How do we design with materials that have their own agency?

Human-designed objects have traditionally been constructed of relatively inert matter, and some recently examples been enhanced using stimuli-responsive ‘active matter’. Biotechnology offers the opportunity to consider living cells as constructional matter. However, living cells are distinct from familiar categories of matter because they were once independent organisms themselves. Construction with living cells involves cybernetic and behavioural concepts as well as the laws of mechanics: cells are ‘agential matter’. They make decisions and solve problems in ways that can be exploited by engineers, much as they have been exploited by evolution in creating multicellular organisms. Building with agential matter poses unique challenges, requiring the bioengineer to tame collective behaviours of cellular swarms by exploiting techniques of top-down control (behaviour-shaping signals) alongside bottom-up reconfiguration of molecular hardware. However, exploiting the multiscale competency of life offers unprecedented opportunities for engineering, regenerative medicine, and robotics. Agential materials have transformative potential but require complex design methods that go beyond our current methods of engineering and the reductionism present in biological research. We invite contributions that design, explain or test these methods.