Department of Mechanical Engineering, Universidad de los Andes, Bogota, Colombia.
PLoS One. 2013 Jul 11;8(7):e68309. doi: 10.1371/journal.pone.0068309. Print 2013.
The study of vesicles in suspension is important to understand the complicated dynamics exhibited by cells in in vivo and in vitro. We developed a computer simulation based on the boundary-integral method to model the three dimensional gravity-driven sedimentation of charged vesicles towards a flat surface. The membrane mechanical behavior was modeled using the Helfrich Hamiltonian and near incompressibility of the membrane was enforced via a model which accounts for the thermal fluctuations of the membrane. The simulations were verified and compared to experimental data obtained using suspended vesicles labelled with a fluorescent probe, which allows visualization using fluorescence microscopy and confers the membrane with a negative surface charge. The electrostatic interaction between the vesicle and the surface was modeled using the linear Derjaguin approximation for a low ionic concentration solution. The sedimentation rate as a function of the distance of the vesicle to the surface was determined both experimentally and from the computer simulations. The gap between the vesicle and the surface, as well as the shape of the vesicle at equilibrium were also studied. It was determined that inclusion of the electrostatic interaction is fundamental to accurately predict the sedimentation rate as the vesicle approaches the surface and the size of the gap at equilibrium, we also observed that the presence of charge in the membrane increases its rigidity.
研究悬浮液中的囊泡对于理解细胞在体内和体外表现出的复杂动力学行为非常重要。我们开发了一种基于边界积分法的计算机模拟方法，用于模拟带电荷的囊泡在重力作用下向平面沉降的三维过程。膜的力学行为采用赫夫里希哈密顿函数进行建模，并通过考虑膜热涨落的模型来强制实现膜的近不可压缩性。模拟结果经过验证，并与使用荧光探针标记的悬浮囊泡获得的实验数据进行了比较，荧光探针允许使用荧光显微镜进行可视化，并赋予膜负表面电荷。囊泡与表面之间的静电相互作用采用线性德扎古金近似法进行建模，适用于低离子浓度溶液。通过实验和计算机模拟确定了囊泡到表面的距离与沉降速率之间的关系。还研究了囊泡与表面之间的间隙以及平衡时囊泡的形状。结果表明，静电相互作用的包含对于准确预测囊泡接近表面时的沉降速率以及平衡时的间隙大小至关重要，我们还观察到膜中电荷的存在会增加其刚性。
