The "missing body problem": cellular microenvironment When an organ is removed, or grown outside its native body, it requires specific signals to support its survival. Developing material-producing organoids encourages the study of CellµEnvs in non-model species, which can lead to unexpected breakthroughs . Key signals from the "missing body" can already be studied, independently from other selfmicrofabrication challenges, using transplants 496 and ex vivo explant cultures 497 . Before growing material-producing organs, explants serve as effective in vitro models to examine their physiology and characterize essential CellµEnv factors for survival 498 . To demonstrate this principle, we have developed a spider silk gland explant that spins fibers in vitro. The MA glands are extracted and cultured in a dish, preserving all structures intact, i.e. tail, ampulla, duct, spigot and the 2 µm diameter threads. Pulling the hanging fibers (the spinning trigger) produces new native spider silk. This explant first demonstrates that spider silk gland may produce material autonomously from the rest of the body and serves as in vitro model for this organ. Other material producing tissues could be studied with explants. As an example, developing a byssusproducing mussel foot explant could leverage existing culture media , growth factors , cell lines 503 and in vitro expression protocols . Other approaches can be considered to circumvent the "missing body problem". A material may be produced in a different organ with similar characteristics (e.g. ChemµEnv). For instance, growth factors and gene editing tools are available in silkworms but not in spiders. Thus, silkworms glands can be edited to produce a spider silk analogue 183 . Although the silk glands of spiders and silkworms have different phylogenies and embryogenic origins , their convergent evolution demonstrates material-processing similarities , enabling transgenic silkworms to produce exogenous materials . Edited spidroin, combined with a silkworm silk promoter, can be transfected in Bombyx mori's genome and sustained through generations, aiming to produce spider-silkworm hybrid fibers at industrial scales 183 . We call this approach "environmental transfer", for producing an exogenous material in an already similar organ. Rather than adapting a material to match a similar tissue, the opposite could be considered by editing an organ to produce the desired material. We refer to this as "environment morphism". This principle of changing the CellµEnv to affect a tissue's physiology is used in transplants 506 , tissue rejuvenation 244 and humanized mice 507 . A tissue can even change its anatomy following the addition of a single cell type, such as thickening skins following volar fibroblast transplantation 247 . Similarly, we suggest that self-microfabrication could eventually affect an organ's physiology to improve material processing.