Evaluation of extruded starch foam for glucose-supplying biomaterials.

The survival rate of mesenchymal stem cells (MSC), a crucial factor in tissue engineering, is highly dependent on glucose supply. The purpose of this paper is to study the potential of starch foams as glucose suppliers. It is investigated through in vitro hydrolysis by amyloglucosidase in conditions that respect physiological constraints (37 °C and pH 7.4), including a duration of 21 days, and no stirring. Nine extruded starch foams with amylose contents ranging from 0 to 74 %, with various cell wall thicknesses (50 to 300 µm), and different crystallinities (0-30 %) were hydrolysed. These kinetics were fitted by a model which shows that the maximum rate of hydrolysis varies from 7 to 100 %, and which allows the rate of hydrolysis at 21 days to be calculated precisely. The results reveal the major role of amylose in glucose delivery kinetics, and the secondary roles of crystallinity and cell wall thickness of the foams. Additional hydrolysis of starch films revealed that thickness positively influences the amylose chain reorganisation during hydrolysis, which, in slows down and limits glucose delivery. A simple glucose delivery kinetics analysis procedure is proposed to select samples for testing as MSC glucose suppliers.

Plant cell wall inspired xyloglucan/cellulose nanocrystals aerogels produced by freeze-casting.

Cellulose nanocrystals (CNC) and xyloglucan (XG) were used to construct new aerogels inspired by the hierarchical organization of wood tissue, i.e., anisotropic porous cellular solid with pore walls containing oriented and stiff cellulose nanorods embedded in hemicellulose matrix. Aerogels with oriented or disordered pores were prepared by directional and non-directional freeze-casting from colloidal dispersions of XG and CNC at different ratios. XG addition induced a clear improvement of the mechanical properties compared to the CNC aerogel, as indicated by the Young modulus increase from 138 kPa to 610 kPa. The addition of XG changed the pore morphology from lamellar to alveolar and it also decreased the CNC orientation (the Hermans' orientation factor was 0.52 for CNC vs 0.36-0.40 for CNC-XG). The aerogels that contained the highest proportion of XG also retained their structural integrity in water without any chemical modification. These results open the route to biobased water-resistant materials by an easy and green strategy based on polymer adsorption rather than chemical crosslinking.

Morphology and mechanical behaviour of pea-based starch-protein composites obtained by extrusion.

Starch-legume protein composites were obtained by extrusion of pea flour and pea starch-protein blend at various specific mechanical energies (100-2000 kJ/kg) and a temperature low enough to avoid expansion. The morphology of these composites displayed protein aggregates dispersed in a starch matrix, revealed by microscopy. Image analysis was used to determine the median width of protein aggregates (D50), their total perimeter and surface, from which a protein/starch interface index (Ii) was derived. The mechanical properties of composites were determined by a three-point bending test. The pea flour composites had a higher interface index Ii (1.8-3.1) with lower median particle width D50 (8-18 µm) and a more brittle behaviour than the blend composites that had a lower Ii (1-1.1) and higher D50 (22-31 µm). For both materials, rupture stress and strain were negatively correlated with Ii. This result suggested that there was a poor interfacial adhesion between the pea starch and proteins.

Shape-memory starch for resorbable biomedical devices.

Shape-memory resorbable materials were obtained by extrusion-cooking of potato starch with 20% glycerol under usual conditions. They presented an efficient shape-memory with a high recovery ratio (Rr>90%). Their recovery could be triggered at 37°C in water. After water immersion at 37°C, the modulus decreased from 1GPa to 2.4MPa and remained almost constant over 21 days. Gamma-ray sterilization did not have a dramatic impact on their mechanical properties, despite a large decrease of molecular mass analyzed by asymmetrical flow field-flow fractionation coupled with multi-angle laser light scattering (AFFFF-MALLS). Samples implanted in a rat model exhibited normal tissue integration with a low inflammatory response. Thus, as previously investigated in the case of shape-memory synthetic polymers, natural starch, without chemical grafting, can now be considered for manufacturing innovative biodegradable devices for less-invasive surgery.

Imbibition, desiccation and mechanical deformations of zein pills in relation to their porosity.

This paper deals with the interaction between zein (the main protein component of corn grain) and water. It induces macroscopic properties changes and may allow for the understanding of the basis of zein endosperm structure: vitreous endosperm is compact and floury endosperm is porous, giving the endosperm its hard and soft textures, respectively. In that aim porous pills made by compaction of zein powder submitted to different hydration/dehydration processes have been prepared and studied. In particular, imbibition measurements of a pure-water drop deposited onto a zein pill were performed. Also, desiccation of a zein pill previously imbibed induces strong mechanical stresses leading to crack formation and/or large deformations.

Lignin incorporation combined with electron-beam irradiation improves the surface water resistance of starch films.

We investigated the potential of an electron-beam post-treatment to tailor the properties of 70/30 and 80/20 wt. extruded starch-lignin films. The effect of a 400 kGy radiation on films differing essentially by the kind of lignins incorporated (lignosulfonates/alkali lignins) was assessed both at the macroscopic and the molecular levels. Changes in the polymer molecular structure were studied by IR spectroscopy, by thioacidolysis as well as by model compound experiments. Electron beam-irradiation at 400 kGy, a rather high dose for processing natural polymers, alters to some extent the mechanical resistance of the starch-based materials. However this treatment substantially reduces the hydrophilic surface properties of the films, while not harming their biodegradability. Involved in radical cross-coupling reactions, lignin phenolic compounds are likely to play a primary role in the formation of a hydrophobic condensed network. This study suggests that lower irradiation doses might yield biomaterials with improved usage properties.