Phosphate glass fibrous scaffolds: tailoring of the properties and improvement of the bioactivity through the incorporation of mesoporous glasses

Introduction. Synthetic bone scaffolds are proposed as an alternative to the use of bone grafting technique for bone regeneration. Porous scaffold obtained from glass fibres randomly arranged into a mould shows an interconnected porosity generated by the free space between fibres and they do not need of any further material or processing step before sintering. In this work, a resorbable phosphate glass was selected for the fibre drawing and bioactive mesoporous glasses with different morphology and size were incorporated into the fibrous scaffold to combine the resorption property of the fibres with the bioactivity of the mesoporous powders. Materials and methods. Fibres of a TiO2-containing phosphate glass (TiPS2.5) were fabricated following the preform drawing approach as described elsewhere [1]. A dense silica-based bioactive glass (CEL2) [2] was produced by melt quenching as reference sample. Spherical micro-sized mesoporous glass based on SiO2-CaO system (SD_MBG) was produced by an aerosol-assisted spray-drying technique [3]. Cu-containing (85SiO2-13CaO-2CuO, % mol, referred as Cu_BGn2%) mesoporous glass nanoparticles were synthetized by an ultra-sound assisted sol-gel method to impart antibacterial properties. To fabricate the fibrous scaffolds, the selected powder and phosphate glass fibres, cut at precise length, were placed in a beaker containing 2 ml of ethanol. After ethanol evaporation, the powder/fibre mixture was randomly placed inside a zirconia cylindrical mould [4]. After the thermal treatment, the scaffolds were analyzed through micro-CT in order to investigate their inner structure. Furthermore, their ability to form hydroxyapatite was studied by soaking them in a simulated body fluid (SBF). The scaffold morphology before and after immersion in SBF was studied by FESEM. Results and discussion. FESEM micrographs show that CEL2 are not well incorporated into the fibre surface. On the contrary, SD-MBG (Figure 1.a, Figure 1.b and Figure 1.d) and Cu_BGn2% particles homogeneously cover the whole surface. Micro-CT analysis did not reveal the presence of powder agglomerates for all the observed scaffolds and showed a homogeneous porosity of 58 vol.% for CEL2/fibre scaffold, 53 vol.% for SD_MBG/scaffold (Figure 1.c) and 33% for Cu_BGn2%/scaffold. In CEL2/fibre scaffolds, glass particles were removed during soaking in SBF, leaving some pits on the fibre surface: FESEM analysis revealed few particles still anchored to the scaffold surface after 7 days. On the contrary, after 7 days in SBF, SD-MBG and Cu_BGn2% particles were clearly visible on the surface of the scaffolds and after 1 day of soaking in SBF, they appeared (Figure 2) fully covered with a HA layer, showing the typical "cauliflower-like" morphology. Conclusion. The incorporation of mesoporous bioactive glass powder in the phosphate glass fibrous scaffold resulted to be a very interesting strategy to impart multifunctional properties to the scaffold. These promising results encourage further investigation in order to fully exploit the ability of mesoporous particles to act as a system for smart release of therapeutic ions and drugs

Structure optimisation and biological evaluation of bone scaffolds prepared by co-sintering of silicate and phosphate glasses

A degradable phosphate glass (ICEL) and a bioactive silicate glass (CEL2) were mixed in different ratios (wt-%: 100%ICEL, 70%ICEL-30%CEL2, 30%ICEL-70%CEL2, 100%CEL2; codes 100-0, 70-30, 30-70, 0-100) and then co-sintered to obtain three-dimensional porous scaffolds by gel casting foaming. Thermal analyses were carried out on the glass mixtures and were used as a starting point for the optimisation of the scaffold sintering treatment. The microcomputed tomography and field emission scanning electron microscope analyses allowed the selection of the optimal sintering temperature to obtain an adequate structure in terms of total and open porosity. The scaffolds showed an increasing solubility with increasing ICEL glass content, and for 30-70 and 0-100, the precipitation of hydroxyapatite in simulated body fluid was observed. In vitro tests indicated that all the scaffolds showed no cytotoxic effect. The co-sintering of silicate and phosphate glasses showed to be a promising strategy to tailor the scaffold osteoconductivity, degradation and bioactivit

Characterisation of Bioglass based foams developed via replication of natural marine sponges

A comparative characterisation of Bioglass based scaffolds for bone tissue engineering applications developed via a replication technique of natural marine sponges as sacrificial template is presented, focusing on their architecture and mechanical properties. The use of these sponges presents several advantages, including the possibility of attaining higher mechanical properties than those scaffolds made by foam replica method (up to 4 MPa) due to a decrease in porosity (68-76%) without affecting the pore interconnectivity (higher than 99%). The obtained pore structure possesses not only pores with a diameter in the range 150-500 mm, necessary to induce bone ingrowth, but also pores in the range of 0-200 mm, which are requested for complete integration of the scaffold and for neovascularisation. In this way, it is possible to combine the main properties that a three-dimensional scaffold should have for bone regeneration: interconnected and high porosity, adequate mechanical properties and bioactivity

Characterisation of CorGlaes (R) Pure 107 fibres for biomedical applications

A degradable ultraphosphate (55 mol % P2O5) quinternary phosphate glass composition has been characterised in terms of its chemical, mechanical and degradation properties both as a bulk material and after drawing into fibres. This glass formulation displayed a large processing window simplifying fibre drawing. The fibres displayed stiffness and strength of 65.5 ± 20.8 GPa and 426±143 MPa. While amorphous discs of the glass displayed a linear dissolution rate of 0.004 mg cm−2 h−1 at 37 °C, in a static solution with a reduction in media pH. Once drawn into fibres, the dissolution process dropped the pH to <2 in distilled water, phosphate buffer saline and corrected-simulated body fluid, displaying an autocatalytic effect with >90 % mass loss in 4 days, about seven times faster than anticipated for this solution rate. Only cell culture media was able to buffer the pH taking over a week for full fibre dissolution, however, still four times faster dissolution rate than as a bulk material. However, at early times the development of a HCA layer was seen indicating potential bioactivity. Thus, although initial analysis indicated potential orthopaedic implant applications, autocatalysis leads to accelerating degradation in vitro