The purpose of this study is to prepare tricalcium phosphate (TCP) ceramic by dual dopants of magnesium (Mg) and zinc (Zn), and investigate the influence of dopants on the physical, mechanical and biological properties of TCP. TCP were synthesized with 1 wt% Mg, 0.3 wt% Zn and dual dopants using the precipitation process. Phase composition and microstructures were characterized. Mechanical properties and dissolution behavior in vitro were investigated. Human osteoblast cell culture was used to determine the influence of dopants on cell-materials interactions. XRD analysis indicated that Mg delayed phase transformation from beta to alpha-TCP and pure beta-TCP phase was obtained for Mg-doped TCP after sintered at 1250 degrees C. Addition of Mg improved densification behavior of TCP. Compression strength also increased from 24.0 MPa to 77.2 MPa after doping with Mg and Zn. Furthermore, Mg additive reduced the solubility of TCP in vitro. Osteoblast culture studies indicated that the presence of Mg stabilized the cell-material interface and thus improved cell attachment and growth. Zn-doped TCP exhibited good bioactivity, which enhanced cell differentiation and alkaline phosphatase (ALP) expression. The highest cell proliferation and ALP expression were found on dual Mg and Zn doped TCP. The results indicate that Mg and Zn dopants play a significant role towards improving mechanical properties and cell-materials interactions of TCP. This work also demonstrates the potential for dual Mg and Zn doped TCP to be used in orthopedics and dentistry, which displays high mechanical strength, low resorption and improved cell-material interaction.
Twenty four young (mean age 29-2 years, range [25][26][27][28][29][30][31][32][33][34][35] and 21 elderly (mean age 66-5, range 60-80) healthy subjects collected their urine in timed aliquots over 24 hours. The elderly subjects had been selected for their fitness by clinical and laboratory examinations and all lived independently at home. Sodium and potassium excretions were reduced in the elderly subjects compared with the young subjects, potassium excretion considerably so. This was despite similar 24 hour urine volumes and total solute excretion by both groups.The ratios of rates of excretion of water, electrolytes, and solutes during the night to the rates of excretion during the day were found to be higher in the elderly than the young subjects.Reduced day to night ratios of urinary excretion may be partly responsible for complaints of nocturia and sleep disturbance in elderly people. Introduction For many years it has been known that urine flow is lower at night than during the day in healthy subjects.' There is also an accompanying nocturnal reduction in electrolyte excretion.2 It has been speculated that reduction in urine flow at night in mammals may have evolved to permit undisturbed sleep.3Several studies of excretory rhythms in old patients have been reported.4-9 The first study was of patients in psychiatric hospitals4 5; the second of elderly patients in hospitals long term6; the third of nine patients in hospital, only two of whom were
Although sub-Saharan Africa has the highest rates of tuberculosis (TB) and human immunodeficiency virus (HIV) infection in the world, the rates of TB amongst its health care workers (HCWs) are poorly documented. We therefore conducted a country-wide investigation. All district/government and mission hospitals in Malawi that diagnose and care for TB patients were visited in order to obtain information on hospital-based HCWs and their incidence of TB in 1996. Hospital TB case loads, country-wide TB notification numbers and national population estimates for 1996 were obtained, which enabled TB case notification rates to be calculated. In 1996, 108 (3.6%) of 3042 HCWs from 40 hospitals were registered and treated for TB: 22 with smear-positive pulmonary TB (PTB), 40 with smear-negative PTB and 46 with extrapulmonary TB. The overall case fatality rate was 24%. Compared with the adult general population aged > or = 15 years, the relative risk [95% confidence interval (CI)] in HCWs of all types of TB was 11.9 [9.8-14.4], of smear-positive PTB 5.9 [3.9-9.0], of smear-negative PTB 13.0 [9.5-17.7] and of extrapulmonary TB 18.4 [13.8-24.6], P < 0.05. The 1996 hospital TB case load ranged from 29 to 915: there were no cases of TB in HCWs in hospitals whose case load was < or = 100 patients, while the TB case rate among HCWs was similar in hospitals with annual case loads of 101-300 or > 300. The annual risk of TB was high among all categories of HCW, especially clinical officers. This study shows a high rate of TB in HCWs in Malawi, and emphasizes the need for practical and affordable control measures for the protection of HCWs from TB in low-income countries.
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