Defense of Doctoral Thesis with Veronica Nessi, INRAe, Nantes, France, December 2019

Supervisor: Denis Lordin

Abstract: The main purpose of this study is to characterize the structure-properties relationships in physiological conditions of composite materials developed by extrusion from potato starch plasticized with glycerol and reinforced with cellulose (CNCs) or chitin (ChNCs) nanocrystals. To predict their behavior in biomedical applications such as degradable implants, the multi-scale characterization of the structure (molecular mass, crystalline and local structure, starch granular structure) is linked to the mechanical properties of the materials at the dry state and their behavior in physiological conditions (swelling, enzymatic degradation, release of the plasticizer). A preliminary study on purely starch-based matrices has enabled to separate the effects of extrusion parameters and plasticizer from the ones of the nanofillers. The samples, up to 2.5wt% CNCs, present a milder swelling and slowed-down enzymatic hydrolysis when compared to a pure starch-based matrix, due to strong starch/nanofiller interactions. However, the opposite effect (stronger swelling, faster hydrolysis) is observed when increasing the CNCs concentration (up to 10wt%) or by replacing cellulose with chitin: this comes from the nanocrystals aggregating and/or dispersing more heterogeneously in the matrix. In order to study the in vitro response to these materials, cytotoxicity and cellular adhesion assays have been developed for 24 and 48h by using epithelial and fibroblastic cells. All matrices and composite materials are non-cytotoxic within the limits of these tests but more precise tests, specific to nanofillers, should be performed to evaluate their safety more accurately.

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