Sidelobe Modulation Scrambling Transmitter Using Fourier Rotman Lens

A means for scrambling the digital modulation content in the sidelobes of a radio transmission from a steerable antenna array is presented. The method uses a Fourier transform beam-forming network simultaneously excited by an RF information stream and orthogonally injected interference streams. The proposed system is implemented using a Fourier Rotman lens and its operational characteristics are validated for a 10 GHz QPSK transmission.

Preliminary investigation of mixed adsorbents for the removal of copper and methylene blue from aqueous solutions

With most recent studies being focused on the development of<br/>advanced chemical adsorbents, this paper investigates the possibility of<br/>using two natural low-cost materials for selective adsorption. Multiadsorbent<br/>systems containing tea waste and dolomite have been tested for<br/>their effectiveness in the removal of copper and methylene blue from<br/>aqueous solutions. The effects of contact time, solution pH and<br/>adsorption isotherms on the sorption behaviour were investigated. The<br/>Langmuir and Freundlich isotherms adequately described the adsorption of<br/>copper ions and methylene blue by both materials in different systems.<br/>The highest adsorption capacities for Cu and MB were calculated as 237.7<br/>at pH 4.5 and 150.44 mg.g‒1 at pH 7 for DO and TW+DO respectively. Tea<br/>waste (TW) and dolomite (DO) were characterized by Fourier transform<br/>infrared spectroscopy, scanning electron microscopy and Energy dispersive<br/>X-ray analysis. The removal of Cu and MB by dolomite was mainly via<br/>surface complexation while physisorption was responsible for most of the<br/>Cu and MB adsorption onto tea waste. Identifying the fundamental mechanisms and behaviour is key to the development of practical multi-adsorbent packed columns.

Identification of vegetable oil botanical speciation in refined vegetable oil blends using an innovative combination of chromatographic and spectroscopic techniques

European Regulation 1169/2011 requires producers of foods that contain refined vegetable oils to label the oil types. A novel rapid and staged methodology has been developed for the first time to identify common oil species in oil blends. The qualitative method consists of a combination of a Fourier Transform Infrared (FTIR) spectroscopy to profile the oils and fatty acid chromatographic analysis to confirm the composition of the oils when required. Calibration models and specific classification criteria were developed and all data were fused into a simple decision-making system. The single lab validation of the method demonstrated the very good performance (96% correct classification, 100% specificity, 4% false positive rate). Only a small fraction of the samples needed to be confirmed with the majority of oils identified rapidly using only the spectroscopic procedure. The results demonstrate the huge potential of the methodology for a wide range of oil authenticity work.

Milling plant and soil material in plastic tubes over-estimates carbon and under-estimates nitrogen concentrations

<p>Milling of plant and soil material in plastic tubes, such as microcentrifuge tubes, over-estimates carbon (C) and under-estimates nitrogen (N) concentrations due to the introduction of polypropylene into milled samples, as identified using Fourier-transform infra-red spectroscopy.</p><p>This study compares C and N concentrations of roots and soil milled in microcentrifuge tubes versus stainless steel containers, demonstrating that a longer milling time, greater milling intensity, smaller sample size and inclusion of abrasive sample material all increase polypropylene contamination from plastic tubes leading to overestimation of C concentrations by up to 8 % (0.08 g g(-1)).</p><p>Erroneous estimations of C and N, and other analytes, must be assumed after milling in plastic tubes and milling methods should be adapted to minimise such error.</p>

Photoionization cross section calculations for the halogen-like ions Kr + and Xe +

Photoionization cross section calculations on the halogen-like ions; Kr + and Xe + have been performed for a photon energy range from each ion threshold to 15 eV, using large-scale close-coupling calculations within the Dirac--Coulomb R -matrix approximation. The results from our theoretical work are compared with recent measurements made at the ASTRID merged-beam set-up at the University of Aarhus in Denmark and from the Fourier transform ion cyclotron resonance trap method at the SOLEIL synchrotron radiation facility in Saint-Aubin, France Bizau et al (2011 J. Phys. B: At. Mol. Opt. Phys. 44 055205) and the advanced light source M{ü}ller (2012 private communication), Aguliar et al (2012 J. Phys.: Conf. Ser . at press). For each of these complex ions our theoretical cross section results over the photon energy range investigated are seen to be in excellent agreement with experiment. Resonance energy positions and quantum defects of the prominent Rydberg resonances series identified in the spectra are compared with experiment for these complex halogen-like ions.

A comparison of gold nanoparticle surface co-functionalization approaches using Polyethylene Glycol (PEG) and the effect on stability, non-specific protein adsorption and internalization

<p>To create clinically useful gold nanoparticle (AuNP) based cancer therapeutics it is necessary to co-functionalize the AuNP surface with a range of moieties; e.g. Polyethylene Glycol (PEG), peptides and drugs. AuNPs can be functionalized by creating either a mixed monolayer by attaching all the moieties directly to the surface using thiol chemistry, or by binding groups to the surface by means of a bifunctional polyethylene glycol (PEG) linker. The linker methodology has the potential to enhance bioavailability and the amount of functional agent that can be attached. While there is a large body of published work using both surface arrangements independently, the impact of attachment methodology on stability, non-specific protein adsorption and cellular uptake is not well understood, with no published studies directly comparing the two most frequently employed approaches. This paper compares the two methodologies by synthesizing and characterizing PEG and Receptor Mediated Endocytosis (RME) peptide co-functionalized AuNPs prepared using both the mixed monolayer and linker approaches. Successful attachment of both PEG and RME peptide using the two methods was confirmed using Dynamic Light Scattering, Fourier Transform Infrared Spectroscopy and gel electrophoresis. It was observed that while the 'as synthesized' citrate capped AuNPs agglomerated under physiological salt conditions, all the mixed monolayer and PEG linker capped samples remained stable at 1M NaCl, and were stable in PBS over extended periods. While it was noted that both functionalization methods inhibited non-specific protein attachment, the mixed monolayer samples did show some changes in gel electrophoresis migration profile after incubation with fetal calf serum. PEG renders the AuNP stable in-vivo however, studies with MDA-MB-231 and MCF 10A cell lines indicated that functionalization with PEG, blocks cellular uptake. It was observed that co-functionalization with RME peptide using both the mixed monolayer and PEG linker methods greatly enhanced cellular internalization compared to PEG capped AuNPs.</p>

Caracterização e transformação de Lenhosulfonatos de Eucalyptus globulus

Os lenhosulfonatos representam um sub-produto formado durante o cozimento ao sulfito ácido, sendo queimados para a regeneração da base e recuperação de energia. No entanto, os lenhosulfonatos são também considerados uma importante matéria-prima para a produção de vários produtos de valor acrescentado. Os objectivos principais deste trabalho foram contribuir para uma melhor compreensão sobre a caracterização química e estrutural dos lenhosulfonatos do Eucalyptus globulus, assim como, para complementar a informação disponível sobre a síntese e a caracterização estrutural e térmica de materiais poliméricos obtidos a partir de compostos modelo dos produtos de oxidação dos lenhosulfonatos. O licor de cozimento ao sulfito foi analisado em termos do teor de cinzas, extractáveis, compostos voláteis, açúcares e lenhosulfonatos. O teor de cinzas e açúcares no licor de cozimento é muito elevado, tendo sido necessário purificar o mesmo (2,8-13,8 % e 3,2-9,1 %, respectivamente). A análise dos açúcares mostrou uma quantidade considerável de pentoses, sendo o açúcar predominante a xilose. Os lenhosulfonatos foram purificados, isolados e caracterizados por química molhada (titulação potenciométrica e oxidação com permanganato), análise elementar, espectroscopia de ultravioleta/visível (UV/Vis), espectroscopia de infravermelho de transformada de Fourier (FTIR), espectroscopia de ressonância magnética nuclear de protão (RMN de 1H) e carbono (RMN de 13C), espectrometria de massa de ionização por electrospray (ESI-MS), cromatografia de permeação em gel (GPC), termogavimetria (TGA) e calorimetria diferencial de varrimento (DSC). Os lenhosulfonatos são constituídos principalmente por unidades S, são parcialmente sulfonados e possuem um peso molecular relativamente baixo (Mw = 1250-2400 Da). A ruptura das ligações β-O-4 e α-O-4 da lenhina do Eucalyptus globulus após cozimento ao sulfito ácido originam olígomeros de baixo peso molecular cuja estrutura foi elucidada por RMN 1D/2D e ESI-MS. A degradação térmica dos lenhosulfonatos apresentou dois máximos de degradação a 188-190ºC e a 315-380ºC. As curvas de DSC mostraram um pico endotérmico para temperaturas inferiores a 130ºC e um pico exotérmico a 300-500ºC. Os lenhosulfonatos foram despolimerizados na presença de oxigénio molecular em meio alcalino. Os produtos de oxidação principais foram o aldeído siríngico, a vanilina, o ácido vanílico e o ácido siríngico. A adição do catalisador (sal de cobre) promoveu a oxidação dos lenhosulfonatos aumentando o rendimento dos aldeídos aromáticos (< 50%). A presença de açúcares nos lenhosulfonatos teve um efeito negativo no rendimento dos produtos de oxidação principais. Alguns compostos modelo dos produtos de oxidação dos lenhosulfonatos foram polimerizados por poliadição (catiónica e radicalar) e policondensação. Os monómeros e os polímeros foram caracterizados por espectroscopia de infravermelho de transformada de Fourier e reflectância total atenuada (FTIR-ATR), RMN em solução e no estado sólido, UV/Vis no estado sólido, GPC, difracção de raios-X (XRD), TGA e DSC. Os compostos modelo estudados foram os estirenos metoxi-substituídos (p-metoxiestireno e 3,4-dimetoxiestireno) e os ácidos hidroxi aromáticos metoxi-substituídos (ácido vanílico e ácido siríngico). O 3,4-dimetoxiestireno foi ainda copolimerizado com o éter isobutil vinílico e os seus copolímeros foram desmetilados, assim como, o poli(p-metoxiestireno) e o poli(3,4-dimetoxiestireno). A polimerização catiónica do p-metoxiestireno e 3,4-dimetoxiestireno é mais rápida e mais completa do que a polimerização radicalar produzindo polímeros com pesos moleculares elevados. O poli(p-metoxiestireno) (Mw = 235000 Da) possui um peso molecular maior do que o poli(3,4-dimetoxiestireno) (Mw = 18800 Da). A estabilidade térmica e a temperatura de transição vítrea diminuiram com a presença do segundo grupo metoxilo. A desmetilação dos homopolímeros foi bem sucedida, tendo sido corroborada por FTIR-ATR e RMN. A policondensação do ácido siríngico foi dificultada pela presença do segundo grupo metoxilo, tendo sido necessário adicionar uma maior quantidade do agente de condensação devido a factores estéricos. O poli(ácido vanílico) e poli(ácido siríngico) são insolúveis na maior parte dos solventes orgânicos, sendo parcialmente solúveis em clorofórmio, ácido triflúoracético, 1,1,2,2- tetracloroetano, dimetilsulfóxido, tetrahidrofurano, N,N’-dimetilformamida e 1,1,1,3,3,3-hexaflúor-2-propanol. A estabilidade térmica diminuiu com a presença do segundo grupo metoxilo e os dois polímeros não exibiram temperatura de transição vítrea. O poli(ácido vanílico) e poli(ácido siríngico) apresentaram uma estrutura muito cristalina (grau de cristalinidade 70% e 50%, respectivamente). O segundo grupo metoxilo aumentou o valor da absorvância, mas a forma do espectro de UV/Vis foi similar. A polimerização catiónica do éter isobutil vinílico resultou na produção de um polímero muito viscoso com peso molecular elevado (Mw = 20400 Da). A degradação térmica do polímero ocorreu em várias gamas de temperatura e foi completa (0% de resíduo a 800ºC). A copolimerização catiónica do 3,4-dimetoxiestireno com o éter isobutil vinílico foi realizada com proporções diferentes 80:20, 50:50 e 20:80. Os copolímeros apresentaram uma viscosidade elevada e um peso molecular baixo (Mw = 2000-4000 Da) que aumentou com a quantidade de éter isobutil vinílico. A degradação térmica dos copolímeros ocorreu também em várias gamas de temperatura, sendo a sua degradação completa (0,9-1,5% de resíduo a 800ºC). A desmetilação dos copolímeros não foi bem sucedida, tendo sido confirmada por FTIR-ATR e RMN.

Híbridos orgânicos-inorgânicos para aplicações de baixo custo em óptica integrada

O objectivo desta tese é a utilização de materiais híbridos orgânicos-inorgânicos, designados por di-ureiasis modificados pela adição de tetra-propóxido de zircónio (Zr(i-OPr)4) estabilizado com ácido metacrílico (CH2=C(CH3)COOH), obtidos pela via sol-gel, para aplicações em dispositivos ópticos integrados de baixo custo. A estrutura local dos di-ureiasis com diferentes concentrações de propóxido de zircónio (20 a 80 % mol) foi estudada por difracção de raios-X, espalhamento de raios X a baixos ângulos, microscopia de força atómica, ressonância magnética nuclear dos núcleos dos átomos de 29Si e 13C, espectroscopia no infravermelho por transformada de Fourier, espectroscopia de Raman por transformada de Fourier e termogravimetria. A influência dos parâmetros de síntese, concentração de tetra propóxido de zircónio e rácio tetra propóxido de zircónio: ácido metacrilico na estrutura e propriedades das amostras em monólito e filmes finos (depositados pela técnica de deposição por rotação do substrato) foram avaliadas, permitindo obter amostras transparentes, fotopolimerizáveis e estáveis termicamente até aos 100 ºC. Foram determinadas as propriedades dos guias planares em substratos de vidro borosilicato e silício oxidado (1<WSiO2< 5μm) relevantes para aplicação em óptica integrada tais como : índice de refracção (1,4774-1,5149 a 1550 nm), espessura (6-10 μm), perdas por propagação (~1,5 dB/cm) e rugosidade (~5,0 nm). Posteriormente o processo de escrita laser directa permitiu a gravação de dispositivos para óptica integrada de que são exemplos: guias de onda em canal com diâmetros modais de 2,5 μm (monomodo) e de 15-20 μm (multimodo) e contraste de valor do índice de refracção de 2x10-3; divisores de potência óptica com geometria em Y com rácios de divisão de ~50:50; filtros ópticos baseados em redes de Bragg com valores de rejeição do sinal óptico de 10 dB (monólitos) e 24 dB (filmes finos); cavidades ópticas do tipo Fabry-Perot com valores de rejeição de ~5 dB e gama espectral livre de 16,5 e 35,5 GHz. A actuação termo-óptica de uma estrutura do tipo Mach-Zhender simétrica conduziu a uma atenuação do sinal óptico de 7,5 dB.

Spectral analysis of embolic signals

Tese de dout., Engenharia Electrónica e Computação, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2005

Enzymatic grafting: A novel approach to develop multifunctional materials of interest

Today more than 99% of plastics are petroleum-based because of the availability and cost of the raw material. The durability of disposed plastics contributes to the environmental problems as waste and their persistence in the environment causes deleterious effects on the ecosystem. Environmental pollution awareness and the demand for green technology have drawn considerable attention of both academia and industry into biodegradable polymers. In this regard green chemistry technology has the potential to provide solution to this issue. Enzymatic grafting has recently been the focus of green chemistry technologies due to the growing environmental concerns, legal restrictions, and increasing availability of scientific knowledge. Over the last several years, research covering various applications of robust enzymes like laccases and lipases has been increased rapidly, particularly in the field of polymer science, to graft multi-functional materials of interest. In principle, enzyme-assisted grafting may modify/impart a variety of functionalities to the grafted composites which individual materials fail to demonstrate on their own. The modified polymers through grafting have a bright future and their development is practically boundless. In the present study series of graft composites with poly(3-hydroxybutyrate) (P(3HB) as side chain and cellulose as a backbone polymer were successfully synthesised by introducing enzymatic grafting technique where laccase and lipase were used as model catalysts [1-3]. Subsequently, the resulting composites were removed from the casting surface under ambient environment and characterised by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) in detail. Moreover, the thermo-mechanical behaviours of the grafted composites were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analyser (DMA) measurements, respectively. In addition, hydrophobic and hydrophilic characteristics of the grafted polymers were studied through drop contour analysis using water contact angle (WCA). In comparison to the individual counterparts improvement was observed in the thermo- mechanical properties of the composites to varied extent. The tensile strength, elongation at break, and Young’s modulus values of the composites reached their highest levels in comparison to the films prepared with pure P(3HB) only which was too fragile to measure any of the above said characteristics. Interestingly, untreated P(3HB) was hydrophobic in nature and after lipase treatment P(3HB) and P(3HB)-EC-based graft composite attained higher level of hydrophilicity. This is a desired characteristic that enhances the biocompatibility of the materials for proper cell adhesion and proliferation therefore suggesting potential candidates for tissue engineering/bio-medical type applications [3]. The present research will be a first step in the biopolymer modification. To date no report has been found in literature explaining the laccase/lipase assisted grafting of P(3HB) [1-3]. The newly grafted composites exhibit unique functionalities with wider range of potential applications in bio-plastics, pharmaceutical, and cosmetics industries, tissue engineering, and biosensors. [1] H.M.N. Iqbal, G. Kyazze, T. Tron and T. Keshavarz, Cellulose 21, 3613-3621 (2014). [2] H.M.N. Iqbal, G. Kyazze, T. Tron and T. Keshavarz, Carbohydrate Polymers 113, 131-137 (2014). [3] H.M.N. Iqbal, G. Kyazze, T. Tron and T. Keshavarz, Polymer Chemistry In-Press, DOI: 10.1039/C4PY0 0857J (2014).

Laccase from Aspergillus niger: A novel tool to graft multifunctional materials of interests and their characterization

In the present study, we propose a green route to prepare poly(3-hydroxybutyrate) [(P(3HB)] grafted ethyl cellulose (EC) based green composites with novel characteristics through laccase-assisted grafting. P(3HB) was used as a side chain whereas, EC as a backbone material under an ambient processing conditions. A novel laccase obtained from Aspergillus niger through its heterologous expression in Saccharomyces cerevisiae was used as a green catalyst for grafting purposes without the use of additional initiator and/or cross-linking agents. Subsequently, the resulting P(3HB)-g-EC composites were characterized using a range of analytical and imagining techniques. Fourier transform infrared spectroscopy (FT-IR) spectra showed an increase in the hydrogen-bonding type interactions between the side chains of P(3HB) and backbone material of EC. Evidently, X-ray diffraction (XRD) analysis revealed a decrease in the crystallinity of the P(3HB)-g-EC composites as compared to the pristine individual polymers. A homogeneous P(3HB) distribution was also achieved in case of the graft composite prepared in the presence of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as a mediator along with laccase as compared to the composite prepared using pure laccase alone. A substantial improvement in the thermal and mechanical characteristics was observed for grafted composites up to the different extent as compared to the pristine counterparts. The hydrophobic/hydrophilic properties of the grafted composites were better than those of the pristine counterparts.

Electrochemical biosensor based on biomimetic material for myoglobin detection

A novel reusable molecularly imprinted polymer (MIP) assembled on a polymeric layer of carboxylated poly(vinyl chloride) (PVCsingle bondCOOH) for myoglobin (Myo) detection was developed. This polymer was casted on the gold working area of a screen printed electrode (Au-SPE), creating a novel disposable device relying on plastic antibodies. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Fourier transform infrared spectroscopy (FTIR) studies confirmed the surface modification. The MIP/Au-SPE devices displayed a linear behaviour in EIS from 0.852 to 4.26 μg mL−1, of positive slope 6.50 ± 1.48 (kΩ mL μg−1). The limit of detection was 2.25 μg mL−1. Square wave voltammetric (SWV) assays were made in parallel and showed linear responses between 1.1 and 2.98 μg mL−1. A current decrease was observed against Myo concentration, producing average slopes of −0.28 ± 0.038 μA mL μg−1. MIP/Au-SPE also showed good results in terms of selectivity. The error% found for each interfering species were 7% for troponin T (TnT), 11% for bovine serum albumin (BSA) and 2% for creatine kinase MB (CKMB), respectively. Overall, the technical modification over the Au-SPE was found a suitable approach for screening Myo in biological fluids.

Heparinized nanohydroxyapatite/collagen granules for controlled release of vancomycin

The purpose of this study was to develop a bone substitute material capable of preventing or treating osteomyelitis through a sustainable release of vancomycin and simultaneously inducing bone regeneration. Porous heparinized nanohydroxyapatite (nanoHA)/collagen granules were characterized using scanning electron microscopy, micro-computed tomography and attenuated total reflectance Fourier transform infrared spectroscopy. After vancomycin adsorption onto the granules, its releasing profile was studied by UV molecular absorption spectroscopy. The heparinized granules presented a more sustainable release over time, in comparison with nonheparinized nanoHA and nanoHA/collagen granules. Vancomycin was released for 360 h and proved to be bioactive until 216 h. Staphylococcus aureus adhesion was higher on granules containing collagen, guiding the bacteria to the material with antibiotic, improving their eradication. Moreover, cytotoxicity of the released vancomycin was assessed using osteoblast cultures, and after 14 days of culture in the presence of vancomycin, cells were able to remain viable, increasing their metabolic activity and colonizing the granules, as observed by scanning electron microscopy and confocal laser scanning microscopy. These findings suggest that heparinized nanoHA/collagen granules are a promising material to improve the treatment of osteomyelitis, as they are capable of releasing vancomycin, eliminating the bacteria, and presented morphological and chemical characteristics to induce bone regeneration.

Development of composite particles for pulmonary delivery

In this work, biocompatible and biodegradable poly(D-L-lactide-co-glycolide) (PLGA) microparticles with the potential for use as a controlled release system of vaccines and other drugs to the lung were manufactured using supercritical CO2, through the Supercritical Assisted Atomization (SAA) technique. After performing a controlled variance in production parameters (temperature, pressure, CO2/solution flow ratio) PLGA microparticles were characterized and later used to encapsulate active pharmaceutical ingredients (API). Bovine serum albumin (BSA) was chosen as model protein and vaccine, while sildenafil was the chosen drug to treat pulmonary artery hypertension and their effect on the particles characteristics was evaluated. All the produced formulations were characterized in relation to their morphology (Morphologi G3 and scanning electronic microscopy (SEM)), to their physical-chemical properties (X-ray diffraction (XRD, differential scanning calorimetry (DSC), Fourier transform infrared (FTIR)) and aerodynamic performance using an in vitro aerosolization study – Andersen cascade impactor (ACI) - to obtain data such as the fine particle fraction (FPF) and the mass median aerodynamic diameter (MMAD). Furthermore, pharmacokinetic, biodegradability and biocompatibility tests were performed in order to verify the particle suitability for inhalation. The resulting particles showed aerodynamic diameters between the 3 and 5 μm, yields up to 58% and FPF percentages rounding the 30%. Taken as a whole, the produced microparticles do present the necessary requests to make them appropriate for pulmonary delivery.

Étude des propriétés de transport dans les hydrogels de curdlan

Les hydrogels de polysaccharide sont des biomatériaux utilisés comme matrices à libération contrôlée de médicaments et comme structures modèles pour l’étude de nombreux systèmes biologiques dont les biofilms bactériens et les mucus. Dans tous les cas, le transport de médicaments ou de nutriments à l’intérieur d’une matrice d’hydrogel joue un rôle de premier plan. Ainsi, l’étude des propriétés de transport dans les hydrogels s’avère un enjeu très important au niveau de plusieurs applications. Dans cet ouvrage, le curdlan, un polysaccharide neutre d’origine bactérienne et formé d’unités répétitives β-D-(1→3) glucose, est utilisé comme hydrogel modèle. Le curdlan a la propriété de former des thermogels de différentes conformations selon la température à laquelle une suspension aqueuse est incubée. La caractérisation in situ de la formation des hydrogels de curdlan thermoréversibles et thermo-irréversibles a tout d’abord été réalisée par spectroscopie infrarouge à transformée de Fourier (FT-IR) en mode réflexion totale atténuée à température variable. Les résultats ont permis d’optimiser les conditions de gélation, menant ainsi à la formation reproductible des hydrogels. Les caractérisations structurales des hydrogels hydratés, réalisées par imagerie FT-IR, par microscopie électronique à balayage en mode environnemental (eSEM) et par microscopie à force atomique (AFM), ont permis de visualiser les différentes morphologies susceptibles d’influencer la diffusion d’analytes dans les gels. Nos résultats montrent que les deux types d’hydrogels de curdlan ont des architectures distinctes à l’échelle microscopique. La combinaison de la spectroscopie de résonance magnétique nucléaire (RMN) à gradients pulsés et de l’imagerie RMN a permis d’étudier l’autodiffusion et la diffusion mutuelle sur un même système dans des conditions expérimentales similaires. Nous avons observé que la diffusion des molécules dans les gels est ralentie par rapport à celle mesurée en solution aqueuse. Les mesures d’autodiffusion, effectuées sur une série d’analytes de diverses tailles dans les deux types d’hydrogels de curdlan, montrent que le coefficient d’autodiffusion relatif décroit en fonction de la taille de l’analyte. De plus, nos résultats suggèrent que l’équivalence entre les coefficients d’autodiffusion et de diffusion mutuelle dans les hydrogels de curdlan thermo-irréversibles est principalement due au fait que l’environnement sondé par les analytes durant une expérience d’autodiffusion est représentatif de celui exploré durant une expérience de diffusion mutuelle. Dans de telles conditions, nos résultats montrent que la RMN à gradients pulsés peut s’avérer une approche très avantageuse afin de caractériser des systèmes à libération contrôlée de médicaments. D’autres expériences de diffusion mutuelle, menées sur une macromolécule de dextran, montrent un coefficient de diffusion mutuelle inférieur au coefficient d’autodiffusion sur un même gel de curdlan. L’écart mesuré entre les deux modes de transport est attribué au volume différent de l’environnement sondé durant les deux mesures. Les coefficients d’autodiffusion et de diffusion mutuelle similaires, mesurés dans les deux types de gels de curdlan pour les différents analytes étudiés, suggèrent une influence limitée de l’architecture microscopique de ces gels sur leurs propriétés de transport. Il est conclu que les interactions affectant la diffusion des analytes étudiés dans les hydrogels de curdlan se situent à l’échelle moléculaire.