Characterization - Lipid Nanoparticles: Production, Characterization and Stability - page 43

Chapter 4
Characterization

Abstract Lipid nanoparticles are known to present three features—a solid nature,
lipid matrix and colloidal (or smaller) particle size. These features are theorized
to impart controlled drug release, biocompatibility and improved drug dissolution
to the colloidal carriers. Appropriate characterization of lipid nanoparticle formu-
lations is required to allow for the development of dispersions with the desired
properties for the intended application. The structural complexity and the colloi-
dal size of the lipid nanoparticle dispersions make characterization a difficult task.
The colloidal size of the particles alters physical features (e.g., increasing solu-
bility and the tendency to form supercooled melts). The properties of bulk mate-
rials such as polymorphism and crystallinity may drastically change when these
materials are dispersed into nanoparticles. Further complicating characterization is
the potential co-existence of other colloidal structures such as micelles, vesicles
and emulsions in the dispersions. A detailed characterization scheme is required
to investigate the structure and behavior of these complex colloidal carriers. This
chapter introduces a number of methods commonly applied for characterization
of lipid nanoparticle dispersions. The main focus of the chapter is lipid nanoparti-
cles, however the methods are often generic and occasional mention of their use in
other colloidal structures is made.

Keywords Particle characterization · Photon correlation spectroscopy · Laser
diffraction · Surface charge · Electron microscopy · Differential scanning
microscopy · X-ray diffraction · Nuclear magnetic resonance · Electron spin
resonance

4.1 Particle Size

Colloidal particles are defined on the basis of the size of their structure and are
defined as having any dimension smaller than 1 µm. Often, colloidal particles are
spherical, or at least regular in shape, and particle size measurements can confirm
their colloidal size range.