Synchrotron X-ray microtomography (on a micron scale) provides three-dimensional imaging representation of bone ingrowth in calcium phosphate biomaterials

Fabrication and X-ray microtomography of sandwich-structured PEEK implants for skull defect repair

Bone defects pose a significant risk to human health. Medical polyetheretherketone (PEEK) is an excellent implant material for bone defect repair, but it faces the challenge of bone osteoconduction and osseointegration. Osteoconduction describes the process by which bone grows on the surface of the implant, while osseointegration is the stable anchoring of the implant achieved by direct contact between the bone and the implant. Bone defects repair depends on the implant's three-dimensional spatial structure, including pore size, porosity, and interconnections to a great extent. However, it is challenging to fabricate the porous structures to meet specific requirements and to characterize them without causing damage. In this study, we designed and fabricated sandwich-like PEEK implants mimicking the three-layer structures of the skull, whose defects imposes a significant burden on young adulthood and paediatric populations, and performed in-line phase-contrast synchrotron X-ray microtomography to non-destructively investigate the internal porous microstructures. The sandwich-like three-layer microstructure, comprising a dense layer, a loose layer and a dense layer in succession, exhibits structural similarity to that in a natural skull. This work demonstrated the fabrication of the sandwich-like PEEK implant that could potentially enhance osteoconduction and osseointegration. Furthermore, the interior structures and residual porogen sodium chloride particles were observed within the PEEK implant, which cannot be realized by other microscopic methods without destroying the sample. It highlights the advantages and potential of using synchrotron X-ray microtomography to analyze the structure of biomedical materials. This study provides theoretical guidance for the further design and fabrication of PEEK bone repair materials and will advance the clinical application of innovative bioactive bone repair materials.

Phase-contrast imaging with synchrotron hard X-ray reveals the effect of icariin on bone tissue morphology and microstructure in rabbits with early glucocorticoid-induced osteonecrosis of the femoral head

Background: Phase-contrast imaging (PCI) with synchrotron hard X-ray was used to observe the changes in bone tissue morphology and microstructure in rabbit models of early glucocorticoid-induced osteonecrosis of the femoral head (ONFH), and to evaluate the intervention effect of Icariin. Methods: Fifty mature New Zealand rabbits (weighing 2.5-3.0 kg) were randomly divided into a control group (n = 10), a glucocorticoid group (n = 20), and an Icariin group (n = 20). The glucocorticoid group and the Icariin group were sequentially injected with lipopolysaccharide (LPS) and methylprednisolone (MPS) to establish a glucocorticoid-induced ONFH animal model. The Icariin group was given Icariin solution when methylprednisolone was injected for the first time, and the control group and glucocorticoid group were given the same amount of normal saline. Animals were sacrificed after 6 weeks, and bilateral femoral head specimens were taken for research. The right femoral head was observed by PCI with synchrotron hard X-ray technology, and the left femoral head was verified by Micro-CT scanning and HE staining. Results: Forty-three animals (nine in the control group, sixteen in the glucocorticoid group, and eighteen in the Icariin group) were included in the study. PCI with synchrotron hard X-ray revealed that the trabecular bone in the glucocorticoid group was thinned, broken, and structurally damaged, whereas the trabecular bone in the Icariin group had normal volume, thickness, and a relatively intact structure. Micro-CT scan reconstruction and HE staining were used to verify the reliability of this technique in identifying osteonecrosis. Conclusion: The effects of Icariin were observed in an early glucocorticoid-induced ONFH rabbit model using PCI with synchrotron hard X-ray. Icariin weakens the destructive effect of glucocorticoids on bone tissue structure, improves bone tissue morphology, and stabilizes bone microstructure. This technique may provide a definitive, non-invasive alternative to histological examination for the diagnosis of early ONFH.

A practical guide for in situ mechanical testing of musculoskeletal tissues using synchrotron tomography

Musculoskeletal tissues are complex hierarchical materials where mechanical response is linked to structural and material properties at different dimensional levels. Therefore, high-resolution three-dimensional tomography is very useful for assessing tissue properties at different scales. In particular, Synchrotron Radiation micro-Computed Tomography (SR-microCT) has been used in several applications to analyze the structure of bone and biomaterials. In the past decade the development of digital volume correlation (DVC) algorithms applied to SR-microCT images and its combination with in situ mechanical testing (four-dimensional imaging) have allowed researchers to visualise, for the first time, the deformation of musculoskeletal tissues and their interaction with biomaterials under different loading scenarios. However, there are several experimental challenges that make these measurements difficult and at high risk of failure. Challenges relate to sample preparation, imaging parameters, loading setup, accumulated tissue damage for multiple tomographic acquisitions, reconstruction methods and data processing. Considering that access to SR-microCT facilities is usually associated with bidding processes and long waiting times, the failure of these experiments could notably slow down the advancement of this research area and reduce its impact. Many of the experimental failures can be avoided with increased experience in performing the tests and better guidelines for preparation and execution of these complex experiments; publication of negative results could help interested researchers to avoid recurring mistakes. Therefore, the goal of this article is to highlight the potential and pitfalls in the design and execution of in situ SR-microCT experiments, involving multiple scans, of musculoskeletal tissues for the assessment of their structural and/or mechanical properties. The advice and guidelines that follow should improve the success rate of this type of experiment, allowing the community to reach higher impact more efficiently.

Computed Tomography as a Characterization Tool for Engineered Scaffolds with Biomedical Applications

The ever-growing field of materials with applications in the biomedical field holds great promise regarding the design and fabrication of devices with specific characteristics, especially scaffolds with personalized geometry and architecture. The continuous technological development pushes the limits of innovation in obtaining adequate scaffolds and establishing their characteristics and performance. To this end, computed tomography (CT) proved to be a reliable, nondestructive, high-performance machine, enabling visualization and structure analysis at submicronic resolutions. CT allows both qualitative and quantitative data of the 3D model, offering an overall image of its specific architectural features and reliable numerical data for rigorous analyses. The precise engineering of scaffolds consists in the fabrication of objects with well-defined morphometric parameters (e.g., shape, porosity, wall thickness) and in their performance validation through thorough control over their behavior (in situ visualization, degradation, new tissue formation, wear, etc.). This review is focused on the use of CT in biomaterial science with the aim of qualitatively and quantitatively assessing the scaffolds’ features and monitoring their behavior following in vivo or in vitro experiments. Furthermore, the paper presents the benefits and limitations regarding the employment of this technique when engineering materials with applications in the biomedical field.

High resolution imaging in bone tissue research-review

This review article focuses on imaging of bone tissue to understand skeletal health with regards to bone quality. Skeletal fragility fractures are due to bone diseases such as osteoporosis which result in low bone mass and bone mineral density (BMD) leading to high risk of fragility fractures. Recent advances in imaging and analysis technologies have highly benefitted the field of biological sciences. In particular, their application in skeletal health has been of significant importance in understanding bone mechanical behavior (structure and properties) at the tissue level. While synchrotron based microCT technique has remained the gold standard for non-destructive evaluation of structure in material and biological sciences, several lab based microCT systems have been developed to provide high resolution imaging of specimens with greater access, and ease of use in laboratory settings. Lab based microCT scanners are widely used in the bone field as a standard tool to evaluate three-dimensional (3D) morphologies of bone structure at image resolutions appropriate for bone samples from small animals to bone biopsy specimens from humans. Both synchrotron and standard lab based microCT systems provide high resolution imaging ex vivo for a small sized specimen. A few X-ray based systems are also commercially available for in vivo scanning at relatively low image resolutions. Synchrotron-based CT microscopy is being used for various ultra-high-resolution image analyses using complex 3D software. However, the synchrotron-based CT technology is in high demand, allows only limited numbers of specimens, expensive, requires complex additional instrumentation, and is not easily available to researchers as it requires access to a synchrotron source which is always limited. Therefore, desktop laboratory scanners (microXCT, Zeiss/Xradia, Scanco, SkyScan. etc.), mimicking the synchrotron based CT technology or image resolution, have been developed to solve the accessibility issues. These lab based scanners have helped both material science, and the bone field to investigate bone tissue morphologies at submicron mage resolutions. Considerable progress has been made in both in vivo and ex vivo imaging towards providing high resolution images of bone tissue. Both clinical and research imaging technologies will continue to improve and help understand osteoporosis and other related skeletal issues in order to develop targeted treatments for bone fragility. This review summarizes the high resolution imaging work in bone research.

Trabecular architecture during the healing process of a tibial diaphysis defect

The adaptation of trabecular bone microstructure to mechanical loads has been intensively investigated. However, loading-unrelated aspects of trabecular architecture remain unclear. We used synchrotron radiation-based X-ray microtomography to study the 3D microarchitecture of newly formed trabecular tissue in a defect produced in the cortical region of the rat tibia diaphysis, in the absence (7, 14, and 21 days) or the presence (21 days) of carbonated hydroxyapatite/alginate (cHA) microspheres. This work provides the first evidence that the woven bone trabecular network, formed during the healing process, displays a well-organized 3D microarchitecture consisting of nodes with 3 (3-N), 4 (4-N) and 5 (5-N) connecting trabeculae, with a mean relative abundance of (3-N)/(4-N)/(5-N) = 66/24/7, for the analyzed periods. The measured inter-trabecular angles (ITA) distribution presented a Gaussian profile, with mean value at 115° for 3-N nodes, and 105° for 4-N nodes, close to the angles of idealized 3D regular structures (120° and 109.5°, respectively). Changes in the dispersion of ITA distribution suggested that a highly symmetric trabecular fabric organized under tensegrity principles is formed early during the bone healing process. Post-implantation, cHA disaggregated into multiple fragments (~20-400 μm), stimulating osteoconduction and bone growth toward the interior of the medullary cavity. The presence of biomaterials in bone defects affected the trabecular dimensions; however, it did not interfere with the formation of geometrical motifs with topological parameters similar to those found in the sham-defects. STATEMENT OF SIGNIFICANCE: The trabecular bone microstructure enables the tissue to meet the necessary mechanical and functional demands. However, the process of trabecular microarchitecture formation during healing, in the absence or presence of a bone graft, is not yet well understood. This work demonstrated that, from the beginning of its formation in cortical bone defects, the woven-bone trabecular network is spatially organized according to the principle of tensegrity. This microarchitecture is comprised of highly symmetric geometric motifs and is an intrinsic characteristic of trabecular growth, regardless of hierarchical scale or mechanical stimulation. The addition of a biodegradable nanostructured calcium phosphate graft did not disrupt trabecular microarchitecture; however, graft biodegradation should be controlled to optimize the reproduction of intrinsic trabecular motifs throughout the defect.

A Novel 3D-bioprinted Porous Nano Attapulgite Scaffolds with Good Performance for Bone Regeneration

Background

Natural clay nanomaterials are an emerging class of biomaterial with great potential for tissue engineering and regenerative medicine applications, most notably for osteogenesis.

Materials and Methods

Herein, for the first time, novel tissue engineering scaffolds were prepared by 3D bioprinter using nontoxic and bioactive natural attapulgite (ATP) nanorods as starting materials, with polyvinyl alcohol as binder, and then sintered to obtain final scaffolds. The microscopic morphology and structure of ATP particles and scaffolds were observed by transmission electron microscope and scanning electron microscope. In vitro biocompatibility and osteogenesis with osteogenic precursor cell (hBMSCs) were assayed using MTT method, Live/Dead cell staining, alizarin red staining and RT-PCR. In vivo bone regeneration was evaluated with micro-CT and histology analysis in rat cranium defect model.

Results

We successfully printed a novel porous nano-ATP scaffold designed with inner channels with a dimension of 500 µm and wall structures with a thickness of 330 µm. The porosity of current 3D-printed scaffolds ranges from 75% to 82% and the longitudinal compressive strength was up to 4.32±0.52 MPa. We found firstly that nano-ATP scaffolds with excellent biocompatibility for hBMSCscould upregulate the expression of osteogenesis-related genes bmp2 and runx2 and calcium deposits in vitro. Interestingly, micro-CT and histology analysis revealed abundant newly formed bone was observed along the defect margin, even above and within the 3D bioprinted porous ATP scaffolds in a rat cranial defect model. Furthermore, histology analysis demonstrated that bone was formed directly following a process similar to membranous ossification without any intermediate cartilage formation and that many newly formed blood vessels are within the pores of 3D-printed scaffolds at four and eight weeks.

Conclusion

These results suggest that the 3D-printed porous nano-ATP scaffolds are promising candidates for bone tissue engineering by osteogenesis and angiogenesis.

Human iPSC-derived iMSCs improve bone regeneration in mini-pigs

Autologous bone marrow concentrate (BMC) and mesenchymal stem cells (MSCs) have beneficial effects on the healing of bone defects. To address the shortcomings associated with the use of primary MSCs, induced pluripotent stem cell (iPSC)-derived MSCs (iMSCs) have been proposed as an alternative. The aim of this study was to investigate the bone regeneration potential of human iMSCs combined with calcium phosphate granules (CPG) in critical-size defects in the proximal tibias of mini-pigs in the early phase of bone healing compared to that of a previously reported autograft treatment and treatment with a composite made of either a combination of autologous BMC and CPG or CPG alone. iMSCs were derived from iPSCs originating from human fetal foreskin fibroblasts (HFFs). They were able to differentiate into osteoblasts in vitro, express a plethora of bone morphogenic proteins (BMPs) and secrete paracrine signaling-associated cytokines such as PDGF-AA and osteopontin. Radiologically and histomorphometrically, HFF-iMSC + CPG transplantation resulted in significantly better osseous consolidation than the transplantation of CPG alone and produced no significantly different outcomes compared to the transplantation of autologous BMC + CPG after 6 weeks. The results of this translational study imply that iMSCs represent a valuable future treatment option for load-bearing bone defects in humans.

Synchrotron radiation techniques boost the research in bone tissue engineering

X-ray Synchrotron radiation-based techniques, in particular Micro-tomography and Micro-diffraction, were exploited to investigate the structure of bone deposited in vivo within a porous ceramic scaffold. Bone formation was studied by implanting Mesenchymal Stem Cell (MSC) seeded ceramic scaffolds in a mouse model. Osteoblasts derived from the seeded MSC and from differentiation of cells migrated within the scaffold together with the blood vessels, deposited within the scaffold pores an organic collagenous matrix on which a precursor mineral amorphous liquid-phase, containing Ca++ and PO₄^-- crystallized filling the gaps between the collagen molecules. Histology offered a valid instrument to investigate the engineered tissue structure, but, unfortunately, limited itself to a macroscopic analysis. The evolution of the X-ray Synchrotron radiation-based techniques and the combination of micro X-ray diffraction with X-ray phase-contrast imaging enabled to study the dynamic of the structural and morphological changes occurring during the new bone deposition, biomineralization and vascularization. In fact, the unique features of Synchrotron radiation, is providing the high spatial resolution probe which is necessary for the study of complex materials presenting heterogeneity from micron-scale to meso- and nano-scale. Indeed, this is the occurrence in the heterogeneous and hierarchical bone tissue where an organic matter, such as the collagenous matrix, interacts with mineral nano-crystals to generate a hybrid multiscale biomaterial with unique physical properties. In this framework, the use of advanced synchrotron radiation techniques allowed to understand and to clarify fundamental aspects of the bone formation process within the bioceramic, i.e. biomineralization and vascularization, including to obtain deeper knowledge on bone deposition, mineralization and reabsorption in different health, aging and pathological conditions. In this review we present an overview of the X-ray Synchrotron radiation techniques and we provide a general outlook of their applications on bone Tissue Engineering, with a focus on our group work. STATEMENT OF SIGNIFICANCE: Synchrotron Radiation techniques for Tissue Engineering In this review we report recent applications of X-ray Synchrotron radiation-based techniques, in particular Microtomography and Microdiffraction, to investigations on the structure of ceramic scaffolds and bone tissue regeneration. Tissue engineering has made significant advances in bone regeneration by proposing the use of mesenchymal stem cells in combination with various types of scaffolds. The efficacy of the biomaterials used to date is not considered optimal in terms of resorbability and bone formation, resulting in a poor vascularization at the implant site. The review largely based on our publications in the last ten years could help the study of the regenerative model proposed. We also believe that the new imaging technologies we describe could be a starting point for the development of additional new techniques with the final aim of transferring them to the clinical practice.

Recent advances in stem cell therapeutics and tissue engineering strategies

Background

Tissue regeneration includes delivering specific types of cells or cell products to injured tissues or organs for restoration of tissue and organ function. Stem cell therapy has drawn considerable attention since transplantation of stem cells can overcome the limitations of autologous transplantation of patient’s tissues; however, it is not perfect for treating diseases. To overcome the hurdles associated with stem cell therapy, tissue engineering techniques have been developed. Development of stem cell technology in combination with tissue engineering has opened new ways of producing engineered tissue substitutes. Several studies have shown that this combination of tissue engineering and stem cell technologies enhances cell viability, differentiation, and therapeutic efficacy of transplanted stem cells.

Main body

Stem cells that can be used for tissue regeneration include mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells. Transplantation of stem cells alone into injured tissues exhibited low therapeutic efficacy due to poor viability and diminished regenerative activity of transplanted cells. In this review, we will discuss the progress of biomedical engineering, including scaffolds, biomaterials, and tissue engineering techniques to overcome the low therapeutic efficacy of stem cells and to treat human diseases.

Conclusion

The combination of stem cell and tissue engineering techniques overcomes the limitations of stem cells in therapy of human diseases, and presents a new path toward regeneration of injured tissues.

Incorporation of fast dissolving glucose porogens and poly(lactic-co-glycolic acid) microparticles within calcium phosphate cements for bone tissue regeneration

This study investigated the effects of incorporating glucose microparticles (GMPs) and poly(lactic-co-glycolic acid) microparticles (PLGA MPs) within a calcium phosphate cement on the cement's handling, physicochemical properties, and the respective pore formation. Composites were fabricated with two different weight fractions of GMPs (10 and 20 wt%) and two different weight fractions of PLGA MPs (10 and 20 wt%). Samples were assayed for porosity, pore morphology, and compressive mechanical properties. An in vitro degradation study was also conducted. Samples were exposed to a physiological solution for 3 days, 4 wks, and 8 wks in order to understand how the inclusion of GMPs and PLGA MPs affects the composite's porosity and mass loss over time. GMPs and PLGA MPs were both successfully incorporated within the composites and all formulations showed an initial setting time that is appropriate for clinical applications. Through a main effects analysis, we observed that the incorporation of GMPs had a significant effect on the overall porosity, mean pore size, mode pore size, and in vitro degradation rate of PLGA MPs as early as after 3 days (p < 0.05). After 4 wks and 8 wks, these same properties were affected by the inclusion of both types of MPs (p < 0.05). Advanced polymer chromatography confirmed that the degradation of PLGA MPs coincided with an increase in composite porosity, mean pore size, and mode pore size. Finally, it was observed that the inclusion of GMPs slowed the degradation of PLGA MPs in vitro and reduced the solution acidity due to PLGA degradation products. Our results suggest that the dual inclusion of GMPs and PLGA MPs is a valuable approach for the generation of early macropores, while also mitigating the effect of acidic degradation products from PLGA MPs on their degradation kinetics.

STATEMENT OF SIGNIFICANCE

A multitude of strategies and techniques have been investigated for the introduction of macropores with calcium phosphate cements (CPC). However, many of these strategies take several weeks to months to generate a maximal porosity or the degradation products of the porogen can trigger a localized inflammatory response in vivo. As such, it was hypothesized that the fast dissolution of glucose microparticles (GMPs) in a CPC composite also incorporating poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) will create an initial macroporosity and increase the surface area within the CPC, thus enhancing the diffusion of PLGA degradation products and preventing a significant decrease in pH. Furthermore, as PLGA degradation occurs over several weeks to months, additional macroporosity will be generated at later time points within CPCs. The results offer a new method for generating macroporosity in a multimodal fashion that also mitigates the effects of acidic degradation products.

Bone regeneration with adipose derived stem cells in a rabbit model

It has been shown that stem cells are able to calcify both in vitro and in vivo once implanted under the skin, if conveniently differentiated. Nowadays, however, a study on their efficiency in osseous regeneration does not exist in scientific literature and this very task is the real aim of the present experimentation. Five different defects of 6 mm in diameter and 2 mm in depth were created in the calvaria of 8 white New Zealand rabbits. Four defects were regenerated using 2 different conveniently modified scaffolds (Bio-Oss® Block and Bio-Oss Collagen®, Geistlich), with and without the aid of stem cells. After the insertion, the part was covered with a collagen membrane fixed by 5 modified titan pins (Altapin®). The defect in the front was left empty on purpose as an internal control to each animal. Two animals were sacrificed respectively after 2, 4, 6, 10 weeks. The samples were evaluated with micro-CT and histological analysis. Micro-CT analysis revealed that the quantity of new bone for samples with Bio-Oss® Block and stem cells was higher than for samples with Bio-Oss® Block alone. Histological analysis showed that regeneration occurred in an optimal way in every sample treated with scaffolds. The findings indicated that the use of adult stem cells combined with scaffolds accelerated some steps in normal osseous regeneration.

Biphasic calcium phosphate ceramics for bone reconstruction: A review of biological response

Autologous bone graft is considered as the gold standard in bone reconstructive surgery. However, the quantity of bone available is limited and the harvesting procedure requires a second surgical site resulting in severe complications. Due to these limits, scientists and clinicians have considered alternatives to autologous bone graft. Calcium phosphates (CaPs) biomaterials including biphasic calcium phosphate (BCP) ceramics have proven efficacy in numerous clinical indications. Their specific physico-chemical properties (HA/TCP ratio, dual porosity and subsequent interconnected architecture) control (regulate/condition) the progressive resorption and the bone substitution process. By describing the most significant biological responses reported in the last 30years, we review the main events that made their clinical success. We also discuss about their exciting future applications as osteoconductive scaffold for delivering various bioactive molecules or bone cells in bone tissue engineering and regenerative medicine.

STATEMENT OF SIGNIFICANCE

Nowadays, BCPs are definitely considered as the gold standard of bone substitutes in bone reconstructive surgery. Among the numerous clinical studies in literature demonstrating the performance of BCP, Passuti et al. and Randsford et al. studies largely contributed to the emergence of the BCPs. It could be interesting to come back to the main events that made their success and could explain their large adhesion from scientists to clinicians. This paper aims to review the most significant biological responses reported in the last 30years, of these BCP-based materials. We also discuss about their exciting future applications as osteoconductive scaffold for delivering various bioactive molecules or bone cells in bone tissue engineering and regenerative medicine.

Synchrotron Imaging Assessment of Bone Quality

Bone is a complex hierarchical structure, and its principal function is to resist mechanical forces and fracture. Bone strength depends not only on the quantity of bone tissue but also on the shape and hierarchical structure. The hierarchical levels are interrelated, especially the micro-architecture, collagen and mineral components; hence, analysis of their specific roles in bone strength and stiffness is difficult. Synchrotron imaging technologies including micro-CT and small/wide angle X-ray scattering/diffraction are becoming increasingly popular for studying bone because the images can resolve deformations in the micro-architecture and collagen-mineral matrix under in situ mechanical loading. Synchrotron cannot be directly applied in vivo due to the high radiation dose but will allow researchers to carry out systematic multifaceted studies of bone ex vivo. Identifying characteristics of aging and disease will underpin future efforts to generate novel devices and interventional therapies for assessing and promoting healthy aging. With our own research work as examples, this paper introduces how synchrotron imaging technology can be used with in situ testing in bone research.

Carboxylate-Terminated Double-Hydrophilic Block Copolymer as an Effective Inhibitor for Carbonate and Sulphate Scales

For the control of carbonate and sulphate scales, a new type of green scale inhibitors AQn was synthesized. The thermal stability and the molecular weight of the copolymers were investigated by thermal gravimetric analysis and gel permeation chromatography, respectively. The anti-scale property of the AQn copolymers towards CaCO3 and CaSO4 in the artificial cooling water was studied through static scale inhibition tests. The results show that both CaCO3 and CaSO4 inhibition increase with increasing the degree of polymerization of AQn from 5 to 15. The dosage of AQn plays also an important role on CaCO3 and CaSO4 inhibition. Surface morphology characterization of CaCO3 and CaSO4 was investigated with combination of scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) analysis. An inhibition mechanism is proposed that the interactions between calcium and polyethylene glycol (PEG) are the fundamental impetus to restrain the formation of the scale in cooling water systems.

Scanning Small- and Wide-Angle X-ray Scattering Microscopy Selectively Probes HA Content in Gelatin/Hydroxyapatite Scaffolds for Osteochondral Defect Repair

This study is aimed at investigating the structure of a scaffold made of bovine gelatin and hydroxyapatite for bone tissue engineering purposes. In particular, the detailed characterization of such a material has a great relevance because of its application in the healing process of the osteochondral defect that consists of a damage of cartilage and injury of the adjacent subchondral bone, significantly compromising millions of patient's quality of life. Two different techniques exploiting X-ray radiation, with table-top setups, are used: microtomography (micro-CT) and microdiffraction. Micro-CT characterizes the microstructure in the three dimensions at the micrometer scale spatial resolution, whereas microdiffraction provides combined structural/morphological information at the atomic and nanoscale, in two dimensional microscopy images with a hundred micrometer spatial resolution. The combination of these two techniques allowed an appropriate structural characterization for the purpose of validating the engineering approach used for the realization of the hydroxyapatite gradient across the scaffold, with properties close to the natural model.

Visualization and quantification of deformation behavior of clopidogrel bisulfate polymorphs during tableting

The deformation behavior of particles under pressure dominates the mechanical properties of solid dosage forms. In this study, the in situ 3D deformation of two polymorphs (I and II) of clopidogrel bisulfate (CLP) was determined to illustrate pressure distribution profiles within the tablet by the deformation of the crystalline particles for the first time. Synchrotron radiation X-ray computed microtomography (SR-μCT) was utilized to visualize and quantify the morphology of thousands crystalline particles of CLP I and CLP II before and after compression. As a result, the deformation was examined across scale dimensions from microns to the size of the final dosage form. Three dimensional parameters such as volume, sphericity, oblate and prolate of individual particle and distributions were computed and analyzed for quantitative comparison to CLP I and CLP II. The different degrees of deformation under the same compression conditions of CLP I and CLP II were observed and characterized quantitatively. The map of deformation degrees within the tablet illustrated the heterogeneous pressure distribution in various regions of the compacted tablet. In conclusion, the polymorph deformation behaviors demonstrated by SR-μCT quantitative structure analysis deepen understanding of tableting across dimensions from microns to millimeters for the macrostrcuture of tablet.

Pre-clinical characterization of tissue engineering constructs for bone and cartilage regeneration

Pre-clinical animal models play a crucial role in the translation of biomedical technologies from the bench top to the bedside. However, there is a need for improved techniques to evaluate implanted biomaterials within the host, including consideration of the care and ethics associated with animal studies, as well as the evaluation of host tissue repair in a clinically relevant manner. This review discusses non-invasive, quantitative, and real-time techniques for evaluating host-materials interactions, quality and rate of neotissue formation, and functional outcomes of implanted biomaterials for bone and cartilage tissue engineering. Specifically, a comparison will be presented for pre-clinical animal models, histological scoring systems, and non-invasive imaging modalities. Additionally, novel technologies to track delivered cells and growth factors will be discussed, including methods to directly correlate their release with tissue growth.

The composite of bone marrow concentrate and PRP as an alternative to autologous bone grafting

One possible alternative to the application of autologous bone grafts represents the use of autologous bone marrow concentrate (BMC). The purpose of our study was to evaluate the potency of autologous platelet-rich plasma (PRP) in combination with BMC. In 32 mini-pigs a metaphyseal critical-size defect was surgically created at the proximal tibia. The animals were allocated to four treatment groups of eight animals each (1. BMC+CPG group, 2. BMC+CPG+PRP group, 3. autograft group, 4. CPG group). In the BMC+CPG group the defect was filled with autologous BMC in combination with calcium phosphate granules (CPG), whereas in the BMC+CPG+PRP group the defect was filled with the composite of autologous BMC, CPG and autologous PRP. In the autograft group the defect was filled with autologous cancellous graft, whereas in the CPG group the defect was filled with CPG solely. After 6 weeks radiological and histomorphometrical analysis showed significantly more new bone formation in the BMC+CPG+PRP group compared to the BMC+CPG group and the CPG group. There were no significant differences between the BMC+CPG+PRP group and the autograft group. In the PRP platelets were enriched significantly about 4.7-fold compared to native blood. In BMC the count of mononuclear cells increased significantly (3.5-fold) compared to the bone marrow aspirate. This study demonstrates that the composite of BMC+CPG+PRP leads to a significantly higher bone regeneration of critical-size defects at the proximal tibia in mini-pigs than the use of BMC+CPG without PRP. Furthermore, within the limits of the present study the composite BMC+CPG+PRP represents a comparable alternative to autologous bone grafting.

The relevance of biomaterials to the prevention and treatment of osteoporosis

Osteoporosis is a worldwide disease with a very high prevalence in humans older than 50. The main clinical consequences are bone fractures, which often lead to patient disability or even death. A number of commercial biomaterials are currently used to treat osteoporotic bone fractures, but most of these have not been specifically designed for that purpose. Many drug- or cell-loaded biomaterials have been proposed in research laboratories, but very few have received approval for commercial use. In order to analyze this scenario and propose alternatives to overcome it, the Spanish and European Network of Excellence for the Prevention and Treatment of Osteoporotic Fractures, "Ageing", was created. This network integrates three communities, e.g. clinicians, materials scientists and industrial advisors, tackling the same problem from three different points of view. Keeping in mind the premise "living longer, living better", this commentary is the result of the thoughts, proposals and conclusions obtained after one year working in the framework of this network.

Resolving the CaP-bone interface: a review of discoveries with light and electron microscopy

It has long been known that the interfacial relationship between synthetic materials and tissue is influential in the success of implant materials. Instability at the implant interface has been shown, in some cases, to lead to complete implant failure. Bioceramics, and in particular calcium phosphates, form a large fraction of the implantable devices on the market today due to the biocompatibility they exhibit in contact with bone and tooth-like tissues. The characterization of such bioceramic-tissue interfaces has played a crucial role in understanding the behavior of bioceramics in vivo. In this review, we shed light on the preparation methods, technological approaches and key advances in resolving the interface between calcium phosphate bioceramics and bone, and share a future outlook on this field.

Evaluation of 3D printing and its potential impact on biotechnology and the chemical sciences

Nearing 30 years since its introduction, 3D printing technology is set to revolutionize research and teaching laboratories. This feature encompasses the history of 3D printing, reviews various printing methods, and presents current applications. The authors offer an appraisal of the future direction and impact this technology will have on laboratory settings as 3D printers become more accessible.

Gelatin powders accelerate the resorption of calcium phosphate cement and improve healing in the alveolar ridge

The aim of this study was to show the effectiveness of combining calcium phosphate cement and gelatin powders to promote bone regeneration in the canine mandible. We mixed gelatin powders with calcium phosphate cement to create a macroporous composite. In four beagle dogs, two saddle-type bone defects were created on each side of the mandible, and calcium phosphate cement alone or calcium phosphate cement containing composite gelatin powders was implanted in each of the defects. After a healing period of six months, mandibles were removed for µCT and histological analyses. The µCT and histological analyses showed that at experimental sites at which calcium phosphate cement alone had been placed new bone had formed only around the periphery of the residual calcium phosphate cement and that there had been little or no ingrowth into the calcium phosphate cement. On the other hand, at experimental sites at which calcium phosphate cement containing composite gelatin powders had been placed, we observed regenerated new bone in the interior of the residual calcium phosphate cement as well as around its periphery. The amount of resorption of calcium phosphate cement and bone regeneration depended on the mixing ratio of gelatin powders to calcium phosphate cement. New bone replacement was significantly better in the sites treated with calcium phosphate cement containing composite gelatin powders than in those treated with calcium phosphate cement alone.

The early phase influence of bone marrow concentrate on metaphyseal bone healing

Bone marrow concentrate (BMC) contains high densities of progenitor cells. Therefore, in critical size defects BMC may have the potency to support bone healing. The aim of this study was to investigate the effect of BMC in combination with calcium phosphate granules (CPG) on bone defect healing in a metaphyseal long bone defect in mini-pigs. A metaphyseal critical-size bone defect at the proximal tibia of 24 mini-pigs was filled with CPG combined with BMC, CPG solely (control group) or with an autograft. Radiological and histomorphometrical evaluations after 6 weeks (42 days) showed significantly more bone formation in the BMC group in the central area of the defect zone and the cortical defect zone compared to the CPG group. At the same time the resorption rate of CPG increased significantly in the BMC group. Nevertheless, compared to the BMC group the autograft group showed a significantly higher new bone formation radiologically and histomorphometrically. In BMC the count of mononuclear cells was significantly higher compared to the bone marrow aspirate (3.5-fold). The mesenchymal progenitor cell characteristics of the cells in BMC were confirmed by flow cytometry. Cells from BMC created significantly larger colonies of alkaline phosphatase-positive colony forming units (CFU-ALP) (4.4-fold) compared to cells from bone marrow aspirate. Nevertheless, even in the BMC group complete osseous bridging was only detectable in isolated instances of the bone defects. Within the limitations of this study the BMC+CPG composite promotes bone regeneration in the early phase of bone healing significantly better than the isolated application of CPG. However, the addition of BMC does not lead to a solid fusion of the defect in the early phase of bone healing an still does not represent an equal alternative to autologous bone.

Recent developments of functional scaffolds for craniomaxillofacial bone tissue engineering applications

Autogenous bone grafting remains a gold standard for the reconstruction critical-sized bone defects in the craniomaxillofacial region. Nevertheless, this graft procedure has several disadvantages such as restricted availability, donor-site morbidity, and limitations in regard to fully restoring the complicated three-dimensional structures in the craniomaxillofacial bone. The ultimate goal of craniomaxillofacial bone reconstruction is the regeneration of the physiological bone that simultaneously fulfills both morphological and functional restorations. Developments of tissue engineering in the last two decades have brought such a goal closer to reality. In bone tissue engineering, the scaffolds are fundamental, elemental and mesenchymal stem cells/osteoprogenitor cells and bioactive factors. A variety of scaffolds have been developed and used as spacemakers, biodegradable bone substitutes for transplanting to the new bone, matrices of drug delivery system, or supporting structures enhancing adhesion, proliferation, and matrix production of seeded cells according to the circumstances of the bone defects. However, scaffolds to be clinically completely satisfied have not been developed yet. Development of more functional scaffolds is required to be applied widely to cranio-maxillofacial bone defects. This paper reviews recent trends of scaffolds for crania-maxillofacial bone tissue engineering, including our studies.

Imaging challenges in biomaterials and tissue engineering

Biomaterials are employed in the fields of tissue engineering and regenerative medicine (TERM) in order to enhance the regeneration or replacement of tissue function and/or structure. The unique environments resulting from the presence of biomaterials, cells, and tissues result in distinct challenges in regards to monitoring and assessing the results of these interventions. Imaging technologies for three-dimensional (3D) analysis have been identified as a strategic priority in TERM research. Traditionally, histological and immunohistochemical techniques have been used to evaluate engineered tissues. However, these methods do not allow for an accurate volume assessment, are invasive, and do not provide information on functional status. Imaging techniques are needed that enable non-destructive, longitudinal, quantitative, and three-dimensional analysis of TERM strategies. This review focuses on evaluating the application of available imaging modalities for assessment of biomaterials and tissue in TERM applications. Included is a discussion of limitations of these techniques and identification of areas for further development.

Gelation behavior of in situ forming gels based on HPMC and biphasic calcium phosphate nanoparticles

In this study, in situ forming gels are prepared using biphasic calcium phosphate (BCP) as filler and hydroxypropyl methylcellulose (HPMC) as a matrix exhibiting temperature-sensitive behavior. BCP was composed of β-tricalcium phosphate (β-TCP) with plate-like morphology and nano-sized hyadroxyapatite (HAp). Gel permeation chromatography (GPC) and rheological results showed that low molecular weight HPMC had lower gelation temperature. Effects of BCP content and HAp/β-TCP ratio on rheological behavior of the gels were investigated. According to the results, all samples showed a pseudoplastic behavior and their viscosity increased with increasing mineral phase, especially β-tricalcium phosphate. In order to investigate interaction mechanisms between the mineral phase and polymer and also the effects of ion release, particle size, hydrophobisity, and hydrophilisity, hydrophobic and hydrophilic silica with different particle sizes were also utilized. Results showed that factors affecting the hydrophobisity and hydrophilisity of solution may influence the rheological properties.

In Vivo Behavior of a Custom-Made 3D Synthetic Bone Substitute in Sinus Augmentation Procedures in Sheep

In this study, the in vivo behavior of a custom-made three-dimensional (3D) synthetic bone substitute was evaluated when used as scaffold for sinus augmentation procedures in an animal model. The scaffold was a calcium phosphate ceramic fabricated by the direct rapid prototyping technique, dispense-plotting. The geometrical and chemical properties of the scaffold were first analyzed through light and electron scanning microscopes, helium picnometer, and semi-quantitative X-ray diffraction measurements. Then, 6 sheep underwent monolateral sinus augmentation with the fabricated scaffolds. The animals were euthanized after healing periods of 45 and 90 days, and block sections including the grafted area were obtained. Bone samples were subjected to micro computerized tomography, morphological and histomorphometric analyses. A complete integration of the scaffold was reported, with abundant deposition of newly formed bone tissue within the biomaterial pores. Moreover, initial foci of bone remodeling were mainly localized at the periphery of the implanted area after 45 days, while continuous bridges of mature lamellar bone were recorded in 90-day specimens. This evidence supports the hypothesis that bone regeneration proceeds from the periphery to the center of the sinus cavity. These results showed how a technique allowing control of porosity, pore design, and external shape of a ceramic bone substitute may be valuable for producing synthetic bone grafts with good clinical performances.

Synthetic bone substitute engineered with amniotic epithelial cells enhances bone regeneration after maxillary sinus augmentation

Background

Evidence has been provided that a cell-based therapy combined with the use of bioactive materials may significantly improve bone regeneration prior to dental implant, although the identification of an ideal source of progenitor/stem cells remains to be determined.

Aim

In the present research, the bone regenerative property of an emerging source of progenitor cells, the amniotic epithelial cells (AEC), loaded on a calcium-phosphate synthetic bone substitute, made by direct rapid prototyping (rPT) technique, was evaluated in an animal study.

Material And Methods

Two blocks of synthetic bone substitute (∼0.14 cm³), alone or engineered with 1×10⁶ ovine AEC (oAEC), were grafted bilaterally into maxillary sinuses of six adult sheep, an animal model chosen for its high translational value in dentistry. The sheep were then randomly divided into two groups and sacrificed at 45 and 90 days post implantation (p.i.). Tissue regeneration was evaluated in the sinus explants by micro-computer tomography (micro-CT), morphological, morphometric and biochemical analyses.

Results And Conclusions

The obtained data suggest that scaffold integration and bone deposition are positively influenced by allotransplantated oAEC. Sinus explants derived from sheep grafted with oAEC engineered scaffolds displayed a reduced fibrotic reaction, a limited inflammatory response and an accelerated process of angiogenesis. In addition, the presence of oAEC significantly stimulated osteogenesis either by enhancing bone deposition or making more extent the foci of bone nucleation. Besides the modulatory role played by oAEC in the crucial events successfully guiding tissue regeneration (angiogenesis, vascular endothelial growth factor expression and inflammation), data provided herein show that oAEC were also able to directly participate in the process of bone deposition, as suggested by the presence of oAEC entrapped within the newly deposited osteoid matrix and by their ability to switch-on the expression of a specific bone-related protein (osteocalcin, OCN) when transplanted into host tissues.

Preparation and Characterization of a Phosphorous Free and Non-Nitrogen Antiscalant in Industrial Cooling Systems

A novel nonpolluting type of calcium phosphate and iron(III) antiscalant MCn was synthesized. The observation shows that MCn causes a disordered calcium phosphate. Furthermore, both calcium phosphate and iron(III) inhibition increase with increasing degree of polymerization of MCn from 5 to 13, and the dosage of MCn plays an important role on calcium phosphate and iron(III) inhibition. Inhibition mechanism is proposed the interactions between calcium or iron ions and polyethylene glycol (PEG) are the fundamental impetus to restrain the formation of the scale in cooling water systems.

Phase retrieval in in-line x-ray phase contrast imaging based on total variation minimization

State-of-the-art techniques for phase retrieval in propagation based X-ray phase-contrast imaging are aiming to solve an underdetermined linear system of equations. They commonly employ Tikhonov regularization - an L2-norm regularized deconvolution scheme - despite some of its limitations. We present a novel approach to phase retrieval based on Total Variation (TV) minimization. We incorporated TV minimization for deconvolution in phase retrieval using a variety of the most common linear phase-contrast models. The results of our TV minimization was compared with Tikhonov regularized deconvolution on simulated as well as experimental data. The presented method was shown to deliver improved accuracy in reconstructions based on a single distance as well as multiple distance phase-contrast images corrupted by noise and hampered by errors due to nonlinear imaging effects.

Double-Hydrophilic Block Copolymer as an Effective and Environmentally Friendly Inhibitor for Phosphate and Carbonate Scales in Cooling Water Systems

In this paper, a series of linear-dendritic block copolymers allyloxy poly(ethylene glycol) polyglycerol (APEG-PG-(OH)n) copolymer, was synthesized by anionic polymerization of glycerol using allyloxy poly(ethylene glycol) (APEG). The polymers were characterized by FT-IR and 1H NMR. The polymers were tested as novel environment-friendly inhibitors for industrial cooling water circulation. The performance of AA/APEG-PG-(OH)n on inhibition of calcium phosphate and calcium carbonate precipitation was studied by static scale inhibition tests. It was shown that AA/APEG-PG-(OH)n exhibited excellent ability to control inorganic minerals, with approximately 99 % calcium phosphate inhibition and 85 % calcium carbonate inhibition at levels of 4 and 10 mg/L AA/APEG-PG-(OH)n, respectively. The effect on formation of calcium phosphate and calcium carbonate was investigated with combination of scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) analysis, respectively.

In vivo degradation and new bone formation of calcium phosphate cement-gelatin powder composite related to macroporosity after in situ gelatin degradation

Calcium phosphate cement (CPC) is reported to have excellent biocompatibility and osteoconductivity. However, its biodegradability must be improved to promote bone regeneration. We have mixed gelatin powder with CPC to create a composite containing macropores with interconnectivity. Sixty rabbits were grouped as follows: 85 wt% CPC to 15 wt% gelatin powder (C15), 90 wt% CPC to 10 wt% gelatin powder (C10), 100 wt% CPC (C0) as control group and Sham group. Trabecular bone defects of distal femurs were made and implanted with the composites. The femurs were harvested for histomorphometry at 4, 12, 24 weeks after implantation, and mechanical testing at 3 days, 1, 4, 12, 24 weeks. Compared with C0, X-ray and micro-CT results of the composites revealed a progressive increase in the amount of CPC-gelatin powder composite which was replaced by trabeculae. New bone area increased from 3.8 to 18% in C10, and 4.2 to 22% in C15, residual composite area decreased from 65 to 31% in C10, and 70 to 20% in C15. The compressive strength of C15 was 9.2 MPa, which was inferior to 14.6 MPa (normal cancellous bone), but was 27.4 MPa in C10 at 1 week. Further improvement of this composite may make a suitable scaffold for bone regeneration.

In-Line Phase-Contrast X-ray Imaging and Tomography for Materials Science

X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conventional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast imaging highlights edges and internal boundaries of a sample and is thus complementary to absorption contrast, which is more sensitive to the bulk of the sample. Phase-contrast can also be used to image low-density materials, which do not absorb X-rays sufficiently to form a conventional X-ray image. In the context of materials science, X-ray phase-contrast imaging and tomography have particular value in the 2D and 3D characterization of low-density materials, the detection of cracks and voids and the analysis of composites and multiphase materials where the different components have similar X-ray attenuation coefficients. Here we review the use of phase-contrast imaging and tomography for a wide variety of materials science characterization problems using both synchrotron and laboratory sources and further demonstrate the particular benefits of phase contrast in the laboratory setting with a series of case studies.

High-resolution three-dimensional probes of biomaterials and their interfaces

Interfacial relationships between biomaterials and tissues strongly influence the success of implant materials and their long-term functionality. Owing to the inhomogeneity of biological tissues at an interface, in particular bone tissue, two-dimensional images often lack detail on the interfacial morphological complexity. Furthermore, the increasing use of nanotechnology in the design and production of biomaterials demands characterization techniques on a similar length scale. Electron tomography (ET) can meet these challenges by enabling high-resolution three-dimensional imaging of biomaterial interfaces. In this article, we review the fundamentals of ET and highlight its recent applications in probing the three-dimensional structure of bioceramics and their interfaces, with particular focus on the hydroxyapatite-bone interface, titanium dioxide-bone interface and a mesoporous titania coating for controlled drug release.

Potential for imaging engineered tissues with X-ray phase contrast

As the field of tissue engineering advances, it is crucial to develop imaging methods capable of providing detailed three-dimensional information on tissue structure. X-ray imaging techniques based on phase-contrast (PC) have great potential for a number of biomedical applications due to their ability to provide information about soft tissue structure without exogenous contrast agents. X-ray PC techniques retain the excellent spatial resolution, tissue penetration, and calcified tissue contrast of conventional X-ray techniques while providing drastically improved imaging of soft tissue and biomaterials. This suggests that X-ray PC techniques are very promising for evaluation of engineered tissues. In this review, four different implementations of X-ray PC imaging are described and applications to tissues of relevance to tissue engineering reviewed. In addition, recent applications of X-ray PC to the evaluation of biomaterial scaffolds and engineered tissues are presented and areas for further development and application of these techniques are discussed. Imaging techniques based on X-ray PC have significant potential for improving our ability to image and characterize engineered tissues, and their continued development and optimization could have significant impact on the field of tissue engineering.

Experimental study on phase-contrast imaging with synchrotron hard X-ray for repairing osteonecrosis of the femoral head

Synchrotron radiation light is 1 of 4 artificial light sources, the others being electric light, X-ray, and laser. Phase-contrast imaging with hard X-ray has achieved wide application in many scientific fields, such as biomedicine and material science. This article compares the effectiveness of nanohydroxyapatite/collagen (nHAC) and autologous mesenchymal stem cell for the repair of defects in a rabbit model with osteonecrosis of the femoral head under the monitoring of phase-contrast imaging with synchrotron hard X-ray. We established models of bilateral osteonecrosis of the femoral head defect using New Zealand rabbits and divided them into 3 groups. Imaging techniques such as phase-contrast imaging and diffraction enhanced imaging with synchrotron hard X-ray were applied to assess the degradation and repair process of nHAC and mesenchymal stem cell at 4, 8, and 12 weeks postoperatively. We found phase-contrast imaging with synchrotron hard X-ray displayed the reparative process of the bone defect, degradation of nHAC, and osteocyte substitution. There were significant differences in the repair of the bone defect and osteogenesis in groups B and C compared with group A (control). Osteogenesis was more significant in group C. We provided experimental data for the development and application of synchrotron hard X-ray imaging techniques and concluded that phase-contrast microimaging with synchrotron hard X-ray displays the reparative process of bone tissue at a micro-level and plays an important role in the development of tissue engineering.