3D-Bioprinted Aptamer-Functionalized Bio-inks for Spatiotemporally Controlled Growth Factor Delivery

Introduction Spatiotemporally controlled growth factors delivering systems are crucial for tissue engineering. However, most of the current strategies for growth factors delivery often focuses on the immobilization or coupling of growth factors within the engineered matrices (hydrogel) via various linker proteins or peptides. These systems provide passive release rates and growth factor delivery on demand, but fail to adapt their release rates in accordance with the tissue development. To overcome this limitation, the present study employed nucleic acid based aptamers for achieving spatiotemporally controlled growth factor delivery. Aptamers are affinity ligands selected from DNA/RNA libraries to recognize proteins with high affinity and specificity.1 Aptamer based growth factor delivery systems are able to load/release multiple growth factors on demand with high specificity. In the present study, the authors have 3D-bioprinted aptamer-functionalized bio-inks to evaluate their potential for growth factor sequestering, programmable release and for studying their effect on vascular network formation. Methods The aptamer-functionalized hydrogels were prepared via photo-polymerization of gelatin methacryloyl (GelMA) and acrydite functionalized aptamers having sequence specific for binding to vascular endothelial growth factor (VEGF165). Visible light photoinitiator, tris(2,2′-bipyridyl)dichloro-ruthenium(II) hexahydrate with sodium persulfate was used. The 3D-bioprinting experiments were carried out using Rokit Invivo 3D printer. The viscoelastic properties of the bio-inks were evaluated and compared with control GelMA bio-ink. To study the programmable growth factor release efficiency, VEGF antibody immunostaining was used. For studying the effect of triggered growth factor release on vascular network formation, human umbilical vein endothelial cells (HUVECs) and mesenchymal stem cells (MSCs) were encapsulated within the bio-inks. Results & Discussion The results obtained from VEGF antibody immunostainings confirmed the sequestration and triggered release of VEGF in response to complementary sequence addition from the 3D bioprinted construct after 5 days of culture. The bioprinted construct showed high cellular viability. The F-Actin/DAPI staining showed cellular sprouting and vascular network formation within the 3D printing aptamer functionalized bio-ink regions. In addition, the endothelial cells showed variations in cellular organization based on the VEGF bound aptamer availability within the bioprinted construct. These observations altogether confirms the bioactivity of VEGF bound aptamers within the printed constructs. Conclusions The present study shows the vasculogenic potential of 3D bioprinted aptamer-functionalized bio-inks via spatiotemporally controlling VEGF availability within the hydrogel system. Acknowledgements: This work is supported by an ERC Consolidator Grant under grant agreement no 724469. References 1. M.R. Battig, et. al., J. Am. Chem. Soc. 134 (2012) 12410-12413.