We can now make objects move through water just by shining a light through them, no matter their shape.
Usually, light-powered motors require very specific, asymmetric shapes to catch the 'wind' of photons. These researchers 3D-printed particles that are perfectly round on the outside but have a 'broken' internal structure. This allows them to move simply by refracting light unevenly, decoupling how they look from how they swim. It is like a perfectly spherical car that can drive forward because its engine is built off-center inside. This could lead to 'smart' drugs that navigate through your bloodstream steered entirely by external light.
Light-propelled microparticles based on symmetry-broken refractive index profiles
arXiv · 2604.14917
Active colloidal microparticles require reliable actuation to sustain directed motion. Light-based propulsion is particularly attractive as it provides persistent energy supply and enables direct spatiotemporal control. Here, we introduce 3D-printable particles with symmetry-broken refractive index profiles (SBRIP particles) that achieve propulsion through direct momentum transfer from asymmetric light refraction. Internal refractive-index gradients provide optical symmetry breaking independent