Jared D. Bender

Development of Biodegradable Polyphosphazene- Nanohydroxyapatite Composite Nanofibers Via Electrospinning

Abstract : Biodegradable polymeric nanofibers are of great interest as scaffolds for tissue engineering and drug delivery due to their extremely high surface area, high aspect ratio and similarity in structure to the extracellular matrix (ECM). Polyphosphazenes due to their synthetic flexibility, wide range of physico-chemical properties, non-toxic and neutral degradation products and excellent biocompatibility are suitable candidates for biomedical applications. The objective of the present study was to develop and evaluate composite nanofibers of a biodegradable polyphosphazene, polyBIS(ETHYL ALANATO)PHOSPHAZENE (PNEA) and nanocrystals of hydroxyapatite (nHAp) via electrospinning. A suspension of nHAp in dimethyl formamide (DMF) sonicated with PNEA solution in tetrahydrofuran (THF) was used to develop composite nanofiber matrices via electrospinning at ambient conditions. In the present study the theoretical loading of nHAp was varied from 50%-90% (w/w) to PNEA. The nHAp content (actual loading of nHAp) of the composite nanofibers was determined by gravimetric estimation. The composite nanofibers were characterized by transmission electron microscopy (TEM), gravimetry and energy dispersive X-ray mapping. This study demonstrated the feasibility of developing novel composite nanofibers of biodegradable polyphosphazenes with more than 50% (w/w) loading of nHAp on and within the nanofibers.

Development of Novel Biodegradable Amino Acid Ester Based Polyphosphazene– Hydroxyapatite Composites for Bone Tissue Engineering

Abstract : Hydroxyapatite formed from low temperature setting calcium phosphate cements (CPC) are currently been used for various orthopaedic applications. CPCs are attractive candidates for the development of scaffolds for bone tissue engineering, since they are moldable, resorbable, set at physiological temperature without the use of toxic chemicals, and can be processed in an operating room setting. However they may have mechanical disadvantages which seriously limit them to non-load bearing orthopaedic applications, The aim of the present study was to develop composites from ployphosphazenes and calcium deficient hydroxyapatite precursors to form poorly crystalline hydroxyapatite-polymer composites. Composites were formed from calcium deficient hydroxyapatite precursors (Ca/P - 1.5, 1.6) and biodegradable polyphosphazenes, polyBIS(ETHYL ALANATO)PHOSPHAZENE (PNEA50mPh50) at physiological temperature. The results demonstrated that poorly crystalline hydroxyapatite that resembled the mineral component of bone was formed in the presence of biodegradable polyphosphazenes. The surface morphology of all the four composites was identical with a porous microstructure. The composites supported the adhesion and proliferation of osteoblast like MC3T3-E1 cells making them potential candidates for bone tissue engineering.

Design and Syntheses of Poly(Norbornenyldecaborane) Precursors to Boron Carbide and Boron-Carbide/Silicon-Carbide Ceramics

Poly(norbornenyldecaborane) (PND) was synthesized via ruthenium catalyzed ring opening metathesis polymerization and was found to be a good single-source polymeric boron carbide precursor. Polymer blends of PND and allylhydridopolycarbosilane (AHPCS) were also found to be excellent precursors to boron-carbide/silicon-carbide composite materials.

Electrostatic Spinning, Pyrolysis, and Characterization of Boron Carbide Nanofibers Prepared from Poly(norbornenyldecaborane) - a Polymeric Ceramic Precursor

Electrostatic spinning is a well-developed technique for the fabrication of fibers in the nanoscale domain. Novel boron carbide nanofibers were generated by the electrostatic spinning and ceramic conversion of poly(norbornenyldecaborane) (PND) - a polymeric ceramic precursor. The prepyrolyzed fibers were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The ceramic fibers were characterized by SEM, X-ray diffraction (XRD), 11 B magic-angle spinning nuclear magnetic resonance (MAS NMR) and DRIFT spectroscopy. SEM analysis showed retention of the nanostructure in the pre- and postpyrolyzed fibers.