Propriedades Mecânicas da Biovitrocerâmica Biosilicato

Abstract

Biosilicate® glass (1.5Na2O-1.5CaO-3SiO2 + 4wt% P2O5) is a bioactive material capable of interacting with biological tissues. Designed to be compatible with both soft tissues, such as cartilage, and hard tissues, such as bone, this material exhibits mechanical properties similar to those of human bone. The combination of high bioactivity and good mechanical properties represents one of the major challenges in the field of biomaterials. The Biosilicate® glass- ceramic was developed precisely to overcome this obstacle. In this context, understanding the correlation between the material's microstructure and its mechanical properties is fundamental for designing bioceramics with optimized performance. This research aimed to systematically characterize the mechanical properties of this glass-ceramic by independently varying two microstructural features: crystal size and crystalline volume fraction. The average crystal diameter was set at 15 μm and 45 μm , while the crystallized volume fraction was controlled from 0% (fully amorphous glass) to 100%. X-ray diffraction and Rietveld refinement identified two crystalline phases of combeite: one high-temperature and one low-temperature phase. The mechanical results demonstrated that Vickers hardness decreased with an increasing crystalline fraction. In contrast, indentation fracture toughness (KC) increased significantly, rising from 0.37 ± 0,10 MPa·m1/2 to 0.72 ± 0.10 MPa·m1/2 (15 μm crystals) and 0.78 ± 0.1 MPa·m1/2 (45 μm crystals), also showing an increase with crystal size. Mechanical strength, measured by the ball-on-three-balls (B3B) technique, yielded values of 140 ± 20 MPa for the amorphous glass, 120 ± 10 MPa for the 100% crystallized glass-ceramic with 15 μm crystals, and 120 ± 10 MPa for the 100% crystallized glass-ceramic with 45 μm crystals. These results indicate lower strength for low crystalline fractions, which is subsequently recovered and surpassed with an increase in both crystal size and crystalline fraction.The variation in fracture toughness (KIC) as a function of the crystallized volume fraction followed a similar trend to KC for glass-ceramics with different crystal sizes. For the glass, KIC was 0.65 ± 0.07 MPa·m1/2, increasing for the 20% crystallized fraction and remaining constant with further crystallization, reaching values of 0.7 ± 0.02 MPa·m1/2 and 0.8 ± 0.1 MPa·m1/2 for the fully crystallized glass-ceramics with 15 μm and 45 μm, respectively. Optical profilometry of the fractured surfaces revealed greater roughness with increasing crystalline fraction and crystal size. The crystalline phase contributes strongly to this increase. The increase in fracture toughness is attributed to crack twist and tilt. The obtained data reveal that the microstructure, specifically the crystal size and crystalline volume fraction, exerts a positive influence on the mechanical properties of Biosilicato®. These results provide valuable knowledge for the design and fabrication of new glass-ceramics that are simultaneously strong and tough, guiding the development of more efficient and durable biomedical applications.