US scientists are creating tissue mimics by fixing together tiles of cells.

To create synthetic tissue researchers need to control where each cell is placed and which type of cell is used at each site. Holographic optical tweezers provide one method of manipulating cells in this way; however, this approach uses optical-trap lasers and prolonged exposure to these damages cells. 'The trouble with optical tweezers is that they kill things,' explains Gregory Timp of the University of Illinois of Urbana-Champaign, who led the team behind the research. 'We're looking for the gentlest possible way to position cells in a tissue.'

Cells are moved into an array and fixed into position with a hydrogel that mimics the extracellular matrix surrounding cells in real tissue

With this in mind, Timp and co-workers designed a microfluidic system to move cells that minimises their exposure to optical tweezers, limiting the photo-damage.The device uses the tweezers to move cells before fixing them in position with a photopolymerisable hydrogel. Repeating this process allows the team to assemble microscopic tiles of cells which they can arrange - without optical tweezers - to create a larger structure. By using Escherichia coli cells engineered to produce fluorescent proteins the team could easily prove that the new structure was made of living cells.

Isaac Kuo-Kang Liu an expert in biomedical engineering at Keele University, in Newcaster-under-Lyme, UK, suggests the new micro-fabrication technique could eventually allow scientists to prepare synthetic tissue for medical applications. 'Such a high throughput and cell-friendly method for making tissue constructs will create a new paradigm for tissue engineering and regenerative medical applications,' he says.

Martin Gijs, an expert of microfabrication at the Swiss Federal Institute of Technology in Lausanne, points out that the technology could also allow scientists to analyse biological responses in biofilms - arrangements of single-celled organisms such as bacteria. He explains that it could be used to study chemical gradients across a biofilm or monitor how biofilms respond to antibiotics. 'The method brings the generation of artificial tissue samples that can be used for in vitro assaysand in drug discovery one step closer,' says Gijs.

Russell Johnson