Showing papers on "Indentation published in 2009"

An optical coherence tomography (OCT)-based air jet indentation system for measuring the mechanical properties of soft tissues.

Abstract: A novel noncontact indentation system with the combination of an air jet and optical coherence tomography (OCT) was presented in this paper for the quantitative measurement of the mechanical properties of soft tissues. The key idea of this method is to use a pressure-controlled air jet as an indenter to compress the soft tissue in a noncontact way and utilize the OCT signals to extract the deformation induced. This indentation system provides measurement and mapping of tissue elasticity for small specimens with high scanning speed. Experiments were performed on 27 silicone tissue-mimicking phantoms with different Young's moduli, which were also measured by uniaxial compression tests. The regression coefficient of the indentation force to the indentation depth (N mm(-1)) was used as an indicator of the stiffness of tissue under air jet indentation. Results showed that the stiffness coefficients measured by the current system correlated well with the corresponding Young's moduli obtained by conventional mechanical testing (r = 0.89, p < 0.001). Preliminary in vivo tests also showed that the change of soft tissue stiffness with and without the contraction of the underlying muscles in the hand could be differentiated by the current measurement. This system may have broad applications in tissue assessment and characterization where alterations of mechanical properties are involved, in particular with the potential of noncontact micro-indentation for tissues.

Spherical indentation of soft matter beyond the Hertzian regime: numerical and experimental validation of hyperelastic models

Abstract: The lack of practicable nonlinear elastic contact models frequently compels the inappropriate use of Hertzian models in analyzing indentation data and likely contributes to inconsistencies associated with the results of biological atomic force microscopy measurements. We derived and validated with the aid of the finite element method force-indentation relations based on a number of hyperelastic strain energy functions. The models were applied to existing data from indentation, using microspheres as indenters, of synthetic rubber-like gels, native mouse cartilage tissue, and engineered cartilage. For the biological tissues, the Fung and single-term Ogden models achieved the best fits of the data while all tested hyperelastic models produced good fits for the synthetic gels. The Hertz model proved to be acceptable for the synthetic gels at small deformations (strain < 0.05 for the samples tested), but not for the biological tissues. Although this finding supports the generally accepted view that many soft materials can be assumed to be linear elastic at small deformations, the nonlinear models facilitate analysis of intrinsically nonlinear tissues and large-strain indentation behavior.

Harder than diamond: superior indentation strength of wurtzite BN and lonsdaleite.

Abstract: Recent indentation experiments indicate that wurtzite BN (w-BN) exhibits surprisingly high hardness that rivals that of diamond Here we unveil a novel two-stage shear deformation mechanism responsible for this unexpected result We show by first-principles calculations that large normal compressive pressures under indenters can compel w-BN into a stronger structure through a volume-conserving bond-flipping structural phase transformation during indentation which produces significant enhancement in its strength, propelling it above diamond's We further demonstrate that the same mechanism also works in lonsdaleite (hexagonal diamond) and produces superior indentation strength that is 58% higher than the corresponding value of diamond, setting a new record

Indentation techniques for evaluating the fracture toughness of biomaterials and hard tissues

Abstract: Indentation techniques for assessing fracture toughness are attractive due to the simplicity and expediency of experiments, and because they potentially allow the characterization of both local and bulk fracture properties. Unfortunately, rarely have such techniques been proven to give accurate fracture toughness values. This is a concern, as such techniques are seeing increasing usage in the study of biomaterials and biological hard tissues. Four available indentation techniques are considered in the present article: the Vickers indentation fracture (VIF) test, the cube corner indentation fracture (CCIF) test, the Vickers crack opening displacement (VCOD) test and the interface indentation fracture (IIF) test. Each technique is discussed in terms of its suitability for assessing the absolute and relative toughness of materials or material interfaces based on the published literature on the topic. In general, the VIF and CCIF techniques are found to be poor for quantitatively evaluating toughness of any brittle material, and the large errors involved (approximately +/-50%) make their applicability as comparative techniques limited. Indeed, indentation toughness values must differ by at least by a factor of three to conclude a significant difference in actual toughness. Additionally, new experimental results are presented on using the CCIF test to evaluate the fracture resistance of human cortical bone. Those new results indicate that inducing cracking is difficult, and that the cracks that do form are embedded in the plastic zone of the indent, invalidating the use of linear elastic fracture mechanics based techniques for evaluating the toughness associated with those cracks. The VCOD test appears to be a good quantitative method for some glasses, but initial results suggest there may be problems associated with applying this technique to other brittle materials. Finally, the IIF technique should only be considered a comparative or semi-quantitative technique for comparing material interfaces and/or the neighboring materials.

A practical guide for analysis of nanoindentation data.

Abstract: Mechanical properties of biological materials are increasingly explored via nanoindentation testing. This paper reviews the modes of deformation found during indentation: elastic, plastic, viscous and fracture. A scheme is provided for ascertaining which deformation modes are active during a particular indentation test based on the load–displacement trace. Two behavior maps for indentation are presented, one in the viscous–elastic–plastic space, concerning homogeneous deformation, and one in the plastic versus brittle space, concerning the transition to fracture behavior when the threshold for cracking is exceeded. Best-practice methods for characterizing materials are presented based on which deformation modes are active; the discussion includes both nanoindentation experimental test options and appropriate methods for analyzing the resulting data.

Characterization of the mechanical properties of a dermal equivalent compared with human skin in vivo by indentation and static friction tests

Abstract: Background/aims: The study of changes in skin structure with age is becoming all the more important with the increase in life. The atrophy that occurs during aging is accompanied by more profound changes, with a loss of organization within the elastic collagen network and alterations in the basal elements. The aim of this study is to present a method to determine the mechanical properties of total human skin in vivo compared with dermal equivalents (DEs) using indentation and static friction tests. Methods: A new bio-tribometer working at a low contact pressure for the characterization the mechanical properties of the skin has been developed. This device, based on indentation and static friction tests, also allows to characterize the skin in vivo and reconstructed DEs in a wide range of light contact forces, stress and strain. Results: This original bio-tribometer shows the ability to assess the skin elasticity and friction force in a wide range of light normal load (0.5–2 g) and low contact pressure (0.5–2 kPa). The results obtained by this approach show identical values of the Young's modulus E* and the shear modulus G* of six DEs obtained from a 62-year-old subject (E*=8.5±1.74 kPa and G*=3.3±0.46 kPa) and in vivo total skin of 20 subjects aged 55 to 70 years (E*=8.3±2.1 kPa, G*=2.8±0.8 kpa).

Dynamic indentation on human skin in vivo: ageing effects

Abstract: Background/purpose: Knowledge of the mechanical properties of the human skin is very important for cosmetic and clinical research. Objective and quantitative measurements are essential to compare studies performed by different experimenters in different centres. The aim of this paper is to present a method to measure the viscoelastic properties of human skin in vivo using dynamic indentation. Methods: A complete device to assess the stiffness and damping of skin has been developed. The frequency and strain amplitude range from 10 to 60 Hz and from 1 to 10mm. Tests on pure elastic inert materials have been performed to validate the device. An in vivo study including dynamic indentation, suction test, hydration measurement and topographic analysis has been performed on 46 subjects aged from 18 to 70 years, divided into three groups. Results: Results on inert materials show the validity of the device developed. The mechanical behaviour of the skin can be described by a Kelvin–Voight model under dynamic indentation. A comparison with a suction test, hydration and topographic measurements shows that the stiffness and the damping measured by dynamic indentation correspond mainly to the natural tense state of the skin on the body due to the dermis. A weak correlation has been found between dynamic indentation and suction parameters. The complex modulus measured by dynamic indentation at 10 Hz frequency stress ranges from 7.2 � 2.1 kPa for the oldest group to 10.7 � 2.6 kPa for the youngest group. Conclusion: The device presented gives convincing results. The measurement of stiffness and damping complements the viscoelastic phenomenological parameters of the suction test.

Determining the elastic modulus and hardness of an ultra-thin film on a substrate using nanoindentation

Abstract: A data analysis procedure has been developed to estimate the contact area in an elastoplastic indentation of a thin film bonded to a substrate. The procedure can be used to derive the elastic modulus and hardness of the film from the indentation load, displacement, and contact stiffness data at indentation depths that are a significant fraction of the film thickness. The analysis is based on Yu’s elastic solution for the contact of a rigid conical punch on a layered half-space and uses an approach similar to the Oliver-Pharr method for bulk materials. The methodology is demonstrated for both compliant films on stiff substrates and the reverse combination and shows improved accuracy over previous methods.

Nanoindentation analysis as a two-dimensional tool for mapping the mechanical properties of complex surfaces

Abstract: Instrumented indentation (referred to as nanoindentation at low loads and low depths) has now become established for the single point characterization of hardness and elastic modulus of both bulk and coated materials. This makes it a good technique for measuring mechanical properties of homogeneous materials. However, many composite materials are composed of material phases that cannot be examined in bulk form ex situ (e.g., carbides in a ferrous matrix, calcium silicate hydrates in cements, etc.). The requirement for in situ analysis and characterization of chemically complex phases obviates conventional mechanical testing of large specimens representative of these material components. This paper will focus on new developments in the way that nanoindentation can be used as a two-dimensional mapping tool for examining the properties of constituent phases independently of each other. This approach relies on large arrays of nanoindentations (known as grid indentation) and statistical analysis of the resulting data.

Nanoindentation analysis as a two-dimensional tool for mapping the mechanical properties of complex surfaces

Abstract: Instrumented indentation (referred to as nanoindentation at low loads and low depths) has now become established for the single point characterization of hardness and elastic modulus of both bulk and coated materials. This makes it a good technique for measuring mechanical properties of homogeneous materials. However, many composite materials are composed of material phases that cannot be examined in bulk form ex situ (e.g., carbides in a ferrous matrix, calcium silicate hydrates in cements, etc.). The requirement for in situ analysis and characterization of chemically complex phases obviates conventional mechanical testing of large specimens representative of these material components. This paper will focus on new developments in the way that nanoindentation can be used as a two-dimensional mapping tool for examining the properties of constituent phases independently of each other. This approach relies on large arrays of nanoindentations (known as grid indentation) and statistical analysis of the resulting data.

Review: Indentation size effect, indentation cracks and microhardness measurement of brittle crystalline solids – some basic concepts and trends

Abstract: Indentation size effect, indentation cracks and microhardness measurement of some brittle crystals are reviewed against the background of the existing concepts of indentation deformation of crystalline solids. Several approaches reported in the literature devoted to relationships between applied indentation test load P and indentation diagonal length d are applied to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds. Using typical examples of normal and reverse ISE it is shown that the indentation induced cracking model does not give load-independent hardness and the final expression describing the experimental data for various compounds is essentially another form of the Meyer law. Analysis of experiment data on crack lengths and indentation diagonals for different indentation loads suggests that the origin of ISE is associated with the processes of formation of indentation cracks following the general concepts of fracture mechanics. The load-independent hardness H0 may be determined reliably from plots of P /d against d of the proportional resistance model or of HV against 1/d as predicted by strain gradient plasticity theories. It was found that the load-independent hardness of depends on crystal orientation and state of the indented surface. Finally, some comments on determination of fracture toughness and brittle index of crystals are made. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Viscoelastic and poroelastic mechanical characterization of hydrated gels

Abstract: Measurement of the mechanical behavior of hydrated gels is challenging due to a relatively small elastic modulus and dominant time-dependence compared with traditional engineering materials. Here polyacrylamide gel materials are examined using different techniques (indentation, unconfined compression, dynamic mechanical analysis) at different length-scales and considering both viscoelastic and poroelastic mechanical frameworks. Elastic modulus values were similar for nanoindentation and microindentation, but both indentation techniques overestimated elastic modulus values compared to homogeneous loading techniques. Hydraulic and intrinsic permeability values from microindentation tests, deconvoluted using a poroelastic finite element model, were consistent with literature values for gels of the same composition. Although elastic modulus values were comparable for viscoelastic and poroelastic analyses, time-dependent behavior was length-scale dependent, supporting the use of a poroelastic, instead of a viscoelastic, framework for future Studies of gel mechanical behavior under indentation.

Evolution of metastable phases in silicon during nanoindentation: mechanism analysis and experimental verification

Abstract: This paper explores the evolution mechanisms of metastable phases during the nanoindentation on monocrystalline silicon. Both the molecular dynamics (MD) and the in situ scanning spreading resistance microscopy (SSRM) analyses were carried out on Si(100) orientation, and for the first time, experimental verification was achieved quantitatively at the same nanoscopic scale. It was found that under equivalent indentation loads, the MD prediction agrees extremely well with the result experimentally measured using SSRM, in terms of the depth of the residual indentation marks and the onset, evolution and dimension variation of the metastable phases, such as β-Sn. A new six-coordinated silicon phase, Si-XIII, transformed directly from Si-I was discovered. The investigation showed that there is a critical size of contact between the indenter and silicon, beyond which a crystal particle of distorted diamond structure will emerge in between the indenter and the amorphous phase upon unloading.

Local Membrane Mechanics of Pore-Spanning Bilayers

Abstract: The mechanical behavior of lipid bilayers spanning the pores of highly ordered porous silicon substrates was scrutinized by local indentation experiments as a function of surface functionalization, lipid composition, solvent content, indentation velocity, and pore radius. Solvent-containing nano black lipid membranes (nano-BLMs) as well as solvent-free pore-spanning bilayers were imaged by fluorescence and atomic force microscopy prior to force curve acquisition, which allows distinguishing between membrane-covered and uncovered pores. Force indentation curves on pore-spanning bilayers attached to functionalized hydrophobic porous silicon substrates reveal a predominately linear response that is mainly attributed to prestress in the membranes. This is in agreement with the observation that indentation leads to membrane lysis well below 5% area dilatation. However, membrane bending and lateral tension dominate over prestress and stretching if solvent-free supported membranes obtained from spreading giant liposomes on hydrophilic porous silicon are indented. An elastic regime diagram is presented that readily allows determining the dominant contribution to the mechanical response upon indentation as a function of load and pore radius.

Spatial and temporal variations of mechanical properties and mineral content of the external callus during bone healing

Abstract: After bone fracture, various cellular activities lead to the formation of different tissue types, which form the basis for the process of secondary bone healing. Although these tissues have been quantified by histology, their material properties are not well understood. Thus, the aim of this study is to correlate the spatial and temporal variations in the mineral content and the nanoindentation modulus of the callus formed via intramembranous ossification over the course of bone healing. Midshaft tibial samples from a sheep osteotomy model at time points of 2, 3, 6 and 9 weeks were employed. PMMA embedded blocks were used for quantitative back scattered electron imaging and nanoindentation of the newly formed periosteal callus near the cortex. The resulting indentation modulus maps show the heterogeneity in the modulus in the selected regions of the callus. The indentation modulus of the embedded callus is about 6 GPa at the early stage. At later stages of mineralization, the average indentation modulus reaches 14 GPa. There is a slight decrease in average indentation modulus in regions distant to the cortex, probably due to remodelling of the peripheral callus. The spatial and temporal distribution of mineral content in the callus tissue also illustrates the ongoing remodelling process observed from histological analysis. Most interestingly the average indentation modulus, even at 9 weeks, remains as low as 13 GPa, which is roughly 60% of that for cortical sheep bone. The decreased indentation modulus in the callus compared to cortex is due to the lower average mineral content and may be perhaps also due to the properties of the organic matrix which might be different from normal bone.

Importance of surface preparation on the nano-indentation stress-strain curves measured in metals

Abstract: In this work, we investigated experimentally the various factors influencing the extraction of indentation stress-strain curves from spherical nanoindentation on metal samples using two different tip radii. In particular, we focused on the effects of (i) the surface preparation techniques used, (ii) the presence of a surface oxide layer, and (iii) the occurrence of pop-ins at the elastic-plastic transition on our newly developed data analysis methods for extracting reliable indentation stress-strain curves. Rough mechanical polishing was shown to introduce a large scatter in the measured indentation yield strengths, whereas electropolishing or vibropolishing produced consistent results reflective of the pristine sample. The data analysis techniques used were able to discard the portions of the raw data affected by a thin oxide layer, present on most metal surfaces, and yield reasonable indentation stress-strain curves. Experiments with different indenter tip radii on annealed and cold-worked samples indicated that pop-ins are caused by delayed nucleation of dislocations in the sample under the indenter.

Indentation of bone tissue: a short review

Abstract: IntroductionBone is a highly hierarchical natural composite material,which mechanical properties are investigated from thephysiological elastic behavior up to impact or fatiguedamage accumulation responsible for traumatic or stressfractures. Each hierarchical level of organization contrib-utes to the global mechanical response of a bone structure:– The mineralized collagen fibril (MCF, 200 nm)– The lamella (2–7 μm)– The bone structural unit (BSU, 60 μm)– Bone tissue, cortical shell, or trabeculae (100–3,000 μm)– Trabecular bone (TB, mm)– Organ (cm)Bone matrix quality becomes a central focus in under-standing the etiology of fractures in diseases such asosteoporosis. Macroscopic indentation was adopted in thefirst half of the 20th century to investigate hardness of boneat the tissue level (compact and trabecular) and wasextended to micro- and nano-indentation in the past 10 yearsto evaluate specific mechanical properties of bone structuralunits and single lamellae, respectively. Over this period oftime, more than 375 papers or reviews were published(Scopus, “*indentation and bone,” June 23rd 2008).Consequently, the objective of this paper is to review therecent progress of indentation techniques to evaluate themechanical properties of human bone at these intermediatelevels of organization.Materials and methodsIndentationIndentation consists in pressing a hard tip with a knownforce into a semi-infinite half-space and measuring directlyor indirectly the contact area. In the classical hardness testperformed at the macroscopic or microscopic level, thecontact area is estimated optically from the imprint createdby the tip on the material and leads to the definition ofhardness as the force divided by this area. The mostcommon hardness measuring indenters are sphere (Brinell,Rockwell), four-sided pyramid (Vickers), and asymmetricpyramid (Knoop).Recent depth-sensing technologies allow for measure-ment of the tip displacement during the indentation processof a semi-infinite half-space with micro- and even nano-precision. Indirect estimation of the contact area is obtainedby preliminary calibration of the tip shape and systemcompliance. Shallow indentation depths down to 100 nmallow for spatial resolution of the measurements in themicron range, and the sample position is typically con-trolled by high-precision motorized tables or piezoelectricscanners. Micro- and nano-indentation tips are often madeof diamond and can be found in spherical, conical, andmost commonly, three-sided pyramidal (Berkovich) shapes.The blunted extremity of the tip has a radius of approxi-mately 100 nm. Spherical tips minimize plastic deformationand damage but are difficult to manufacture, flat puncheslead to high stress concentrations, conical tips have an axialsymmetry that remains in the assumption of most theoret-

Correlation between phase evolution, mechanical properties and instrumented indentation response of TiB2-based ceramics

Abstract: In densifying non-oxide high temperature ceramics, like titanium di-boride (TiB2), the type and amount of sinter-aid critically determine the microstructural developments and consequently the mechanical properties. In this perspective, the present work is carried out to assess the feasibility whether MoSi2 addition (up to 10 wt.%) can potentially improve the mechanical properties (hardness, fracture toughness, flexural strength), while enhancing the densification behaviour of TiB2. In order to answer such an important issue and to understand the mechanisms contributing to the variations in mechanical properties, we have evaluated sharp instrumented indentation response (2 N load) of a range of hot pressed TiB2–MoSi2 compositions. In addition, the Vickers indentation data obtained at macro load (up to 100 N) are also analyzed. Our experimental results reveal that the addition of only 2.5 wt.% MoSi2 to TiB2 results in the attainment of high sinter density (>99% ρth), after hot pressing at 1700 °C. The dense TiB2–2.5 wt.% MoSi2 composite composition has been found to possess a good combination of mechanical properties, including high hardness (Hv5∼30 GPa) and moderate fracture toughness (∼6 MPa m1/2). Furthermore, the four-point flexural strength values vary in the range of 370–400 MPa, with the maximum value for 2.5 wt.% MoSi2 containing composite. Interestingly, an increase in the additive (MoSi2) content above 5 wt.% degrades the mechanical properties. The degradation in mechanical properties has been attributed to the presence of secondary phases (Ti5Si3, Mo5Si3) and its effect has been critically analyzed. The mechanical response data, recorded using depth sensing instrumented Vickers indenter has been analyzed in the light of the elastic/plastic work done, and the elastic modulus (E) values, as computed from the initial slopes of unloading curves, have been found to vary in the range of 460–500 GPa. Additionally, the analysis of macro Vickers hardness measurements reveal ‘indentation-size effect’, which has been discussed in terms of mechanical response at the indented zone, and in correlation with the material properties.

Flexural Strength, Fatigue Life, and Stress-Induced Phase Transformation Study of Y-TZP Dental Ceramic

Abstract: Objectives: Yttria partially-stabilized zirconia polycrystalline (Y-TZP) has been the subject of extensive research because of its high strength and toughness. The aim of this study was to evaluate the biaxial flexural strength, fatigue life, and to investigate in more detail on single cycle specimens, the pressure-induced phase transformation of a Y-TZP dental ceramic using Raman microspectroscopy. Materials and Methods: Thirty standardized discs (15 x 1.2 mm(2)) were used to examine the biaxial flexural strength (ISO 6872 standard) using a Dartec HC10 Servohydraulic testing machine (Zwick Ltd., UK). The specimens were also submitted to Vickers hardness (on polished and as-received surfaces within the same specimen) and dynamic fatigue test. The initial bulk phases were examined via X-ray diffraction and the local phase transformations that occurred in the zirconia induced by the various Vickers indentation loads (20-50 kg) were examined via Raman microspectroscopy on single cycle specimens. The fracture surface after biaxial flexural testing was also examined via Raman spectroscopy. Results: The Cercon specimens tested had flexural strength and Weibull modulus (m) of similar to 823.3 (+/- 114.7) MPa and 8.3, respectively. As-received surfaces (1378.7 +/- 51.8 Hv) had slightly higher hardness value compared with polished surfaces (1354.33 +/- 50.9 Hv); however, two-way analysis of variance showed no significant difference in hardness values between polished and as-received surfaces (P > 0.05). Additionally, the specimens survived to 5 x 10(5) cycles when using a load of 70% of the mean biaxial flexural strength or lower. Raman microspectroscopy showed transformation of tetragonal to cubic and monoclinic phases within the indentation area. The fraction of monoclinic phase showed only limited variation with load or distance from the center to indentation edge. The level of cubic phase, however, was greatest at the indentation center. Transformation to cubic phase was observed on the lower surfaces (tension side) of fractured specimens. It was also observed near the specimen center exposed upon fracture. In the latter region an increase in monoclinic phase was additionally observed. Further work will be carried out using Raman microspectroscopy to assess the effect of fatigue on phase transformations. Conclusion: The zirconia based ceramic has mechanical properties that may allow it to withstand the loading found in posterior areas. Transformation toughening was found when high loads impacted on the surface of zirconia. However it should be born in mind that this work was not carried out on veneered specimens, which exhibit different failure modes. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 88B: 366-377, 2009

Laser damage precursors in fused silica

Abstract: There is a longstanding, and largely unexplained, correlation between the laser damage susceptibility of optical components and both the surface quality of the optics, and the presence of near surface fractures in an optic. In the present work, a combination of acid leaching, acid etching, and confocal time resolved photoluminescence (CTP) microscopy has been used to study laser damage initiation at indentation sites. The combination of localized polishing and variations in indentation loads allows one to isolate and characterize the laser damage susceptibility of densified, plastically flowed and fractured fused silica. The present results suggest that: 1) laser damage initiation and growth are strongly correlated with fracture surfaces, while densified and plastically flowed material is relatively benign, and 2) fracture events result in the formation of an electronically defect rich surface layer which promotes energy transfer from the optical beam to the glass matrix.

Atomic force microscopy and indentation force measurement of bone.

Abstract: This review is summarizing the results obtained from atomic force microscopy (AFM) and nanoindentation experiments to date. The combination of both techniques is especially powerful. It allows to carefully choose indentation locations as well as the post-hoc analysis of the created indents, and hence the possibility to assess the properties of microstructural elements of bonessue. In addition, AFM has improved our understanding of bone ultrastructure and force spectroscopy experiments have led to the discovery of a molecular self-healing effect of bone that may be based on a small fraction of unstructured proteins. Nanoindentation measurements on bone, pose inherent problems since bone is an anisotropic solid showing elastic, viscoelastic, and time-dependent plastic behavior. Hence, derived parameters such as elastic modulus and hardness are to some extent dependent on measurement protocols. However, the development of extensions to the Oliver-Pharr method, being the most widely used analysis method, as well as novel dynamic testing techniques could improve the situation. Nanoindentation is widely used to study bone tissue and some important principal findings have been reported to date. These are presented here together with specific results from nanoindentation experiments of human and animal bones and tables are presented collating the data that can be found in the literature to date.