Structural and elemental characterization of glass and ceramic particles for bone surgery

Retention of strength and ion release of some restorative materials

This study aimed to investigate the retention of strength in accelerated aging condition and ion release from an experimental fiber-reinforced bioactive flowable composite resin (Bio-SFRC), comparing it with various commercially available ion-releasing materials. The flexural strength of Bio-SFRC and other materials (Biodentine, TheraCal LC, Fuji II LC and Surefil one) was evaluated (n = 8) before and after hydrothermal accelerated aging. Ion concentrations of silica and phosphorus were measured after 1, 2, 3, 4, 7, 10, 14, and 21 days of specimen immersion in simulated body fluids (SBF) using UV-Vis spectrometry. In addition, ion release and pH change were studied in a continuous dynamic system in SBF over a period of 72 h. SEM and EDS were used to evaluate the microstructure on the top surface of the materials after SBF immersion. Data were statistically analyzed using variance ANOVA analysis (p = 0.05). Bio-SFRC showed higher flexural strength before (134.9 MPa) and after (63.1 MPa) hydrothermal aging compared to other tested materials (p < 0.05). Flexural strength significantly decreased after aging (p < 0.05) except for Fuji II LC which showed no significant differences. Ion release data showed that experimental Bio-SFRC slowly released phosphate ions. Biodentine and TheraCal LC had the strongest ability to form calcium phosphate precipitation on the material surface. Phosphate ion release cannot be detected clearly from these materials. Surefil one and Fuji II LC were more stable materials without any observable ion release. The advantages of fiber containing structure and slow release of ions suggest that experimental Bio-SFRC is a promising bioactive material to provide ions for mineralization of surrounding tissues, and keeping the durability of the materials at higher level than that of other tested materials.

Electrochemical behavior and surface stability of dental zirconia ceramics in acidic environments

Dental zirconia ceramics, widely employed in dentistry for their biocompatibility and mechanical properties, face challenges in long-term viability within the oral cavity. This study focuses on analyzing the electrochemical behavior of a commercial dental zirconia ceramic type in acidic environments. Through extensive electrochemical investigations, including Electrochemical Impedance Spectroscopy (EIS) and cyclic polarization resistance (Cpol), corrosion resistance was assessed. Despite indications of material dissolution, our results demonstrate significant corrosion resistance, as reflected in low corrosion current density (Icorr) values. Notably, the study reveals the development of a protective oxide layer at the ceramic-electrolyte interface, contributing to material stability. XRD analysis confirms the presence of stable crystallographic phases (t-ZrO2) even after exposure to acidic media. Surface characterizations utilizing scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) affirm minimal surface damage and maintained elemental composition. These findings illuminate the intricate electrochemical behavior of dental zirconia ceramics in challenging environments, underscoring their potential for durable dental restorations. This interdisciplinary research bridges dentistry and materials science, providing valuable insights for optimizing material properties and advancing dental materials and restorative techniques.

Bioactive glasses promote rapid pre-osteoblastic cell migration in contrast to hydroxyapatite, while carbonated apatite shows migration inhibiting properties

Different biomaterials have been clinically used as bone filling materials, although the mechanisms behind the biological effects are incompletely understood. To address this, we compared the effects of five different biomaterials: two bioactive glasses (45S5 and S53P4), hydroxyapatite (HAP), carbonated apatite (CAP), and alumina on the in vitro migration and viability of pre-osteoblastic cells. In addition, we studied the effects of biomaterials' calcium release on cell migration, viability and differentiation. We found differences between the materials as the bioactive glasses promoted rapid pre-osteoblastic cell migration. In contrast, CAP decreased cell migration, which was also associated with lower activity of migration related kinases. Bioactive glasses released significant amounts of calcium into the media, while CAP decreased the calcium concentration. The response of cells to calcium was mechanistically studied by blocking calcium sensing receptor (CaSR) and ATP-gated ion channel P2X7, but this had no effect on cell migration. Surprisingly, HAP and CAP initially decreased cell viability. In summary, bioactive glasses 45S5 and S53P4 had significant and long-lasting effects on the pre-osteoblastic cell migration, which could be related to the observed calcium dissolution. Additionally, bioactive glasses had no negative effects on cell viability, which was observed with HAP and CAP.

Synthesis of Silanized Bioactive Glass/Gelatin Methacrylate (GelMA/Si-BG) composite hydrogel for Bone Tissue Engineering Application

Bioactive glass (BG) has been widely employed in the field of bone tissue engineering owing to its osteoconductive properties. These properties increase the stiffness and bioactivity of polymeric hydrogels, making them ideal for the repair, replacement, and regeneration of damaged bones. In this study, we investigated the effects of incorporating silanized 45S5 bioactive glass (Si-BG) into gelatin methacrylate (GelMA) hydrogel (GelMA/Si-BG) for potential bone tissue engineering. Our findings revealed that crosslinking GelMA with Si-BG had a striking increase in bioactivity with and without osteogenic induction of human mesenchymal stem cells (hMSCs) when compared to GelMA/BG hydrogels. Meanwhile, both GelMA/Si-BG and GelMA/BG hydrogels were able to maintain the cell viability of hMSC for up to 14 days. Additionally, GelMA/Si-BG hydrogels were shown to have a significantly higher compressive modulus than GelMA/BG hydrogels. This study has demonstrated the introduction of silanized 45S5 BG into GelMA hydrogel bioactivity and mechanical properties of GelMA hydrogels, exemplifying the potential application of silanization of BG in bone tissue engineering.

Tetracalcium phosphate/polycaprolactone composite scaffold: Mechanical reinforcement, biodegradability regulation and bioactivity induction

Polycaprolactone (PCL) is considered a potential biomaterial due to its good biocompatibility, but its slow degradability and insufficient mechanical properties limit its wide application in bone tissue engineering. Tetracalcium phosphate's (TTCP) good degradability and inherent high stiffness are expected to compensate for the aforementioned defects of PCL and endow it with good biological activity. This goal of this study was to obtain bioactive PCL composite scaffolds with tuneable degradation properties and good mechanical strength via selective laser sintering technology (SLS). Composite porous scaffolds with TTCP contents of 0%, 5%, 10%, 15%, 20%, and 25% were prepared, and the experimental results showed that the addition of TTCP significantly improved the mechanical properties of the scaffold. Notably, the tensile strength of the composite scaffold with 20% TTCP content reached 15.2 MPa, which was 2.9 times that of pure PCL, and the best flexural strength was found in the scaffold with 15% TTCP content (4.7 MPa). More importantly, the introduced TTCP not only achieved the effective pH regulation of the soaking solution and the promotion of biodegradation, but also provided the scaffold with good bioactivity and biocompatibility.

Development and characterization of ion-releasing fiber-reinforced flowable composite

OBJECTIVE

This study aimed to develop and characterize an ion-releasing experimental fiber-reinforced flowable composite (Bio-SFRC) and dentin treatment solution made of poly(acrylic acid) (PAA) with a high molecular weight. In addition we also evaluated the interface structure and mineralization potential between the Bio-SFRC and dentin.

METHODS

Some mechanical properties (flexural properties and fracture toughness) of Bio-SFRC in comparison with commercial inert (G-aenial Flo X) and ion-releasing materials (ACTIVA-BioActive Base/Liner and Fuji II LC) were assessed (n = 8/group). Calcium-release at different time-points was measured during the first six weeks by using a calcium-ion selective electrode. Surface analysis of composites after being stored in simulated body fluid (SBF) was investigated by using SEM/EDS. Dentin disks (n = 50) were prepared from extracted sound teeth and demineralization was simulated by acid etching. SEM/EDS was used to evaluate the microstructure of dentin on the top surface and at interface with composites after being stored in SBF.

RESULTS

Bio-SFRC showed higher fracture toughness (1.6 MPa m^1/2) (p < 0.05) compared to Flo X (1.2 MPa m^1/2), ACTIVA (1 MPa m^1/2) and Fuji II LC (0.8 MPa m^1/2). Accumulative calcium release after six weeks from Bio-SFRC (15 mg/l) was higher than other tested ion-releasing materials (≈ 6 mg/l). Mineralization was clearly seen at the interface between treated dentin and Bio-SFRC. None of the commercial tested materials showed signs of mineralization at the interface and dentinal tubules remained open.

SIGNIFICANCE

Developing such reinforced ion-releasing flowable composite and PAA solution might offer the potential for mineralization at the interface and inside the organic matrix of demineralized dentin.