Fabrication and biological characteristics of β-tricalcium phosphate porous ceramic scaffolds reinforced with calcium phosphate glass

The fabrication process, compressive strength and biocompatibility of porous β-tricalcium phosphate (β-TCP) ceramic scaffolds reinforced with 45P₂O₅–22CaO–25Na₂O–8MgO bioglass (β-TCP/BG) were investigated for their suitability as bone engineering materials. Porous β-TCP/BG scaffolds with macropore sizes of 200–500 μm were prepared by coating porous polyurethane template with β-TCP/BG slurry. The β-TCP/BG scaffolds showed interconnected porous structures and exhibited enhanced mechanical properties to those pure β-TCP scaffolds. In order to assess the effects of chemical composition of this bioglass on the behavior of osteoblasts cultured in vitro, porous scaffolds were immersed in simulated body fluid (SBF) for 2 weeks, and original specimens (without soaked in SBF) seeded with MC3T3-E1 were cultured for the same period. The ability of inducing apatite crystals in simulated body fluid and the attachment of osteoblasts were examined. Results suggest that apatite agglomerates are formed on the surface of the β-TCP/BG scaffolds and its Ca/P molar ratio is ~1.42. Controlling the crystallization from the β-TCP/BG matrix could influence the releasing speed of inorganic ions and further adjust the microenvironment of the solution around the β-TCP/BG, which could improve the interaction between osteoblasts and the scaffolds.     

Composite bone substitute materials based on β-tricalcium phosphate and magnesium-containing sol–gel derived bioactive glass

In the present study, bioceramic composites with improved mechanical and biological properties were synthesized by sintering mixtures of β-tricalcium phosphate and SiO₂–CaO–MgO–P₂O₅ sol–gel derived bioactive glass at 1000–1200°C. The physical, mechanical, structural and biological properties of the composites were evaluated by appropriate experiments such as microhardness, bending strength, XRD, SEM and MTT. The results showed that 1000 and 1100°C were not appropriate temperatures for sintering the composites and in contrast, the microhardness, bending strength and bulk density significantly increased by increasing in quantity of bioglass phase when the samples were sintered at 1200°C. No significant difference was found between the fracture toughness of the composites and pure β-tricalcium phosphate. β-tricalcium phosphate was structurally stable up to 1200°C and did not transform to its alpha form even in the presence of the bioglass phase but migration of magnesium cations from the glass composition into its lattice structure was found by right-shift in XRD patterns, especially when the composite contained higher amount of bioglass component. Calcium silicate was also crystallized in the composition of the composites, which was more detectable in higher sintering temperatures. The results of the MTT test showed that proliferation of human osteosarcoma cells on the composites was considerably better than that of pure β-TCP.     

Bioactive borate glass scaffolds: in vitro and in vivo evaluation for use as a drug delivery system in the treatment of bone infection

The objective of this work was to evaluate borate bioactive glass scaffolds (with a composition in the system Na₂O–K₂O–MgO–CaO–B₂O₃–P₂O₅) as devices for the release of the drug Vancomycin in the treatment of bone infection. A solution of ammonium phosphate, with or without dissolved Vancomycin, was used to bond borate glass particles into the shape of pellets. The in vitro degradation of the pellets and their conversion to a hydroxyapatite-type material in a simulated body fluid (SBF) were investigated using weight loss measurements, chemical analysis, X-ray diffraction, and scanning electron microscopy. The results showed that greater than 90% of the glass in the scaffolds degraded within 1 week, to form poorly crystallized hydroxyapatite (HA). Pellets loaded with Vancomycin provided controlled release of the drug over 4 days. Vancomycin-loaded scaffolds were implanted into the right tibiae of rabbits infected with osteomyelitis. The efficacy of the treatment was assessed using microbiological examination and histology. The HA formed in the scaffolds in vivo, resulting from the conversion of the glass, served as structure to support the growth of new bone and blood vessels. The results in this work indicate that bioactive borate glass could provide a promising biodegradable and bioactive material for use as both a drug delivery system and a scaffold for bone repair.     

Biocompatible glass–ceramic materials for bone substitution

A new bioactive glass composition (CEL2) in the SiO₂–P₂O₅–CaO–MgO–K₂O–Na₂O system was tailored to control pH variations due to ion leaching phenomena when the glass is in contact with physiological fluids. CEL2 was prepared by a traditional melting-quenching process obtaining slices that were heat-treated to obtain a glass-ceramic material (CEL2GC) that was characterized thorough SEM analysis. Pre-treatment of CEL2GC with SBF was found to enhance its biocompatibility, as assessed by in vitro tests. CEL2 powder was then used to synthesize macroporous glass–ceramic scaffolds. To this end, CEL2 powders were mixed with polyethylene particles within the 300–600 μm size-range and then pressed to obtain crack-free compacted powders (green). This was heat-treated to remove the organic phase and to sinter the inorganic phase, leaving a porous structure. The biomaterial thus obtained was characterized by X-ray diffraction, SEM equipped with EDS, density measurement, image analysis, mechanical testing and in vitro evaluation, and found to be a glass–ceramic macroporous scaffold with uniformly distributed and highly interconnected porosity. The extent and size-range of the porosity can be tailored by varying the amount and size of the polyethylene particles.     

Electrophoretic deposition of porous CaO–MgO–SiO<Subscript>2</Subscript> glass–ceramic coatings with B<Subscript>2</Subscript>O<Subscript>3</Subscript> as additive on Ti–6Al–4V alloy

The sub-micron glass–ceramic powders in CaO–MgO–SiO₂ system with 10 wt% B₂O₃ additive were synthesized by sol–gel process. Then bioactive porous CaO–MgO–SiO₂ glass–ceramic coatings on Ti–6Al–4V alloy substrates were fabricated using electrophoretic deposition (EPD) technique. After being calcined at 850°C, the above coatings with thickness of 10–150 μm were uniform and crack-free, possessing porous structure with sub-micron and micron size connected pores. Ethanol was employed as the most suitable solvent to prepare the suspension for EPD. The coating porous appearance and porosity distribution could be controlled by adjusting the suspension concentration, applied voltage and deposition time. The heat-treated coatings possessed high crystalline and was mainly composed of diopside, akermanite, merwinite, calcium silicate and calcium borate silicate. Bonelike apatite was formed on the coatings after 7 days of soaking in simulated body fluid (SBF). The bonding strength of the coatings was needed to be further improved.     

Glass–ceramic scaffolds containing silica mesophases for bone grafting and drug delivery

Glass–ceramic macroporous scaffolds were prepared using glass powders and polyethylene (PE) particles of two different sizes. The starting glass, named as Fa-GC, belongs to the system SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O–CaF₂ and was synthesized by a traditional melting-quenching route. The glass was ground and sieved to obtain powders of specific size which were mixed with PE particles and then uniaxially pressed in order to obtain crack-free green samples. The compact of powders underwent a thermal treatment to remove the organic phase and to sinter the Fa-GC powders. Fa-GC scaffolds were characterized by means of X-Ray Diffraction, morphological observations, density measurements, image analysis, mechanical tests and in vitro tests. Composite systems were then prepared combining the drug uptake-delivery properties of MCM-41 silica micro/nanospheres with the Fa-GC scaffold. The system was prepared by soaking the scaffold into the MCM-41 synthesis batch. The composite scaffolds were characterized by means of X-Ray Diffraction, morphological observations, mechanical tests and in vitro tests. Ibuprofen was used as model drug for the uptake and delivery analysis of the composite system. In comparison with the MCM-41-free scaffold, both the adsorption capacity and the drug delivery behaviour were deeply affected by the presence of MCM-41 spheres inside the scaffold.     

Feasibility, tailoring and properties of polyurethane/bioactive glass composite scaffolds for tissue engineering

This research work aims to propose highly porous polymer/bioactive glass composites as potential scaffolds for hard-tissue and soft-tissue engineering. The scaffolds were prepared by impregnating an open-cells polyurethane sponge with melt-derived particles of a bioactive glass belonging to the SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O system (CEL2). Both the starting materials and the composite scaffolds were investigated from a morphological and structural viewpoint by X-ray diffraction analysis and scanning electron microscopy. Tensile mechanical tests, carried out according to international ISO and ASTM standards, were performed by using properly tailored specimens. In vitro tests by soaking the scaffolds in simulated body fluid (SBF) were also carried out to assess the bioactivity of the porous composites. It was found that the composite scaffolds were highly bioactive as after 7 days of soaking in SBF a HA layer grew on their surface. The obtained polyurethane/CEL2 composite scaffolds are promising candidates for tissue engineering applications.     

High strength bioactive glass-ceramic scaffolds for bone regeneration

This research work is focused on the preparation of macroporous glass-ceramic scaffolds with high mechanical strength, equivalent with cancellous bone. The scaffolds were prepared using an open-cells polyurethane sponge as a template and glass powders belonging to the system SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O. The glass, named as CEL2, was synthesized by a conventional melting-quenching route, ground and sieved to obtain powders of specific size. A slurry of CEL2 powders, polyvinyl alcohol (PVA) as a binder and water was prepared in order to coat, by a process of impregnation, the polymeric template. A thermal treatment was then used to remove the sponge and to sinter the glass powders, in order to obtain a replica of the template structure. The scaffolds were characterized by means of X-ray diffraction analysis, morphological observations, density measurements, volumetric shrinkage, image analysis, capillarity tests, mechanical tests and in vitro bioactivity evaluation.     

Fabrication of bioglass infiltrated Al2O3–(m-ZrO2) composites

Using 80 vol.% of poly methyl methacrylate (PMMA) as a pore-forming agent to obtain interconnected porous bodies, porous Al₂O₃–(m-ZrO₂) bodies were successfully fabricated. The pores were about 200 μm in diameter and were homogeneously dispersed in the Al₂O₃–25 vol.% (m-ZrO₂) matrix. To obtain Al₂O₃–(m-ZrO₂)/bioglass composites, the molten bioglass was infiltrated into porous Al₂O₃–(m-ZrO₂) bodies at 1400°C. The material properties of the Al₂O₃–(m-ZrO₂)/bioglass composites, such as relative density, hardness, compressive strength, fracture toughness and elastic modulus were investigated.     

Synthesis,bioactivity and preliminary biocompatibility studies of glasses in the system CaO–MgO–SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaF<Subscript>2</Subscript>

New compositions of bioactive glasses are proposed in the CaO–MgO–SiO₂–Na₂O–P₂O₅–CaF₂ system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO₄) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts’ cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).     

Degradable phosphate glass fiber reinforced polymer matrices: mechanical properties and cell response

The development of biodegradable materials for internal fracture fixation is of great interest, as they would both eliminate the problem of stress shielding and obviate the need for a second operation to remove fixation devices. Preliminary investigations for the production of degradable fiber reinforced polymer composite materials are detailed. Composites were produced of phosphate invert glass fibers of the glass system P₂O₅–CaO–MgO–Na₂O–TiO₂, which showed a low solubility in previous work. The fibers were embedded into a matrix of a degradable organic polymer network based on methacrylate-modified oligolactide. Fracture behavior, bending strength and elastic modulus were evaluated during 3-point bending tests and the fracture surface of the composites was investigated using a scanning electron microscope. Short-term biocompatibility was tested in an FDA/EtBr viability assay using MC3T3-E1 murine pre-osteoblast cells and showed a good cell compatibility of the composite materials. Results suggested that these composite materials are biocompatible and show mechanical properties which are of interest for the production of degradable bone fixation devices.     

Hydrogen peroxide versus water synthesis of bioglass–nanocrystalline hydroxyapatite composites

This article reports a comparison of the structural and textural properties of bioglass–hydroxyapatite (HA) composites obtained in the SiO₂–CaO–P₂O₅ system by sol–gel method, with different amounts of hydrogen peroxide (3% H₂O₂) or water (H₂O). X-ray diffraction, Raman, and FT-IR spectroscopy reveal the presence of nanocrystalline HA. Scanning electron microscopy images illustrate that the HA phase is mainly distributed on the glass surface. The results point out that the sintering at 550 °C of a sol–gel derived SiO₂–CaO–P₂O₅ bioglass leads to a single crystalline phase of HA, and validate a new processing method for obtaining bioglass–HA composites. Structural analyses of the investigated composites indicate the existence of a silicate network built up from Q₃ and Q₂ units. The replacement of water with hydrogen peroxide has as consequence the increase of depolymerization degree of silica network. Textural properties were investigated with N₂-adsorption technique. The composites prepared with hydrogen peroxide exhibit a more uniform and narrow mesoporous distribution that recommends them for drug uptake and release applications. It was found that the specific surface area and pore volume are clearly influenced by the H₂O₂(H₂O):TEOS molar ratio.     

Effect of preparation conditions on the properties of bioactive glasses for testing SBF

A simulated body fluid (SBF) with ion concentrations similar to body fluid, proposed by Kokubo et al., is widely used to evaluate bone-bonding potential through the formation of an apatite layer. To be confident of the evaluation of the potential for the apatite formation in SBF, standard substrates are required. Although Na₂O–CaO–SiO₂ glasses have been focused upon as candidate standard substrates, it has not been clarified whether the preparation conditions of the glasses affect their apatite formation potential in SBF. In this study, Na₂O–CaO–SiO₂ glasses were prepared by a conventional melting–quenching method with different melting periods and annealing processes to examine their properties, including apatite formation in SBF. The Na₂O–CaO–SiO₂ glasses show reproducible apatite-forming ability when prepared using moderate melting and annealing processes, and can be useful substrates to test the reproducibility of SBF.     

Strontium oxide doped quaternary glasses: effect on structure,degradation and cytocompatibility

This preliminary study focuses on the effect of adding SrO to a Ti-containing quaternary phosphate glass system denoted by P₂O₅–Na₂O–CaO–TiO₂. The following four different glass compositions were manufactured: 0.5P₂O₅–0.17Na₂O–0.03TiO₂–(0.3−x)CaO–xSrO where x = 0, 0.01, 0.03 and 0.05. Structural characterisation revealed glass transition temperatures in the range 427–437°C and the presence of sodium calcium phosphate as the dominant phase in all the glasses. Degradation and ion release studies conducted over a 15-day period revealed that the Sr-containing glasses showed significantly higher degradation and ion release rates than the Sr-free glass. Cytocompatibility studies performed over a 7-day period using MG63 cells showed that the addition of 5 mol% SrO yielded glasses with cell viability nearly equivalent to that observed for quaternary TiO₂ glasses.     

Porous alumina ceramics prepared by slurry infiltration of expanded polystyrene beads

To produce highly porous MgO-doped alumina (Al₂O₃) ceramics, expanded polystyrene (EPS) beads were packed as a pore former and well-dispersed alumina slurry was used to infiltrate the pore space in the EPS bead compacts. The alumina particle-EPS bead green compacts were then heated to 1550°C in air to burn out the pore former and subsequently densify the MgO-doped alumina struts. The porous Al₂O₃ ceramics were featured with uniformly distributed open pore structures with porosities ranging from 72 to 78% and a pore interconnectivity of about 96%. The macropore size and the pore window size could be controlled by adjusting the size of the EPS beads and the contacting area between the EPS beads. The compressive strengths of the porous Al₂O₃ ceramics were in the range of 5.5–7.5 MPa, similar to those of cancellous bones (2–12 MPa). The porous alumina ceramics were further made bioactive after the dip coating of a sol-gel derived 58 S bioglass powder, followed by sintering at 1200°C.     

Viscosities of Multicomponent Silicate Melts at High Temperatures

In the present work; the viscosities in the quaternaries CaO–Fe _n O–MgO–SiO₂, Fe _n O-MgO–MnO–SiO₂, and CaO–MgO–MnO–SiO₂ and the quinary CaO–Fe _n O–MgO–MnO–SiO₂ were studied. The experimental technique employed was the well-established rotating cylinder method, using a Brookfield digital viscometer mounted over a specially designed graphite furnace. Generally, iron crucibles were used along with iron spindles. Periodic calibrations of the experimental setup were made using the standard reference slag recommended by the European Union. The measurement's were carried out up to a maximum temperature of 1773 K in all cases. The reliability of the measurements were checked at different rotation speeds as well as during thermal cycling, and excellent reproducibility of the results was noted. The experimental viscosity values were incorporated into a viscosity model. Equations based on the model for calculating the viscosities of the quarternary systems CaO–Fe _n O–MgO–SiO₂, Fe _n O–MgO–MnO–SiO₂, and CaO–MgO–MnO–SiO₂ and the quinary system CaO–Fe _n O–MgO–MnO–SiO₂ are provided.     

Effect of the addition of t-ZrO2 on the material properties of β-TCP/PCL composites

Using poly-methyl methacrylate as a pore-forming agent, porous β-tricalcium phosphate (β-TCP)/t-ZrO₂ composites were fabricated depending on the volume percentages (vol.%) of t-ZrO₂ powder. In the porous sintered bodies, hybrid pores, about 20 and 200 μm in diameter, were homogenously dispersed in the β-TCP/t-ZrO₂ matrix and showed good interconnection. On the other hand, β-TCP-(t-ZrO₂)/polycaprolactone (PCL) composites were fabricated by the melt infiltration process using porous β-TCP/t-ZrO₂ bodies. The relative density of the β-TCP-(t-ZrO₂)/PCL composites increased as the vol.% of t-ZrO₂ increased and its maximum value was about 98.6%. However, the hardness, bending strength and elastic modulus of β-TCP-(t-ZrO₂)/PCL composites decreased due to the low densification of porous β-TCP/t-ZrO₂ bodies as the volume percentages of t-ZrO₂ content increased. The values (using 20 vol.% of t-ZrO₂) were 11.4 Hv, 25.5 MPa and 17.2 GPa, respectively.     

Early stage reactivity and in vitro behavior of silica-based bioactive glasses and glass-ceramics

The surface reactivity of different sets of glasses and glass-ceramics belonging to the SiO₂–P₂O₅–CaO–MgO–K₂O–Na₂O system have been investigated. The attention was focused on the role of their composition on the bioactivity kinetics, in terms of pH modifications, silica-gel formation and its evolution toward hydroxycarbonatoapatite, after different times of soaking in simulated body fluid. Glasses and glass ceramics have been characterized by thermal analysis, SEM-EDS observations and phase analysis (XRD). XPS measurements have been carried out on the most representative set of sample in order to evaluate the evolution of the surface species during the growth of silica-gel and hydroxycarbonatoapatite. The response of murine fibroblast 3T3 to the material before and after a conditioning pre-treatment (immersion in SBF) has been investigated on the same set of samples in order to point out the role of the bioactivity mechanism on cell viability. The main differences among the various glasses have been related to the modifier oxides ratio and to the MgO content, which seems to have an influence on the glass stability, both in terms of thermal properties and surface reactivity. The surface characterization and in vitro tests revealed few variations in the reactivity of the different glasses and glass-ceramics in their pristine form. On the contrary, the different surface properties before and after the pre-treatment in SBF seem to play a role on the biocompatibility of both glass and glass-ceramics, due to the different ion release and hydrophilicity of the surfaces, affecting both cell viability and protein adsorption.     

Magnetic bioactive glass ceramic in the system CaO-P2O5-SiO2-MgO-CaF2-MnO2-Fe2O3 for hyperthermia treatment of bone tumor

Magnetic bioactive glass ceramic (MG) in the system CaO–SiO₂–P₂O₅–MgO–CaF₂–MnO₂–Fe₂O₃ for hyperthermia treatment of bone tumor was synthesized. The phase composition was investigated by XRD. The magnetic property was measured by VSM. The in vitro bioactivity was investigated by simulated body fluid (SBF) soaking experiment. Cell growth on the surface of the material was evaluated by co-culturing osteoblast-like ROS17/2.8 cells with materials for 7 days. The results showed that MG contained CaSiO₃ and Ca₅(PO₄)₃F as the main phases, and MnFe₂O₄ and Fe₃O₄ as the magnetic phases. Under a magnetic field of 10,000 Oe, the saturation magnetization and coercive force of MG were 6.4 emu/g and 198 Oe, respectively. After soaking in SBF for 14 days, hydroxyapatite containing CO₃ ²⁻ was observed on the surface of MG. The experiment of co-culturing cells with material showed that cells could successfully attach and well proliferate on MG.     

Effect of PEG amount in amorphous calcium phosphate on its crystallized products

Biphasic α-tricalcium phosphate/β-tricalcium phosphate (α/β-TCP) with a designed phase ratio is thought to have controllable dissolution–reprecipitation behavior that is significant in the repair and regeneration of bone. Amorphous calcium phosphate (ACP) was selected as a precursor to prepare biphasic α/β-TCP. The influence of polyethylene glycol (PEG) content in ACP on its crystallization, or on the phase ratio of the resulting biphasic TCP, was investigated. ACP was synthesized by the reaction of Ca(NO₃)₂ with (NH₄)₂HPO₄ using PEG as an additive. Depending on the amount of PEG addition, resulting ACP could be crystallized to α-TCP, β-TCP or biphasic α/β-TCP after heat-treatment at 800°C, showing that PEG addition is a critical factor to tailor the phase ratio of biphasic α/β-TCP. One reason for the influence of PEG is that ACP with different PEG content could have two types of unit structures that tend to form α-TCP and β-TCP after crystallization.