Membrane edge tension

Measuring Membrane Edge Tension from Vesicle Electroporation... 

In this sechon some applicahon aspects of giant vesicle electroporation are considered. In parhcular, it will be demonstrated that creahng macropores in GUVs and observing their closing dynamics can be successfully apphed to the evaluation of material properties of membranes. While in Section 7.4.2 we saw that such experiments can be used to characterize membrane stability in terms of the crihcal porahon potenhal f c, here we will find out how one can also evaluate the edge tension of porated membranes. In addition, another apphcation based on electro-porahon, namely vesicle electrofusion, is introduced whereby the use of GUVs as microreactors suitable for the synthesis of nanoparhcles is demonstrated. 

As demonstrated above, the edge tension is a sensitive parameter, which effectively characterizes the stability of pores in membranes. Compiling a database for the effect of various types of membrane inclusions will be useful for understanding the lifetime of pores in membranes with more complex compositions, which is important for achieving control over medical applications for drug and gene delivery in cells. 

Here Tframe is the stress or frame tension, Ap is the projected area in the plane of applied stress, and we have omitted the membrane edge term. Let us cmisider a membrane with fixed total area A. In Monge representation, one has... 

Various tests may be used to determine the survivability of unexposed polymeric GMs. Puncture tests are frequently used to estimate the survivability of FMLs in the held. During a puncture test, a 5/16 steel rod with rounded edges is pushed down through the membrane. A very hexible membrane that has a high strain capacity under biaxial tension may allow that rod to penetrate almost to... 

Below 45 MPa, the high dispersive precipitated silica sample with or without membrane collapses without mercury intrusion. The buckling mechanism of pores edges can be assumed as in the case of low density xerogels. Consequently, equation (2) can be used to interpret the mercury porosimetry curve in this low pressure domain. The constant A, to be used in equation (2) can be calculated from the P, value using equation (4). With a mercury surface tension 0.485 N/m, a contact angle 0= 130° and P, = 45 MPa, one obtains K = 86.3 nm MPa" . 

To employ this approach in the considered example, the membrane was described in a continuum limit through a surface, h(y,z), identified as the position of the bilayer midplane. The results of such an analysis for the cases of a tensionless and a 10% stretched membrane are shown in the main panel of Fig. 11 with red and black solid symbols, respectively. The solid lines are fits of the power spectrum It2 with (21). It can be seen that, indeed, Aa = 0.066/f2 g) (predicted by the free edge simulations) corresponds to the membrane tensionless state. The bending rigidity of the bilayer is 4.5kBT and seems to decrease with tension, presumably due to membrane thinning. 

Remove all the remaining thick albumen from the vitelline membrane surrounding or covering the embryo. To do this, fold a piece of soft tissue, lower it onto the albumen at the edge of the embryo, and gently pull away from it (Fig. IB). Repeat this process until no albumen is left. This is an important step, since albumen prevents the vitelline membrane from attaching to the filter paper. Without sufficient contact, the vitelline membrane loses its tension, and it is difficult to recover the embryo intact. 

Fig. 4.2. A schematic diagram of a film with a free edge bonded to a substrate is shown in the upper portion. The lower portion depicts the same system but with the film and substrate separated to reveal the shear traction distribution q x) through which they interact across their interface and the internal membrane tension t x) in the film.

The restriction that the overall deformation should be elastic can be examined by considering the state of stress at the edge a = a of the buckled zone. The membrane force resultant has the value ta < 0 throughout the zone —a < x < a. On the other hand, the bending moment mx x) varies throughout the zone, but it is readily confirmed that it does so between the limits of —ma and ma. The tensile stress (Txx that is largest in absolute value for this state of combined tension and bending is... 

---