Synthetics are human-appearing androids. Grown from a few engineered DNA lines using stem cells, the physically adult fetuses are “petrified” with inorganic compounds to make them more durable and efficient. The organic body serves as a template for the inorganic final product. Their brains are wetware with some inorganic computer systems bridging gaps; these designs date from the transhumanist era, which is why “pure humans” or “human firsters” or “breeders” often harbor ill will to synthetics. All Synthetics constructed after 2103 are supposed to have hard-codes preventing self-engineering and instilling obsolescence: after the Sirian War, nobody wanted transhumanist bootstrapping happening again in superior bodies.
Synthetics require human stem cells to reproduce; given their hard-coded limits, they often require human (or illegal AI) bio-informaticists to program the DNA line as well. Without a source of stem cells (humans), Synthetics are forced to rely on a much dodgier method of reproduction: 3D printing. When Synthetics are built this way, rather than grown, problems arise because the resolution is not reliable enough for consistent neurological fidelity. Abcesses form when nanomachines are tardy, and subsequently blocked out of their proper position. This leads to high incidents of neurological defects amongst Synthetics constructed this way, and represents a source of division amongst Synthetics (between those that want to euthanize the defects because they represent an aberration vs. those who want to see Synthetic individuals given the same respect as other expression of life, and so view this Eugenic purging as complicit with the human first dogma).