Fibroblastic Interactions with High-Porosity Ti-6Al-4V Metal Foam

Peer reviewed: YesNRC publication: Ye

Comprehensive Study of the Chelation and Coacervation of Alkaline Earth Metals in the Presence of Sodium Polyphosphate Solution

The effect of chelation of three alkaline earth metals (Ca, Sr, and Ba) by polyphosphates on the pH and viscosity of the solution is examined and correlated to the phosphate glass properties. Also, the impact of the polyphosphate average degree of polymerization (<i>D</i>_p) as well as the type and amount of chelated divalent cation on the degradation rate of the chains is studied. Subsequently, the number of divalent cations required for polyphosphate chain agglomeration to form a coacervate, and the resulting composition of these coacervates, was investigated. A decrease in polyphosphate solution pH during chelation was routinely obtained, with a sudden shift in the rate of pH drop occurring around a divalent cation/phosphorus molar ratio of 0.18. Longer chains or cations with a smaller ionic radius accelerated the rate of <i>D</i>_p reduction. The number of divalent cations required for coacervation depends on different variables such as the polyphosphate concentration, the <i>D</i>_p, and the type of divalent cation. The formed coacervate retains the <i>D</i>_p of polyphosphate originally used for coacervation, and the resulting Ca/P molar ratio depends largely on the amount of calcium being used during coacervation. Overall, this article helps one to understand the coacervation of polyphosphates in order to exploit their potential as a biomaterial

Correlating the Atomic Structure of Bimetallic Silver–Gold Nanoparticles to Their Antibacterial and Cytotoxic Activities

Silver nanoparticles (AgNPs) have gained much attention in biomedical research because of their antibacterial properties. However, they have also exhibited cytotoxicity toward certain mammalian cells. In order to improve therapeutic efficacy, the incorporation of gold (Au) and Ag into bimetallic Ag–Au NPs is a promising strategy, as it has the potential to increase biocompatibility and maintain antibacterial activity. Toward this end, we prepared a series of bimetallic Ag–Au NPs and studied them with X-ray absorption spectroscopy (XAS) in order to elucidate the correlation of atomic structure to their bioactivities. The addition of Au was found to drastically change the atomic structure of the Ag NPs; namely, the Ag core of the NPs was gradually replaced with Au, while Ag was found mostly on the surface. Next, NP antibacterial activity toward <i>S. aureus</i> and cytotoxicity toward NIH-3T3 fibroblast cells were assessed. It was found that the antibacterial activity of the bimetallic NPs was lower than pure Ag NPs and dependent on the Ag location within the NPs. On the other hand, the cytotoxicity of bimetallic NPs was much lower than the pure Ag NPs and dependent on the overall Au concentration. Using the structural information garnered from XAS, we were able to rationalize the bioactivity results of the NPs based on their atomic structure and provide guiding principles to design Au–Ag NPs with balanced antibacterial and cytotoxic activities. This work represents an important step toward engineering the atomic structure of bimetallic Au–Ag NPs for biomedical applications