Gehrer Simone, Schmiele Martin, Westermann Martin, Steiniger Frank, Unruh Tobias
Physik Department, Friedrich-Alexander-Universität Erlangen-Nürnberg , Staudtstrasse 3, 91058 Erlangen, Germany.
J Phys Chem B. 2014 Sep 25;118(38):11387-96. doi: 10.1021/jp506787v. Epub 2014 Sep 15.
The presence of liquid crystalline phases in suspensions of solid lipid nanoparticles can increase the risk of their gelling upon administration through fine needles. Here we study the formation of liquid crystalline phases in aqueous suspensions of platelet-like shaped solid lipid nanoparticles. A native lecithin-stabilized trimyristin (20 wt %) suspension was investigated at different dilution levels by small-angle X-ray scattering (SAXS) and visual inspection of their birefringence between two crossed polarizers. For trimyristin concentrations φMMM < 6 wt %, the dispersed platelets are well separated from each other whereas they start to self-assemble into stacked lamellae for 6 wt % ≤ φMMM < 12 wt %. For φMMM ≥ 12 wt %, the SAXS patterns become increasingly anisotropic, which is a signature of an evolving formation of a preferred orientation of the platelets on a microscopic scale. Simultaneously, the suspensions become birefringent, which proves the existence of an anisotropic liquid crystalline phase formed in the still low viscous liquid suspensions. Spatially resolved SAXS scans and polarization microscopy indicate rather small domains in the (sub)micrometer size range in the nematic liquid crystalline phase and the presence of birefringent droplets (tactoids). The observed critical concentrations for the formation of stacks and the liquid crystalline phase are significantly higher as for equivalent suspensions prepared from triglycerides with longer chains. This can be explained with the lower aspect ratio of trimyristin platelets. Special emphasis is put on the isotropic-liquid crystalline phase transition as a function of the ionic strength of the dispersion medium and φMMM. Higher salt concentrations allow shifting of the phase transition to higher trimyristin concentrations. This can be attributed to a partial screening of the repulsive forces between the platelets, which allows higher packing densities within the platelet stacks and of remaining isolated platelets.
固体脂质纳米颗粒悬浮液中液晶相的存在会增加其通过细针给药时发生胶凝的风险。在此，我们研究了血小板状固体脂质纳米颗粒水悬浮液中液晶相的形成。通过小角X射线散射（SAXS）以及在两个正交偏振器之间对其双折射进行目视检查，研究了天然卵磷脂稳定的肉豆蔻酸甘油酯（20 wt%）悬浮液在不同稀释水平下的情况。对于肉豆蔻酸甘油酯浓度φMMM < 6 wt%，分散的血小板彼此分离良好，而当6 wt% ≤ φMMM < 12 wt%时，它们开始自组装成堆叠的薄片。对于φMMM ≥ 12 wt%，SAXS图谱变得越来越各向异性，这是血小板在微观尺度上形成择优取向不断演变的标志。同时，悬浮液变得具有双折射性，这证明在仍然低粘度的液体悬浮液中形成了各向异性液晶相。空间分辨的SAXS扫描和偏振显微镜表明，向列型液晶相中存在相当小的（亚）微米尺寸范围的区域以及双折射液滴（类晶团聚体）。观察到的形成堆叠和液晶相的临界浓度明显高于由具有更长链的甘油三酯制备的等效悬浮液。这可以用肉豆蔻酸甘油酯血小板较低的纵横比来解释。特别强调了各向同性 - 液晶相转变作为分散介质离子强度和φMMM的函数。较高的盐浓度允许相转变向更高的肉豆蔻酸甘油酯浓度移动。这可归因于血小板之间排斥力的部分屏蔽，这允许在血小板堆叠内以及剩余孤立血小板内有更高的堆积密度。
