Aim To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems. Methods A free diffusion model was used to evaluate the effects of c...Aim To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems. Methods A free diffusion model was used to evaluate the effects of concentration, the property of drugs, as well as the gel compositions on the diffusivity of drugs. Results Drug transport through the aqueous channels of the gel followed Fickian mechanism, and no significant influence on the diffusivity was observed when the drug concentration was lowered from 5% to 0.25%. The diffusion coefficients of propranolol, timolol maleate, and salbutamol sulfate were 0.91, 1.32, and 3.30×10 -6 cm 2·s -1 , respectively. The flux of hydrophilic drug was 3.6 fold faster than that of the lipophilic one implied the latter partitioned into the hydrophobic micellar core, and consequently the diffusion was retarded. The diffusivity was decreased with increased poloxamer and sodium hyaluronate concentration, due to the distorted aqueous channels and higher microviscosity. Conclusion The result suggested that sustained release could be achieved for the thermosensitive in situ gel by incorporating lipophilic drug or increasing polymer concentration.展开更多
The effect of heat treatment on microstructure and mechanical properties of the Ti-steel explosive-rolling clad plate was elaborated by optical microscopy （OM）, scanning electron microscopy （SEM）, X-ray diffracti...The effect of heat treatment on microstructure and mechanical properties of the Ti-steel explosive-rolling clad plate was elaborated by optical microscopy （OM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, micro-hardness test and shear test. The composites were subjected to heat treatment at temperature of 650-950 ~C for 60 min. The results show that the heat treatment process results in a great enhancement of diffusion and microstructural transformation. The shear strength decreases as the treatment temperature increases. Heated at 850 ℃ or below, their shear strength decreases slowly as a result of the formation of TiC in the diffusion interaction layer; while at the temperature of 850 ℃ or above, the shear strength decreases obviously, which is the consequence of a large amount of Ti-Fe intermetaUics （Fe2Ti/FeTi） along with some TiC distributing continuously at diffusion reaction layer.展开更多
Gaomiaozi （GMZ） bentonite is regarded as the favorable candidate backfilling material for a potential repository in China. It is important to understand the diffusion behavior of ^125I in GMZ bentonite and compare t...Gaomiaozi （GMZ） bentonite is regarded as the favorable candidate backfilling material for a potential repository in China. It is important to understand the diffusion behavior of ^125I in GMZ bentonite and compare the diffusion behavior in GMZ and other types of bentonite like MX-80, Avonlea, etc. Therefore, through- and out-diffusion experiments were conducted to obtain the effective diffusion coefficient （De） and distribution coefficient （Kd）. A computer code named Fitting for diffusion coefficient （FDP） was used for the experimental data processing and theoretical modeling. At the dry density of GMZ bentonite from 1600-2000 kg/m^3, the De values of ^125I were （2.4-20.4）×10 ^-12 m^2/s and Ka values were constants. At dry density above 1800 kg/m^3, the diffusion behaviors were almost the same, indicating that the anion exclusion was ineffective. Out-diffusion results showed that the species of ^125I may be changed during the diffusion processing. It was probably caused by some organic mat- ters or reducing substances in GMZ bentonite. Since the main composition of bentonite is montmorillonite, similar diffusion parameters were obtained in GMZ and other types of bentonite. The relationship of DE and accessible porosity （εacc） could be described by Archie＇s law with exponent n = 1.2-2.8 for ^125I diffusion in bentonite, whereas n = 2.0 in GMZ bentonite. Fur- thermore, bentonite with the dry density of 1800 kg/m^3 was proposed as the backfilling materials used in the construction of high level radioactivity waste repository.展开更多
文摘Aim To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems. Methods A free diffusion model was used to evaluate the effects of concentration, the property of drugs, as well as the gel compositions on the diffusivity of drugs. Results Drug transport through the aqueous channels of the gel followed Fickian mechanism, and no significant influence on the diffusivity was observed when the drug concentration was lowered from 5% to 0.25%. The diffusion coefficients of propranolol, timolol maleate, and salbutamol sulfate were 0.91, 1.32, and 3.30×10 -6 cm 2·s -1 , respectively. The flux of hydrophilic drug was 3.6 fold faster than that of the lipophilic one implied the latter partitioned into the hydrophobic micellar core, and consequently the diffusion was retarded. The diffusivity was decreased with increased poloxamer and sodium hyaluronate concentration, due to the distorted aqueous channels and higher microviscosity. Conclusion The result suggested that sustained release could be achieved for the thermosensitive in situ gel by incorporating lipophilic drug or increasing polymer concentration.
文摘The effect of heat treatment on microstructure and mechanical properties of the Ti-steel explosive-rolling clad plate was elaborated by optical microscopy （OM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, micro-hardness test and shear test. The composites were subjected to heat treatment at temperature of 650-950 ~C for 60 min. The results show that the heat treatment process results in a great enhancement of diffusion and microstructural transformation. The shear strength decreases as the treatment temperature increases. Heated at 850 ℃ or below, their shear strength decreases slowly as a result of the formation of TiC in the diffusion interaction layer; while at the temperature of 850 ℃ or above, the shear strength decreases obviously, which is the consequence of a large amount of Ti-Fe intermetaUics （Fe2Ti/FeTi） along with some TiC distributing continuously at diffusion reaction layer.
基金supported by Qianjiang Talents Project in Zhejiang ProvinceProject Supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry
文摘Gaomiaozi （GMZ） bentonite is regarded as the favorable candidate backfilling material for a potential repository in China. It is important to understand the diffusion behavior of ^125I in GMZ bentonite and compare the diffusion behavior in GMZ and other types of bentonite like MX-80, Avonlea, etc. Therefore, through- and out-diffusion experiments were conducted to obtain the effective diffusion coefficient （De） and distribution coefficient （Kd）. A computer code named Fitting for diffusion coefficient （FDP） was used for the experimental data processing and theoretical modeling. At the dry density of GMZ bentonite from 1600-2000 kg/m^3, the De values of ^125I were （2.4-20.4）×10 ^-12 m^2/s and Ka values were constants. At dry density above 1800 kg/m^3, the diffusion behaviors were almost the same, indicating that the anion exclusion was ineffective. Out-diffusion results showed that the species of ^125I may be changed during the diffusion processing. It was probably caused by some organic mat- ters or reducing substances in GMZ bentonite. Since the main composition of bentonite is montmorillonite, similar diffusion parameters were obtained in GMZ and other types of bentonite. The relationship of DE and accessible porosity （εacc） could be described by Archie＇s law with exponent n = 1.2-2.8 for ^125I diffusion in bentonite, whereas n = 2.0 in GMZ bentonite. Fur- thermore, bentonite with the dry density of 1800 kg/m^3 was proposed as the backfilling materials used in the construction of high level radioactivity waste repository.
