ABSTRACT
Injection moulding of Lab-on-a-chip devices provides planar channel structures, similar to those produccd by cast moulding and lamination, but offers the additional benefit of incorporating other elcments in the third dimension. The simplest cxample of this is to directly form the sample and reagent reservoirs within the substrate half that defines the separation channels in an ITP device. The choice of fabrication matcrials allows for the mass production of very low cost devices. Polymers, such as polycarbonate, polystyrene, and PMMA, are readily available as medical grade granules, and are well suited to the manufacture of miniaturized devices. Typical labon-a-chip dcvices have been injection moulded from polystyrene, onto which is laminated a sealing cover, using a compression adhesive polyester laminate film (Plastic Art, Manchester, UK). This work has used a Babyplast (Cronoplast S.A., Spain) automatic injection moulding machine, which is a precision micro-injection moulder with a shot size of up to 7g. Tool platens have been made to accommodate planar tool inserts (J.E.T. Ltd. UK), to allow rapid changeover of mould tools. This has enabled a route for rapid prototyping of injection moulded designs for Lab-on-a-chip deviccs, such as the ITP and t10w cytometer systems described. The tool inserts are machined in-house with a CAT 3D (Datron. UK) precision milling machine, with feature sizes down to lO~m possible (the milling machine has a repeatability of 3 ~lm). The tool inserts are made from prc-cut brass blocks and are polished by hand to remove any burring left from thc milling opcration. Dcsigns are created using AutoCAD Mechanical Desktop v5.0 (Autodesk, San Josc. CA. USA) and tools-paths computed with EdgeCAM v.6.75 (Pathtrace, Reading, UK) for any specified milling tool. In our work many designs are cut with a Imm end mill with a 2° tapered draft angle to facilitate clean ejection of the device from the mould cavity. Although 1 OO~m end mills are available, the selection of the Imm mill is a sensible compromise between the minimum fcature radius of 500~m, the time required to cut a tool insert, and allowance for tool
wear. This work employed polystyrene (Northern Industrial Plastics, Chaderton, UK) for the bulk of the lab-on-a-chip devices, and 40% carbon fibre loaded high-impact polystyrene (RTP 487, RTP Company UK Plastics, Bury, UK).
