Scientists have crossed a startling new frontier in bioengineering: they can now fabricate intricate three-dimensional objects inside living cells. Instead of sculpting tissue from the outside, they are effectively building microscopic tools, tags, and even whimsical shapes directly within the cell’s own interior. The work hints at a future in which the machinery of life can be customized from the inside out, with precision measured in micrometers.
The most eye-catching proof of concept is a tiny elephant, 3D printed inside a human cell, but the real story is the technique behind it and what that method could mean for medicine, basic biology, and even computing. By shrinking industrial-grade 3D printing into a form gentle enough for fragile cells, researchers are turning the cell itself into a construction site.
How to 3D-print an elephant inside a living cell
The core trick is to bring a standard 3D printing workflow into one of the most delicate environments imaginable, the cytosol of a living cell. Physicist Matjaž Humar and colleagues first inject a liquid photoresist into the cell, then use a tightly focused laser to solidify that material voxel by voxel into a chosen shape, including a microscopic elephant that fits comfortably inside a single human cell. The team’s approach relies on carefully controlling how the photoresist spreads and how the laser energy is delivered so that only the intended regions harden while the rest of the material remains fluid and can later disperse, a process described in detail in their work on structures inside a.
Because the laser is focused so sharply, only a tiny fraction of the injected photoresist solidifies at any given moment, which allows the researchers to draw features far smaller than the width of a human hair. The resulting elephant, along with other microstructures, is built layer by layer using this two-photon polymerization process, which activates the photoresist only at the exact focal point of the beam. As a result, the team can create complex 3D geometries, including microlasers and barcodes, inside living cells without destroying them, a capability that has been highlighted in coverage of the laser’s beam.
From microlasers to barcodes, cells become tiny factories
While the elephant grabs headlines, the more consequential creations are functional devices like microlasers and optical barcodes that can operate from within the cell. Using the same printing strategy, the researchers have fabricated microstructures that act as tiny light sources and identifiers, effectively turning individual cells into tagged, trackable units. These internal barcodes can encode information about the cell’s identity or treatment history, and they can be read out optically without needing to stain or genetically modify the cell, as shown in work where new tech created inside living cells.
The same platform has been used to embed microlasers that exploit the cell’s own environment as part of the optical cavity, producing light that carries information about local conditions. In some experiments, the printed structures include tiny barcodes and laser elements that remain stable as the cell moves, divides, and responds to its surroundings, effectively turning the cytosol into a microfabrication lab. Reports on these experiments describe how elephant is among several microstructures, including functional optical components, that can be produced in this way.
The physics behind two-photon printing in the cytosol
Technically, the breakthrough rests on adapting two-photon polymerization, a method normally used to print micrometer-scale objects in resin, to the cramped and curved interior of a cell. In conventional setups, the resin is static and the optics are carefully aligned, but inside a cell the photoresist droplet is curved and the refractive index varies, which can distort the laser focus. To address this, the team used simulations and microscopy to assess how the droplet shape would bend light and to quantify any focus shift, then tuned their system so that the laser still triggered polymerization only at the intended point, a strategy described in detail in work that relied on simulation and microscopy.
Two-photon polymerization has been used for years to build intricate microdevices outside of cells, but applying it inside living systems required rethinking both the chemistry and the optics. Researchers had to identify photoresist formulations that would remain inert until illuminated, then solidify rapidly without releasing toxic byproducts, and they had to deliver laser pulses that were intense enough to trigger polymerization yet gentle enough to avoid killing the cell. A recent overview of this approach describes how a novel method finally made it possible to insert microlasers and even an elephant directly into the cytosol of living cells.
Keeping cells alive while turning them into construction sites
Printing inside a living cell is only meaningful if the cell survives and continues to function, so the researchers devoted significant effort to testing biocompatibility. They evaluated how cells responded to the injected photoresist, the laser exposure, and the presence of solid microstructures, tracking survival, division, and behavior over time. In one set of experiments, the team printed multiple examples of the same structure inside human cells and then monitored whether those cells could still divide and maintain normal morphology, a milestone that has been described as the first time they were able to 3D print microstructures inside living human cells while those cells remained alive.
To quantify safety, the group drew on established methods from nanomedicine, including cytotoxicity evaluation and luminescence microscopy in Human cervical cancer cells such as HeLa. These assays measure how many cells die, how their metabolism changes, and whether their internal structures are disrupted after treatment, providing a rigorous check on whether the printing process is tolerable. Earlier work on nanomaterials used similar cytotoxicity evaluation in Human cells to validate new materials, and the 3D printing researchers have followed that template to show that their photoresists and laser doses can be tuned to keep cells viable.
Why intracellular 3D printing matters for medicine and beyond
The ability to sculpt custom structures inside cells could reshape how scientists study and treat disease. In cancer research, for example, internal barcodes and microlasers could let clinicians track how individual tumor cells respond to drugs in real time, rather than averaging signals across a whole tissue sample. The same technique could be used to build scaffolds that steer how a cell organizes its internal components, potentially nudging stem cells toward specific fates or stabilizing fragile therapeutic cells used in treatments. Commentators have already noted that 3D printing has many scientific fields, and shrinking it into the intracellular realm extends that revolution into the basic units of life.
There is also a broader technological arc at work, as researchers refine the method and explore new materials and applications. Recent reports describe how researchers develop new to 3D print micrometer-sized structures within cells, building on the initial demonstrations of elephants and microlasers. Other coverage has highlighted how researchers found that cells can tolerate a surprising variety of internal shapes, and how illustration of the elephant has become a symbol of this new capability. As the field matures, I expect the playful shapes to give way to highly engineered intracellular devices, but the underlying idea will remain the same: using light to write new structures directly into the living fabric of the cell.
More from Morning Overview