title: Precision of nanoindentation protocols for measurement of viscoelasticity in cortical and trabecular bone.
abstract: Nanoindentation has recently gained attention as a characterization technique for mechanical properties of biological tissues, such as bone, on the sub-micron level. However, optimal methods to characterize viscoelastic properties of bones are yet to be established. This study aimed to compare the time-dependent viscoelastic properties of bone tissue obtained with different nanoindentation methods. Bovine cortical and trabecular bone samples (n=8) from the distal femur and proximal tibia were dehydrated, embedded and polished. The material properties determined using nanoindentation were hardness and reduced modulus, as well as time-dependent parameters based on creep, loading-rate, dissipated energy and semi-dynamic testing under load control. Each loading protocol was repeated 160 times and the reproducibility was assessed based on the coefficient of variation (CV). Additionally, three well-characterized polymers were tested and CV values were calculated for reference. The employed methods were able to characterize time-dependent viscoelastic properties of bone. However, their reproducibility varied highly (CV 9-40%). The creep constant increased with increasing dwell time. The reproducibility was best with a 30s creep period (CV 18%). The dissipated energy was stable after three repeated load cycles, and the reproducibility improved with each cycle (CV 23%). The viscoelastic properties determined with semi-dynamic test increased with increase in frequency. These measurements were most reproducible at high frequencies (CV 9-10%). Our results indicate that several methods are feasible for the determination of viscoelastic properties of bone material. The high frequency semi-dynamic test showed the highest precision within the tested nanoindentation protocols.
authors.affiliation: Department of Physics and Mathematics, University of Eastern Finland, PO Box 1627, Kuopio 70211, Finland. hanna.isaksson@uef.fi
authors.forename: Hanna
authors.initials: H
authors.lastname: Isaksson
authors.forename: Shijo
authors.initials: S
authors.lastname: Nagao
authors.forename: Marta
authors.initials: M
authors.lastname: Małkiewicz
authors.forename: Petro
authors.initials: P
authors.lastname: Julkunen
authors.forename: Roman
authors.initials: R
authors.lastname: Nowak
authors.forename: Jukka S
authors.initials: JS
authors.lastname: Jurvelin
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000502:physiology*; D002417:Cattle; D055119:Elastic Modulus; D005269:Femur / Q000502:physiology; D006244:Hardness; D066298:In Vitro Techniques; D036103:Nanotechnology / Q000379:methods* / Q000706:statistics & numerical data; D013977:Tibia / Q000502:physiology; D014783:Viscosity