When I was a kid in the 80's there were a number of gross/gore/horror trading cards for kids - Garbage Pail Kids being the prime example. One of the sets I had was set in some far flung future, I can barely remember the series but part of the theme were living, biological machines. The only card I can clearly remember featured a flying prisoner transport where the prisoners were seated in the ships cavernous stomach and "if upset during transport could accidentally digest the prisoners." (Honorable mention to HL2 featuring "synthtech" - the drop ship, strider and gun ships were living biological machines.)

This stuck in my head as the idea of designing machines which grow like plants or raised like animals was an incredibly amazing and interesting concept. But as I got older and educated the idea them seemed as far flung as the cards themselves. Though reading you post makes me think, maybe they aren't so far flung after all. Though I still fell that a creature which grows steel or titanium skeletons is still quite firmly in the realm of sci-fi.