Hybrid Carbon-modified Polymer-based Silica Aerogels with Low Thermal Conductivity and Improved Mechanical Properties

Recently, graphene nanoplatelets (GnPs) have attracted a great deal of attention as a multifunctional reinforcing nanofiller in polymer composites, which is due to their unique two-dimensional layer structure with honeycomb characteristics, their excellent mechanical properties and their isotropic reinforcement capability in more than one direction. Here, the effect of the spinodal decomposition process in creating a nonparticulate morphology in the GnPs' orientation and dispersion is investigated. It is also studied how the gelation reaction can participate in the inclusion of GnPs in the aerogel backbone during the sol-gel process to strengthen the body of the gel. Meanwhile, the process of GnP exfoliation and restacking elimination during sol-gel transition is comprehensively studied. The present thesis also analyzes the gelation kinetics and thermodynamics in the presence of GnP and graphene oxide (GO) using in-situ rheology, light scattering (DLS), small-angle X-ray scattering (SAXS) and pore-structure-analyzer. The data collected during the gel network formation obtained with and without GnP or GO are analyzed in which to fully study the kinetics of structure evolution during the gelation. It is confirmed that the use of spinodal decomposition to create a nonparticulate gel network helps to offset the required long aging step during the sol-gel process, which is inevitable to strengthen the particle-to-particle neck using conventional methods such as nucleation and growth. It is also verified that this gelation technique enables the system to take advantage of GnP's full potential through correct exfoliation and elimination of restacking and re-agglomeration. The carbon-modified polymeric silica-based aerogels were first modified to enhance their mechanical properties by the addition of flexible nanofibers and stiff nanosheets into the structurer. The composites assembled homogeneously into the carbon-modified polymeric silica-based aerogel structure to create a uniform network of the solid struts along with the backbone. With such a network, the mechanical properties of the aerogels increased dramatically while preserving/advancing their unique features such as high surface area and thermal stability. The new aerogels could operate a high temperature with a high surface area. Furthermore, such material could resist moisture, which makes this material ideal to be used in high temperatures and humid environments.Ph.D.2021-06-22 00:00:0

Development and evaluation of a novel approach to producing uniform 3-D tumor spheroid constructs

In vitro tumor spheroid models have been developed using microfluidic systems to generate 3-D hydrogel beads containing components of alginate and ECM protein, such as collagen, with high uniformity and throughput. During bead gelation, alginate acts as a fast gelling component helping to maintain the spherical shape of beads and to prevent adjacent or underlying beads from coalescing when working with the slower gelling temperature and pH-sensitivity of collagen components. There are also well-known limitations in using microfluidic systems when working with temperature-sensitive components of collagen type I, and it is determined that to produce uniform hydrogel droplets through a microfluidic system, the mixtures must be homogeneous. However, the issue of collagen’s sensitivity to temperature causes concern for chunks of collagen gel inside of the mixture before bead encapsulation; therefore causing the mixture to become non-uniform and risking chip clogging. In order to overcome this limitation, previous approaches have used a cooling system during bead encapsulation while tumor cells were also present in the mixture, but this procedure assisted in postponing collagen gelation prior to bead production and potentially contributing to a delay in cell proliferation. Here a novel yet simple method is developed to prepare homogeneous pre-bead-encapsulation-mixtures containing collagen through ultrasonication, while extending cell viability and proliferation. This method allows the cultivation of homogenous TS cultures with high uniformity and compact structure, and not only maintains cell viability but also stimulates the proliferation of cells in alginate/collagen hydrogel bead cultures. Depending on the sonication parameters, time and temperature, gelation of collagen is controlled by small sized fibrils to thick fibers. Human-source-Michigan-Cancer-Foundation-7 (MCF-7) cells isolated from a breast cancer cell line are successfully incorporated into alginate/collagen mixtures, followed by sonication, and then bead production. After bead gelation, the encapsulated MCF-7 cells remained viable and proliferated to form uniform TSs when the beads contained alginate and collagen. Results indicate that ultrasound treatment provides a powerful technique to change the structure of collagen from fiber to fibril, and to disperse collagen fibers in the mixture homogeneously for an application to generate uniform hydrogel beads and spheroids while not disturbing cell proliferation.Applied Science, Faculty ofGraduat

Nanocomposite Aerogel Network Featuring High Surface Area and Superinsulation Properties

A nanocomposite strategy for the combination of a polymerized silica precursor, such as polyvinyl­trimethoxysilane (P-VTMS), together with electrospun thermoplastic polyurethane (TPU) nanofiber in the aerogel backbone is demonstrated to create effective stress transfer pathways in three-dimensional (3-D) aerogel composites with thermal insulation characteristics and special porous structure. Inspired by the bone architecture in the human body, with large amounts of hard segments and small amounts of soft segments, the 3-D interconnected TPU-embedded P-VTMS-based composite (P-VTMS/TPU) aerogel achieves synergistic strengthening in the nanofiber orientation direction. The sol–gel approach followed by first spinodal decomposition and later binodal decomposition phase separation has been taken in this study to initiate network formation throughout the P-VTMS/TPU backbone to form a 3-D network porous structure. The structure obtained offers full hierarchical multimodal porosity and an unprecedentedly large surface area of 2146 m2 g–1 due to a special approach taken in the sol–gel process in designing the interface between electrospun TPU nanofibers and P-VTMS chains. Owing to the combination of excellent mechanical and thermal insulation properties, the P-VTMS/TPU composite aerogel can be used as a thermal insulation material. Such a hierarchical multimodal porous architecture opens the door to fabricating new 3-D multifunctional and mechanically durable nanocomposite aerogels for flexible devices

Aerogel‐Based Biomaterials for Biomedical Applications: From Fabrication Methods to Disease‐Targeting Applications

Abstract Aerogel‐based biomaterials are increasingly being considered for biomedical applications due to their unique properties such as high porosity, hierarchical porous network, and large specific pore surface area. Depending on the pore size of the aerogel, biological effects such as cell adhesion, fluid absorption, oxygen permeability, and metabolite exchange can be altered. Based on the diverse potential of aerogels in biomedical applications, this paper provides a comprehensive review of fabrication processes including sol‐gel, aging, drying, and self‐assembly along with the materials that can be used to form aerogels. In addition to the technology utilizing aerogel itself, it also provides insight into the applicability of aerogel based on additive manufacturing technology. To this end, how microfluidic‐based technologies and 3D printing can be combined with aerogel‐based materials for biomedical applications is discussed. Furthermore, previously reported examples of aerogels for regenerative medicine and biomedical applications are thoroughly reviewed. A wide range of applications with aerogels including wound healing, drug delivery, tissue engineering, and diagnostics are demonstrated. Finally, the prospects for aerogel‐based biomedical applications are presented. The understanding of the fabrication, modification, and applicability of aerogels through this study is expected to shed light on the biomedical utilization of aerogels