Cell Adhesion and Migration on Thickness Gradient Bilayer Polymer Brush Surfaces: Effects of Properties of Polymeric Materials of the Underlayer

In the field of tissue engineering and biomaterials, controlling the surface properties and mechanical properties of scaffold materials is crucial and has attracted much attention. Here, two types of bilayer polymer brushes composed of a hydrophilic underlying layer and a cationic surface layer [made of poly(2-aminoethyl methacrylate)] with a thickness gradient were prepared by surface-initiated atom-transfer radical polymerization. To investigate the influence of the stiffness as a mechanical property of the polymer brush on cell behavior, the underlayer was prepared from either 2-methacryloyloxyethyl phosphorylcholine or oligo(ethylene glycol) methyl ether methacrylate, with the bilayers designated as gradient poly(2-methacryloyloxyethyl phosphorylcholine)-block-poly(2-aminoethyl methacrylate) [grad-pMbA] and gradient poly(oligo[ethylene glycol] methyl ether methacrylate)-block-poly(2-aminoethyl methacrylate) [grad-pEGbA], respectively. Characterization of these surfaces was performed by spectroscopic ellipsometry, X-ray reflectivity, and determination of the zeta potential, static contact angle, and force curve. These diblock copolymer brushes with a thickness gradient helped to distinguish the effects of the mechanical and surface properties of the brushes on cell behavior. The attachment and motility of L929 fibroblasts and epithelial MCF 10A cells on the fabricated brushes were then assessed. L929 cells had a round shape on the thin surface layer of grad-pMbA and spread well on thicker areas. In contrast, MCF 10A cells spread well in areas of any thickness of either grad-pMbA or grad-pEGbA. Single MCF 10A cells migrated randomly on grad-pMbA, whereas grouped cells started to climb up along the thickness gradient of grad-pMbA. In contrast, both single and grouped MCF 10A cells migrated randomly on grad-pEGbA. These thickness gradient diblock copolymer brushes are simple, reproducible, and reasonable platforms that can facilitate practical applications of biomaterials, for example, in tissue engineering and biomaterials.