Date of Award

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Systems Engineering

First Advisor

Desai, Salil Dr.

Abstract

Surface modification of biomaterials is of critical value to attain desired functionality of biomedical devices and implants. Many of the conventional manufacturing methods used for the fabrication of thin film coatings lack the ability to precisely dispense biological compounds without compromising its chemical integrity. This research investigates the use of direct-write inkjet technique for the deposition of multi-layer coatings of biodegradable polymers. The Direct Write inkjet method provides selective deposition and patterning capability for depositing multi-material coatings on biomaterials for a vast array of surgical implant devices (e.g. stents for cardiovascular applications and orthopedic implants). In the first phase of the research, an elastomeric polymer, namely polyesterurethane urea (PEUU) was used to encapsulate an anti-proliferation drug paciltaxel (Taxol). The direct-writing process was employed to coat multiple layers of this polymeric formulation on a model titanium alloy surface. Characterization experiments were conducted to observe the influence of drug dosage and coating thickness on the release kinetics of the multilayer coatings. Drug release kinetics were characterized using an ultraviolet-visible spectrum (UV-Vis) spectrophotometer and surface morphology was assessed using optical microscopy and scanning electron microscopy (SEM). Biocompatibility tests were conducted to assess the smooth muscle cell inhibition and platelet adhesion properties of the coatings. The effects of drug dosage and layer thickness were evaluated via statistical significance tests. Tunable drug release coatings can be developed for an intended application by manipulating a given set of input factors. In the second phase of the research, the direct-write printing process was utilized to deposit precise layers of multilayer polymeric coatings on magnesium alloy surface. Biodegradable magnesium alloys provide substitutes for permanent metal implant materials such as titanium or stainless steel. Polymeric coatings provide a barrier layer that can retard the corrosion process of the magnesium alloys for vascular and orthopedic applications. Poly(lactic-co-glycolic acid (PLGA), polycaprolactone (PCL), and PEUU were chosen based on their varying degradation properties. Immersion studies were conducted in a simulated body fluid (SBF) to determine the corrosion behaviors of different sample types using inductively coupled plasma spectroscopy (ICP). Biocompatability tests such as the lactate dehydrogenase (LDH) assay were conducted to assess the cytotoxicity levels induced from magnesium ion exposure. A reduction in magnesium ion content was observed from the polymer-coated samples. Findings also showed correlation between the release of the magnesium alloy and the health of normal human bronchial epithelial cells evaluated using the COX-2 gene expression. This research establishes a foundation for identifying candidate polymer coatings to control the corrosion of magnesium alloys.

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