Membrane-Based Nanotechnology and Drug Delivery - Membrane Biophysics, Biological and Medical Physics, Biomedical Engineering - page 134

vature) as well as electrostatic (screened Coulomb and van der Waal's interactions)
between lipid-lipid and lipid-membrane agents (e.g. dendrimer, as is the case in
Fig. 6.4 ), the value of

γ needs to be reassessed. The interested reader is encour-
aged to solve this rather simple problem as an advanced-level exercise, following the
theoretical and computational protocols explained in Chap. 5 in the case of the lipid
bilayer-ion channel interactions using screened Coulomb interactions.

Membrane Disruption Depends on Lipid Phase Properties

Chapter 3 has provided details regarding various lipid phases. These lipid phases, cor-
responding to various lipid organizations, vary greatly between inter- and intrastates
in both the bilayer and nonbilayer lipid phases. Nanoparticles' membrane disruption
mechanisms have been found not only to depend on nanoparticle properties such as
size, charge, etc., but also on the lipid phase properties. In Fig. 6.5 it is shown that
the liquid-crystalline phase of the bilayer favors nanoparticles to induce holes into
the bilayer. The L - β phase appeared not be a favorable condition for the nanoparti-
cles' membrane effects. This rather important result should be considered seriously
in developing new nanotechnology where the membrane's physical properties need
to be considered.

6.3.3 Certain Nanoparticles Avoid Membrane Interactions

The previous section (Sect. 6.3.2 ) introduced the phenomena of nanoparticle inter-
actions with lipid bilayers. There we have found that certain nanoparticles integrate
themselves with lipids under special conditions and, as a result, holes or pores are
created in themembrane. In this section, we investigate a different type of interactions
of a certain class of nanoparticles, which are silica nanoparticles ranging from 1 to
200 nm in diameter with supported lipid bilayer membranes prepared from DMPC.
These nanoparticles, in fact, exhibit a general lack of interactions with membranes,
but their specific properties strongly depend on the rank of the geometric mismatch
between bilayer thickness and nanoparticle dimensions.
The model diagrams presented in Fig. 6.6 describe various possible effects of
nanoparticles on the membrane integrity, depending on the size of the nanoparticles.
In all cases, nanoparticles are assumed to avoid interactions with lipids but, as the
nanoparticle dimension increases from very small to much larger than the bilayer
thickness, both bilayer deformation and pore formation are found to occur. The non-
spherical nature of nanoparticle dimensions can also induce pore formation. All these
schematic diagrams are drawn based on specific experimental observations.
Figures 6.7 , 6.8 , and 6.9 provide AFM data which suggest that the model pre-
sented here in Fig. 6.6 showing membrane effects exerted by the nanoparticles with
variedmismatch between the nanoparticle diameter andmembrane thickness is valid.
These results clearly indicate that the nanoparticles avoid binding with lipids and try