טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBernstein Michael
SubjectDevelopment of Bioresorbable Load Bearing Nanostructured
Ceramic-Polymer Composites for Bone Graft
Substitutes
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Elazar Gutmanas
Dr. Irena Gotman
Full Thesis textFull thesis text - English Version


Abstract

Bone grafts are required to assist bones in bridging large (>5 mm) gaps. Polymers, ceramics and also bioresorbable polymer-ceramic composites with high volume fraction of polymer currently used for graft substitutes are not strong enough for load bearing applications. In present research an attempt is made to develop strong bioresorbable ceramic-polymer composites via processing of nanoscale structures with high volume fraction of ceramic, with a special attention to processing of composites at relatively low temperatures and short exposures.

Bioresorbable β-TCP (beta tricalcium phosphate) nanoscale powder was synthesized at room temperature (RT) using wet chemical method. It was calcinated at T=350-740°C for 1h and mixed with 5-15vol % of bioresorbable polymers: polycaprolactone (PCL) and polylactic acid. The composite were consolidated employing high pressure (0.5-3GPa) at RT and 62°C (slightly above Tm of PCL). β-TCP powders and β-TCP-PCL nano-composites were characterized employing XRD, FTIR, HR-SEM. EDS and DSC. The effect of composition and consolidating parameters on final density, strength and dissolution kinetics in simulated body fluid (SBF) and in PBS of β-TCP-PCL nano-composites was investigated.

Synthesis of β-TCP resulted in agglomerates of partly amorphous powder. The powder particle size was about 20 nm and had a needle shape. Calcination at 740°C resulted in full crystallisation of the powder, coarsening (up to 80 nm) and change of shape to rounded one. Consolidation of as synthesized β-TCP at P=3GPa resulted in density slightly above 70% of theoretical, most of the porosity being closed porosity, while consolidation of calcinated β-TCP resulted in 85% dense samples. Strength in compression of specimens was 300÷400MPa with higher values corresponding to smaller grain size of β-TCP. Addition of the PCL resulted in densities up to 90%, mainly due to penetration of the PCL into the open pores. This was accompanied by decrease in compressive strength and increase in ductility of β-TCP-PCL nano-composites.

Dissolution rate of β-TCP-PCL nano-composites in SBF with as synthesized β-TCP was almost 10 times higher than calcinated β-TCP. Dissolution rate decreases at longer exposures, probably due to deposition of Ca phosphates from SBF that was observed in the experiments. It was shown that dissolution of β-TCP-PCL nano-composites with lower density in PBS have higher dissolution rate. Calcinations of β-TCP significantly reduces dissolution rate of the β-TCP/PCL composites, probably due to crystallization of the amorphous phase. The specimens of β-TCP-PCL nano-composites retained their compressive strength after dissolution in PBS for a period of two weeks.