**6. Galectins in biomaterial research**

As discussed in chapter 5.1 galectins can act pro- and antiadhesive which *in vivo* seems to be mainly regulated by concentration and oligomerisation status of the galectins. In the context of biomaterial research it is also of huge importance if the galectins are immobilised or soluble presented. Immobilised galectins act mainly proadhesive as they crosslink the surface they are immobilised on with glycosylated structures on the cell-membrane. Soluble galectins can either facilitate or reduce adhesion for example to functionalised surfaces as discussed for the *in vivo* situation in chapter 5.1 depending on concentration, oligomerisation and cell type (respectively receptor availability on this cell type) (Elola et al., 2007).

Galectins: Structures, Binding Properties and Function in Cell Adhesion 17

Our recent work shows the potential of galectins and glycans in the preparation of biomaterial surfaces (figure 4). The assembly of an artificial extracellular matrix consisting of immobilised glycans, galectins and other extracellular matrix components was proven with a fungal model lectin (CGL2) (Sauerzapfe et al., 2009). In this approach poly-*N*acetyllactosamine structures which are well known ligands for galectins (see chapter 3.2) are enzymatically produced. Those structures can be immobilised to different functionalised materials by a free amino group coupled to the reducing sugar. Concentration dependent binding of lectins to immobilised glycans was proven showing differences for specific glycan ligands. Lectin-mediated crosslinking of the surface with ECM-glycoproteins was also shown (Sauerzapfe et al., 2009). This galectin-mediated binding of ECM-glycoproteins

leads to a natural presentation of these structures for subsequent adhesion of cells.

Groll, manuscript in preparation).

inflammatory or carcinogenic effects.

**8. Acknowledgements** 

**9. References** 

ERS@RWTH Aachen University.

**7. Conclusion** 

Our ongoing work focuses on the transfer of this set-up to applicable biomaterial surfaces. On the one hand recombinant human galectins are used instead of the fungal lectin to provide a more natural set-up (unpublished data). On the other hand the assembly of this artificial extracellular matrix is transferred to a special hydrogel surface. Star shaped NCO-sP(EO-stat-PO) is used as inert biomaterial which prevents unspecific protein adsorption and can be further functionalised with specific structures such as sugar molecules (Bruellhoff et al., 2010; Grafahrend et al., 2011). On the basis of these glycans an artificial extracellular matrix composed of galectins and ECM-glycoproteins can be built up. Fibroblasts show excellent adhesion and cell spreading on these surfaces (Rech, Beer, Elling,

The importance of galectins in cell adhesion and signal transduction has been shown in several investigations. Therefore a possible application of galectins in the assembly of a biomaterial surface mimicking the natural microenvironment seems to be obvious. Anyhow only few articles regarding the use of galectins in biomaterial research have been published. This might be explained by the fact that the fine regulation of galectin mediated cell adhesion and signalling is still not fully understood yet. Therefore it is important to evaluate galectin function under specified conditions to reduce or exclude the risk of unwanted

Taking the presented literature and our own work regarding the biofunctionalisation of surfaces with glycans and galectins together, there is clear evidence that galectins play an important role in cell adhesion and proliferation on specifically functionalised biomaterial surfaces. However, further research has to be done to adopt the fundamental understanding of galectin-glycan mediated cell adhesion processes to an applicable biomaterial surface.

The authors acknowledge financial support by the DFG (Deutsche Forschungsgemeinschaft) within the Research Training Group 1035 "Biointerface", by the DFG (project EL 135/10-1), and by the excellence initiative of the German federal and state governments through

Abbott, W. M. & Feizi, T. (1991). Soluble 14-kDa beta-galactoside-specific bovine lectin -

evidence from mutagenesis and proteolysis that almost the complete polypeptide-

The pro-adhesive properties of galectins have been shown several times. But only few efforts have been done to elucidate the potential of galectins as coatings for biomaterial surfaces. In contrast other components of the extracellular matrix are often used. Coatings with peptides from ECM proteins such as RGD or YIGSR peptide are one of the most common methods to modify biomaterial surfaces. Also coatings with complete ECM proteins or specific adhesion proteins have been investigated. Another important molecule class used in biomaterial research today are growth factors (Chan & Mooney, 2008; Shekaran & Garcia, 2011; Straley et al., 2010). The functionalisation with glycans or lectins seems to be underrepresented although their function in natural processes is well known. Only few studies show the potential of galectins and glycans as biomaterial coatings:

The positive influence of galectins was shown for example as the coating of PLGA scaffolds with recombinant galectin-1 promotes adhesion and growth of immortal rat chondrocytes. Therefore this surface is mentioned to have potential as biomaterial in tissue engineering (Chen et al., 2005). The potential of glycans in biomaterial coatings has also been shown. For example galactose derivatives immobilised on material surfaces were proven to influence the growth and function of liver cells positively. But in this study the receptor molecules and mechanisms of signal transduction were not investigated and binding of an asialoglycoprotein receptor (and not galectin mediated binding) is assumed (De Bartolo et al., 2006). Another study shows combined use of immobilised glycans with galectins as it evidences positive effects of endogenous galectin-1 for adhesion of chondrocytes to a lactose-modified surface (Marcon et al., 2005). These findings prove the possible use of glycan and/or galectin modified materials for improved cell adhesion.

Fig. 4. Schematic representation of a possible biomaterial set-up using immobilised glycans as scaffold for subsequent galectin-mediated protein and cell-adhesion

Our recent work shows the potential of galectins and glycans in the preparation of biomaterial surfaces (figure 4). The assembly of an artificial extracellular matrix consisting of immobilised glycans, galectins and other extracellular matrix components was proven with a fungal model lectin (CGL2) (Sauerzapfe et al., 2009). In this approach poly-*N*acetyllactosamine structures which are well known ligands for galectins (see chapter 3.2) are enzymatically produced. Those structures can be immobilised to different functionalised materials by a free amino group coupled to the reducing sugar. Concentration dependent binding of lectins to immobilised glycans was proven showing differences for specific glycan ligands. Lectin-mediated crosslinking of the surface with ECM-glycoproteins was also shown (Sauerzapfe et al., 2009). This galectin-mediated binding of ECM-glycoproteins leads to a natural presentation of these structures for subsequent adhesion of cells.

Our ongoing work focuses on the transfer of this set-up to applicable biomaterial surfaces. On the one hand recombinant human galectins are used instead of the fungal lectin to provide a more natural set-up (unpublished data). On the other hand the assembly of this artificial extracellular matrix is transferred to a special hydrogel surface. Star shaped NCO-sP(EO-stat-PO) is used as inert biomaterial which prevents unspecific protein adsorption and can be further functionalised with specific structures such as sugar molecules (Bruellhoff et al., 2010; Grafahrend et al., 2011). On the basis of these glycans an artificial extracellular matrix composed of galectins and ECM-glycoproteins can be built up. Fibroblasts show excellent adhesion and cell spreading on these surfaces (Rech, Beer, Elling, Groll, manuscript in preparation).
