| Atmospheric Particulate matter, which is also known as atmospheric aerosol, is all kinds of solid and liquid particles in the atmosphere quality floorboard. In recent years, atmospheric particulate matter has become the one of the hot issues in environment as recognition of atmospheric pollution and human health improved, the effect of atmospheric particles in the respiratory system and its function has caused wide public concern among human over the environmental health effect. Particles has three ways to enter human body, first one is inhaled through respiratory tract, second is intaking with food and water and third is surface contact, and breathing is the most important and the most harmful way. Particulate matter contact into the body through the respiratory and different particle size of particulate matter has different influence to the human body. Atmospheric Particulate matter which particle size is larger than 10 μm are easily obstructed by respiratory tract but some atmospheric fine particulate matter, especially the PM2.5, is very easy to enter the alveoli due to their features of small volume, light weight, large surface area, and a long standing time in the air. Furthermore, some elements those in harm to human health, such as Br, As, Pb, Cu and Cr are concentrated in fine particulate matter whose particle size less than 3 μm. The smaller size of the particle the deeper in the human respiratory tract deposition and required for longer periods of time to clear so the harm is greater. In conclusion, compared with large particles, the fine particle can adsorb more harmful substances and deposit deeper into the lungs, even can cause more harmful adverse effect.Pulmonary alveolar is the main place of gas exchange for human body as it is the main structure and function unit of the lung. Particles tract into the alveoli through the respiratory will contact with lung surface active material directly at first, may cause the change of the structure and function of pulmonary surfactant even trigger a series of symptoms of the body. Pulmonary surfactant (PS) is a complex compound of lipoprotein and phospholipids produced by pulmonary type II epithelial cells. Including phospholipids and four types of protein, its main ingredients are dipalmitoyl phosphatidylcholine (DPPC), this saturated phospholipid is the major thing responsible for the physicochemical properties of PS as it can lower the surface tension at the air-water interface to allowing proper respiratory function. DPPC can spread quickly on the alveolar gas-liquid interface to form monolayer film under the auxiliary of proteins, so as to effectively reduce the surface tension, prevent alveolar collapse atrophy, ensure the normal breathing function of the human body. DPPC monolayers is a typical biological membrane model to replace PS in vitro experiment. Particulate matter into the alveolar is bound to cause damage changes of DPPC monolayers.In this study, we focus on the biophysical impact of silica fume of different exposure time on the monolayers at higher temperatures than room temperature. We have investigated the adsorption and penetration behavior of silica fume into DPPC monolayers at the air-water interface. Both the interfacial properties and phase behavior of DPPC monolayers are very well studied. This can broaden insight into mechanisms of particle-surfactant interaction in biological systems through surface pressure isotherms, surfactant microstructure, and collapse in monolayers.The main research results and conclusions of this study are as follows:(1) The particle size of silica fume used in experiment is a bimodal distribution, which proved that silica fume belong to the coal fly ash. The size range of silica fume is from 0.2 to 500 μm and the main portion which ranged from 0.3 to 120 μm accounted for more than 90%. The median particle diameter (D50) is 6.15 μm. The main components of silica fume is silicon dioxide, which account for 96%, other constituents are some metallic oxide whose proportion are almost the same, and the content is low. The morphology of silica fume was mostly anomalistic that the surface was coarse.(2) Increasing of temperature can accelerate the phase transformation and extend transformation time of DPPC monolayers. but high temperature is adverse for DPPC monolayers to reach the maximum surface pressure.(3) The surface pressure increasing within the squeezing of DPPC monolayer film under different pH. pH almost had no effect on gas membrane phase, but in liquid phase, low pH (≈ 4.0) can help to increase the rate of and promote DPPC monomolecular membrane to form stable structure. Phospholipid molecules arrange more closely to form a lower energy lattice structure then delay phase transition under high pH (≈9.0).(4) Metal cation (Na+. Ca2+) and Cl- had little obvious impact on the DPPC monolayer film at air-water interface. But due to the electrostatic interaction between metal ions and polar groups enhance the capacity of the combination between the phospholipid molecules, membrane phospholipid molecules arranged more closely to accelerate the formation of stable molecular membrane. Bovine serum albumin (BSA) can promote the DPPC spread out on the gas-liquid interface effectively and accelerating the phase transition.(5) The contact time less than 1 hours did not influence the π-A isotherms of DPPC monolayers. However, the silica fume particles incorporated into the DPPC monolayers at the air-water interface when the contract time is more than 3 hours and the lifting area/molecule isotherms of DPPC monolayers increased with the increasing of contact time. Furthermore, silica fume did affect the ability of the DPPC film to reach the maximum surface pressure and collapse pressure was observed from π-A isotherms.(6) The main ingredients that should in PS including:phosphatidylcholine(PC), phosphatidyl glycerol (PG), phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI) and sphingomyelin (S) were all detected in the extracting PS, the content of main ingredients of PC is 54%.The yield of PS is 0.05 g/1000 ml. |
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