9.3 Chemistry of Laminarin
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9.3.3 Solubility Branching
The degree of branching varies in different species; for instance, laminarin extracted
from the L. digitata brown algae has a degree of branching of about 12.5% while that
of E. bicyclis has a much higher degree of branching (Ojima et al. 2018). Laminarin
is generally referred to as a soluble sulphated polysaccharide. However, the solubility
of laminarin varies with structure and medium. Highly branched laminarin is more
readily soluble in cold or hot water while less branched laminarin will only dissolve
in hot water (Misurcova et al. 2012). This solubility variation also serves as a basis
for the extraction of laminarin where the degree of branching of isolated fraction can
be controlled by the temperature. The more branched can first be isolated at lower
temperature, and the more linear laminarin can be isolated at elevated temperature.
When dissolved in the aqueous solvent, laminarin, like other polymers, will result
in an increase in the viscosity of the solution. This increase in viscosity is related to
the molecular weight. As a low molecular weight polymer laminarin solutions will
not have the thickening effect of other higher molecular weight polysaccharides such
as carrageenan. However, the lower viscosity at higher solution concentration will
give less flow limitations during extraction and processing of liquid phases.
9.3.4 Methacrylated Laminarin
Modification of laminarin can be achieved by replacing some of the –OH groups
with methyl groups. These methacrylated laminarins are applied in tissue engineering for enhancing cell adhesion, for example (Martins et al. 2018; Wang et al. 2018).
Polysaccharides form hydrogels; however, they are limited in terms of maintaining
their mechanical properties when exposed to the physiological conditions in the body.
Although other materials exist for producing hydrogen with desirable mechanical
properties at physiological condition, biocompatibility and biodegradability limit the
application of such hydrogel-forming materials for biomedical applications. Modifying laminarin with glycidyl methacrylate prior to cross-linking results in a hydrogel
with improved mechanical properties compared to unmodified laminarin hydrogels.
An example process for the production of methacrylated laminarin is as follows
(Wang et al. 2018): laminarin is dissolved in dimethyl sulfoxide (DMSO) in a mass (g)
of laminarin to volume (mL) of DMSO ratio of 1:10. This is carried out under nitrogen
atmosphere to prevent reaction with atmospheric air. This takes 1 h to dissolve and
is followed by the addition of 167 mg of 4-(N,N Dimethylamino) pyridine and then
dropwise addition of glycidyl methacrylate. The amount of glycidyl methacrylate
added determines the level of methacrylation. The methacrylation process takes 48 h
under room temperature. The reaction is terminated by bringing the pH to neutral
by adding hydrochloric acid. On completion, the methacrylated laminarin is then
separated from the reaction components to obtain purified methacrylated laminarin.
This purification can be achieved using dialysis for a period of 7 days. An example
193
9.3.3 Solubility Branching
The degree of branching varies in different species; for instance, laminarin extracted
from the L. digitata brown algae has a degree of branching of about 12.5% while that
of E. bicyclis has a much higher degree of branching (Ojima et al. 2018). Laminarin
is generally referred to as a soluble sulphated polysaccharide. However, the solubility
of laminarin varies with structure and medium. Highly branched laminarin is more
readily soluble in cold or hot water while less branched laminarin will only dissolve
in hot water (Misurcova et al. 2012). This solubility variation also serves as a basis
for the extraction of laminarin where the degree of branching of isolated fraction can
be controlled by the temperature. The more branched can first be isolated at lower
temperature, and the more linear laminarin can be isolated at elevated temperature.
When dissolved in the aqueous solvent, laminarin, like other polymers, will result
in an increase in the viscosity of the solution. This increase in viscosity is related to
the molecular weight. As a low molecular weight polymer laminarin solutions will
not have the thickening effect of other higher molecular weight polysaccharides such
as carrageenan. However, the lower viscosity at higher solution concentration will
give less flow limitations during extraction and processing of liquid phases.
9.3.4 Methacrylated Laminarin
Modification of laminarin can be achieved by replacing some of the –OH groups
with methyl groups. These methacrylated laminarins are applied in tissue engineering for enhancing cell adhesion, for example (Martins et al. 2018; Wang et al. 2018).
Polysaccharides form hydrogels; however, they are limited in terms of maintaining
their mechanical properties when exposed to the physiological conditions in the body.
Although other materials exist for producing hydrogen with desirable mechanical
properties at physiological condition, biocompatibility and biodegradability limit the
application of such hydrogel-forming materials for biomedical applications. Modifying laminarin with glycidyl methacrylate prior to cross-linking results in a hydrogel
with improved mechanical properties compared to unmodified laminarin hydrogels.
An example process for the production of methacrylated laminarin is as follows
(Wang et al. 2018): laminarin is dissolved in dimethyl sulfoxide (DMSO) in a mass (g)
of laminarin to volume (mL) of DMSO ratio of 1:10. This is carried out under nitrogen
atmosphere to prevent reaction with atmospheric air. This takes 1 h to dissolve and
is followed by the addition of 167 mg of 4-(N,N Dimethylamino) pyridine and then
dropwise addition of glycidyl methacrylate. The amount of glycidyl methacrylate
added determines the level of methacrylation. The methacrylation process takes 48 h
under room temperature. The reaction is terminated by bringing the pH to neutral
by adding hydrochloric acid. On completion, the methacrylated laminarin is then
separated from the reaction components to obtain purified methacrylated laminarin.
This purification can be achieved using dialysis for a period of 7 days. An example