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This study sought to investigate the effect of delayed pulsed-wave ultrasound with low frequency on drug release from and the antimicrobial efficacy of vancomycin-loaded acrylic bone cement in vivo and the possible mechanism of this effect. After the implantation of cement and the inoculation of Staphylococcus aureus into the bilateral hips of rabbits, ultrasound (average intensity, 300 mW/cm 2 ; frequency, 46.5 kHz; on/off ratio, 20 min/10 min) was applied to animals in the normal ultrasound group (UG 0-12 ) from 0 through 12 h after surgery and to those in the delayed-ultrasound group (UG 12-24 ) from 12 through 24 h after surgery. The control group (CG) was not exposed to ultrasound. Based on vancomycin concentrations in left hip cavities at projected time intervals, the amount of time during which the local drug concentration exceeded the MIC (T >MIC ) in UG 12-24 was significantly prolonged compared with that in either CG or UG 0-12 , and the ratios between the areas under the concentration-time curves over 24 h and the MIC for UG 0-12 and UG 12-24 were both increased compared with that for CG. The greatest reductions in bacterial densities in both right hip aspirates and right femoral tissues at 48 h were achieved with UG 12-24 . Local hemorrhage in rabbits of UG 0-12 during the 12-h insonation was more severe than that in rabbits of UG 12-24 . Of four variables, the T >MIC and the bioacoustic effect were both identified as parameters predictive of the enhancement of the antimicrobial efficacy of cement by ultrasound. Sustained concentrations above the MIC replaced early high maximum concentrations and long-term subtherapeutic release of the drug, provided that ultrasound was not applied until local hemorrhage was relieved. The enhancement of the antimicrobial efficacy of cement by ultrasound may be attributed to the prolonged T >MIC and the bioacoustic effect caused by ultrasound.Of the patients worldwide undergoing total joint replacement per year, approximately 0.3 to 2.2% develop prosthesis-related infections resulting in devastating surgical failure (23,25). Antibiotic-loaded bone cement is the treatment of choice because of its high local dose and low systemic toxicity compared with those of intravenous antibiotics (23,25). However, it is sometimes deficient in antimicrobial efficacy (21). Many authors have attributed this defect to the incomplete release of the antibiotic from the cement (4,5,6,8,20,23,24). The matrix of polymethylmethacrylate is, to a large extent, impermeable to antibiotics. Not only is the bioavailability of the antibiotic decreased, but the prolonged exposure to the antibiotic also allows selective bacterial resistance to occur (20).Recently, low-frequency ultrasound has been found to enhance the release of gentamicin from cement (4, 8). Two possible mechanisms behind this phenomenon include acoustic streaming and an accelerated rate of mass transfer as a result of stable cavitation and the ultrasonic pressure wave. Also, such enhanced release of gentamicin may contribute to a d...

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The mechanism of forest ground fire is thermal decomposition and smoldering combustion of forest peat or duff. The availability of oxygen is believed to influence the processes. This paper aims to investigate the thermal decomposition of peat under inert and oxidative atmospheres. Experiments were monitored under nitrogen and air atmospheres, using the non-isothermal thermogravimetric (TG) and differential thermal analysis (DTA) methods. The pyrolysis curves of peat showed three main stages, i.e., the stage of moisture evaporation (together with low stability of organic compounds) (315-432 K, with the heating rate of 10 K/min), organic matter pyrolysis (432-805 K), and inorganic compound decomposition (805-1075 K). The stage of organic matter pyrolysis also contained three steps, corresponding to hemicellulose, cellulose, and lignin pyrolysis. Because the temperature of inorganic compound decomposition was higher than the peatsmoldering temperature, this stage of inorganic compound decomposition was not important for peat pyrolysis. Therefore, the peat pyrolysis processes were simulated using reactions of four fractions: moisture, hemicellulose, cellulose, and lignin. In the combustion curves, the inorganic compound decomposition stage was not distinct, while the organic matter pyrolysis stage became two consecutive stages, i.e., the stage of organic matter decomposition (427-575 K) and char oxidative combustion (575-800 K). A scheme containing moisture evaporation (together with low stability of organic compounds) and two consecutive reactions was proposed to simulate the combustion processes. The good agreement between the experimental and simulated curves validated the proposed models for pyrolysis and combustion of peat. The kinetic parameters of main components/steps were compared to those reported for lignocellulosic biomass.

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