An electric field is used to create acceptable droplets of charged liquid coming out
from a thin capillary nozzle. The accumulation of charge on the surface of the liquid
is instigated by the electric field between the liquid and counter-electrode. Solvent
evaporation leaves a dry residue, which is followed by dispersal of the solution
collected on suitable removal substrates. Insulin nanoparticles of size between 88
and 110 nm were prepared in this manner [56]. However, the biological activity of
the electrosprayed protein-based nanoparticles is not affected by the process
conditions [56]. When the potential difference is sufficient, the electrostatic forces
overcome the surface tension, the surface becomes unstable and the meniscus
develops a conical shape [57]. If the cone is then disturbed by a further charge, it
will break into small charged droplets that will detach from the liquid cone and fly
towards a counter-electrode. Several different spraying modes exist [58, 59], but for
the production of monodisperse nanosized droplets the cone-jet mode (known as a
Taylor cone) is the most desired. Abundant studies have shown that electrospray
generated by electrostatic atomization remains functional [60, 61], including an
amalgamation of polymeric drug micro- and nanoparticles [62].
5 Characterization of Biopolymeric Micro- and Nanoparticles
5.1 Particle Size
The foremost use of micro- and nanoparticles is their discharge and targeting to the
destined site. Particle size plays an important role that adversely affects the targeted
delivery of the drug. Smaller particles have a larger surface area, due to which a
maximum of the loaded drug will be at the particle surface for quick release. An
enlarged surface area of the system indicates augmented surface interactions with
the particle environment, which refines, e.g., dissolution to gastrointestinal fluids.
Consequently, by decreasing the particle size the dissolution rate can be increased,
hence increasing the effectiveness and limiting resistance to the diffusion of
substrates. Polymer degradation can also be affected by the particle size. For
example, the degradation rate of poly(lactic-co-glycolic acid) was found to proliferate with increasing particle size in vitro [63]. Hence, therapeutic nanocarriers or
other micro- and nanostructured materials can be potentially beneficial for the
engineering of composite drug delivery applications. A major disadvantage is that
the smaller particles tend to aggregate during storage and transportation of the
nanoparticle dispersion. Hence, there needs to be a balance between minimum size
and maximum stability of the nanoparticles.
However, the use of new technologies for determining particle size is in current
operation. Techniques such as photon-correlation spectroscopy (PCS) or dynamic
light scattering (DLS) are widely used to determine the size of Brownian
nanoparticles in colloidal suspensions in the nano- and submicron ranges [64].
With insignificant alteration to PCS, nanoparticle tracking analysis (NTA) is a
method industrialized by NanoSight Ltd. to decide the size distribution profile of
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
283
from a thin capillary nozzle. The accumulation of charge on the surface of the liquid
is instigated by the electric field between the liquid and counter-electrode. Solvent
evaporation leaves a dry residue, which is followed by dispersal of the solution
collected on suitable removal substrates. Insulin nanoparticles of size between 88
and 110 nm were prepared in this manner [56]. However, the biological activity of
the electrosprayed protein-based nanoparticles is not affected by the process
conditions [56]. When the potential difference is sufficient, the electrostatic forces
overcome the surface tension, the surface becomes unstable and the meniscus
develops a conical shape [57]. If the cone is then disturbed by a further charge, it
will break into small charged droplets that will detach from the liquid cone and fly
towards a counter-electrode. Several different spraying modes exist [58, 59], but for
the production of monodisperse nanosized droplets the cone-jet mode (known as a
Taylor cone) is the most desired. Abundant studies have shown that electrospray
generated by electrostatic atomization remains functional [60, 61], including an
amalgamation of polymeric drug micro- and nanoparticles [62].
5 Characterization of Biopolymeric Micro- and Nanoparticles
5.1 Particle Size
The foremost use of micro- and nanoparticles is their discharge and targeting to the
destined site. Particle size plays an important role that adversely affects the targeted
delivery of the drug. Smaller particles have a larger surface area, due to which a
maximum of the loaded drug will be at the particle surface for quick release. An
enlarged surface area of the system indicates augmented surface interactions with
the particle environment, which refines, e.g., dissolution to gastrointestinal fluids.
Consequently, by decreasing the particle size the dissolution rate can be increased,
hence increasing the effectiveness and limiting resistance to the diffusion of
substrates. Polymer degradation can also be affected by the particle size. For
example, the degradation rate of poly(lactic-co-glycolic acid) was found to proliferate with increasing particle size in vitro [63]. Hence, therapeutic nanocarriers or
other micro- and nanostructured materials can be potentially beneficial for the
engineering of composite drug delivery applications. A major disadvantage is that
the smaller particles tend to aggregate during storage and transportation of the
nanoparticle dispersion. Hence, there needs to be a balance between minimum size
and maximum stability of the nanoparticles.
However, the use of new technologies for determining particle size is in current
operation. Techniques such as photon-correlation spectroscopy (PCS) or dynamic
light scattering (DLS) are widely used to determine the size of Brownian
nanoparticles in colloidal suspensions in the nano- and submicron ranges [64].
With insignificant alteration to PCS, nanoparticle tracking analysis (NTA) is a
method industrialized by NanoSight Ltd. to decide the size distribution profile of
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
283