X-ray microdiffraction for engineered bone study: scaffold resorption analysis

Abstract

In this study we evaluated the behaviour of SkeliteTM (Millenium Biologix Corp., Kingston, Canada), a clinically available scaffold based on hydroxyapatite (HA) and Silicon-stabilized Tricalcium Phosphate (Si-TCP). Previous analysis by computed tomography (CT) revealed a progressive disappearance of the scaffold with the implantation time and its subsequent replacement with highly mineralized lamellar bone. However the resorption mechanism was not clearly understood in details. In this work bone formation and scaffold remodeling were evaluated by high spatial resolution (<1 micron) Wide Angle X-ray Scattering and Small and X-ray Scattering on sections of embedded implants retrieved from animals sacrificed at different times. With a special software we obtained microscopic images displaying the spatial variation of different structural features, thus allowing to map the mineralization intensity and bone orientation degree around the scaffold pore. The remarkable organization of the bone crystals and collagen fibres with respect to the scaffold geometry, reported in this work, appears to be the essential key to impose the 3-D desired architecture to the growing bone. A quantitative study of the diffraction data acquired at the interface, showed that the progressive scaffold resorption and bone formation are coupled to a significant depletion of Si-TCP with respect to the HA. Similar experiments where scaffolds were implanted in the absence of osteogenic cells, revealed that neither bone formation nor changes in scaffold chemical composition took place, thus indicating that SkeliteTM scaffold resorption and bone formation are interrelated processes. These results indicate the great potentialities of crystallographic analysis taken at high spatial resolution.