Most of us are used to hearing about 3D printing in factories or in makerspaces, not inside the tiniest units of the human body. Yet that is exactly what a team in Slovenia has done by using a finely-tuned laser to build solid three-dimensional objects inside living human cells.<\/p>\n\n\n\n
The work, led by physicist Maru\u0161a Mur<\/a> at the Jo\u017eef Stefan Institute together with colleagues at the University of Ljubljana and CENN Nanocenter, shows that custom shaped microstructures can be printed directly inside living HeLa cells using a laser technique known as two-photon polymerization<\/a>.<\/p>\n\n\n\n The researchers report that many cells survive the procedure and keep dividing, suggesting a new way to engineer cell interiors in a controlled way.<\/p>\n\n\n\n Human cells are tiny, roughly twenty micrometers across, about one fifth the width of a human hair. Inside that cramped space sit the nucleus, mitochondria, and many other components, all swimming in cytoplasm, the fluid interior of the cell. <\/p>\n\n\n\n Trying to park a solid object in that crowded room without breaking something has been a long-standing problem.<\/p>\n\n\n\n Until now, most methods either brought in small molecules or genetic material, or relied on the cell itself to swallow particles from the outside. When immune cells engulf foreign material, they wrap it in a membrane bubble, which keeps it locked away from the rest of the cytoplasm.<\/p>\n\n\n\n Techniques that punch temporary holes in the cell membrane can deliver cargo, yet free-standing solid structures tend to cause serious damage or end up trapped in compartments.<\/p>\n\n\n\n The Slovenian team approached the problem in a different way by building the object inside the cell rather than trying to push it in from outside. First they microinjected a droplet of a light sensitive resin called IP S into individual HeLa cells using ultra-fine glass needles. <\/p>\n\n\n\n The resin was chosen because it is relatively well tolerated while still liquid, becomes non toxic once hardened, and slowly dissolves if it is not fully solidified.<\/p>\n\n\n\n Once the droplet was in place, the scientists focused an ultrafast infrared laser into it through a high precision microscope. <\/p>\n\n\n\n Two photon polymerization means that the resin hardens only at the exact point where the laser light is most intense, where two packets of light are absorbed almost at the same time. By steering that focus through the droplet layer by layer, they could trace out complex three-dimensional shapes while leaving the surrounding cell interior mostly untouched.<\/p>\n\n\n\n To show what is possible, the team printed a hollow sphere, lattice-like scaffolds, barcodes for tracking cells, tiny optical components, and even a ten micrometer long model of an elephant.<\/p>\n\n\n\n Imaging confirmed that these solid structures sat freely in the cytoplasm and that the nucleus often bent and shifted to make room for them. At the end of the day, the cell looked like it had been furnished with custom-built microscopic furniture.<\/p>\n\n\n\n A natural question follows. If you build a rigid object inside a living cell, does the cell survive? The answer is mixed but informative. <\/p>\n\n\n\n After twenty four hours, about half of the cells that received an injected droplet and a printed structure were no longer viable, a rate similar to cells that only experienced the needle injection without any printing. That pattern suggests that the main damage comes from piercing the membrane, not from the light or the hardened resin.<\/p>\n\n\n\n For the most part, the surviving cells kept their usual appearance and behavior. Time lapse videos showed them moving, dividing, and passing the printed object on to one of the daughter cells during mitosis. <\/p>\n\n\n\nWhy putting solid objects inside cells was so hard<\/h2>\n\n\n\n
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How the laser-based 3D printing method works<\/h2>\n\n\n\n
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How cells react to tiny structures inside them<\/h2>\n\n\n\n