The antibacterial activity, the cytotoxicity and the cell function of a sintered Ti-10 wt% Cu alloy were investigated in order to assess the suitability of the alloy for biomedical application. The antibacterial activity of the alloy was investigated by a plate-count method and the cytotoxicity was studied by examining the MG63 cell response by CCK8 assessment. The cell function was monitored by measuring the AKP activity. The Cu ion released from the Ti-Cu alloy was also measured by an inductively coupled plasma spectrometer at different immersion durations. The results show that the antibacterial rates of the alloy against Escherichia coli and Staphylococcus aureus increase with an increase in the incubation duration. After 7 h of incubation, the alloy showed an antibacterial rate of 91.66% against S. aureus and 99. 01% against E. coli. With a further extension of incubation time to 24 h, the antibacterial rate increased to 100% against S. aureus and 99.93% against E. coli. No cytotoxicity was observed on the alloy by a CKK8 test during three days of incubation in comparison with commercially available pure titanium (cp-Ti). AKP test results showed a significantly high AKP value (p = 0.001 < 0.01) on the Ti-Cu alloy on day 1. The Cu ion release was thought to contribute to the strong antibacterial property, but the Cu ion did not lead to cell cytotoxicity. Strong antibacterial activity and good cell biocompatibility suggest that the Ti-Cu alloy could reduce bacterial infection and have a potential application as an implant material.
Brown
carbon (BrC) absorbs radiation in the near-UV and visible
ranges, affecting atmospheric photochemistry and radiative forcing.
Our understanding on the photochemical transformation of BrC is still
limited, especially when mixed with the abundant and photochemically
labile inorganic salt, nitrate. Herein, we investigate the photochemical
reactions of four BrC chromophores, including two methoxyphenols and
two nitrophenols. Experiments were conducted in the absence and presence
of different concentrations of H2O2 and nitrate
with lights of 254 and 313 nm. The results show that the pseudo-first-order
decay rate constants (k) of these four BrC compounds
at 313 nm illumination were approximately 10 times lower than those
at 254 nm, demonstrating longer lifetimes of these BrC chromophores
under tropospherically relevant irradiation. Photo-enhancement in
the visible range was observed in most experiments, with those under
313 nm illumination lasting longer, indicating the prolonged effects
of nascent and transformed BrC chromophores on radiative forcing.
Methoxyphenols had higher averaged k values than
nitrophenols during direct photolysis with 254 or 313 nm lights, but
the k values for nitrophenols under high-nitrate
(or high-H2O2) conditions approached those of
methoxyphenols. The photo-enhancement in the visible range for methoxyphenols
in the presence of nitrate was substantially contributed by nitro
products, while that for nitrophenols was mainly contributed by hydroxylated
and/or dimerized products. Our results reveal the similarity and difference
between the photolysis of methoxyphenols and nitrophenols, which may
help better understand the aging of different types of BrC for better
model representation of their effects on radiative forcing.
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