German researchers have used 3-D printing to craft a microscopic camera small enough to pass through the needle in a syringe. To put it another way, the camera is something like the size of a grain of salt.

The micro build was described in an article in the Nature Photonics journal. The build team, comprising researchers from the University of Stuttgart, combined backgrounds in photonic engineering and technical optics in working on their design objective. The team constructed a three-lens camera and attached it to the end of an optical fiber with the diameter of two human hairs.

The University of Stuttgart press announcement said that this level of miniaturization "permits the construction of novel and extremely small endoscopes which are suited for smallest body openings or machine parts that can be inspected." Other potential applications could include installing micro-cams in drones the size of a bee, equipping tiny robots with "autonomous vision" sensors, and setting up virtually undetectable surveillance monitors.

For the general population, the most relevant application would seem to be the potential for minimally invasive medical probes for surgery and research on the human body. Since the camera is extremely miniscule, it can be injected into a bodily organ or even the brain using a standard medical syringe.

Phys.org reported that the entire project build, from design to manufacture to testing, took only a few hours. The process involved 3-D printing, which constructs three-dimensional objects by stacking up multiple layers of a material such as plastic or ceramic.

Technological limitations have prevented the manufacture of extremely compact lenses until now. The Stuttgart team's 3-D printing method was able to produce a compound lens with a width of only 120 micrometers (including its casing).

The 3-D printing method applies a femtolaser in hardening a liquid polymer that is set onto a glass substrate or an optical fiber. Once the laser beam has passed over, the unexposed polymer is washed off, leaving a hardened remnant that makes up the optical instrument.