Novel processing of porous bioceramic structures

Bone is one of the most commonly replaced tissues in the body. Bone tissue engineering has become one of the key areas of research as a successful treatment option for bone regeneration. Scaffolds are used in tissue engineering to direct tissue development and open pore scaffolds with a pore size range of 100 – 400 μm and porosity >90%, are preferred. Bioceramics have been used in numerous orthopaedic applications since the 1960s. While bioinert materials such as zirconia have been used in load bearing applications due to their impressive mechanical properties, bioactive materials such as hydroxyapatite (HA) have been used to promote bone growth. Porous bioceramic structures have found uses as scaffolds which act as frameworks to support and guide tissue growth in tissue engineering applications. There is constant demand for new processing methods for producing structures of both graded and uniform porosity. The current methods used for producing structures of graded porosity involve complex and multiple manufacturing steps. This thesis investigates the feasibility of using electrohydrodynamic (EHD) atomisation to produce foams with graded porosity as a ‘one-step’ processing method, using zirconia as the ceramic material due to its extensive use in industrial and biomedical applications. Modifications have been made to the electrospraying set–up configuration and a range of suspension concentrations have been utilised to determine the experimental conditions. Control of porosity, pore size and depth of penetration has been obtained by varying parameters such as spray time, sintering temperature and the sacrificial template. Secondly, a combination of the traditional slurry dipping method and the EHD method have been introduced and used to process scaffolds with better surface and mechanical properties than using each method individually. For this work, a nano–HA suspension has been used and the scaffolds produced have been characterised by X-ray diffraction, X-ray microtomography, scanning electron microscopy and compression testing. Due to limitations in the HA suspension, zirconia was used as the ceramic material to produce scaffolds using the EHD method, which was manipulated to enhance its efficiency. The effects of changing and modifying the polymeric template by subjecting the templates to various pre–treatment methods on the microstructure and mechanical properties were investigated. It has been possible to achieve porous scaffolds of mechanical strength within the recommended region for cancellous bone. Finally, these mechanically strong scaffolds have been dipped in a nano–HA suspension and sintered at a lower temperature with an attempt to make the scaffolds bioactive since zirconia is bioinert. These composite structures have been tested for their bioactivity using simulated body fluid (SBF). The SBF results have proved to be favourable and apatite growth has been observed on the composite scaffolds using SEM images, additional apatite peaks on the XRD spectra and the increase in the mechanical properties.

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

UCL (University College London)

Year dc:date.issued

2009

Author dc:creator

• Muthutantri, A.I.

• Department of Mechanical Engineering

Language dc:language

en, eng