Unraveling the control of reversibility for actuators based on cellulose nanofibers.

In this work, we have prepared cellulose-based actuators taking advantage of the pH-sensitive solubility of chitosan (CH) and the mechanical strength of CNFs. Bilayer films were prepared by vacuum filtration inspired by plant structures that exhibit reversible deformation under pH changes. The presence of CH in one of the layers led to asymmetric swelling at low pH, thanks to the electrostatic repulsion between charged amino groups of CH, and the subsequent twisting with the CH layer on the outside. Reversibility was achieved by substituting pristine CNFs with carboxymethylated CNFs (CMCNFs), that are charged at high pH and thus competed with the effects of amino groups. Swelling and mechanical properties of layers under pH changes were studied by gravimetry and dynamic mechanical analysis (DMA) to quantify the contribution of chitosan and the modified CNFs on the reversibility control. This work evidenced the key role of surface charge and layer stiffness to achieve reversibility. Bending was triggered by the different water uptake of each layer, and shape recovery was achieved when the shrunk layer shower higher rigidity than the swollen layer.

Monitoring of water sorption and swelling of potato starch-glycerol extruded blend by magnetic resonance imaging and multivariate curve resolution.

Magnetic resonance microimaging (MRµI) is an outstanding technique for studying water transfers in millimetric bio-based materials in a non-destructive and non-invasive manner. However, depending on the composition of the material, monitoring and quantification of these transfers can be very complex, and hence reliable image processing and analysis tools are necessary. In this study, a combination of MRµI and multivariate curve resolution-alternating least squares (MCR-ALS) is proposed to monitor the water ingress into a potato starch extruded blend containing 20% glycerol that was shown to have interesting properties for biomedical, textile, and food applications. In this work, the main purpose of MCR is to provide spectral signatures and distribution maps of the components involved in the water uptake process that occurs over time with various kinetics. This approach allowed the description of the system evolution at a global (image) and a local (pixel) level, hence, permitted the resolution of two waterfronts, at two different times into the blend that could not be resolved by any other mathematical processing method usually used in magnetic resonance imaging (MRI). The results were supplemented by scanning electron microscopy (SEM) observations in order to interpret these two waterfronts in a biological and physico-chemical point of view.

Melt processing of paramylon using a water:ionic liquid mixture as plasticizer.

Paramylon is a linear ß-1,3-glucan produced by the microalgae Euglena Gracilis. Due to its native crystalline structure, involving hexagonally packed triple helices, paramylon is neither water soluble nor thermoplastic. While such properties are generally obtained by chemical modification of paramylon, the present work demonstrates that using ionic liquid/water mixtures as solvents or plasticizers may be an alternative: A mixture of water with cholinium glycinate (40:60) allowed: i) obtaining paramylon solutions at 80 °C, that form reversible ionogels upon cooling at 20 °C, when used as a solvent, and ii) the thermomechanical processing of paramylon below 100 °C by extrusion and hot-press into transparent films, when used as a plasticizer. The thermoplastic paramylon obtained consists of an amorphous matrix, self-reinforced by oriented triple helices packed as nanofibers. This results in a storage modulus ranging from 300 to 450 MPa at 25 °C, depending on the plasticizer content, and in a tensile strain at break of 27 %. For storage times larger than 1 month, a recrystallization of paramylon is observed, with an unidentified crystalline structure different from the native one. Recrystallized samples can be reprocessed into amorphous films by hot pressing.

Release kinetics of [lidocainium][ibuprofenate] as Active Pharmaceutical Ingredient-Ionic Liquid from a plasticized zein matrix in simulated digestion.

An in vitro approach is proposed to study the release of an Active Pharmaceutical Ingredient-Ionic Liquid (API-IL) from a natural biopolymer matrix based on zein, a maize storage protein. Zein can be processed in the molten state with 20 w% [Lidocainium][Ibuprofenate] added as API-IL also acting as plasticizer and potentially co-plasticized by glycerol. The thermal stability of the matrix is checked, as well as the in vivo biological activity of the API-IL confirming anesthetic and anti-inflammatory activities. Model tablets are thermomolded at 130 °C (∅20 mm, 0.2 mm thick) and submitted to simulated digestion based on the INFOGEST static protocol of gastrointestinal food digestion at 37 °C (2 h under gastric conditions followed by 2 h under intestinal ones). The release of the API-IL is evaluated by HPLC-UV to dissociate lidocainium, that shows a progressive release (35 % after 2 h and 60 % after 4 h digestion), from ibuprofenate, that is mainly released under intestinal conditions due to low solubility in acidic conditions. The monitoring of the tablets reveals release mechanisms based on diffusion without noticeable erosion of the matrix. These results demonstrate the interest of this thermoplastic material to provide a relevant drug delivery system.

Chitin Pickering Emulsion for Oil Inclusion in Composite Films.

A film containing a stable and well-dispersed hydrophobic phase in a surfactant-free bio-based hydrophilic matrix is proposed. In this study, an aqueous suspension of rod-like chitin nanocrystals (ChiNCs), mixed with paraffin oil, form an oil-in-water Pickering emulsion with a droplet diameter of 3 µm. These emulsions mixed with a 5 wt% starch solution formed homogeneous composite films by solvent casting. Various amounts of emulsion were incorporated, leading to self-supported films with a volume of oil as high as 45 vol%, with less than 1% of ChiNCs. This model inclusion system leads to droplets homogeneously dispersed throughout the composite films, as revealed by microscopy (SEM and CLSM) with mechanical properties controlled by the matrix. Finally, the droplets were easily released from the matrix by enzymatic hydrolysis. This easy-to-implement transparent film proved to be a good candidate when it is desirable to disperse a poor water-soluble component in a hydrophilic edible matrix.

A drug delivery system obtained by hot-melt processing of zein plasticized by a pharmaceutically active ionic liquid.

Zein-based filaments containing 20 weight% [Lidocainium][Ibuprofenate] used as a doubly Active Pharmaceutical Ingredient-Ionic Liquid (API-IL) were obtained by extrusion at 130 °C. The plasticizing effect of the active ingredient on the zein amorphous matrix was assessed by differential scanning calorimetry, with a decrease in the glass transition temperature (Tg) from 77 °C, for the raw zein, to 53 °C. After storage under standard conditions (relative humidity 59%, 20 °C) the extrudates were rigid, with a high storage modulus (E') of about 3 GPa at ambient temperature. They had a main mechanical relaxation (Tα) beginning at 55 °C, leading to their flowing at temperatures above 130 °C, as determined by dynamic mechanical analysis, with E' below 1 MPa and tan δ above 1. Their structure was evaluated by wide angle X-ray scattering and NMR analysis was used to evaluate the API-IL stability after thermomechanical processing. Release experiments performed under simulated physiological conditions on filaments evidenced a release of 85% after 7 days immersion. These results demonstrate the advantage of using an API-IL as plasticizer of a resorbable biopolymer. The resulting material can be shaped by a continuous thermomechanical process and used as a drug delivery system.

Influence of ionic plasticizers on the processing and viscosity of starch melts.

Maize starch was plasticized by glycerol, choline chloride ([Chol][Cl]) and ionic liquids (Choline acetate ([Chol][Ace]), 1-Ethyl-3-methylimidazolium Chloride ([EMIM][Cl]) and 1-Ethyl-3-methylimidazolium acetate ([EMIM][Ace]). Melt rheology at 120 °C was assessed with a twin-screw micro-compounder used for processing small quantities (8-10 g), and with a capillary rheometer with pre-shearing (Rheoplast). Qualitative agreement was found between shear viscosities obtained by both rheometry devices, showing the interest of the micro-compounder for screening of plasticizers' influence. The lower shear viscosity values were obtained in presence of [EMIM][Ace] whereas [Chol][Cl] led to the largest ones. Rather than processing induced macromolecular degradation, the glass transition temperature depressing effect of the plasticizers was found to better explain viscosity differences. This underlines the strong influence of the nature of the plasticizers on starch melt rheology. Finally, results from extensional viscosity shows the specific influence of [EMIM][Ace], suggesting that this plasticizer could be particularly relevant for thermoplastic starch processing.

Cellulose nanocrystals-starch nanocomposites produced by extrusion: Structure and behavior in physiological conditions.

Different amounts of cellulose nanocrystals (CNCs) were added to glycerol-plasticized thermoplastic starch (TPS) to obtain bio-based nanocomposites. First, nanocomposites are prepared by extrusion and their structure is studied at different scales using WAXS (Wide Angle X-ray Scattering) and solid-state NMR (Nuclear Magnetic Resonance) for local/crystalline organization, AF4 (Asymmetrical Flow Field-Flow Fractionation) for molecular weight and chain length, and SEM (Scanning Electron Microscopy) for the morphology at a larger scale. Then, relevant mechanical properties and behavior in physiological conditions (swelling, enzymatic degradation) are characterized. The results show that the incorporation of cellulose nanocrystals up to 2.5 wt% causes a mechanical reinforcement as determined by DMTA (Dynamic Mechanical Thermal Analysis) and reduces the swelling and the enzymatic degradation of the materials compared to reference TPS. This could be linked to the formation of starch-cellulose hydrogen and hydroxyl bonds. Conversely, above 5 wt% CNC content nanocrystals seem to aggregate which in turn worsens the behavior in physiological conditions.

Macromolecular characteristics and fine structure of amylomaltase-treated cassava starch.

This work investigates the macromolecular structure of native and amylomaltase (AM) treated cassava starch at various reaction times. AM-treated starches showed lower amylose content compared to their parental starch. Long chain proportions (DP 25-80) increased with reaction time up to 4 h and then slightly decreased at 24 h. Macromolecular and fine structure of AM-treated starches for 5 min (AM5min) and 4 h (AM4 h) were characterized more deeply by using HPSEC-MALLS and H1 NMR combined with ß-amylolysis and MALDI-TOF-MS. Molar mass and dispersity of both AM-treated starches were lowered. Nevertheless, AM5min had longer external chains whereas AM4 h exhibited a larger and denser macromolecular core. A cyclo-structure with DP 8 was found in both AM-treated starches; however, AM4 h contained cyclo-structures with various sizes (DP 8-32). Finally, by controlling reaction time and substrate constituents, which are important factors affecting the AM action modes, AM-treated starch with various structural features can be obtained.

Design, fabrication, and implantation of tube-shaped devices for the treatment of salivary duct diseases.

Introduction: Starch-based materials were designed using a special extrusion die in order to obtain a tube-shaped device for application to salivary duct treatment in the field of endoscopy, i.e., sialendoscopy . Methods: Extrusion process was used to produce starch tubes. Mechanical properties of the dry tube before implantation were determined using an axial compression test. A finite element study was carried out to simulate the behavior of the hydrated tube under external axial pressure. Hydrolysis of these devices in a simulated salivary solution was studied, as well as its glycerol kinetics release. An animal short-term implantation model for salivary ducts was proposed as a feasibility study for starch tube-shaped devices. Results: A continuous production of regular and size-controlled tubes was obtained. The very small diameter obtained, less than 2 mm, corresponds to the requirement of being insertable in a human salivary duct using sialendoscopy guidewire. Finite element analysis showed that the starch tube can still support an external pressure higher than 0.2 MPa without irreversible damage. After 4 days of implantation, the host response is encouraging and the inflammatory response for this type of procedure remains normal. Conclusion: These devices were adapted to sialendoscopic guidewires and able to be implanted in the salivary ducts of pigs. If a longer lasting tube is required, the crystallinity of the starch material should be improved.

Multi-scale characterization of thermoplastic starch structure using Second Harmonic Generation imaging and NMR.

Starch granules can be extruded to obtain a thermoplastic material. Thermoplastic starch (TPS) usually requires a significant break down of the starch granular organization to form a continuous polysaccharide matrix. In this work, we extrude potato starch with and without a plasticizer and store samples at high humidity to generate recrystallization. A multi-scale investigation of the microstructure is performed by combining different techniques: WAXS and solid-state NMR to describe macromolecule organization and Second Harmonic Generation (SHG) imaging to provide spatial information. Finally, the ability of the material to swell and remain sound in water is assessed. Glycerol-plasticized samples swell the least despite many granules with native-like structure embedded in the starch matrix. Glycerol limits the fragmentation and melting of the granules and crystallites during extrusion but also reduces the proportion of starch molecules in constrained conformations, enabling the formation of a polymer network that can sustain the penetration of water.

In-Situ Quantitative and Multiscale Structural Study of Starch-Based Biomaterials Immersed in Water.

The behavior upon immersion in water of two types of starchy materials of biomedical relevance, amorphous potato starch and glycerol-plasticized potato starch, is analyzed in depth. Synchrotron X-ray scattering, specifically wide-angle X-ray scattering (WAXS), and magnetic resonance microimaging (MRµI) are used as very precise and nondestructive quantitative methods to monitor water transfers and structure changes in the samples, with refined spatial and kinetics results. The ingress of water in the cylinder-shaped samples can be inferred from both techniques, and from this, a diffusion mechanism is deduced for each sample type. Qualitatively, scattering and imaging give comparable results: plasticized samples are shown to behave close to a Fickian diffusion case, amorphous samples close to a case II. WAXS results also provide an in-depth knowledge of the crystalline structures associated to each step of the water ingress, and these are in turn correlated to water diffusion. To refine these observations, a recrystallized starch sample is also analyzed via WAXS. This study gives better insight into the structure of a material with a huge biomedical potential (as implants, for example), and for such applications, the behavior upon immersion in water is particularly relevant.

Macromolecular structure and film properties of enzymatically-engineered high molar mass dextrans.

New α(1→2) or α(1→3) branched dextrans with high molar masses and controlled architecture were synthesized using a dextransucrase and branching sucrases. Their molecular structure, solubility, conformation, film-forming ability, as well as their thermal and mechanical properties were determined. These new dextrans present structures with low densities from 9,500 to 14,000gm-3 in H2O/DMSO medium, their molar mass, size and dispersity increase with increasing branching degree (weight-average molar mass up to 109gmol-1 and radius of gyration around 500nm). Dextrans exhibit a glass transition between 40.5 and 63.2°C for water content varying from 12.2 to 14.1%. The effect of branching is mainly observed on the ability of dextran to crystallize. They have a good film-forming ability with a storage modulus which varies from 2 to 4GPa within a relative humidity range of 10-50%.

Choline chloride vs choline ionic liquids for starch thermoplasticization.

Native starch containing 12% water was melt processed in presence of 23% of various plasticizers at 120°C, either by simple compression molding or by extrusion using a laboratory scale microcompounder. Glycerol, a typical starch plasticizer, was used as a reference and compared to three choline salts: raw choline chloride (which is a solid in dry state with a melting point above 300°C), and two ionic liquids synthesized from this precursor (choline acetate and choline lactate, liquids below 100°C). These ionic plasticizers were shown to allow a more efficient melting of native starch in both processes. The investigation of macromolecular structure changes during processing shows that this efficiency can be ascribed to a starch chain scission mechanism, resulting in lower specific mechanical energy input need for starch thermoplasticization compared to glycerol plasticized starch. Compared to the synthesized ionic liquids, raw commercial choline chloride leads to a good compromise between limited chain scission, and final water uptake and thermomechanical properties.

Glass transition of anhydrous starch by fast scanning calorimetry.

By means of fast scanning calorimetry, the glass transition of anhydrous amorphous starch has been measured. With a scanning rate of 2000Ks-1, thermal degradation of starch prior to the glass transition has been inhibited. To certify the glass transition measurement, structural relaxation of the glassy state has been investigated through physical aging as well as the concept of limiting fictive temperature. In both cases, characteristic enthalpy recovery peaks related to the structural relaxation of the glass have been observed. Thermal lag corrections based on the comparison of glass transition temperatures measured by means of differential and fast scanning calorimetry have been proposed. The complementary investigations give an anhydrous amorphous starch glass transition temperature of 312±7°C. This estimation correlates with previous extrapolation performed on hydrated starches.

On the representative elementary size concept to evaluate the compatibilisation of a plasticised biopolymer blend.

This study combines experimental and numerical approaches to investigate the microstructure and mechanical behaviour of non-miscible plasticised starch/zein blends. The concept of Representative Elementary Size (RES) is used to rank the effect of five different plasticisers (cholinium acetate, glycerol, butyl methyl imidazolium chloride, glycerol-choline chloride, urea-choline chloride) inducing microstructural and mechanical changes in the blends. Microstructural and mechanical RESs are derived from microscopy image analysis and Finite Element Modelling of elasticity behaviour of studied blends. Compared to the usual consideration of ultimate mechanical properties (elongation and stress at break), the RES-based approach allows detecting the presence of perfect or imperfect interface between starch and zein particles depending on the nature of plasticiser.

All-natural bio-plastics using starch-betaglucan composites.

Grain polysaccharides represent potential valuable raw materials for next-generation advanced and environmentally friendly plastics. Thermoplastic starch (TPS) is processed using conventional plastic technology, such as casting, extrusion, and molding. However, to adapt the starch to specific functionalities chemical modifications or blending with synthetic polymers, such as polycaprolactone are required (e.g. Mater-Bi). As an alternative, all-natural and compostable bio-plastics can be produced by blending starch with other polysaccharides. In this study, we used a maize starch (ST) and an oat ß-glucan (BG) composite system to produce bio-plastic prototype films. To optimize performing conditions, we investigated the full range of ST:BG ratios for the casting (100:0, 75:25, 50:50, 25:75 and 0:100 BG). The plasticizer used was glycerol. Electron Paramagnetic Resonance (EPR), using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a spin probe, showed that the composite films with high BG content had a flexible chemical environment. They showed decreased brittleness and improved cohesiveness with high stress and strain values at the break. Wide-angle X-ray diffraction displayed a decrease in crystallinity at high BG content. Our data show that the blending of starch with other natural polysaccharides is a noteworthy path to improve the functionality of all-natural polysaccharide bio-plastics systems.

Nanostructured cellulose-xyloglucan blends via ionic liquid/water processing.

In this work, the properties of cellulose (CE)/xyloglucan (XG) biopolymer blends are investigated, taking inspiration from the outstanding mechanical properties of plant cell walls. CE and XG were first co-solubilized in an ionic liquid, 1-ethyl-3-methylimidazolium acetate, in order to blend these biopolymers with a varying CE:XG ratio. The biopolymers were then regenerated together using water to produce solid blends in the form of films. Water-soluble XG persisted in the films following regeneration in water, indicating an attractive interaction between the CE and XG. The final CE:XG ratio of the blends was close to the initial value in solutions, further suggesting that intimate mixing takes place between CE and XG. The resulting CE/XG films were found to be free of ionic liquid, transparent and with no evidence of phase separation at the micron scale. The mechanical properties of the blend with a CE:XG ratio close to one revealed a synergistic effect for which a maximum in the elongation and stress at break was observed in combination with a high elastic modulus. Atomic force microscopy indicates a co-continuous nanostructure for this composition. It is proposed that the non-monotonous variation of the mechanical performance of the films with XG content is due to this observed nanostructuration.

Relationship between Young's Modulus and Film Architecture in Cellulose Nanofibril-Based Multilayered Thin Films.

Young's moduli of cellulose nanofibril (CNF)-poly(allylamine hydrochloride) (PAH) multilayered thin films were measured using strain-induced elastic buckling instability for mechanical measurements (SIEBIMM) and the quantitative nanomechanical mapping technique (PF-QNM). To establish the relationship between structure and mechanical properties, three types of films with various architectures were built using the layer-by-layer method by changing the ionic strength of the dipping solution. Both methods demonstrate that the architecture of a film has a strong impact on its mechanical properties even though the film has similar cellulose content, emphasizing the role of the architecture. Films with lower porosity (Φair = 0.34) and a more intricate network display the highest Young's moduli (9.3 GPa), whereas others with higher and similar porosity (Φair = 0.46-0.48) present lower Young's moduli (4.0-5.0 GPa). PF-QNM measurements indicate a reverse ranking that is probably indicative of the surface composition of the films.

Thermomechanical characterization of an amylose-free starch extracted from cassava (Manihot esculenta, Crantz).

The aim of this study was to determine and compare the melting (Tm), glass transition (Tg) and mechanical relaxation (Tα) temperatures of a new waxy cassava starch. Thermal transitions measurements were obtained by Differential Scanning Calorimetry (DSC) and Dynamical Mechanical Thermal Analysis (DMTA). The experimental data showed a high correlation between water volume fraction and melting temperature (Tm) indicating that the Flory-Huggins theory can be used to describe the thermal behavior of this starch. The Tm of waxy cassava starch-water mixes were lower than a waxy corn starch-water reference system, but differences were not statistically significant. The mechanical relaxation temperatures taken at tan δ peaks were found 29-38°C larger than Tg. The Tα and Tg measured for waxy cassava starch exhibited similar properties to the ones of waxy corn starch, implying that waxy cassava starch can be used in food and materials industry.