Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Amin S. Rizkalla

2nd Supervisor

Dr. S. Jeffrey Dixon

Joint Supervisor

Abstract

Bone defects are a prevalent problem in orthopedics and dentistry. Calcium phosphate-based coatings and nanocomposites offer unique solutions towards producing scaffolds with suitable physical, mechanical and biological properties for bone regeneration.

We developed a novel method to synthesize hydroxyapatite (HA) particles with high aspect ratio using sol-gel chemistry and hydrothermal treatment. We obtained tunable pure-phase carbonated-HA in the form of micro/nanorods and nanowires (diameters 25-800 nm). To mimic the structure of bone, HA nanowires were homogenously mixed within poly(ε-caprolactone) (PCL) to produce nanocomposites with improved mechanical properties as determined by uniaxial tensile testing.

Surface chemistry and topography of biomaterials play prominent roles in regulating cell adhesion and differentiation. Bone-like apatite coatings, produced by incubating materials in a simulated body fluid (SBF), improve the osteoconductivity of scaffold materials. However, few studies have controlled the surface topography of biomimetic HA. We assessed the effect of SBF ion concentration and soaking time on the surface properties of apatite coatings. Calcium phosphates such as carbonated-HA with similar chemical composition and stiffness were deposited onto PCL films. Characterization of these coatings revealed an increase in topographical complexity and surface roughness with increasing ion concentration of SBF and soaking time.

To investigate their potential application in bone regeneration, we studied the influence of topography of biomimetic HA coatings on the behavior of osteoblasts and osteoclasts in vitro. Osteoblast attachment and differentiation were significantly greater when cultured on rougher HA surfaces (Ra ~2 μm) than on smoother topographies (Ra ~1 μm). In contrast, activity of tartrate-resistant acid phosphatase (an osteoclast marker) was greater on smoother than on rougher HA surfaces. Furthermore, osteoclastic resorption lacunae were found exclusively on smoother HA coatings. Inhibition of resorption on rougher HA surfaces was associated with disruption of filamentous actin sealing zones. In conclusion, HA coatings can be prepared with different topographies, which regulate responses of osteoblasts and osteoclasts.

Thus, it may be possible to design HA-polymer composites and HA-coated polymers with physical, mechanical and biological properties suitable for tissue engineering. By modulating topography, rates of bone formation and biodegradation could be tailored for specific applications in orthopedics and dentistry.