Preparation of polymeric samples containing a graduated modulus region and development of nanoindentation linescan techniques

This work concerns the development of a technique for the nanoindentation of polymeric samples containing a graduated modulus region, and a method for the preparation of samples. The samples studied were prototype intervertebral disc prostheses, which were manufactured from polycarbonate urethanes using a single-step injection moulding procedure. Discs were sectioned, mounted and polished using a series of increasingly fine grades of silicon carbide paper. It was found that the smoothest samples exhibited a significant degree of polishing damage around the interface and that slightly rougher samples were in fact more uniform and more suitable for studying using nanoindentation. The variation of the measured Young's modulus value with surface roughness was also investigated using calibration samples, and a nanoindentation linescan method was developed, which allows the variation in modulus across a polymeric sample to be investigated.