Reference point indentation is not indicative of whole mouse bone measures of stress intensity fracture toughness.
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ABSTRACT:
SUBMITTER: Carriero A
PROVIDER: S-EPMC4228060 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Reference point indentation (RPI) is a microindentation technique involving 20 cycles of loading in "force-control" that can directly assess a patient׳s bone tissue properties. Even though preliminary clinical studies indicate a capability for fracture discrimination, little is known about what mechanical behavior the various RPI properties characterize and how these properties relate to traditional mechanical properties of bone. To address this, the present study investigated the sensitivity of RPI properties to anatomical location and tissue organization as well as examined to what extent RPI measurements explain the intrinsic mechanical properties of human cortical bone. Multiple indents with a target force of 10N were done in 2 orthogonal directions (longitudinal and transverse) per quadrant (anterior, medial, posterior, and lateral) of the femoral mid-shaft acquired from 26 donors (25-101 years old). Additional RPI measurements were acquired for 3 orthogonal directions (medial only). Independent of age, most RPI properties did not vary among these locations, but they did exhibit transverse isotropy such that resistance to indentation is greater in the longitudinal (axial) direction than in the transverse direction (radial or circumferential). Next, beam specimens (~2mm×5mm×40mm) were extracted from the medial cortex of femoral mid-shafts, acquired from 34 donors (21-99 years old). After monotonically loading the specimens in three-point bending to failure, RPI properties were acquired from an adjacent region outside the span. Indent direction was orthogonal to the bending axis. A significant inverse relationship was found between resistance to indentation and the apparent-level mechanical properties. Indentation distance increase (IDI) and a linear combination of IDI and the loading slope, averaged over cycles 3 through 20, provided the best explanation of the variance in ultimate stress (r(2)=0.25, p=0.003) and toughness (r(2)=0.35, p=0.004), respectively. With a transverse isotropic behavior akin to tissue hardness and modulus as determined by micro- and nano-indentation and a significant association with toughness, RPI properties are likely influenced by both elastic and plastic behavior of bone tissue.
| S-EPMC4112765 | biostudies-literature
Project description:Reference point indentation (RPI) was developed as a novel method to assess mechanical properties of bone in vivo, yet it remains unclear what aspects of bone dictate changes/differences in RPI-based parameters. The main RPI parameter, indentation distance increase (IDI), has been proposed to be inversely related to the ability of bone to form/tolerate damage. The goal of this work was to explore the relationshipre-intervention RPI measurebetween RPI parameters and traditional mechanical properties under varying experimental conditions (drying and ashing bones to increase brittleness, demineralizing bones and soaking in raloxifene to decrease brittleness). Beams were machined from cadaveric bone, pre-tested with RPI, subjected to experimental manipulation, post-tested with RPI, and then subjected to four-point bending to failure. Drying and ashing significantly reduced RPI's IDI, as well as ultimate load (UL), and energy absorption measured from bending tests. Demineralization increased IDI with minimal change to bending properties. Ex vivo soaking in raloxifene had no effect on IDI but tended to enhance post-yield behavior at the structural level. These data challenge the paradigm of an inverse relationship between IDI and bone toughness, both through correlation analyses and in the individual experiments where divergent patterns of altered IDI and mechanical properties were noted. Based on these results, we conclude that RPI measurements alone, as compared to bending tests, are insufficient to reach conclusions regarding mechanical properties of bone. This proves problematic for the potential clinical use of RPI measurements in determining fracture risk for a single patient, as it is not currently clear that there is an IDI, or even a trend of IDI, that can determine clinically relevant changes in tissue properties that may contribute to whole bone fracture resistance.
| S-EPMC4862890 | biostudies-literature
Project description:Here we describe a novel, hand-held reference point indentation (RPI), instrument that is designed for clinical measurements of bone material properties in living patients. This instrument differs from previous RPI instruments in that it requires neither a reference probe nor removal of the periosteum that covers the bone, thus significantly simplifying its use in patient testing. After describing the instrument, we discuss five guidelines for optimal and reproducible results. These are: (1) the angle between the normal to the surface and the axis of the instrument should be less than 10°, (2) the compression of the main spring to trigger the device must be performed slowly (>1 s), (3) the probe tip should be sharper than 10 μm; however, a normalized parameter with a calibration phantom can correct for dull tips up to a 100 μm radius, (4) the ambient room temperature should be between 4 °C and 37 °C, and (5) the effective mass of the bone or material under test must exceed 1 kg, or if under 1 kg, the specimen should be securely anchored in a fixation device with sufficient mass (which is not a requirement of previous RPI instruments). Our experience is that a person can be trained with these guidelines in about 5 min and thereafter obtain accurate and reproducible results. The portability, ease of use, and minimal training make this instrument suitable to measure bone material properties in a clinical setting.
| S-EPMC3331866 | biostudies-other
Project description:Greater understanding of the determinants of skeletal fragility is highly sought due to the great burden that bone affecting diseases and fractures have on economies, societies and health care systems. Being a complex, hierarchical composite of collagen type-I and non-stoichiometric substituted hydroxyapatite, bone derives toughness from its organic phase. In this study, we tested whether early observations that a strong correlation between bone collagen integrity measured by thermomechanical methods and work to fracture exist in a more general and heterogeneous sampling of the population. Neighboring uniform specimens from an established, highly characterized and previously published collection of human cortical bone samples (femur mid-shaft) were decalcified in EDTA. Fifty-four of the original 62 donors were included (26 male and 28 females; ages 21-101?years; aging, osteoporosis, diabetes and cancer). Following decalcification, bone collagen was tested using hydrothermal isometric tension (HIT) testing in order to measure the collagen's thermal stability (denaturation temperature, Td) and network connectivity (maximum rate of isometric tension generation; Max.Slope). We used linear regression and general linear models (GLMs) with several explanatory variables to determine whether relationships between HIT parameters and generally accepted bone quality factors (e.g., cortical porosity, pentosidine content [pen], pyridinoline content [pyd]), age, and measures of fracture toughness (crack initiation fracture toughness, Kinit, and total energy release/dissipation rate evaluated at the point of unstable fast fracture, J-int) were significant. Bone collagen connectivity (Max.Slope) correlated well with the measures of fracture toughness (R2?=?24-35%), and to a lesser degree with bound water fraction (BW; R2?=?7.9%) and pore water fraction (PW; R2?=?9.1%). Significant correlations with age, apparent volumetric bone mineral density (vBMD), and mature enzymatic [pyd] and non-enzymatic collagen crosslinks [pen] were not detected. GLMs found that Max.Slope and vBMD (or BW), with or without age as additional covariate, all significantly explained the variance in Kinit (adjusted-R2?=?36.7-49.0%). Also, the best-fit model for J-int (adjusted-R2?=?35.7%) included only age and Max.Slope as explanatory variables with Max.Slope contributing twice as much as age. Max.Slope and BW without age were also significant predictors of J-int (adjusted-R2?=?35.5%). In conclusion, bone collagen integrity as measured by thermomechanical methods is a key factor in cortical bone fracture toughness. This study further demonstrates that greater attention should be paid to degradation of the overall organic phase, rather than a specific biomarker (e.g. [pen]), when seeking to understand elevated fracture rates in aging and disease.
| S-EPMC6360115 | biostudies-literature
Project description:The influence of ageing on the fracture mechanics of cortical bone tissue is well documented, though little is known about if and how related material properties are further affected in two of the most prominent musculoskeletal diseases, osteoporosis and osteoarthritis (OA). The femoral neck, in close proximity to the most pertinent osteoporotic fracture site and near the hip joint affected by osteoarthritis, is a site of particular interest for investigation. We have recently shown that Reference Point micro-Indentation (RPI) detects differences between cortical bone from the femoral neck of healthy, osteoporotic fractured and osteoarthritic hip replacement patients. RPI is a new technique with potential for in vivo bone quality assessment. However, interpretation of RPI results is limited because the specific changes in bone properties with pathology are not well understood and, further, because it is not conclusive what properties are being assessed by RPI. Here, we investigate whether the differences previously detected between healthy and diseased cortical bone from the femoral neck might reflect changes in fracture toughness. Together with this, we investigate which additional properties are reflected in RPI measures. RPI (using the Biodent device) and fracture toughness tests were conducted on samples from the inferomedial neck of bone resected from donors with: OA (41 samples from 15 donors), osteoporosis (48 samples from 14 donors) and non age-matched cadaveric controls (37 samples from 10 donoros) with no history of bone disease. Further, a subset of indented samples were imaged using micro-computed tomography (3 osteoporotic and 4 control samples each from different donors) as well as fluorescence microscopy in combination with serial sectioning after basic fuchsin staining (7 osteoporotic and 5 control samples from 5 osteoporotic and 5 control donors). In this study, the bulk indentation and fracture resistance properties of the inferomedial femoral neck in osteoporotic fracture, severe OA and control bone were comparable (p > 0.05 for fracture properties and <10% difference for indentation) but fracture toughness reduced with advancing age (7.0% per decade, r = -0.36, p = 0.029). Further, RPI properties (in particular, the indentation distance increase, IDI) showed partial correlation with fracture toughness (r = -0.40, p = 0.023) or derived elastic modulus (r = -0.40, p = 0.023). Multimodal indent imaging revealed evidence of toughening mechanisms (i.e. crack deflection, bridging and microcracking), elastoplastic response (in terms of the non-conical imprint shape and presence of pile-up) and correlation of RPI with damage extent (up to r = 0.79, p = 0.034) and indent size (up to r = 0.82, p < 0.001). Therefore, crack resistance, deformation resistance and, additionally, micro-structure (porosity: r = 0.93, p = 0.002 as well as pore proximity: r = -0.55, p = 0.027 for correlation with IDI) are all contributory to RPI. Consequently, it becomes clear that RPI measures represent a multitude of properties, various aspects of bone quality, but are not necessarily strongly correlated to a single mechanical property. In addition, osteoporosis or osteoarthritis do not seem to further influence fracture toughness of the inferomedial femoral neck beyond natural ageing. Since bone is highly heterogeneous, whether this finding can be extended to the whole femoral neck or whether it also holds true for other femoral neck quadrants or other material properties remains to be shown.
| S-EPMC5619645 | biostudies-literature
Project description:Fracture risk does not solely depend on strength but also on fracture toughness; ie, the ability of bone material to resist crack initiation and propagation. Because resistance to crack growth largely depends on bone properties at the tissue level, including collagen characteristics, current X-ray based assessment tools may not be suitable to identify age-related, disease-related, or treatment-related changes in fracture toughness. To identify useful clinical surrogates that could improve the assessment of fracture resistance, we investigated the potential of (1)H nuclear magnetic resonance spectroscopy (NMR) and reference point indentation (RPI) to explain age-related variance in fracture toughness. Harvested from cadaveric femurs (62 human donors), single-edge notched beam (SENB) specimens of cortical bone underwent fracture toughness testing (R-curve method). NMR-derived bound water showed the strongest correlation with fracture toughness properties (r = 0.63 for crack initiation, r = 0.35 for crack growth, and r = 0.45 for overall fracture toughness; p < 0.01). Multivariate analyses indicated that the age-related decrease in different fracture toughness properties were best explained by a combination of NMR properties including pore water and RPI-derived tissue stiffness with age as a significant covariate (adjusted R(2) = 53.3%, 23.9%, and 35.2% for crack initiation, crack growth, and overall toughness, respectively; p < 0.001). These findings reflect the existence of many contributors to fracture toughness and emphasize the utility of a multimodal assessment of fracture resistance. Exploring the mechanistic origin of fracture toughness, glycation-mediated nonenzymatic collagen crosslinks and intracortical porosity are possible determinants of bone fracture toughness and could explain the sensitivity of NMR to changes in fracture toughness. Assuming fracture toughness is clinically important to the ability of bone to resist fracture, our results suggest that improvements in fracture risk assessment could potentially be achieved by accounting for water distribution (quantitative ultrashort echo time magnetic resonance imaging) and by a local measure of tissue resistance to indentation, RPI.
| S-EPMC4478129 | biostudies-literature
Project description:The assessment of fracture risk often relies primarily on measuring bone mineral density, thereby accounting for only a single pathology: the loss of bone mass. However, bone's ability to resist fracture is a result of its biphasic composition and hierarchical structure that imbue it with high strength and toughness. Reference point indentation (RPI) testing is designed to directly probe bone mechanical behavior at the microscale in situ, although it remains unclear which aspects of bone composition and structure influence the results at this scale. Therefore, our goal in this study was to investigate factors that contribute to bone mechanical behavior measured by cyclic reference point indentation, impact reference point indentation, and three-point bending. Twenty-eight female cadavers (ages 57-97) were subjected to cyclic and impact RPI in parallel at the unmodified tibia mid-diaphysis. After RPI, the middiaphyseal tibiae were removed, scanned using micro-CT to obtain cortical porosity (Ct.Po.) and tissue mineral density (TMD), then tested using three-point bending, and lastly assayed for the accumulation of advanced glycation end-products (AGEs). Both the indentation distance increase from cyclic RPI (IDI) and bone material strength index from impact RPI (BMSi) were significantly correlated with TMD (r=-0.390, p=0.006; r=0.430, p=0.002; respectively). Accumulation of AGEs was significantly correlated with IDI (r=0.281, p=0.046), creep indentation distance (CID, r=0.396, p=0.004), and BMSi (r=-0.613, p<0.001). There were no significant relationships between tissue TMD or AGEs accumulation with the quasi-static material properties. Toughness decreased with increasing tissue Ct.Po. (r=-0.621, p<0.001). Other three-point bending measures also correlated with tissue Ct.Po. including the bending modulus (r=-0.50, p<0.001) and ultimate stress (r=-0.56, p<0.001). The effects of Ct.Po. on indentation were less pronounced with IDI (r=0.290, p=0.043) and BMSi (r=-0.299, p=0.037) correlated modestly with tissue Ct.Po. These results suggest that RPI may be sensitive to bone quality changes relating to collagen.
| S-EPMC4862905 | biostudies-literature
Project description:Amplification in toughness and balance with stiffness and strength are fundamental characteristics of biological structural composites, and a long sought-after objective for engineering design. Nature achieves these properties through a combination of multiscale key features. Yet, emulating all these features into synthetic de novo materials is rather challenging. Here, we fine-tune manual lamination, to implement a newly designed bone-inspired structure into fiber-reinforced composites. An integrated approach, combining numerical simulations, ad hoc manufacturing techniques, and testing, yields a novel composite with enhanced fracture toughness and balance with stiffness and strength, offering an optimal lightweight material solution with better performance than conventional materials such as metals and alloys. The results also show how the new design significantly boosts the fracture toughness compared to a classic laminated composite, made of the same building blocks, also offering an optimal tradeoff with stiffness and strength. The predominant mechanism, responsible for the enhancement of fracture toughness in the new material, is the continuous deviation of the crack from a straight path, promoting large energy dissipation and preventing a catastrophic failure. The new insights resulting from this study can guide the design of de novo fiber-reinforced composites toward better mechanical performance to reach the level of synergy of their natural counterparts.
| S-EPMC6395722 | biostudies-literature
Project description:Brushite cements are promising bone regeneration materials with limited biological and mechanical properties. Here, we engineer a mechanically improved brushite-collagen type I cement with enhanced biological properties by use of chiral chemistry; d- and l-tartaric acid were used to limit crystal growth and increase the mechanical properties of brushite-collagen cements. The impact of the chiral molecules on the cements was examined with Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A 3-point bend test was utilized to study the fracture toughness, and cell attachment and morphology studies were carried out to demonstrate biocompatibility. XRD and SEM analyses showed that l-, but not d-tartaric acid, significantly restrained brushite crystal growth by binding to the {010} plane of the mineral and increased brushite crystal packing and the collagen interaction area. l-Tartaric acid significantly improved fracture toughness compared to traditional brushite by 30%. Collagen significantly enhanced cell morphology and focal adhesion expression on l-tartaric acid-treated brushite cements.
| S-EPMC7461128 | biostudies-literature
Project description:Reference point indentation (RPI) was developed to measure material-level mechanical properties of bone in vivo. Studies using RPI in vivo have discriminated between human subjects with previous skeletal fractures and those without and among dogs given different anti-remodeling drugs. Recently, this technology was extended to rats, providing the first in vivo data for rodents. The goal of the present study was to perform in vivo RPI measurements in mice, the most common animal model used to study bone. Twelve 16-week-old female C57BL/6 mice were subjected to RPI (three tests) on the anterior tibia, followed by a repeat test session on the contralateral limb 28 days later. A custom MATLAB program was used to derive several outcome parameters from RPI force-displacement curves: first cycle indentation distance (ID-1st), ID increase (IDI), total ID (TID), first cycle unloading slope (US-1st) and first cycle energy dissipation (ED-1st). Data within an individual were averaged across the three tests for each time point. Within-animal variation of all RPI parameters on day 1 ranged from 12.8 to 33.4% and from 14.1 to 22.4% on day 28. Between-animal variation on day 1 ranged from 11.4% to 22.8% and from 7.5% to 24.7% on day 28. At both time points, within- and between-animals, US-1st was the least variable parameter and IDI was most variable. All parameters were nonsignificantly lower at day 28 compared with day 1. These data are important to demonstrate the feasibility of collecting bone material property data longitudinally in mice and will inform the design of future studies in terms of statistical power and appropriate sample size considerations.
| S-EPMC4478874 | biostudies-other