Paper BI-ThP6
A Novel Technique for the Determination of Orientational Effects in Bio-Composite Materials

Thursday, November 12, 2009, 6:00 pm, Room Hall 3

Dentin is a natural composite material consisting of highly mineralized tubules (peritubular dentin, PTD) embedded in an intertubular matrix (ITD) consisting predominantly of collagen. Although the mechanics of dentin has been studied for over a century, only recently has the advent of nanomechanical testing allowed investigation of its microscopic characteristics. In particular, the role of the PTD in overall dentin mechanics can now be explored. By selecting small enough volumes of dentin, the orientational effect of the tubules can be examined. In this study, micron-sized pillars were fashioned by a novel femtosecond laser ablation technique, which avoids the material damage induced when milling is performed by a high energy ion beam or ablation by slower laser pulses. Testing of these structures was performed in a nanoindenter by recording force vs. deformation curves under constant strain rate (until failure) while compressing the pillar with a flat punch tip. These data provided both the modulus and strength of the sample. The small size of the pillars, approximately 20 x 20 microns in cross-section and 100 microns height, guarantee that the tubular orientation is well-defined within a single pillar compression experiment. A statistical correlation was observed between the tubule orientation and measured modulus, with a higher modulus being recorded when the tubule axis was oriented along or near the axis of compression. Such studies allow correlations between the local tubular orientation and biomechanical function. The new method described in this work does not expose the sample to dehydration in vacuum or high energy ions, and does not require coating with conductive materials. It is generally applicable to a variety of biological specimens.