Microstructural design of biopolymer blends and related elasticity with imperfect interfacial bonding

Cell walls of extruded pea snacks: Morphological and mechanical characterisation and finite element modelling

Pulses extruded foods can be envisaged asall solid foams with voids and walls, the latter being considered as a dense starch/protein composite. Pea flour (PF) and blends of pea starch and pea protein isolate (PPI) with different protein contents (0.5-88% dry basis) were extruded to obtain models of dense starch-protein composites. Their morphology was revealed by CLSM microscopy, and their mechanical properties were investigated using a three-point bending test complemented by Finite Element Method (FEM) modelling. Composite morphology revealed protein aggregates dispersed in the starch matrix. It was described by a starch-protein interface index Ii computed from the measured total area and perimeter of protein aggregates. The mechanical test showed that the extruded PF and PPI ruptured in the elastic domain, while the extruded starch-PPI (SP) blends ruptured in the plasticity domain. The mechanical properties of pea composites were weakened by increasing the particle volume fractions, including proteins and fibres, probably due to the poor adhesion between starch and the other constituents. The mechanical behaviour of pea composites did not accurately follow simple mixing laws because of their morphological heterogeneity. Modelling results show that the elastoplastic constitutive model using the Voce plasticity model satisfactorily described the hardening behaviour of SP blend composites. Reasonable agreement (2-10%) was found between the experimental and modelling approaches for most materials. The computed Young's modulus (1.3-2.5 GPa) and saturation flow stress (20-45 MPa) increased with increasing Ii (0.7-3.1), reflecting the increase of interfacial stiffening with the increase of contact area between starch and proteins. FEM modelling allowed to identify the mechanical effect of structural heterogeneities.

Physical characterization and modeling of chitosan/peg blends for injectable scaffolds

Injectable scaffolds find many applications on the biomedical field due to several advantages on preformed scaffolds such as being able to fill any defect can be used in minimal invasion surgeries and are ready to use products. The most critical parameter for an injectable scaffold usage is its injectability, which can be related with rheological properties. Therefore, the objective of the present work was to increase knowledge about the critical parameters influencing injectability of biopolymers used for injectable scaffolds. Rheological and mechanical properties of a biopolymer blend in combination with injectability tests for a given design space controlled by the concentrations of both polymers and temperatures was made. Then those results were modeled to better understand the impact of parameters on injectability. The biopolymer blend chosen was Chitosan physically blended with Poly(ethylene glycol) where variations of both polymer concentrations and molecular weights were tested. Rheological and mechanical properties of all samples were determined, together with the injection force using a compression test at different injection conditions. All solutions were clear and transparent suggesting perfect miscibility. Rheological results were modeled using Ostwald-Waelle law and revealed a shear thinning pseudo-plastic solution at any composition and temperature, being chitosan concentration the most influencing variable. Compression tests results revealed mean injection forces ranging from 9.9 ± 0.06N to 29.9 ± 0.65N and it was possible to accurately estimate those results. Simulations revealed draw speed as the most influencing parameter. Cell viability tests revealed a non-cytotoxic biopolymer blend.