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.

Poly(2-aminoethyl methacrylate)-based polyampholyte brush surface with carboxylic groups to improve blood compatibility.

Zwitterionic material-based polymer brush significantly prevents protein adsorption and cell adhesion, which leads to the blood compatibility. However, zwitterionic polymer itself is difficult to be modified further, for the blood compatibility since the charged balance is impaired after the modification. In this research, chemically modifiable mixed charge polymer brush is designed, without impairing its characteristics. Condensed mixed charge polymer brush will work like zwitterionic material because neighbouring opposite charge is reported to be important in the zwitterionic material. Cationic polymer brush with primary amine group, which is based on 2-aminoethyl methacrylate (AEMA), was prepared and modified by succinic anhydride to obtain carboxylic group induced poly(AEMA). The ratio of primary amine group and carboxylic group was optimized to obtain the polyampholyte brush. The blood compatibility was evaluated by measuring coagulation/complement activation, protein adsorption and cell adhesion induced by the polymer. Our designed cationic-based polyampholyte brush prevented coagulation/complement activation comparable to poly(2-methacryloyloxyethyl phosphorylcholine) brush, based on intra-monomer interaction, because condensed mix charge works like zwitterion.

Nano-structural comparison of 2-methacryloyloxyethyl phosphorylcholine- and ethylene glycol-based surface modification for preventing protein and cell adhesion.

Polymer brush, owing to its precisely controllable nanostructure, has great potential for surface modification in the biomedical field. In this study, we evaluated the bio-inertness of polymer brush, monomer monolayers, and polymer-coated surfaces based on their structures, to identify the most effective bio-inert modification. We focused on two well-known bio-inert materials, 2-methacryloyloxyethyl phosphorylcholine (MPC) and ethylene glycol (EG). The amount of adsorbed proteins on the surface was found to be dependent on the monomer unit density in the case of MPC, whereas this correlation was not observed in the case of EG. Cell adhesion was suppressed on the brush structure of both MPC and EG units, regardless of their density. The brush structure of MPC and EG units showed better anti-protein- and anti-cell-adhesion than monolayers and polymer-coated surfaces. Thus, the steric repulsion was not only important in EG units-based surface, but also in MPC-based surface. In addition, multiple polymer layers formed by MPC-based polymer coating also displayed similar properties.

Enhancement of Cell Adhesion on a Phosphorylcholine-Based Surface through the Interaction with DNA Mediated by Ca2+ Ions.

2-Methacryloyloxyethyl phosphorylcholine (MPC) has a PC group and is one of the most well-known bioinert polymers. In this study, we evaluated the interaction between MPC and DNA, which specifically interacts with the phospholipid head group via Ca2+ ions. A MPC monolayer and poly(MPC) brush were fabricated to observe the effect of the structure on the interaction between MPC and DNA via Ca2+ ions. The poly(MPC) brush, which shows higher MPC unit density, more efficiently interacted with DNA via Ca2+ ions. Also, serum protein could interact with the poly(MPC) brush via DNA, although the brush itself hardly interacted with serum proteins. Cell adhesion was significantly provoked on poly(MPC)/DNA compared with poly(MPC) because serum protein adsorption was induced on poly(MPC)/DNA.

Cellular Response to Non-contacting Nanoscale Sublayer: Cells Sense Several Nanometer Mechanical Property.

Cell adhesion is influenced not only from the surface property of materials but also from the mechanical properties of the nanometer sublayer just below the surface. In this study, we fabricated a well-defined diblock polymer brush composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate (AEMA). The underlying layer of poly(MPC) is a highly viscous polymer, and the surface layer of poly(AEMA) is a cell-adhesive cationic polymer. The adhesion of L929 mouse fibroblasts was examined on the diblock polymer brush to see the effect of a non-contacting underlying polymer layer on the cell-adhesion behavior. Cells could sense the viscoelasticity of the underlying layers at the nanometer level, although the various fabricated diblock polymer brushes had the same surface property and the functional group. Thus, we found a new factor which could control cell spread at the nanometer level, and this insight would be important to design nanoscale biomaterials and interfaces.