Deposition of patterned glycosaminoglycans on silanized glass surfaces

A versatile salt-based method to immobilize glycosaminoglycans and create growth factor gradients

Glycosaminoglycans (GAGs) are known to play pivotal roles in physiological processes and pathological conditions. To study interactions of GAGs with proteins, immobilization of GAGs is often required. Current methodologies for immobilization involve modification of GAGs and/or surfaces, which can be time-consuming and may involve specialized equipment. Here, we use an efficient and low-cost method to immobilize GAGs without any (chemical) modification using highly concentrated salt solutions. A number of salts from the Hofmeister series were probed for their capacity to immobilize heparin and chondroitin-6-sulfate on microtiter plates applying single chain antibodies against GAGs for detection (ELISA). From all salts tested, the cosmotropic salt ammonium sulfate was most efficient, especially at high concentrations (80–100% (v/v) saturation). Immobilized GAGs were bioavailable as judged by their binding of FGF2 and VEGF, and by their susceptibility towards GAG lyases (heparinase I, II and III, chondroitinase ABC). Using 80% (v/v) saturated ammonium sulfate, block and continuous gradients of heparin were established and a gradient of FGF2 was created using a heparin block gradient as a template. In conclusion, high concentrations of ammonium sulfate are effective for immobilization of GAGs and for the establishment of gradients of both GAGs and GAG-binding molecules, which enables the study to the biological roles of GAGs.

A tenascin-C mimetic peptide amphiphile nanofiber gel promotes neurite outgrowth and cell migration of neurosphere-derived cells

Biomimetic materials that display natural bioactive signals derived from extracellular matrix molecules like laminin and fibronectin hold promise for promoting regeneration of the nervous system. In this work, we investigated a biomimetic peptide amphiphile (PA) presenting a peptide derived from the extracellular glycoprotein tenascin-C, known to promote neurite outgrowth through interaction with β1 integrin. The tenascin-C mimetic PA (TN-C PA) was found to self-assemble into supramolecular nanofibers and was incorporated through co-assembly into PA gels formed by highly aligned nanofibers. TN-C PA content in these gels increased the length and number of neurites produced from neurons differentiated from encapsulated P19 cells. Furthermore, gels containing TN-C PA were found to increase migration of cells out of neurospheres cultured on gel coatings. These bioactive gels could serve as artificial matrix therapies in regions of neuronal loss to guide neural stem cells and promote through biochemical cues neurite extension after differentiation. One example of an important target would be their use as biomaterial therapies in spinal cord injury.

STATEMENT OF SIGNIFICANCE

Tenascin-C is an important extracellular matrix molecule in the nervous system and has been shown to play a role in regenerating the spinal cord after injury and guiding neural progenitor cells during brain development, however, minimal research has been reported exploring the use of biomimetic biomaterials of tenascin-C. In this work, we describe a selfassembling biomaterial system in which peptide amphiphiles present a peptide derived from tenascin-C that promotes neurite outgrowth. Encapsulation of neurons in hydrogels of aligned nanofibers formed by tenascin-C-mimetic peptide amphiphiles resulted in enhanced neurite outgrowth. Additionally, these peptide amphiphiles promoted migration of neural progenitor cells cultured on nanofiber coatings. Tenascin-C biomimetic biomaterials such as the one described here have significant potential in neuroregenerative medicine.

Human macrophage adhesion on polysaccharide patterned surfaces

Despite many advances in designing biocompatible materials, inflammation remains a problem in medical devices and implants. We report two methods, microcontact printing and photodegradation by UV exposure, to pattern dextran and hyaluronic acid on glass, as well as demonstrate their utility for use as an anti-inflammatory biomaterial. The dextran/glass patterned surface can be further modified by grafting hyaluronic acid to glass, creating a binary polysaccharide patterned surface. We used two geometries, 90 µm squares and 22 µm stripes, to study the human macrophage (THP-1) adhesion on the patterned surfaces containing dextran, hyaluronic acid and the binary pattern. The results indicate that a majority of the macrophages are non-adherent on hyaluronic acid for three day culture. The ranking of surfaces according to macrophage adhesion is 3-aminopropyl triethoxysilane-modified glass culture dish, dextranized surfaces, glass, and hyaluronic acid-modified surfaces. On the binary pattern of dextran and hyaluronic acid, macrophages preferentially attach and adhere to the dextranized area. Patterned surfaces provide an excellent platform for mimicking the complexity of the glycocalyx and investigating the interface between this surface and cells. This binary polysaccharide pattern also offers a new route to address anti-inflammatory potential of surface coatings on biomaterials in a high through-put fashion.

Photo-Generation of Carbohydrate Microarrays

The unparalleled structural diversity of carbohydrates among biological molecules has been recognized for decades. Recent studies have highlighted carbohydrate signaling roles in many important biological processes, such as fertilization, embryonic development, cell differentiation and cellȁ4cell communication, blood coagulation, inflammation, chemotaxis, as well as host recognition and immune responses to microbial pathogens. In this chapter, we summarize recent progress in the establishment of carbohydrate-based microarrays and the application of these technologies in exploring the biological information content in carbohydrates. A newly established photochemical platform of carbohydrate microarrays serves as a model for a focused discussion.

Quantitation of surface-reducing-end covalently bound polysaccharides via hydrazinolysis and deamination

Depending on the method of deposition, reactive sites of polysaccharides on substrates may not be available when their reducing ends have been used to covalently bind them to the substrates. Here we present a method that allows surface density measurements of reducing-end covalently bound polysaccharides in a procedure that cleaves the polysaccharide chain from the surface via hydrazinolysis and deamination, leaving on the surface a disaccharide that is later radiolabeled with an aldehyde in a reaction with enamine formation. The method described has the advantage that it may be used with any polysaccharide patterned to any surface exposing an amino-terminated monolayer by reductive amination of their galactosamine or glucosamine repeating units. We illustrate the technique with the quantitation of glycosaminoglycans (GAGs) on silanized glass surfaces.

Static adhesion of cancer cells to glass surfaces coated with glycosaminoglycans

Using a previously described method for the functionalization of glass substrates with glycosaminoglycans (GAGs), in vitro experimental comparison of adhesion levels of cancer cells to glycosaminoglycan-modified substrates was performed with non-treated and heparin-treated human cancer cells of different metastatic activity. For both non-treated and heparin-treated cells, our results indicate that heparan sulfate is the preferred substrate for adhesion while keratan sulfate shows anti-adhesive properties. The observed net effect of heparin is a cell-dependent reduction in the adhesion figures. Overall, our results suggest that tissues with higher composition of heparan sulfate chains may be preferential metastatic targets and indicate that the effective use of heparin as anti-metastatic or anti-inflammatory agent may also depend on glycosaminoglycan composition of the affected organs.