"Polysaccharides belong to the most abundant biomaterials on earth. They form structural elements of plant and animal tissues, but many of them have also important regulatory functions towards cells, tissues and organs. Glycosaminoglycans (GAG) and other carboxylated and sulfated polysaccharides possess a bioactivity that is due to their high affinity to a plethora of proteins that belong to insoluble and soluble components of cell environments, but also by direct interaction of these carbohydrates with cell receptors. Hence, making surface coatings or hydrogels from natural or semisynthetic GAG for implants that guide cell behavior towards differentiation to bone or cartilage might be an promising approach ti mimik the natural environment of cells in tissues.
Here, covalent binding mechanisms based on oxidation of pendant hydroxyl groups or introduction of reactive side groups like thiols in monosaccharide subunits permit direct coupling to surfaces or cross-linking mechanisms using Schiff´s base or disulfide bond formation, respectively. Physical immobilization can exploit the inherent charge of these molecules that permits formation of multilayers on surfaces kept together by ion pairing, but also intrinsic cross-linking of activated GAG. Both mechanism can be also used to form 3D structures as in situ gelling hydrogels that permit embedding of growth factors and cells.
Native and oxidized GAGs have been used to prepare multilayer coatings that could promote either osteogenic or chrondrogenic differentiation using chondroitin sulfate (CS)and hyaluronan as polyanions, respectively. Multilayer systems with oxidized CS were also useful as system for controlled presentation of osteogenic growth factor BMP-2. Thiolated CS and chitosan could be also used for redox-sensitive multilayer coatings that change their cell adhesion properties in dependence on disulfide bond formation, which functions as stimuli-responsive system for cell culture. Apart from making bioactive surface coatings both cross-linking mechanisms can be also used to form 3D structures as in situ gelling hydrogels that permit embedding of growth factors and cells.
In conclusion of our studies we could fabricate 2D and 3D systems that are instructive in controlling cell spreading, growth and differentiation of mesenchymal stem and other cells, which will be shown with examples of chondrogenic and osteogenic differentiation of cells."