I don't think the size of the structure is that important, although there must be some lower limit.
The definition of what is and isn't alive is a difficult one, some people say the ability for a system to reproduce its self is the only criteria. For instance are viruses alive? (The herpes virus measures only 100 nanometres across} they contain genetic information but can only reproduce inside a host cell.
Plenty of people are working towards creating self reproducing man-made systems and I don't think it will be long before someone succeeds if they haven't already:-)
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The definition of what is and isn't alive is a difficult one, some people say the ability for a system to reproduce its self is the only criteria. For instance are viruses alive? (The herpes virus measures only 100 nanometres across} they contain genetic information but can only reproduce inside a host cell.
Plenty of people are working towards creating self reproducing man-made systems and I don't think it will be long before someone succeeds if they haven't already :-)