Date of Award
Master of Science (MS)
Silk is a highly promising biomaterial with unique bio-physicochemical properties, such as excellent mechanical and optical properties, biocompatibility and programmable biodegradability. Among many different types, silk from domesticated silkworm, bombyx mori has received wide attention owing to its availability in virtually unlimited quantities and ease of extraction. In this study, we investigated silkworm silk as a protein glue to realize nacre-like composites. We have employed spin assisted layer-by-layer technique to fabricate ultrathin free-standing biocomposite films. Two different composites have been studied: (i) graphene oxide (GO)/silk and (ii) chitin/silk. From our prior work, it is known that the adsorption of amphiphilic silk on amphiphilic GO flakes is highly sensitive to the pH of the silk solution. In this study, we investigated the influence of pH of the silk solution on the mechanical properties of silk/GO composites. We found that the pH of silk solution has a significant influence on the structure and elastic modulus of the composite films. Over the pH rage studied here (pH4 to pH10), the modulus of composite films could be varied from 8 GPa to 31 GPa. Apart from the relative volume fractions of the two components, our results show that interfacial interaction between protein glue and graphene oxide plays a determining role in the ultimate mechanical properties of the film.
Additionally, we fabricated first protein-polysaccharide biocomposite layer-by-layer assembled composite using silk and chitin. Chitin is known for its chemical stability and excellent mechanical properties. However, it is a very difficult material to process due to its poor solubility, requiring strong organic solvent of hexafluoro-2-proponal (HFIP) to dissolve. Despite these difficulties, we have successfully developed a robust fabrication approach to realize chitin-silk biocomposite with different volume fractions of chitin, and demonstrate the release of these film from substrate into freestanding state. We have investigated the mechanical properties of these ultrathin films. The highest elastic modulus of the composite was found to be 6.9 GPa with 0.3% chitin, which is significantly higher than that of the composite film made with chitosan, a highly deacetylate form of chitin.
Taken together, our studies provide novel insights into the nanoscale structure and mechanical properties of ultrathin free-standing bionanocomposites fabricated using layer-by-layer assembly.
Parag Banerjee Jeremiah Morrissey