Cell Wall Polysaccharides of Marine Algae 22.5 Biological Activities and Medicinal Applications 569
Part D | 22.5
their nontoxicity. Among these polysaccharides, commercially available, low-cost alginates are known to
be the most suitable for the preparation of biomedical materials based on pure and composite films,
gels, and fibers [22.428, 429]. Due to the high water content, porosity, elasticity, permeability, and the
ability to create a moist environment, alginate gels
are effective in wound healing, drug delivery, and tissue engineering. Partially, calcium alginate hydrogels
demonstrate both haemostatic activity due to Ca
2C
and promotion of the aggregation of platelets and
erythrocytes. The hydration, swelling, and erosion behavior of alginate matrices depend on pH, which is
also true for drug release mechanisms [22.430]. As
was mentioned above, alginic acid/alginate is able
to form two types of gel at acidic and neutral conditions, which is a good prerequisite for the construction of controlled-release systems [22.431, 432].
Two types of diffusion systems have been prepared
based on alginates [22.431]: (i) the polymer membrane system, in which the drug formulation (solid,
suspension, or solution) is inside semipermeable gellike polymeric capsules, and (ii) the polymer matrix
system, in which the drug is homogeneously dispersed
in a rate-controlling polymeric matrix of swelling microspheres or conventional tablets. Sodium alginate
matrices can effectively sustain drug release even for
highly water-soluble drugs [22.433, 434]. Alginatebased dressings are widely used to treat various surgery
wounds [22.435–437]. The medicinal effect of calcium alginate as a wound dressing is based on its
cation exchange properties [22.435]. After application,
Ca
2C of the film/fibre surface is partially replaced by
Na
C from blood serum, which leads to swelling, partial dissolution of the polysaccharide, and gelation.
The effectiveness of this process depends on the structure and source of the alginate. Some properties of
alginate films like transparency, thermal stability, water absorption, and swelling behavior improve with
the presence of various additives, for example Aloe
vera [22.438]. Composite materials consisting of alginate and other natural or modified polysaccharides have
been shown to be potentially useful in drug delivery
systems and other medicinal applications [22.131, 439].
Much fewer references in the literature are devoted
to using fucoidan for wound healing. Because it has
various biological activities, this polysaccharide is interesting as a component of wound dressing materials.
Fucoidan-chitosan films might be a potential treatment
system for dermal burns [22.298]. Local administration
of fucoidan films safely reduced post-surgical adhesion in model animals [22.440]. Fucoidan improves the
physical/chemical properties (roughness, hydrophilicity and surface sulfate content) of silk fibroin films,
and brings about anticoagulant activity and enhanced
endothelial cell affinity to silk fibroin [22.441]. Thus,
fucoidan/silk fibroin films can be applied as bloodcontacting biomaterials.
22.5.8 How to Improve Algal
Polysaccharides
There are many ways to improve initially inactive
or weakly active natural algal polysaccharides to fit
various medicinal applications. First of all, partial
degradation of algal polysaccharides leads to obtaining polymeric molecules of lower molecular mass,
smaller oligomeric molecules (oligosaccharides), and
small molecules (monosaccharides or their fragments).
Smaller fragments of algal polysaccharides are more
soluble in water, less viscous, and may interact with
various biological targets like cell receptors or viral particles. Marine algal polysaccharides or derived
oligosaccharides can be also chemically modified by
the addition of polar or nonpolar groups. Partially,
sulfation of nonsulfated polysaccharides (alginate) or
oversulfation of sulfated algal polysaccharides (galactans, fucoidans) is the way to increase the negative
charge density of the macromolecules, which may have
a beneficial effect on their immunomodulation, anticoagulant, and other properties.
22.5.9 Partial Degradation
Marine algal polysaccharides can be degraded by
the use of chemical or enzymatic treatment. Examples of microbial enzymes and microorganisms that
are able to cleavage algal polysaccharides are shown
in Table 22.13. Biological functions of oligosaccharides originating from marine algae were reviewed
by [22.454]; some of these activities are similar
to the corresponding activities of native polysaccharides. For example, both native algal polysaccharides
and their oligomeric fragments may stimulate defence responses and protect plants against various
pathogens [22.455]. However, in other cases, algal
oligosaccharides exhibit novel activities that are nontypical for the initial polysaccharides, even the way
of cleavage could be important. Partially, alginate
oligosaccharides obtained by enzymatic degradation
promote growth and influence the fatty acid composition of the biohydrogen producer of the green algae
Part D | 22.5
their nontoxicity. Among these polysaccharides, commercially available, low-cost alginates are known to
be the most suitable for the preparation of biomedical materials based on pure and composite films,
gels, and fibers [22.428, 429]. Due to the high water content, porosity, elasticity, permeability, and the
ability to create a moist environment, alginate gels
are effective in wound healing, drug delivery, and tissue engineering. Partially, calcium alginate hydrogels
demonstrate both haemostatic activity due to Ca
2C
and promotion of the aggregation of platelets and
erythrocytes. The hydration, swelling, and erosion behavior of alginate matrices depend on pH, which is
also true for drug release mechanisms [22.430]. As
was mentioned above, alginic acid/alginate is able
to form two types of gel at acidic and neutral conditions, which is a good prerequisite for the construction of controlled-release systems [22.431, 432].
Two types of diffusion systems have been prepared
based on alginates [22.431]: (i) the polymer membrane system, in which the drug formulation (solid,
suspension, or solution) is inside semipermeable gellike polymeric capsules, and (ii) the polymer matrix
system, in which the drug is homogeneously dispersed
in a rate-controlling polymeric matrix of swelling microspheres or conventional tablets. Sodium alginate
matrices can effectively sustain drug release even for
highly water-soluble drugs [22.433, 434]. Alginatebased dressings are widely used to treat various surgery
wounds [22.435–437]. The medicinal effect of calcium alginate as a wound dressing is based on its
cation exchange properties [22.435]. After application,
Ca
2C of the film/fibre surface is partially replaced by
Na
C from blood serum, which leads to swelling, partial dissolution of the polysaccharide, and gelation.
The effectiveness of this process depends on the structure and source of the alginate. Some properties of
alginate films like transparency, thermal stability, water absorption, and swelling behavior improve with
the presence of various additives, for example Aloe
vera [22.438]. Composite materials consisting of alginate and other natural or modified polysaccharides have
been shown to be potentially useful in drug delivery
systems and other medicinal applications [22.131, 439].
Much fewer references in the literature are devoted
to using fucoidan for wound healing. Because it has
various biological activities, this polysaccharide is interesting as a component of wound dressing materials.
Fucoidan-chitosan films might be a potential treatment
system for dermal burns [22.298]. Local administration
of fucoidan films safely reduced post-surgical adhesion in model animals [22.440]. Fucoidan improves the
physical/chemical properties (roughness, hydrophilicity and surface sulfate content) of silk fibroin films,
and brings about anticoagulant activity and enhanced
endothelial cell affinity to silk fibroin [22.441]. Thus,
fucoidan/silk fibroin films can be applied as bloodcontacting biomaterials.
22.5.8 How to Improve Algal
Polysaccharides
There are many ways to improve initially inactive
or weakly active natural algal polysaccharides to fit
various medicinal applications. First of all, partial
degradation of algal polysaccharides leads to obtaining polymeric molecules of lower molecular mass,
smaller oligomeric molecules (oligosaccharides), and
small molecules (monosaccharides or their fragments).
Smaller fragments of algal polysaccharides are more
soluble in water, less viscous, and may interact with
various biological targets like cell receptors or viral particles. Marine algal polysaccharides or derived
oligosaccharides can be also chemically modified by
the addition of polar or nonpolar groups. Partially,
sulfation of nonsulfated polysaccharides (alginate) or
oversulfation of sulfated algal polysaccharides (galactans, fucoidans) is the way to increase the negative
charge density of the macromolecules, which may have
a beneficial effect on their immunomodulation, anticoagulant, and other properties.
22.5.9 Partial Degradation
Marine algal polysaccharides can be degraded by
the use of chemical or enzymatic treatment. Examples of microbial enzymes and microorganisms that
are able to cleavage algal polysaccharides are shown
in Table 22.13. Biological functions of oligosaccharides originating from marine algae were reviewed
by [22.454]; some of these activities are similar
to the corresponding activities of native polysaccharides. For example, both native algal polysaccharides
and their oligomeric fragments may stimulate defence responses and protect plants against various
pathogens [22.455]. However, in other cases, algal
oligosaccharides exhibit novel activities that are nontypical for the initial polysaccharides, even the way
of cleavage could be important. Partially, alginate
oligosaccharides obtained by enzymatic degradation
promote growth and influence the fatty acid composition of the biohydrogen producer of the green algae