Adam Shearer

Bismuth has recently emerged as a multifunctional element bridging the gap among bioactivity, diagnostics, and therapy in advanced glass and ceramic systems. Beyond its well-known clinical use in pharmaceutical compounds, bismuth exhibits distinctive physicochemical properties, including high atomic number, strong polarization ability, and redox versatility that enable unique biological and functional responses. This review consolidates current knowledge on the biological roles of bismuth, including its antibacterial, anticancer, hemostatic, and photothermal effects, as well as its use as a safe radiopacifier in medical imaging. Emphasis is placed on the incorporation of bismuth into bioceramics, including bioactive glasses, glass-ceramics, calcium phosphates, and piezoelectric ceramics, highlighting how Bi3+ substitution alters network structure, crystallization, and ion-release behavior. Across reported studies, Bi incorporation at levels of 1–10 mol. % has been shown to increase radiopacity by 2- to 4-fold, produce up to 90% reductions in bacterial viability, and generate photothermal heating above 50 °C under near-infrared exposure. These quantitative effects underscore how Bi-driven structural modifications translate into measurable biological and functional performance. The multifunctionality of these Bi-containing materials positions them at the forefront of next-generation biomaterials for soft and hard tissue repair, drug delivery, and image-guided therapy.

This study investigates the structural, thermal, optical, and mechanical properties of calcium aluminate glasses upon incremental substitution with germania (GeO ₂ ). A series of glasses with the molar formula xGeO ₂ ·(1− x )(0.64CaO·0.36Al ₂ O ₃ ), where x = 0–0.50 mole fraction, was synthesized and characterized. Germanium speciation was analyzed, showing a transition from Q ² to Q⁴ and N ₆ species with increasing GeO ₂ content, which results in enhanced network connectivity. The incorporation of GeO ₂ increases glass density and oxygen packing efficiency due to the germanate anomaly, with Ge shifting to higher coordination states. The liquid fragility index is observed to decrease with GeO ₂ addition, indicating improved thermal stability and broader processing windows. Mechanical testing revealed a reduction in moduli and hardness with GeO ₂ content, attributed to the replacement of stronger Al–O bonds with more flexible Ge–O bonds. Optical measurements showed improved ultraviolet and visible transparency, with a progressive red shift in the UV cutoff and a slight decrease in the optical band gap. Notably, infrared transmission was enhanced by GeO ₂ incorporation, extending the transparency window and reducing OH ⁻ ‐related absorption. These results suggest that partially germanated calcium aluminate glasses offer a promising platform for cost‐effective mid‐IR applications, combining thermal robustness, improved processability, and expanded IR transmission with relatively low material cost.

Topological constraint theory has enabled the successful prediction of glass properties over a wide range of compositions. In this study, a topological constraint model is constructed for alkaline earth vanadate glasses based on experimental data. The change in vanadate structural units from VO ₅ to VO ₄ was modeled as a function of alkaline earth content and related to thermal and mechanical properties. The model covers both high‐ and low‐temperature properties to probe the temperature dependence of constraint rigidity for each constituent of the glass network. The model is changed to describe anomalies in magnesium sites potentially implying that magnesium can form locally rigid structures. Furthermore, the traditional understanding of vanadate glass structure is compared to recent results concluding that the terminal oxygen must exist as a part of the VO ₄ units. Results for the model explain that bridging oxygen constraints are the main contributors to network rigidity in both low‐ and high‐temperature regimes. Vanadate glass networks are highly connected even with the introduction of modifier species, which introduce their own bond constraints. Corroboration between experimental data and the topological constraint model illustrates the role of alkaline earth oxides in the glass network.

Larry L. Hench's research group first introduced gel‐derived bioactive glasses (BGs) in 1991. These BGs offer a broader range of bioactivity than traditional melt‐derived BGs. Highly porous gel‐derived glasses are suitable for various applications, such as bone and soft tissue engineering. The sol–gel process has significant versatility in developing BGs, and recent studies have investigated new compositions, including 58S glass (60SiO ₂ –36CaO–4P ₂ O ₅ mol%) modified with metal oxides. The addition of bismuth to BGs has recently been studied to enhance radiopacity, antibacterial properties, and effectiveness in cancer therapy. We investigated the effects of bismuth addition on the structural and biological properties of 60SiO ₂ –(36 − x )CaO–4P ₂ O ₅ – x Bi ₂ O ₃ ( x = 0, 0.5, 1, 1.5 mol%) gel‐derived glasses. The glasses were prepared by hydrolysis and polycondensation of tetraethyl orthosilicate, triethyl phosphate, Ca(NO ₃ ) ₂ ·4H ₂ O, and Bi(NO ₃ ) ₃ ·5H ₂ O. They were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, differential thermal analysis/thermogravimetry, and nuclear magnetic resonance after successfully converting the gels to glass at 600°C. The in vitro bioactivity, cytotoxicity, antimicrobial activity, and radiopacity of all samples were then analyzed. We found that glasses with 0.5, 1, and 1.5 mol% bismuth can be synthesized via a simple sol–gel route. In vitro tests confirmed that hydroxycarbonate apatite covers the surface of glass particles after 24 h of immersion in simulated body fluid. An in vitro biocompatibility assay demonstrated that the new materials are non‐cytotoxic and antibacterial against Escherichia coli . Furthermore, the glass doped with 1.5 mol% of bismuth exhibited radiopacity equivalent to a 3.05 mm aluminum scale, meeting the standard limit.

Glasses formed from transition metal oxides have shown tailorable electrical and optical properties depending on the valence state and individual element. Vanadate glasses have received specific attention for their high conductivities as compared to most glass families. In this study, the frequency‐dependent capacitance and direct current (dc) conductivity properties of alkaline earth vanadate glasses were investigated. Glasses in the x SrO–(100 − x )V ₂ O ₅ and x BaO–(100 − x )V ₂ O ₅ systems, where x = 30, 40, and 50 in mol%, were prepared via melt‐quench synthesis. Capacitance measurements were used to calculate dielectric constants, dielectric loss, and alternating current (ac) conductivity for each sample. Dielectric constants varied between 10–13 and 14–16 for SrO–V ₂ O ₅ and BaO–V ₂ O ₅ glasses, respectively, at 1 MHz. Current measurements were made as a function of temperature and voltage for each glass sample. A strong dependence on vanadate content was noted where temperature had a less strong effect. Activation energies were calculated to describe electrical transport mechanisms. All samples showed activation energies governed by electron hopping mechanisms. Such vanadate glasses have properties suitable for applications as cathode materials for batteries, solid state electrolytes, and conductive glass paste with potential for electro‐optic effects involving nonlinear processes.

Topological constraint theory has emerged as a rapid, predictive method to quantify the relationship between structural rigidity and glass properties. Understanding the structure of telluro‐vanadate (TeO ₂ –V ₂ O ₅ ) glasses has remained difficult owing to their complex mixture of structural units. Here, we propose a topological model that accurately captures the glass structure and can be used to predict properties such as glass transition temperature and hardness. The experimentally obtained properties are in agreement with predicted properties by the model suggesting that this simplified structural model accurately describes the V ₂ O ₅ –TeO ₂ structure.

This article reviews promising studies on the design, manufacturing, microstructure, properties, and applications of glass‐ceramics containing ZrO₂ and relevant glass‐ceramic matrix composites. After the addition of ZrO₂ to a glass‐ceramic composition, it can persist in the residual glassy phase, facilitate nucleation, and/or precipitate as ZrO₂ or another zirconate crystalline phase. Also, ZrO₂‐reinforced or ZrO₂‐toughened glass‐ceramics can be designed as composites. In this article, the term “ZrO₂‐containing glass‐ceramics” encompasses all these scenarios in which ZrO₂ is present. Such glass‐ceramics offer a wide range of applications in modern industries, including but not limited to architecture, optics, dentistry, medicine, and energy. Since S. Donald Stookey's discovery of glass‐ceramics in the early 1950s, the most important scientific efforts reported in the literature are reviewed. ZrO₂ is commonly added to glass‐ceramics to promote nucleation. As a result, the role of ZrO₂ in structural modification of residual glass and stimulating the nucleation in glass‐ceramic is first discussed. ZrO₂ can also be designed into the main crystalline phase of glass‐ceramics, contributing achieving super high fracture toughness above 4 MPa·m^0.5. Experimental and computational studies are reviewed in detail to elucidate how the transformation toughening and other mechanisms help to achieve such high values of fracture toughness. Sintered and glass‐ceramic matrix composites also show promise, where ZrO₂ contributes to improved stability and mechanical properties. Finally, we hope this article will provoke interest in glass‐ceramic materials in both the scientific and industrial communities so that their tremendous technological potential in developing, for example, tough, thermally stable, transparent, and biologically compatible materials can be realized more widely.

Both unwanted and induced crystallization can impact bioactivity, physical and mechanical properties of bioactive glasses (BGs). Uncontrolled crystallization has negative consequences, rendering BGs unreliable. However, by manipulating the type, size, shape, and quantity of crystals in BGs, plenty of opportunities arise for controlling, for example, mechanical properties and degradability, leading to unique applications and improved performance. Understanding crystallization is a key step in developing bioactive glasses and glass‐ceramics (BGCs), and both fundamental and experimental research can aid in the design of BGCs for processing and biological function. In this perspective, we discuss the sources of crystallization and how controlled crystallization facilitates the functionalization of bioactive scaffolds, hybrids, coatings, composites, cements, and fibers.