Use of low-field NMR for the characterization of gels and biological tissues

Abrami, Michaela; Chiarappa, Gianluca; Farra, Rossella; Grassi, Gabriele; Marizza, Paolo

doi:10.5599/admet.6.1.430

Cited by 22 publications

(45 citation statements)

References 30 publications

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“…The NMR signal attenuation after the pulsed gradient is dependent on the diffusion coefficient of the molecule [10]. It can be exploited to study the dynamics of polymers in solution or inside porous materials [11,12]. Although interesting for polymer characterization, these two techniques will not be further addressed in this review, since we decided to deal with the basic equipment for LF-TD-NMR in the characterization of polymeric items.…”

Section: Introductionmentioning

confidence: 99%

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

2019

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Highly controlled polymers and nanostructures are increasingly translated from the lab to the industry. Together with the industrialization of complex systems from renewable sources, a paradigm change in the processing of plastics and rubbers is underway, requiring a new generation of analytical tools. Here, we present the recent developments in time domain NMR (TD-NMR), starting with an introduction of the methods. Several examples illustrate the new take on traditional issues like the measurement of crosslink density in vulcanized rubber or the monitoring of crystallization kinetics, as well as the unique information that can be extracted from multiphase, nanophase and composite materials. Generally, TD-NMR is capable of determining structural parameters that are in agreement with other techniques and with the final macroscopic properties of industrial interest, as well as reveal details on the local homogeneity that are difficult to obtain otherwise. Considering its moderate technical and space requirements of performing, TD-NMR is a good candidate for assisting product and process development in several applications throughout the rubber, plastics, composites and adhesives industry.

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Section: Introductionmentioning

confidence: 99%

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

2019

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“…The second component, with signals in the range of 10–100 ms refers to immobilized water, while the signals with the longest relaxation time (100–1000 ms) are considered to be due to free water. 58…”

Section: Results and Discussionmentioning

confidence: 99%

Colloidal Behavior of Cellulose Nanocrystals Grafted with Poly(2-alkyl-2-oxazoline)s

Gauche

Felisberti

2019

ACS Omega

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Polymer grafting onto cellulose nanocrystals (CNCs) has been used as a tool to improve CNC dispersion in nonpolar solvents or polymeric matrixes. The grafting of flexible polymer chains onto rigid particle surfaces leads to significant modifications in colloidal behavior. Here, poly(2-alkyl-2-oxazoline)s of well-defined molar mass and narrow molar mass distribution were synthesized by cationic ring-opening polymerization and grafted onto CNC surfaces, where the coupling reaction was favored when partially hydrolyzed polymers were used (reaching 64% reaction yield). The particles grafted with polymer chains could be redispersed in water after freeze-drying, producing stable dispersions, and they were not cell-toxic up to 10 wt % aqueous dispersion. Colloidal stability, nanostructure organization, and rheological behavior of grafted CNC and CNC-grafted CNC mixtures were evaluated. The rheological behavior of grafted nanoparticles, meanwhile, showed new features when compared to original CNC dispersions. Aqueous CNC dispersions showed a liquid crystal nematic organization and rheological behavior characteristic of true gel (at 5 wt %) prior to drying. On the other hand, nanoparticle dispersions behaved as weak gels upon the addition of 10 wt % of CNC- g -(PEtOx 95 - s -Ei 5 ) under the same conditions. Dispersions of CNC- g -P(PEtOx- s -Ei) particles obtained by redispersion of freeze-dried particles behaved as a fluid, without the presence of the nematic organization. Through oscillatory rheology and time-domain NMR results, it can be concluded that polymer–water interactions are dominant over CNC–water interactions, being responsible for CNC nematic phase disruption. By introducing polymer chains, the introduction of isotropic character modifies water organization, changing the flow behavior of CNC-grafted with poly(oxazoline)s.

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“…The irradiation time and polymer concentration are expected to affect both the hydrogen relaxation time ( T 2m ) and the polymeric network mesh size (ξ). Indeed, it is well known [25,26,27] that the average value of the inverse relaxation time (1/ T 2 ) m (see Equation (6)) referring to hydrogens belonging to water molecules trapped in the polymeric network is related to the polymer volume fraction, φ, and ξ, by the following equation: (1T2)m=1T2H2O+2Msans-serifξC0C1 1−0.58φφwhere T 2H2O is the relaxation time of the free water hydrogens (≈ 3008 ms at 25 °C, 20 MHz [28]), i.e., the relaxation time of water hydrogens in the absence of polymer network. scriptM is a parameter, called relaxivity, representing the ratio between the thickness and the relaxation time of the water layer close to polymeric chains (bound water layer) while C 0 and C 1 are two constants that, for a cubical network, are equal to 1 and 3π, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The inverse linear correlation between T 2m and φ is theoretically correct as the φ increase implies the increase of the solid surface, represented by the polymeric chains’ surface, in contact with the water molecules. In turn, the solid surface is responsible for faster hydrogen relaxation [27]. On the contrary, the absence of a correlation between ξ and φ and between T 2m and ξ simply states that, whatever φ, the mesh size is almost constant.…”

Section: Resultsmentioning

confidence: 99%

“…In this frame, the experimental outcomes descending from the combined use of rheology and LF-NMR proved to be a very useful strategy for the determination of the network characteristics. Indeed, the interpretation of these outcomes by means of proper theoretical models [24,25,26,27] allowed the evaluation of ξ and φ. In turn, ξ and φ knowledge allowed an estimation of the drug diffusion coefficient inside the polymeric network ( D ) to be formed according to the model proposed by Lusting and Peppas assuming Y = 1 [30].…”

Section: Discussionmentioning

confidence: 99%

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Theoretical Importance of PVP-Alginate Hydrogels Structure on Drug Release Kinetics

Abrami

Marizza

Zecchin

et al. 2019

Gels

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Background: The new concepts of personalized and precision medicine require the design of more and more refined delivery systems. In this frame, hydrogels can play a very important role as they represent the best surrogate of soft living tissues for what concerns rheological properties. Thus, this paper focusses on a global theoretical approach able to describe how hydrogel polymeric networks can affect the release kinetics of drugs characterized by different sizes. The attention is focused on a case study dealing with an interpenetrated hydrogel made up by alginate and poly(N-vinyl-2-pyrrolidone). Methods: Information about polymeric network characteristics (mesh size distribution and polymer volume fraction) is deduced from the theoretical interpretation of the rheological and the low field Nuclear Magnetic Resonance (NMR) characterization of hydrogels. This information is then, embodied in the mass balance equation whose resolution provides the release kinetics. Results: Our simulations indicate the influence of network characteristics on release kinetics. In addition, the reliability of the proposed approach is supported by the comparison of the model outcome with experimental release data. Conclusions: This study underlines the necessity of a global theoretical approach in order to design reliable delivery systems based on hydrogels.

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Use of low-field NMR for the characterization of gels and biological tissues

Abstract: The focus of this paper is on the theoretical interpretation of Low Field Nuclear Magnetic Resonance (LF-NMR) data regarding hydrogels architecture and on the most interesting applications of LF-NMR

Cited by 22 publications

References 30 publications

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

Colloidal Behavior of Cellulose Nanocrystals Grafted with Poly(2-alkyl-2-oxazoline)s

Theoretical Importance of PVP-Alginate Hydrogels Structure on Drug Release Kinetics

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