Abstract
This work used a hydrophobic polymer pair, i.e. polystyrene (PS) and polyisoprene (PI), to construct well-organized polymer templates for the patterning of proteins through a selective adsorption process. This is a bottom-up method to pattern proteins. The nanopatterned protein surfaces were used as substrates to investigate cell adhesion behaviour. PS-b-PI copolymer ultrathin films formed well-ordered two-dimensional surface structures after spin-coating because of the confinement of substrate-polymer and polymer-air interfaces. A symmetric diblock copolymer film with an 18 nm thickness formed a structure with PI dots dispersed in a PS matrix, and an asymmetric diblock copolymer film of the same thickness formed a stripe-like structure. After incubating these templates in bovine serum albumin (BSA) solution, the ring-like and stripe-like protein nanopatterns were prepared, which resembled their underlying copolymer templates. ToF-SIMS confirmed that there is more BSA adsorption on the PS-b-PI template surface when there is more PS component exposed on the surface. Further, AFM and SIMS analysis confirmed that BSA molecules were localized on the PS domains rather than on the PI domains. The protein's selective adsorption is attributed to the great mobility of PI chains at room temperature. The PS, PI, PS-b-PI binary and ternary blends also formed a variety of structures. For thick films, the free surfaces of films are entirely covered by a thin PI layer because its surface energy is lower than PS. When the film thickness is less than 15 nm, both PS and PI components were exposed on the free surface. The resulting complicated surface structures also patterned BSA molecules. After an extracellular matrix protein, fibronectin (FN), was adsorbed on copolymer substrates, the ring-like and stripe-like FN nanopatterns were incubated in CHO cell suspensions. The ring-like FN pattern adhered more cells than the stripe-like and the control surfaces. The cells on the ring-like FN surface formed more actin fibers and spread better. This can be explained by the ring-like pattern increasing the FN ligand local density and further increasing the integrin clusters and focal adhesion. The ECM protein nanopattern has relevance for tissue engineering.