Lorentz contact resonance spectroscopy for nanoscale characterisation of structural and mechanical properties of biological, dental and pharmaceutical materials

Abstract

Scanning probe microscopy has been widely used to obtain topographical information and to quantify nanostructural properties of different materials. Qualitative and quantitative imaging is of particular interest to study material-material interactions and map surface properties on a nanoscale (i.e. stiffness and viscoelastic properties). These data are essential for the development of new biomedical materials. Currently, there are limited options to map viscoelastic properties of materials at nanoscale and at high resolutions. Lorentz contact resonance (LCR) is an emerging technique, which allows mapping viscoelasticity of samples with stiffness ranging from a few hundred Pa up to several GPa. Here we demonstrate the applicability of LCR to probe and map the viscoelasticity and stiffness of 'soft' (biological sample: cell treated with nanodiamond), 'medium hard' (pharmaceutical sample: pMDI canister) and 'hard' (human teeth enamel) specimens. The results allowed the identification of nanodiamond on the cells and the qualitative assessment of its distribution based on its nanomechanical properties. It also enabled mapping of the mechanical properties of the cell to demonstrate variability of these characteristics in a single cell. Qualitative imaging of an enamel sample demonstrated variations of stiffness across the specimen and precise identification of enamel prisms (higher stiffness) and enamel interrods (lower stiffness). Similarly, mapping of the pMDI canister wall showed that drug particles were adsorbed to the wall. These particles showed differences in stiffness at nanoscale, which suggested variations in surface composition-multiphasic material. LCR technique emerges as a valuable tool for probing viscoelasticity of samples of varying stiffness's.

The importance of correcting for variable probe–sample interactions in AFM-IR spectroscopy: AFM-IR of dried bacteria on a polyurethane film

“…Other AFM-based methods used to quantitatively map dissipative forces may also be suitable for incorporation. 23,24 Development of corrective approaches and further understanding of relationships between thermomechanical properties, probesample interactions, and AFM-IR signal transduction will likely require further experimental work with well-defined model structures. Lahiri et al, have previously reported rigorous experimental evaluation of AFM-IR response to nanopatterned poly(methyl methacrylate) structures prepared by electron beam lithography.…”

Nanotoxicity of nanodiamond in two and three dimensional liver models

“…Semi-thin sections were transferred to zinc selenide prisms (Anasys instruments) and scanned on SPM (AFM NanoIR, Anasys instruments) in LCR mode to evaluate morphology in 3D and the variations in nanomechanical properties across the section [37]. To obtain the nanomechanical spectra, images were taken in LCR mode over a drive frequency range of 1-1000 kHz at an increment rate of 100 kHz.s -1 with following parameters: scan rate of 0.30 Hz, resolution 500 × 200 points and drive strength of 15%.…”

Probing Chemical and Mechanical Nanodomains in Copolymer Nanorods with Correlative Atomic Force Microscopy—Nano‐correscopy

“…In terms of mechanical properties characterization, conventional approaches such as acoustic impedance, spherical indentation, and nanoindentation are also suitable only for larger particles and simply cannot determine the nanomechanical domain with a resolution <20 nm . To address these limitations, a number of advanced AFM modes have been developed such as the amplitude modulation–frequency modulation atomic force microscopy, force modulation, friction force microscopy, and contact resonance microscopic techniques such as piezoresponse microscopy and atomic force acoustic microscopy .…”

“…A promising new approach for mapping nanomechanical properties is the use of Lorentz contact resonance (LCR) spectroscopy. In LCR, the actuation of the cantilever is achieved with an oscillating Lorentzian force ( Figure b) and it is not sample specific . The sample is characterized based on the force modulation and the detection of changes to the cantilever deflection (frequency and amplitude), which directly correlate with viscous and elastic properties .…”

“…Therefore, substrate (here prism) stiffness has negligible influence on measured viscoelasticity, in particular for particles of high >200 nm. Unlike other techniques (e.g., indentation), LCR uniquely provides a measure of elastic and viscous properties based on the frequency and amplitude of recorded signal . Indentation‐based methods enable only the calculation of apparent elastic moduli, which is influenced by the elastic component at different levels.…”