Mineral evolution of bone

Revisiting the physical and chemical nature of the mineral component of bone

The physico-chemical characteristics of bone mineral remain heavily debated. On the nanoscale, bone mineral resides both inside and outside the collagen fibril as distinct compartments fused together into a cohesive continuum. On the micrometre level, larger aggregates are arranged in a staggered pattern described as crossfibrillar tessellation. Unlike geological and synthetic hydroxy(l)apatite, bone mineral is a unique form of apatite deficient in calcium and hydroxyl ions with distinctive carbonate and acid phosphate substitutions (CHAp), together with a minor contribution of amorphous calcium phosphate as a surface layer around a crystalline core of CHAp. In mammalian bone, an amorphous solid phase has not been observed, though an age-dependent shift in the amorphous-to-crystalline character is observed. Although octacalcium phosphate has been postulated as a bone mineral precursor, there is inconsistent evidence of calcium phosphate phases other than CHAp in the extracellular matrix. In association with micropetrosis, magnesium whitlockite is occasionally detected, indicating pathological calcification rather than a true extracellular matrix component. Therefore, the terms 'biomimetic' or 'bone-like' should be used cautiously in descriptions of synthetic biomaterials. The practice of reporting the calcium-to-phosphorus ratio (Ca/P) as proxy for bone mineral maturity oversimplifies the chemistry since both Ca2+ and PO43- ions are partially substituted. Moreover, non-mineral sources of phosphorus are ignored. Alternative compositional metrics should be considered. In the context of bone tissue and bone mineral, the term 'mature' must be used carefully, with clear criteria that consider both compositional and structural parameters and the potential impact on mechanical properties. STATEMENT OF SIGNIFICANCE: Bone mineral exhibits a unique hierarchical structure and is classified into intrafibrillar and extrafibrillar mineral compartments with distinct physico-chemical characteristics. The dynamic nature of bone mineral, i.e., evolving chemical composition and physical form, is poorly understood. For instance, bone mineral is frequently described as "hydroxy(l)apatite", even though the OH- content of mature bone mineral is negligible. Moreover, the calcium-to-phosphorus ratio is often taken as an indicator of bone mineral maturity without acknowledging substitutions at calcium and phosphate sites. This review takes a comprehensive look at the structure and composition of bone mineral, highlighting how experimental data are misinterpreted and unresolved concerns that warrant further investigation, which have implications for characterisation of bone material properties and development of bone repair biomaterials.

Evaluation of stiffness-matched, 3D-printed, NiTi mandibular graft fixation in an ovine model

BACKGROUND

Manually bent, standard-of-care, Ti-6Al-4V, mandibular graft fixation devices are associated with a significant post-operative failure rate. These failures require the patient to endure stressful and expensive re-operation. The approach recommended in this report demonstrates the optimization of graft fixation device mechanical properties via "stiffness-matching" by varying the fixation device's location, shape, and material composition through simulation of the device's post-operative performance. This provides information during pre-operative planning that may avoid future device failure. Optimized performance may combine translation of all loading into compression of the bone graft with the adjacent bone segments and elimination or minimization of post-healing interruption of normal stress-strain (loading) trajectories.

RESULTS

This study reports a sheep mandibular graft model where four animals received virtually optimized, experimental nickel-titanium (NiTi) fixation plates fabricated using laser beam powder bed fusion (LPBF) additive manufacturing (AM). The last animal, our control, received a standard-of-care, manually bent, Ti-6Al-4V (aka Ti64) fixation plate. A 17.5-mm mandibular graft healed completely in all four animals receiving the experimental device. Experimental NiTi-implanted sheep experienced mandibular bone healing and restoration. The Ti64 plate, in the control animal, fractured and dislocated shortly after being implanted.

CONCLUSION

The use of stiffness-matched implants, by means of plate material (NiTi) and geometry (porosity) enhanced bone healing and promoted better load transfer to the healed bone when compared to the bulk Ti64 found in the fixation plate that the Control animal received. The design technique and screw orientation and depth planning improved throughout the study leading to more rapid healing. The large animal model reported here provides data useful for a follow-on clinical trial.

Bone hierarchical organization through the lens of materials science: Present opportunities and future challenges

Multiscale characterization is essential to better understand the hierarchical architecture of bone and an array of analytical methods contributes to exploring the various structural and compositional aspects. Incorporating X-ray tomography, X-ray scattering, vibrational spectroscopy, and atom probe tomography alongside electron microscopy provides a comprehensive approach, offering insights into the diverse levels of organization within bone. X-ray scattering techniques reveal information about collagen-mineral spatial relationships, while X-ray tomography captures 3D structural details, especially at the microscale. Electron microscopy, such as scanning and transmission electron microscopy, extends resolution to the nanoscale, showcasing intricate features such as collagen fibril organization. Additionally, atom probe tomography achieves sub-nanoscale resolution and high chemical sensitivity, enabling detailed examination of bone composition. Despite various technical challenges, a correlative approach allows for a comprehensive understanding of bone material properties. Real-time investigations through in situ and in operando approaches shed light on the dynamic processes in bone. Recently developed techniques such as liquid, in situ transmission electron microscopy provide insights into calcium phosphate formation and collagen mineralization. Mechanical models developed in the effort to link structure, composition, and function currently remain oversimplified but can be improved. In conclusion, correlative analytical platforms provide a holistic perspective of bone extracellular matrix and are essential for unraveling the intricate interplay between structure and composition within bone.

Animal Models for Investigating Osseointegration: An Overview of Implant Research over the Last Three Decades

Dental implants and bone augmentation are among dentistry's most prevalent surgical treatments; hence, many dental implant surfaces and bone grafts have been researched to improve bone response. Such new materials were radiologically, histologically, and histomorphometrically evaluated on animals before being used on humans. As a result, several studies used animals to evaluate novel implant technologies, biocompatibility, surgical techniques, and osseointegration strategies, as preclinical research on animal models is essential to evaluate bioactive principles (on cells, compounds, and implants) that can act through multiple mechanisms and to predict animal behavior, which is difficult to predict from in vitro studies alone. In this study, we critically reviewed all research on different animal models investigating the osseointegration degree of new implant surfaces, reporting different species used in the osseointegration research over the last 30 years. Moreover, this is the first study to summarize reviews on the main animal models used in the translational research of osseointegration, including the advantages and limitations of each model and determining the ideal location for investigating osseointegration in small and large animal models. Overall, each model has advantages and disadvantages; hence, animal selection should be based on the cost of acquisition, animal care, acceptability to society, availability, tolerance to captivity, and housing convenience. Among small animal models, rabbits are an ideal model for biological observations around implants, and it is worth noting that osseointegration was discovered in the rabbit model and successfully applied to humans.

Characterization of Human, Ovine and Porcine Mesenchymal Stem Cells from Bone Marrow: Critical In Vitro Comparison with Regard to Humans

For research and clinical use of stem cells, a suitable animal model is necessary. Hence, the aim of this study was to compare human-bone-marrow-derived mesenchymal stem cells (hBMSCs) with those from sheep (oBMSCs) and pigs (pBMSCs). The cells from these three species were examined for their self-renewal potential; proliferation potential; adhesion and migration capacity; adipogenic, osteogenic and chondrogenic differentiation potential; and cell morphology. There was no significant difference between hBMSCs and pBMSCs in terms of self-renewal potential or growth potential. The oBMSCs exhibited a significantly higher doubling time than hBMSCs from passage 7. The migration assay showed significant differences between hBMSCs and pBMSCs and oBMSCs—up to 30 min, hBMSCs were faster than both types and after 60 min faster than pBMSCs. In the adhesion assay, hBMSCs were significantly better than oBMSCs and pBMSCs. When differentiating in the direction of osteogenesis, oBMSCs and pBMSCs have shown a clearer osteogenic potential. In all three species, adipogenesis could only be evaluated qualitatively. The chondrogenic differentiation was successful in hBMSCs and pBMSCs in contrast to oBMSCs. It is also important to note that the cell size of pBMSCs was significantly smaller compared to hBMSCs. Finally, it can be concluded that further comparative studies are needed to draw a clear comparison between hBMSCs and pBMSCs/oBMSCs.

A review of bioceramics scaffolds for bone defects in different types of animal models: HA andβ-TCP

Increased life expectancy has led to an increase in the use of bone substitutes in numerous nations, with over two million bone-grafting surgeries performed worldwide each year. A bone defect can be caused by trauma, infections, and tissue resections which can self-heal due to the osteoconductive nature of the native extracellular matrix components. However, natural self-healing is time-consuming, and new bone regeneration is slow, especially for large bone defects. It also remains a clinical challenge for surgeons to have a suitable bone substitute. To date, there are numerous potential treatments for bone grafting, including gold-standard autografts, allograft implantation, xenografts, or bone graft substitutes. Tricalcium phosphate (TCP) and hydroxyapatite (HA) are the most extensively used and studied bone substitutes due to their similar chemical composition to bone. The scaffolds should be testedin vivoandin vitrousing suitable animal models to ensure that the biomaterials work effectively as implants. Hence, this article aims to familiarize readers with the most frequently used animal models for biomaterials testing and highlight the available literature forin vivostudies using small and large animal models. This review summarizes the bioceramic materials, particularly HA andβ-TCP scaffolds, for bone defects in small and large animal models. Besides, the design considerations for the pre-clinical animal model selection for bone defect implants are emphasized and presented.

The burning maze: The potential value of the human bony labyrinth in estimating sex of calcined remains

Estimating sex from burnt human remains is a challenging task in bioanthropology, mainly due to their high level of alteration and fragmentation. Protected within the petrous part of the temporal bone, the bony labyrinth may be particularly valuable for assessing the sex of burnt remains. This prospective study aims at testing predictive models, already found reliable on unburnt bony labyrinths, to burnt specimens. Six discriminant functions were applied on six bony labyrinths of donated adult cadavers of known sex, before and after outdoor burning experiments. Comparisons between unburnt and burnt measurements were executed using Mann-Whitney U tests while shape and size differences induced by fire exposure were examined through a geometric morphometrics (GM) analysis. Predicted sex on unburnt bony labyrinths was consistent with known sex in five cases while a systematic misclassification for males was highlighted on burnt specimens. Higher values of shrinkage were found in males for two measurements included in the equations. GM analysis revealed significant differences in centroid size among males after calcination. Visualization of mean consensus of both female and male bony labyrinths evidenced a reduction in cochlear size and variations in the width and length of semicircular canals of burnt specimens. This exploratory study seems to confirm that designing sex estimation standards specifically for burnt bony labyrinth may be advisable. Understanding how the burning process could impact its morphology is highly recommended through further experiments on larger samples and in controlled environments.

Bone mineral concentration predicted by dual energy X-ray absorptiometry and its relationship with lamb eating quality

Lumbar bone mineral concentration, as predicted by dual energy x-ray absorptiometry (DEXA), may reflect changes in lamb maturity and eating quality. New season (n = 60) and old season (n = 60) lambs were slaughtered and DEXA scanned at a commercial abattoir across 2 kill groups. The second lumbar vertebra was isolated from the spine for determination of calcium, phosphorus, and magnesium concentration (mg/g). The loin and rack cuts were collected for consumer sensory grilling and roasting analyses. Mineral concentration was significantly higher in old season lambs within kill group 1 (P < 0.05). DEXA was a positive predictor of phosphorus and calcium concentration, but only when DEXA lean % (P < 0.05) was included in the model. Calcium and phosphorus were significant positive predictors of overall liking scores (P < 0.05), but only for the rack roast. These effects became insignificant when DEXA lean % was included. These results suggest that DEXA values likely reflect changes in both DEXA lean % and bone minerals, and that DEXA lean % was the driver of eating quality, rather than maturity.

Autogenous bone ring for vertical bone augmentation procedure with simultaneous implant placement: A systematic review of histologic and histomorphometric outcomes in animal studies

STATEMENT OF PROBLEM

The performance of the autogenous bone ring (ABR) technique used for the vertical bone augmentation procedure has not yet been determined.

PURPOSE

The purpose of this systematic review was to investigate whether the ABR technique for the vertical bone augmentation procedure with simultaneous implant placement enhances the histologic and histomorphometric outcomes in surgically created bone defects in animal models.

MATERIAL AND METHODS

An electronic search of 3 databases, Medline/PubMed, Science Direct, Lilacs, and a manual search of a reference list of relevant studies were performed. Only animal studies regarding vertical bone augmentation by using the ABR technique with simultaneous implant placement in surgically created bone defects were included in the review. The SYstematic Review Center for Laboratory Animal Experimentation tool was used to determine the risk of bias assessment, and the quality of included studies was assessed by using the Animal Research: Reporting in Vivo Experiments guidelines.

RESULTS

Five studies were included in the qualitative analysis based on the inclusion and exclusion criteria. One study comparing the ABR technique with the bovine and biphasic ring reported a high percentage of bone area and bone implant contact of the ABR at 5 weeks of osseointegration. Similar histologic findings were reported in another study at 4 months of healing, but contrasting data were reported at 8 months. Another study reported an increase in the percentage of bone area and bone implant contact of the ABR technique from 3 months to 6 months of osseointegration. Two studies reported an increase in the percentage of bone area, and 1 study reported a decrease in the mean of bone implant contact, both with simultaneous and staged implant procedures.

CONCLUSION

Based on the limited available studies, the use of the ABR technique for the vertical bone augmentation procedure with simultaneous implant placement presented optimal histologic and histomorphometric outcomes in surgically created bone defects in animal models. However, the results of the current review are not sufficiently robust to support the use of the ABR technique for vertical bone augmentation in humans.

Pre-Clinical Evaluation of Biological Bone Substitute Materials for Application in Highly Loaded Skeletal Sites

The development of bone substitute materials (BSMs) intended for load-bearing bone defects is highly complicated, as biological and mechanical requirements are often contradictory. In recent years, biological BSMs have been developed which allow for a more efficient integration of the material with the surrounding osseous environment and, hence, a higher mechanical stability of the treated defect. However, while these materials are promising, they are still far from ideal. Consequently, extensive preclinical experimentation is still required. The current review provides a comprehensive overview of biomechanical considerations relevant for the design of biological BSMs. Further, the preclinical evaluation of biological BSMs intended for application in highly loaded skeletal sites is discussed. The selected animal models and implantation site should mimic the pathophysiology and biomechanical loading patterns of human bone as closely as possible. In general, sheep are among the most frequently selected animal models for the evaluation of biomaterials intended for highly loaded skeletal sites. Regarding the anatomical sites, segmental bone defects created in the limbs and spinal column are suggested as the most suitable. Furthermore, the outcome measurements used to assess biological BSMs for regeneration of defects in heavily loaded bone should be relevant and straightforward. The quantitative evaluation of bone defect healing through ex vivo biomechanical tests is a valuable addition to conventional in vivo tests, as it determines the functional efficacy of BSM-induced bone healing. Finally, we conclude that further standardization of preclinical studies is essential for reliable evaluation of biological BSMs in highly loaded skeletal sites.

Newly formed and remodeled human bone exhibits differences in the mineralization process

During human skeletal growth, bone is formed via different processes. Two of them are: new bone formation by depositing bone at the periosteal (outer) surface and bone remodeling corresponding to a local renewal of tissue. Since in remodeling formation is preceded by resorption, we hypothesize that modeling and remodeling could require radically different transport paths for ionic precursors of mineralization. While remodeling may recycle locally resorbed mineral, modeling implies the transport over large distances to the site of bone apposition. Therefore, we searched for potential differences of size, arrangement and chemical composition of mineral particles just below surfaces of modeling and remodeling sites in femur midshaft cross-sections from healthy children. These bone sites were mapped using scanning synchrotron X-ray scattering, Raman microspectroscopy, energy dispersive X-ray analysis and quantitative backscattered electron microscopy. The results show clear differences in mineral particle size and composition between the sites, which cannot be explained by a change in the rate of mineral apposition or accumulation. At periosteal modeling sites, mineral crystals are distinctly larger, display higher crystallinity and exhibit a lower calcium to phosphorus ratio and elevated Na and Mg content. The latter may originate from Mg used for phase stabilization of mineral precursors and therefore indicate different time periods for mineral transport. We conclude that the mineralization process is distinctively different between modeling and remodeling sites due to varying requirements for the transport distance and, therefore, the stability of non-crystalline ionic precursors, resulting in distinct compositions of the deposited mineral phase. STATEMENT OF SIGNIFICANCE: In growing children new bone is formed either due to apposition of bone tissue e.g. at the outer ridge of long bones to allow growth in thickness (bone modeling), or in cavities inside the mineralized matrix when replacing tissue (bone remodeling). We demonstrate that mineral crystal shape and composition are not the same between these two sites, which is indicative of differences in mineralization precursors. We suggest that this may be due to a longer mineral transport distance to sites of new bone formation as compared to remodeling where mineral can be locally recycled.

A preclinical large-animal model for the assessment of critical-size load-bearing bone defect reconstruction

Critical-size bone defects, which require large-volume tissue reconstruction, remain a clinical challenge. Bone engineering has the potential to provide new treatment concepts, yet clinical translation requires anatomically and physiologically relevant preclinical models. The ovine critical-size long-bone defect model has been validated in numerous studies as a preclinical tool for evaluating both conventional and novel bone-engineering concepts. With sufficient training and experience in large-animal studies, it is a technically feasible procedure with a high level of reproducibility when appropriate preoperative and postoperative management protocols are followed. The model can be established by following a procedure that includes the following stages: (i) preoperative planning and preparation, (ii) the surgical approach, (iii) postoperative management, and (iv) postmortem analysis. Using this model, full results for peer-reviewed publication can be attained within 2 years. In this protocol, we comprehensively describe how to establish proficiency using the preclinical model for the evaluation of a range of bone defect reconstruction options.

Ivory vs. osseous ivory substitutes-Non-invasive diffractometric discrimination

A new discrimination method for the bioapatite materials bone, antler and ivory was developed using X-ray diffractometry and comprises non-invasive measurements in order to take valuable objects into account. Our approach deals with the analysis of peak intensity ratios resulting from several measurements on each object. For instance, the intensity ratio of the apatite reflections 002 and 310 has been described in the literature as representing the degree of apatite crystal orientation and varies depending on the sample orientation. The decisive factor for the material identification is the value dispersion of intensity ratios resulting from the total of all measurements on one object. This pattern of data points, visualised via kernel density estimation (KDE), is characteristic for ivory, bone and antler, respectively, and enables the discrimination of these materials. The observation is justifiable since apatite crystal orientation adapts to the collagen fibre arrangement which shows major differences between different sorts of bioapatite materials. The patterns of data points were received via analysis of 88 objects made of bone (n = 30), antler (n = 27) and ivory (n = 31). In order to verify several identifications X-ray computer tomography was supplemented. The presented method usefully supplements already existing approaches concerning microscopic, elementary and biochemical analyses.

Comparison of autogenous and allograft bone rings in surgically created vertical bone defects around implants in a sheep model

OBJECTIVES

The aim of this study was to compare autogenous and allograft bone rings in surgically created vertical bone defects.

MATERIAL AND METHODS

Four male, 1-year-old sheep were used in this study. In each sheep, eight vertical bone defects 7 mm in diameter were created using trephine drill in the iliac wing. Autogenous and allograft bone rings 5 mm in height and 7 mm in diameter were used for vertical augmentation around implants. The study consisted of four groups according to the bone ring type and amount of vertical augmentation, autogenous 2 mm, allograft 2 mm, autogenous 4 mm, and allograft 4 mm. Two of the animals were sacrificed after 4 months, and the remaining two animals were sacrificed after 8 months. Undecalcified sections were prepared from harvested samples. Histological assessment and histomorphometric analysis were performed.

RESULTS

Autogenous 2 mm group showed higher values than allograft 2 mm group, and autogenous 4 mm group showed higher values than allograft 4 mm group in terms of bone area and bone-to-implant contact (BIC) after 4 months. However, allograft 2 mm group showed higher bone area and BIC values than autogenous 2 mm group after 8 months. Also, autogenous 4 mm and allograft 4 mm groups showed comparable results after 8 months. Allograft 2 mm and allograft 4 mm groups showed higher bone area and BIC values at 8 months compared with 4 months.

CONCLUSIONS

Allograft bone ring looks promising in augmentation of surgically created vertical bone defects around implants after 8 months of healing.

Effects of phosphorus supplementation in high-grain diets on blood, chemical and physical parameters of bones of feedlot Nellore bulls

The study was conducted to evaluate the effects of phosphorus supplementation (PS) on blood, chemical and physical parameters from bones of feedlot Nellore bulls. Forty-two animals were distributed in a completely randomised design consisting of three treatments and 14 replicates. The treatments consisted of no supplementary phosphorus (P; T1; 2.4 g P/kg DM), a commercial mineral supplement formulated according to recommendations from the main Brazilian industries of mineral supplements for feedlot beef cattle (T2; 4.2 g P/kg DM) and dicalcium phosphate (T3; 5.0 g P/kg DM) in high-grain diets. The animals submitted or not to PS had similar calcium (Ca) and P values, Ca : P ratio, specific gravity, cortical thickness and bone mineral density in the 12th rib. However, a decrease in magnesium (Mg) concentration was observed in the 12th rib in T1 and T3 treatments throughout the study (P < 0.05). The animals in T1 had lower cortical thickness of the metacarpus (P < 0.05), without compromising its resistance and stiffness (P > 0.05). To evaluate the P status in the animals, we performed the needle test, which allowed an assessment of differences in bone strength on the basis of the resistance to needle penetration on the transverse process (TP) of the lumbar vertebrae. Throughout the trial period, no animals were positive for the needle test conducted in the transverse processes of the lumbar vertebrae. The PS significantly changed parathyroid hormone and alkaline phosphatase concentrations (P < 0.05) and the animals in T1 had lower concentrations of these hormones. However, there was no effect of PS on the concentration of Ca and P in the serum of animals (P > 0.05). The inclusion of a mineral mix supplement in T2 resulted in higher Mg concentrations in the serum of animals (P > 0.05). P supplementation for Nellore bulls, fed high proportions of concentrate during the feedlot period, resulted in no benefits in neither chemical nor physical properties of their bones and the level in the control diet appeared adequate in these circumstances.

Bone turnover markers in sheep and goat: A review of the scientific literature

Bone turnover markers (BTMs) are product of bone cell activity and are generally divided in bone formation and bone resorption markers. The purpose of this review was to structure the available information on the use of BTMs in studies on small ruminants, especially for monitoring their variations related to diet, exercise, gestation and metabolic lactation state, circadian and seasonal variations, and also during skeletal growth. Pre-clinical and translational studies using BTMs with sheep and goats as animal models in orthopaedic research studies to help in the evaluation of the fracture healing process and osteoporosis research are also described in this review. The available information from the reviewed studies was systematically organized in order to highlight the most promising BTMs in small ruminant research, as well as provide a wide view of the use of sheep and goat as animal models in orthopaedic research, type of markers and commercial assay kits with cross-reactivity in sheep and goat, method of sample and storage of serum and urine for bone turnover markers determination and the usefulness and limitations of bone turnover markers in the different studies, therefore an effective tool for researchers that seek answers to different questions while using BTMs in small ruminants.

Evaluation of perforated demineralized dentin scaffold on bone regeneration in critical-size sheep iliac defects

OBJECTIVES

Regenerating critical-size bone injury is a major problem that continues to inspire the design of new graft materials. Therefore, tissue engineering has become a novel approach for targeting bone regeneration applications. Human teeth are a rich source of stem cells, matrix, trace metal ions, and growth factors. A vital tooth-derived demineralized dentin matrix is acid-insoluble and composed of cross-linked collagen with growth factors. In this study, we recycled human non-functional tooth into a unique geometric dentin scaffold, entitled perforated root-demineralized dentin matrix (PR-DDM). The aim of this study was to evaluate the feasibility of PR-DDM as the scaffold for regenerating bone in critical-size iliac defects.

MATERIAL AND METHODS

Artificial macro-pores (1 mm in diameter) were added to human vital wisdom tooth after removing the enamel and pulp portions. The modified tooth was demineralized in 0.34 N HNO₃ for 30 min and is referred to as PR-DDM scaffold. Critical-size defect (10 mm × 15 mm × 9 mm Ø) was created in the iliac crest of six adult sheep. The in vivo bone regeneration by the scaffold was evaluated by micro-CT, 3D micro-CT, and histological examination at 2 and 4 months post-implantation.

RESULTS

PR-DDM exhibited better bone ingrowth, especially in the artificial macro-pores. The results of micro-CT and 3D micro-CT revealed good union between scaffold and native bone. New bone formation was observed in almost all portions of PR-DDM. Higher bone volume inside the scaffold was detected at 4 months compared with 2 months. New bone ingrowth was ankylosed with PR-DDM, and both osteoinduction and osteoconduction capability of PR-DDM were confirmed histologically. The ratio of new bone formation was higher at 4 months compared with 2 months by histomorphometric analysis.

CONCLUSIONS

Altogether, these results demonstrated that the human tooth-derived graft material with a unique geometric structure, PR-DDM, contributed to active bone ingrowth in critical-size bone defects. This novel scaffold may have great utility in the near-future clinical application.

Bone Regeneration in Iliac Crestal Defects: An Experimental Study on Sheep

Background. Oral rehabilitation of partially fully edentulous patients with dental implants has become a routine procedure in clinical practice. In a site with a lack of bone GBR is a surgical procedure that provides an augmentation in terms of volume for the insertion of dental implants. Materials and Methods. In the iliac crest of six sheep 4 defects were created where an implant was inserted, three of them with different biomaterials and a control site. All animals were sacrificed after a 4-month healing period. All specimens were processed and analyzed with histomorphometry. Statistical evaluation was done to evaluate percentage of bone defect filled by new bone. Results. All experimental groups showed an increase of the new bone. Higher and highly statistically significant differences were found in the percentages of bone defect filled by new bone in group filled with corticocancellous 250-1000 microns particulate porcine bone mix. Conclusions. This study demonstrates that particulate porcine bone mix and porcine corticocancellous collagenate prehydrated bone mix when used as scaffold are able to induce bone regeneration. Moreover, these data suggest that these biomaterials have higher biocompatibility and are capable of inducing faster and greater bone formation.

Understanding the Crystallinity Indices Behavior of Burned Bones and Teeth by ATR-IR and XRD in the Presence of Bioapatite Mixed with Other Phosphate and Carbonate Phases

We have critically investigated the ATR-IR spectroscopy data behavior of burned human teeth as opposed to the generally observed behavior in human bones that were subjected to heat treatment, whether deliberate or accidental. It is shown that the deterioration of the crystallinity index (CI) behavior sometimes observed in bones subjected to high temperature appears to be of higher frequency in the case of bioapatite from teeth. This occurs because the formation of the β-tricalcium phosphate (β-TCP) phase, otherwise known as whitlockite, clearly ascertained by the X-ray diffraction (XRD) patterns collected on the same powdered specimens investigated by ATR-IR. These results point to the need of combining more than one physicochemical technique even if apparently well suitable, in order to verify whether the assumed conditions assessed by spectroscopy are fully maintained in the specimens after temperature and/or mechanical processing.

The outstanding mechanical response and bone regeneration capacity of robocast dilute magnesium-doped wollastonite scaffolds in critical size bone defects

Mechanically strong, highly osteogenic dilute magnesium-doped wollastonite robocast scaffolds.

Preclinical testing of drug delivery systems to bone

Bone defects do not heal in 5-10% of the fractures. In order to enhance bone regeneration, drug delivery systems are needed. They comprise a scaffold with or without inducing factors and/or cells. To test these drug delivery systems before application in patients, they finally need to be tested in animal models. The choice of animal model depends on the main research question; is a functional or mechanistic evaluation needed? Furthermore, which type of bone defects are investigated: load-bearing (i.e. orthopedic) or non-load-bearing (i.e. craniomaxillofacial)? This determines the type of model and in which type of animal. The experiments need to be set-up using the 3R principle and must be reported following the ARRIVE guidelines.

Large animal in vivo evaluation of a binary blend polymer scaffold for skeletal tissue-engineering strategies; translational issues

Binary blend polymers offer the opportunity to combine different desirable properties into a single scaffold, to enhance function within the field of tissue engineering. Previous in vitro and murine in vivo analysis identified a polymer blend of poly(l‐lactic acid)–poly(ε‐caprolactone) (PLLA:PCL 20:80) to have characteristics desirable for bone regeneration. Polymer scaffolds in combination with marrow‐derived skeletal stem cells (SSCs) were implanted into mid‐shaft ovine 3.5 cm tibial defects, and indices of bone regeneration were compared to groups implanted with scaffolds alone and with empty defects after 12 weeks, including micro‐CT, mechanical testing and histological analysis. The critical nature of the defect was confirmed via all modalities. Both the scaffold and scaffold/SSC groups showed enhanced quantitative bone regeneration; however, this was only found to be significant in the scaffold/SSCs group (p = 0.04) and complete defect bridging was not achieved in any group. The mechanical strength was significantly less than that of contralateral control tibiae (p < 0.01) and would not be appropriate for full functional loading in a clinical setting. This study explored the hypothesis that cell therapy would enhance bone formation in a critical‐sized defect compared to scaffold alone, using an external fixation construct, to bridge the scale‐up gap between small animal studies and potential clinical translation. The model has proved a successful critical defect and analytical techniques have been found to be both valid and reproducible. Further work is required with both scaffold production techniques and cellular protocols in order to successfully scale‐up this stem cell/binary blend polymer scaffold. © 2015 The Authors. Journal of Tissue Engineering and Regenerative Medicine published by John Wiley & Sons, Ltd.

In situ micropillar compression reveals superior strength and ductility but an absence of damage in lamellar bone

Ageing societies suffer from an increasing incidence of bone fractures. Bone strength depends on the amount of mineral measured by clinical densitometry, but also on the micromechanical properties of the hierarchical organization of bone. Here, we investigate the mechanical response under monotonic and cyclic compression of both single osteonal lamellae and macroscopic samples containing numerous osteons. Micropillar compression tests in a scanning electron microscope, microindentation and macroscopic compression tests were performed on dry ovine bone to identify the elastic modulus, yield stress, plastic deformation, damage accumulation and failure mechanisms. We found that isolated lamellae exhibit a plastic behaviour, with higher yield stress and ductility but no damage. In agreement with a proposed rheological model, these experiments illustrate a transition from a ductile mechanical behaviour of bone at the microscale to a quasi-brittle response driven by the growth of cracks along interfaces or in the vicinity of pores at the macroscale.

Relationship between the v₂PO₄/amide III ratio assessed by Raman spectroscopy and the calcium content measured by quantitative backscattered electron microscopy in healthy human osteonal bone

Raman microspectroscopy and quantitative backscattered electron imaging (qBEI) of bone are powerful tools to investigate bone material properties. Both methods provide information on the degree of bone matrix mineralization. However, a head-to-head comparison of these outcomes from identical bone areas has not been performed to date. In femoral midshaft cross sections of three women, 99 regions (20×20 μm²) were selected inside osteons and interstitial bone covering a wide range of matrix mineralization. As the focus of this study was only on regions undergoing secondary mineralization, zones exhibiting a distinct gradient in mineral content close to the mineralization front were excluded. The same regions were measured by both methods. We found a linear correlation (R²=0.75) between mineral/matrix as measured by Raman spectroscopy and the wt. %Mineral/(100-wt. %Mineral) as obtained by qBEI, in good agreement with theoretical estimations. The observed deviations of single values from the linear regression line were determined to reflect biological heterogeneities. The data of this study demonstrate the good correspondence between Raman and qBEI outcomes in describing tissue mineralization. The obtained correlation is likely sensitive to changes in bone tissue composition, providing an approach to detect potential deviations from normal bone.

Use of perfusion bioreactors and large animal models for long bone tissue engineering

Tissue engineering and regenerative medicine (TERM) strategies for generation of new bone tissue includes the combined use of autologous or heterologous mesenchymal stem cells (MSC) and three-dimensional (3D) scaffold materials serving as structural support for the cells, that develop into tissue-like substitutes under appropriate in vitro culture conditions. This approach is very important due to the limitations and risks associated with autologous, as well as allogenic bone grafiting procedures currently used. However, the cultivation of osteoprogenitor cells in 3D scaffolds presents several challenges, such as the efficient transport of nutrient and oxygen and removal of waste products from the cells in the interior of the scaffold. In this context, perfusion bioreactor systems are key components for bone TERM, as many recent studies have shown that such systems can provide dynamic environments with enhanced diffusion of nutrients and therefore, perfusion can be used to generate grafts of clinically relevant sizes and shapes. Nevertheless, to determine whether a developed tissue-like substitute conforms to the requirements of biocompatibility, mechanical stability and safety, it must undergo rigorous testing both in vitro and in vivo. Results from in vitro studies can be difficult to extrapolate to the in vivo situation, and for this reason, the use of animal models is often an essential step in the testing of orthopedic implants before clinical use in humans. This review provides an overview of the concepts, advantages, and challenges associated with different types of perfusion bioreactor systems, particularly focusing on systems that may enable the generation of critical size tissue engineered constructs. Furthermore, this review discusses some of the most frequently used animal models, such as sheep and goats, to study the in vivo functionality of bone implant materials, in critical size defects.

Autologous vs. allogenic mesenchymal progenitor cells for the reconstruction of critical sized segmental tibial bone defects in aged sheep

Mesenchymal progenitor cells (MPCs) represent an attractive cell population for bone tissue engineering. Their special immunological characteristics suggest that MPCs may be used in allogenic applications. The objective of this study was to compare the regenerative potential of autologous vs. allogenic MPCs in an ovine critical size segmental defect model. Ovine MPCs were isolated from bone marrow aspirates, expanded and cultured with osteogenic medium for 2weeks before implantation. Autologous and allogenic transplantation was performed using the cell-seeded scaffolds and unloaded scaffolds, while the application of autologous bone grafts served as a control group (n=6). Bone healing was assessed 12weeks after surgery by radiology, microcomputed tomography, biomechanical testing and histology. Radiology, biomechanical testing and histology revealed no significant differences in bone formation between the autologous and allogenic groups. Both cell groups showed more bone formation than the scaffold alone, whereas the biomechanical data showed no significant differences between the cell groups and the unloaded scaffolds. The results of the study suggest that scaffold-based bone tissue engineering using allogenic cells offers the potential for an off-the-shelf product. Thus the results of this study serve as an important baseline for translation of the assessed concepts into clinical applications.

The use of preserved tissue in finite element modelling of fresh ovine vertebral behaviour

The aim of this study was to investigate whether the predicted finite element (FE) stiffness of vertebral bone is altered when using images of preserved rather than fresh tissue to generate specimen-specific FE models. Fresh ovine vertebrae were used to represent embalmed (n = 3) and macerated dry-bone (n = 3) specimens and treated accordingly. Specimens were scanned pre- and post-treatment using micro-computed tomography. A constant threshold level derived from these images was used to calculate the respective bone volume fraction (BV/TV) from which the conversion factor validated for fresh tissue was used to determine material properties that were assigned to corresponding FE models. Results showed a definite change in the BV/TV between the fresh and the preserved bone. However, the changes in the predicted FE stiffness were not generally greater than the variations expected from assignment of loading and boundary conditions. In conclusion, images of preserved tissue can be used to generate FE models that are representative of fresh tissue with a tolerable level of error.

Development of a clinically relevant animal model for the talar osteonecrosis in sheep

There are a lot of reports and reviews about osteonecrosis of the talus (ONT), yet reports about the animal model of ONT to evaluate proper therapeutic approaches are rarely heard. In our study, a novel animal model was established. Pure ethanol was injected into the cancellous bone of sheep's talus. Macroscopic observation, X-ray, CT and histology were performed at two, four, 12 and 24 weeks postoperatively. It was revealed that the trabeculae of talar head began to change their structure after two weeks postoperatively compared to the normal talus. The ONT was obvious at the end of the fourth week, and their outstanding feature was the damage of trabeculae bone and formation of cavities. CT scans and pathological changes of the subjects all showed characteristics of the early stage of osteonecrosis, also the sections of the specimens confirmed necrosis of tali. By 12 weeks, the phenomenon of necrosis still existed but fibrous tissue proliferated prominently and bone reconstruction appeared in certain area. Most specimens (3/4) got late stage necrosis which presented as synarthrosis in X-ray and mass proliferation of fibrous tissue in histology at the end of 24 weeks. The novel animal model of ONT was successful, and it is inclined to deteriorate without any intervention. The study provides us a new way to evaluate various treatments on ONT in laboratory, which may eventually pave way to clinical applications.

Natural mineralized scaffolds promote the dentinogenic potential of dental pulp stem cells via the mitogen-activated protein kinase signaling pathway

The selection of a suitable scaffold material is important for dentin tissue regeneration, as the characteristics of biomaterials can potentially influence cell proliferation and differentiation. We compared the effects of different scaffolds on dentin regeneration based on dental pulp stem cells (DPSCs) and investigated the regulatory mechanisms of odontogenic differentiation of DPSCs by these scaffolds. Five different scaffolds were tested: demineralized dentin matrix (DDM), ceramic bovine bone (CBB), small intestinal submucosa (SIS), poly-L-lactate-co-glycolate, and collagen-chondroitin sulfate-hyaluronic acid. DPSCs cultured on DDM and CBB exhibited higher levels of alkaline phosphatase (ALP) activity and mRNA expression of bone sialoprotein, osteocalcin, dentin sialophosphoprotein (DSPP), and dentin matrix protein-1 (DMP-1) than those cultured on the other three scaffolds. Further, the phosphorylation levels of mitogen-activated protein kinase (MAPK) ERK1/2 and p38 in DPSCs cultured on DDM and CBB were also significantly enhanced compared with the other three scaffolds, and their inhibitors significantly inhibited odontogenic differentiation as assessed by ALP activity and mRNA expression of DSPP and DMP-1. The implantation experiment confirmed these results and showed a large amount of regular-shaped dentin-pulp complex tissues, including dentin, predentin, and odontoblasts only in the DDM and CBB groups. The results indicated that natural mineralized scaffolds (DDM and CBB) have potential as attractive scaffolds for dentin tissue-engineering-promoted odontogenic differentiation of DPSCs through the MAPK signaling pathway.

The reliability of osteometric techniques for the sex determination of burned human skeletal remains

The influence of heat-induced shrinkage on the osteometric sexual dimorphism of human skeletons is still poorly known. In order to investigate this issue, a sample composed of 84 Portuguese individuals cremated at a modern crematorium was examined using standard measurements from the femur, the talus and the calcaneus. In addition, sex determination of the sample was attempted by using osteometric standards developed from the Coimbra collection of identified skeletons. This was carried out to assess the extent of the effect of heat-induced shrinkage on the correct classification of known-sex skeletons while using standards developed on unburned skeletons. Results demonstrated that sexual dimorphism was still observable in the sample of calcined bones despite shrinkage. However, the application of conventional osteometric standards was unsuccessful. As expected, shrinkage caused most females to be correctly classified according to sex, but the sex allocation of males was very poor for all standard measurements. The results were obtained on a small sample but suggest that univariate metric techniques specifically developed for calcined bones may be valuable for sex determination. This would bring new methodological possibilities for biological anthropology and would enlarge the set of techniques regarding sex determination of burned skeletal remains.

Post-mortem volatiles of vertebrate tissue

Volatile emission during vertebrate decay is a complex process that is understood incompletely. It depends on many factors. The main factor is the metabolism of the microbial species present inside and on the vertebrate. In this review, we combine the results from studies on volatile organic compounds (VOCs) detected during this decay process and those on the biochemical formation of VOCs in order to improve our understanding of the decay process. Micro-organisms are the main producers of VOCs, which are by- or end-products of microbial metabolism. Many microbes are already present inside and on a vertebrate, and these can initiate microbial decay. In addition, micro-organisms from the environment colonize the cadaver. The composition of microbial communities is complex, and communities of different species interact with each other in succession. In comparison to the complexity of the decay process, the resulting volatile pattern does show some consistency. Therefore, the possibility of an existence of a time-dependent core volatile pattern, which could be used for applications in areas such as forensics or food science, is discussed. Possible microbial interactions that might alter the process of decay are highlighted.

Composite transcriptome assembly of RNA-seq data in a sheep model for delayed bone healing

Background

The sheep is an important model organism for many types of medically relevant research, but molecular genetic experiments in the sheep have been limited by the lack of knowledge about ovine gene sequences.

Results

Prior to our study, mRNA sequences for only 1,556 partial or complete ovine genes were publicly available. Therefore, we developed a composite de novo transcriptome assembly method for next-generation sequence data to combine known ovine mRNA and EST sequences, mRNA sequences from mouse and cow, and sequences assembled de novo from short read RNA-Seq data into a composite reference transcriptome, and identified transcripts from over 12 thousand previously undescribed ovine genes. Gene expression analysis based on these data revealed substantially different expression profiles in standard versus delayed bone healing in an ovine tibial osteotomy model. Hundreds of transcripts were differentially expressed between standard and delayed healing and between the time points of the standard and delayed healing groups. We used the sheep sequences to design quantitative RT-PCR assays with which we validated the differential expression of 26 genes that had been identified by RNA-seq analysis. A number of clusters of characteristic expression profiles could be identified, some of which showed striking differences between the standard and delayed healing groups. Gene Ontology (GO) analysis showed that the differentially expressed genes were enriched in terms including extracellular matrix, cartilage development, contractile fiber, and chemokine activity.

Conclusions

Our results provide a first atlas of gene expression profiles and differentially expressed genes in standard and delayed bone healing in a large-animal model and provide a number of clues as to the shifts in gene expression that underlie delayed bone healing. In the course of our study, we identified transcripts of 13,987 ovine genes, including 12,431 genes for which no sequence information was previously available. This information will provide a basis for future molecular research involving the sheep as a model organism.

Ovine bone- and marrow-derived progenitor cells and their potential for scaffold-based bone tissue engineering applications in vitro and in vivo

Recently, research has focused on bone marrow derived multipotent mesenchymal precursor cells (MPC) and osteoblasts (OB) for clinical use in bone engineering. Prior to clinical application, cell based treatment concepts need to be evaluated in preclinical, large animal models. Sheep in particular are considered a valid model for orthopaedic and trauma related research. However, only sheep aged > 6 years show secondary osteon formation characteristic of human bone. Osteogenic cells isolated from animals of this age group remain poorly characterized. In the present study, ex vivo expanded MPC isolated from ovine bone marrow proliferated at a higher rate than OB derived from tibial compact bone as assessed in standard 2D cultures. MPC expressed the respective phenotypic profile typical for different mesenchymal cell populations (CD14(-)/CD31(-)/CD45(-)/CD29(+)/CD44(+)/CD166(+)) and showed a multilineage differentiation potential. When compared to OB, MPC had a higher mineralization potential under standard osteogenic culture conditions and expressed typical bone related markers such as osteocalcin, osteonectin and type I collagen at the mRNA and protein level. After 4 weeks in 3D culture, MPC constructs demonstrated higher cell density and mineralization, whilst cell viability on the scaffolds was assessed > 90%. Cells displayed a spindle-like morphology and formed interconnected networks. In contrast, when implanted subcutaneously into NOD/SCID mice, MPC presented a lower osteogenic potential than OB. In summary, this study provides a detailed characterisation of ovine MPC and OB from a bone engineering perspective and suggests that MPC and OB provide promising means for future bone disease related treatment applications.

Establishment of a preclinical ovine model for tibial segmental bone defect repair by applying bone tissue engineering strategies

Currently, well-established clinical therapeutic approaches for bone reconstruction are restricted to the transplantation of autografts and allografts, and the implantation of metal devices or ceramic-based implants to assist bone regeneration. Bone grafts possess osteoconductive and osteoinductive properties; however, they are limited in access and availability and associated with donor-site morbidity, hemorrhage, risk of infection, insufficient transplant integration, graft devitalization, and subsequent resorption resulting in decreased mechanical stability. As a result, recent research focuses on the development of alternative therapeutic concepts. The field of tissue engineering has emerged as an important approach to bone regeneration. However, bench-to-bedside translations are still infrequent as the process toward approval by regulatory bodies is protracted and costly, requiring both comprehensive in vitro and in vivo studies. The subsequent gap between research and clinical translation, hence, commercialization, is referred to as the "Valley of Death" and describes a large number of projects and/or ventures that are ceased due to a lack of funding during the transition from product/technology development to regulatory approval and subsequently commercialization. One of the greatest difficulties in bridging the Valley of Death is to develop good manufacturing processes and scalable designs and to apply these in preclinical studies. In this article, we describe part of the rationale and road map of how our multidisciplinary research team has approached the first steps to translate orthopedic bone engineering from bench to bedside by establishing a preclinical ovine critical-sized tibial segmental bone defect model, and we discuss our preliminary data relating to this decisive step.

Mechanical properties of organically modified silicates for bone regeneration

In this paper, different organic-inorganic hybrid materials based in the CaO-SiO(2)-poly(dimethyl siloxane) PDMS system have been characterised by means of nanoindentation and their static mechanical properties (Young's modulus, and hardness) have been investigated. These mechanical properties have been discussed in relation to the chemical composition and structure of the different hybrid materials. Besides, the mechanical behaviour of hybrid materials is visco-elastic and it therefore presents phenomena of creep that will be influenced by the temperature of the mechanical test; undoubtedly, a temperature of 37 degrees C accelerates the processes of creep.

An asymmetric coating composed of gelatin and hydroxyapatite for the delivery of water insoluble drug

An asymmetric coating composed of gelatin and hydroxyapatite on Ti6Al4V alloy implant was prepared to control the release of water-insoluble drug ibuprofen and improve the surface properties of the implant. The asymmetric coating developed into a thin dense outer layer and a thick porous inner layer using a dip-coating method and a succedent phase-inversion process. The drug loading ranged from 10 to 30% (w/w), and depended on the immersion time and drug concentration in the quenching solution. The in vitro release from this system was always at an approximately zero-order rate and at least lasted for 30 days. The in vitro studies in SBF revealed that the coating could induce the formation of apatite, and was fully covered after 14 days soaking in SBF solution. This asymmetric coating had better bioactivity of inducing the formation of apatite in vitro, compared with pure gelatin coating and bare Ti6Al4V implant.

The challenge of establishing preclinical models for segmental bone defect research

A considerable number of international research groups as well as commercial entities work on the development of new bone grafting materials, carriers, growth factors and specifically tissue-engineered constructs for bone regeneration. They are strongly interested in evaluating their concepts in highly reproducible large segmental defects in preclinical and large animal models. To allow comparison between different studies and their outcomes, it is essential that animal models, fixation devices, surgical procedures and methods of taking measurements are well standardized to produce reliable data pools and act as a base for further directions to orthopaedic and tissue engineering developments, specifically translation into the clinic. In this leading opinion paper, we aim to review and critically discuss the different large animal bone defect models reported in the literature. We conclude that most publications provide only rudimentary information on how to establish relevant preclinical segmental bone defects in large animals. Hence, we express our opinion on methodologies to establish preclinical critically sized, segmental bone defect models used in past research with reference to surgical techniques, fixation methods and postoperative management focusing on tibial fracture and segmental defect models.