The ability of cells to sense and respond to endogenous electric fields is important in processes such as wound healing, development, and nerve regeneration. In cell culture, many epithelial and endothelial cell types respond to an electric field of magnitude similar to endogenous electric fields by moving preferentially either parallel or antiparallel to the field vector, a process known as galvanotaxis. Here we report on the influence of dc electric field and confinement on the motility of fibroblast cells using a chip-based platform. From analysis of cell paths we show that the influence of electric field on motility is much more complex than simply imposing a directional bias towards the cathode or anode. The cell velocity, directedness, as well as the parallel and perpendicular components of the segments along the cell path are dependent on the magnitude of the electric field. Forces in the directions perpendicular and parallel to the electric field are in competition with one another in a voltage-dependent manner, which ultimately govern the trajectories of the cells in the presence of an electric field. To further investigate the effects of cell reorientation in the presence of a field, cells are confined within microchannels to physically prohibit the alignment seen in 2D environment. Interestingly, we found that confinement results in an increase in cell velocity both in the absence and presence of an electric field compared to migration in 2D.
Amphiphilic peptide-polymer conjugates can lead to hierarchically structured, biomolecular materials. Because the peptide structure determines the size, shape, and intermolecular interactions of these building blocks, systematic understanding of how the peptide structure and functionality are affected upon implementing hydrophobicity is required to direct their assemblies in solution and in the solid state. However, depending on the peptide sequence and native structure, previous studies have shown that the hydrophobic moieties affect peptide structures differently. Here, we present a solution study of amphiphilic peptide-polymer conjugates, where a hydrophobic polymer, polystyrene, is covalently linked to the N-terminus of a coiled-coil helix bundle-forming peptide. The effect of conjugated hydrophobic polymers on the peptide secondary and tertiary structures was examined using two types of model, coiled-coil helix bundles. In particular, the integrity of the binding pocket within the helix bundle upon hydrophobic polymer conjugation was evaluated. Upon attachment of polystyrene to the peptide N-terminus, the coiled-coil helices partially unfolded and functionality within the bundle core was inhibited. These observations are attributed to favorable interactions between hydrophobic residues with the PS block at the peptide-polymer interface that lead to rearrangement of peptide residues and consequently, unfolding of peptide structures. Thus, the hydrophobicity of the covalently linked polymers modifies the conjugates' architecture, size, and shape and may be used to tailor the assembly and disassembly process. Furthermore, the hydrophobicity of the covalently linked polymer needs to be taken into consideration to maintain the built-in functionalities of protein motifs when constructing amphiphilic peptide-polymer conjugates.
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