We can now make objects move through water just by shining a light through them, no matter their shape.
April 17, 2026
Original Paper
Light-propelled microparticles based on symmetry-broken refractive index profiles
arXiv · 2604.14917
The Takeaway
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.
From the abstract
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