nanoparticles. The zeta potential can also provide information concerning the nature
of material encapsulated within the nanocapsule or coated onto the surface [65]. In
colloids, equilibrium instead of permanent aggregation can be recognized by means
of steric (physical barrier) and/or electrostatic stabilization (surface charge) on the
surface of the nanoparticles. Ionic or non-ionic surfactants and polymers have been
commonly used to provide a barrier against the aggregation of nanoparticles [66,
67]. Steric stabilization can be attained by covering the particles with polymers,
which prevent the access of particles to the range of attractive forces by forming a
physical barrier. Furthermore, a non-ionic amphiphilic polymer or surfactant with a
hydrophobic chain around the hydrophobic drug surface allows the hydrophilic part
to project into the water and, thus, increase its hydrophilicity. Steric interactions are
more sensitive to temperature fluctuations than electrostatic repulsions [68]. In
contrast, ionic stabilizers are very sensitive to changes in pH and ionic strength,
and are also incapable of stabilizing nanoparticles in the dry state [69]. Nevertheless,
storing of nanoparticles in suspensions for a long period of time leads to many
disadvantages. The risk of microbiological adulteration, degradation of premature
polymer by hydrolysis, physicochemical instability due to particle aggregation,
sedimentation and chemical instability of the drug are a few examples. To avoid
such complications, dry formulations are generally favoured over suspensions. To
overcome this major drawback, the use of various drying methods have been
practiced and the alteration of a liquid samples into a dry product can be accomplished by means of sensitive methods such as freeze-drying or spray-drying
processes. Lyophilization (freeze-drying) is considered to be an extremely useful
process that is generally functional in augmenting the physicochemical stability of
the nanoparticles in order to obtain a pharmaceutically satisfactory product. This is
especially useful for cases in which the storage circumstances are unfavourable.
6 Applications of Micro- and Nanoparticles Based
on Biopolymers
Drug loading in micro- and nanoparticulate systems is generally carried out by one of
two methods, i.e. during the preparation of particles (incorporation) or after their
formation (incubation). The drug delivery properties are also essentially dependent on
the chemical and textural properties of the matrices, the porosity, wettability, erosion
and the surface area. The matrix equally has an impact on the discharge profile for the
bioavailability of the entrapped drug. Nanoparticle-based delivery systems have the
potential power to improve drug stability, increase the duration of the therapeutic
effect and permit enteral or parenteral administration, which may prevent or minimize
drug degradation and metabolism as well as cellular efflux [70, 71]. Protein
nanoparticles can conveyance medications transversely across the blood–brain barrier
that are not usually passed across after injection. A number of authors have
demonstrated a considerable tendency for an accumulation of protein nanoparticles
in certain tumours. The binding of a variety of cytotoxic drugs, such as 5-fluorouracil,
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
285
of material encapsulated within the nanocapsule or coated onto the surface [65]. In
colloids, equilibrium instead of permanent aggregation can be recognized by means
of steric (physical barrier) and/or electrostatic stabilization (surface charge) on the
surface of the nanoparticles. Ionic or non-ionic surfactants and polymers have been
commonly used to provide a barrier against the aggregation of nanoparticles [66,
67]. Steric stabilization can be attained by covering the particles with polymers,
which prevent the access of particles to the range of attractive forces by forming a
physical barrier. Furthermore, a non-ionic amphiphilic polymer or surfactant with a
hydrophobic chain around the hydrophobic drug surface allows the hydrophilic part
to project into the water and, thus, increase its hydrophilicity. Steric interactions are
more sensitive to temperature fluctuations than electrostatic repulsions [68]. In
contrast, ionic stabilizers are very sensitive to changes in pH and ionic strength,
and are also incapable of stabilizing nanoparticles in the dry state [69]. Nevertheless,
storing of nanoparticles in suspensions for a long period of time leads to many
disadvantages. The risk of microbiological adulteration, degradation of premature
polymer by hydrolysis, physicochemical instability due to particle aggregation,
sedimentation and chemical instability of the drug are a few examples. To avoid
such complications, dry formulations are generally favoured over suspensions. To
overcome this major drawback, the use of various drying methods have been
practiced and the alteration of a liquid samples into a dry product can be accomplished by means of sensitive methods such as freeze-drying or spray-drying
processes. Lyophilization (freeze-drying) is considered to be an extremely useful
process that is generally functional in augmenting the physicochemical stability of
the nanoparticles in order to obtain a pharmaceutically satisfactory product. This is
especially useful for cases in which the storage circumstances are unfavourable.
6 Applications of Micro- and Nanoparticles Based
on Biopolymers
Drug loading in micro- and nanoparticulate systems is generally carried out by one of
two methods, i.e. during the preparation of particles (incorporation) or after their
formation (incubation). The drug delivery properties are also essentially dependent on
the chemical and textural properties of the matrices, the porosity, wettability, erosion
and the surface area. The matrix equally has an impact on the discharge profile for the
bioavailability of the entrapped drug. Nanoparticle-based delivery systems have the
potential power to improve drug stability, increase the duration of the therapeutic
effect and permit enteral or parenteral administration, which may prevent or minimize
drug degradation and metabolism as well as cellular efflux [70, 71]. Protein
nanoparticles can conveyance medications transversely across the blood–brain barrier
that are not usually passed across after injection. A number of authors have
demonstrated a considerable tendency for an accumulation of protein nanoparticles
in certain tumours. The binding of a variety of cytotoxic drugs, such as 5-fluorouracil,
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
285