application in the delivery of bioactive bilberry anthocyanins by protein gels
[78–80]. Kulozik et al. in 2012 reported the development of a novel whey
protein-based aerogel for the delivery of various active ingredients [81].
2.2 Drug Release Properties
The major factors affecting the release of a payload from a polymeric nanocarrier
are: (1) degradation rate of the polymer, (2) diffusion of the drug from the matrix,
and (3) surface modification of the drug carrier. When nanoparticles come in
contact with the dissolution medium, weakly bound molecules on the surface of
the matrix desorb into the medium resulting in burst release. Subsequently, carbohydrate nanocarriers become hydrated and swell, forming a gel diffusion layer that
hampers the outward transport of the drug within the matrix thereby providing a
controlled release effect [17]. Proteins on the other hand, are easily digested by
endogenous proteolytic enzymes of the host thereby may result in a faster release.
The release kinetics can be altered by the degree of crosslinking, adequate surface
modification, and the choice of the matrix. Figure 1 illustrates the different
parameters that regulate the burst release or slow and sustained release of drugs
from within carbohydrates and polymers.
2.2.1 Drug Release from Carbohydrates
For carbohydrates, the swelling mechanism (i.e., the wetting), which results in loss
of integrity of the matrix (mainly for hydrophilic polymers), can be reinforced by
aiding proper crosslinking. Since release is carried out in the aqueous media, the
hydrophilic drug moieties show a faster release from the matrix than hydrophobic
drugs. This is illustrated through the drug release experiment carried out using
propyl starch and three model drugs, i.e., flufenamic acid, testosterone, and caffeine
(Fig. 2). The hydrophobic drugs flufenamic acid and testosterone showed a
sustained release with nearly null burst effect, whereas the hydrophilic drug caffeine showed a much faster, yet linear release within the first 10 h before it reached
a plateau phase [35].
The release rate is also observed to be inversely proportional to the molecular
weight of the encapsulated drug molecule [82]. The rate of drug release can also be
varied by altering the drug–polymer interaction as well as by chemically
immobilizing the drug to the polymer backbone using the reactive functional
groups, for example, the carboxylate groups in alginate [83, 84]. Other than
swelling, degradation can also occur due to the natural enzymatic splitting of
polysaccharide bonds. Drug release occurring via matrix degradation can be controlled through appropriate modifications of the native molecule [85]. Surface
engineering or modification of nanocarriers with carbohydrates is yet another
alternative for obtaining sustained drug release [86]. For certain carbohydrates
Proteins and Carbohydrates as Polymeric Nanodrug Delivery Systems. . .
249
[78–80]. Kulozik et al. in 2012 reported the development of a novel whey
protein-based aerogel for the delivery of various active ingredients [81].
2.2 Drug Release Properties
The major factors affecting the release of a payload from a polymeric nanocarrier
are: (1) degradation rate of the polymer, (2) diffusion of the drug from the matrix,
and (3) surface modification of the drug carrier. When nanoparticles come in
contact with the dissolution medium, weakly bound molecules on the surface of
the matrix desorb into the medium resulting in burst release. Subsequently, carbohydrate nanocarriers become hydrated and swell, forming a gel diffusion layer that
hampers the outward transport of the drug within the matrix thereby providing a
controlled release effect [17]. Proteins on the other hand, are easily digested by
endogenous proteolytic enzymes of the host thereby may result in a faster release.
The release kinetics can be altered by the degree of crosslinking, adequate surface
modification, and the choice of the matrix. Figure 1 illustrates the different
parameters that regulate the burst release or slow and sustained release of drugs
from within carbohydrates and polymers.
2.2.1 Drug Release from Carbohydrates
For carbohydrates, the swelling mechanism (i.e., the wetting), which results in loss
of integrity of the matrix (mainly for hydrophilic polymers), can be reinforced by
aiding proper crosslinking. Since release is carried out in the aqueous media, the
hydrophilic drug moieties show a faster release from the matrix than hydrophobic
drugs. This is illustrated through the drug release experiment carried out using
propyl starch and three model drugs, i.e., flufenamic acid, testosterone, and caffeine
(Fig. 2). The hydrophobic drugs flufenamic acid and testosterone showed a
sustained release with nearly null burst effect, whereas the hydrophilic drug caffeine showed a much faster, yet linear release within the first 10 h before it reached
a plateau phase [35].
The release rate is also observed to be inversely proportional to the molecular
weight of the encapsulated drug molecule [82]. The rate of drug release can also be
varied by altering the drug–polymer interaction as well as by chemically
immobilizing the drug to the polymer backbone using the reactive functional
groups, for example, the carboxylate groups in alginate [83, 84]. Other than
swelling, degradation can also occur due to the natural enzymatic splitting of
polysaccharide bonds. Drug release occurring via matrix degradation can be controlled through appropriate modifications of the native molecule [85]. Surface
engineering or modification of nanocarriers with carbohydrates is yet another
alternative for obtaining sustained drug release [86]. For certain carbohydrates
Proteins and Carbohydrates as Polymeric Nanodrug Delivery Systems. . .
249