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1.
Recently, great attention has been focused on using epoxy polymers in different fields such as aerospace, automotive, biotechnology, and electronics, owing to their superior properties. In this study, the classical molecular dynamics (MD) was used to simulate the cross linking of diglycidyl ether of bisphenol-A (DGEBA) with diethylenetriamine (DETA) curing agent, and to study the behavior of resulted epoxy polymer with different conversion rates. The constant-strain (static) approach was then applied to calculate the mechanical properties (Bulk, shear and Young’s moduli, elastic stiffness constants, and Poisson’s ratio) of the uncured and cross-linked systems. Estimated material properties were found to be in good agreement with experimental observations. Moreover, the dependency of mechanical properties on the cross linking density was investigated and revealed improvements in the mechanical properties with increasing the cross linking density. The radial distribution function (RDF) was also used to study the evolution of local structures of the simulated systems as a function of cross linking density.  相似文献   

2.
We present a study on the effects of cross-linking on the adhesive properties of bio-inspired 3,4-dihydroxyphenylalanine (DOPA). DOPA has a unique catechol moiety found in adhesive proteins in marine organisms, such as mussels and polychaete, which results in strong adhesion in aquatic conditions. Incorporation of this functional group in synthetic polymers provides the basis for pressure-sensitive adhesives for use in a broad range of environments. A series of cross-linked DOPA-containing polymers were prepared by adding divinyl cross-linking agent ethylene glycol dimethacrylate (EGDMA) to monomer mixtures of dopamine methacrylamide (DMA) and 2-methoxyethyl acrylate (MEA). Samples were prepared using a solvent-free microwave-assisted polymerization reaction and compared to a similar series of cross-linked MEA materials. Cross-linking with EGDMA tunes the viscoelastic properties of the adhesive material and has the advantage of not reacting with the catechol group that is responsible for the excellent adhesive performance of this material. Adhesion strength was measured by uniaxial indentation tests, which indicated that 0.001 mol % of EGDMA-cross-linked copolymer showed the highest work of adhesion in dry conditions, but non-cross-linked DMA was the highest in wet conditions. The results suggest that there is an optimal cross-linking degree that displays the highest adhesion by balancing viscous and elastic behaviors of the polymer but this appears to depend on the conditions. This concentration of cross-linker is well below the theoretical percolation threshold, and we propose that subtle changes in polymer viscoelastic properties can result in significant improvements in adhesion of DOPA-based materials. The properties of lightly cross-linked poly(DMA-co-MEA) were investigated by measurement of the frequency dependence of the storage modulus (G') and loss modulus (G'). The frequency-dependence of G' and magnitude of G' showed gradual decreases with the fraction of EGDMA. Loosely cross-linked DMA copolymers, containing 0% and 0.001 mol % of EGDMA-cross-linked copolymers, displayed rheological behavior appropriate for pressure-sensitive adhesives characterized by a higher G' at high frequencies and lower G' at low frequencies. Our results indicate that dimethacrylate cross-linking of DMA copolymers can be used to enhance the adhesive properties of this unique material.  相似文献   

3.
Cohn D  Sosnik A  Garty S 《Biomacromolecules》2005,6(3):1168-1175
The objective of this study was to explore the use of reverse thermo-responsive (RTG) polymers for generating implants at their site of performance, following minimally invasive surgical procedures. Aiming at combining syringability and enhanced mechanical properties, a new family of injectable RTG-displaying polymers that exhibit improved mechanical properties was created, following two different strategies: (1) to synthesize high-molecular-weight polymers by covalenty joining poly(ethylene glycol) and poly(propylene glycol) chains using phosgene as the coupling molecule and (2) to cross-link poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblocks after end-capping them with triethoxysilane or methacrylate reactive groups. While the methacrylates cross-linked rapidly, the triethoxysilane groups enabled the system to cross-link gradually over time. The chain-extended PEO/PPO copolymers had molecular weights in the 39 000-54 000 interval and exhibited improved mechanical properties. Reverse thermo-responsive systems displaying gradually increasing mechanical properties were generated by cross-linking triethoxysilane-capped (EO)(99)-(PO)(67)-(EO)(99) (F127) triblocks. Over time, the ethoxysilane groups hydrolyzed and created silanol moieties that subsequently condensated. With the aim of further improving their mechanical behavior, F127 triblocks were reacted with methacryloyl chloride and the resulting dimethacrylate was subsequently cross-linked in an aqueous solution at 37 degrees C. The effect of the concentration of the F127 dimethacrylate on the mechanical properties and the porous structure of the cross-linked matrixes produced was assessed. Rheometric studies revealed that the cross-linked hydrogels attained remarkable mechanical properties and allowed the engineering of robust macroscopic constructs, such as large tubular structures. The microporosity of the matrixes produced was studied by scanning electron microscopy. Monolayered conduits as well as structures comprising two and three layers were engineered in vitro, and their compliance and burst strength were determined.  相似文献   

4.
In this study it was investigated whether hydrogels could be used for an accommodating lens. The requirements of such a hydrogels are a low modulus, high refractive index, transparency, and strength. Since conventional hydrogels do not possess this combination of properties, a novel preparation method and new polymers are introduced. As starting materials poly(1-hydroxy-1,3-propanediyl), poly(ethylene-co-vinyl alcohol), poly(vinyl alcohol), and poly(allyl alcohol) were used. The first three were cross-linked with a number of diisocyanate compounds. Network formation was performed at low concentrations in a good solvent. Mixing of the polymer solution and cross-linker appeared to be crucial for transparency. Poly(1-hydroxy-1,3-propanediyl), cross-linked with a slow reacting diisocyanate block, shows the most promising properties with respect to refractive index, transparency, tensile strength, and modulus. Poly(allyl alcohol) hydrogel was made by compression molding. The hydrogel was transparent and had a high refractive index and low modulus. It was concluded that hydrogels could be used as accommodating lens material.  相似文献   

5.
Glycated polymers have already been widely employed for cell transfection studies, as cells possess specific lectins. However, up to now, these glycated polymers have barely been investigated for their cell adhesive properties, save macrophages. In this work, we use polyelectrolyte multilayer films made of poly(L-lysine) and poly(L-glutamic) acid as polymeric substrates to investigate the role of sugar molecules (e.g., mannose and lactose) on the adhesion of primary cells as compared to that of a tumor cell line. The glycated polymeric films were compared to ungrafted and chemically cross-linked films, which are known to present opposite adhesive properties. A differential adhesion could be evidenced on mannose grafted films: primary chondrocytes adhere and proliferate well on these films, whereas chondrosarcoma cells do not grow well. Although present, the effect of lactose on cell adhesion was much less important. This adhesion, mediated by glycated polymers, appears to be specific. These results show that it is possible to use glycated polyelectrolytes not only as nonviral vectors but also as cell adhesive substrates.  相似文献   

6.
Various oxidized mono/di/tri/poly saccharides were studied as potential hemoglobin (Hb) cross-linkers in order to produce oxygen carriers with high oxygen affinities (low P(50)'s) and high molecular weights (therefore lower macromolecular diffusivities compared to tetrameric Hb). Such physical properties were desired to produce polymerized hemoglobins (PolyHbs) with oxygen release profiles similar to that of human blood, as was demonstrated in work by Winslow (1). In this present study, bovine hemoglobin was cross-linked with a variety of oxidized (ring-opened) saccharides, which resulted in cross-linked Hb species ranging in size from 64 to 6400 kDa (depending on the particular oxidized saccharide used in the reaction) and P(50)'s ranging from 6 to 15 mmHg. A parallel synthetic approach was used to synthesize these carbohydrate-hemoglobin conjugates, and asymmetric flow field-flow fractionation (AFFF) coupled with multi-angle static light scattering (MASLS) was used to measure the absolute molecular weight distribution of these PolyHb dispersions. Cross-linking reactions were conducted at two pHs (6 and 8), with larger cross-linked Hb species produced at pH 8 (where hydrolysis was most likely to occur between glycosidic bonds linking adjacent saccharide rings) rather than at pH 6. The largest molecular weight species formed from these reactions consisted of Hb cross-linked with ring-opened lactose, maltose, methylglucopyranoside, sucrose, trehalose, and 15 kDa and 71 kDa dextran at high pH (pH 8). The most promising Hb cross-linker was methylglucopyranoside, which resulted in very large cross-linked Hb species, with low P(50)'s and lower methemoglobin (metHb) levels compared to the other Hb cross-linking reagents.  相似文献   

7.
Previous studies afforded on peptides and polypeptides containing repetitive sequences of elastin have largely demonstrated that their molecular and supramolecular properties are fully representative of those of tropoelastin, the soluble, linear precursor of elastin itself. In the attempt to synthesize cross-linked elastin-mimetic polypeptides, the repeating sequence VGGVG (V: valine; G: glycine), typical of elastin, was modified to incorporate lysine residues, yielding the polymer poly(KGGVG) (K: lysine). This imparts primary amine functionality susceptible to cross-linking reaction with appropriate bifunctional cross-linking reagents. We report herein the chemical synthesis and cross-linking of poly(KGGVG) with glutaraldehyde (GTA) and with disuccinimidyl glutarate (DSG). In both cases, the characterization of the polymers, both linear and cross-linked, has been carried out by CD spectroscopy and transmission electron microscopy measurements. The obtained results, although not conclusive, demonstrate that poly(KGGVG), both linear and cross-linked, may be considered very similar to tropoelastin and mature elastin, as concerns its molecular and supramolecular properties.  相似文献   

8.
In this work, living/controlled radical polymerization (LRP) is compared with conventional free radical polymerization in the creation of highly and weakly cross-linked imprinted poly(methacrylic acid-co-ethylene glycol dimethacrylate) networks. It elucidates, for the first time, the effect of LRP on the chain level and begins to explain why the efficiency of the imprinting process is improved using LRP. Imprinted polymers produced via LRP exhibited significantly higher template affinity and capacity compared with polymers prepared using conventional methods. The use of LRP in the creation of highly cross-linked imprinted polymers resulted in a fourfold increase in binding capacity without a decrease in affinity; whereas weakly cross-linked gels demonstrated a nearly threefold increase in binding capacity at equivalent affinity when LRP was used. In addition, by adjusting the double bond conversion, we can choose to increase either the capacity or the affinity in highly cross-linked imprinted polymers, thus allowing the creation of imprinted polymers with tailorable binding parameters. Using free radical polymerization in the creation of polymer chains, as the template-monomer ratio increased, the average molecular weight of the polymer chains decreased despite a slight increase in the double bond conversion. Thus, the polymer chains formed were shorter but greater in number. Using LRP neutralized the effect of the template. The addition of chain transfer agent resulted in slow, uniform, simultaneous chain growth, resulting in the formation of longer more monodisperse chains. Reaction analysis revealed that propagation time was extended threefold in the formation of highly cross-linked polymers when LRP techniques were used. This delayed the transition to the diffusion-controlled stage of the reaction, which in turn led to the observed enhanced binding properties, decreased polydispersity in the chains, and a more homogeneous macromolecular architecture.  相似文献   

9.
Dithienogermole‐co‐thieno[3,4‐c]pyrroledione (DTG‐TPD) polymers incorporating chemically cross‐linkable sidechains are reported and their properties compared to a parent polymer with simple octyl sidechains. Two cross‐linking groups and mechanisms are investigated, UV‐promoted radical cross‐linking of an alkyl bromide cross‐linker and acid‐promoted cationic cross‐linking of an oxetane cross‐linker. It is found that random copolymers with a 20% incorporation of the cross‐linker demonstrate a higher performance in bulk heterojunction solar cells than the parent polymer, while 100% cross‐linker incorporation results in deterioration in device efficiency. The use of 1,8‐diiodooctane (DIO) as a processing additive improves as‐cast solar cell performance, but is found to have a significant deleterious impact on solar cell efficiency after UV exposure. The instability to UV can be overcome by the use of an alternative additive, 1‐chloronapthalene, which also promotes high device efficiency. Cross‐linking of the polymer is investigated in the presence and absence of fullerene highlighting significant differences in behavior. Intractable films cannot be obtained by radical cross‐linking in the presence of fullerene, whereas cationic cross‐linking is successful.  相似文献   

10.
In recent years, solution‐processed conjugated polymers have been extensively used as anode interfacial layer (AIL) materials in organic solar cells (OSCs) due to their excellent film‐forming property and low‐temperature processing advantages. In this review, the authors focus on the recent advances in conjugated polymers as AIL materials in OSCs. Several of the main classes of solution‐processable conjugated polymers, including poly(3,4‐ethylenedioxythiophene):(styrenesulfonate), polyaniline, polythiophene, conjugated polyelectrolytes, sulfonated poly(diphenylamine), and crosslinked polymers as AIL materials are discussed in depth, and the mechanisms of these AIL materials in enhancing OSC performances are also elucidated. The structure–property relationships of various conjugated polymer AIL materials are analyzed, and some important design rules for such materials toward high efficiencies and stable OSCs are presented. In addition, some chemical and physical approaches to optimize the photoelectronic and physic properties of conjugated polymer AIL materials, which improve their performance in modifying OSCs, are also highlighted. Considering the significance of tandem OSCs, the relevant applications of conjugated polymer AIL materials in constructing interconnection layers for tandem OSCs are also mentioned. Finally, a brief summary is presented and some perspectives to help researchers understand the current challenges and opportunities in this area are proposed.  相似文献   

11.
In this work, we investigated the mechanism involved in the photoinitiated cross-linking of the polyester poly(propylene fumarate) (PPF) using the initiator bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (BAPO). It was hypothesized that BAPO has the ability to cross-link PPF into solid polymer networks, without the use of a cross-linking monomer, because two pairs of radicals, both involving a fast adding phosphinoyl radical, were formed upon UV irradiation of BAPO. Spectroscopic investigation first confirmed the addition of BAPO derived radicals to the PPF olefin. Investigations of fumarate conversion and bulk network properties were then undertaken, using the BAPO initiator and a monoacylphosphine oxide (MAPO) initiator which contains a single photolabile bond. Results show that a single BAPO phosphinoyl radical was primarily responsible for the formation of a highly cross-linked PPF network and the additional radical pair which may be formed does not dramatically alter fumarate conversion or bulk network properties. From these results, the network structure of BAPO initiated, photo-cross-linked PPF may be deduced. Finally, this study demonstrates a method for inferring cross-linked network structures by contrasting properties of bulk materials formed from similar cross-linking initiators.  相似文献   

12.
Liu Z  Wang L  Bao C  Li X  Cao L  Dai K  Zhu L 《Biomacromolecules》2011,12(6):2389-2395
A new series of degradable and water-swellable cross-linked PEG phosphoester polymers (CPPs) based on a facile cross-linked reaction between diphosphoesters of polyethylene glycol (P-PEG-P) and diglycidyl ether of polyethylene glycol (E-PEG-E) has been prepared and characterized. The molecular weights and ratios of the prepolymers played an important role for the properties of CPPs polymers, such as mechanical property, swelling, and degradation rates. In the curing process, the glycidyl ether was consumed by both hydroxyl of the phosphoester (P-OH) and hydroxyl generated from the opened glycidyl ethers (C-OH) with the presence of acid, which generated degradable phosphate esters as cross-linked points and ether bonds as the short branches, respectively. Drug entrapment and release test and biological cytotoxicity studies in vitro suggested that the polymers and generated hydrogels have great potential applications in drug delivery system and biological materials.  相似文献   

13.
Advances in development of nanocomposite gels that provide localized delivery of pharmaceuticals for treatment of chronic wounds are being highly pursued. To design such materials, the use of natural polymers is recommendable due to their intrinsic biocompatibility and biodegradability. Moreover, the use of biocatalytic approaches for composite assembling is preferred compared to harsh chemical cross‐linking reagents. In this study, HRP catalyzed cross‐linking of hydrogels from aqueous solution of thiolated chitosan to in situ incorporated sonochemically synthesized epigallocatechin gallate nanospheres (EGCG NSs). The potential of the generated NSs for chronic wound treatment was evaluated by assessing their antibacterial properties and inhibitory effect on myeloperoxidase and collagenase—major enzymes of inflamed chronic wounds. The EGCG NSs displayed better antibacterial and antienzymatic properties compared to the EGCG in solution. Also, the NSs were incorporated into hydrogels without affecting their integrity and were released intact in a sustained manner (during 6 days). The cytotoxicity assay confirmed the compatibility of the hybrid material with human fibroblasts that suffered less than 10% decrease in viability during 24 h. Release of functional phenolic NSs and good compatibility of the composite hydrogel with cells suggested its potential application in chronic wound management.  相似文献   

14.
Poly(L-lysine)/hyaluronan (PLL/HA) films were chemically cross-linked with a water soluble carbodiimide (EDC) in combination with a N-hydroxysulfo-succinimide (NHS) to induce amide formation. Fourier transform infrared spectroscopy confirms the conversion of carboxylate and ammonium groups into amide bonds. Quartz crystal microbalance-dissipation reveals that the cross linking reaction is accompanied by a change in the viscoelastic properties of the films leading to more rigid films. After the cross-linking reaction, both positively and negatively ending films exhibit a negative zeta potential. It is shown by fluorescence recovery after photobleaching measured by confocal laser scanning microscopy that cross-linking dramatically reduces the diffusion of the PLL chains in the network. Cross linking also renders the films highly resistant to hyaluronidase, an enzyme that naturally degrades hyaluronan. Finally, the adhesion of chondrosarcoma cells on the films terminating either with PLL or HA is also investigated. Whereas the non cross-linked films are highly resistant to cell adhesion, the cells adhere and spread well on the cross-linked films.  相似文献   

15.
Reale A  Malanga M  Zardo G  Strom R  Scovassi AI  Farina B  Caiafa P 《Biochemistry》2000,39(34):10413-10418
It is well-known that H1-H1 interactions are very important for the induction of 30 nm chromatin fiber and that, among all posttranslational modifications, poly(ADP-ribosyl)ation is one of those capable of modifying chromatin structure, mainly through H1 histone. As this protein can undergo both covalent and noncovalent modifications by poly(ADP-ribosyl)ation, our aim was to investigate whether and how ADP-ribose polymers, by themselves, are able to affect the formation of H1-H1 oligomers, which are normally present in a condensed chromatin structure. The results obtained in our in vitro experimental system indicate that ADP-ribose polymers are involved in chromatin decondensation. This conclusion was reached as the result of two different observations: (a) H1 histone molecules can be hosted in clusters on ADP-ribose polymers, as shown by their ability to be chemically cross-linked, and (b) H1 histone has a higher affinity for ADP-ribose polymers than for DNA; ADP-ribose polymers compete, in fact, with DNA for H1 histone binding.  相似文献   

16.
Mixing of aqueous solutions of poly(acrylic acid) and (hydroxypropyl)cellulose results in formation of hydrogen-bonded interpolymer complexes, which precipitate and do not allow preparation of homogeneous polymeric films by casting. In the present work the effect of pH on the complexation between poly(acrylic acid) and (hydroxypropyl)cellulose in solutions and miscibility of these polymers in solid state has been studied. The pH-induced complexation-miscibility-immiscibility transitions in the polymer mixtures have been observed. The optimal conditions for preparation of homogeneous polymeric films based on blends of these polymers have been found, and the possibility of radiation cross-linking of these materials has been demonstrated. Although the gamma-radiation treatment of solid polymeric blends was found to be inefficient, successful cross-linking was achieved by addition of N,N'-methylenebis(acrylamide). The mucoadhesive potential of both soluble and cross-linked films toward porcine buccal mucosa is evaluated. Soluble films adhered to mucosal tissues undergo dissolution within 30-110 min depending on the polymer ratio in the blend. Cross-linked films are retained on the mucosal surface for 10-40 min and then detach.  相似文献   

17.
Polymer nanoparticles (NPs) are promising systems for the delivery of protein drugs, as they enhance circulation half‐life, reduce degradation, and increase selectivity of the encapsulated agent. Among the different methods for the preparation of protein‐loaded NPs, ionotropic gelation—which exploits cross‐linking between charged groups in the polymer and counterions in the protein solution—has been extensively investigated for chitosan NPs. The present study aims at exploring the possibility to apply the method to prepare BSA‐loaded polyurethane NPs. A poly(ε‐caprolactone)/poly(ethyleneglicol)‐based polyurethane bearing tert‐butyloxycarbonyl‐protected amino groups was synthesized by a two‐step synthesis procedure. Amino functionalities were exposed under acidic conditions, as confirmed by ninhydrin assay, and then exploited to obtain ionic cross‐linking with sodium tripolyphosphate counterions. The effect of polymer and sodium tripolyphosphate concentration on particles size and BSA encapsulation has been investigated, showing that the PUR concentration plays a major role. Small particles, at 300 nm, with high BSA loading (90%) have been obtained. Sustained BSA release and low burst effect (20%) have been observed, indicating good interaction between the protein and the polymer matrix. The study highlights the possibility of introducing alternative polymers to improve loading and release of proteins from NPs obtained through the ionotropic gelation method.  相似文献   

18.
The catalase (E.C. 1.11.1.6) enzyme was covalently immobilized on textile carrier fabrics made of poly(ethylene terephthalate) or polyamide 6.6 by a new photochemical process in the presence of cross‐linking agents. The enzyme and the bifunctional organic compound (diallylphthalate or cyclohexane‐1,4‐dimethanoldivinylether) were emulated in water using a non‐ionic surfactant. After wetting, the textile carrier materials were irradiated with a monochromatic excimer UV lamp (222 nm) in an inert atmosphere. Depending on the support and the cross‐linking agent used 20 – 30 mg enzyme per gram carrier could be fixed durably, which can be quantitatively analyzed by atomic absorption spectroscopy due to the iron content of the catalase. The efficiency of the immobilization products was investigated by measuring the enzymatic decomposition of hydrogen peroxide compared to the free enzyme. The relative activity of the catalase after the immobilization reached 10–20 % of the free, non‐fixed catalase. Even after 20 applications, the immobilized enzyme showed a distinct activity and the integral activity trough the period of all applications was higher by a factor of around 3.5 than the activity of the free catalase, which could be used only once in technical processes. Summing up the results, fabrics of a high protein load and a distinct activity can be produced with low preparative and economic expense by irradiating the materials by means of excimer UV lamps in the presence of cross‐linking agents.  相似文献   

19.
Amino acid-based core cross-linked star (CCS) polymers (poly(L-lysine)(arm)poly(L-cystine)(core)) with peripheral allyl functionalities were synthesized by sequential ring-opening polymerization (ROP) of amino acid N-carboxyanhydrides (NCAs) via the arm-first approach, using N-(trimethylsilyl)allylamine as the initiator. Subsequent functionalization with a poly(ethylene glycol) (PEG)-folic acid conjugate via thiol-ene click chemistry afforded poly(PEG-b-L-lysine)(arm)poly(L-cystine)(core) stars with outer PEG coronas decorated with folic acid targeting moieties. Similarly, a control was prepared without folic acid, using just PEG. A fluorophore was used to track both star polymers incubated with breast cancer cells (MDA-MB-231) in vitro. Confocal microscopy and flow cytometry revealed that the stars could be internalized into the cells, and higher cell internalization was observed when folic acid moieties were present. Cytotoxicity studies indicate that both stars are nontoxic to MDA-MB-231 cells at concentrations of up to 50 μg/mL. These results make this amino acid-based star polymer an attractive candidate in targeted drug delivery applications including chemotherapy.  相似文献   

20.
Soluble linear (non-cross-linked) poly(monoacryloxyethyl phosphate) (PMAEP) and poly(2-(methacryloyloxy)ethyl phosphate) (PMOEP) were successfully synthesized through reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization and by keeping the molecular weight below 20 K. Above this molecular weight, insoluble (cross-linked) polymers were observed, postulated to be due to residual diene (cross-linkable) monomers formed during purification of the monomers, MOEP and MAEP. Block copolymers consisting of PMAEP or PMOEP and poly(2-(acetoacetoxy)ethyl methacrylate) (PAAEMA) were successfully prepared and were immobilized on aminated slides. Simulated body fluid studies revealed that calcium phosphate (CaP) minerals formed on both the soluble polymers and the cross-linked gels were very similar. Both the PMAEP polymers and the PMOEP gel showed a CaP layer most probably brushite or monetite based on the Ca/P ratios. A secondary CaP mineral growth with a typical hydroxyapatite (HAP) globular morphology was found on the PMOEP gel. The soluble PMOEP film formed carbonated HAP according to Fourier transform infrared (FTIR) spectroscopy. Block copolymers attached to aminated slides showed only patchy mineralization, possibly due to the ionic interaction of negatively charged phosphate groups and protonated amines.  相似文献   

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