Cell jet printers
While printing with various kinds of molecules instead of ink has already become a routine procedure listed in textbooks, printing cells is a different matter. Depending on the type of inkjet printer chosen, cells might suffer vibrations, heat or pressure at fatal levels. Thomas Boland and colleagues at Clemson University in South Carolina considered both piezo-electric and thermal inkjet printers for their experiments, but found that the vibrations in the former were too powerful. In the thermal printer, temperatures can rise to around 300°C, but the researchers reasoned that the fast flow of the solution might ensure that the cells do not spend too much time in the dangerous heat zone.
Having previously shown that bacterial cells are still viable after passing through an inkjet nozzle (1), Boland's group has now taken on the bigger challenge of mammalian cells, represented by Chinese hamster ovary (CHO) and rat motoneuron cells (2). For each cell type, they specifically designed - in lieu of printing paper - a hydrogel material that would prolong cell survival after printing. Thus equipped with printer, biological 'ink' and suitable 'paper', the researchers started printing. They found that more than 90 per cent of the cells survived the process. Cultivating the printed patterns over several weeks, they observed the normal behaviour expected for each cell type, eg the neurons made new connections with each other.
Biophysicist Peter Fromherz, whose work involves growing nerve cells in specific patterns such that they can be connected to electronic components (Chemistry World, September 2004, p30) is not going to switch to the inkjet method yet. 'Nothing is shown with respect to guided growth of nerve cells,' he sighs. 'Things are not so simple.'
But simple things are where one has to start. So far, the researchers have printed the cells only in a ring-shaped pattern. The next challenge will be to extend the method to biologically meaningful patterns including tissue structures and arrangements including more than one cell type. Using a four-colour inkjet cartridge, a colour coded diagram on the computer screen could be directly converted into a living tissue on the gel substrate.
1 E A Roth et al., Biomaterials, 2004, 25, 3707
2 T Xu et al., Biomaterials 2005, 26, 93