Artificial Neuron

Why can't we develop a programmable artificial neuron for implantation into the human body? It would be based on the properties of stem cells, which adapt to the area of the brain or nerve where they are injected, replacing missing or damaged nerve cells. All we'd need is a basic understanding of what biochemical signals are responsible for the natural transformation of stem cells, and then we could program the artificial cells to respond in the same way. All the benefits of stem cell research; none of the idiotic controversy. As for the signalling aspect, the artificial neuron could easily be programmed to respond to neurotransmitter signals from real neurons; the output, though, would have to be electrical, because I can't imagine an artificial way of synthesizing neurotransmitter. But real neurons can be stimulated just as well electrically as they can biochemically, so it would work just the same.