Fungi-based prosthetic system
Paste limbs are the lowest-tier prosthetic option available. They're built on a genetically modified yeast strain engineered with chitin-synthase genes and receptors for human growth factors. You buy a skeleton frame, coat it in paste, strap it to your stump, and wait.
Hyphae navigate toward nerve signals using three systems simultaneously - chemical gradients from growth factors, galvanotropism toward the weak electrical fields your damaged nerves still produce, and mechanoreception along tension lines when you try to move the missing limb. Tissue differentiates based on impulse frequency: high-frequency zones grow contractile fibers, constant-tension zones grow dense collagen-reinforced bundles. Your capillaries grow into the chitin matrix. Your nerves follow. A few weeks later, you have a limb.
Three major strains exist on the market:
Big John (street: "the blob" or "the dietitian's hand") - a mass-building strain optimized purely for bulk. Without regular trimming of stray hyphae, it grows chaotically - enormous blisters, tissue packed around joints where it anatomically shouldn't be. Powerful and graceless. A clear sign you couldn't afford better.
Gold Rush (street: "the rash") - a sinew-focused strain. Limbs grow dense with cord-like golden filaments running the full length. Its signature feature: soft fungal nodules develop on high-impact areas - knuckles, fingertip pads - like natural armor that adapts to how you live or fight.
Lasagna Blue (street: "the cabbage") - Layered, dense, blue-green. Exceptional regeneration and damage resistance, poor strength and speed. Nearly unkillable, barely useful. Named for its cross-section, which looks exactly like what it sounds like.
The deeper problem is what happens to your soul.
In this setting, the body runs a contour - a network of nodes that conducts plasma. A lost limb leaves an active node searching for closure. Fungal tissue, threaded with your own nerves, can partially close that circuit, killing phantom pain and giving basic motor control. But the yeast colony carries its own soul - primitive, nonsentient, thin-membraned - and yours becomes entangled with it.
Long-term users report dulled cold sensitivity, an unaccountable pull toward damp spaces, and occasional dissociation. A "vegetative fog" that isn't quite theirs.
Practitioners who work with plasma avoid paste limbs entirely. Any procedure risks hitting the fungal soul instead of the human one - either necrotizing the colony and killing the limb, or amplifying the fungal emanation and temporarily overwriting the user's will with something slow and rootbound.
Street operators who try anyway almost always make it worse.
Socially, paste limbs are a class marker as much as a medical device. The middle class avoids them. The upper class would sooner commission a full body regrowth than let fungus colonize their contour. For most people in this world, that option was never on the table.