Biobots.

A biobot, or biological robot, is a small body made of living cells that moves and acts on its own, built in a lab rather than grown by an animal. The cells are ordinary: nobody edits their DNA. What’s new is the arrangement, and with it behavior the cells never show in the animal they came from. Biobots are a fraction of a millimeter across, live for days to weeks on the energy stored in their cells, and break down when they stop.

They matter for two reasons. As tools, they hint at living machines that could clean, carry or repair. As science, they show what cells do when released from their usual body plan: the same genome building something different, which asks how much of form and behavior is written in genes and how much is worked out by the cells together.

Most biobots swim with cilia: hair-like projections that beat in waves, many to a cell on the multiciliated cells that cover part of the surface. At this size water is thick: a body stops the instant its cilia stop, as a spoon would in honey, with no coasting. So a bot’s path is set directly by where its ciliated cells sit and which way they beat. A body whose cilia push evenly swims straight; a slight twist in the beat turns it into a circle; an uneven, lopsided body wiggles or spins. Real bots also roll and tumble in 3D.

Xenobots are built from embryo cells of the African clawed frog, Xenopus laevis, a standard lab animal. The first, in 2020, were designed in simulation by an evolutionary algorithm and assembled by hand from skin and heart-muscle cells, the heart cells’ contractions doing the pushing (Kriegman, Blackiston, Levin and Bongard). A year later the same group found that a patch of embryo skin left to heal folds itself into a sphere covered in cilia, and swims: no assembly needed (Blackiston and colleagues, 2021).

Their best-known trick is kinematic replication. Put xenobots in a dish with loose frog cells and, as they swim, they sweep the cells into piles; the piles round up and mature into new xenobots, which can do the same. C-shaped (“Pac-Man”) parents, a shape found by computer search, gather bigger piles and keep the process going for more generations (Kriegman and colleagues, 2021). The offspring inherit nothing from their parents, though: every pile becomes a sphere whatever built it.

Animal cap

The patch of embryo skin xenobots are made from.

Kinematic replication

Making copies by gathering material, not by growing or dividing.

Pac-Man shape

The C-shaped body that replicates best, found by an AI search and then built.

Anthrobots are built from adult human cells: the cells lining the airway (trachea), which carry cilia to sweep mucus out of the lungs. Grown in a gel, the cells form balls with their cilia pointing inward; changing the conditions turns them inside out, cilia outward, and they start to swim (Gumuskaya and colleagues, 2023). They come in different shapes and move in distinct ways: circling, going straight, or wiggling. Laid on a scratched sheet of human neurons, groups of anthrobots helped the neurons grow back across the gap.

A follow-up reported that anthrobots test younger, by an epigenetic clock (an estimate of age from chemical marks on DNA), than the adult cells they were made from: about 25% younger. Why is unknown.

Neurobots are xenobots with a nervous system. While a xenobot forms, a clump of neural precursor cells is placed inside it; the cells become neurons, grow processes through the body and toward its surface, and fire (Fotowat and colleagues, 2025). Neurobots grow larger and longer than plain xenobots, with fewer ciliated cells per area, move differently, respond differently to a seizure-inducing drug, and turn up genes for nervous-system development, synapses and even light sensing. Whether the neurons control the cilia, or change movement some other way, is the open question.

• Whether biobots sense their surroundings and respond, beyond the shape-driven paths their cilia produce.
• Whether their behavior falls into real classes, or a continuum that looks like classes.
• What, if anything, could let offspring inherit from parents. Without inheritance there is no evolution: one reason they are considered safe.
• How neurons in a neurobot affect its movement, and why anthrobots test young.

• Replication Arena: xenobot-style kinematic replication, and Pac-Man parents.
• Biobot Tierra: what invented kinds of inheritance would add to that replication.
• Petri Ecology: communities of biobot species.
• Morphospace Atlas and Chip Archipelago: evolved soft bodies, and bodies evolving with microfluidic chips.
• Anthrobot Lenia, Growing Anthrobots and the Rejuvenation Field: anthrobot motility, growth and age.
• Neurobot Motion: how neurobots’ movement was measured.

Sources: Kriegman et al. (2020); Blackiston et al. (2021); Kriegman et al., kinematic self-replication (2021); Gumuskaya et al., anthrobots (2023); Tufts, on anthrobot age; Fotowat et al., neurobots (2025).