An Active Microscaffold System with Fluid Delivery and Stimulation/Recording Functionalities for Culturing 3-D Neuronal Networks Laura Elizabeth Rowe 215 Pages Directed by Dr. A. Bruno Frazier An active microscaffold system with fluid delivery and electrical stimulation/recording functionalities for 3-D neuronal culture studies is presented. The microscaffolds presented in this dissertation consist of an array of microfabricated towers with integrated microfluidic channels, fluid ports, and electrodes. The microfluidic channels and ports allow for perfusion of nutrients, gas exchange, and biochemical control of the extracellular environment throughout the 3-D culture, while the electrodes allow for active stimulation/recording of the 3-D neuronal network. In essence, the microscaffold serves as an artificial circulatory system to enable 3-D in vitro growth and proliferation of re-aggregate neuronal cell cultures. Increased cell survival on microscaffolds with nutrient perfusion at 14 and 21 days in vitro (DIV) is presented. Additionally, the microtower scaffold is built upon a substrate that is compatible with the Multi Channel Systems preamplifier setup to enable electrical stimulation/recording of the cultured network in a 3-D mutilelectrode array (MEA) environment. Impedance measurements on the functioning microtower electrodes were obtained. The overall goal of this research was to develop a BioMEMS technology to provide neuroscientists with a better investigative tool for studying 3-D in vitro neuronal networks than is currently available.

Titanium alloys are frequently used in the medical field as bone implant materials due to their excellent biocompatibility and corrosion resistance. Yet, their elastic modulus is usually significantly higher than the one of bone, which can lead to a reduction of bone tissue at the implant site. The current research is therefore focused on the development of highly porous implants, which promise a low elastic modulus close to that of bone, an enhanced bone ingrowth and an improved vascularization. However, the appropriate pore size for an optimal osseointegration still remains unclear. To that end, a transparent tubular microsystem is developed to mimic such a porous microenvironment in order to study single bone cell behavior and early bone formation processes. The system is fabricated out of an implant material (β-stabilized Ti-45Nb (wt%)). It is demonstrated that the bulk material composition, which is consisting of a high Nb content, can be closely transferred to transparent thin films by using reactive sputtering. These films then self-assemble into tubular microscaffolds (TS) with a diameter range between 10-42 μm. Biological studies are subsequently performed to investigate the response (e.g. cell adhesion, migration, osteogenic differentiation) of human Mesenchymal Stem Cells (MSC) to the TS. It is shown that cells form fewer, more diffuse focal adhesion points inside the TS compared to a planar surface and the spatial confinement causes a switch in between amoeboid and mesenchymal migration modes. In addition, it is demonstrated that cells can survive inside the TS for at least 12 days during osteogenic differentiation and partly mineralize the TS interior. The observed mineralization process is furthermore linked to the formation of hydroxyapatite crystals inside dead cells bodies, which leads to a crystallization over time. All in all, the TS platform offers an easy way to identify key factors of bone cell-implant interactions that can be used to improve the biocompatibility of the bone-implant interface in the future.