A surface-tethered model to assess size-specific effects of hyaluronan (HA) on endothelial cells

Crosslinked gels (hylans) containing long-chain (MW>1 x 10(6)Da) hyaluronan (HA), a connective tissue GAG, show exceptional biocompatibility for vascular implantation but poorly interact with vascular endothelial cells (ECs). Previous studies showed in situ fragmentation of HA by UV light to bioactivate hylan gels and elicit enhanced EC responses. Since fragmented HA can be pro-inflammatory, it is important to define an optimal size distribution of HA fragments on the hylan surface that will recruit and support normally functional ECs and limit ulterior responses. Related studies have shown that exogenous models of HA do not necessarily replicate cell responses to HA scaffolds. Since scaffolds cannot be created based on fragmented HA alone, we sought to determine size-specific responses of ECs to HA substrates of defined fragment sizes by creation of HA-tethered culture surfaces. HA (1000, 200, 20 kDa) and an oligomer mixture were tethered onto an aminosilane (APTMS)-treated glass surfaces using a carbodiimide reaction. MALDI-TOF showed the HA digests to contain HA 4-8mers with a 75+/-0.4% w/w of 4mers. Immuno-fluorescence, SEM, AFM and XPS analysis revealed homogeneous amine and HA surfaces. An amine s-SDTB assay and HA fluorophore-assisted carbohydrate electrophoresis (FACE) indicated surface densities of 9+/-3 amine groups/nm(2) and 0.57+/-0.44 microg/cm(2), respectively. HA/HA fragments/oligomers were stable over 21 days of incubation in serum-free culture media. EC proliferation on these surfaces resulted was limited, a possible effect of smooth surface topography, high anionicity, and in case of 4mers, non-interaction with primary HA cell-surface receptors (CD44). This work is significant in that it allows testing of cell responses to substrates composed of single-sized fragments of HA that cannot by themselves be cross-linked into a gel. Future work in our lab will use this model to assess the effects of other HA oligomer sizes on EC behavior.