31
artificial syngas mixture. The addition of 10% of CO 2 to the CO feed enhanced the
polymer content compared to cultivations with pure CO.
1.5.4 Extracellular Polymeric Substances
Several microorganism strains synthesize extracellular polymeric substances (EPS),
mainly consisting in polysaccharides, proteins, and DNA (Nouha et al. 2018). Even
though cyanobacteria are natural producers of structurally diverse extracellular
polymeric substances, knowledge on the biosynthetic pathways remains quite limited. Synthesis of EPS begins in the cytoplasm where monosaccharides are degraded
into sugar nucleotides, which are then conveyed to the plasma membrane. An analysis (Pereira et al. 2015) of proteins related to polymerization, assembly, and export
of EPS lets emerge a complex scenario where most cyanobacterial strains harbor
genes belonging to at least the Wzy-, ABC transporter-, and synthase-dependent
pathways.
EPS vary in their functions: they can contribute to carbon reserves and entrapment of nutrients; they can act as pathogenicity and virulence factors; they confer
advantages under abiotic and biotic stresses; and, through mechanical stabilization,
they are responsible for cohesion of microorganisms, adhesion of biofilms to surfaces, and chemical communication. In addition to known antiviral, antibacterial,
and antioxidant pharmacological activities, EPS feature unique characteristics suitable to the production of thickening, suspending, or emulsifying agents which are
relevant in many industrial applications in biomedicine, clinical therapy, and environmental remediation.
EPS biocompatibility, gelling, and thickening capabilities are exploitable in
hydrogel-based technologies. Hydrogels are polymer networks which feature the
following prominent characteristics: (i) they remain insoluble through the formation
of chemical or physical crosslinks between polymer chains in solution, and (ii) they
are able to absorb large amounts of water and thus form an ideal porous environment facilitating cell adaptation. Hydrogel-based materials are materials of choice
to develop effective approaches in medical applications since they can adjust their
physical and chemical properties in response to cancer-specific hallmarks or external stimuli. In the past years, hydrogels have contributed to substantial advances in
tumor modeling and diagnosis and tumor-related therapies allowing to explore the
cells’ responses to changes in the tumor microenvironment or acting as smart carriers for the controllable release of multiple cargos, including both naked and
nanoparticle-encapsulated chemotherapeutics and radioisotopes (Sepantafar et al.
2017). Recently, a photo-polymerizable EPS-based hydrogel (Bellini et al. 2018)
was produced by combining the released EPS from the heterocytous cyanobacterium Trichormus variabilis with polyethylene glycol diacrylate. Hybrid hydrogels
1 Use of Carbon Dioxide in Polymer Synthesis
artificial syngas mixture. The addition of 10% of CO 2 to the CO feed enhanced the
polymer content compared to cultivations with pure CO.
1.5.4 Extracellular Polymeric Substances
Several microorganism strains synthesize extracellular polymeric substances (EPS),
mainly consisting in polysaccharides, proteins, and DNA (Nouha et al. 2018). Even
though cyanobacteria are natural producers of structurally diverse extracellular
polymeric substances, knowledge on the biosynthetic pathways remains quite limited. Synthesis of EPS begins in the cytoplasm where monosaccharides are degraded
into sugar nucleotides, which are then conveyed to the plasma membrane. An analysis (Pereira et al. 2015) of proteins related to polymerization, assembly, and export
of EPS lets emerge a complex scenario where most cyanobacterial strains harbor
genes belonging to at least the Wzy-, ABC transporter-, and synthase-dependent
pathways.
EPS vary in their functions: they can contribute to carbon reserves and entrapment of nutrients; they can act as pathogenicity and virulence factors; they confer
advantages under abiotic and biotic stresses; and, through mechanical stabilization,
they are responsible for cohesion of microorganisms, adhesion of biofilms to surfaces, and chemical communication. In addition to known antiviral, antibacterial,
and antioxidant pharmacological activities, EPS feature unique characteristics suitable to the production of thickening, suspending, or emulsifying agents which are
relevant in many industrial applications in biomedicine, clinical therapy, and environmental remediation.
EPS biocompatibility, gelling, and thickening capabilities are exploitable in
hydrogel-based technologies. Hydrogels are polymer networks which feature the
following prominent characteristics: (i) they remain insoluble through the formation
of chemical or physical crosslinks between polymer chains in solution, and (ii) they
are able to absorb large amounts of water and thus form an ideal porous environment facilitating cell adaptation. Hydrogel-based materials are materials of choice
to develop effective approaches in medical applications since they can adjust their
physical and chemical properties in response to cancer-specific hallmarks or external stimuli. In the past years, hydrogels have contributed to substantial advances in
tumor modeling and diagnosis and tumor-related therapies allowing to explore the
cells’ responses to changes in the tumor microenvironment or acting as smart carriers for the controllable release of multiple cargos, including both naked and
nanoparticle-encapsulated chemotherapeutics and radioisotopes (Sepantafar et al.
2017). Recently, a photo-polymerizable EPS-based hydrogel (Bellini et al. 2018)
was produced by combining the released EPS from the heterocytous cyanobacterium Trichormus variabilis with polyethylene glycol diacrylate. Hybrid hydrogels
1 Use of Carbon Dioxide in Polymer Synthesis