Engineering human tissues and 3D printing are at the forefront of medical research, and the technologies are now critical tools used to advance medical knowledge in general. Shortages of available organs for transplant, issues with tissue rejection and testing crucial drugs are hampered by current methods.

Current process used in bioprinting cells for tissues or organs are limited in that the process itself can't be modified or reversed if it goes wrong. If an ejected droplet of material is misplaced on the first pass, bioprinting can fail.

Now researchers at Brigham and Women's Hospital and Carnegie Mellon University have devised a micro-robotic technique they use to assemble and manipulate various components into complex materials.

Published in the journal Nature Communications, the latest work from Savas Tasoglu, a research fellow in the BWH Division of Renal Medicine, and Utkan Demirci, an associate professor of Medicine in the Division of Biomedical Engineering at BHW, in collaboration with Eric Diller and Metin Sitti from the Department of Mechanical Engineering at Carnegie Mellon University, describes a process which will allow scientists to manipulate cells in three dimensions.

The generation of three-dimensional functional materials made of both soft and rigid microstructures has proved challenging to researchers. This latest work imagines a method to literally code complex materials which can then have their structure, morphology and chemical features tuned using an untethered magnetic micro-robot which is remotely controlled by magnetic fields.

The scientists say this new strategy calls for a micro-robot to be dropped into a microfluidic environment. Soft hydrogels, rigid copper bars, polystyrene beads and silicon chiplets are used to create three-dimensional heterogeneous structures for later manipulation.

The micro-robot, remotely controlled by magnetic fields, can move a single hydrogel at a time. In tissue engineering, different types of cells can be manipulated at various levels and locations, which allows researchers to precisely impact how these structures will function.

It's a high-precision approach which provides designers the ability to code a combination of soft and rigid materials together at resolutions in the tens of microns and the methodology can be adjusted with the size of the micro-robot and monitored with real-time imaging.

"The micro-robot can scan among cells, manipulate them, remove targets or change their orientation at a scale that we could not control before," Demirici says. "It can be thought of as a 'microscale tweezer' that can pick and move cells and cellular aggregates in a 3D fashion."

The researchers add that groups of micro-robots could also be used as a team to create designs which can then be input to a bioprinter to generate tissues and other complex materials in a laboratory environment.

"Compared with earlier techniques, this technology enables true control over bottom-up tissue engineering," Tasoglu said.

According to Tasoglu and Demirci, the work can be performed without affecting cell vitality and proliferation.

They say the technology will ultimately be commercially available as a 3D printer and used to supply various cell types and aggregates for the micro-robot to precisely place them in a 3D configuration. The method is aimed at creating scaffold-free, high-cell-density constructs to mimic the native microenvironment and microarchitecture for applications for in-vitro testing of drugs.