Apr 20th, 1:00 PM - 4:00 PM


Torsional Harmonic Imaging: Expanding the Biological Nano-Mechanical Characterization Techniques at Boise State University


In the biomaterials field, there has been a growing need to increase the spatial resolution and decrease the data acquisition time when characterizing the nano-mechanical properties of a sample surface. A newly developed technique called torsional harmonic imaging is a nondestructive nano-mechanical characterization method that addresses these needs. It is a rapid procedure that quantitatively determines and maps the nanomechanical properties of biomaterials such as collagen. This new technique drives a cantilevered atomic force microscope (AFM) tip near the flexural resonance frequency of the cantilever causing the tip to tap along the surface of the material. The torsional frequency of the cantilever is recorded along with the harmonic modes that are simultaneously used to calculate the stiffness, adhesion, and other tip-sample force interactions. To evaluate the ability of torsional harmonic imaging to characterize biomaterials, the biomaterial rat tail collagen I was investigated because of its nanometer scale structure. Additionally, several polymers were included in the study as a comparative standard. Torsional harmonic imaging was compared to typical nano-mechanical techniques including cantilever-based nanoindentation and vertical probe nanoindentation. A comparative analysis showed that the reduced elastic modulus for collagen I obtained using torsional harmonic imaging and cantilever-based nanoindentation ranged from 1.1 to 2.4 GPa and 2.88 ± 1.45 GPa, respectively. The vertical probe nanoindentation was used with the polymers and compared to torsional harmonic imaging. Torsional harmonic imaging provided similar values for reduced elastic modulus for the collagen and the polymers as compared to the other two nanoindentation methods but with much higher spatial resolution and in significantly less time.