Merging synthetic biology and materials science, researchers genetically coaxed specific populations of neurons to manufacture electronic-tissue "composites" within the cellular architecture of a living animal, a new proof-of-concept report reveals. The approach may enable the creation of diverse, complex and functional synthetic structures and materials within living systems. Similar to optogenetics, which uses pulses of laser light to modulate the behavior of genetically modified neurons, the emerging field of bioelectronic medicine seeks to use electrical stimulation to produce cellular or organ-specific effects. Many cells and tissues respond to electrical fields - particularly neurons - and electrical stimulation has been shown to affect a variety of cellular activities. Clinical applications range from soothing post-amputation pain to tissue regeneration. However, while approaches to modify the electrical properties of a cell and its response to electrical stimulation exist, they often affect large, diverse cell populations or off-target tissue elements, producing undesirable side effects. To date, no approach has been able to integrate electroactive polymers with cell-type specificity, thus enabling a more targeted use of electrical fields and stimulation - a capability that could significantly improve the therapeutic potential of bioelectronic medicine. Leveraging the complex and powerful biosynthetic machinery of living cells, Jia Liu and colleagues present a proof-of-concept of genetically targeted-chemical assembly. Liu et al. engineered an enzyme, which, when expressed, instructed gene-targeted neurons to synthesize and assemble electroactive polymers onto their plasma membrane, effectively changing the electrical properties of specific populations of cells. The targeted approach allowed for in vivo bioelectronic manipulation of neuron properties as well as of specific behaviors in freely moving C. elegans worms, without compromising the natural function of the cells. "Future work will seek to demonstrate long-term integration of these elements for intriguing scientific and translational application via modulating portions of neural activity," write Kevin Otto and Christine Schmidt in a related Perspective.