Replicating bone structure using Apatite-Wollastonite glass ceramic

Abstract

The aim of this project was to develop three-dimensional porous scaffolds which conformed with the natural properties of the native bone as an in-vitro model. This requires in depth knowledge of the biology of the tissue, its morphology and surrounding environment. Many researches focused on developing techniques to produce such highly complex structures which mimic the natural bone in-vitro. This thesis explores techniques for generating repeatable micro and macro porous ApatiteWollastonite (AW2) scaffolds using Thermally Induced Phase Separation (TIPS) methodology, freeze drying and then a two-step heat treatment process (5°C per minute to 779°C for a 1- hour dwell, then 10°C per minute to 1235°C for a 1-hour dwell). The manufacturing process was optimized to produce scaffolds with high porosity (60 – 76%) by altering the heat treatment process, analysing the distribution of pores and evaluating the mechanical characteristics mimicking bone for an in-vitro application. An image processing technique was developed to quantitatively measure the pore size, and its distribution within the AW2 scaffolds using Scanning Electron Microscopy (SEM) images of scaffolds. Open and closed porosity were also measured using Archimedes analysis. Mechanical properties and nutrient diffusion (Glucose release) of the scaffolds were measured and compared against the different scaffold fabrication processes. The scaffolds were designed to be representative of human cancellous bone and to provide a suitable environment for cell adhesion and proliferation of human Osteoblast Cells (HOb). High number of (over 140) scaffolds were manufactured, and some were further modified by incorporating Fused Filament Fabrication (FFF) printing, and the addition of channels and grooves to further improve open porosity and media flow. Both scaffold types (AW2 and modified AW2) were investigated during 21 days of in-vitro tests with human Osteoblast cells, for cell adhesion, infiltration into pores and growth against the controls. Both groups of scaffolds were suitable for nutrient transfer, promoted cellular adhesion (Actin), cellular interaction, extracellular matrix formation (SEM and Energy Dispersive X-ray spectroscopy), and proliferation (Presto Blue). In conclusion the AW2 scaffolds and modified AW2 scaffolds were successful in the invitro tests, the porosity and ability to allow for cell-to-cell interaction enabled Osteoblast growth and extracellular matrix formation. Further investigation is required to determine if these scaffolds can potentially be used as an in-vitro model for disease modelling and drug testing.