nanoindentation
Nanoindentation Meeting
This week’s group meeting will be on Thursday 7th May 2009 in Room B4 at 3 PM. Alastair Selby will discuss a nanoindentation meeting he attended last week at the University of Leicester. The meeting was entitled ‘Advances in Nanomechanical Measurements’ and was the Agilent UK and Ireland User Meeting 2009.
Nanoindentation of Histological Specimens
Our work using nanoindentation to characterise the micromechanical properties of blood vessels has been published in this month’s special issue of Journal of Materials Research: Indentation Methods in Advanced Materials Research. The reference and abstract are below:
“Nanoindentation of histological specimens: Mapping the elastic properties of soft tissues”. R. Akhtar, N. Schwarzer, M.J. Sherratt, R.E.B. Watson, H.K. Graham, A.W. Trafford, P.M. Mummery, B. Derby, J. Mat. Res. 24, 638-646 (2009).
Although alterations in the gross mechanical properties of dynamic and compliant tissues have a major impact on human health and morbidity, there are no well-established techniques to characterize the micromechanical properties of tissues such as blood vessels and lungs. We have used nanoindentation to spatially map the micromechanical properties of 5 µm thick sections of ferret aorta and vena cava and to relate these mechanical properties to the histological distribution of fluorescent elastic fibers. To decouple the effect of the glass substrate on our analysis of the nanoindentation data, we have used the extended Oliver and Pharr method. The elastic modulus of the aorta decreased progressively from 35 MPa in the adventitial (outermost) layer to 8 MPa at the intimal (innermost) layer. In contrast, the vena cava was relatively stiff, with an elastic modulus >30 MPa in both the extracellular matrix-rich adventitial and intimal regions of the vessel. The central, highly cellularized, medial layer of the vena cava, however, had an invariant elastic modulus of ~20 MPa. In extracellular matrix-rich regions of the tissue, the elastic modulus, as determined by nanoindentation, was inversely correlated with elastic fiber density. Thus, we show it is possible to distinguish and spatially resolve differences in the micromechanical properties of large arteries and veins, which are related to the tissue microstructure.
Nanoindentation of Biological Tissues and Hydrogels
Dr Michelle Oyen (Cambridge University) recently visited us at the School of Materials on Friday 13th February 2009, to give a seminar. Her presentation, was entitled ‘Nanoindentation and Microindentation Studies of Biological Tissues and Hydrogels”. We are grateful to her for accepting our invitation and for giving an excellent talk which fits well with the groups interests.
The abstract of her talk is below:
‘Interest in the mechanical behaviour of compliant biological tissues and is growing, and the emphasis on applications necessitating mechanically-robust implant materials motivates further study in this field. Nanoindentation has emerged as a leading technique for mechanical characterization; contact-based techniques are particularly attractive for materials that are difficult to test in tension, including soft biological tissues and hydrogels. However, commercial nanoindenter instrumentation is optimized for stiff, hard materials and therefore testing softer materials can be challenging. In the current study, mechanical testing by nanoindentation and larger scale microindentation were performed on a series of materials including polymeric validation standards, hydrogels of different gel composition and concentration, and hydrated biological tissues including bone and cartilage. Most tests were conducted under displacement control with a spherical indenter tip and using a load-relaxation test method to assess time-dependent deformation; creep characterization was considered when working in load control. Data analysis included a variety of different approaches, including a purely elastic analysis, a linear viscoelastic analysis and a computational analysis based on flow and poroelasticity. Quantitative results compare well for nanoindentation and microindentation, with mean elastic modulus values in the range of 100 kPa to 1-2 MPa for hydrogels and cartilage, respectively. Effects of both air dehydration and ethanol immersion are considered, and while these treatments both change the material elastic modulus by several orders of magnitude, the “dry” materials are found to exhibit profoundly different timedependent behavior depending on the dehydration method. The effects of finite layer thickness were considered in microindentation tests, and the result of faster equilibration for thinner gels was consistent with finite element modelling results for poroelasticity in finite layers. Nanoindentation is found to be a viable technique for mechanical characterization of compliant and hydrated tissues although challenges remain for widespread implementation and routine characterization due to the limitations of commercially available instrumentation.’
An Investigation into Nanoindentation of Hydrogel Contact Lenses
Alastair Selby (First Year PhD student) in the Derby Group gave a presentation entitled ‘An Investigation into Nanoindentation of Hydrogel Contact Lenses’ - click here to download a pdf of the talk.
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