3D patterned substrates for bioartificial blood vessels - The effect of hydrogels on aligned cells on a biomaterial surface.

The optimal bio-artificial blood vessel construct is one that has a compliant tubular core with circumferentially aligned smooth muscle cells (SMCs). Obtaining this well-aligned pattern of SMCs on a scaffold is highly beneficial as this cellular orientation preserves the SMC contractile phenotype. We used 3D patterning to create channels on a polycaprolactone (PCL) scaffold; SMCs were then found to be aligned within the microchannels. To preserve this alignment, and to provide a protective coating that could further incorporate cells, we evaluated the use of two hydrogels, one based on poly(ethylene glycol) diacrylate (PEGDA) and the other based on gelatin. Hydrogels were either physically coated on the PCL surfaces or covalently linked via suitable surface modification of PCL. For covalent immobilization of PEGDA hydrogel, alkene groups were introduced on PCL, while for gelatin covalent linkage, serum proteins were introduced. It is, however, crucial that the hydrogel coating does not disrupt the cellular patterning and distribution. We show in this work that both the process of coating as well as the nature of the coating are critical to preservation of the aligned SMCs. The covalent coating methods involving the crosslinking of hydrogels with the surface of PCL films promoted hydrogel retention time on the film as compared with physical deposition. Furthermore, subsequent hydrogel degradation is affected by the components of the cell culture medium, hinting at a possible route to in vivo biodegradation. STATEMENT OF SIGNIFICANCE: Surface features control cellular orientation and subsequently influence their functionality, a useful effect for cellularized biomedical devices. Such devices also can benefit from protective and cell friendly hydrogel coatings. However, literature is lacking on the fate of cells that have endured hydrogel coating whilst orientated on a biomaterial surface. In particular, elucidation of the cells ability to remain adherent and orientated post hydrogel addition. Coating requires two procedures that may be deleterious to the orientated cells: the surface pretreatment for gel binding and the hydrogel crosslinking reaction. We compare transglutaminase gelatin crosslinking and UV initiated PEGDA crosslinking, coated onto smooth muscle cells orientated on patterned PCL surfaces. This original study will be of considerable use to the wider biomaterials community.