Fabrication and characterization of cellulose and silk biocomposites: a strategy to control morphology and phase separation in materials for medical applications
Creators: name: Love, Stacy Ann
Publisher: name: No Publisher Supplied
Year: 2023

description: Natural polymers such as structural polysaccharides and fibrous proteins are ideal candidates as biomaterials due to their non-toxicity and low cost. Many important applications and technologies include their use in textiles, pharmaceuticals, tissue scaffolding, and drug delivery agents. In particular, cellulose and silk-fibroin can be regenerated into composites with the ability to fine tune distinct material properties such as stiffness and degradability. This specified functionality is valuable to study when used in bionics and other medical devices. However, the modulation of many biopolymers is still relatively challenging due to the non-trivial nature of the transformation from a biopolymer’s native state to a more usable form. This dissertation provides a facile process to fine tune desirable and distinct properties of regenerated cellulose and silk-fibroin films through varying only the fabrication parameters. Four main Aims, each with its own specific hypothesis and unique goal, are discussed in this work. Aim I is to show that biocomposite crystallization is a function of fabrication method; Aim II is to understand the nano structures and phase separation of cellulose/silk fibroin samples upon solvation and coagulation; Aim III is an investigation of the material morphological stability upon hydration and enzymatic degradation; and Aim IV is to test for cell viability on biomaterial membranes as an applicational study. To study the various aims, a distinct three-step process is used where the first step is polymer composition ratio, the second step is dissolution type, and the third step is the regenerative agent. Biocomposites are characterized to determine the effects of fabrication parameters on physicochemical properties including their structure, thermal stability, morphology, topology, elasticity, and degradability. Within this work, two polymer ratios are studied (9:1 and 1:1 cellulose to silk fibroin) where their components are dissolved in three different solvent types (1-Ethyl-3-methylimidazolium acetate, 1-Ethyl-3-methylimidazolium chloride, and 1-Ethyl-3-methylimidazolium bromide) and subsequently regenerated in three competing coagulation baths (water, hydrogen peroxide solutions, and ethanol). The main hypothesis of this work is that the morphology and other functional characteristics of cellulose/silk fibroin biocomposites are dependent upon material composition and solubility and are further dictated by the arrangement of their molecular interactions. Characterization tests are integral to biomaterials research, and complementary techniques such as Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Thermalgravimetric Analysis, X-ray Scattering, and Atomic Force Microscopy were implemented for both the collection and validation of data. Major findings within this work are reported where the polymer ratio has an effect on the number of interface interactions between polymer types, and solubility mainly affects morphology, the amount and/or types of structural interfaces, surface topography, mechanical properties, hygroscopic properties, and enzymatic degradation. While properties related to silk secondary structure content, cellulose crystallite size, and cellulose polymorphism are controlled by the coagulation agent. Furthermore, cell studies report statistically similar cytotoxicity to the control when seeded on cellulose/silk composites with subtle effects on the degree of cell viability. Importantly, this means that material morphological differences can be utilized for different device functionalities, e.g., rate of drug diffusion, structural differences in scaffolds, etc., without a variance in unwanted cellular activities like excessive apoptosis. This information will be extremely useful for the future, as it outlines key parameters that can produce specific properties of a blended biopolymer film useful for a wide range of medical-based devices.