This work investigates the material properties and production parameters of carbon infiltrated carbon nanotube structures (CI-CNT's). The impact of non homogeneous infiltration and the porosity of cross section regions, coupled with changes in designed geometry, in this case beam width, on the density and modulus of elasticity are compared. Three potential geometric models of beam cross section are proposed and evaluated. 3-point bending, SEM images, and numerical optimization are used to assess the validity of each model and the implications they have for future CI-CNT material applications. Carbon capping near exterior beam surfaces is observed and determined to be a contributing factor to variations in material properties correlated with changes in designed geometry and infiltration parameters (temperature, time, and hydrogen flow rate). Unexpected relationships between beam width and elastic modulus are partially explained by modeling the carbon-capped beams as C-shaped structural members consisting of a graphitic carbon shell of varying porosity and thickness and uninfiltrated carbon nanotube internal regions with a near negligible stiffness. Findings of previous works on the effects of infiltration parameters and carbon capping on materials properties are confirmed and expanded. Flange and web thickness and porosity of the graphitic carbon shell are identified as potential design parameters for pursuing tunable material properties in high precision geometry MEMS and compliant mechanism applications.

The purpose of this research is to identify the effects of the carbon-infiltrated carbon nanotube (CICNT) growth process on the material properties of 316L stainless steel, particularly those properties which are essential for biocompatibility. Physically altering the micro-topography of a surface can dramatically affect its capacity to support or prevent biofilm growth. Growing CICNTs on biomedical materials is one approach which has demonstrated success at preventing biofilm growth. Unfortunately, the high temperature and carbon-rich gas exposure required for this procedure has proven to have deleterious effects. Rusting has been observed on samples that have been coated with CICNTs and then placed in culture media. A proper understanding of this rusting phenomenon, along with an exploration of other material properties which could be affected by the procedure, is a necessary prelude to further development of this novel antibacterial method. This thesis proposes a kinetic model derived from Fick's Second Law to predict the growth of chromium carbide as a function of temperature and time. Chromium carbide formation is shown to be the mechanism of corrosion, as chromium atoms are leeched from the the material, preventing the formation of a passivating chromium oxide layer that protects iron oxide from forming. The model is validated using experimental methods, which involve immersion in culture media, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and double loop electrochemical potentiokinetic reactivation (EPR) testing. This thesis further explores how the CICNT growth procedure affects the mechanical properties of 316L stainless steel as a function of temperature, time exposure to ethylene gas flow, and sample geometry. It is shown that the CICNT growth procedure effectively carburizes the stainless steel surface. Tensile tests demonstrate that the carburized surface leads to brittle failure for thin samples that have a relatively small ductile interior. This thesis also examines the adhesion and wear of the CICNTs on the surface of the 316L stainless steel. Tape tests and torsional shearing show strong adhesion between the CICNTs and the metal substrate. External fixator pin drilling also shows remarkably good wear properties for the CICNT surface. The changes in mechanical properties and the overall adhesive performance must be considered and properly managed by biomedical engineers hoping to use CICNT coatings.

Carbon-infiltrated carbon nanotube (CICNT) forests are carbon nanotube (CNT) forests infiltrated with pyrolytic carbon to increase durability by becoming a solid material. This material can be tuned to maintain the nanotube geometry of a CNT forest and can also be fabricated on a variety of materials and geometries. Additionally, the present work has indicated that CICNT forests may resist bacterial proliferation and biofilm formation. This phenomenon is not due to the CICNT chemistry; it is presumably due to the CICNT nanostructure morphology. Thus, both silicon and stainless steel substrates were used to investigate CICNT's structural resistance to Methicillin-resistant Staphylococcus aureus (MRSA) biofilm. From in vitro experimental testing, CICNT on both these substrates resisted MRSA cell attachment and biofilm proliferation. The discovery of this non-pharmaceutical biofilm resistance expands the potential applications of CICNT to include medical devices that are prone to infection and/or devices that contribute to infection. Two representative applications were investigated: external fixator pins and scalpel blades. CICNT-coated versions of these applications underwent additional MRSA biofilm resistance testing as well as mechanical testing. In particular, external fixator pins were identified as a high potential application of CICNT surface coating technology. Previous work on both CNT and CICNT forests has largely been performed on planar structures. However, any potential medical device applications involve curved substrates. In particular, concave curvatures are challenging due to the potential for stress-related CICNT forest defects. Thus, the present work also included a study of the incidence rates and determining factors of these defects. SEM images of the cross-sections revealed different types of microscale forest defects while the top surface showed morphologies that are largely consistent with flat substrates. CICNT forest height and substrate curvature were identified as contributing factors to CICNT forest defect incidence rates. Thus, the present work advances the understanding of bacterial resistance and microstructure-related properties of CICNT surface coatings, with applications in medical devices.