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The plasmodium of Physarum polycephalum (Order Physarales, class Myxomecetes, subclass Myxogastromycetidae) is a single macroscopic cell which can grow to tens of centimetres in length (Stephenson and Stempen, 1994). The plasmodium feeds on bacteria and microscopic food particles by endocytosis; when placed in an environment with distributed sources of nutrients, the plasmodium migrates between each source via contraction of muscle proteins (Stephenson and Stempen, 1994), forming a network of interconnected protoplasmic tubes. Nakagaki et al. (2001) demonstrated that the topology of the plasmodium's protoplasmic network optimizes resource harvesting and increases the efficiency of intraplasmodial transport from the nutrient source to the rest of the plasmodium. In Adamatzky (2010a), we have shown how to construct specialised and general purpose massively-parallel amorphous computers from the plasmodium of P. polycephalum that are capable of solving problems of computational geometry, graph-theory and logic.
When the slime mould develops a network of protoplasmic tubes spanning sources of nutrients, the cell maintains its integrity by pumping nutrients and metabolites between remote parts of its body via cytoplasmic streaming (Allen et al., 1963; Bykov et al., 2009; Gawlitta et al., 1980; Hulsmann and Wohlfarth-Bottermann, 1978; Newton et al., 1977; Stewart & Stewart, 1959). This cytoplasmic streaming may be manipulated experimentally and employed for the transportation of exogenous bio-compatible substances inside the protoplasmic network: in Adamatzky (2010b) we demonstrated that the plasmodium of P. polycephalum consumes various coloured dyes and distributes them throughout its protoplasmic network. By specifically arranging a configuration of attractive (sources of nutrients) and repelling (sodium chloride crystals) fields, it is possible to program the plasmodium to implement the following operations: to take in specific coloured dyes from the closest coloured oat flake; to mix two different colours to produce a third colour; and, to transport colour to a specified locus of an experimental substrate. Transportation of colourings per se is of little interest but shows the potential of P. polycephalum as a programmable transport medium.
We propose that P. polycephalum’s potential for internalisation and re-distribution of foreign particles may be employed for the development of self-growing electronic circuits and/or hybrid slime mould-artificial computing devices, providing that the plasmodium may be manipulated to internalise and propagate suitable artificial circuit components. Inspired by our previous results (Adamatzky, 2010b) and studies on cellular endocytosis of magnetic nano-beads (Li et al., 2005) and fluorescent nano-beads (Bandmann et al., 2012), nanowire scaffolding for living tissue (Tian et al., 2012) and intake of latex beads by the amoeba's endocytotic mechanisms (Goodall & Thompson, 1971), we chose to focus on two types of materials: magnetic magnetite nanoparticles - because they can be used for in situ construction of basic nano-scale electronic devices - and glass microspheres coated with silver, because they have be used to grow conductive pathways, i.e. hybrid bio-artificial wires.