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| The nanoparticles were fabricated using different concentrations of STC (10–35 mM) as a stabilizer. The characterization results of the prepared batches are presented in Table 2. It was observed that the DLE was maximum (98.2%) at 10 mM STC concentration (Batch I), and it decreased drastically with increase in STC concentration. The high DLE achieved was in agreement with the ability of STC to significantly retard solubility of the drug particularly at 10 mM concentration in pH 7.2 (with respect to other surfactant concentrations and the buffer alone), as observed in our earlier study[18]. However, none of the batches with only STC (Batches I–V) as stabilizer were found to be stable as phase separation occurred within 15 days of storage at room temperature (Fig. 1A). In order to achieve a homogenous dispersion, PVA,a polymeric excipient was added to the nanoemulsion. Addition of 1% (w/v) PVA (Batch VI) significantly improved the stability of the nanodispersion, as shown in Fig. 1B. The increased viscosity (from 1.08 cps (Batch I) to 4.3 cps (Batch VI)), by almost four folds, of the nanoemulsion upon addition of PVA may be the factor responsible to prevent the agglomeration by reducing the mobility of the nanoparticles in the dispersion medium. Moreover, PVA being a hydrophilic polymer acts as a coat to shield the particle surface charge responsible to cause their agglomeration [21]. It is probably due to this reason that the nanoparticles were found to be stable despite its low zeta potential. Preparation of a stable nanodispersion in presence of PVA alone (Batch VII) indicates its ability to immobilize nanoparticles by the viscosity imparted by the polymeric solution. However, the DLE of the batch was significantly the lattice arrangement or less ordered crystal lattice of the lipid of Batch V which shows incomplete lipid solidification or the coexistence of its amorphous state. The thermogram of lipid particles of Batches V and VI showed shifted peaks with relatively low heat of enthalpy than that of the pure lipid. This may be due to the presence of drug as a foreign body in the pure lipid and drastic reduction in particle size of lipid which together result in imperfections in the crystal lattice and, therefore, decrease in melting enthalpy. As the quantity of heat required to melt the impure lipid is reduced, a shift in the melting point of the lipid in the nanoparticles is observed. The X-ray diffraction patterns of Batches V and VI along with the pure lipid and drug are presented in Fig. 4(A–D). The XRD results obtained are in good agreement with the results established by DSC measurements. Although, crystalline reflections are visible for SLN of Batch V, the figures demonstrate that the scattering profile exhibited by nanoparticles of Batch VI were of much higher intensity which is again an indication of the existence of lower ordered crystalline state and/or amorphous state of the latter. It can be also observed that after the addition of drug, scattering profile of the lipid remains unchanged, indicating that the lattice order inside the hydrocarbon chains is still conserved. The disappearance of the drug peaks in the formulation shows that the lipid has arrested the re-crystallization of the drug particles from the solvent system upon its evaporation. The investigations related to morphology and solid state characteristics confirm that the crystal structure of the lipid in Batch V has several imperfections and, therefore, exists in a solid liquid transition state or a semisolid state. The inability of the lipid emulsion to recrystallize in presence of Buffer-I may be attributed to partial neutralization of stearic acid in the presence of metallic hydroxide due to which the lipid forms a creamy base and, therefore, fails to regain its solid state in the aqueous medium [22].However, the drug retention ability of the Batches V and VI was independent of the crystal arrangement as no significant difference in their DLE was observed which indicates that the lipid crystals have sufficient space to accommodate the added quantity of drug. The PDI values of Batches VI and VII reveal sufficiently uniform particle size distribution. The comparatively larger PDI of Batch V may be attributed to its physical state, as discussed above, due to which the particles have a tendency of agglomeration and is even to prepare ALN. Approximately, 7–8 ml of the nanodispersion was found to saturate 50 mg of the adsorbent used in each process of each batch. The physiochemical properties of the ALN were evaluated and are presented in Table 3. The drug loading efficiency of the adsorbent was estimated to be 79.8 ± 2.3%. Apart from free drug, the loss during the separation process can also be related to particle size and PDI of the nanoparticles. The improvement in the PDI and relative increase in the average particle size of the re-dispersed nanoparticles relative to that of the nanodispersion indicates that a part of nanoparticles of lower size range were screened and not adsorbed on the adsorbents. This may be due to the fact that the pores of the adsorbents were filled with the nanodispersion and after saturation of these pores; the adsorbent was able to retain nanoparticles of only higher size range trapped in the inter-particulate void space. The above fact was determined by the analysis of the pooled eluent which revealed nano dispersion with 84.5 ± 9.3 nm particle size (PDI = 0.09 ± 0.01). Further drug content analysis on re-dispersion of nanoparticles in aqueous solution containing 1.0% PVA indicated that the re-dispersed amount corresponds to the amount of nanoparticles adsorbed. The photo micrograph of the ALN (Fig. 5) reveals Neusilin particles randomly |
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The nanoparticles were fabricated using different concentrations of STC (10–35 mM) as a stabilizer. The characterization results of the prepared batches are presented in Table 2. It was observed that the DLE was maximum (98.2%) at 10 mM STC concentration (Batch I), and it decreased drastically with increase in STC concentration. 利用不同濃度的STC（10-35mM）作為穩(wěn)定劑，我們成功地合成了納米顆粒。研究結(jié)果表明DLE在STC濃度為10mM的時(shí)候?yàn)樽畲螅?8.2%），而繼后隨著STC的濃度上升而顯著下降。 |
2樓2011-01-09 17:16:29
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kaichang(金幣+30, 翻譯EPI+1):謝謝。 2011-01-09 22:21:52
ringzhu(金幣+10):辛苦~~歡迎常來翻譯版~~O(∩_∩)O~ 2011-01-10 11:15:05
kaichang(金幣+30, 翻譯EPI+1):謝謝。 2011-01-09 22:21:52
ringzhu(金幣+10):辛苦~~歡迎常來翻譯版~~O(∩_∩)O~ 2011-01-10 11:15:05
| 該納米粒子用作為穩(wěn)定劑的不同濃度的STC（10-35mM）制備。樣品的表征結(jié)果見表2。可以看到在STC濃度為10mM(釜I)時(shí)DLE達(dá)到最大（98.2%）。隨著STC濃度的繼續(xù)加大，DLE急劇下降。高濃度DLE的制得與我們?cè)缙谟^察的STC顯著阻礙該藥物在pH7.2、10mM濃度時(shí)的溶解度相吻合（和其它表面活性劑相比）。但是，在室溫儲(chǔ)存15天的時(shí)間內(nèi)，釜I~V沒有發(fā)現(xiàn)一批STC出現(xiàn)穩(wěn)定的相分離（圖1A）。為了達(dá)到均質(zhì)分散的效果，把PVA這樣一種聚合賦形劑加入到納米浮濁液中。釜I添加了1%的PVA可以顯著提高其納米分散液的穩(wěn)定性，如圖1B所示。粘度增加了將近四倍（從釜I的1.08cp增加到釜VI的4.3cp）通過向納米乳濁液中添加PVC可以起到通過減少納米顆粒在分散介質(zhì)中的流動(dòng)性從而阻止顆粒團(tuán)聚的作用。而且PVA作為一種親水聚合物在粒子表面涂膜阻止其團(tuán)聚�？赡苡捎诖嗽�，盡管納米顆粒的電位較低但相對(duì)而言還是比較穩(wěn)定的。在只加PVA的納米分散液（釜VI）表明通過聚合物溶膠的粘度能使納米顆粒固定。該釜里DLE的晶格排列或釜VI的無序晶格排列說明脂類出現(xiàn)固化或同時(shí)存在無定形態(tài)。釜V和釜VI脂類粒子的熱譜分析顯示與純脂類相比有低焓熱同時(shí)顯著減小脂類的粒徑引起晶格的缺陷，因此，引起熔化焓的減小。當(dāng)所需熔化不純脂類的熱值減小時(shí)，觀察到了在納米粒子中脂類熔點(diǎn)的變化。圖4（A-D）為釜V（純脂類）和釜VI（藥類）的XRD圖，XRD結(jié)果與DSC結(jié)果一致。盡管對(duì)釜V的SLN來說其晶型可見，說明了釜VI中納米顆粒的有較高的散射強(qiáng)度再一次說明低有序晶格的存在或者晶格中存在無定形態(tài)。同時(shí)能發(fā)現(xiàn)當(dāng)添加藥物后，脂類的散射圖仍然保持不變，說明C-H鍵仍然保持著。藥物峰的消失說明脂類已經(jīng)使藥物粒子從溶液中由于蒸發(fā)作用發(fā)生重結(jié)晶。形貌表征和固體的性質(zhì)證實(shí)了釜V中脂類晶體結(jié)構(gòu)的幾種缺陷，因此在固液相態(tài)轉(zhuǎn)變的過程中存在著中間態(tài)。添加緩沖劑I的脂類乳濁液不能重結(jié)晶是由于脂類形成奶油狀金屬氫氧化物堿而使硬脂酸部分中和引起的，因此在水介質(zhì)中不能得到其固態(tài)。但釜V和釜VI中藥物的滯留能力與晶格排列的獨(dú)立性有關(guān)，DLE沒有顯著變化說明脂類晶體具有足夠大的空間來儲(chǔ)存加入的藥物。釜VI和VII的PDI值說明粒徑均勻分布，相比較而言釜V的PDI值大一點(diǎn)可以歸因于其物理狀態(tài)。如上所討論，由于在制備ALN時(shí)粒子有團(tuán)聚的趨勢，在每一個(gè)釜的每一步處理過程中，7-8mL納米乳濁液在50mg的吸附劑中達(dá)到飽和，對(duì)ALN生物化學(xué)性質(zhì)的評(píng)價(jià)見表3。吸附劑對(duì)藥物的吸附效率大約為79.8±2.3%。除了游離藥物，分離過程中的損失取決于納米粒子的PDI值。平均粒子尺寸PDI的增大以來于納米乳濁液的再分散，這表明低小尺寸分布的納米粒子不會(huì)被吸附，這可能是由于在孔過飽和后吸附劑的孔和納米乳濁液結(jié)合了；吸附劑只能在寬尺寸的范圍內(nèi)起作用。上述現(xiàn)象可通過洗脫分析證實(shí)，粒徑在84.5±9.3nm之間(PDI = 0.09 ± 0.01).進(jìn)一步對(duì)水中藥物含量的分析可知PVA的含量為1.0%，這表明再分散的量與納米粒子被吸附的量一致。ALN的顯微鏡圖（圖5）揭示了粒子是隨機(jī)分布的。 |
3樓2011-01-09 18:45:05
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