| The work presented in this thesis is based on the modification of surface and bulk properties of polyphosphazenes to form polymers with new and/or improved properties that are useful in advanced applications. Chapter 1 provides an introduction to this field and sketches the history and purpose of research in this area. Chapter 2 reviews the field of hydrophobic polyphosphazenes and their potential applications. Hydrophobic polymers play a crucial role in many biomedical and commercial applications. Hydrophobic polyphosphazenes offer opportunities for the tuning of surface properties that are not found for many conventional hydrophobic materials. Chapter 3 describes a study involving surface modification of a hydrophobic, fluorinated polyphosphazene to form a superhydrophobic surface. Superhydrophobic surfaces, with contact angle to water as high as 159°, were created by electrospinning polymer films of poly[bis(trifluoroethoxy)phosphazene]. The extremely high hydrophobicity of these films was a combined result of a highly fluorinated surface and the inherent surface roughness of an electrospun mat. Surface properties were analyzed by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. The development of these superhydrophobic surfaces constitutes a significant advancement for fluorinated polyphosphazenes. It not only offers great potential as biomaterials and membranes for separation purposes but also widens the scope of applicability of these polymers in fields like self-cleaning surfaces and protective clothing applications.;Chapter 4 discusses the development of biodegradable polyphosphazenes for bone tissue engineering application. This chapter reports on the design, synthesis, characterization and biological evaluation of L-alanine co-substituted polyphosphazenes. Polymer properties, such as, glass transition temperature, hydrolytic degradation, surface wettability, tensile strength and modulus of elasticity varied over a wide range following changes to the type of co-substituents on the polymer backbone, thus demonstrating the tunability of biodegradable polyphosphazenes. Chapter 5 deals with the processing of nanofiber and nanofiber composite scaffolds of poly[bis(ethyl alanato)phosphazene] by the process of electrospinning. The nanofiber scaffolds were characterized by scanning electron microscopy, profilometry and hydrolysis studies. These degradable nanofiber scaffolds are useful in biomedical applications such as tissue engineering and drug delivery.;Chapter 6 reports on the synthesis and characterization of tyrosine-functionalized polyphosphazenes. The physical and chemical properties of the polymers varied with the type of linkage between the tyrosine unit and phosphazene backbone. Poly[(ethyl glycinato) (ethyltyrosinato)phophazenes] (linkage via the amino group of tyrosine) were found to be hydrolytically erodible. Poly[(n-propoxy) (tyrosinato)phosphazene] (linkage via the hydroxyl group of tyrosine) were hydrolytically stable, showed a pH-dependant solubility behavior and formed ionotropic gels. Thus, the tyrosine functionalized polyphosphazene system offers the opportunity to incorporate properties such as bioerosion or pH sensitive behavior into one material by structural variations at the molecular level and are useful in applications such as tissue engineering and controlled drug delivery.;Appendix a describes the development of low temperature setting polyphosphazene/hydroxyapatite composites, potentially useful as bone tissue engineering materials. These composites were characterized by various techniques such as XRD, SEM, solution chemistry and mechanical property evaluation. The in vivo biological response of the composites was tested in a unicortical rabbit model. Appendix b reports on novel blends of hydrophobic, biodegradable polyphosphazene, poly[bis(ethyl alanato) phosphazene] and poly(lactic- co-glycolic)acid (LA: GA; 85:15), developed as candidates for bone tissue engineering applications. Blending of biodegradable polyphosphazenes with PLAGA was attempted in order to combine the beneficial features of PLAGA such as recognized biocompatibility and widespread applicability with the osteoconductivity, well tuned degradability as well as the buffering capacity of the degradation products of polyphosphazenes. |
