Year of Publication

2010

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Engineering

Department

Materials Science and Engineering

First Advisor

Dr. Fuqian Yang

Abstract

Bioactive glasses react with the human physiological solution in control of their biofunctionality. The stress state in bioactive glasses determines the chemomechanical reaction and their biofunctionality. Using the microindentation technique, the effect of the indentation deformation on the surface damage and material dissolution of 45S5 bioglass was investigated.

The indentation-induced residual stresses were calculated. Complete anelastic recoveries of the indentation depths and the impression marks were observed for the first time, which was likely driven by the stored strain energy over the anelastic deformation zone. The indentation-induced local surface damages were revealed before and after the immersion tests in phosphate buffer solution (PBS). The growth of the cracks in the PBS solution displayed the stress-corrosion behavior with the crack-growth speed being a linear function of the indentation load.

45S5-bioglass was crystallized at temperature of 650 ºC. Microindentation technique also was used to study the localized mechanical behavior of the crystallized 45S5-bioglass. The crystallization had little effect on the indentation hardness, and the indentation hardness of the crystallized 45S5-bioglass is the same as that of the corresponding material in vitreous state. The fracture toughness is about 3 times less than that of annealed 45S5-bioglass in vitreous state, suggesting the preference of using bioactive glasses of vitreous state in the implant applications. Also, the effect of crystallization on the material dissolution was examined in phosphate buffer solution.

We also studied the growth and mechanical behaviors of the Ca-P precipitate layers formed on 45S5 bioglass in simulated body fluid. The thickness of the Ca-P precipitate layers was proportional to the square root of the immersion time, and the ratio of Ca/P in the Ca-P precipitate layers increased with the immersion time and approached 1.67, corresponding to the stoichiometric hydroxyapaptite (HA).Using the indentation technique, the indentation behavior of the Ca-P precipitate layers was investigated. The indentation hardness of the HA layers formed in SBF was found to be 0.40 GPa, and the contact modulus was 12.0 GPa. The contact modulus of 12.0 GPa is close to that of cortical bone. In this thesis, the primary mechanical properties of the non-crystalline and crystalline bioglass 45S5 were revealed. The relationship between the dissolution rate and localized residual stresses are discussed. With such knowledge, the evaluation of implants with respect to manufacturing processes, control, and service conditions now has another variable to consider and evaluate against performance.

Share

COinS