title: Multidimensional characterisation of biomechanical structures by combining Atomic Force Microscopy and Focused Ion Beam: A study of the rat whisker.
abstract: Understanding the heterogeneity of biological structures, particularly at the micro/nano scale can offer insights valuable for multidisciplinary research in tissue engineering and biomimicry designs. Here we propose to combine nanocharacterisation tools, particularly Focused Ion Beam (FIB) and Atomic Force Microscopy (AFM) for three dimensional mapping of mechanical modulus and chemical signatures. The prototype platform is applied to image and investigate the fundamental mechanics of the rat face whiskers, a high-acuity sensor used to gain detailed information about the world. Grazing angle FIB milling was first applied to expose the interior cross section of the rat whisker sample, followed by a "lift-out" method to retrieve and position the target sample for further analyses. AFM force spectroscopy measurements revealed a non-uniform pattern of elastic modulus across the cross section, with a range from 0.8GPa to 13.5GPa. The highest elastic modulus was found at the outer cuticle region of the whisker, and values gradually decreased towards the interior cortex and medulla regions. Elemental mapping with EDS confirmed that the interior of the rat whisker is dominated by C, O, N, S, Cl and K, with a significant change of elemental distribution close to the exterior cuticle region. Based on these data, a novel comprehensive three dimensional (3D) elastic modulus model was constructed, and stress distributions under realistic conditions were investigated with Finite Element Analysis (FEA). The simulations could well account for the passive whisker deflections, with calculated resonant frequency as well as force-deflection for the whiskers being in good agreement with reported experimental data. Limitations and further applications are discussed for the proposed FIB/AFM approach, which holds good promise as a unique platform to gain insights on various heterogeneous biomaterials and biomechanical systems.
authors.affiliation: Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Vahid Reza
authors.initials: VR
authors.lastname: Adineh
authors.affiliation: Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Boyin
authors.initials: B
authors.lastname: Liu
authors.affiliation: Department of Physiology, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Rajan
authors.affiliation: Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Wenyi
authors.initials: W
authors.lastname: Yan
authors.affiliation: Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia. Electronic address: jing.fu@monash.edu.
authors.forename: Jing
authors.initials: J
authors.lastname: Fu
mesh_terms: D000818:Animals; D005260:Female; D020342:Finite Element Analysis; D018625:Microscopy, Atomic Force / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014738:Vibrissae
keywords: Atomic Force Microscopy; Biomechanics; Elastic modulus; Focused Ion Beam; Rat whisker