A method for immunohistochemical detection of osteogenic markers in undecalcified bone sections

Effect of Tricalcium Phosphate Foam and Paste Bone Grafting Materials Designed for Improved Surgical Handling on Osteogenesis in a Sheep Scapula Model

Reconstruction of critical-size bone defects (CSDs) with complex defect morphologies remains clinically challenging. The desire to avoid autograft harvesting has prompted an increasing quest for adequate synthetic bone grafting materials. The clinical success rates, which have been achieved with bioactive β-tricalcium phosphate granules (TCP-G) demonstrate that these materials have become an excellent alternative graft choice. In order to improve surgical handling properties, TCP-G have been combined with natural polymers for creating paste- and foam-like materials, which can easily be molded into any desired shape when grafting a given bony defect or deploying them with a syringe. This study assessed the effect of a TCP paste (TCP-P) and a TCP-foam (TCP-F) bone grafting material as compared to TCP-G on bone formation and osteogenic marker expression after 1, 3, 6, 12, and 18 months of implantation in CSD in the sheep scapula and tested the hypothesis that the addition of natural polymers would not diminish the osteogenic properties of TCP-P and TCP-F. The bone and bone graft material area fractions were determined histomorphometrically in order to quantify bone formation and bone graft material resorption. Immunohistochemical analysis of collagen type I, osteocalcin, and bone sialoprotein expression in the various cell and matrix components of the bone tissue was performed on resin-embedded sections for characterizing the osteogenic and bioactive properties of the test materials. By 6 months, all three TCP materials facilitated excellent defect regeneration with further bone remodeling at 12 and 18 months. TCP-F and TCP-P induced greater osteocalcin expression and exhibited more advanced graft material resorption at 1 and 6 months, respectively. At 18 months, all three grafting materials were almost fully resorbed with the original bony architecture being restored. Taken together, the hyaluronic acid and methylcellulose components in TCP-P and porcine collagen components in TCP-F did not diminish the osteogenic capacity of TCP-P and TCP-F, which exhibited an even slightly higher resorbability and enhancement effect on OC expression by osteoblasts.

Effect of a synthetic hydroxyapatite-based bone grafting material compared to established bone substitute materials on regeneration of critical-size bone defects in the ovine scapula

Lately, the potential risk of disease transmission due to the use of bovine-derived bone substitutes has become obvious, demonstrating the urgent need for a synthetic grafting material with comparable bioactive behaviour and properties. Therefore, the effect of a synthetic hydroxyapatite (HA) (Osbone®) bone grafting material on bone regeneration was evaluated 2 weeks, 1 month, and 3, 6, 12 and 18 months after implantation in critical-size bone defects in the ovine scapula and compared to that of a bovine-derived HA (Bio-Oss®) and β-tricalcium phosphate (TCP) (Cerasorb® M). New bone formation and the biodegradability of the bone substitutes were assessed histomorphometrically. Hard tissue histology and immunohistochemical analysis were employed to characterize collagen type I, alkaline phosphatase, osteocalcin, as well as bone sialoprotein expression in the various cell and matrix components of the bone tissue to evaluate the bioactive properties of the bone grafting materials. No inflammatory tissue response was detected with any of the bone substitute materials studied. After 3 and 6 months, β-TCP (Cerasorb® M) showed superior bone formation when compared to both HA-based materials (3 months: β-TCP 55.65 ± 2.03% vs. SHA 49.05 ± 3.84% and BHA 47.59 ± 1.97%; p ≤ 0.03; 6 months: β-TCP 62.03 ± 1.58%; SHA: 55.83 ± 2.59%; BHA: 53.44 ± 0.78%; p ≤ 0.04). Further, after 12 and 18 months, a similar degree of bone formation and bone-particle contact was noted for all three bone substitute materials without any significant differences. The synthetic HA supported new bone formation, osteogenic marker expression, matrix mineralization and good bone-bonding behaviour to an equal and even slightly superior degree compared to the bovine-derived HA. As a result, synthetic HA can be regarded as a valuable alternative to the bovine-derived HA without the potential risk of disease transmission.

Osteogenic Effect of a Bioactive Calcium Alkali Phosphate Bone Substitute in Humans

(1) Background: The desire to avoid autograft harvesting in implant dentistry has prompted an ever-increasing quest for bioceramic bone substitutes, which stimulate osteogenesis while resorbing in a timely fashion. Consequently, a highly bioactive silicon containing calcium alkali orthophosphate (Si-CAP) material was created, which previously was shown to induce greater bone cell maturation and bone neo-formation than β-tricalcium phosphate (β-TCP) in vivo as well as in vitro. Our study tested the hypothesis that the enhanced effect on bone cell function in vitro and in sheep in vivo would lead to more copious bone neoformation in patients following sinus floor augmentation (SFA) employing Si-CAP when compared to β-TCP. (2) Methods: The effects of Si-CAP on osteogenesis and Si-CAP resorbability were evaluated in biopsies harvested from 38 patients six months after SFA in comparison to β-TCP employing undecalcified histology, histomorphometry, and immunohistochemical analysis of osteogenic marker expression. (3) Results: Si-CAP as well as β-TCP supported matrix mineralization and bone formation. Apically furthest away from the original bone tissue, Si-CAP induced significantly higher bone formation, bone-bonding (bone-bioceramic contact), and granule resorption than β-TCP. This was in conjunction with a higher expression of osteogenic markers. (4) Conclusions: Si-CAP induced higher and more advanced bone formation and resorbability than β-TCP, while β-TCP's remarkable osteoconductivity has been widely demonstrated. Hence, Si-CAP constitutes a well-suited bioactive graft choice for SFA in the clinical arena.

A tissue engineered 3D printed calcium alkali phosphate bioceramic bone graft enables vascularization and regeneration of critical-size discontinuity bony defects in vivo

Introduction: Recently, efforts towards the development of patient-specific 3D printed scaffolds for bone tissue engineering from bioactive ceramics have continuously intensified. For reconstruction of segmental defects after subtotal mandibulectomy a suitable tissue engineered bioceramic bone graft needs to be endowed with homogenously distributed osteoblasts in order to mimic the advantageous features of vascularized autologous fibula grafts, which represent the standard of care, contain osteogenic cells and are transplanted with the respective blood vessel. Consequently, inducing vascularization early on is pivotal for bone tissue engineering. The current study explored an advanced bone tissue engineering approach combining an advanced 3D printing technique for bioactive resorbable ceramic scaffolds with a perfusion cell culture technique for pre-colonization with mesenchymal stem cells, and with an intrinsic angiogenesis technique for regenerating critical size, segmental discontinuity defects in vivo applying a rat model. To this end, the effect of differing Si-CAOP (silica containing calcium alkali orthophosphate) scaffold microarchitecture arising from 3D powder bed printing (RP) or the Schwarzwalder Somers (SSM) replica fabrication technique on vascularization and bone regeneration was analyzed in vivo. In 80 rats 6-mm segmental discontinuity defects were created in the left femur. Methods: Embryonic mesenchymal stem cells were cultured on RP and SSM scaffolds for 7d under perfusion to create Si-CAOP grafts with terminally differentiated osteoblasts and mineralizing bone matrix. These scaffolds were implanted into the segmental defects in combination with an arteriovenous bundle (AVB). Native scaffolds without cells or AVB served as controls. After 3 and 6 months, femurs were processed for angio-µCT or hard tissue histology, histomorphometric and immunohistochemical analysis of angiogenic and osteogenic marker expression. Results: At 3 and 6 months, defects reconstructed with RP scaffolds, cells and AVB displayed a statistically significant higher bone area fraction, blood vessel volume%, blood vessel surface/volume, blood vessel thickness, density and linear density than defects treated with the other scaffold configurations. Discussion: Taken together, this study demonstrated that the AVB technique is well suited for inducing adequate vascularization of the tissue engineered scaffold graft in segmental defects after 3 and 6 months, and that our tissue engineering approach employing 3D powder bed printed scaffolds facilitated segmental defect repair.

Calcitonin Gene-Related Peptide Attenuates Hyperoxia-Induced Oxidative Damage in Alveolar Epithelial Type II Cells Through Regulating Viability and Transdifferentiation

As a stem cell of alveolar epithelium, the physiological status of alveolar epithelium type II cells (AECII) after hyperoxia exposure is closely related to the occurrence of hyperoxia-induced lung injury and the restoration of normal morphological function of damaged alveolar epithelium. However, the relevant mechanisms involved are not very clear. Therefore, this study aimed to explore the effect of calcitonin gene-related peptide (CGRP) on AECII exposed to hyperoxia and its potential mechanisms. The AECII viability was detected using MTT assay. The malondialdehyde (MDA) level and superoxide dismutase (SOD) activity were detected by spectrophotometry. The transdifferentiation capacity of AECII was evaluated by flow cytometry. The expression levels of Notch1, Hes, HERP, and AECII markers were detected using immunohistochemistry and/or RT-qPCR or immunofluorescence. ELISA was used for the determination of inflammatory markers. The results showed that CGRP significantly promoted cell viability, and markedly suppressed hyperoxia-induced transdifferentiation of AECII; these biological alterations were coincided with decreased MDA level, increased SOD activity, and activated Notch signaling pathway (upregulated expression levels of Notch1, Hes, and HERP). Notably, the in vitro effects of CGRP on Notch signaling pathway were further investigated in animal model, and the HE staining results showed that CGRP reduced in vivo oxidative injury and inflammation in hyperoxia-treated AECII through the promotion of structural and functional regeneration, accompanied by elevated Notch1 expression and activated Notch signaling cascade as shown by immunohistochemistry and QPCR, respectively. Immunohistochemistry of APQ-5 and SPC indicated that CGRP reversed the transdifferentiation of AECIIs in vivo. Our current results were consistent across both in vitro and in vivo settings, and provide a new direction for the prevention and treatment of bronchopulmonary dysplasia (BPD).

Quality control methods in musculoskeletal tissue engineering: from imaging to biosensors

Tissue engineering is rapidly progressing toward clinical application. In the musculoskeletal field, there has been an increasing necessity for bone and cartilage replacement. Despite the promising translational potential of tissue engineering approaches, careful attention should be given to the quality of developed constructs to increase the real applicability to patients. After a general introduction to musculoskeletal tissue engineering, this narrative review aims to offer an overview of methods, starting from classical techniques, such as gene expression analysis and histology, to less common methods, such as Raman spectroscopy, microcomputed tomography, and biosensors, that can be employed to assess the quality of constructs in terms of viability, morphology, or matrix deposition. A particular emphasis is given to standards and good practices (GXP), which can be applicable in different sectors. Moreover, a classification of the methods into destructive, noninvasive, or conservative based on the possible further development of a preimplant quality monitoring system is proposed. Biosensors in musculoskeletal tissue engineering have not yet been used but have been proposed as a novel technology that can be exploited with numerous advantages, including minimal invasiveness, making them suitable for the development of preimplant quality control systems.

Histopathological Evaluation of Orthopedic Medical Devices: The State-of-the-art in Animal Models, Imaging, and Histomorphometry Techniques

Orthopedic medical devices are continuously evolving for the latest clinical indications in craniomaxillofacial, spine, trauma, joint arthroplasty, sports medicine, and soft tissue regeneration fields, with a variety of materials from new metallic alloys and ceramics to composite polymers, bioresorbables, or surface-treated implants. There is great need for qualified medical device pathologists to evaluate these next generation biomaterials, with improved biocompatibility and bioactivity for orthopedic applications, and a broad range of knowledge is required to stay abreast of this ever-changing field. Orthopedic implants require specialized imaging and processing techniques to fully evaluate the bone-implant interface, and the pathologist plays an important role in determining the proper combination of histologic processing and staining for quality slide production based on research and development trials and validation. Additionally, histomorphometry is an essential part of the analysis to quantify tissue integration and residual biomaterials. In this article, an overview of orthopedic implants and animal models, as well as pertinent insights for tissue collection, imaging, processing, and slide generation will be provided with a special focus on histopathology and histomorphometry evaluation.

Bone Morphogenetic Proteins (BMPs) and Bone Regeneration

Many research methods exist to elucidate the role of BMP-2 during bone regeneration. This chapter briefly reviews important animal models used in these studies and provides details on the rat femur defect model. This animal model is frequently utilized to measure the efficacy of osteogenic factors like BMP-2. Detailed information about delivery methods, dose range, and dose duration used in BMP-2-related studies are provided.

An Optimized Approach to Perform Bone Histomorphometry

Bone histomorphometry allows quantitative evaluation of bone micro-architecture, bone formation, and bone remodeling by providing an insight to cellular changes. Histomorphometry plays an important role in monitoring changes in bone properties because of systemic skeletal diseases like osteoporosis and osteomalacia. Besides, quantitative evaluation plays an important role in fracture healing studies to explore the effect of biomaterial or drug treatment. However, until today, to our knowledge, bone histomorphometry remain time-consuming and expensive. This incited us to set up an open-source freely available semi-automated solution to measure parameters like trabecular area, osteoid area, trabecular thickness, and osteoclast activity. Here in this study, the authors present the adaptation of Trainable Weka Segmentation plugin of ImageJ to allow fast evaluation of bone parameters (trabecular area, osteoid area) to diagnose bone related diseases. Also, ImageJ toolbox and plugins (BoneJ) were adapted to measure osteoclast activity, trabecular thickness, and trabecular separation. The optimized two different scripts are based on ImageJ, by providing simple user-interface and easy accessibility for biologists and clinicians. The scripts developed for bone histomorphometry can be optimized globally for other histological samples. The showed scripts will benefit the scientific community in histological evaluation.

Effect of a Particulate and a Putty-Like Tricalcium Phosphate-Based Bone-grafting Material on Bone Formation, Volume Stability and Osteogenic Marker Expression after Bilateral Sinus Floor Augmentation in Humans

This study examines the effect of a hyaluronic acid (HyAc) containing tricalcium phosphate putty scaffold material (TCP-P) and of a particulate tricalcium phosphate (TCP-G) graft on bone formation, volume stability and osteogenic marker expression in biopsies sampled 6 months after bilateral sinus floor augmentation (SFA) in 7 patients applying a split-mouth design. 10% autogenous bone chips were added to the grafting material during surgery. The grain size of the TCP granules was 700 to 1400 µm for TCP-G and 125 to 250 µm and 500 to 700 µm (ratio 1:1) for TCP-P. Biopsies were processed for immunohistochemical analysis of resin-embedded sections. Sections were stained for collagen type I (Col I), alkaline phosphatase (ALP), osteocalcin (OC) and bone sialoprotein (BSP). Furthermore, the bone area and biomaterial area fraction were determined histomorphometrically. Cone-beam CT data recorded after SFA and 6 months later were used for calculating the graft volume at these two time points. TCP-P displayed more advantageous surgical handling properties and a significantly greater bone area fraction and smaller biomaterial area fraction. This was accompanied by significantly greater expression of Col I and BSP and in osteoblasts and osteoid and a less pronounced reduction in grafting volume with TCP-P. SFA using both types of materials resulted in formation of sufficient bone volume for facilitating stable dental implant placement with all dental implants having been in function without any complications for 6 years. Since TCP-P displayed superior surgical handling properties and greater bone formation than TCP-G, without the HyAc hydrogel matrix having any adverse effect on bone formation or graft volume stability, TCP-P can be regarded as excellent grafting material for SFA in a clinical setting. The greater bone formation observed with TCP-P may be related to the difference in grain size of the TCP granules and/or the addition of the HyAc.

Development of a synthetic tissue engineered three-dimensional printed bioceramic-based bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro

Over the last decade there have been increasing efforts to develop three-dimensional (3D) scaffolds for bone tissue engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo. To this end, 3D scaffolds were developed from a silica-containing calcium alkali orthophosphate, using, first, a replica technique - the Schwartzwalder-Somers method - and, second, 3D printing, (i.e. rapid prototyping). The mechanical and physical scaffold properties and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture were examined. Osteoblastic cells were dynamically cultured for 7 days on both scaffold types with two different concentrations of 1.5 and 3 × 10⁹ cells/l. The amount of cells and bone matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. 3D-printed scaffolds (RPS) exhibited more micropores, greater compressive strength and silica release. RPS seeded with 3 × 10⁹ cells/l displayed greatest cell and extracellular matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of sex-hormone levels, sex, body mass index and other host factors on human craniofacial bone regeneration with bioactive tricalcium phosphate grafts

Little is known regarding the associations between sex-hormone levels, sex, body mass index (BMI), age, other host factors and biomaterial stimulated bone regeneration in the human craniofacial skeleton. The aim of this study was to elucidate the associations between these factors and bone formation after sinus floor augmentation procedures (SFA) utilizing a bioactive tricalcium phosphate (TCP) bone grafting material. We conducted a prospective study in a human population in which 60 male and 60 female participants underwent SFA and dental implant placement using a staged approach. BMI as well as levels of serum estradiol (E2), total testosterone (TT), and the free androgen index (FAI) were measured by radioimmunoassay and electrochemoluminescent-immunoassay. At implant placement, 6 months after SFA, bone biopsy specimens were harvested for hard tissue histology, the amount of bone formation was evaluated by histomorphometry and immunohistochemical analysis of osteogenic marker expression. The Wilcoxon rank-sum U test, Spearman correlations and linear regression analysis were used to explore the association between bone formation and BMI, hormonal and other host factors. BMI and log E2 were significantly positively associated with bone formation in male individuals (p < 0.05). Histomorphometry revealed trends toward greater bone formation and osteogenic marker expression with non-smokers compared to smokers. In male patients, higher E2 levels and higher BMI enhanced TCP stimulated craniofacial i.e. intramembranous bone repair.

Novel Bioceramic Urethral Bulking Agents Elicit Improved Host Tissue Responses in a Rat Model

Objectives. To test the physical properties and host response to the bioceramic particles, silica-calcium phosphate (SCPC10) and Cristobalite, in a rat animal model and compare their biocompatibility to the current clinically utilized urethral bulking materials. Material and Methods. The novel bulking materials, SCPC10 and Cristobalite, were suspended in hyaluronic acid sodium salt and injected into the mid urethra of a rat. Additional animals were injected with bulking materials currently in clinical use. Physiological response was assessed using voiding trials, and host tissue response was evaluated using hard tissue histology and immunohistochemical analysis. Distant organs were evaluated for the presence of particles or their components. Results. Histological analysis of the urethral tissue five months after injection showed that both SCPC10 and Cristobalite induced a more robust fibroblastic and histiocytic reaction, promoting integration and encapsulation of the particle aggregates, leading to a larger bulking effect. Concentrations of Ca, Na, Si, and P ions in the experimental groups were comparable to control animals. Conclusions. This side-by-side examination of urethral bulking agents using a rat animal model and hard tissue histology techniques compared two newly developed bioactive ceramic particles to three of the currently used bulking agents. The local host tissue response and bulking effects of bioceramic particles were superior while also possessing a comparable safety profile.

Efficacy of novel synthetic bone substitutes in the reconstruction of large segmental bone defects in sheep tibiae

The treatment of large bone defects, particularly those with segmental bone loss, remains a significant clinical challenge as current approaches involving surgery or bone grafting often do not yield satisfactory long-term outcomes. This study reports the evaluation of novel ceramic scaffolds applied as bone graft substitutes in a clinically relevant in vivo model. Baghdadite scaffolds, unmodified or modified with a polycaprolactone coating containing bioactive glass nanoparticles, were implanted into critical-sized segmental bone defects in sheep tibiae for 26 weeks. Radiographic, biomechanical, μ-CT and histological analyses showed that both unmodified and modified baghdadite scaffolds were able to withstand physiological loads at the defect site, and induced substantial bone formation in the absence of supplementation with cells or growth factors. Notably, all samples showed significant bridging of the critical-sized defect (average 80%) with evidence of bone infiltration and remodelling within the scaffold implant. The unmodified and modified baghdadite scaffolds achieved similar outcomes of defect repair, although the latter may have an initial mechanical advantage due to the nanocomposite coating. The baghdadite scaffolds evaluated in this study hold potential for use as purely synthetic bone graft substitutes in the treatment of large bone defects while circumventing the drawbacks of autografts and allografts.

Bone regeneration in calvarial defects in a rat model by implantation of human bone marrow-derived mesenchymal stromal cell spheroids

Mesenchymal stem cell (MSC) condensation contributes to membrane ossification by enhancing their osteodifferentiation. We investigated bone regeneration in rats using the human bone marrow-derived MSC-spheroids prepared by rotation culture, without synthetic or exogenous biomaterials. Bilateral calvarial defects (8 mm) were created in nude male rats; the left-sided defects were implanted with MSC-spheroids, β-tricalcium phosphate (β-TCP) granules, or β-TCP granules + MSC-spheroids, while the right-sided defects served as internal controls. Micro-computed tomography and immunohistochemical staining for osteocalcin/osteopontin indicated formation of new, full-thickness bones at the implantation sites, but not at the control sites in the MSC-spheroid group. Raman spectroscopy revealed similarity in the spectral properties of the repaired bone and native calvarial bone. Mechanical performance of the bones in the MSC-implanted group was good (50 and 60% those of native bones, respectively). All tests showed poor bone regeneration in the β-TCP and β-TCP + MSC-spheroid groups. Thus, significant bone regeneration was achieved with MSC-spheroid implantation into bone defects, justifying further investigation.

Different approaches for interpretation and reporting of immunohistochemistry analysis results in the bone tissue - a review

BACKGROUND

Immunohistochemistry (IHC) is a well-established, widely accepted method in both clinical and experimental parts of medical science. It allows receiving valuable information about any process in any tissue, and especially in bone. Each year the amount of data, received by IHC, grows in geometric progression. But the lack of standardization, especially on the post-analytical stage (interpreting and reporting of results), makes the comparison of the results of different studies impossible.

METHODS

Comprehensive PubMED literature search with a combination of search words "immunohistochemistry" and "scoring system" was performed and 773 articles describing IHC results were identified. After further manual analysis 120 articles were selected for detailed evaluation of used approaches.

RESULTS

Six major approaches to the interpretation and presentation of IHC analysis results were identified, analyzed and described.

CONCLUSIONS

The overview of the existing approaches in evaluation and interpretation of IHC data, which are provided in the article, can be used in bone tissue research and for either better understanding of existing scoring systems or developing a new one. Standard multiparametric, semiquantitative IHC scoring systems should simplify and clarify the process of interpretation and reporting of received data.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_221.

In Vivo Osteogenesis Assessment of a Tricalcium Phosphate Paste and a Tricalcium Phosphate Foam Bone Grafting Materials

Calcium phosphates (CaPs) are synthetic bone grafting materials. CaPs are an alternative to overcome the drawbacks present with autologous bone grafting and/or xenograft materials. Among the CaPs, tricalcium phosphate (TCP) stands out as a good candidate due to its physicochemical properties. The clinical performance of β-TCP has already been proven and established. Nevertheless, the format in which TCP is delivered is also important in terms of clinical handling. This work assessed the in vivo performance of TCP-based bone grafting materials with different formats. Materials studied were a TCP paste (TCP-P), a TCP foam (TCP-F) and TCP granules (TCP-G). A sheep scapula model was used to evaluate the osteogenic performance of these bone grafting materials. All materials performed well in terms of bone regenerative capacity and material resorption. However, TCP-P and TCP-F displayed a more pronounced initial material resorption and also exhibited better handling properties compared to TCP-G. TCP-based materials with improved handling properties, such as TCP-P and TCP-F, which at the same time possess the advantageous properties of β-TCP are suitable bone substitute materials for grafting and reconstruction of bone defects in numerous clinical applications.

Effect of Silicon-Doped Calcium Phosphate Bone Substitutes on Bone Formation and Osteoblastic Phenotype Expression In Vivo

This study evaluates the effect of two novel particulate silicon-doped calcium phosphate graft materials as compared to the currently clinically used material β-TCP on osteogenesis and bone formation after implantation in critical-size defects the sheep scapula. These materials were developed in order to create biodegradable bone substitute materials that degrade rapidly, but still stimulate osteogenesis at the same time, thereby resulting in bone repair and regeneration with fully functional bone tissue. All bone substitute materials studied facilitated excellent bony regeneration of critical-size defects in the sheep scapula. Of the three grafting materials studied, the calcium alkali orthophosphate material with the crystalline phase Ca2KNa (PO4)2, with a small amorphous portion containing magnesium potassium phosphate and a small addition of sodium magnesium silicate had the greatest stimulatory effect on bone formation and expression of osteogenic markers, while exhibiting the highest biodegradability.

Histological analysis of cells and matrix mineralization of new bone tissue induced in rabbit femur bones by Mg-Zr based biodegradable implants

The biological efficacy of bone inducing implant materials in situ can be assessed effectively by performing histological analysis. We studied the peri-implant bone regeneration around two types of biodegradable magnesium-zirconium alloys, Mg-5Zr and Mg-Zr-2Sr, using histological, histochemical and immunohistochemical methods in the femur of New Zealand White strain rabbits. Our study includes three animal groups: (a) Mg-5Zr, (b) Mg-Zr-2Sr and (c) control. In each group three animals were used and in groups 'a' and 'b' the respective alloys were implanted in cavities made at the distal ends of the femur; control animals were left without implants to observe natural bone healing. Qualitative assessment of the cellularity and matrix mineralization events of the newly formed bone tissue was done at three months after implantation by histological methods in methyl methacrylate embedded tissue without decalcifying the bone. Quantitative mineral content and density of the new bone (NB) were evaluated by the statistical analysis of dual energy X-ray absorptiometry (DXA) data obtained from three animals in each experimental group. Based on our analysis we conclude that Mg-Zr-2Sr alloy showed better osseointegration of the newly formed bone with the implant surface. Our methodology of studying peri-implant osteoinduction of degradable implants using low temperature methyl methacrylate embedding resin can be useful as a general method for determining the bio-efficacy of implant materials.

Multiple silk coatings on biphasic calcium phosphate scaffolds: effect on physical and mechanical properties and in vitro osteogenic response of human mesenchymal stem cells

Ceramic scaffolds such as biphasic calcium phosphate (BCP) have been widely studied and used for bone regeneration, but their brittleness and low mechanical strength are major drawbacks. We report the first systematic study on the effect of silk coating in improving the mechanical and biological properties of BCP scaffolds, including (1) optimization of the silk coating process by investigating multiple coatings, and (2) in vitro evaluation of the osteogenic response of human mesenchymal stem cells (hMSCs) on the coated scaffolds. Our results show that multiple silk coatings on BCP ceramic scaffolds can achieve a significant coating effect to approach the mechanical properties of native bone tissue and positively influence osteogenesis by hMSCs over an extended period. The silk coating method developed in this study represents a simple yet effective means of reinforcement that can be applied to other types of ceramic scaffolds with similar microstructure to improve osteogenic outcomes.

Unique microstructural design of ceramic scaffolds for bone regeneration under load

During the past two decades, research on ceramic scaffolds for bone regeneration has progressed rapidly; however, currently available porous scaffolds remain unsuitable for load-bearing applications. The key to success is to apply microstructural design strategies to develop ceramic scaffolds with mechanical properties approaching those of bone. Here we report on the development of a unique microstructurally designed ceramic scaffold, strontium-hardystonite-gahnite (Sr-HT-gahnite), with 85% porosity, 500μm pore size, a competitive compressive strength of 4.1±0.3MPa and a compressive modulus of 170±20MPa. The in vitro biocompatibility of the scaffolds was studied using primary human bone-derived cells. The ability of Sr-HT-gahnite scaffolds to repair critical-sized bone defects was also investigated in a rabbit radius under normal load, with β-tricalcium phosphate/hydroxyapatite scaffolds used in the control group. Studies with primary human osteoblast cultures confirmed the bioactivity of these scaffolds, and regeneration of rabbit radial critical defects demonstrated that this material induces new bone defect bridging, with clear evidence of regeneration of original radial architecture and bone marrow environment.

Repairing a critical-sized bone defect with highly porous modified and unmodified baghdadite scaffolds

This is the first reported study to prepare highly porous baghdadite (Ca₃ZrSi₂O₉) scaffolds with and without surface modification and investigate their ability to repair critical-sized bone defects in a rabbit radius under normal load. The modification was carried out to improve the mechanical properties of the baghdadite scaffolds (particularly to address their brittleness) by coating their surfaces with a thin layer (∼400 nm) of polycaprolactone (PCL)/bioactive glass nanoparticles (nBGs). The β-tricalcium phosphate/hydroxyapatite (TCP/HA) scaffolds with and without modification were used as the control groups. All of the tested scaffolds had an open and interconnected porous structure with a porosity of ∼85% and average pore size of 500 μm. The scaffolds (six per scaffold type and size of 4 mm × 4 mm × 15 mm) were implanted (press-fit) into the rabbit radial segmental defects for 12 weeks. Micro-computed tomography and histological evaluations were used to determine bone ingrowth, bone quality, and implant integration after 12 weeks of healing. Extensive new bone formation with complete bridging of the radial defect was evident with the baghdadite scaffolds (modified/unmodified) at the periphery and in close proximity to the ceramics within the pores, in contrast to TCP/HA scaffolds (modified/unmodified), where bone tended to grow between the ulna adjacent to the implant edge. Although the modification of the baghdadite scaffolds significantly improved their mechanical properties, it did not show any significant effect on in vivo bone formation. Our findings suggest that baghdadite scaffolds with and without modification can serve as a potential material to repair critical sized bone defects.

The incorporation of strontium and zinc into a calcium-silicon ceramic for bone tissue engineering

In this study we developed novel scaffolds through the controlled substitution and incorporation of strontium and zinc into a calcium-silicon system to form Sr-Hardystonite (Sr-Ca(2)ZnSi(2)O(7), Sr-HT). The physical and biological properties of Sr-HT were compared to Hardystonite (Ca(2)ZnSi(2)O(7)) [HT]. We showed that Sr-HT scaffolds are porous with interconnected porous network (interconnectivity: 99%) and large pore size (300-500 microm) and an overall porosity of 78%, combined with a relatively high compressive strength (2.16+/-0.52 MPa). These properties are essential for enhancing bone ingrowth in load-bearing applications. Sr-HT ceramic scaffolds induced the attachment and differentiation of human bone derived cells (HOB), compared to that for the HT scaffolds. Sr-HT scaffolds enhanced expression of alkaline phosphatase, Runx-2, osteopontin, osteocalcin and bone sialoprotein. The in vivo osteoconductivity of the scaffolds was assessed at 3 and 6 weeks following implantation in tibial bone defects in rats. Histological staining revealed rapid new growth of bone into the pores of the 3D scaffolds with the Sr-HT and HT, relative to the beta-tricalcium phosphate (beta-TCP). In vivo, HT and Sr-HT produced distinct differences in the patterns of degradation of the materials, and their association with TRAP positive osteoclast-like cells with HT appearing more resistant compared to both Sr-HT and beta-TCP.

Quantification of bone tissue regeneration employing beta-tricalcium phosphate by three-dimensional non-invasive synchrotron micro-tomography--a comparative examination with histomorphometry

PURPOSE

This methodical study presents a novel approach to evaluate the validity of two-dimensional histomorphometric measurements of a bone biopsy specimen after sinus floor elevation by means of high contrast, high resolution, three-dimensional and non-destructive synchrotron micro-tomography (SCT). The aim of this methodical description is to demonstrate the potential of this new approach for the evaluation of bone biopsy samples.

MATERIALS AND METHODS

Unilateral sinus grafting was carried out exemplarily in two patients using a combination of beta-tricalcium phosphate (beta-TCP) and autogenous bone chips. For the first patient a beta-TCP with 35% porosity and in the second with 60% porosity was used. At implant placement, 6 months after sinus grafting, a cylindrical specimen was biopsied from the augmented area. Subsequent to the histological embedding in resin the specimens were imaged using a SCT facility resulting in three-dimensional (3-D) images with approximately 4 microm spatial resolution (1.5 microm pixel size) for each patient's specimen. Subsequent to the SCT acquisition, tissue sections were prepared for histomorphometric analysis.

RESULTS

Bone area fractions determined by two-dimensional (2-D) quantitative histomorphometry and by analysis of the corresponding 2-D slice from the SCT volume data were similar. For the first biopsy specimen (beta-TCP with 35% porosity), the bone area fractions were 53.3% and 54.9% as derived by histomorphometry and by analyzing a SCT slice, respectively. For the second biopsy specimen (beta-TCP with 60% porosity) the bone area fractions were 38.8% and 39% respectively. Although the agreement between the 2-D methods was excellent, the area fractions were somewhat higher than the volume fractions computed by 3-D image analysis on the entire SCT volume data set. The volume fractions were 48.8% (first biopsy specimen) and 36.3% (second biopsy specimen).

CONCLUSION

Although the agreement between the 2-D methods is excellent in terms of computing the area fractions, the structural 3-D insight which can be derived from classical 2-D methods, including histomorphometric analysis is considerably limited. This fact is emphasized by the discrepancy between the measured areas and volume fractions.

Effect of rapidly resorbable bone substitute materials on the temporal expression of the osteoblastic phenotype in vitro

Ideally, bioactive ceramics for use in alveolar ridge augmentation should possess the ability to activate bone formation and, thus, cause the differentiation of osteoprogenitor cells into osteoblasts at their surfaces. Therefore, in order to evaluate the osteogenic potential of novel bone substitute materials, it is important to examine their effect on osteoblastic differentiation. This study examines the effect of rapidly resorbable calcium-alkali-orthophosphates on osteoblastic phenotype expression and compares this behavior to that of beta-tricalcium phosphate (TCP) and bioactive glass 45S5. Test materials were three materials (denominated GB14, GB9, GB9/25) with a crystalline phase Ca(2)KNa(PO(4))(2) and with a small amorphous portion containing either magnesium potassium phosphate (GB14) or silica phosphate (GB9 and GB9/25, which also contains Ca(2)P(2)O(7)); and a material with a novel crystalline phase Ca(10)[K/Na](PO(4))(7) (material denominated 352i). SaOS-2 human bone cells were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for an array of osteogenic markers. GB9 had the greatest stimulatory effect on osteoblastic proliferation and differentiation, suggesting that this material possesses the highest potency to enhance osteogenesis. GB14 and 352i supported osteoblast differentiation to the same or a higher degree than TCP, whereas, similar to bioactive glass 45S5, GB9/25 displayed a greater stimulatory effect on osteoblastic phenotype expression, indicating that GB9/25 is also an excellent material for promoting osteogenesis.

Effect of beta-tricalcium phosphate particles with varying porosity on osteogenesis after sinus floor augmentation in humans

This study examines the effect of two beta-tricalcium phosphate (TCP) particulate bone grafting materials with varying porosity on bone formation and on osteogenic marker expression 6 months after sinus floor augmentation. Unilateral sinus grafting was performed in 20 patients using a combination (4:1 ratio) of beta-TCP particles with 35% porosity (TCP-C) or 65% porosity (TCP-CM) and autogenous bone chips. At implant placement cylindrical biopsies were sampled and processed for immunohistochemical analysis of resin embedded sections. Sections were stained for collagen type I (Col I), alkaline phosphatase (ALP), osteocalcin (OC) and bone sialoprotein (BSP). Furthermore, the area fraction of newly formed bone as well as the particle area fraction were determined histomorphometrically first, apically close to the Schneiderian membrane and second, in the center of the cylindrical biopsies. In the TCP-CM patient group a larger amount of bone formation and particle degradation was observed in the apical area and thus at the largest distance from the crestal bone compared to the TCP-C group. Good bone bonding behaviour was observed with both materials. This was accompanied by expression of ALP, Col I, BSP and OC in the newly formed bone and osteogenic mesenchym in contact with the degrading particles. Both TCP materials supported bone formation in the augmented sinus floor. Six months after implantation of both types of beta-TCP particles, bone formation and matrix mineralization was still actively progressing in the tissue surrounding the particles. Consequently, a greater porosity appears to be advantageous for enhancing bone formation and particle degradation.