The construction of peptides (components of protein) with amino acids is done biologically by ribosomes. An army of 10^18 artificial molecular machines constructed milligrams of a specific peptide simultaneously from amino acids in their path. These machines were designed based on rotaxane which is similar to a ring on an axle. They constructed the peptides from amino acids it picked up from a strand they followed. This is a large step toward nano-scale machines that can create copies of themselves and do more complex stuff.
Original Publication: Sequence-Specific Peptide Synthesis by an Artificial Small-Molecule Machine