according to the application. Surfaces have now been modified with a vast family of chemical compounds, and peptides and proteins have also been printed onto surfaces. Mirkin and colleagues42–44 have also developed a dip-pen nanolithography to directly print micro- and nano-features onto surfaces. They use a modified AFM tip to dip into
protein ink or other solutions, and then transfer these substrates directly onto a previously modified surface, enabling the inscription of diverse patterns. This is much like writing with a feather pen in the Middle Ages. These developments have spurred new research into the control of molecular and cellular patterning, cell morphology, and cellular interactions40,41,45–47 and fueled new technology development.
Work in my laboratory has focused on designing a variety of peptides to self-assemble into a monolayer on surfaces and to allow adhesion molecules to interact with cells and adhere to the surface These peptides have three general
regions along their lengths: a ligand for specific cell recognition and attachment, a linker for physical separation from the surface, and an anchor for covalent attachment to the surface47. The ligands may be of the RGD (arginine–glycine–aspartic acid) motif that is known to promote cell adhesion, or other sequences for specific molecular
recognition or specific cell interactions. The linker is usually a string of hydrophobic amino acids such as alanine or valine. The anchor can be a cysteine residue for gold surfaces, aspartic acid linking on amine
surfaces or lysine linking on carboxylic acid surfaces.
We have used this method, in conjunction with self-assembled monolayers prepared through microcontact printing, to place cells into complex patterns47. This approach may facilitate research into cell-cell communication. Recently, we have moved one step further: using peptides and proteins as ink, we have directly microprinted specific features onto the nonadhesive surface of polyethylene glycol to fabricate arbitrary patterns rapidly without preparing a mask or stamps . The process is similar to using an ink pen for writing—here, the microcontact printing device is the pen and the biological or chemical substances are the inks.