Hydrogel-Forming Algae Polysaccharides: From Seaweed to Biomedical Applications

Abstract

With the increasing growth of the algae industry and the development of algae biorefinery, there is a growing need for high-value applications of algae-extracted biopolymers. The utilization of such biopolymers in the biomedical field can be considered as one of the most attractive applications but is challenging to implement. Historically, polysaccharides extracted from seaweed have been used for a long time in biomedical research, for example, agarose gels for electrophoresis and bacterial culture. To overcome the current challenges in polysaccharides and help further the development of high-added-value applications, an overview of the entire polysaccharide journey from seaweed to biomedical applications is needed. This encompasses algae culture, extraction, chemistry, characterization, processing, and an understanding of the interactions of soft matter with living organisms. In this review, we present algae polysaccharides that intrinsically form hydrogels: alginate, carrageenan, ulvan, starch, agarose, porphyran, and (nano)cellulose and classify these by their gelation mechanisms. The focus of this review further lays on the culture and extraction strategies to obtain pure polysaccharides, their structure-properties relationships, the current advances in chemical backbone modifications, and how these modifications can be used to tune the polysaccharide properties. The available techniques to characterize each organization scale of a polysaccharide hydrogel are presented, and the impact on their interactions with biological systems is discussed. Finally, a perspective of the anticipated development of the whole field and how the further utilization of hydrogel-forming polysaccharides extracted from algae can revolutionize the current algae industry are suggested.

Figure 1

Comparison of four different main gelation mechanisms in algal polysaccharides. (A) Schematic of the complexation in ionic polysaccharides, such as alginates. (B) Aggregation of polysaccharide chains into secondary structures through a formation of double helices. (C) Formation of physical cross-links by induced crystallization in amorphous regions. (D) Gelation of colloids, such as nanocellulose, by colloidal crowding.

Figure 2

Purification and extraction routes that can be used to isolate a polysaccharide according to its chemical structure.

Figure 3

Analytical techniques available for the characterization of hydrogel-forming polysaccharides from algae. Techniques are classified by the scale of the characterized structure. Gray: nuclear magnetic resonance spectroscopy, blue: chromatography, orange: scattering techniques, green: gas and liquid sorption, pink: mechanical properties, red: microscopic techniques.

Figure 4

Reported chemical reactions to modify an algae polysaccharide backbone. The reactions are shown exemplified on glucose or glucuronic acid building blocks.

Figure 5

Common processing techniques of hydrogel-forming polysaccharides to create microbeads, nanoparticles, nanofibers, hydrogels, and aerogels that can be then used for biomedical applications.

Figure 6

Properties of algae-extracted polysaccharides at different scales that impact the biomedical performance and interaction with biological systems.

Figure 7

Proposed life cycle of hydrogel-forming polysaccharides derived from algae culture: their extraction, characterization, and processing into materials for biomedical application. If required a prior chemical modification can be integrated to tune their properties toward a dedicated processing and biomedical application.

Figure 8

Implementation of the valorization of hydrogel-forming polysaccharides for high-value-added applications into existing supply chains for food and industrial applications from algae.