater amount of chains to transition from being present in two-dimensional random coil states to stretched states. Conversely, shorter tinc values resulted in many chains being adsorbed in a stretched state. The orientations of the stretched chains reflected the presence of competition between the effects of the centrifugal force and those of the flow rate gradient. At tinc = 0, the adsorbed chains were stretched, and they exhibited many kinks. It was anticipated that this macromolecular information could aid in controlling buried morphologies near solid surfaces and in fabricating promising materials, such as polymer composites and layered organic devices. We investigated the effect of a force field induced by spin coating on the adsorption of a model polymer, DNA. Observations using atomic force microscopy indicated that the morphologies of adsorbed chains were affected not only by the force field but also by the incubation time (tinc) after deposition and before spinning. Shorter tinc values resulted in many chains being adsorbed in a stretched state. The orientations of the stretched chains reflected the presence of competition between the effects of the centrifugal force and those of the flow rate gradient.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 11","pages":"1041-1050"},"PeriodicalIF":2.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00937-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polymer JournalPub Date : 2024-07-25DOI: 10.1038/s41428-024-00935-4
Tsuyoshi Nishikawa
{"title":"Radical polymerization of alkenyl boronates and C–B bond transformation: polymer synthesis through side-chain replacement for overcoming synthetic limitations","authors":"Tsuyoshi Nishikawa","doi":"10.1038/s41428-024-00935-4","DOIUrl":"10.1038/s41428-024-00935-4","url":null,"abstract":"Vinyl polymers are typically synthesized through the addition polymerization of corresponding vinyl compounds. However, the polymerization ability significantly depends on the substituent on the vinyl moiety, resulting in various synthetic limitations in the molecular structure of vinyl polymers. Given the increasing societal demand for enhanced properties and functions of polymer materials, innovative synthetic technologies are required for developing next-generation polymers through flexible molecular design. The author has made considerable efforts to overcome these limitations in polymer synthesis by employing alkenyl boronates as monomers for radical polymerization. The resulting polymers bear boron on the main chain, allowing the replacement of boron side chains with other elements through the cleavage of carbon–boron bonds in postpolymerization transformations. This strategy, based on “side-chain replacement,” has enabled the synthesis of various polymers that were previously inaccessible. The review highlights the author’s recent discovery of the radical (co)polymerization ability of alkenylboronic acid derivatives and C–B bond-cleaving side-chain replacement in polymer reaction. The polymerization ability is attributed to the vacant p-orbital of boron, which can stabilize chain-growth radical species. In copolymerization and controlled polymerization, the boron monomer behaves as a relatively electron-rich and conjugated monomer. The boron attached to the polymer main chain was replaceable with other elements, providing access to various polymers of which synthesis is not straightforward, such as poly(α-methyl vinyl alcohol), poly(vinyl alcohol-co-styrene), and poly(ethylene-co-acrylate).","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 10","pages":"873-886"},"PeriodicalIF":2.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00935-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Molecular dynamics simulation of the relationship between hydration and water mobilities around piperazine-immobilized polyvinyl alcohol membranes for CO2 capture","authors":"Ryo Nagumo, Ayami Shibata, Ikuo Taniguchi, Shuichi Iwata","doi":"10.1038/s41428-024-00936-3","DOIUrl":"10.1038/s41428-024-00936-3","url":null,"abstract":"The dynamic and structural properties of the water molecules in 3-(1-piperazinyl)-1,2-propanediol-containing polyvinyl alcohol membranes were analyzed by molecular dynamics simulations. The resulting curve of the coordination number with diffusivity yielded important insights into the changes in the state of the water molecules with the water content, clarifying a key factor in determining the membrane performance for CO2 separation.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 10","pages":"933-938"},"PeriodicalIF":2.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polymer JournalPub Date : 2024-07-09DOI: 10.1038/s41428-024-00934-5
Akihiro Nishiguchi
{"title":"Advances in injectable hydrogels with biological and physicochemical functions for cell delivery","authors":"Akihiro Nishiguchi","doi":"10.1038/s41428-024-00934-5","DOIUrl":"10.1038/s41428-024-00934-5","url":null,"abstract":"Injectable hydrogels that can be administered via syringes have enormous potential as cell delivery carriers for cell transplantation therapy. Owing to their beneficial properties, including biocompatibility, biodegradability, tissue adhesion, and scaffold functions, injectable hydrogels can be used to improve the delivery efficacy and survival of transplanted cells posttransplantation. Moreover, delivery via injection does not require culture or invasive surgical procedures, leading to reduced costs, processing time, and patient burden. To develop injectable hydrogels for clinical translation, hydrogels have been functionalized using various biological and physicochemical engineering approaches to induce angiogenesis, suppress immune rejection, provide viscoelasticity, and allow pore formation for cell infiltration. This focus review discusses the design of optimal injectable hydrogels for cell delivery. Moreover, this focus review summarizes the different approaches available to improve the biological and physicochemical features of hydrogels, lists their impacts on cellular functions, and highlights their therapeutic efficacy. Injectable hydrogels hold promise as cell delivery carriers for cell transplantation therapy in regenerative medicine. Injectable hydrogels possess various benefits, including biocompatibility, biodegradability, tissue adhesive properties, scaffold functions, and minimal invasiveness. To overcome the barriers in clinical translation, biological and physicochemical functionalization, which can improve delivery efficacy to the target and graft survival posttransplantation, is desirable. This review discusses the strategies to design injectable hydrogels for cell delivery and summarizes the approaches available to improve the biological and physicochemical features of hydrogels.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 10","pages":"895-903"},"PeriodicalIF":2.3,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141568635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polymer JournalPub Date : 2024-07-09DOI: 10.1038/s41428-024-00931-8
Sipradip Mahapatra, Pradip Dey, Goutam Ghosh
{"title":"Controlled synthesis of cylindrical micelles via crystallization-driven self-assembly (CDSA) and applications","authors":"Sipradip Mahapatra, Pradip Dey, Goutam Ghosh","doi":"10.1038/s41428-024-00931-8","DOIUrl":"10.1038/s41428-024-00931-8","url":null,"abstract":"Recently, crystallization-driven living self-assembly (CDSA) has attracted much attention for its ability to generate 1D cylindrical micelles and mimic chain growth polymerization using seed micelles as nuclei, as this process allows for the continuous growth of polymeric micelles with well-defined and controlled 1D nanostructures. Researchers have developed different techniques, including self-seeding and seeded growth, to form cylindrical block comicelles using the principle of living CDSA. This method is beneficial for the generation of complex nanostructures, such as pentablock comicelles or patchy comicelles, with very low polydispersity. This review sheds light on the living CDSA method, which can be used to precisely control length, shape, and branching during the self-assembly of amphiphilic block copolymers (BCPs) in the solution phase, leading to the creation of monodisperse 1D micelles with a crystalline core and solvated corona in a modular fashion. This paper also highlights the growth kinetics underlying the synthesis of cylindrical micelles via CDSA and its application in various fields, such as drug delivery, optoelectronics, and catalysis, which have been discovered recently. Lastly, the prospects of CDSA and its potential impact on materials science and nanotechnology are discussed. This review sheds light on the living CDSA method, which can be used to precisely control length, shape, and branching during the self-assembly of amphiphilic block copolymers (BCPs) in the solution phase, leading to the creation of monodisperse 1D micelles with a crystalline core and solvated corona in a modular fashion. This paper also highlights the growth kinetics underlying the synthesis of cylindrical micelles via CDSA and its application in various fields, such as drug delivery, optoelectronics, and catalysis, which have been discovered recently.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 11","pages":"949-975"},"PeriodicalIF":2.3,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00931-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141568633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polymer JournalPub Date : 2024-07-05DOI: 10.1038/s41428-024-00933-6
Junpei Miyake
{"title":"Facile and efficient synthesis of N-benzyl chitosan via a one-pot reductive amination utilizing 2-picoline borane","authors":"Junpei Miyake","doi":"10.1038/s41428-024-00933-6","DOIUrl":"10.1038/s41428-024-00933-6","url":null,"abstract":"In this paper, the use of 2-picoline borane (pic-BH3) as a reducing agent for the reductive amination of chitosan is reported for the first time. By optimizing the feed molar ratio of chitosan, benzaldehyde and pic-BH3, a high yield of isolated N-benzyl chitosan with a nearly perfect degree of substitution is successfully obtained. This material has rarely been obtained with previous methods. The newly developed synthetic method herein has many advantages, including being more facile, more efficient, and less harmful than conventional methods; thus, this method is applicable to other aldehydes or ketones, leading to wide varieties of N-modified chitosan in the future. For the first time, this paper revealed that 2-picoline borane (pic-BH3) functioned well in the reductive amination of chitosan. Therefore, N-benzyl chitosan with a nearly perfect degree of substitution was successfully obtained, which has rarely been achieved by other synthetic methods. The new method herein has many advantages, including being more facile, more efficient, and less harmful than conventional methods; thus, this method is applicable to other aldehydes or ketones, leading to a wide variety of N-modified chitosan specimens with desirable degrees of substitution in the future.","PeriodicalId":20302,"journal":{"name":"Polymer Journal","volume":"56 10","pages":"925-931"},"PeriodicalIF":2.3,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41428-024-00933-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141548144","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}