Proof of concept: self-organized production units Self-microfabrication has yet to be fully established. While many examples exist to demonstrate parts of the approach , the hair follicle organoid is the most comprehensive example yet 2 . This organoid self-organizes from human pluripotent stem cells (hPSCs) to produce a hierarchical material: the multilayered hair shaft. It illustrates how relatively simpler engineered conditions can give rise to a highly complex organ producing material (Fig. ). The hair complements the spider silk example by demonstrating a material produced within cells, rather than externally. We describe the hair follicle organoid development in detail to showcase the complex autonomous processes occurring during organogenesis. Hair organoid in vitro growth begins with the aggregation of hPSCs, recapitulating normal stages of embryonic development 254 by differentiating into various cell lineages 255 (Fig. ). A spheroid forms and creates an inner cavity 256 . Mesenchymal cells migrate outwards and selforganize in the dermis while the inner surface ectoderm gives rise to the epidermis 2 . Hair placodes appear, develop into hair germs and bulge out in hair pegs to form the dermal papilla (DP) and bulge 256 . Hair-bearing follicles eventually grow out, each containing tissue-specific stem cells that can be maintained in vitro for half a year . Within each follicle, a hierarchical material is produced -the hair shaft -implying a complex multicellular regulation of the keratinization process 257 . Hair follicle organoids replicate cell types found in vivo 258 and mimic the 3D organization of the real organ, such as DP, melanocytes, and surrounding connective tissue 259 . Even the follicles' patterning is reproduced, with regular intervals between them 260 . This example demonstrates that complex production units can self-organize from stem cells and assemble microstructured materials.