The engineering of living organisms by way of controlled jet approaches is rapidly becoming an area of intense re- search interest as these technologies are explored as a possible means of fabricating three-dimensional tissue structures and organs. One jet process that has received considerable attention is the printing technique referred to as ink-jet printing [1]. In its biological applications, a cellular suspension containing living organisms is squeezed through a needle, either by piezoelectric or ther- mal technology, and a droplet is formed. This droplet is then deposited, via a computer-controlled plotter device, at a desired location, generating either two- or three-di- mensional tissue constructs through the deposition of several layers of droplets upon one another [2, 3]. This technique embraces the solid freeform fabrication con- cept, which builds a structure either by means of a line, point or planar without the aid of a mould. This applica- tion of ink-jet printing has been a great success and sev- eral research groups around the world have generated a variety of architectures from a range of biomaterials (from biopolymers like collagen to living organisms) through to bio-compatible materials (hydroxyapatite, etc.) using this route (see articles by Boland et al., and Sumerel et al., in this issue of the Biotechnology Journal). However, the res- olution of ink-jet printing is restricted to the micrometer level. The success of these first generation studies has led to the investigation of alternative, higher resolution, jet- based technologies for bioengineering applications. Electrospray [4, 5] is a jetting technology that pos- sesses the requisite level of resolution and the capability to handle highly concentrated suspensions containing advanced materials [6, 7], but, until recently, this tech- nique was not applied to living organisms. Although, like ink-jets, cell-containing droplets are formed by means of needles, the driving forces of electrospray technology arise primarily by the charging of the suspension con- taining the living organisms. By exposing the suspension to an external electric field, forces promote the formation of jets that undergo instabilities, brought about by either Short Communication Bio-electrosprays: The next generation of electrified jets Suwan N. Jayasinghe 1 and Andrea Townsend-Nicholson 2 1 Department of Mechanical Engineering, University College London, London, UK 2 Department of Biochemistry and Molecular Biology, University College London, London, UK Biological electrosprays are rapidly becoming a robust means by which to engineer living organ- isms for applications ranging from tissue repair to developmental biology. We previously report- ed the ability to electrospray living organisms without compromising their viability, but found it challenging to achieve stability in the jetting of these organisms as a result of the chemical prop- erties of the living cellular suspensions. Jet stability is required for the generation of a near-mono distribution of droplets, which is necessary for the development of electrospray technology as a “drop and place” biotechnique. Recently, we determined the conditions needed to achieve jet sta- bility and were able to generate droplets with a near-mono distribution (<50 μm). In this commu- nication, we elucidate the relationship between jet behaviour and droplet size under stable jetting conditions, with a view to further reducing the droplet size to deposit a single living cell within a droplet. We believe that this level of resolution will make electrospray jetting superior amongst the jet-based biotechnologies presently being developed for the engineering of biological architectures comprised of living cells. Keywords: Active biological structures · Bio-electrosprays · Drop and place fabrication · Engineering living organisms · Bionanotechnology Correspondence: Dr. Suwan N. Jayasinghe, Department of Mechanical En- gineering, University College London, London, WC1E 6BT, UK E-mail: s.jayasinghe@ucl.ac.uk Fax: +44-207-3880180 Abbreviation: PDMS, polydimethylsiloxane Received 13 July 2006 Accepted 13 July 2006 Biotechnology Journal DOI 10.1002/biot.200600128 Biotechnol. J. 2006, 1, 1018–1022 1018 © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim