Rojas Edith C, Papadopoulos Kyriakos D
Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, LA 70118, USA.
Langmuir. 2007 Jun 19;23(13):6911-7. doi: 10.1021/la063533f. Epub 2007 May 24.
Individual water-in-oil-in-water (W1/O/W2) double-emulsion globules loaded with fluorescently labeled bovine serum albumin (FITC-BSA) were optically monitored within cylindrical capillaries during freeze-thaw cycling. Coalescence of internal aqueous droplets (W1) and external aqueous phase (W2), termed external coalescence, was not observed before or during freezing of the oil phase (O). On the other hand, this instability mechanism was readily promoted during thawing. This realization confirms the previously suggested potential of W1/O/W2 double emulsions to trigger release upon oil thawing and demonstrates that it is a direct result of globule breakage through external coalescence. The presented results also identified a threshold in the relative W1 droplet size above which instability occurred, while smaller droplets remained unperturbed and therefore indicate that optimization of the delivery can be achieved by tuning the size of W1 droplets. In addition, we propose a possible explanation for the occurrence of instability during oil thawing and its dependence on the size of W1 droplets. Because this alternative globule-breakage mechanism simply uses temperature increase (solid-to-liquid-phase transition) as external stimulus, W1/O/W2 double-emulsion delivery systems can be easily tailored by choosing an oil phase with the appropriate phase-transition temperature.
在冻融循环过程中，对装载有荧光标记牛血清白蛋白（FITC - BSA）的水包油包水（W1/O/W2）双乳液微球在圆柱形毛细管内进行光学监测。在油相（O）冷冻之前或期间，未观察到内部水滴（W1）与外部水相（W2）的聚并，即所谓的外部聚并。另一方面，这种不稳定性机制在解冻过程中很容易被促进。这一认识证实了之前所提出的W1/O/W2双乳液在油解冻时触发释放的潜力，并表明这是通过外部聚并导致微球破裂的直接结果。所呈现的结果还确定了相对W1液滴尺寸的一个阈值，高于该阈值会发生不稳定性，而较小的液滴则不受影响，因此表明可以通过调整W1液滴的尺寸来实现递送的优化。此外，我们对油解冻过程中不稳定性的发生及其对W1液滴尺寸的依赖性提出了一种可能的解释。由于这种替代的微球破裂机制仅使用温度升高（固 - 液相转变）作为外部刺激，通过选择具有合适相变温度的油相，可以轻松定制W1/O/W2双乳液递送系统。
