The intrinsic brittleness of bioactive glasses (BGs) is one of the main barriers to the widespread use of three-dimensional porous BG-derived bone grafts (scaffolds) in clinical practice. Among all ...the available strategies for improving the mechanical properties of BG-based scaffolds, strut densification upon sintering treatments at high temperatures represents a relatively easy approach, but its implementation might lead to undesired and poorly predictable decrease in porosity, mass transport properties and bioactivity resulting from densification and devitrification phenomena occurring in the material upon heating. The aim of the present work was to investigate the sinter-crystallization of a highly bioactive SiO2-P2O5-CaO–MgO–Na2O–K2O glass (47.5B composition) in reference to its suitability for the fabrication of bonelike foams. The thermal behavior of 47.5B glass particles was investigated upon sintering at different temperatures in the range of 600–850 °C by means of combined thermal analyses (differential thermal analysis (DTA) and hot-stage microscopy (HSM)). Then, XRD measurements were carried out to identify crystalline phases developed upon sintering. Finally, porous scaffolds were produced by a foam replica method in order to evaluate the effect of the sintering temperature on the mechanical properties under compression loading conditions. Assessing a relationship between mechanical properties and sintering temperature, or in other words between scaffold performance and fabrication process, is a key step towards the rationale design of optimized scaffolds for tissue repair.
Bioactive glasses are often designed as porous implantable templates in which newly-formed bone can grow in three dimensions (3D). This research work aims to investigate the bone regenerative ...capability of silicate bioactive glass scaffolds produced by robocasting in comparison with powder and granule-like materials (oxide system: 47.5SiO2-10Na2O-10K2O-10MgO-20CaO-2.5P2O5, mol.%). Morphological and compositional analyses performed by scanning electron microscopy (SEM), combined with energy dispersive spectroscopy (EDS) after the bioactivity studies in a simulated body fluid (SBF) confirmed the apatite-forming ability of the scaffolds, which is key to allowing bone-bonding in vivo. The scaffolds exhibited a clear osteogenic effect upon implantation in rabbit femur and underwent gradual resorption followed by ossification. Full resorption in favor of new bone growth was achieved within 6 months. Osseous defect healing was accompanied by the formation of mature bone with abundant osteocytes and bone marrow cells. These in vivo results support the scaffold’s suitability for application in bone tissue engineering and show promise for potential translation to clinical assessment.
•Non-isothermal crystallization of 45S5 glass (particles <5 µm or <32 µm) was studied.•Activation energies for crystallization (Ec) and Avrami parameters were calculated.•Surface crystallization was ...dominant for both particle sizes.•Activation energies for viscous flow (Evf) were calculated.•Evf was found higher than Ec for both particle sizes.
The crystallization behavior of 45S5 bioactive glass powders with two different particle sizes (<5 µm, BG5 and <32 µm. BG32) was investigated under non-isothermal conditions. The Ozawa and Augis-Bennett methods provided an Avrami coefficient close to 1 for both glass types, which suggests that surface crystallization was predominant during heat treatment. The Kissinger equation was used to determine the apparent activation energies for crystallization (Ec) that were found to be 250 ± 3 and 311 ± 9 kJ/mol for BG5 and BG32, respectively. The activation energies for viscous flow have also been assessed and were found higher than Ec (284 ± 8 and 338 ± 9 kJ/mol) for both particle sizes. It was noted that the process of crystallization for 45S5 glass could not be properly described by the Johnson-Mehl-Avrami (JMA) model and it appeared more complex than a simple nucleation-growth mechanism.
Sol‐gel route has shown its enormous potential in tissue engineering applications as an advantageous method for the production of bioactive glasses aimed at regenerating both hard and soft tissues. ...This review discusses the chemical aspects of the method with emphasis on the morphological, chemical, mechanical, and biological properties of sol‐gel derived materials. The attention will be particularly focused on sol‐gel bioactive glasses and sol‐gel foam scaffolds for bone regeneration. The advantages deriving from the versatility of the sol‐gel method compared to the traditional melt‐quenching route will be underlined in terms of bioactivity, compositions, and processing parameters.
The genomic clones containing elements that regulate transcription of the three known rice (Oryza sativa L.) alpha-tubulin isotypes (Ostua1, Ostua2 and Ostua3) have been isolated. We have used these ...genomic regions to identify the regulatory elements that contribute to the expression of a marker gene (gusA) in transient assays performed on rice calli derived from mature embryos. In all cases, we found that the first intron was required to achieve high levels of expression. This is consistent with data already reported for the α-tubulin isotypel and indicates that a common regulatory mechanism is active on all the members of the rice α-tubulin gene family. The enhancing effect of the first intron was then tested by constructing illegitimate combinations of α-tubulin promoter and intron sequences (Ostua1pro—Ostua2intro; Ostua1pro—Ostua3intro; Ostua2pro—Ostua3intro; Ostua3pro—Ostua2intro) and then by assaying β-glucuronidase (GUS) activity in transformed rice calli. All illegitimate combinations expressed GUS at high level, suggesting that rice α-tubulin promoters and introns can be exchanged among the different isotypes. This did not occur when the intron of the rice β-tubulin isotype16, known to enhance transcription of its own gene, was used in place of the α-tubulin intron. We have also analysed the effect of abscisic acid (ABA) on GUS expression in rice calli transformed with chimeric tubα2pro-intro::gusA and tubα3pro-intro::gusA constructs. ABA was able to reduce GUS expression only in the presence of the tubα2pro-intro sequence. We discuss these data in terms of mechanisms that in rice, as opposed to other plants, may control tubulin isotype-specific expression and the involvement of ABA in the regulation of α-tubulin expression.
Bioactive glasses exhibit the unique ability of bone bonding, thus creating a stable interface by stimulating bone cells toward mechanisms of regeneration and self‐repair activated by ionic ...dissolution products. Therefore, 3D glass‐derived scaffolds can be considered ideal porous templates to be used in bone tissue engineering strategies and regenerative medicine. This review provides a comprehensive overview of all technological aspects relevant to the fabrication of bioactive glass scaffolds, including the fundamentals of materials processing, a summary of the conventional porogen, and template‐based methods and of recent additive manufacturing technologies, which are promising for large‐scale production of highly reproducible and reliable implants suitable for a wide range of clinical applications.
Porosity is known to play a pivotal role in dictating the functional properties of biomedical scaffolds, with special reference to mechanical performance. While compressive strength is relatively ...easy to be experimentally assessed even for brittle ceramic and glass foams, elastic properties are much more difficult to be reliably estimated. Therefore, describing and, hence, predicting the relationship between porosity and elastic properties based only on the constitutive parameters of the solid material is still a challenge. In this work, we quantitatively compare the predictive capability of a set of different models in describing, over a wide range of porosity, the elastic modulus (7 models), shear modulus (3 models) and Poisson’s ratio (7 models) of bioactive silicate glass-derived scaffolds produced by foam replication. For these types of biomedical materials, the porosity dependence of elastic and shear moduli follows a second-order power-law approximation, whereas the relationship between porosity and Poisson’s ratio is well fitted by a linear equation.
This work deals with the additive manufacturing and characterization of hydroxyapatite scaffolds mimicking the trabecular architecture of cancellous bone. A novel approach was proposed relying on ...stereolithographic technology, which builds foam‐like ceramic scaffolds by using three‐dimensional (3D) micro‐tomographic reconstructions of polymeric sponges as virtual templates for the manufacturing process. The layer‐by‐layer fabrication process involves the selective polymerization of a photocurable resin in which hydroxyapatite particles are homogeneously dispersed. Irradiation is performed by a dynamic mask that projects blue light onto the slurry. After sintering, highly‐porous hydroxyapatite scaffolds (total porosity ~0.80, pore size 100‐800 µm) replicating the 3D open‐cell architecture of the polymeric template as well as spongy bone were obtained. Intrinsic permeability of scaffolds was determined by measuring laminar airflow alternating pressure wave drops and was found to be within 0.75‐1.74 × 10−9 m2, which is comparable to the range of human cancellous bone. Compressive tests were also carried out in order to determine the strength (~1.60 MPa), elastic modulus (~513 MPa) and Weibull modulus (m = 2.2) of the scaffolds. Overall, the fabrication strategy used to print hydroxyapatite scaffolds (tomographic imaging combined with digital mirror device DMD‐based stereolithography) shows great promise for the development of porous bioceramics with bone‐like architecture and mass transport properties.
The plant seed is a major nutritional source for humans as well as an essential embryo development and dispersal unit. To ensure proper seed formation, fine spatial and temporal coordination between ...the embryo, endosperm, and maternal seed components must be achieved. However, the intercellular signaling pathways that direct the synchronous development of these tissues are poorly understood. Here we show that the Arabidopsis thaliana peptide ligand CLAVATA3/EMBRYO SURROUNDING REGION-RELATED8 (CLE8) is exclusively expressed in young embryos and endosperm, and that it acts cell and noncell autonomously to regulate basal embryo cell division patterns, endosperm proliferation, and the timing of endosperm differentiation. CLE8 positively regulates expression of the transcription factor gene WUSCHEL-LIKE HOMEOBOX8 (WOX8), and together CLE8 and WOX8 form a signaling module that promotes seed growth and overall seed size. These results demonstrate that seed development is coordinated by a secreted peptide ligand that plays a key early role in orchestrating cell patterning and proliferation in the embryo and endosperm.
•Fe-containing sols are foamed to produce hierarchical silicate glass scaffolds.•The scaffolds exhibit a hierarchical porosity from the macro- to the meso-scale.•Specific surface area and mesopore ...size decrease as iron content increases.•All the scaffolds are highly bioactive in vitro regardless of iron content.•Applying these scaffolds for bone cancer treatment by hyperthermia can be suggested.
Multifunctional scaffolds were prepared by foaming Fe-containing sols according to a composition-optimized approach. These foams exhibited high specific surface area (16–80 m2/g) and hierarchical porosity from the macro- (50–600 µm) to the meso-scale (4–20 nm). The effects of iron content on the textural properties and in vitro bioactivity were investigated. It was observed that the increase of iron content involved a decrease of specific surface and mesopore size. Interestingly, an excellent apatite-forming ability was observed regardless of the material composition. The potential osteoconductivity of these bioactive foams, coupled with their ferrimagnetic properties, open new perspectives as regards the hyperthermia-assisted treatment and regeneration of osseous defects caused by bone cancer.
PDF
