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Marco Boi [1] and Gregorio Marchiori [1] and Maria Sartori [2] and Francesca Salamanna [3] and Gabriela Graziani [1] and Alessandro Russo [1] and Andrea Visani [4] and Mauro Girolami [5] and Milena Fini [3] and Michele Bianchi [1]

Academic Editor: Renal Backov

1, Rizzoli Orthopaedic Institute, NanoBiotechnology Laboratory (NaBi), Research Innovation and Technology Department (RIT), Via di Barbiano 1/10, 40136 Bologna, Italy, ior.it

2, Rizzoli Orthopaedic Institute, Laboratory of Biocompatibility, Technological Innovations and Advanced Therapies, Research Innovation and Technology Department (RIT), Via di Barbiano 1/10, Bologna, Italy, ior.it

3, Rizzoli Orthopaedic Institute, Laboratory of Preclinical and Surgical Studies, 40136 Bologna, Italy, ior.it

4, Rizzoli Orthopaedic Institute, Laboratory of Biomechanics and Technology Innovation, Via di Barbiano 1/10, 40136 Bologna, Italy, ior.it

5, Rizzoli Orthopaedic Institute, Orthopedics and Traumatology Department, Via Pupilli 1, 40010 Bologna, Italy, ior.it

Received Jun 19, 2017; Accepted Jul 25, 2017

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Bone tissue is a highly anisotropic, heterogeneous, and viscoelastic material exhibiting a complex hierarchical structure at multiple length scales [1, 2]. Conventional macroscopic mechanical tests are not able to detect the mechanical properties at the trabecula or osteon level [3, 4]. On the other hand, instrumented indentation (or “nanoindentation”) is a widely accepted method to investigate the mechanical properties of bone tissue at the micro- and nanoscale [5–7]. In bone engineering context, it is still common practice to utilize the well-known Oliver and Pharr (OP) model [8] to analyze indentation data in terms of elastic/plastic contribution, which however overlooks the viscous behavior of bone tissue [9].

During the last decade, Oyen’s group developed and validated a viscoelastic-plastic (VEP) model that foresees a three-step consecutive fitting of a loading-creep-unloading curve in order to extract the main mechanical parameters of the viscoelastic material such as elastic modulus (ER), contact hardness (HC), hardness (H), and viscosity index (ηQ) [10, 11]. The hypothesis is that the VEP model can provide additional details over bone maturation process not directly accessible through the common OP analysis. However, to date, the application of the VEP...

   

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