微脂粒在生物學上、製藥及醫學上的研究與應用皆扮演著重要的角色，然而，由於微脂粒存在的穩定性的問題，因而限制其應用與發展。所以本研究著眼於瞭解添加物對微脂粒穩定性的影響及其機制探討，期望能提昇微脂粒在應用上的潛力與發展。 本研究嘗試著在膜組成中添加以聚乙基醚(PEO)及聚丙基醚(PPO)為主的三團聯共聚物Pluronic(PF-127)；在微脂粒溶液中添加鎂離子，探討其對微脂粒物理穩定性的影響，再由分子層面說明其交互作用機制。物理穩定性的觀測部份，主要是觀測微脂粒粒徑隨時間之變化及包覆物質流失的情形。機制探討部份，本研究以恆溫滴定微卡計(Isothermal Titration Calorimetry, ITC)量測系統的稀釋熱以求得粒子間交互作用位能，進而瞭解微脂粒粒子間的淨作用力，最後以微脂粒粒子間的交互作用力(intervesicle interaction)及磷脂質分子間的交互作用力(intravesicle interaction)兩方面來說明其作用機制。 物理穩定性的觀測部份，結果顯示：在微脂粒膜組成中添加三團聯共聚物(PF-127)能增加微脂粒粒徑的穩定性，在實驗的濃度範圍內，隨著添加量的增加其穩定性也隨之提昇，在水溶液中添加鎂離子亦有相同的情形。在微脂粒膜組成中添加PF-127會促進包覆物質的滲透，隨著量的增加其滲透率隨之增加，此情形在37℃特別明顯；在水溶液中添加鎂離子亦有相同的情形。DSC實驗的結果可知，在微脂粒膜組成中添加PF-127並不影響脂質分子間之交互作用力(intravesicle interaction)，配合滲透實驗的結果：PF-127會促進包覆物質的滲透，因此推論，PF-127的疏水端部份嵌入脂雙層的結構中，但嵌入的不夠深。由於PF-127的嵌入影響了脂雙層的排列結構，使得包覆物質的滲透情形增加。從ITC的結果可知，在膜組成中添加PF-127能增加粒子間的排斥位能(repulsive potential)，配合界面電位的結果可說明，排斥位能的增加主要是來自於微脂粒表面的親水端(PEO)所形成的立體障礙及水合斥力。當溫度提高至37℃，由於熱波動加強且水合斥力增強，導致排斥位能增加。在37℃，微脂粒膜組成中添加不同量之PF-127, 在水溶液中添加100mM Mg2+，粒子間之交互作用位能減少，推論此時粒子間主要的作用力為凡得瓦力；在水溶液中添加500mM Mg2+，粒子間之交互作用位能增加，此時粒子間主要的作用力為水合斥力。 所以由本實驗可瞭解PF-127及Mg2+對微脂粒穩定性的影響主要是在於粒子間的交互作用力方面，而利用恆溫滴定微卡計有助於探討、瞭解粒子間的交互作用，以說明影響穩定性的機制。 Liposomes are thermodynamically unstable vesicles and have been widely utilized as a model of biomembrane and as a carrier in drug delivery systems. Hence, control and predict stability of vesicle against aggregation and fusion are essential for the various applications. With an attempt to study the effects of tri-block copolymer (PF-127) and Mg2+ ion on liposomes physical stability and interaction mechanisms , liposomes consisted of DMPC, vitamin E and various quantities of PF-127 were prepared by the probe sonication method. The physical stability of liposomes were monitored by examining the changes in size with time and hydrophilic fluroscence (5(6)-carbixyfluroscence) permeability. The interaction mechanisms between liposomes were demonstracted in terms of zeta potential and interaction potential(b2/B0). The results revealed that incorporation of PF-127 and Mg2+ reduced the change in size at 37℃. In addition, PF-127 and Mg2+ greatly promoted the permeability of hydrophilic fluroscence both at 22℃ and 37℃. Furthermore, as the quantities of PF-127 increased, the permeability greatly increased. From the results of DSC spectrum, PF-127 affect the phase transition temperature insignificantly, indicating that PF-127 has no great impact on the intravesicle structure packing. The dates obtained from zeta potential and ITC experiments confirmed that addition of PF-127 enhanced the repulsive potential that was mainly attributed to steric force resulted from PEO group. With regard to the effects of Mg2+ on intervesicle interaction, we concluded that in the presence of 100mM Mg2+ the dominate force between liposomes is van der Waals force. However, in the case of 500mM Mg2+ the dominate force between liposomes is shifted to hydration repulsive force. In conclusions, the effects of PF-127 on liposome physical stability is mainly attributed to intervesicle interaction.
