In vivo Performance of Biodegradable Calcium Phosphate Glass Ceramics using the Rabbit Model: Histological and SEM Observation

50 years of scanning electron microscopy of bone-a comprehensive overview of the important discoveries made and insights gained into bone material properties in health, disease, and taphonomy

Bone is an architecturally complex system that constantly undergoes structural and functional optimisation through renewal and repair. The scanning electron microscope (SEM) is among the most frequently used instruments for examining bone. It offers the key advantage of very high spatial resolution coupled with a large depth of field and wide field of view. Interactions between incident electrons and atoms on the sample surface generate backscattered electrons, secondary electrons, and various other signals including X-rays that relay compositional and topographical information. Through selective removal or preservation of specific tissue components (organic, inorganic, cellular, vascular), their individual contribution(s) to the overall functional competence can be elucidated. With few restrictions on sample geometry and a variety of applicable sample-processing routes, a given sample may be conveniently adapted for multiple analytical methods. While a conventional SEM operates at high vacuum conditions that demand clean, dry, and electrically conductive samples, non-conductive materials (e.g., bone) can be imaged without significant modification from the natural state using an environmental scanning electron microscope. This review highlights important insights gained into bone microstructure and pathophysiology, bone response to implanted biomaterials, elemental analysis, SEM in paleoarchaeology, 3D imaging using focused ion beam techniques, correlative microscopy and in situ experiments. The capacity to image seamlessly across multiple length scales within the meso-micro-nano-continuum, the SEM lends itself to many unique and diverse applications, which attest to the versatility and user-friendly nature of this instrument for studying bone. Significant technological developments are anticipated for analysing bone using the SEM.

Scaffolds of bioactive glass-ceramic (Biosilicate®) and bone healing: A biological evaluation in an experimental model of tibial bone defect in rats

This study aimed to investigate the in vivo tissue response of the Biosilicate® scaffolds in a model of tibial bone defect. Sixty male Wistar rats were distributed into bone defect control group (CG) and Biosilicate® scaffold group (BG).  Animals were euthanized 15, 30 and 45 days post-surgery. Stereomicroscopy, scanning electron microscopy, histopathological, immunohistochemistry and biomechanical analysis were used. Scaffolds had a total porosity of 44%, macroporosity of 15% with pore diameter of 230 μm. Higher amount of newly formed bone was observed on days 30 and 45 in BG. Immunohistochemistry analysis showed that the COX-2 expression was significantly higher on days 15 and 30 in BG compared with the CG. RUNX-2 immunoexpression was significantly higher in BG on days 15 and 45. No statistically significant difference was observed in RANKL immunoexpression in all experimental groups. BMP-9 immunoexpression was significantly upregulated in the BG on day 45. Biomechanical analysis showed a decrease in the biomechanical properties of the bone callus on days 30 and 45. The implantation of the Biosilicate® scaffolds was effective in stimulating newly bone formation and produced an increased immunoexpression of markers related to the bone repair.

Effect of a new bioactive fibrous glassy scaffold on bone repair

Researchers have investigated several therapeutic approaches to treat non-union fractures. Among these, bioactive glasses and glass ceramics have been widely used as grafts. This class of biomaterial has the ability to integrate with living bone. Nevertheless, bioglass and bioactive materials have been used mainly as powder and blocks, compromising the filling of irregular bone defects. Considering this matter, our research group has developed a new bioactive glass composition that can originate malleable fibers, which can offer a more suitable material to be used as bone graft substitutes. Thus, the aim of this study was to assess the morphological structure (via scanning electron microscope) of these fibers upon incubation in phosphate buffered saline (PBS) after 1, 7 and 14 days and, also, evaluate the in vivo tissue response to the new biomaterial using implantation in rat tibial defects. The histopathological, immunohistochemistry and biomechanical analyzes after 15, 30 and 60 days of implantation were performed to investigate the effects of the material on bone repair. The PBS incubation indicated that the fibers of the glassy scaffold degraded over time. The histological analysis revealed a progressive degradation of the material with increasing implantation time and also its substitution by granulation tissue and woven bone. Histomorphometry showed a higher amount of newly formed bone area in the control group (CG) compared to the biomaterial group (BG) 15 days post-surgery. After 30 and 60 days, CG and BG showed a similar amount of newly formed bone. The novel biomaterial enhanced the expression of RUNX-2 and RANK-L, and also improved the mechanical properties of the tibial callus at day 15 after surgery. These results indicated a promising use of the new biomaterial for bone engineering. However, further long-term studies should be carried out to provide additional information concerning the material degradation in the later stages and the bone regeneration induced by the fibrous material.

Biocompatibility of a porous alumina ceramic scaffold coated with hydroxyapatite and bioglass

This study aimed to evaluate the osteointegration and genotoxic potential of a bioactive scaffold, composed of alumina and coated with hydroxyapatite and bioglass, after their implantation in tibias of rats. For this purpose, Wistar rats underwent surgery to induce a tibial bone defect, which was filled with the bioactive scaffolds. Histology analysis (descriptive and morphometry) of the bone tissue and the single-cell gel assay (comet) in multiple organs (blood, liver, and kidney) were used to reach this aim after a period of 30, 60, 90, and 180 days of material implantation. The main findings showed that the incorporation of hydroxyapatite and bioglass in the alumina scaffolds produced a suitable environment for bone ingrowth in the tibial defects and did not demonstrate any genotoxicity in the organs evaluated in all experimental periods. These results clearly indicate that the bioactive scaffolds used in this study present osteogenic potential and still exhibit local and systemic biocompatibility. These findings are promising once they convey important information about the behavior of this novel biomaterial in biological system and highlight its possible clinical application.

Titanium phosphate glass microspheres for bone tissue engineering

We have demonstrated the successful production of titanium phosphate glass microspheres in the size range of ∼10-200 μm using an inexpensive, efficient, easily scalable process and assessed their use in bone tissue engineering applications. Glasses of the following compositions were prepared by melt-quench techniques: 0.5P₂O₅-0.4CaO-(0.1-x)Na₂O-xTiO₂, where x=0.03, 0.05 and 0.07 mol fraction (denoted as Ti3, Ti5 and Ti7 respectively). Several characterization studies such as differential thermal analysis, degradation (performed using a novel time lapse imaging technique) and pH and ion release measurements revealed significant densification of the glass structure with increased incorporation of TiO₂ in the glass from 3 to 5 mol.%, although further TiO₂ incorporation up to 7 mol.% did not affect the glass structure to the same extent. Cell culture studies performed using MG63 cells over a 7-day period clearly showed the ability of the microspheres to provide a stable surface for cell attachment, growth and proliferation. Taken together, the results confirm that 5 mol.% TiO₂ glass microspheres, on account of their relative ease of preparation and favourable biocompatibility, are worthy candidates for use as substrate materials in bone tissue engineering applications.

Titanium-containing bioactive phosphate glasses

The use of biomaterials has revolutionized the biomedical field and has received substantial attention in the last two decades. Among the various types of biomaterials, phosphate glasses have generated great interest on account of their remarkable bioactivity and favourable physical properties for various biomedical applications relating to both hard and soft tissue regeneration. This review paper focuses mainly on the development of titanium-containing phosphate-based glasses and presents an overview of the structural and physical properties. The effect of titanium incorporation on the glassy network is to introduce favourable properties. The biocompatibility of these glasses is described along with recent developments in processing methodologies, and the potential of Ti-containing phosphate-based glasses as a bone substitute material is explored.

Development of Self-assembled Nanoceramic Carrier Construct(s) for Vaccine Delivery

Hydroxyapatite (HA) has been extensively investigated as scaffolds for tissue engineering, as drug delivery agents, as non-viral gene carriers, as prosthetic coatings, and composites. Recent studies in our laboratory demonstrated the immunoadjuvant properties of HA when administered with malarial merozoite surface protein-119 (MSP-119). HA nanoceramic carrier was prepared by co-precipitation method that comprises of sintering and spray-drying technique. Prepared systems were characterized for crystallinity, size, shape, and antigen loading efficiency. Small size and large surface area of prepared HA demonstrated good adsorption efficiency of immunogens. Prepared nanoceramic formulations also showed slower in vitro antigen release and slower biodegrability behavior, which may lead to a prolonged exposure to antigen-presenting cells and lymphocytes. Furthermore, addition of mannose in nanoceramic formulation may additionally lead to increased stability and immunological reactions. Immunization with MSP-119 in nanoceramic-based adjuvant systems induced a vigorous immunoglobulin G (IgG) response, with higher IgG2a than IgG1 titers. In addition considerable amount of IFN-g and IL-2 was observed in spleen cells of mice immunized with nanoceramic-based vaccines. On the contrary, mice immunized with MSP-119 alone or with alum did not exhibit a significant cytotoxic response. The antibody responses to vaccine co-administered with HA was a mixed Th1/Th2 compared to the Th2-biased response obtained with alum. The prepared HA nanoparticles exhibit physicochemical properties that appear promising to make them a suitable immunoadjuvant to be used as antigen carriers for immunopotentiation.

Bone regeneration using an injectable calcium phosphate/autologous iliac crest bone composites for segmental ulnar defects in rabbits

BACKGROUND

Treatment of segmental bone loss remains a challenge in skeletal repair. A major therapeutic goal is the development of implantable materials that will promote bone regeneration.

OBJECTIVE

We evaluate bone regeneration in grafts containing different concentrations autologous iliac crest bone (ACB) particles, carried in a new injectable calcium phosphate cement (CPC), in ulnar bone defects in rabbits.

METHODS

Large upper-mid-diaphyseal defects (10 mm) were created in the left ulnae of 60 skeletally mature New Zealand white rabbits. ACB concentrations of 0, 25, 50, 75, and 100% (by volume) in CPC were used to fill operated sites. Defect bridging was monitored by serial radiography at 4, 8, and 12 weeks post-operation. Samples were then examined histologically and by manual palpation to determine the extent of new bone formation.

RESULTS

At 4 weeks, we observed more elaborate structures and extensive absorption in ulnae treated with mixtures containing low concentrations of ACB (such as 0% and 25% volume of ACB/CPC), compared with those treated with mixtures containing high concentrations of ACB (such as 75% and 100% volume of ACB/CPC). At 8 weeks, histomorphometry revealed increased trabecular area and volume in the group treated with high ACB concentrations compared with those treated with low ACB concentrations. At 12 weeks, complete cortical bridging and regeneration of marrow space were detected in groups treated with high concentrations of ACB, and the amount of new bone regeneration was greater in these groups than in those treated with low ACB concentrations.

CONCLUSIONS

Treatment of rabbit ulnar defects with injectable CPC carrying an optimized concentration of ACB particles can lead to cortical bridging and bone marrow regeneration within 12 weeks.

Cell Distribution in a Scaffold with Random Architectures under the Influence of Fluid Dynamics

Fluid dynamic environment and scaffold architectures have an important influence on cell growth and distribution inside the scaffold. A porous cylindrical scaffold with a central channel is seeded with the sheep mesenchymal stem cells (MSCs) in this study. Then the cell seeded scaffold is continuously perfused with α-MEM medium by a peristaltic pump for 7, 14, and 28 days. Histological study shows that the cell proliferation rates are different throughout the whole scaffolds. The different cell coverage is shown in various positions of the scaffold. A computational fluid dynamics (CFD) modeling is used to simulate the flow conditions within perfused cell-seeded scaffolds to give insight into the mechanisms of these cell growth phenomena. Relating the simulation results to perfusion experiments, the even fluid velocity (~0.26—0.64 mm/s) and shear stress (~0.0029—0.027 Pa) are found to correspond to increased cell proliferation within the cell-scaffold constructs. This method exhibits novel capabilities to compare results obtained for different perfusion rates or different scaffold microarchitectures and may allow specific fluid velocities and shear stresses to be determined that optimize the perfusion flow rate, porous scaffold architecture, and distribution of in vitro tissue growth.

Physicochemical degradation studies of calcium phosphate glass ceramic in the CaO-P2O5-MgO-TiO2 system

The aim of this work was to evaluate the in vitro degradation behaviour of a 45CaO-37P(2)O(5)-5MgO-13TiO(2) (mol.%) glass ceramic, under two different simulated physiological conditions: normal physiological pH 7.4, and pH 3.0, which was designed to simulate the acidic conditions produced by osteoclast cells. The in vitro testing was carried out at 37 degrees C for up to 42 days for the pH 7.4 solution and for up to 1 day for the pH 3.0 solution. The incorporation of TiO(2) into the glass structure leads to the precipitation of specific crystalline phases in the glass matrix, namely alpha- and beta-Ca(2)P(2)O(7), TiP(2)O(7) and CaTi(4)(PO(4))(6). The degradation testing at pH 3.0 showed a higher weight loss compared with degradation testing at pH 7.4; the weight loss under the acidic condition after 1 day (24 h) was about 10 times higher than the weight loss after 42 days of immersion at pH 7.4. The ionic release profile of Ca(2+), PO(4)(3-), Mg(2+) and Ti(4+) showed a continuous increase in concentration over all immersion times for both testing solutions. After 1 day of immersion at pH 3.0, the concentration levels of Mg(2+), Ca(2+), PO(4)(3-) were about six times higher than the levels achieved after 42 days of immersion at pH 7.4. The glass ceramic showed similar degradation to hydroxyapatite, and therefore has potential to be used in certain clinical applications where relatively slow resorption of the implant and replacement by bone is required, e.g. cranioplasty.