Electronic Supplementary Material (ESI) for Journal of Materials Chemistry B. This journal is © The Royal Society of Chemistry 2018 Contact angle and surface energy analysis Methods: contact angles with water and glycerin were measured with OCA20 data physics instruments (Data physics, Germany) using sessile drop technique. Samples were mounted onto glass slides using double –sided adhesive tape. The contact angles testing were conducted at four different positions at the membrane surface. Each θ value used for free energy was the average of three determined. The polar and dispersive components of the surface energy of the samples were calculated using the Owens-Wendt approach that come with OCA20. Results: (a) (b) (d) (c) (e) (f) Fig S1. Images of contact angles of water on the BC (a) , PDA- BC (c) and PLGA-BC (e), glycerin on the BC (a) , PDA- BC (d) and PLGA-BC (f).Water and glycerin droplets 3μl were placed 60s. Fig S2. The Polar and dispersive components of the surface energy of BC, PDA-BC and PLGA-BC The contact angles of water and glycerin on various surface were measured respectively as shown in Fig.1. The dispersion and polar surface tension components of the liquids which were used to obtain the components of surface energy of the various samples are shown in Fig.2, suggesting that both dispersion and polar components increased after modification of PDA. As expected, the decrease in the surface energy, especially the polar component, can be observed in PLGA-BC membrane. Discussion BC membrane is composed of nano-size fibres and therefore possess a very high surface energy. The polar component of the surface free energy of bared BC membrane is due to hydroxyl groups. For the case of PDA-BC, due to the increase of polar hydroxyl groups which come with the PDA molecular, the polar components increased. Moreover, the nanoparticles of PDA, which display nano-size effects, show higher surface free energy. Those effects contribute to the highest surface energy of PDA-BC membrane. As a typical nonpolar copolymer, PLGA substitutes some surface hydroxyl groups by weak hydrogen bond. As a result, the surface free energy and polar component decreased after modification of PLGA. Cells preferentially interact with the layer of adsorbed protein rather than come into direct contact with the surface of the material. Adsorbed proteins spread out less as the surface energy of the substrate increases [1], so that the cells on PLGA-BC were more elongated and stretched (Fig 6 (f) in main article) compared to those on bared and PDA-coated BC membranes. As we discussed in main article, the protein adsorption theory failed to explain the cells morphologies on the DPA-BC surface which had highest surface energy.In current situation, PDA prefers to form a covalent bond with cells before protein adsorption. Refence [1] T. M. Pandey, S. K.Pattanayek, D. Delabouglise, J. Phys. Chem. C 2013 , 117,6151.