Variation of nanomechanical properties of bone by gene mutation in the zebrafish

Bone Phenotyping Approaches in Human, Mice and Zebrafish - Expert Overview of the EU Cost Action GEMSTONE ("GEnomics of MusculoSkeletal traits TranslatiOnal NEtwork")

A synoptic overview of scientific methods applied in bone and associated research fields across species has yet to be published. Experts from the EU Cost Action GEMSTONE ("GEnomics of MusculoSkeletal Traits translational Network") Working Group 2 present an overview of the routine techniques as well as clinical and research approaches employed to characterize bone phenotypes in humans and selected animal models (mice and zebrafish) of health and disease. The goal is consolidation of knowledge and a map for future research. This expert paper provides a comprehensive overview of state-of-the-art technologies to investigate bone properties in humans and animals - including their strengths and weaknesses. New research methodologies are outlined and future strategies are discussed to combine phenotypic with rapidly developing -omics data in order to advance musculoskeletal research and move towards "personalised medicine".

Zebrafish as a model to study bone maturation: Nanoscale structural and mechanical characterization of age-related changes in the zebrafish vertebral column

Zebrafish (Danio rerio) is a useful model for understanding biomedical properties of bone and are widely employed in developmental and genetics studies. Here, we have studied the development of zebrafish vertebral bone at the nanoscale from adolescence (6 months), early adulthood (10 months) to mid-life (14 months). Characterization of the bone was conducted using energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and PeakForce QNM atomic force microscopy (AFM) techniques. SEM and AFM revealed a lamellar structure with mineralized collagen fibrils. There was a significant increase in the wall thickness from 6 to 10 months (76%) and 10 months to 14 months (26%), which is positively correlated with nanomechanical behavior. An increase in the Ca/P ratio was found which was also positively correlated with nanomechanical properties. The change in mechanical properties and Ca/P are similar to those expected in humans when transitioning from adolescence to mid-life. We suggest that zebrafish serve as a suitable model for further studies on age-related changes in bone ultrastructure.

Micro/Nanostructures and Mechanical Properties of Trabecular Bone in Ovariectomized Rats

Bone mechanical properties encompass both geometric and material factors, while the effects of estrogen deficiency on the material and structural characteristics of bone at micro- to nanoscales are still obscure. We performed a series of combined methodological experiments, including nanoindentation assessment of intrinsic material properties, atomic force microscopy (AFM) characterization of trabecular (Tb) nanostructure, and Tb microarchitecture and 2D BMD. At 15 weeks after surgery, we found significantly less Tb bone mineral density (BMD) at organ (-27%) and at tissue level (-12%), Tb bone volume fraction (-29%), Tb thickness (-14%), and Tb number (-17%) in ovariectomy (OVX) rats than in sham operated (SHAM) rats, while the structure model index (+91%) and Tb separation (+19%) became significantly greater. AFM images showed lower roughness Tb surfaces with loosely packed large nodular structures and less compacted interfibrillar space in OVX than in SHAM. However, no statistically significant changes were in the Tb intrinsic material properties-nanoindentation hardness, elastic modulus, and plastic deformation-nanoindentation depths, and residual areas. Therefore, estrogen deprivation results in a dramatic deterioration in Tb micro/nanoarchitectures, 3D volumetric BMD at both organ and tissue levels, and 2D BMD, but not in the nanomechanical properties of the trabeculae per se.

Comparison of structural, architectural and mechanical aspects of cellular and acellular bone in two teleost fish

The histological diversity of the skeletal tissues of fishes is impressive compared with that of other vertebrate groups, yet our understanding of the functional consequences of this diversity is limited. In particular, although it has been known since the mid-1800s that a large number of fish species possess acellular bones, the mechanical advantages and consequences of this structural characteristic – and therefore the nature of the evolution of this feature – remain unclear. Although several studies have examined the material properties of fish bone, these have used a variety of techniques and there have been no direct contrasts of acellular and cellular bone. We report on a comparison of the structural and mechanical properties of the ribs and opercula between two freshwater fish – the common carp Cyprinus carpio (a fish with cellular bone) and the tilapia Oreochromis aureus (a fish with acellular bone). We used light microscopy to show that the bones in both fish species exhibit poor blood supply and possess discrete tissue zones, with visible layering suggesting differences in the underlying collagen architecture. We performed identical micromechanical testing protocols on samples of the two bone types to determine the mechanical properties of the bone material of opercula and ribs. Our data support the consensus of literature values, indicating that Young’s moduli of cellular and acellular bones are in the same range, and lower than Young’s moduli of the bones of mammals and birds. Despite these similarities in mechanical properties between the bone tissues of the fish species tested here, cellular bone had significantly lower mineral content than acellular bone; furthermore, the percentage ash content and bone mineral density values (derived from micro-CT scans) show that the bone of these fishes is less mineralized than amniote bone. Although we cannot generalize from our data to the numerous remaining teleost species, the results presented here suggest that while cellular and acellular fish bone may perform similarly from a mechanical standpoint, there are previously unappreciated differences in the structure and composition of these bone types.

Mechanistic modeling of a nanoscratch test for determination of in situ toughness of bone

The objective of this study was to develop a nanoscratch technique that can be used to measure the in situ toughness of bone at micro/nanostructural levels. Among the currently possible techniques, the surface scratch test may be conducted on very small regions, thus exhibiting a potential in determining the in situ failure behavior of materials. To adapt such a technique for assessing bone toughness at the micro/nanostructural levels and for limited stocks in small animal bone models (e.g. zebra finish and mice), a simple but reasonably accurate mechanistic model for the nanoscratch test was developed in this study. This model was based on the assumption that the removal energy of the tissue required during the nanoscratch test is the manifestation of the in situ toughness and the shear flow stress during the removal process is a measure of the in situ strength of bone. In addition, the experimental methodologies were developed to determine the elastic recovery force and frictional coefficients between the scratch tip and bone specimens that are required by the model. Finally, the efficacy of the nanoscratch technique was verified by testing bone samples from control (wild type), mild, and severe osteogenesis imperfecta (OI) mice, which have a distinct degree of brittleness. The experimental results indicated that the nanoscratch test could sensitively detect the in situ brittleness and strength of bone from the animal models.

The use of nanoindentation for characterizing the properties of mineralized hard tissues: state-of-the art review

The use of nanoindentation to determine nanomechanical properties of mineralized tissues has been investigated extensively. A detailed, critical, and comprehensive review of this literature is the subject of the present work. After stating the motivation for the review, a succinct presentation of the challenges, advantages, and disadvantages of the various quasi-static nanoindentation test methods (to obtain elastic modulus, E, and hardness, H) and dynamic test methods (to obtain storage and loss moduli and/or loss/damping factor) is given in the form of a primer. Explicative summaries of literature reports on various intrinsic and extrinsic factors that significantly influence E and H, followed by 15 suggested topics for future research, are included additionally. This review is designed to present a compact guide to the principles of the nanoindentation technique and to emphasize considerations when determining material properties of mineralized tissues.

Measurement of fracture callus material properties via nanoindentation

In bone fracture healing, the extent to which the injured bone regains stability and strength depends on the mechanical properties of the tissues that are formed during healing. While many techniques have been used to quantify the overall mechanical behavior of fracture calluses, few data exist on the material properties of individual callus tissues. The overall goal of this study was to quantify these material properties. Nanoindentation was performed at multiple locations across thin (200mum), longitudinal sections of rat fracture callus at 35 days post fracture. Following indentation, sections were stained with alizarin red S and alcian blue to obtain semi-quantitative estimates of tissue mineral content and proteoglycan content, respectively. Indentation moduli varied over three orders of magnitude (0.61-1010MPa) throughout the callus. Much of this variation was due to the presence of multiple tissue types: the indentation moduli of granulation tissue, chondroid tissue and woven bone ranged 0.61-1.27MPa (median=0.99MPa), 1.39-4.42MPa (median=2.89MPa) and 26.92-1010.00MPa (median=132.00MPa), respectively. In regions of alizarin red staining, the indentation modulus was correlated (r=0.62, P=0.04) with stain intensity, suggesting a positive correlation between modulus and mineral content in woven bone. In addition, the indentation modulus of woven bone along the periosteal aspect of the cortex increased with distance from the fracture gap (P=0.004). These results demonstrate the usefulness of nanoindentation in characterizing the elastic properties of the heterogeneous mixture of tissues present in bone fracture callus.

Nanomechanical Properties of Tooth and Bone Revealed by Nanoindentation and AFM

In this paper, an overview on nanoindentation and its combination with AFM is presented with regard to current instrument technology and applications on dental and bony tissues. Nanoindentation has been a widely used technique to determine the mechanical properties such as nanohardness and Young’s modulus for nanostructured materials. Especially, atomic force microscopy (AFM) combined with nanoindentation, with the pit positions controlled accurately, become a powerful technique used to measure mechanical properties of materials on the nanoscale, and has been applied to the study of biological hard tissues, such as bone and tooth. Examples will be shown that significantly different nanohardness and modulus in the isolated domains within single enamel, the prisms, interprisms, the surrounding sheaths and the different parts of skeletal bone, could been distinguished, while such information was unable to be obtained by traditional methods of mechanical measurements.

An improved method for the measurement of mechanical properties of bone by nanoindentation

Nanoindentation is widely used to measure the mechanical properties of bio-tissues. However, viscoelastic effects during the nanoindentation are seldom considered rigorously, although they are in general very significant in bio-tissues. In this study, a recently developed method for correcting the viscoelastic effects during nanoindentation is applied to mice bone samples. This method is found to yield reliable elastic modulus and hardness results from forelimb and femur cortical bone samples of C57 BL/6N and ICR mice. The creep properties of the samples are also characterized by a novel procedure using nanoindentation. The measured mechanical properties correlate well with the calcium content of the bone samples.

Property variations in the prism and the organic sheath within enamel by nanoindentation

Atomic force microscopy (AFM) combined with nanoindentation technique was used to definitely, site-specifically, test the nanomechanical properties, including nanohardness and elastic modulus, of the isolated domains within single enamel, the prisms and the surrounding sheaths, of mature human maxillary third molars. In this way, it is for the first time that evident differences of nanomechanical properties were revealed between these domains. The nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms, respectively. Measuring the residual impressions with AFM supported the similar conclusion. The variations of mechanical properties in these domains are considered to be mainly relative to their different component and fibrils arrangement.

Hierarchical structural comparisons of bones from wild-type and liliput(dtc232) gene-mutated Zebrafish

The alterations of hierarchical structures of bone by gene mutation in the zebrafish, which is associated with abnormal bone mineralization and bone disease, were reported for the first time in this paper. Bone samples from the liliput(dtc232) (lil) mutants as well as normal controls were studied by polarized light microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and atomic force microscope (AFM). Light microscopy examinations reveal that the lil bone has asymmetric mineralization and much thinner bone wall. The SEM studies show a lot of microcracks in lil bone wall. And the plywood-like structure of the normal bone does not exist in the lil bone, which is confirmed by the measurements of polarized light microscope. Furthermore, the TEM investigations display the collagen fibrils with two typical diameters. For the thinner collagen fibrils, the diameter of lil bone is about twice larger than that of the wild-type bone. And for the thicker one, there is a small increase in diameter after mutation and the band periodicity of the lil bone is similar with that of wild-type bone, which is consistent with the result of AFM. The morphologies of the minerals revealed that the mutated mineral was in bigger size and the shape was irregular but not plate-shaped.