Polyhydroxybutyrate-based osteoinductive mineralized electrospun structures that mimic components and tissue interfaces of the osteon for bone tissue engineering.

Scaffolds for bone tissue engineering should enable regeneration of bone tissues with its native hierarchically organized extracellular matrix (ECM) and multiple tissue interfaces. To achieve this, inspired by the structure and properties of bone osteon, we fabricated polyhydroxybutyrate (PHB)-based mineralized electrospun fibrous scaffolds. After studying multiple PHB-based fibers, we chose 7%PHB/1%Gelatin fibers (PG) to fabricate mineralized fibers that mimic mineralized collagen fibers in bone. The mineralized PG (mPG) surface had a rough, hydrophilic layer of low crystalline calcium phosphate which was biocompatible to bone marrow stromal cells (BMSCs), induced their proliferation and was osteoinductive. Subsequently, by modulating the electrospinning process, we fabricated mPG-based novel higher order fibrous scaffolds that mimic the macroscale geometries of osteons of bone ECM. Inspired by the aligned collagen fibers in bone lamellae, we fabricated mPG scaffolds with aligned fibers that could direct anisotropic elongation of mouse BMSC (mBMSCs). Further, we fabricated electrospun mPG-based osteoinductive tubular constructs which can mimic cylindrical bone components like osteons or lamellae or be used as long bone analogues based on their dimensions. Finally, to regenerate tissue interfaces in bone, we introduced a novel bi-layered scaffold-based approach. An electrospun bi-layered tubular construct that had PG in the outer layer and 7%PHB/0.5%Polypyrrole fibers (PPy) in the inner layer was fabricated. The bi-layered tubular construct underwent preferential surface mineralization only on its outer layer. This outer mineralized layer supported osteogenesis while the inner PPy layer could support neural cell growth. Thus, the bi-layered tubular construct may be used to regenerate haversian canal in the osteons which hosts nerve fibers. Overall, the study introduced novel techniques to fabricate biomimetic structures that can regenerate components of bone osteon and its multiple tissue interfaces. The study lays foundation for the fabrication of a modular scaffold that can regenerate bone with its hierarchical structure and complex tissue interfaces.

Prevalence of drifting osteons distinguishes human bone.

The histological, or microscopic, appearance of bone tissue has long been studied to identify species-specific traits. There are several known histological characteristics to discriminate animal bone from human, but currently no histological characteristic that has been consistently identified in human bone exclusive to other mammals. The drifting osteon is a rare morphotype found in human long bones and observationally is typically absent from common mammalian domesticates. We surveyed previously prepared undecalcified histological sections from 25 species (human n = 221; nonhuman primate n = 24; nonprimate n = 169) to see if 1) drifting osteons were indeed more common in humans and 2) this could be a discriminating factor to identify human bone histologically. We conclude that drifting osteons are indeed more prevalent in human and nonhuman primate bone relative to nonprimate mammalian bone. Two criteria identify a rib or long bone fragment as human, assuming the fragment is unlikely to be from a nonhuman primate given the archaeological context: 1) at least two drifting osteons are present in the cross-section and 2) a drifting osteon prevalence (or as a percentage of total secondary osteons) of ≥ 1%. We present a quantitative histological method that can positively discriminate human bone from nonprimate mammalian bone in archaeological contexts.

How osteons form: A quantitative hypothesis-testing analysis of cortical pore filling and wall asymmetry.

Osteon morphology provides valuable information about the interplay between different processes involved in bone remodelling. The correct quantitative interpretation of these morphological features is challenging due to the complexity of interactions between osteoblast behaviour, and the evolving geometry of cortical pores during pore closing. We present a combined experimental and mathematical modelling study to provide insights into bone formation mechanisms during cortical bone remodelling based on histological cross-sections of quiescent human osteons and hypothesis-testing analyses. We introduce wall thickness asymmetry as a measure of the local asymmetry of bone formation within an osteon and examine the frequency distribution of wall thickness asymmetry in cortical osteons from human iliac crest bone samples from women 16-78 years old. Our measurements show that most osteons possess some degree of asymmetry, and that the average degree of osteon asymmetry in cortical bone evolves with age. We then propose a comprehensive mathematical model of cortical pore filling that includes osteoblast secretory activity, osteoblast elimination, osteoblast embedment as osteocytes, and osteoblast crowding and redistribution along the bone surface. The mathematical model is first calibrated to symmetric osteon data, and then used to test three mechanisms of asymmetric wall formation against osteon data: (i) delays in the onset of infilling around the cement line; (ii) heterogeneous osteoblastogenesis around the bone perimeter; and (iii) heterogeneous osteoblast secretory rate around the bone perimeter. Our results suggest that wall thickness asymmetry due to off-centred Haversian pores within osteons, and that nonuniform lamellar thicknesses within osteons are important morphological features that can indicate the prevalence of specific asymmetry-generating mechanisms. This has significant implications for the study of disruptions of bone formation as it could indicate what biological bone formation processes may become disrupted with age or disease.

Age-dependent change and intraskeletal variability in secondary osteons of elderly Australians.

There is a need to fully understand intra-skeletal variability within different populations to develop and improve age-at-death estimation methods. This study evaluates age-related histomorphometric changes in three different bones intra-individually in a modern Australian sample. Four female and 13 male elderly Australian adult donors (67-93 years) were examined for osteon population density (OPD), osteon area (On.Ar), and Haversian canal area (H.Ar) of secondary osteons to compare between femora, ribs, and humeri and assess against age. In the pooled sex sample, no statistically significant correlations were observed between age and each histological variable. In the males, OPD of the femur increased significantly with age, as did porosity in the rib. In the male humeri, OPD increased moderately with age, while H.Ar was decreased moderately with age. Intra-bone comparisons showed that males had significantly higher osteon counts in their ribs compared to their femora, while their ribs showed statistically significantly less porosity than their humeri. When bone size was accounted for, by adjusting the femur and humerus histology data by robusticity indices, histology values were found to be similar between bones within the same individual. This is despite the upper and lower limbs receiving different ranges and types of biomechanical load. Our findings demonstrate that bone size influences histomorphometry, and this could confound age-at-death estimations that have not been adjusted for robusticity. Future studies would benefit from examining bone histomorphometry within a larger sample size and incorporating bone robusticity measures into histology analyses.

Towards understanding how bisphosphonate-dependent alterations to nutrient canal integrity can contribute to risk for atypical femoral fractures: Biomechanical considerations and potential relationship to a real-world analogy.

Bisphosphonates are a class of drugs which have shown good efficacy in the treatment of post-menopausal osteoporosis, as well as a good safety profile. However, side-effects such as risk for atypical femoral fractures (AFF) have appeared, leading to a decline in use of the drugs by many patients who would benefit from the treatment. While patient characteristics have contributed to improved understanding of risk factors, the mechanisms involved that explain AFF risk have not appeared. Recently, the possibility that the mechanism(s) involved drug-induced modification of cells of the nutrient canals of the femur and subsequent compromise in the bone matrix has been published. The present Hypothesis article builds on the concept presented earlier and expands into biomechanical considerations. An analogy of the mechanisms involved to a real-life scenario is also presented. While this analogy has limitations, consideration of the biomechanical implications of progressive alterations to defects presented by compromised nutrient canal-bone matrix also presents potential relationships with AFF risk.

Microstructural changes in the irradiated and osteoradionecrotic bone: a SEM study.

Radiation exposure is a major health concern due to bone involvement including mandible, causing deleterious effects on bone metabolism, and healing with an increasing risk of infection and osteoradionecrosis. This study aims to investigate the radiotherapy-induced microstructural changes in the human mandible by scanning electron microscopy (SEM). Mandibular cortical bone biopsies were obtained from control, irradiated, and patients with osteoradionecrosis (ORN). Bone samples were prepared for light microscopy and SEM. The SEM images were analyzed for the number of osteons, number of Haversian canal (HC), diameter of osteon (D.O), the diameter of HC (D.HC), osteonal wall thickness (O.W.Th), number of osteocytes, and number of osteocytic dendrites. The number of osteons, D.O, D.HC, O.W.Th, the number of osteocytes, and osteocytic dendrites were significantly decreased in both irradiated and ORN compared to controls (p < .05). The number of HCs decreased in irradiated and ORN bone compared to the control group. However, this was statistically not significant. The deleterious effect of radiation continues gradually altering the bone quality, structure, cellularity, and vascularity in the long term (>5 years mean radiation biopsy interval). The underlying microscopic damage in bone increases its susceptibility and contributes further to radiation-induced bone changes or even ORN.

Age estimation in the combined long bones and ribs by histomorphometry: Past, present, and future.

Numerous age estimation methods in unidentified bone have been a long time developing for application in forensic anthropology. The histomorphometric technique is one of the alternative methods that relied upon the evaluation of the cortical bone microstructure over the lifespan as a result of the remodeling process in bone. Remodeling is a sophisticated event occurring from the coupled function of bone formation and resorption cells for maintaining mineral homeostasis and repairment of microdamage in bone tissue. Products derived from remodeling are primary changes in the osteon or haversian system in various regions in the cortical bone, including periosteum, endosteum, and trabecular bone. Throughout life, bone remodeling rate with osteon alteration can be predictable. In the forensic field, histological methods are getting more attention due to the unavailability of macroscopic methods. Histomorphometry approach can be accomplished in fragmentary or incomplete bone remains indicating the limited use of gross morphological methods. In addition, the microscopic methods can aid to increase the more accuracy of analyses and diminish the biased subjective assessment for determining age. Most histomorphometry method utilizes a cross-section of the midshaft of the long bones including the mandible, rib, and clavicle. This review provides the basic knowledge of bone biology and anatomy, several age-estimating methods of histology, and crucial factors for age methods. Studies regarding overall age determination methods from the past until now contribute to obtaining more benefits for developing methods of histomorphometry using human bone in forensic identification.

3D relationship between hierarchical canal network and gradient mineralization of shark tooth osteodentin.

Osteodentin is a dominant mineralized collagenous tissue in the teeth of many fishes, with structural and histological characteristics resembling those of bone. Osteodentin, like bone, comprises osteons as basic structural building blocks, however, it lacks the osteocytes and the lacuno-canalicular network (LCN), which are known to play critical roles in controlling the mineralization of the collagenous matrix in bone. Although numerous vascular canals exist in osteodentin, their role in tooth maturation and the matrix mineralization process remain poorly understood. Here, high resolution micro-computed tomography (micro-CT) and focused ion beam-scanning electron microscopy (FIB-SEM) were used to obtain 3D structural information of osteodentin in shark teeth at multiple scales. We observed a complex 3D network of primary canals with a diameter ranging from ∼10 µm to ∼120 µm, where the canals are surrounded by osteon-like concentric layers of lamellae, with 'interosteonal' tissue intervening between neighboring osteons. In addition, numerous hierarchically branched secondary canals extended radially from the primary canals into the interosteonal tissue, decreasing in diameter from ∼10 µm to hundreds of nanometers. Interestingly, the mineralization degree increases from the periphery of primary canals into the interosteonal tissue, suggesting that mineralization begins in the interosteonal tissue. Correspondingly, the hardness and elastic modulus of the interosteonal tissue are higher than those of the osteonal tissue. These results demonstrate that the 3D hierarchical canal network is positioned to play a critical role in controlling the gradient mineralization of osteodentin, also providing valuable insight into the formation of mineralized collagenous tissue without osteocytes and LCN. STATEMENT OF SIGNIFICANCE: Bone is a composite material with versatile mechanical properties. Osteocytes and their lacuno-canalicular network (LCN) are known to play critical roles during formation of human bone. However, the bone and osteodentin of many fishes, although lacking osteocytes and LCN, exhibit similar osteon-like structure and mechanical functions. Here, using various high resolution 3D characterization techniques, we reveal that the 3D network of primary canals and numerous hierarchically branched secondary canals correlate with the mineralization gradient and micromechanical properties of osteonal and interosteonal tissues of shark tooth osteodentin. This work significantly improves our understanding of the construction of bone-like mineralized tissue without osteocytes and LCN, and provides inspirations for the fabrication of functional materials with hierarchical structure.

Multiscale theoretical model shows that aging-related mechanical degradation of cortical bone is driven by microstructural changes in addition to porosity.

This study aims to gain mechanistic understanding of how aging-related changes in the microstructure of cortical bone drive mechanical consequences at the macroscale. To that end, cortical bone was modeled as a bundle of elastic-plastic, parallel fibers, which represented osteons and interstitial tissue, loaded in uniaxial tension. Distinct material properties were assigned to each fiber in either the osteon or interstitial fiber "families." Models representative of mature (20-60 yrs.) bone, and elderly (60+) bone were created by modeling aging via the following changes to the input parameters: (i) increasing porosity from 5% to 15%, (ii) increasing the ratio of the number of osteon fibers relative to interstitial fibers from 40% to 50%, and (iii) changing the fiber material properties from representing mature bone samples to representing elderly bone samples (i.e., increased strength and decreased toughness of interstitial fibers together with decreased toughness of osteon fibers). To understand the respective contributions of these changes, additional models isolating one or two of each of these were also created. From the computed stress-strain curve for the fiber bundle, the yield point (ϵy, σy), ultimate point (ϵu, σu), and toughness (UT) for the bundle as a whole were measured. We found that changes to all three input parameters were required for the model to capture the aging-related decline in cortical bone mechanical properties consistent with those previously reported in the literature. In both mature and elderly bundles, rupture of the interstitial fibers drove the initial loss of strength following the ultimate point. Plasticity and more gradual rupture of the osteons drove the remainder of the response. Both the onset and completion of interstitial fiber rupture occurred at lower strains in the elderly vs. mature case. These findings point to the importance of studying microstructural changes beyond porosity, such as the area fraction of osteons and the material properties of osteon and interstitial tissue, in order to further understanding of aging-related changes in bone.

Prolonged cyclical loading induces Haversian remodeling in mandibles of growing rabbits.

Bone adaptation to mechanical loading happens predominantly via modeling and remodeling, but the latter is poorly understood. Haversian remodeling (cortical bone replacement resulting in secondary osteons) is thought to occur in regions of low strain as part of bone maintenance or high strain in response to microdamage. However, analyses of remodeling in primates have revealed an unappreciated association with the number of daily load cycles. We tested this relationship by raising 30 male domestic rabbits (Oryctolagus cuniculus) on disparate diets from weaning to adulthood (48 weeks), facilitating a naturalistic perspective on mandibular bone adaptation. A control group consumed only rabbit pellets and an 'overuse' group ate hay in addition to pellets. To process hay, which is tougher and stiffer, rabbits increase chewing investment and duration without increasing bite force (i.e. corpus mean peak strain is similar for the two foods). Corpus remodeling in overuse rabbits was ∼1.5 times that of controls, measured as osteon population density and percentage Haversian bone. In the same subjects, there was a significant increase in overuse corpus bone formation (ratio of cortical area to cranial length), consistent with previous reports on the same dietary manipulation and bone formation in rabbits. This is the first evidence that both modeling and remodeling are simultaneously driven by the number of load cycles, independent of strain magnitude. This novel finding provides unique data on the feeding apparatus, challenges traditional thought on Haversian remodeling, and highlights the need for experimental studies of skeletal adaptation that examine mechanical factors beyond strain magnitude.

Absence of secondary osteons in femora of aged rats: Implications of lifespan on Haversian remodeling in mammals.

Bone is a dynamic tissue capable of adapting to its loading environment, allowing the skeleton to remain structurally sound throughout life. One way adaptation occurs in mammals is via Haversian remodeling: the site-specific, coupled resorption and formation of cortical bone that results in secondary osteons. Remodeling occurs at a baseline rate in most mammals, but it also occurs in relation to strain by repairing deleterious microdamage. Yet, not all animals with bony skeletons remodel. Among mammals, there is inconsistent or absent evidence for Haversian remodeling among monotremes, insectivores, chiropterans, cingulates, and rodents. Three possible explanations for this disparity are discussed: the capacity for Haversian remodeling, body size as a constraint, and age and lifespan as constraints. It is generally accepted, although not thoroughly documented, that rats (a common model used in bone research) do not typically exhibit Haversian remodeling. The present aim is to more specifically test the hypothesis that rats of advanced age do remodel intracortically because of the longer lifespan over which baseline remodeling could occur. Most published histological descriptions of rat bone only include young (3-6 months) rats. Excluding aged rats possibly overlooks a transition from modeling (i.e., bone growth) to Haversian remodeling as the primary mode of bone adaptation. Here, midshaft and distal femora (typical sites for remodeling in other mammals) of 24-month-old rats were examined for presence of secondary osteons. None were found, suggesting that Haversian remodeling does not occur in rats under normal physiological conditions at any age. A likely explanation is that modeling of cortical bone continues throughout most of the short rat lifespan, negating the stimulus for Haversian remodeling. Thorough sampling of key rodent taxa of varying body sizes and lifespans is key to elucidating the reasons why (i.e., body size, age/lifespan, phylogenetic factors) Haversian remodeling might not occur in all mammals.

Effect of graphene-oxide-modified osteon-like concentric microgrooved surface on the osteoclastic differentiation of macrophages.

OBJECTIVES: This study aimed to investigate the effect of new biomimetic micro/nano surfaces on the osteoclastic differentiation of RAW264.7 macrophages by simulating natural osteons for the design of concentric circular structures and modifying graphene oxide (GO). METHODS: The groups were divided into smooth titanium surface group (SS), concentric microgrooved titanium surface group (CMS), and microgroove modified with GO group (GO-CMS). The physicochemical properties of the material surfaces were studied using scanning electron microscopy (SEM), contact-angle measurement, atomic force microscopy, X-ray photoelectron spectroscopy analysis, and Raman spectroscopy. The effect of the modified material surface on the cell biological behavior of RAW264.7 was investigated by cell-activity assay, SEM, and laser confocal microscopy. The effect on the osteoclastic differentiation of macrophages was investiga-ted by tartrate-resistant acid phosphatase (TRAP) immunofluorescence staining and quantitative real-time polymerase chain reaction (qRT-PCR) experiments. RESULTS: Macrophages were arranged in concentric circles along the microgrooves, and after modification with GO, the oxygen-containing groups on the surface of the material increased and hydrophilicity increased. Osteoclasts in the GO-CMS group were small in size and number and had the lowest TRAP expression. Although it promoted the proliferation of macrophages in the GO-CMS group, the expression of osteoclastic differentiation-related genes was lower than that in the SS group, and the difference was statistically significant (P<0.05). CONCLUSIONS: Concentric circular microgrooves restricted the fusion of osteoclasts and the formation of sealing zones. Osteomimetic concentric microgrooves modified with GO inhibited the osteoclastic differentiation of RAW 264.7 macrophages.

Topographical study of scapular foramina and scapular nutrient foramina in dried skeletons.

PURPOSE: The aim of our study is to study the prevalence and anatomy of scapular foramina (SF) and scapular nutrient foramina (SNF) in dried skeletons from the Northeastern Thai population. METHODS: A total of 150 dried scapulae were investigated. Both SF and SNF were identified using a metal wire with a diameter of 0.36 mm. The number, locations, lengths, and diameters of SF were recorded. Subsequently, SNF were identified using the same metal wire. Their number and locations were recorded. Two observers performed the evaluations and measurements. RESULTS: SF were present in 78.0% of scapulae. They could have up to five openings. Eighteen types were found. On average they were longer in males (21.7 ± 5.0 mm) than females (19.45 ± 4.6 mm). The mean diameters of both the superior and inferior openings were significantly greater in females (p < 0.01). SNF, in contrast, were present in 100% of scapulae. They were located in the supraspinous fossa (36.7%), subscapular fossa (31.3%), infraspinous fossa (22.8%), and peri-glenoid area (10.0%). CONCLUSION: Unlike previous studies, the present study suggests that SF are normal anatomical findings, present in 78.0% of the scapulae investigated. Surgeons should be aware of both SNF and SF when operating or interpreting radiological findings.

Bone mineral properties and 3D orientation of human lamellar bone around cement lines and the Haversian system.

Bone is a complex, biological tissue made up primarily of collagen fibrils and biomineral nanoparticles. The importance of hierarchical organization in bone was realized early on, but the actual interplay between structural features and the properties on the nanostructural and crystallographic level is still a matter of intense discussion. Bone is the only mineralized tissue that can be remodeled and, at the start of the formation of new bone during this process, a structure called a cement line is formed on which regular bone grows. Here, the orientational relationship of nanostructural and crystallographic constituents as well as the structural properties of both nanostructural and crystallographic constituents around cement lines and the Haversian system in human lamellar bone are investigated. A combination of small- and wide-angle X-ray scattering tensor tomography is employed together with diffraction tomography and synchrotron computed tomography to generate a multi-modal image of the sample. This work shows that the mineral properties vary as a function of the distance to the Haversian canal and, importantly, shows that the cement line has differing mineral properties from the surrounding lamellar bone, in particular with respect to crystallite size and degree of orientation. Cement lines make up a significant portion of the bone matrix despite their small size, hence the reported findings on an altered mineral structure, together with the spatial modulation around the Haversian canal, have implications for the formation and mechanics of bone.

Cone-beam-computed tomography evaluation of mandibular nutrient canals in patients with periodontal diseases.

Background and Aim: The aim of this study was to evaluate radiographically the prevalence of mandibular nutrient canals (NCs) in patients with/without periodontal bone loss with aging and to correlate the number of NCs with the severity of bone loss using cone-beam-computed tomography (CBCT). Patients and Methods: CBCT examinations of 208 patients were evaluated retrospectively of all patients, 114 had periodontal bone loss, whereas 94 patients were control subjects. Alveolar bone loss investigations were performed according to the Progressive Rate Index. Results: NCs were observed in 55% of the control group and 86% of the periodontitis patients. NCs were more prevalent in the elderly age group with periodontal bone loss. In the study group, the NCs were statistically more frequent than in the control subjects (P > 0.05). Conclusion: Statistical analysis showed a significant difference between the age groups and the prevalence of NCs increased in patients with periodontal alveolar bone loss with aging (P < 0.05).

Design of a Haversian system-like gradient porous scaffold based on triply periodic minimal surfaces for promoting bone regeneration.

INTRODUCTION: The bone ingrowth depth in the porous scaffolds is greatly affected by the structural design, notably the pore size, pore geometry, and the pore distribution. To enhance the bone regeneration capability of scaffolds, the bionic design can be regarded as a potential solution. OBJECTIVES: We proposed a Haversian system-like gradient structure based on the triply periodic minimal surface architectures with pore size varying from the edge to the center. And its effects in promoting bone regeneration were evaluated in the study. METHODS: The gradient scaffold was designed using the triply periodic minimal surface architectures. The mechanical properties were analyzed by the finite element simulation and confirmed using the universal machine. The fluid characteristics were calculated by the computational fluid dynamics analysis. The bone regeneration process was simulated using a in silico computational model containing the main biological, physical, and chemical variation during the bone growth process. Finally, the in vitro and in vivo studies were carried out to verify the actual osteogenic effect. RESULTS: Compared to the uniform scaffold, the biomimetic gradient scaffold demonstrated better performance in stress conduction and reduced stress shielding effects. The fluid features were appropriate for cell migration and flow diffusion, and the permeability was in the same order of magnitude with the natural bone. The bone ingrowth simulation exhibited improved angiogenesis and bone regeneration. Higher expression of the osteogenesis-related genes, higher alkaline phosphatase activity, and increased mineralization could be observed on the gradient scaffold in the in vitro study. The 12-week in vivo study proved that the gradient scaffold had deeper bone inserting depth and a more stable bone-scaffold interface. CONCLUSION: The Haversian system-like gradient structure can effectively promote the bone regeneration. This structural design can be used as a new solution for the clinical application of prosthesis design.

Quasi-static and dynamic Brazilian testing and failure analysis of a deer antler in the transverse to the osteon growth direction.

The transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5-44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces.

Human femur morphology and histology variation with ancestry and behaviour in an ancient sample from Vietnam.

BACKGROUND: There is a genetic component to the minimum effective strain (MES)-a threshold which determines when bone will adapt to function-which suggests ancestry should play a role in bone (re)modelling. Further elucidating this is difficult in living human populations because of the high global genetic admixture. We examined femora from an anthropological skeletal assemblage (Mán Bac, Vietnam) representing distinct ancestral groups. We tested whether femur morphological and histological markers of modelling and remodelling differed between ancestries despite their similar lifestyles. METHODS: Static histomorphometry data collected from subperiosteal cortical bone of the femoral midshaft, and gross morphometric measures of femur robusticity, were studied in 17 individuals from the Mán Bac collection dated to 1906-1523 cal. BC. This assemblage represents agricultural migrants with affinity to East Asian groups, who integrated with the local hunter-gatherers with affinity to Australo-Papuan groups during the mid-Holocene. Femur robusticity and histology data were compared between groups of 'Migrant' (n = 8), 'Admixed' (n = 4), and 'Local' (n = 5). RESULTS: Local individuals had more robust femoral diaphyses with greater secondary osteon densities, and relatively large secondary osteon and Haversian canal parameters than the migrants. The Migrant group showed gracile femoral shafts with the least dense bone made up of small secondary osteons and Haversian canals. The Admixed individuals fell between the Migrant and Local categories in terms of their femoral data. However, we also found that measures of how densely bone is remodelled per unit area were in a tight range across all three ancestries. CONCLUSIONS: Bone modelling and remodelling markers varied with ancestral histories in our sample. This suggests that there is an ancestry related predisposition to bone optimising its metabolic expenditure likely in relation to the MES. Our results stress the need to incorporate population genetic history into hierarchical bone analyses. Understanding ancestry effects on bone morphology has implications for interpreting biomechanical loading history in past and modern human populations.

Effect of geometrical structure variations on strength and damage onset of cortical bone using multi-scale cohesive zone based finite element method.

Three-dimensional multi-scale finite element models were designed to examine the effects of geometrical structure variations on the damage onset in cortical bone at multiple structural scales. A cohesive zone finite element approach, together with anisotropic damage initiation criteria, is used to predict the onset of damage. The finite element models are developed to account for the onset of microdamage from the microscopic length scales consisting of collagen fibres, to the macroscopic level consisting of osteons and the Haversian canals. Numerical results indicated that the yield strain at the initiation of microcracks is independent of variations in the local mineral volume fraction at each structural scale. Further, the yield strain and strength properties of cortical bone are dependent on its structural anisotropy and hierarchical structure. A positive correlation is observed between bone strength and mineral content at each length scale.

Development of osteon-like scaffold-cell construct by quadruple coaxial extrusion-based 3D bioprinting of nanocomposite hydrogel.

Despite advances in bone tissue engineering, fabricating a scaffold which can be used as an implant for large bone defects remains challenge. One of the great importance in fabricating a biomimetic bone implant is considering the possibility of the integration of the structure and function of implants with hierarchical structure of bone. Herein, we propose a method to mimic the structural unit of compact bone, osteon, with spatial pattern of human umbilical vein endothelial cells (HUVECs) and human mesenchymal stem cells (hMSCs) in the adjacent layers that mimic Haversian canal and lamella, respectively. To this end, coaxial extrusion-based bioprinting technique via a customized quadruple-layer core-shell nozzle was employed. 3D implant scaffold-cell construct was fabricated by using polyethylene glycol as a hollowing agent in the first layer, gelatin methacryloyl (GelMA) and alginate blended hydrogel encapsulating HUVEC cells with vascular endothelial growth factor nanoparticles in the second layer (vasculogenic layer) to mimic vascular vessel, and GelMA and alginate blended hydrogel containing hMSCs cells in the outer osteogenic layer to imitate lamella. Two types of bone minerals, whitlockite and hydroxyapatite, were incorporated in osteogenic layer to induce osteoblastic differentiation and enhance mechanical properties (the young's modules of nanocomposite increased from 35 kPa to 80 kPa). In-vitro evaluations demonstrated high cell viability (94 % within 10 days) and proliferation. Furthermore, ALP enzyme activity increased considerably within 2 weeks and mineralized extra cellular matrix considerably produced within 3 weeks. Also, a significant increase in osteogenic markers was observed indicating the presence of differentiated osteoblast cells. Therefore, the work indicates the potential of single step 3D bioprinting process to fabricate biomimetic osteons to use as bone grafts for regeneration.