Elektrohemijska sinteza i karakterizacija nanokompozita polivinil-alkohola I nanočestica srebra

In this doctoral dissertation, a composite hydrogel consisting of poly(vinyl alcohol), graphene and silver nanoparticles, (Ag/PVA/Gr), was prepared by the immobilization of silver nanoparticles (AgNPs) in poly(vinyl alcohol)/graphene (PVA/Gr) hydrogel matrix in two steps. The first step was cross linking of the PVA/Gr colloid solution by the freezing/thawing method, while in the second step, in situ electrochemical method was used to incorporate AgNPs inside the PVA/Gr hydrogel matrix. The main aim of this study was to produce the nanocomposite graphene-based biomaterial with incorporated silver nanoparticles using in situ electrochemical method, aimed for soft tissue implants, wound dressings and drug delivery. The electrochemical route of nanoparticles synthesis is especially attractive for biomedical applications due to high purity and precise size control of metal particles and the absence of chemical cross linking agents and undesired products. Repeated cyclic freezing/thawing method was used to prepare poly(vinyl alcohol) PVA and poly(vinyl alcohol)/graphene (PVA/Gr) hydrogel discs, followed by electrochemical reduction method of different concentrations of Ag+ ions (0.25, 0.5,1.0 and 3.9 mM AgNO3 swelling solution) inside the hydrogel polymer matrices at a constant voltage that enables the silver particle size control, in a specially designed electrochemical cell. Silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) nanocomposites were characterized by UV–visible spectroscopy. The absorption spectra at about 405-420 nm proved existence of AgNPs in both Ag/PVA and Ag/PVA/Gr nanocomposites. Cyclic voltammetry revealed some oxidation and reduction peaks suggesting the presence of AgNPs between polymer chains. Raman spectroscopy analysis confirmed the graphene structure in its pure form, X-ray diffraction was used to reveal the additional interactions established between the PVA molecules and graphene sheets and the AgNPs situated between the polymer chains in viii the Ag/PVA/Gr nanocomposite. The calculated interspacing (d-spacing) value for (002) lattice plane of the PVA and Ag/PVA hydrogels was 0.457 nm, while the obtained value changed slightly with the introduction of graphene sheets (0.449 nm for Ag/PVA/Gr nanocomposite). Fourier transform infrared spectroscopy (FTIR) results for both Ag/PVA and Ag/PVA/Gr nanocomposites suggested the interaction between AgNPs and hydroxyl groups of the PVA molecules through decoupling between the corresponding vibrations. Thermogravimetric analysis and corresponding differential thermal analysis were done to investigate the role of graphene sheets in the thermal stability of thus prepared nanocomposite samples, and the results showed higher stability of Ag/PVA/Gr than Ag/PVA nanocomposites. Morphology of the prepared PVA, PVA/Gr, Ag/PVA and Ag/PVA/Gr samples were examined by field-emission scanning electron microscopy (FE-SEM) technique and the microphotographs showed sphere-shaped AgNPs at nanoscale levels which were around 36 nm in the Ag/PVA and around 17 nm in the Ag/PVA/Gr nanocomposites...Ova doktorska disertacija se bavi sintezom hidrogelova polivinil-alkohola, grafena i nanočestica srebra (Ag/PVA/Gr), imobilizacijom nanočestica srebra u matrici hidrogela polivinil-alkohol/grafen (PVA/Gr) u dva koraka. Prvi korak je umrežavanje koloidnog rastvora PVA/Gr metodom zamrzavanja i odmrzavanja, dok je u drugom koraku primenjena in situ elektrohemijska metoda za inkorporaciju nanočestica srebra u matrici PVA/Gr hidrogela. Glavni cilj ovog istraživanja je bila priprema nanokompozitnih biomaterijala na bazi grafena sa inkorporisanim nanočesticama srebra, sa mogućom primenom u vidu implantata mekog tkiva, obloga za rane i nosača za lekove. Elektrohemijski postupak sinteze nanočestica je posebno atraktivan za primene u biomedicini, zbog velike čistoće i mogućnosti precizne kontrole dobijenih nanočestica, kao i zbog odsustva hemijskih agenasa i neželjenih produkata. Metoda umrežavanja cikličnim zamrzavanjem i odmrzavanjem je korišćena u cilju dobijanja polivinil-alkohol (PVA) i polivinil-alkohol/grafen (PVA/Gr) hidrogelova u obliku diskova, a zatim je izvršena elektrohemijska redukcija Ag+ jona različitih koncentracija (0,25, 0,5,1,0 i 3,9 mM AgNO3 swelling solution) u polimernoj matrici hidrogela, na konstantnom naponu, što omogućava kontrolu dimenzija čestica srebra, u posebno dizajniranoj elektrohemijskoj ćeliji. Srebro/polivinil-alkohol (Ag/PVA) i srebro/polivinil-alkohol/grafen (Ag/PVA/Gr) nanokompoziti su karakterisani UV-vidljivom spektroskopijom. Apsorpcioni spektri sa maksimumom na oko 405-420 nm su dokazali prisustvo nanočestica srebra u Ag/PVA i Ag/PVA/Gr nanokompozitima. Cikličnom voltametrijom su pokazani pikovi oksidacije i redukcije koji ukazuju na prisustvo nanočestica srebra u polimernoj matrici. Ramanova spektroskopija je potvrdila čistu grafensku strukturu, dok je rendgenska difrakcija korišćena za ispitivanje interakcija između PVA molekula sa grafenom i nanočesticama srebra, smeštenim između polimernih lanaca Ag/PVA/Gr nanokompozita. Izračunato rastojanje između krisalnih xi ravni za (002) ravan u PVA i Ag/PVA hidrogelovima je iznosilo 0.457 nm, dok se ova vrednost promenila nakon inkorporacije grafena (0.449 nm za Ag/PVA/Gr nanokompozit). Rezultati analize infracrvenom spektroskopijom sa Furijeovom transformacijom (FTIR) za Ag/PVA i Ag/PVA/Gr nanokompozite su ukazali na interakcije između nanočestica srebra i hidroksilnih grupa na PVA molekulima, na osnovu razdvajanja odgovarajućih vibracionih traka. Termogravimetrijska analiza i diferencijalna termogravimetrijska analiza su korišćene radi ispitivanja termičke stabilnosti dobijenih uzoraka hidrogelova, a rezultati su pokazali povećanu stabilnost Ag/PVA/Gr u odnosu na Ag/PVA nanokompozite. Morfologija dobijenih uzoraka PVA, PVA/Gr, Ag/PVA i Ag/PVA/Gr je ispitana tehnikom skenirajuće elektronske mikroskopije (FE-SEM), a na mikrografijama su uočene čestice srebra sfernog oblika i nanometarskih dimenzija oko 36 nm u Ag/PVA i oko 17 nm u Ag/PVA/Gr nanokompozitu..

The Use of Poly(vinyl alcohol)-based Hydrogels in Biomedical Applications

Polymers have found increasing favor in biomedical applications due to the greater control that researchers can exert over their properties. Researchers have focused on the development of therapies using biologically compatible polymers due to their ability to limit potentially harmful interactions with the body. This research has led to advances in tissue engineering, controlled and targeted drug delivery, and other biomedical fields, with the goal of improving both the effectiveness and accessibility of health care. Poly(vinyl alcohol) (PVA) hydrogels possess several chemical properties that make them well suited for biomedical applications. These include inertness and stability, biocompatibility, and pH-responsiveness. As a result, PVA based materials have been studied for potential applications in areas of biomedicine such as targeted drug delivery, tissue engineering, and wound healing. This thesis examines the properties of PVA and seeks to understand how the chemical and physical structure affects their properties. It then examines how these properties enhance their utility in potential biomedical applications. Finally, it reviews the research into development of PVA based materials for three different biomedical applications.Chemical Engineerin

High performance of alkaline anion-exchange membranes based on chitosan/poly (vinyl) alcohol doped with graphene oxide for the electrooxidation of primary alcohols

Mixed matrix membranes (MMM) based on chitosan (CS) and poly (vinyl) alcohol (PVA) with a 50:50 w/w ratio doped with graphene oxide (GO) are prepared by solution casting and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), water uptake, alcohol permeability, ion exchange capacity (IEC) and OH−conductivity measurements. The SEM analysis revealed a dense MMM where the GO nanosheets were well dispersed over the entire polymer matrix. The incorporation of GO increased considerably the thermal stability of the CS:PVA membrane. The GO-based MMM exhibited a low conductivity of 0.19 mS·cm−1 in part because the GO sheets did not change the crystallinity of the CS:PVA matrix. The reinforced structure created by the hydrogen bonds between the GO filler and the CS:PVA matrix resulted to be a good physical barrier for alcohol permeability, achieving a coefficient of diffusion of 3.38 × 10−7 and 2.43 × 10−7 cm2·s−1 after 60 and 120 min, respectively, thus avoiding additional alcohol crossover. Finally, the electrochemical performance of the GO-based MMM in the electrooxidation of propargyl alcohol was investigated in a Polymer Electrolyte Membrane Electrochemical Reactor (PEMER) under alkaline conditions, through the polarization curve and the electrolysis reactions, showing a performance comparable to anion-exchange commercial membranes.This work has been funded by the Spanish MINECO through projects CTQ2012-31229 and the “Ramón y Cajal” grant RYC2011-08550 (C.C.C.), at the University of Cantabria, and the PhD fellowship BES-2011-045147 and EEBB-14-09094 mobility grant for L.G.C’s research stay at the University of Cantabria

PVA-Based Nanofibers Containing Chitosan Modified with Graphene Oxide and Carbon Quantum Dot-Doped TiO2 Enhance Wound Healing in a Rat Model

Electrospun nanofibrous constructs based on nanoparticles and biopolymers have recently been used in tissue engineering because of their similarity to the extracellular matrix in nature. In this study, electrospun chitosan-carbon quantum dot-titanium dioxide-graphene oxide (CS-CQD-TiO2-GO) nanofibrous mats were synthesized for use as wound dressings by the electrospinning method. To increase the biodegradation rate and water resistance, the fabricated nanofibrous mats were cross-linked. SEM images showed a uniform and coherent structure of CS-CQD-TiO2-GO nanocomposites and CS-CQD-TiO2-GO electrospun nanofibers mats. FTIR analysis, XRD pattern, SEM mapping, and EDS spectrum demonstrate the accuracy of the synthesis as well as the elemental and chemical structure of the nanofibrous mat. The water contact angle indicated that the nanofibrous mat had a hydrophilic property, which is essential for controlling wound exudates. The tensile strength and elongation tests showed that the nanofibrous mat has suitable mechanical properties for wound dressing, including significant flexibility and strength. Interestingly, antimicrobial testing illustrated that the fabricated nanofibrous mat had antibacterial activity against Gram-negative and Gram-positive bacteria. Appropriate cell viability and cytocompatibility of treated mouse fibroblast NIH3T3 cells with the nanofibrous mat were determined using an MTT assay. The animal study results confirmed the proper potential of the nanofibrous mat in wound dressing applications

Poly(2-hydroxyethyl acrylate) hydrogels reinforced with graphene oxide: Remarkable improvement of water diffusion and mechanical properties

[EN] A series of hybrid hydrogels of poly(2-hydroxyethyl acrylate), PHEA, and graphene oxide, GAO, with GAO content up to 2 wt % has been prepared by in situ polymerization. Because PHEA has been used as biomaterial in various applications, has a side chain with the hydroxyl functional group and its mechanical properties are poor, it is a good candidate for reinforcement with GAO. Fourier transform (infrared) spectroscopy, atomic force microscopy, differential scanning calorimetry, the thermal, mechanical, and water sorption properties of neat PHEA and PHEA/GAO composites have been studied in order to elucidate the dispersion and interaction between both components. An increase in the water diffusion coefficient and dramatic changes in its mechanical proper- ties are the most remarkable results. Thus, at a nanofiller load of 2 wt %, the novel materials present an increased diffusion coeffi- cient higher than 380% and the elastic modulus is enhanced by more than 650% in dry state and by more than 100% in swollen state, both compared to neat PHEA. These results have been attributed to the excellent interaction between the matrix, PHEA, and the reinforcement, GAO, and could open the door to new applications in the field of biomaterials with higher structural requisites.This work was supported by Project GV/2016/067 of the Generalitat Valenciana. AFM, and the stress-strain assay was conducted by the authors in the Microscopy Service of the Universitat Politecnica de Valencia, whose advice is greatly appreciated. The authors acknowledge M. Monleon-Pradas for his helpful discussions.Sánchez-Correa, FV.; Vidaurre Agut, CM.; Serrano Aroca, Á.; Campillo Fernández, AJ. (2018). Poly(2-hydroxyethyl acrylate) hydrogels reinforced with graphene oxide: Remarkable improvement of water diffusion and mechanical properties. Journal of Applied Polymer Science. 135(15). https://doi.org/10.1002/app.46158S1351

A Novel Electrochemical Biosensor Based On Fe3O4 Nanoparticles-Polyvinyl Alcohol Composite for Sensitive Detection of Glucose

In this research, a new electrochemical biosensor was constructed for the glucose detection. Iron oxide nanoparticles (Fe3O4) were synthesized through co-precipitation method. Polyvinyl alcohol-Fe3O4 nanocomposite was prepared by dispersing synthesized nanoparticles in the polyvinyl alcohol (PVA) solution. Glucose oxidase (GOx) was immobilized on the PVA-Fe3O4 nanocomposite via physical adsorption. The mixture of PVA, Fe3O4 nanoparticles and GOx was drop cast on a tin (Sn) electrode surface (GOx/PVA-Fe3O4/Sn). The Fe3O4 nanoparticles were characterized by X-ray diffraction (XRD). Also, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FE-SEM) techniques were utilized to evaluate the PVA-Fe3O4 and GOx/PVA-Fe3O4 nanocomposites. The electrochemical performance of the modified biosensor was investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Presence of Fe3O4nanoparticles in the PVA matrix enhanced the electron transfer between enzyme and electrode surface and the immobilized GOx showed excellent catalytic characteristic toward glucose. The GOx/PVA-Fe3O4/Sn bioelectrode could measure glucose in the range from 5 × 10−3 to 30 mM with a sensitivity of 9.36 μA mM−1 and exhibited a lower detection limit of 8 μM at a signal-to-noise ratio of 3. The value of Michaelis-Menten constant (KM) was calculated as 1.42 mM. The modified biosensor also has good anti-interfering ability during the glucose detection, fast response (10 s), good reproducibility and satisfactory stability. Finally, the results demonstrated that the GOx/PVA-Fe3O4/Sn bioelectrode is promising in biosensor construction

Preparation of Poly(Vinyl) Alcohol/Chitosan Hybrid Membranes Doped with Graphene Nanosheets

The development of ion exchange membrane technology has allowed its introduction in many industrial sectors, such as electrodialysis and electrolysis. Nowadays, membranes are the crucial element in electrochemical energy conversion and storage devices. This work is aimed at examining new eco-friendly membranes materials to improve structural, mechanical, electrical and barrier properties. A simple and ecological synthesis of alkaline anion exchange membranes based on a mixed matrix membrane of chitosan (CS) and poly(vinyl) alcohol (PVA) – CS:PVA polymeric matrix – was developed by using a 50:50 wt. % ratio. The CS:PVA matrix was modified with variable loadings of graphene pristine sheets (GPH) ranging between 0,5 and 4.0 wt. %. The physico-chemical characterization of each of the membranes prepared was carried out in order to examine the topology, structure, thermal stability, surface chemistry, and water content (WC), as well as the ionic conductivity by using electrochemical impedance spectroscopy (EIS). Results revealed that the incorporation of graphene (GPH) into the CS:PVA polymeric matrix leads to the improvement of the thermal stability, and the ionic conductivity of the pristine polymeric matrix. The loading of 1.0 wt. % of GPH into CS:PVA was optimal in terms of specific ionic conductivity that is related to surface chemistry of the membrane, WC, and slight roughness of the membrane topology. The presence of GPH only provided a slight loss of crystallinity of the memebrane compared to the unmodified CS:PVA membrane, which also resulted in the reduction of water content with moderately GPH loadings. With regard to the ionic conductivity, an almost twofold increase was obtained compared to the pure CS:PVA for an optimal loading of 1.0 wt. %.The authors thank the Ministerio de Economía y Competitividad for its financial support (CTQ2013-48280-C3-3-R). Also, Jesús Iniesta gives thanks to Relaciones Internacionales for the PPI grant suppoted by the University of Alicante, Spain

Incorporating graphene oxide into biomimetic nano-microfibrous cellulose scaffolds for enhanced breast cancer cell behavior

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03078-w) contains supplementary material, which is available to authorized users.The impact of graphene oxide (GO) on normal cells has been widely investigated. However, much less is known on its effect on cancer cells. Herein, GO nanosheets were incorporated into electrospun cellulose acetate (CA) microfibers. The GO-incorporated CA (GO/CA) microfibers were combined with bacterial cellulose (BC) nanofibers via in situ biosynthesis to obtain the nano-microfibrous scaffolds. The GO/CA-BC scaffolds were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The GO/CA-BC scaffolds were used for breast cancer cell culture to evaluate the effect of GO on cancer cell behavior. Fluorescence images revealed large multicellular clusters on the surface of GO/CA-BC scaffolds. Compared to the bare CA-BC scaffold, the GO/CA-BC scaffolds not only showed enhanced mechanical properties but also improved cell proliferation. It is expected that the GO/CA-BC scaffolds would provide a suitable microenvironment for the culture of cancer cells which is necessary for drug screening and cell biology study.This work was supported by National Natural Science Foundation of China (Grant nos. 51572187, 51973058, 31660264, 31870963), the Key Research and Development Program of Jiangxi Province (No. 20192ACB80008), and the Youth Science Foundation of Jiangxi Province (No. 20181BAB216010), and Key Project of Natural Science Foundation of Jiangxi Province (No. 20161ACB20018).info:eu-repo/semantics/publishedVersio

Functional Nanocomposite Coatings for Use in Food Packaging

Plastics are a class of materials known for their cost and property advantages, increasing significantly in their usage worldwide. Unfortunately, these benefits come with an increasingly concerning environmental impact. A combination of inadequate disposal options and combinations of materials have led to environmental disasters that will impact generations. One of the worst areas for plastic waste is food packaging. Plastic as a material generally excels at durability and longevity, but as food packaging, it outlives its intended purpose by several orders of magnitude. This leads to plastic food packaging materials sitting in landfill or leading to the environment for hundreds of years. Because of this, there is a strong motivation to develop food packaging materials that are biodegradable, yet still maintain the properties that make plastic better than other classes of materials. Food packaging has many forms, but in general, the most important aspects are cost, mechanical, and oxygen and water barrier properties. To achieve an end-product that excels in these aspects, combinations of materials called composites may be developed. Nanocomposites are a subcategory of composites composed of a matrix material and nanomaterials, separate phases that interact with one another in a number of ways. This research is focused on increasing the mechanical and barrier properties of polyvinyl alcohol, the most commercially-viable biodegradable polymer. The nanomaterials used were graphene oxide (GO) and cellulose nanofibers (CNF) for mechanical and barrier reinforcement. Five sample compositions were produced: a control PVA, CNF, 1 wt% GO, 5 wt% GO, and 10 wt% GO, which were drawn down on uncoated paper and cast by themselves. Testing of these nanocomposites included oxygen transmission, mechanical, and thermal property analysis, and various solvent-interaction testing including absorption of water and oil, Cobb testing, and water vapor permeation. With the addition of CNF and GO to PVA, there was an observed increase in barrier properties through a reduction of hydrophilicity and water absorption, and oxygen permeability