Influence of Calcium Phosphate Composition and Design on Bone Regeneration, Degradation and Mechanical Function

Abstract

Influence of Calcium Phosphate Composition and Design on Bone Regeneration, Degradation and Mechanical Function

The prevalence of bone or bone-related injuries has been the impetus for the discovery of surgical procedures resulting in the tissue’s repair and eventual return to function. Solutions for such injuries and defects have often been based on the implantation of materials with desired mechanical and structural function, yet limitations of treatment options include donor site morbidity, mechanical failure, and inadequate tissue infiltration and implant fixation. Ideal scaffolding solutions should be osteoconductive, encourage bonding with nascent tissue, provide requisite mechanical support, and in the end, have degradation by-products that are efficiently removed from the body. For these reasons, an understanding of the dynamic of mutable properties of degrading scaffolds and their impact on bone regeneration would have clear value; perhaps allowing for the development of methods to control property loss over the lifetime of the implant. This dissertation targets the identification of critical scaffold properties that drive performance in terms of bone regeneration within the calcium phosphate ceramic (CaP) construct.

Composition and sintering temperature were demonstrated to influence powder sinterability and microporosity; properties which in turn influence initial scaffold properties, strength retention through degradation, and ultimately regeneration. “High” and “low” levels of various design variables (macroporosity, permeability, and surface area) were combined with materials processing parameters (composition and thermal treatment) to produce CaP scaffolds with regular architectures. Bone growth and structural quality were evaluated in an ectopic mouse model. Macroporosity was most influential in the amount of newly generated bone. Low macroporosity scaffolds promoted better bone ingrowth and supported better tissue penetration into the scaffold center than its high macroporosity counterpart. These scaffold designs were also low in permeability and high in surface area. The structural quality of the neotissue was dependent on both composition and thermal treatment, where -TCP scaffolds and high sintering temperatures produced tissue that was higher in trabecular thickness and spacing, mineral content, and mineral density.

We demonstrate that designed architectural features were more critical in facilitating bone regeneration, but inherent materials attributes were more instrumental in the quality of tissue growth