Glass-ceramic Scaffolds Research Articles

Micro-CT based finite element models for elastic properties of glass–ceramic scaffolds

In this study, the mechanical properties of porous glass–ceramic scaffolds are investigated by means of three-dimensional finite element models based on micro-computed tomography (micro-CT) scan data. In particular, the quantitative relationship between the morpho-architectural features of the obtained scaffolds, such as macroscopic porosity and strut thickness, and elastic properties, is sought.The macroscopic elastic properties of the scaffolds have been obtained through numerical homogenization approaches using the mechanical characteristics of the solid walls of the scaffolds (assessed through nanoindentation) as input parameters for the numerical simulations. Anisotropic mechanical properties of the produced scaffolds have also been investigated by defining a suitable anisotropy index. A comparison with morphological data obtained through the micro-CT scans is also presented. The proposed study shows that the produced glass–ceramic scaffolds exhibited a macroscopic porosity ranging between 29% and 97% which corresponds to an average stiffness ranging between 42.4GPa and 36MPa. A quantitative estimation of the isotropy of the macroscopic elastic properties has been performed showing that the samples with higher solid fractions were those closest to an isotropic material.

Effect of bioactive glass-ceramic scaffold associated with bone marrow - or adipose-derived mesenchymal stem cells on bone formation under osteoporotic conditions

Effect of bioactive glass-ceramic scaffold associated with bone marrow - or adipose-derived mesenchymal stem cells on bone formation under osteoporotic conditions

Mechanical characterization of glass-ceramic scaffolds at multiple characteristic lengths through nanoindentation

The mechanical behaviour of implantable scaffolds is of relevant interest in all applications which require load-bearing capability. This study aims at establishing a quantitative relationship between the mechanical properties of glass-ceramic scaffolds for bone repair and the nano/micro-scale properties of their constituent materials. A nanoindentation study is carried out spanning different penetration depth on bulk (pore-free) glass-ceramic samples and on the walls of porous scaffolds. Micro-tomographical investigations allow assessing small-scale porosity of the scaffold walls. A simple homogenization model is used to establish the relationship between the elastic modulus of the bulk material and that of the micro-porous walls of the scaffolds. The elastic modulus of scaffold walls was found to be approximately 50% lower than that of the bulk glass-ceramic. The properties estimated experimentally on the walls of the scaffolds are quantitatively consistent with the analytical predictions provided by the homogenization model and the micro-porosity measured through tomographical analyses.

Study of the mechanical stability and bioactivity of Bioglass® based glass-ceramic scaffolds produced via powder metallurgy-inspired technology

Large bone defects are challenging to heal, and often require an osteoconductive and stable support to help the repair of damaged tissue. Bioglass-based scaffolds are particularly promising for this purpose due to their ability to stimulate bone regeneration. However, processing technologies adopted so far do not allow for the synthesis of scaffolds with suitable mechanical properties. Also, conventional sintering processes result in glass de-vitrification, which generates concerns about bioactivity. In this work, we studied the bioactivity and the mechanical properties of Bioglass® based scaffolds, produced via a powder technology inspired process. The scaffolds showed compressive strengths in the range of 5–40 MPa, i.e. in the upper range of values reported so far for these materials, had tunable porosity, in the range between 55 and 77%, and pore sizes that are optimal for bone tissue regeneration (100–500 μm). We immersed the scaffolds in simulated body fluid (SBF) for 28 d and analyzed the evolution of the scaffold mechanical properties and microstructure. Even if, after sintering, partial de-vitrification occurred, immersion in SBF caused ion release and the formation of a Ca-P coating within 2 d, which reached a thickness of 10–15 μm after 28 d. This coating contained both hydroxyapatite and an amorphous background, indicating microstructural amorphization of the base material. Scaffolds retained a good compressive strength and structural integrity also after 28 d of immersion (6 MPa compressive strength). The decrease in mechanical properties was mainly related to the increase in porosity, caused by its dissolution, rather than to the amorphization process and the formation of a Ca-P coating. These results suggest that Bioglass® based scaffolds produced via powder metallurgy-inspired technique are excellent candidates for bone regeneration applications.

Using porous bioceramic scaffolds to model healthy and osteoporotic bone

Bioceramics are clinically used as implantable materials to alleviate pain and restore function to diseased or damaged hard tissues in the body. Bone is especially vulnerable to deterioration and fracture in elderly people because of a loss of bone mass and strength with age (osteoporosis). The goal of this research work is to design and fabricate 3-D bioceramic scaffolds with different pore/strut features that can mimic the architecture of both healthy and osteoporotic bone. The scaffolds were fabricated by sponge replica method using a SiO2–P2O5–CaO–MgO–Na2O–K2O bioactive glass (CEL2) as starting material. Key processing parameters were systematically varied and their influence on the architectural and mechanical features of the scaffolds was assessed. Porosity-strength relationship was studied and modelled by using the theory of cellular solid mechanics. These glass-ceramic scaffolds open new perspectives for bone regenerative approaches and could act as model substrates for a more accurate investigation of bone pathologies.

Design and Fabrication of 3D printed Scaffolds with a Mechanical Strength Comparable to Cortical Bone to Repair Large Bone Defects.

A challenge in regenerating large bone defects under load is to create scaffolds with large and interconnected pores while providing a compressive strength comparable to cortical bone (100–150 MPa). Here we design a novel hexagonal architecture for a glass-ceramic scaffold to fabricate an anisotropic, highly porous three dimensional scaffolds with a compressive strength of 110 MPa. Scaffolds with hexagonal design demonstrated a high fatigue resistance (1,000,000 cycles at 1–10 MPa compressive cyclic load), failure reliability and flexural strength (30 MPa) compared with those for conventional architecture. The obtained strength is 150 times greater than values reported for polymeric and composite scaffolds and 5 times greater than reported values for ceramic and glass scaffolds at similar porosity. These scaffolds open avenues for treatment of load bearing bone defects in orthopaedic, dental and maxillofacial applications.

Sol-Gel Derived Mg-Based Ceramic Scaffolds Doped with Zinc or Copper Ions: Preliminary Results on Their Synthesis, Characterization, and Biocompatibility.

Glass-ceramic scaffolds containing Mg have shown recently the potential to enhance the proliferation, differentiation, and biomineralization of stem cells in vitro, property that makes them promising candidates for dental tissue regeneration. An additional property of a scaffold aimed at dental tissue regeneration is to protect the regeneration process against oral bacteria penetration. In this respect, novel bioactive scaffolds containing Mg2+ and Cu2+ or Zn2+, ions known for their antimicrobial properties, were synthesized by the foam replica technique and tested regarding their bioactive response in SBF, mechanical properties, degradation, and porosity. Finally their ability to support the attachment and long-term proliferation of Dental Pulp Stem Cells (DPSCs) was also evaluated. The results showed that conversely to their bioactive response in SBF solution, Zn-doped scaffolds proved to respond adequately regarding their mechanical strength and to be efficient regarding their biological response, in comparison to Cu-doped scaffolds, which makes them promising candidates for targeted dental stem cell odontogenic differentiation and calcified dental tissue engineering.

Design, selection and characterization of novel glasses and glass-ceramics for use in prosthetic applications

The objective of this work is to design and characterize crystallizable silicate and borosilicate compositions for use in the production of smart, unconventional coatings on bioceramic implants. The concept behind this research is the development of a three-layer implantable system (joint prosthesis) comprising a ceramic substrate, a glass-derived trabecular coating and a glass-ceramic interlayer that joins the other two elements together. The outer porous coating should exhibit bone-like architecture, high mechanical strength and good bioactivity to bond to bone, whereas the interlayer should be chemically stable in biological fluids to avoid detachment between the joined parts. Glasses in the SiO2–Na2O–K2O–CaO–P2O5–B2O3–Al2O3 system have been synthesized by a melting route and thermally treated to obtain glass-ceramic products. A selection of potentially suitable materials for the trabecular coating and interlayer was carried out on the basis of thermal properties and tendency to dissolve in simulated body fluids (SBF) so that the integrity of the final device might be maintained upon implantation. The glass selected for the trabecular coating was processed by sponge replica method to produce glass-ceramic scaffolds, in order to evaluate the material properties and performance in an embodiment plausibly close to the final application. The mechanical properties of the porous glass-ceramic, which mimicked the 3-D pore architecture of cancellous bone, were adequate for load-bearing applications such as joint prostheses. Formation of a surface apatite layer on scaffold struts upon soaking in SBF confirmed the excellent bioactivity of the material, which is a key precondition for in vivo osteointegration.

Effect of 830-nm laser phototherapy on olfactory neuronal ensheathing cells grown in vitro on novel bioscaffolds.

The purpose of this study was to analyze olfactory ensheathing cell (OEC) proliferation and growth on Biosilicate and collagen bioscaffolds, and to determine whether the application of laser phototherapy would result in increased OEC proliferation on the scaffolds. The use of bioscaffolds is considered a promising strategy in a number of clinical applications where tissue healing is suboptimal. As in vitro OEC growth is a slow process, laser phototherapy could be useful to stimulate proliferation on bioscaffolds. OEC cells were seeded on the Biosilicate and collagen scaffolds. Seeded scaffolds were irradiated with a single exposure of 830-nm laser. Nonirradiated seeded scaffolds acted as negative controls. Cell proliferation was assessed 7 days after irradiation. OECs were successfully grown on discs composed of a glass-ceramic and collagen composite. Laser irradiation produced a 32.7% decrease and a 13.2% increase in OEC proliferation on glass-ceramic discs and on collagen scaffolds, respectively, compared with controls. Laser phototherapy resulted in a reduction in cell growth on the Biosilicate scaffolds and an increase in cell proliferation on collagen scaffolds. These results were probably due to the nature of the materials. Future research combining laser phototherapy and glass-ceramic scaffolds should take into account possible interactions of the laser with matrix compounds.

Assessment of in vitro testing approaches for bioactive inorganic materials

This paper deals with non-standard in vitro testing of bioactive inorganic materials shaped as granules or scaffolds. The ISO 23317 standard describes the in vitro test arrangement of bulk bioactive materials under static conditions. However, this norm has not dealt with bioactive materials shaped as granules (with large surface area) that are commonly used in clinical practice. We found that in the case of highly reactive (bioactive) materials, the biogenic elements were exhausted from simulated body fluid (SBF) solution very quickly (within hours) under static conditions. In such exhausted SBF solution the formation of Ca–P layer (hydroxyapatite — HAp) was stopped in agreement with the decrease of Ca and P concentrations. On the contrary, highly soluble materials (glass-ceramic scaffold) induced the formation of a new mineral layer also on the walls of the PE container used. For a non-standard shape of the tested materials the usage of dynamic or static–dynamic in vitro test arrangement was confirmed to be a better option to test bioactivity. However, also for this type of arrangement it is essential to determine the S/V or S/F ratios (the surface area/volume or flow of SBF solution) very precisely. For detailed understanding of the interaction between the tested material and SBF it is important to analyze the leachates (monitoring Ca2+, (PO4)3− and minor element concentrations) and to monitor the pH value. An expected result of the in vitro test (according ISO standard) is the formation of HAp on the surfaces of tested samples in SBF. However, the formation of hydroxyapatite may not be the proof of their potential bioactivity necessarily (e.g. due to the use of TRIS buffer).

Electrophoretic deposition of mesoporous bioactive glass on glass-ceramic foam scaffolds for bone tissue engineering.

In this work, the coating of 3-D foam-like glass-ceramic scaffolds with a bioactive mesoporous glass (MBG) was investigated. The starting scaffolds, based on a non-commercial silicate glass, were fabricated by the polymer sponge replica technique followed by sintering; then, electrophoretic deposition (EPD) was applied to deposit a MBG layer on the scaffold struts. EPD was also compared with other techniques (dipping and direct in situ gelation) and it was shown to lead to the most promising results. The scaffold pore structure was maintained after the MBG coating by EPD, as assessed by SEM and micro-CT. In vitro bioactivity of the scaffolds was assessed by immersion in simulated body fluid and subsequent evaluation of hydroxyapatite (HA) formation. The deposition of a MBG coating can be a smart strategy to impart bioactive properties to the scaffold, allowing the formation of nano-structured HA agglomerates within 48 h from immersion, which does not occur on uncoated scaffold surfaces. The mechanical properties of the scaffold do not vary after the EPD (compressive strength ~19 MPa, fracture energy ~1.2 × 10(6) J m(-3)) and suggest the suitability of the prepared highly bioactive constructs as bone tissue engineering implants for load-bearing applications.

Effective cell growth potential of Mg-based bioceramic scaffolds towards targeted dentin regeneration

New emerging approaches in tissue engineering include incorporation of metal ions involved in various metabolic processes, such as Cu, Zn, Si into bioceramic scaffolds for enhanced cell growth and differentiation of specific cell types. The aim of the present work was to investigate the attachment, morphology, growth and mineralized tissue formation potential of Dental Pulp Stem Cells (DPSCs) seeded into Mg-based glass-ceramic scaffolds with incorporated Zn and Cu ions. Bioceramic scaffolds containing Si 60%, Ca 30%, Mg 7.5% and either Zn or Cu 2.5%, sintered at different temperatures were synthesized by the foam replica technique and seeded with DPSCs for up to 21 days. Scanning Electron Microscopy with associated Energy Dispersive Spectroscopy (SEM-EDS) was used to evaluate their ability to support the DPSCs's attachment and proliferation, while the structure of the seeded scaffolds was investigated by X-Ray Diffraction Analysis (XRD). Zn-doped bioceramic scaffolds promoted the attachment and growth of human DPSCs, while identically fabricated scaffolds doped with Cu showed a cytotoxic behaviour, irrespective of the sintering temperature. A mineralized tissue with apatite-like structure was formed on both Cu-doped scaffolds and only on those Zn-doped scaffolds heat-treated at lower temperatures. Sol-gel derived Zn-doped scaffolds sintered at 890oC support DPSC growth and apatite-like tissue formation, which renders them as promising candidates towards dental tissue regeneration.

Synthesis and characterisation of porous luminescent glass ceramic scaffolds containing europium for bone tissue engineering

Eu2O3 was added to bioactive glass ceramic in the system CaO–SiO2–P2O5–MgO–CaF2 to prepare porous luminescent scaffold with high mechanical property. The crystal structure, compressive strength, in vitro bioactivity, cell affinity and luminescent property under ultraviolet of samples was evaluated. According to results, Eu2O3 improved the crystallisation behaviour but inhibited fluorapatite formation in the glass ceramics. Although scaffolds had connective porous structure, the compressive strength could be improved to as high as 3·6 MPa with the addition of Eu2O3. The in vitro bioactivity test showed a decrease in Ca release ability and a retardation of apatite forming on the samples with increasing substitution of Eu2O3 for CaO. The 3-(4,5-dimethylthiazol-2-yl)-2,5-dipheyltetrazolium bromide assay and SEM observation results displayed that ROS17/2·8 cells could attach and differentiate on all the scaffolds. Moreover, the Eu2O3 doped scaffolds fluoresced well a red colour under ultraviolet, and a decrease in the emission intensities could be observed after the cell coculturing process.

Key role of the expression of bone morphogenetic proteins in increasing the osteogenic activity of osteoblast-like cells exposed to shock waves and seeded on bioactive glass-ceramic scaffolds for bone tissue engineering

In this work, the role of shock wave-induced increase of bone morphogenetic proteins in modulating the osteogenic properties of osteoblast-like cells seeded on a bioactive scaffold was investigated using gremlin as a bone morphogenetic protein antagonist. Bone-like glass-ceramic scaffolds, based on a silicate experimental bioactive glass developed at the Politecnico di Torino, were produced by the sponge replication method and used as porous substrates for cell culture. Human MG-63 cells, exposed to shock waves and seeded on the scaffolds, were treated with gremlin every two days and analysed after 20 days for the expression of osteoblast differentiation markers. Shock waves have been shown to induce osteogenic activity mediated by increased expression of alkaline phosphatase, osteocalcin, type I collagen, BMP-4 and BMP-7. Cells exposed to shock waves plus gremlin showed increased growth in comparison with cells treated with shock waves alone and, conversely, mRNA contents of alkaline phosphatase and osteocalcin were significantly lower. Therefore, the shock wave-mediated increased expression of bone morphogenetic protein in MG-63 cells seeded on the scaffolds is essential in improving osteogenic activity; blocking bone morphogenetic protein via gremlin completely prevents the increase of alkaline phosphatase and osteocalcin. The results confirmed that the combination of glass-ceramic scaffolds and shock waves exposure could be used to significantly improve osteogenesis opening new perspectives for bone regenerative medicine.

Preparation and characterization of PHBV microsphere/45S5 bioactive glass composite scaffolds with vancomycin releasing function

PHBV microsphere/45S5 bioactive glass (BG) composite scaffolds with drug release function were developed for bone tissue engineering. BG-based glass-ceramic scaffolds with high porosity (94%) and interconnected pore structure prepared by foam replication method were coated with PHBV microspheres (nominal diameter=3.5μm) produced by water-in-oil-in-water double emulsion solvent evaporation method. A homogeneous microsphere coating throughout the porous structure of scaffolds was obtained by a simple dip coating method, using the slurry of PHBV microspheres in hexane. Compressive strength tests showed that the microsphere coating slightly improved the mechanical properties of the scaffolds. It was confirmed that the microsphere coating did not inhibit the bioactivity of the scaffolds in SBF. Hydroxyapatite crystals homogeneously grew not only on the struts of the scaffolds but also on the surface of microspheres within 7days of immersion in SBF. Vancomycin was successfully encapsulated into the PHBV microspheres. The encapsulated vancomycin was released with a dual release profile involving a relatively low initial burst release (21%) and a sustained release (1month), which is favorable compared to the high initial burst release (77%) and short release period (4days) measured on uncoated scaffolds. The developed bioactive composite scaffold with drug delivery function has thus the potential to be used advantageously in bone tissue engineering.

Modelling of the strength–porosity relationship in glass-ceramic foam scaffolds for bone repair

Abstract Foam-like glass-ceramic scaffolds based on three different glass compositions (45S5 Bioglass and two other experimental formulations, CEL2 and SCNA) were produced by sponge replication and characterized from morphological, architectural and mechanical viewpoints. The relationships between porosity and compressive or tensile strength were systematically investigated and modelled, respectively, by using the theory of cellular solids mechanics or quantized fracture mechanics. Models results are in good agreement with experimental findings, which highlights the satisfactory predictive capabilities of the presented approach. The developed models could contribute to improve the rational design of porous bioceramics with custom-made properties. Knowing the scaffold recommended strength for a specific surgical need, the application of the models allows to predict the corresponding porosity, which can be tailored by varying the fabrication parameters in a controlled way so that the device fulfils the desired mechanical requirements.

Mechanical properties and reliability of glass–ceramic foam scaffolds for bone repair

The development of reliable, synthetic scaffolds to repair large defects in load-bearing bones is one of the key challenges of regenerative medicine of hard tissues. This study addresses the mechanical properties of experimental glass–ceramic scaffolds fabricated by sponge replication and exhibiting a bone-like 3-D trabecular architecture, as assessed by micro-computed tomography investigations. The scaffolds have a strength of 18MPa, an elastic modulus around 380MPa, a Weibull modulus of 4 and a fracture energy of 544kJm−3 when tested in compression. Such results were compared with and found similar or even superior to those reported in the literature for bioceramic scaffolds and human cancellous bone. These key mechanical data, together with the peculiar foam-like porous architecture, indicate the great potential of this type of scaffolds for use in load-bearing bone tissue engineering applications.

Novel resorbable glass-ceramic scaffolds for hard tissue engineering: From the parent phosphate glass to its bone-like macroporous derivatives

One of the major challenges of hard tissue engineering research focuses on the development of scaffolds that can match the mechanical properties of the host bone and resorb at the same rate as the bone is repaired. The aim of this work was the synthesis and characterization of a resorbable phosphate glass, as well as its application for the fabrication of three dimensional (3-D) scaffolds for bone regeneration. The glass microstructure and behaviour upon heating were analysed by X-ray diffraction, differential scanning calorimetry and hot stage microscopy. The glass solubility was investigated according to relevant ISO standards using distilled water, simulated body fluid (SBF) and Tris-HCl as testing media. The glass underwent progressive dissolution over time in all three media but the formation of a hydroxyapatite-like layer was also observed on the samples soaked in SBF and Tris-HCl, which demonstrated the bioactivity of the material. The glass powder was used to fabricate 3-D macroporous bone-like glass-ceramic scaffolds by adopting polyethylene particles as pore formers: during thermal treatment, the polymer additive was removed and the sintering of glass particles was allowed. The obtained scaffolds exhibited high porosity (87 vol.%) and compressive strength around 1.5 MPa. After soaking for 4 months in SBF, the scaffolds mass loss was 76 wt.% and the pH of the solution did not exceed the 7.55 value, thereby remaining in a physiological range. The produced scaffolds, being resorbable, bioactive, architecturally similar to trabecular bone and exhibiting interesting mechanical properties, can be proposed as promising candidates for bone repair applications.

Preparation and characterization of vancomycin releasing PHBV coated 45S5 Bioglass®-based glass–ceramic scaffolds for bone tissue engineering

Abstract Porous 45S5 Bioglass®-based glass–ceramic scaffolds with high porosity (96%) and interconnected pore structure (average pore size 300 μm) were prepared by foam replication method. In order to improve the mechanical properties and to incorporate a drug release function, the scaffolds were coated with a drug loaded solution, consisting of PHBV and vancomycin. The mechanical properties of the scaffolds were significantly improved by the PHBV coating. The bioactivity of scaffolds upon immersion in SBF was maintained in PHBV coated scaffolds although the formation of hydroxyapatite was slightly retarded by the presence of the coating. The encapsulated drug in coated scaffolds was released in a sustained manner (99.9% in 6 days) as compared to the rapid release (99.5% in 3 days) of drug directly adsorbed on the uncoated scaffolds. The obtained drug loaded and bioactive composite scaffolds represent promising candidates for bone tissue engineering applications.

Preparation and chemical stability of CaO–P2O5–Na2O–B2O3 porous glass ceramics

CaO–P2O5–Na2O–B2O3 (CaO/P2O5 molar ratio is 1.25) glass ceramic scaffolds with good bioactivity and chemical stability for tissue engineering applications have been prepared by coating polyurethane foams with glass slurry, and subsequent heat treatment of the obtained porous structures. When heat treated at 700°C for 1h, the resultant foam structure has a porosity of 67–72%, and fine crystals of CaP2O6, Ca(PO3)2 and BPO4 crystallized and precipitated homogeneously in the glass matrix which conferred the scaffolds a high mechanical property. The scaffolds were soaked in the simulated body fluid to determine the solubility and observe apatite formation. The results show that B2O3 plays an important role in the crystallization of the glass and can improve the chemical stability. And the formation of an apatite-like layer covering certain areas of the scaffold surface exhibited a good ability of inducing calcification in the simulated body fluid. In vitro cell studies showed that cells exhibit normal morphologies and spread well on the scaffold specimens, indicating that the glass ceramics were biocompatible.