Surface Modification of Bioactive Glass Promotes Cell Attachment and Spreading

Phosphate glasses have several advantages over traditional silicate-based bioglasses but are inferior in the crucial step of cell attachment to their surface. Here, as a proof of concept, we analyze fibroblast attachment to the phosphate glass surface subjected to basic treatment and silanization. Silicate (S53P4)- and phosphate (Sr50)-based bioactive glasses were either untreated or surface-treated with basic buffer and functionalized with silane. The surface-treated samples were studied as such and after fibronectin was adsorbed on to their surface. With both glass types, surface treatment enhanced fibroblast adhesion and spreading in comparison to the untreated glass. The surface-treated Sr50 glass allowed for cell adhesion, proliferation, and spreading to a similar extent as seen with S53P4 and borosilicate control glasses. Here, we show that surface treatment of bioactive glass can be used to attract cell adhesion factors found in the serum and promote cell-material adhesion, both important for efficient tissue integration.

Surface Modification of Bioresorbable Phosphate Glasses for Controlled Protein Adsorption

The traditional silicate bioactive glasses exhibit poor thermal processability, which inhibits fiber drawing or sintering into scaffolds. The composition of the silicate glasses has been modified to enable hot processing. However, the hot forming ability is generally at the expense of bioactivity. Metaphosphate glasses, on the other hand, possess excellent thermal processability, congruent dissolution, and a tailorable degradation rate. However, due to the layer-by-layer dissolution mechanism, cells do not attach to the material surface. Furthermore, the congruent dissolution leads to a low density of OH groups forming on the glass surface, limiting the adsorption of proteins. It is well regarded that the initial step of protein adsorption is critical as the cells interact with this protein layer, rather than the biomaterial itself. In this paper, we explore the possibility of improving protein adsorption on the surface of phosphate glasses through a variety of surface treatments, such as washing the glass surface in acidic (pH 5), neutral, and basic (pH 9) buffer solutions followed or not by a treatment with (3-aminopropyl)triethoxysilane (APTS). The impact of these surface treatments on the surface chemistry (contact angle, ζ-potential) and glass structure (FTIR) was assessed. In this manuscript, we demonstrate that understanding of the material surface chemistry enables to selectively improve the adsorption of albumin and fibronectin (used as model proteins). Furthermore, in this study, well-known silicate bioactive glasses (i.e., S53P4 and 13-93) were used as controls. While surface treatments clearly improved proteins adsorption on the surface of both silicate and phosphate glasses, it is of interest to note that protein adsorption on phosphate glasses was drastically improved to reach similar protein grafting ability to the silicate bioactive glasses. Overall, this study demonstrates that the limited cell/phosphate glass biological response can easily be overcome through deep understanding and control of the glass surface chemistry.

Polymer-Based Honeycomb Films on Bioactive Glass: Toward a Biphasic Material for Bone Tissue Engineering Applications

The development of innovative materials for bone tissue engineering to promote bone regeneration while avoiding fibrous tissue infiltration is of paramount importance. Here, we combined the known osteopromotive properties of bioactive glasses (BaGs) with the biodegradability, biocompatibility, and ease to shape/handle of poly-l-co-d,l-lactic acid (PLDLA) into a single biphasic material. The aim of this work was to unravel the role of the surface chemistry and topography of BaG surfaces on the stability of a PLDLA honeycomb membrane, in dry and wet conditions. The PLDLA honeycomb membrane was deposited using the breath figure method (BFM) on the surface of untreated BaG discs (S53P4 and 13-93B20), silanized with 3-aminopropyltriethoxysilane (APTES) or conditioned (immersed for 24 h in TRIS buffer solution). The PLDLA membranes deposited onto the BaG discs, regardless of their composition or surface treatments, exhibited a honeycomb-like structure with pore diameter ranging from 1 to 5 μm. The presence of positively charged amine groups (APTES grafting) or the precipitation of a CaP layer (conditioned) significantly improved the membrane resistance to shear as well as its stability upon immersion in the TRIS buffer solution. The obtained results demonstrated that the careful control of the substrate surface chemistry enabled the deposition of a stable honeycomb membrane at their surface. This constitutes a first step toward the development of new biphasic materials enabling osteostimulation (BaG) while preventing migration of fibrous tissue inside the bone defect (honeycomb polymer membrane).

Structures and Dissolution Behaviors of Quaternary CaO-SrO-P2O5-TiO2 Glasses

Calcium phosphate glasses have a high potential for use as biomaterials because their composition is similar to that of the mineral phase of bone. Phosphate glasses can dissolve completely in aqueous solution and can contain various elements owing to their acidity. Thus, the glass can be a candidate for therapeutic ion carriers. Recently, we focused on the effect of strontium ions for bone formation, which exhibited dual effects of stimulating bone formation and inhibiting bone resorption. However, large amounts of strontium ions may induce a cytotoxic effect, and there is a need to control their releasing amount. This work reports fundamental data for designing quaternary CaO-SrO-P₂O₅-TiO₂ glasses with pyro- and meta-phosphate compositions to control strontium ion-releasing behavior. The glasses were prepared by substituting CaO by SrO using the melt-quenching method. The SrO/CaO mixed composition exhibited a mixed cation effect on the glassification degree and ion-releasing behavior, which showed non-linear properties with mixed cation compositions of the glasses. Sr²⁺ ions have smaller field strength than Ca²⁺ ions, and the glass network structure may be weakened by the substitution of CaO by SrO. However, glassification degree and chemical durability of pyro- and meta-phosphate glasses increased with substituted all CaO by SrO. This is because titanium groups in the glasses are closely related to their glass network structure by SrO substitution. The P-O-Ti bonds in pyrophosphate glass series and TiO₄ tetrahedra in metaphosphate glass series increased with substitution by SrO. The titanium groups in the glasses were crosslink and/or coordinate phosphate groups to improve glassification degree and chemical durability. Sr²⁺ ion releasing amount of pyrophosphate glasses with >83% SrO substitution was larger than 0.1 mM at day seven, an amount that reported enhanced bone formation by stimulation of osteogenic markers.

Impact of Glass Composition on Hydrolytic Degradation of Polylactide/Bioactive Glass Composites

Understanding the degradation of a composite material is crucial for tailoring its properties based on the foreseen application. In this study, poly-L,DL-lactide 70/30 (PLA70) was compounded with silicate or phosphate bioactive glass (Si-BaG and P-BaG, respectively). The composite processing was carried out without excessive thermal degradation of the polymer and resulted in porous composites with lower mechanical properties than PLA70. The loss in mechanical properties was associated with glass content rather than the glass composition. The degradation of the composites was studied for 40 weeks in Tris buffer solution Adding Si-BaG to PLA70 accelerated the polymer degradation in vitro more than adding P-BaG, despite the higher reactivity of the P-BaG. All the composites exhibited a decrease in mechanical properties and increased hydrophilicity during hydrolysis compared to the PLA70. Both glasses dissolved through the polymer matrix with a linear, predictable release rate of ions. Most of the P-BaG had dissolved before 20 weeks in vitro, while there was still Si-BaG left after 40 weeks. This study introduces new polymer/bioactive glass composites with tailorable mechanical properties and ion release for bone regeneration and fixation applications.

Impact of Ag2O Content on the Optical and Spectroscopic Properties of Fluoro-Phosphate Glasses

Glasses with the system (84.60-x) NaPO₃-5 ZnO-(9.40-x) NaF-x Ag₂O-1 Er₂O₃, (x = 0, 2, 4, and 6) (mol%) were synthesized by the conventional melt-quenching method. The impact of the addition of Ag₂O on the physical, thermal, structural, and optical properties of the glasses is discussed. The Judd-Oflet analysis was used to evaluate the radiative properties of the emission transitions of the glasses. The enhancement of luminescence properties due to Ag₂O is discussed in terms of consequent changes in the local electromagnetic field, symmetry, and the ligand field around the Er³⁺ ion. The heat treatment of the glass was performed in order to precipitate Ag nanoparticles (NPs), which form as a layer at the surface of the heat-treated glasses as confirmed using scanning electron microscopy (SEM). The Ag NPs were found to increase the intensity of the emission at 1.5 µm.

In-vitro dissolution characteristics and human adipose stem cell response to novel borophosphate glasses

The main drawbacks of traditional silicate bioactive glasses are their narrow hot forming domain and noncongruent dissolution. In this article, we report on new borophosphate glasses [xM_n O_m  + (100 - x) (47.5P₂ O₅  + 2.5B₂ O₃  + 10Na₂ O + 20CaO + 20SrO)], M_n O_m being CuO, Ag₂ O, and CeO₂ , having high thermal processability, hence suitable for fiber drawing and sintering into scaffolds. Furthermore, the glasses dissolve congruently in simulated body fluid (SBF) and TRIS buffer solution, eventually leading to the precipitation of a reactive layer. Human adipose stem cells (hASC) were cultured in media enriched with glass extract at different dilutions, to investigate the optimal ion concentration for cell survival. Cells grew in all the extracts, except in the undiluted Cu-doped glass extract. At dilution 1:10, the lactate dehydrogenase (LDH) activity and cell proliferation were comparable to the control, while at 1:100, the cells proliferated faster than the control. Thus, the reference (undoped), Ag and Ce-doped glasses were found to be suitable for cell viability and proliferation. Cytotoxicity assessments using the LDH assay indeed revealed the high cytotoxicity of the Cu extract. This raises questions about the use of Cu in bioactive glasses and its optimal concentration as a dopant.

Core-clad phosphate glass fibers for biosensing

Recently, a phosphate glass with composition 20 CaO-20 SrO-10 Na₂O-50 P₂O₅ (mol%) was found to have good potential as a biomaterial and to possess thermal properties suitable for fiber drawing. This study opened the path towards the development of fully bioresorbable fibers promising for biosensing. In the past, this phosphate glass with CeO₂ was found to increase the refractive index and the glass stability. Therefore, a new SrO-containing glass was prepared with 1 mol% of CeO₂ and core fibers were drawn from it. A core-clad fiber was also processed, where the core was a Ce-doped glass and the clad undoped, to allow for total internal reflection. The mechanical properties of the core and core-clad fibers are discussed as a function of immersion time in TRIS-buffer solution. Finally, a sensing region was created, in the core-clad fiber, by etching the cladding using phosphoric acid. Then, the change in light transmission, upon immersion in TRIS-buffer solution, was quantified to assess the potential use of the novel core-clad fiber as a biosensor. Upon immersion in TRIS, the core-clad fiber was found to guide light effectively and to maintain a tensile strength of ~150-200 MPa up to 6 weeks in TRIS, clearly showing that this fiber has potential as a biosensing device.