Metallic implant materials possess adequate mechanical properties such as strength, elastic modulus, and ductility for long term support and stability in vivo. Traditional metallic biomaterials, including stainless steels, cobalt-chromium alloys, and titanium and its alloys, have been the gold standards for load-bearing implant materials in hard tissue applications in the past decades. Biodegradable metals including iron, magnesium, and zinc have also emerged as novel biodegradable implant materials with different in vivo degradation rates. However, they do not possess good bioactivity and other biological functions. Bioactive glasses have been widely used as coating materials on the metallic implants to improve their integration with the host tissue and overall biological performances. The present review provides a detailed overview of the benefits and issues of metal alloys when used as biomedical implants and how they are improved by bioactive glass-based coatings for biomedical applications.
The effect of B2O3/SiO2 substitution in SrO-containing 55S4.3 bioactive glasses on glass structure and properties, such as ionic diffusion and glass transition temperature, was investigated by combining experiments and molecular dynamics simulations with newly developed potentials. Both short-range (such as bond length and bond angle) and medium-range (such as polyhedral connection and ring size distribution) structures were determined as a function of glass composition. The simulation results were used to explain the experimental results for glass properties such as glass transition temperature and bioactivity. The fraction of bridging oxygen increased linearly with increasing B2O3 content, resulting in an increase in overall glass network connectivity. Ion diffusion behavior was found to be sensitive to changes in glass composition and the trend of the change with the level of substitution is also temperature dependent. The differential scanning calorimetry (DSC) results show a decrease in glass transition temperature (Tg) with increasing B2O3 content. This is explained by the increase in ion diffusion coefficient and decrease in ion diffusion energy barrier in glass melts, as suggested by high-temperature range (above Tg) ion diffusion calculations as B2O3/SiO2 substitution increases. In the low-temperature range (below Tg), the Ea for modifier ions increased with B2O3/SiO2 substitution, which can be explained by the increase in glass network connectivity. Vibrational density of states (VDOS) were calculated and show spectral feature changes as a result of the substitution. The change in bioactivity with B2O3/SiO2 substitution is discussed with the change in pH value and release of boric acid into the solution.
One of the key challenges of developing next-generation solid-state lithium ion batteries is to discover solid-state electrolytes (SSEs) with high lithium ion conductivity and interfacial stability. By using molecular dynamics (MD) simulations with recently developed partial charge effective potentials, we have systematically investigated Li1+x Al x Ge2–x (PO4)3 crystalline SSEs to understand the effect of gradual Al3+/Ge4+ substitution on the defect behaviors and lithium ion transport mechanisms. Defect formation energies in simulation crystals were first calculated using the Mott–Littleton method. This was followed by extensive MD simulations of wide ranges of compositions and at various temperatures. Structural analysis shows that lithium ions occupy both the 36f and M2 interstitial sites, which are formed as a result of Al3+ to Ge4+ substitution. Lithium ion diffusion through these interstitial sites is the main diffusion path that results in high lithium ion conductivity in the lithium aluminum germanium phosphate (LAGP) system. Diffusion activation energy barriers were obtained from diffusion coefficients at different temperatures, and a minimum close to x = 0.5 substitution was observed, which is in good agreement with experimental results. Our simulation results reveal that the 36f sites play an essential role in decreasing diffusion energy barriers. Through the analysis of the trajectories of lithium ion diffusion and related structural evolution, we proposed a model for lithium diffusion that links the structural and energetic aspects of Li+ migration in the LAGP crystals. The results show that MD simulations, with both static and dynamic analysis, can be an effective tool to explore and design novel SSEs with high ionic conductivity.
Boron-containing bioactive glasses display a strong potential in various biomedical applications lately due to their controllable dissolution rates. In this paper, we prepared a series of BO/SiO-substituded 45S5 bioactive glasses and performed in vitro biomineralization tests with both simulated body fluid and KHPO solutions to evaluate the bioactivities of these glasses as a function of boron oxide to silica substitution. The samples were examined with scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry after immersing them in the two solutions (simulated body fluid and KHPO) up to 3 weeks. It was found that introduction of boron oxide delayed the formation of hydroxyapatite, but all the glasses were shown to be bioactive. Molecular dynamics (MD) simulations were used to complement the experimental efforts to understand the structural changes due to boron oxide to silica substitution by using newly developed partial charge composition-dependent potentials. Local structures around the glass network formers, medium-range structural information, network connectivity, and self-diffusion coefficients of ions were elucidated from MD simulation. Relationships between boron content and glass properties such as structure, density, glass transition temperature, and in vitro bioactivity were discussed in light of both experimental and simulation results.
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