In a step towards cell mimics, an inkjet printer is being used to make lipid-coated balls containing proteins. 

Daniel Fletcher from the University of California in Berkeley and coworkers from the US and France, developed the method to make single-lipid vesicles - fluid spheres encased in a lipid bilayer. 

Fletcher explains that the work's significance is in allowing them to load complex biomolecular mixtures into cell-like particles. 'Despite the recent achievements of genetic engineering,' he comments, 'it remains a significant challenge to harness and amplify useful cellular functions, while attenuating peripheral functions and keeping the cell alive.' An alternative approach is to create more sophisticated cell mimics. 'This method will enable the construction of cell-like synthetic structures of unprecedented complexity and potential,' says Fletcher. 

Each vesicle is formed when a set of pulses is applied to the inkjet, creating a jet of fluid. The inkjet is directed so that the fluid, which contains a protein, crosses a planar lipid bilayer, which then deforms to form protein-containing vesicles. 

Increasing the number of pulses in a set increases the vesicle diameter, allowing the researchers to tune the vesicle size, offering an advantage over the researchers' previous microfluidic method for preparing vesicles. Thomas Pfohl, at the University of Basel, Switzerland, whose research area is in the dynamics of biological matter and microfluidics, explains that this allows the researchers to form and load uniform vesicles with 'a huge variety of diameters - from cell-sized to giant.' 

The inkjet approach also allows faster vesicle production, as pauses between the pulse sets can be tuned to adjust the vesicle formation frequency. Currently several vesicles can be produced at a rate of 200Hz, followed by pauses of two to four seconds. Pfohl adds that future challenges could be to find the right experimental parameters to make this a continuous process. 

Pfohl suggests that 'the method opens a wide range of new and exciting fundamental research and applications.' Something Fletcher's team intends to pursue. 'The initial application of our work will likely be the bottom-up reconstitution of biological processes in order to gain fundamental scientific insights,' says Fletcher. 'For example, to find the role of specific biochemical components in a process or the necessary and sufficient components to recreate a specific cellular function. Further applications of our technique could include designing smart therapeutics that encapsulate drugs and guide them to specific delivery sites within the body.' 

Mary Badcock

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