Sodium alginate is a sodium salt of alginic acid, a naturally occurring polysaccharide acquired from marine brown algae. Alginate contains two uronic acids,
α-L-guluronic acid and β-D-mannuronic acid, and is composed of homopolymeric
blocks and blocks with an alternating sequence. Made from a chelated structure
with metal ions, the polyguluronate units in the alginate molecules (known as an
“egg-box” junction) have apertures that allow the cations to become packed or
coordinated [11]. The intersection flanked by the polyguluronate shackles is kinetically stable in the direction of dissociation, whereas the polymannuronate
components demonstrate the usual polyelectrolyte characteristics of cation binding
[12]. Thus, the two types of connections result in establishment of spherical beads.
The composition of alginate is an important parameter for the formation of
alginate particles. The variation in monomer content and viscosity of alginates in
brown seaweed with season generally increases from the lowest at the youngest
stage of the plant to the maximum at a mature stage. Because sodium and calcium
proportions strongly determine the swelling and healing properties of the alginate,
this proves to be a significant property [13]. Viscosity classically fluctuates with the
percentage of the guluronic content. During alginate gelling, divalent cations bind
preferentially to guluronic acid blocks in a highly cooperative manner; the size of
the cooperative unit is reported to be more than 20 monomers [14]. A high content
of guluronic acid and homopolymer blocks leads to higher interaction between
alginate and calcium, which results in a stronger and more stable gel. However, in
the emulsification step high guluronic content gives premature gelation, resulting in
larger beads with larger dispersions [15] and more porous gels. On the other hand,
high mannuronic acid content produces more elastic and weaker gels with good
freeze–thaw behaviour. However, at low or very high Ca
2+ concentrations, high
mannuronic alginates produce weaker gels.
3 Proteins Used in Preparation of Micro- and Nanoparticles
3.1 Albumin
Albumin is a protein present in blood plasma and is an attractive macromolecular
carrier, widely used to prepare nanospheres and nanocapsules due to its availability in
pure form and its biodegradability, non-toxicity and non-immmunogenicity. It also
acts as an significant extracellular antioxidant [16] and defence mechanism against
free radicals and extra-destructive chemical agents [17]. Albumin is easy to formulate
in defined sizes, and reactive groups (thiol, amino and carboxylic groups) can be
attached to the surface for ligand binding and other surface modifications. Also,
albumin nanoparticles have the advantage that ligands can be easily attached by
covalent linkage. Drugs captured within albumin nanoparticles can be digested by
proteases, and drug loading can be quantified. A number of studies have revealed
that albumin gathers in compacted tumours, which makes it a prospective macromolecular transporter for the site‐directed delivery of anti-tumour drugs [18]. From the
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
277
α-L-guluronic acid and β-D-mannuronic acid, and is composed of homopolymeric
blocks and blocks with an alternating sequence. Made from a chelated structure
with metal ions, the polyguluronate units in the alginate molecules (known as an
“egg-box” junction) have apertures that allow the cations to become packed or
coordinated [11]. The intersection flanked by the polyguluronate shackles is kinetically stable in the direction of dissociation, whereas the polymannuronate
components demonstrate the usual polyelectrolyte characteristics of cation binding
[12]. Thus, the two types of connections result in establishment of spherical beads.
The composition of alginate is an important parameter for the formation of
alginate particles. The variation in monomer content and viscosity of alginates in
brown seaweed with season generally increases from the lowest at the youngest
stage of the plant to the maximum at a mature stage. Because sodium and calcium
proportions strongly determine the swelling and healing properties of the alginate,
this proves to be a significant property [13]. Viscosity classically fluctuates with the
percentage of the guluronic content. During alginate gelling, divalent cations bind
preferentially to guluronic acid blocks in a highly cooperative manner; the size of
the cooperative unit is reported to be more than 20 monomers [14]. A high content
of guluronic acid and homopolymer blocks leads to higher interaction between
alginate and calcium, which results in a stronger and more stable gel. However, in
the emulsification step high guluronic content gives premature gelation, resulting in
larger beads with larger dispersions [15] and more porous gels. On the other hand,
high mannuronic acid content produces more elastic and weaker gels with good
freeze–thaw behaviour. However, at low or very high Ca
2+ concentrations, high
mannuronic alginates produce weaker gels.
3 Proteins Used in Preparation of Micro- and Nanoparticles
3.1 Albumin
Albumin is a protein present in blood plasma and is an attractive macromolecular
carrier, widely used to prepare nanospheres and nanocapsules due to its availability in
pure form and its biodegradability, non-toxicity and non-immmunogenicity. It also
acts as an significant extracellular antioxidant [16] and defence mechanism against
free radicals and extra-destructive chemical agents [17]. Albumin is easy to formulate
in defined sizes, and reactive groups (thiol, amino and carboxylic groups) can be
attached to the surface for ligand binding and other surface modifications. Also,
albumin nanoparticles have the advantage that ligands can be easily attached by
covalent linkage. Drugs captured within albumin nanoparticles can be digested by
proteases, and drug loading can be quantified. A number of studies have revealed
that albumin gathers in compacted tumours, which makes it a prospective macromolecular transporter for the site‐directed delivery of anti-tumour drugs [18]. From the
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
277