Quantifying the mechanical properties of polymeric tubing and scaffold using atomic force microscopy and nanoindentation

Measurement of mechanical parameters of polymeric scaffolds presents a significant challenge due to their intricate shape and small characteristics dimensions of their elements – around 100μm. In this study, mechanical properties of polymeric tubing and scaffold, made of biodegradable poly (l-lactic) acid (PLLA), were characterised using atomic force microscopy (AFM) and nanoindentation, complemented with tensile testing. AFM was employed to assess the properties of the tube and scaffold locally, whilst nanoindentation produced results with a dependency on the depth of indentation. As a result, the AFM-measured elastic modulus differs from the nanoindentation data due to a substantial difference in indentation depth between the two methods. With AFM, a modulus between 2 and 2.5 GPa was measured, while a wide range was obtained from nanoindentation on both the tube and scaffold, depending on the indentation scale. Changes in the elastic modulus with in-vitro degradation and ageing were observed over the one-year period. To complement the indentation measurements, tensile testing was used to study the structural behaviour of the tube, demonstrating the yielding, hardening and fracture properties of the material.