Methacrylated gellan gum (GG-MA) for cell encapsulation
Description
Methacrylated gellan gum (GG-MA) is a modified water-soluble product of low-acyl gellan gum (GG) which forms hydrogels in the presence of ions or in the presence of photo-initiator and ultraviolet light. GG-MA enables to combine in a unique hydrogel system the most advantageous characteristics of gellan gum with an increased temporal and spatial control of polymerization.
Characteristics
Gellan gum is a linear, unbranched, anionic hetero-polysaccharide composed of repeating units of glucose-glucuronic acid-glucose-rhamnose. This polysaccharide is naturally secreted by gram+ bacteria Sphingomonas elodea and forms a gel in the presence of metallic ions and upon temperature decrease.
Methacrylated gellan gum is produced by chemical reaction of an aqueous solution of GG with glycidyl methacrylate (GMA) at controlled pH. The control of reaction pH stimulates the incorporation of methacrylate groups into the free carboxylic groups of GG. The products of reaction are precipitated with acetone and purified by dialysis for several days. The GG-MA powder is obtained after lyophilization and can be sterilized under an ethylene oxide atmosphere when required. Different degrees of methacrylation can be obtained by varying the molar ratio of GMA to GG repeating unit and the reaction time (e.g., from 1 hour until 15 days).
The GG-MA system can be dissolved in aqueous solutions at mild temperatures and allows spatial and temporal control of hydrogel formation, which is dependent on the application of the crosslinking agent. GG-MA aqueous solution is capable of undergoing ionic-crosslinking in the presence of ions or free radical polymerization with a photo-initiator at mild temperatures and exposure to ultraviolet light. Both processes, i.e., ionic- and photo-crosslinking, enable to control crosslinking and withstand the encapsulation of human and animal cells and/or drugs, and any combination thereof.
This system also allows for limited control of structural and mechanical properties of the final product, since its physicochemical and biological properties can be easily adjusted by combining different concentrations of GG or GMA and reaction conditions according to the desired applications.
Applications
Methacrylated gellan gum is useful in a number of research purposes and biomedical applications. GG-MA is biocompatible and capable of chemical manipulation to incorporate attachment peptides, degradable peptides, and other moieties useful for tissue engineering and regenerative medicine applications, as well as for controlled delivery of biological molecules.
GG-MA hydrogels can be used either as an acellular or cellular system, dispensed manually or automatically by injection and crosslinked directly at the site of application, and can be processed using manual or automated systems in different types of scaffolds, such as hydrogels, fibres, 3D structures and micro- or nanoparticles.
References
Silva-Correia J., Oliveira J.M., Caridade S.G., Oliveira J.T., Sousa R.A., Mano J.F. and Reis R.L. (2011) Gellan gum-based hydrogels for intervertebral disc tissue engineering applications. Journal of Tissue Engineering and Regenerative Medicine, 5(6):e97-e107.
Silva-Correia J., Oliveira J.M., Oliveira J.T., Sousa R.A. and Reis R.L. Photo-crosslinked Gellan gum-based hydrogels: methods and uses thereof. WIPO submitted (Priority date: March 2010).
Discount Voucher
Discount of 100 EUR for purchases above 500 EUR (VAT not included). Use promotion code: STM.ESAO.IFAO.2011
Ulvan
Description
Ulvan is an algae heteropolysaccharide mostly composed of sulphated rhamnose and uronic acids, namely glucuronic and iduronic acids1
The presence of rare sugars within its backbone confers to this polysaccharide a peculiar character and many of its intrinsic biological properties are correlated to the presence of these moieties. Its large biomedical and pharmaceutical application potential relates to the presence of glucuronic and iduronic acids since they are important constituents of mammalian glycosaminoglycans.
Characteristics
Marine algae constitute a rich and largely available source of sulphated polysaccharides with peculiar structures associated with different biological activities. In this context, different properties have already been recognized in ulvan, such as antiviral, antioxidant, anticoagulant and antihyperlipidemic. Furthermore, it has been shown that ulvan demonstrates an antiproliferative activity towards various cancer cells.
Ulvan is extracted from the green algae Ulva by methodologies involving an extraction step using hot aqueous solutions and precipitation with organic solvents2. This non-animal origin adds relevant benefits to this polysaccharide, avoiding the deleterious effects of pathogens, inherent to animal origin biomaterials, such as prions or other infectious agents or allergens that may initiate harmful events.
Ulvan is rich on negative groups promptly able to interact with water molecules, increasing its ability to retain moisture, which can be as high as 2000 %(*) (of its initial dry weight) of water uptake. (Water uptake determined on a cross-linked freeze-dried ulvan structure).
Cytotoxicity of ulvan was evaluated according to ISO/EN 10993 part 5 guidelines. Ulvan is a cytocompatible polysaccharide, demonstrating similar cellular effect, in comparative studies, to gold standard hyaluronic acid 3.
Few enzymes with ulvan lyase activity (e.g. endo-ulvan lyase, β-glucuronidase and glucuronan lyase), isolated from diverse sources, have already been identified. The richness in uronic acids and the similarity of this polysaccharide with mammalian glycosaminoglycans may define the enzymatic susceptibility of ulvan towards naturally occurring mammalian enzymes that degrade this type of molecules into sulphate residues and monosaccharides, such as β-glucuronidase, hyaluronidase and aryl sulphate.
Applications
The presence of different functional groups, such as hydroxyl or carboxyl moieties, susceptible to modification and functionalization, allow the production of different structures and devices with appropriate biocompatibility and desired physicochemical properties 4-6. Furthermore, processing of this particular polysaccharide can be performed through the employment of chemistries already recognized and approved by regulatory agencies.
The use of ulvan as a strategic alternative to various synthetic or animal origin macromolecules can take advantage of high availability and low production cost, low cytotoxicity and broad spectrum of biological activities.
References
- Lahaye, M.; Robic, A, Biomacromolecules 2007, 8 (6), 1765-1774.
- Alves, A.; Caridade, S. G.; Mano, J. F.; Sousa, R. A.; Reis, R. L., Carbohydrate Research 2010, 345 (15), 2194-2200.
- Alves, A.; Sousa, R. A.; Reis, R. L., In vitro cytotoxicity assessment of ulvan, a polysaccharide extracted from green algae. Submitted 2011.
- Alves, A.; Duarte, A. R. C.; Mano, J. F.; Sousa, R. A.; Reis, R. L., PDLLA enriched with ulvan capsules as a 3D porous scaffold targeted for cancellous bone engineering Submitted 2011.
- Alves, A.; Pinho, E. D.; Neves, N. M.; Sousa, R. A.; Reis, R. L., Processing ulvan into 2D structures: cross-linked ulvan membranes as new biomaterials for drug delivery applications. Submitted 2011.
- Alves, A.; Sousa, R. A.; Reis, R. L., Processing of degradable and biocompatible ulvan 3D porous structures with tuneable properties envisaged for biomedical applications. Submitted 2011.
Physicochemical Properties
| Colour | Whitish to white powder |
| Solubility | Soluble in water and insoluble in organic solvents such as ethanol or acetone |
| Protein | 1.3 % |
| Sulphate | 32.2 % |
| Total ash | 26.2 % |
| Sulphate-free ash | 10.3 % |
| Average molecular weight | 800 kDa |
| Melting temperature | Non-meltable polysaccharide |
| Glass transition temperature | Not detected |
| Cristallinity | Semi-crystalline polysaccharide |
Discount Voucher
Discount of 100 EUR for purchases above 500 EUR (VAT not included). Use promotion code: STM.ESAO.IFAO.2011