Biomedical Engineering Reference
In-Depth Information
(Matsumoto et al., 2003) that suitably processed through specific fermentation processes
would provide renewable and sustainable biofuel.
Algae represent also an advantageous resource of chemicals and building block materials
that can be tailored through proper biorefinering processes according to the different
envisaged applications. The rising demand for natural instead of synthetic materials
especially in biomedical applications where high biocompatibility and no adverse effects for
the host organism are required (Mano et al., 2007), has led to an outburst of scientific papers
involved in the study of biobased materials. Among these, polysaccharides could represent
the best candidate since abundant, biocompatible and displaying a pronounced chemical
versatility given by the great number of chemical functionalities present in their structures.
The list of known natural carbohydrates is continuously growing, owing to new discoveries
in animal and plant material (Tsai, 2007). They can be used in their native form or after
proper chemical modifications made according to the final applications (d'Ayala et al.,
2008). The use of polysaccharides of animal origin (e.g. heparin and hyaluronic acid) in
biomedical applications is not straightforward since it can raise concerns about
immunogenicity and risk of disease transmission (Stevens, 2008) Indeed these materials
require very accurate purification treatments aimed to free them from biological
contaminants, in contrary to polysaccharides of plant (e.g. cellulose and starch) or algal
origin (e.g. alginate). Polysaccharides of algal origins are gaining particular attention due to
their abundance, renewability (Matsumoto et al., 2003) and to their peculiar chemical
composition not found in any other organisms. Over the last few years medical and
pharmaceutical industries have shown an increasing interest in alginate (d'Ayala et al.,
2008), an anionic polysaccharide widely distributed in the cell walls of brown algae. This
biopolymer has been largely used for its gel forming properties. Due to its non-toxicity,
unique tissue compatibility, and biodegradability, alginate has been studied extensively in
tissue engineering, including the regeneration of skin (Hashimoto et al., 2004), cartilage
(Bouhadir et al., 2001), bone (Alsberg et al., 2001), liver (Chung et al., 2002) and cardiac
tissue (Dar et al., 2002).
A very intriguing feature that distinguishes algal biomass from other resources is that it
contains large amounts of sulphated polysaccharides, whose beneficial biological properties
(Wijesekara et al., 2011) prompt scientists to increase their use in the biomedical fields.
Indeed the presence and the distribution of sulphate groups in these polysaccharides are
reported to play an important role in the antiviral (Damonte et al., 2004), anticoagulant
(Melo et al., 2004), antioxidant (Rocha de Souza et al., 2007) and anticancer (Athukorala et
al., 2009) activity of these materials.
The chemical composition of the sulphated polysaccharides extracted from algae, including
the degree and the distribution of the sulphate groups, varies according to the species, and
the ecophysiological origin of the algal sources (Rioux et al., 2007). Anyhow, a structural
differentiation depending on the different taxonomic classification of the algal origin, has
been found. According to the mentioned classification the major sulphated polysaccharides
found in marine algae include fucoidan from brown algae, carrageenan from red algae and
ulvan obtained from green algae (Figure 1).
Ulvan polysaccharides possess unique structural properties since the repeating unit shares
chemical affinity with glycoaminoglycan such as hyaluronan and chondroitin sulphate due
to its content of glucuronic acid and sulphate (Figure 2).
