The ability to engage and inspire younger generations in novel areas of science is important for bringing new researchers into a burgeoning field, such as lab-on-a-chip. We recently held a lab-on-a-chip workshop for secondary school students, for which we developed a number of hands-on activities that explained various aspects of microfluidic technology, including fabrication (milling and moulding of microfluidic devices, and wax printing of microfluidic paper-based analytical devices, so-called μPADs), flow regimes (gradient formation via diffusive mixing), and applications (tissue analysis and μPADs). Questionnaires completed by the students indicated that they found the workshop both interesting and informative, with all activities proving successful, while providing feedback that could be incorporated into later iterations of the event.
Lab-on-a-chip is a powerful technology with huge potential for impacting diagnostics, chemistry, and biology,1–4 but even after developing to a great extent over the last quarter of a century5–14 and with commercialisation starting to really take off,15–18 the general public is still largely unaware of it. Many universities and institutes hold showcase events intended to instruct the public on the research being undertaken and its real-world applications, and more-and-more frequently, these events are being extended to incorporate activities for schoolchildren. Introducing schoolchildren to new areas of science beyond their curriculum is important in engaging and inspiring potential future researchers in exciting fields. However, this is easier said than done, since many aspects of science require a certain level of background knowledge and, while exciting to the researchers in a field, can sometimes be a “dry” subject when explaining to a wider audience. Thus, the challenge when discussing novel fields to children is to keep the main points simple, relevant, and as far as possible, jargon-free, while making them exciting and fun. This is best achieved by preparing hands-on activities that allow schoolchildren to experience a scientific concept in a fun way while being intuitively instructed in its fundamentals.
A literature search shows that a number of hands-on activities have been developed over the last decade or so to introduce scientific concepts, dealing with the fabrication, operation, and application of microfluidic devices, to schoolchildren, undergraduate students, and the general public.
Activities focussed on fabrication have been developed, for example, by Yang et al.,19 who prepared inexpensive moulds out of wooden coffee stirrers to form Jell-O chips as an analogy to the soft lithography fabrication of polydimethylsiloxane (PDMS) devices.20,21 Other groups have since utilised this methodology for their own educational experiments,22,23 while Jimenez and Bridle24 formed channels out of FIMO® soft polymer clay by moulding it around wooden structures. Nguyen et al.25 developed their shrink-film based microfluidic production technique26 for educational purposes to form a mould for PDMS, and this has been used by several groups.27,28 DeVore et al.29 and Berkowski et al.30 prepared photolithography experiments for students using positive and negative photoresists, respectively. Yuen and Goral31 demonstrated a low-cost glass fabrication technique for university students that utilised an inexpensive glass-etching cream available from stores.
A variety of hands-on microfluidic experiments have been demonstrated for educational purposes at various levels, employing conventional microfluidic devices or platforms fabricated via the above methodologies. Experiments have included laminar flow and diffusive mixing,19,27,32–35 gradient formation,28,36,37 droplet generation,23 pH sensing,28,33,35,38 particle separation,24,39 capillary electrophoresis,34,40,41 crystal precipitation,33 particle synthesis,27 chemical synthesis,27 water electrolysis,22 enzyme-linked immunosorbent assays (ELISA),42 and the modular construction of microfluidic setups and instrumentation (using LabSmith Inc. products).43
Paper microfluidics44–46 are also proving popular for educational demonstrations and experiments due to the ease and speed of fabrication, and the simplicity of experiments that can be performed. Devices have been fabricated by melting wax designs onto filter paper,47 punching leaf-shaped devices out of chromatography paper,48 using a PMMA (polymethyl methacrylate) stencil to draw designs onto filter paper,49 and by melting parafilm designs into tissue paper.50 Such paper microfluidic devices have been used to perform colourimetric assays of simple analytes in a range of common samples47,49,50 and to simulate forensic analysis of a mock crime scene.48
Recent examples of introducing microfluidic concepts to students have involved preparing apparatus and activities that often do not use microfluidic channels themselves, but rather simple and fun exercises demonstrating the core principles. For example, Drazer and Frechette51–53 developed a working analogy of the Deterministic Lateral Displacement (DLD) particle separation method54,55 using a pillar array fabricated out of Lego®. Heriot-Watt University (UK) has prepared several workshop events and activities for introducing microfluidic concepts to schoolchildren.24,35 In one instance, the group prepared three workstations with microfluidic devices that instructed students on (1) laminar flow, (2) mixing, and (3) DNA analysis using pH sensing as an analogue.35 Jimenez and Bridle24 from the same group reported a number of hands-on exercises for introducing the detection of waterborne pathogens56,57 to schoolchildren. Each stage of pathogen analysis was shown in an entertaining way, making good use of FIMO® soft polymer clay to fabricate microfluidic channels and to demonstrate immunomagnetic separation (IMS). For the IMS activity, clay was moulded around magnets to form spheres, allowing their separation from non-magnetic clay spheres, and this was shown in both an oversized Petri dish and an oversized microfluidic chip. Fluorescent FIMO® spheres were also used to mimic fluorescence microscopy. In addition, the group demonstrated a Lego® DLD array based on the aforementioned work.51–53
The University of Hull (UK) has been showcasing its research to the general public for several years. However, for the Hull Science Festival 2015 (#HullSciFest), held in March 2015,58 the microfluidics group at the University of Hull developed a one hour workshop for secondary school children (aged 13–14) with the purpose of instructing them in the design, fabrication, operation, and application of lab-on-a-chip technology in a fun and interesting manner that incorporated a variety of hands-on activities. In particular, the activities were intended to not only teach the students about lab-on-a-chip in general, but to highlight the microfluidic fabrication facilities at the University and the related research activities being performed. However, many of these processes have not been covered in the previous literature, while most of the reported educational experiments are aimed at a higher level than secondary school students or required setup and execution time frames that could not be achieved in a one hour workshop. Thus, a number of new hands-on activities had to be developed for the lab-on-a-chip workshop that were simple, exciting, informative, relatable to actual scientific concepts/techniques, and interactive, while being short enough (10–15 min each) to allow multiple activities to be performed in one hour.
The teaching outcomes of this exercise were actually two-fold, as a group of undergraduate project students were tasked with developing the activities, under the supervision of PhD students and PostDocs, as part of a group project titled “Explaining Lab-on-a-Chip to the Public”. Five workstation activities were developed that explained lab-on-a-chip using a mixture of analogous exercises and oversized devices that the schoolchildren could operate (Fig. 1). These activities taught the students about (i) the manufacture and prototyping of microfluidic devices by computer numerical controlled (CNC) milling, as demonstrated via the analogous use of a pantograph sketching apparatus, (ii) polymer injection moulding via chocolate moulding in silicone, (iii) paper microfluidics using wax crayon designs on filter paper, (iv) gradient formation using an oversized gradient chip, and (v) on-chip tissue studies using an oversized device.
II. MATERIALS AND SETUP
Yellow food dye powder (Tartrazine), blue food dye powder (Erioglaucine disodium salt), and red food dye powder (Erythrosin B) were purchased from Sigma-Aldrich (Dorset, UK), prepared in purified water, and then passed through 0.22 μm syringe filters (Millipore, Cole-Parmer, UK). pH indicator paper (Whatman) was purchased from VWR (UK). Filter paper discs (110 mm diameter, grade 390, Sartorius Stedim Biotech) were purchased from Scientific Laboratory Supplies (Nottingham, UK). Milk chocolate bars, fruit juices, lemon juice (as a source of citric acid), and wax crayons were purchased from local supermarkets. Paramount crystals (partially hydrogenated palm kernel oil combined with soy lecithin and citric acid) used for working with the chocolate were ordered from The Cake Decorating Co. (Nottingham, UK). Smooth-On SORTA-Clear 18 Translucent Silicone Mold Rubber, used for preparation of silicone moulds, was purchased from Bentley Advanced Materials (Worcestershire, UK).
B. CNC milling: Pantograph
“Baker Ross Scratch Art Doodle Sheets,” featuring a rainbow coloured sheet coated with a layer of black wax, and a “John Adams Sketch-a-Graph” pantograph were purchased from Amazon (UK). The scratch art sheets were cut to rectangular pieces of 10.5 cm × 7 cm. The pantograph was mounted to a square piece of board via one of its arms, allowing movement from a fixed point. A piece of steel rod (∼250 g) was machined using a CNC milling machine and placed over a blunted graphite nib in order to weight the nib down. The weighted nib setup was fixed to the end of a free arm of the pantograph for scratching designs into the scratch art sheets. Extra weight and stabilisation had to be added to the middle of the same arm, so an aluminium cylinder was milled and fixed underneath the arm to add support to the pantograph structure. A plastic stylus was fixed into the end of another pantograph arm, which was used to trace the designs from a reference image. An A4 size sheet featuring four common microfluidic chip designs (see Fig. S1 in the supplementary material)59 was printed, laminated, and taped to the board such that the chip designs were positioned beneath the plastic stylus, while a scratch art card was positioned and taped down beneath the weighted nib. The designs included (i) a serpentine channel, (ii) a Y-shaped channel, (iii) four straight, parallel channels, and (iv) a gradient channel design.
C. Injection moulding: Chocolate chips
Keyrings, fabricated in PMMA polymer and featuring the letters “LOC” (Lab-On-Chip) and a serpentine microchannel design, were manufactured in bulk to give away to students and the general public at the Hull Science Festival 2015. These were prepared by first designing a mould in SolidWorks (Dassault Systèmes SolidWorks Corporation, France) and creating a G-code for the design in SolidCAM (SolidCAM UK, Barnsley, UK). The G-code was transferred to a CNC milling machine (Datron M7, Datron, Germany), and the keyring mould was milled out of aluminium. The aluminium mould was fixed into an injection moulding machine (Babyplast 6/10P, Rambaldi+Co, Molteno, Italy) (Fig. 2(a)) and used to produce the keyrings (5.5 cm × 2.5 cm × 0.2 cm) from PMMA granules (Sabic, Middlesbrough, UK) (Fig. 2(b)).
Silicone moulds were prepared by placing the PMMA keyrings into the compartments of accessory boxes that featured adjustable plastic dividers. Each compartment had dimensions of 6.5 cm × 3.5 cm, and had a total of 18 compartments into which keyrings (minus the actual rings) were fixed using double-sided tape. SORTA-Clear® 18 is a silicone moulding rubber that is certified as being safe for food contact, and came in two parts (Part A and Part B). 80 g of Part A was mixed thoroughly with 6.5 g of Part B for at least 3 min, before being degassed in a vacuum desiccator. The vacuum was slowly increased to 0.9 MPa and held at that pressure for 10 min, before being slowly decreased. The silicone rubber mixture was poured over the keyrings in each compartment of the accessory boxes and left to set for 24 h. Once set, the cured silicone pieces were removed from their compartments to yield the final chocolate moulds (Fig. 2(c)).
Molten chocolate was prepared using an improvised bain-marie water bath comprising a saucepan of water on a hot plate, with a mixing bowl placed in the pan. 100 g of milk chocolate, broken into pieces, and 4 g of paramount crystals were added to the mixing bowl, then melted by boiling the water in the bain-marie, and mixed with a spoon. The paramount crystals allowed the chocolate to be thinned to the point that the mixture could easily be drawn into and pushed out of a 10 ml disposable syringe (BD Plastipak, VWR). A coolbox was located nearby for rapid cooling of the molten chocolate when required.
D. Paper-based analytical devices: Wax on filter paper
Paper microfluidic devices were prepared by drawing channel designs with wax crayons onto discs of filter paper (Sartorius), similar to the method of Cai et al.,47 then placing the discs onto a hot plate for 30 s in order to melt the wax into the paper, rather than placing them in an oven. The process could also be sped up by placing a metal block on top of the paper on the hot plate. Three main designs were employed for the workshop demonstration: (1) a Y-shaped channel for showing diffusion of two coloured liquids (Fig. 3(a)), (2) a gradient channel for demonstrating the ability to generate multiple shades of colour from only two coloured starting liquids (Fig. 3(b)), and (3) a straight channel with a bulb that was used to demonstrate laminar flow assays (Fig. 3(c)). The straight channel chip was further prepared by fixing a rectangular strip of universal pH indicator paper with sellotape on to the back of the filter paper, such that it crossed the straight channel. A rectangular strip of filter paper was cut out from a separate filter disc and immersed in a solution of blue food dye (Erioglaucine disodium salt), then removed and allowed to dry, before being sellotaped across the straight channel between the pH paper and the bulb part of the design. The designs on each paper device were simply drawn by hand with wax crayons, since the nature of the experiments did not require accurate fabrication, and about 30–50 devices of each design were prepared for the workshop.
The workstation for the paper devices was set up such that each student had vials of yellow food dye (Tartrazine) and blue food dye (Erioglaucine disodium salt) in water. Students were also given vials of either water or lemon juice. Each student was given a few plastic Pasteur pipettes, some wax crayons, and a few filter paper discs. Experiments were performed on blue roll (Kimwipe) to soak up any spilled liquids. The hot plate was set up at the workstation to ensure that freshly drawn wax designs could be melted into the paper.
E. Gradient formation by diffusive mixing: Oversized gradient microfluidic chips
Gradient mixing devices were designed in SolidWorks based on upscaled versions of microfluidic devices used in the literature.60–63 Two devices were prepared, each featuring two inlet channels that would repeatedly split, mix, and recombine the fluid streams over several levels of branching channels and serpentine mixing channel structures. The designs were converted to G-code via SolidCAM and milled into 6 mm thick sheets of PMMA polymer using a CNC milling machine (Datron M7). Design 1 (the “demo chip”) featured four levels of branching/serpentine channels that resulted in six outlet channels and was milled into a 30 cm × 21 cm polymer sheet (Fig. 4(a)). The channels were 1 mm wide and 300 μm deep, with holes milled into the inlet and outlet channels. Design 2 (the “juice chip”) consisted of two levels of branching, yielding four outlets that opened into reservoirs, that was milled into a 14 cm × 10 cm polymer sheet (Fig. 4(b)). These channels were 1 mm wide and 1 mm deep. The milled chips were bonded to bottom sheets of 6 mm thick PMMA using double-sided tape to yield the final devices.
Plastic pipette tips (100 μl) were cut to size and glued, using Araldite Rapid or Araldite 2014 epoxy resins (RS Components, Northants, UK), into the inlet holes of designs 1 and 2, and into the outlet holes of design 1. Design 1 was set up to be constantly running during the workshop in order to show students the chip in operation. Polytetrafluoroethylene (PTFE) tubing (0.3 mm ID, 1.58 mm OD, Supelco, Dorset, UK) was glued into the pipette tips in the two inlet holes of design 1 and attached at its other end to two 10 ml disposable syringes (BD Plastipak) via syringe adapters (Upchurch). The syringes contained aqueous solutions of blue food dye (Erioglaucine disodium salt) and red food dye (Erythrosin B) and were placed on a syringe pump (PHD 22/2000, Harvard Apparatus, UK). The dye solutions were continuously pumped through the chip at a flow rate of 20 μl/min.
Design 2 was set up to be operated by hand by the students during the workshop. This was achieved by attaching 10 ml disposable syringes filled with fruit juices (e.g., cranberry juice, blackcurrent juice, orange juice, pineapple juice) to the cut-down pipette tips in the inlet holes of the device.
F. Tissue-on-a-chip: Oversized tissue chip
Microfluidic devices for performing investigations on tissue biopsies have been used for several years at the University of Hull.64 Here the chips feature a microfluidic channel that passes through a tissue chamber, a lidded compartment that allows placement of the tissue in the flow path such that media and reagents can be pumped over the tissue. For the workshop, an oversized tissue chip was fabricated that incorporated these basic concepts. The chip design (Fig. 5) was prepared in SolidWorks and transferred to a CNC milling machine (Datron M7) via a G-code prepared in SolidCAM. A single flow channel, with a length of 11 cm and a width of 3 mm, was milled to a depth of 6 mm in a 15 cm × 15 cm sheet of 12 mm thick PMMA polymer. Three access holes were milled into a second sheet of 150 cm × 150 cm × 12 mm PMMA: a 3.5 mm diameter inlet hole, a 3.5 mm diameter outlet hole, and a 20 mm diameter hole in the centre of the sheet that would act as the “tissue chamber.” Double-sided tape was applied to the plate that featured the channel design, and the section of tape covering the channel was cut away with a scalpel. This channel plate was then bonded to the access hole plate via the double-sided tape.
A “tissue” chamber was prepared by taking a 50 ml centrifuge tube (VWR, UK) with a screw-on lid and cutting it to a length of 4 cm from the top. The section featuring the lid was glued onto the central chamber (20 mm diameter) of the access hole plate using Araldite Rapid epoxy resin. PTFE tubing (0.3 mm ID, 1.58 mm OD) was glued into the inlet and outlet holes and was set up to introduce solutions by negative pressure. The outlet tubing was connected to a 20 ml disposable syringe (BD Plastipak), while the inlet tubing was fed into a plastic beaker containing either water or lemon juice. Books of universal pH indicator paper were also placed at the workstation.
Full risk assessments were carried out for each of the workstation activities. Efforts were made to ensure that experiments could be performed using standard household items, for example, using lemon juice as a source of citric acid, the use of fruit juices and solutions of food dyes as sources of coloured liquids, and food-grade silicone for the preparation of the chocolate moulds. Care was taken that students did not touch the hot plates employed for melting wax during the preparation of paper microfluidic devices and for melting the chocolate used for the moulding of chocolate microfluidic chips.
IV. WORKSHOP PROCEDURES
The Hull Science Festival 2015 Lab-on-a-Chip Workshop was held for three groups of students (aged 13–14) from different schools, with the workshop taking one hour for each school group. The purpose was to introduce lab-on-a-chip technology to school students, while demonstrating some of the types of microfluidic chip fabrication and research that takes place at the University of Hull. The workshop was held in a large room, with one table setup per workstation throughout the room and each station manned by the undergraduate student (demonstrator) who had developed the activity for it. When a group of students entered the room, they were given an initial introductory talk by the Professor, who supervised the overall execution of the workshop, which briefly described what lab-on-a-chip is and why it is useful, before discussing the purpose of the workshop and general safety concerns. The larger cohort was then split into smaller groups of 4–5 students and each group directed to a workstation.
There, students were given a short talk by the demonstrator about that station, with a description of the technique that was being demonstrated and how it was related to the use of microfluidics in a research setting. They would then be instructed in how to perform the workstation activity, and each student was given an opportunity to undertake every activity. Posters (A4 size) were designed by the undergraduate student demonstrators (Figs. S1–S6 in the supplementary material)59 and were placed at each workstation to describe the activity. However, given the time limitations and the fact that many aspects of the field would be completely new to the students, the introductions and explanations were kept short and simple, describing only the core aspects of each technique without going into too much detail. A workshop ran for one hour, with each workstation running for approximately 10–15 min, after which the student groups would be directed to a new workstation. During the final workstation activity of each session, the students were given a questionnaire to fill in (see the supplementary material)59 in order to determine their thoughts on the workshop in general, each individual activity, and how the workshop had affected their knowledge of lab-on-a-chip technology. Sections IV A–IV E describe the purpose of each workstation and how it was described to the students, in addition to how each activity was performed by the students.
A. CNC milling: Pantograph
Micromilling is a powerful fabrication technique that can be used to manufacture microfluidic devices, particularly for rapid prototyping, although it is a relatively underused technique in microfluidic research presumably due to relatively high start-up costs, required lab space, and expertise. A recent review by Guckenberger et al.65 gives an excellent overview of protocols and considerations for the micromilling of microfluidic devices. Here, chip designs are prepared in CAD (computer aided design) software and transferred to a CNC milling machine, which uses a cutting tool to cut the design out of a substrate. CNC micromilling is employed at the University of Hull for the direct milling of microfluidic designs into glass and polymer and for the milling of masters out of metals (e.g., aluminium) for microinjection moulding of polymer chips or for the fabrication of PDMS devices.
Since CNC micromilling involves the cutting of channels into a substrate, the activity for this workstation was intended to mimic this process using a pantograph. By modifying the pantograph to include a weighted nib, channel designs could be traced from a template (Fig. S1 in the supplementary material)59 into scratch art cards, with the nib cutting away a layer of black wax from the card as it was moved to reveal the coloured design beneath. The background of micromilling for microfluidic chip fabrication and its relation to the pantograph activity was explained to the students by the demonstrator with reference to the poster (Fig. S2 in the supplementary material).59 Specifically, the students were informed of the following: (1) the key components and principles of a CNC milling machine, by which a computer controls a cutting tool to precision cut an uploaded design drawing out of a workpiece; (2) that milling can be used to cut microfluidic channels directly out of a material (e.g., plastic or glass) for device fabrication or alternatively can be used to cut a design out of metal for use as a master in injection moulding of microfluidic devices (with suitable reference made to the chocolate moulding workstation); (3) the pantograph setup, and how its components can be related to CNC micromilling. In particular, students were informed that the channel template on the poster represented the CAD drawing on a computer, the stylus and arms of the pantograph demonstrated the transfer of the design to the cutting tool (via computer aided manufacturing, CAM, software), the weighted nib imitated the spindle and cutting tool, and the scratch art card served as the workpiece (Fig. 6(a)); and (4) the operation of the pantograph, by which students would trace designs from the template while the nib cut the design into a scratch card. It should be noted, however, that the focus of the activity and application was based on only two of the core components of CNC milling: (i) the transfer of a design from a drawing to a physical workpiece, and (ii) the cutting of that design into the substrate via a moving arm and a cutting tool. Hence, the actual computer numerical control part of the procedure was not explained in any great detail beyond the fact that the cutting arm is precision controlled by a computer based on the design.
The students selected a microchannel design from the template sheet (Fig. S1 in the supplementary material),59 and the demonstrator fixed the template design and scratch art card to the pantograph board such that the stylus of the pantograph was placed on the template, while the weighted nib was located on the scratch art card (Fig. 6(b)). The students then slowly and carefully traced the template design in order to ensure that the weighted nib was stable enough to cut into the black wax in a steady manner; moving the stylus too fast would result in poor transfer of some of the lines being cut into the scratch art card. Upon finishing, the students were then given a metal stylus so that they could cut their name into the wax on their scratch art card, and took their finished cards home with them.
Fig. 6(c) shows examples of the channel designs cut into scratch art cards compared to the template designs on the poster, demonstrating a good transfer of each design via the pantograph. Furthermore, two sets of scratch art cards were used: some that were thick and rigid and others that were thin and a little more flimsy. It was determined that it was easier to transfer designs into the thicker cards, while the channel lines did not always come out very well in the thinner cards. On the whole, the students were able to recognise the association between the pantograph “etching” and the CNC milling of microfluidic devices, and this is shown by the results of the questionnaire that are described later. On the whole, the students responded positively to the activity, with one writing in their feedback that it was “Explanatory but enjoyable, creative, fun and a lot more hands on” compared to some other stations.
B. Injection moulding: Chocolate chips
Injection moulding is an extremely popular mass production technique that involves the fabrication of a mould into which molten polymer is injected under high pressure, filling the mould and forming the final product upon cooling and release of the polymer. Microinjection moulding for the fabrication of microfluidic devices has thus also proven successful since a larger number of almost identical devices can be produced in a short time using a mould,66–70 and has been used extensively for the production of PMMA, PC (polycarbonate), COC (cyclic olefin copolymer), and COP (cyclic olefin polymer) microfluidic chips at the University of Hull. In order to demonstrate this process to school students, an activity was set up to introduce molten chocolate into a mould, which would then be allowed to cool to provide a chocolate microfluidic chip.
As described in Section II C, food-safe silicone moulds were prepared from PMMA keyrings (Figs. 2(b) and 2(c)) that had been themselves injection moulded as give-away items at the Hull Science Festival for several years. The silicone moulds featured a microfluidic channel design and the letters “LOC.” Prior to the school groups starting the workshop, the demonstrator of the workstation set up an improvised bain-marie to melt a bowl of chocolate (mixed with paramount crystals to decrease the viscosity of the chocolate), such that the chocolate would be kept molten throughout the course of the hour. Once a group of students had been taken to the workstation, the demonstrator gave an introductory talk regarding the technique of polymer injection moulding for microfluidic device fabrication and how the chocolate moulding method relates to it, with the help of a poster showing both a typical injection moulding setup and the chocolate moulding activity (Fig. S3 in the supplementary material).59 Specifically, the demonstrator explained the following: (1) the operation of a polymer injection moulder, as described above, with reference to the major components of such a machine (i.e., a hopper containing granules of plastic, a mould tool (master), and a heated barrel and screw that melts the polymer granules and forces them into the mould tool. (2) The use of injection moulding for the fabrication of polymer microfluidic devices based on a design that had been milled into the metal mould, with reference to the pantograph workshop activity (as an analogy of micromilling) and to the PMMA keyrings. The keyrings were shown to the students both as examples of moulded polymer chips and to highlight the fact that these keyrings had themselves been used as masters for the food-grade silicone moulds that the students would be using here. (3) An explanation of the chocolate workstation activity and its relation to polymer injection moulding, in which the silicone moulds represented an aluminium master, the chocolate pieces the polymer granules, the bain-marie as the heated barrel and nozzle of the injection moulder for melting the chocolate/polymer, and a 10 ml disposable syringe as the barrel/screw of the machine.
The students were then invited to take the 10 ml disposable syringe and draw 4 ml of the molten chocolate into it (Fig. 7(a)), before carefully filling a silicone mould with the chocolate (Fig. 7(b)). 4 ml had been found to provide enough material for the mould with room for some error and spillage. After a few minutes, the moulds containing the chocolate were wrapped in aluminium foil and labelled, and then placed in the coolbox in order to try to rapidly cool them to solid form so that the final chocolate chips (Fig. 7(c)) could be handed back to the students at the end of the workshop session. However, due to students performing the activity one group after another, many of the chocolate chips were not fully set before the end of the workshop. This issue had been anticipated, so the demonstrator had prepared a batch of chocolate chips the previous day to ensure that each student received a chip. Prior tests with the chocolate chips had demonstrated that, for the given amount and thickness of chocolate in the mould, it took less than 10 min to solidify the chips in a conventional fridge (∼4 °C); hence, it could be feasible in future to provide all students with their own chocolate chips with a more suitable cooling unit.
This workstation, perhaps unsurprisingly, proved to be the most popular of the activities, with the students enjoying both the activity itself but also the fact that they received a chocolate treat at the end. In the feedback provided, many students called it “interesting” and “well explained,” with one comment stating that “The chocolate station was my favourite because the explanation was good and it was really fun, also I think I learned a lot from it.” An interesting problem experienced with the activity, however, involved trying to discourage students from eating the molten chocolate directly from the syringes.
As a side note, while the silicone moulds and chocolate chips were used here as an analogue for microinjection moulding, the method and explanation could easily be repurposed to describe the moulding of PDMS devices. Here, the silicone moulds would represent an SU-8 master, while the chocolate would represent PDMS.
C. Paper-based analytical devices: Wax on filter paper
Modern microfluidic paper-based analytical devices (μPADs) were introduced in 2007 by the group of Whitesides.46 By patterning hydrophobic channel structures on hydrophilic paper, aqueous solutions are able to wick through the porous paper structure while being directed by the hydrophobic barriers.4,44,45,71–74 Such channels can be prepared via a number of techniques including photolithography, screen printing, laser cutting, plasma treatment, inkjet printing, and wax printing. Detection zones can be formed at desired locations on a paper microfluidic device by spotting reagents onto the paper, and upon addition of a sample (e.g., blood, serum, urine, tears, saliva) to the μPAD, the presence of different analytes in the sample can be determined at different detection zones. Multiple techniques have been employed for detection on paper-based devices, including fluorescence, chemiluminescence, and electrochemical sensing. However, colourimetric assays have proven the most popular detection method, particularly in combination with image collection via smartphone cameras and scanners and analysis via custom applications. The low cost and ease of fabrication of μPADs has made them very popular as point-of-care (POC) diagnostic devices for use in rural and developing areas.45,72
In recent years, the University of Hull has begun investigating the fabrication and operation of μPADs for diagnostics;75 hence, we wished to introduce the school students to this exciting field. Wax printing has proven a popular method of fabricating μPADs,76,77 since it requires only that a design is first deposited onto the paper in wax using a conventional wax printer. The paper is then placed on a hot plate to melt the wax into the paper, thus forming the hydrophobic barriers. This process was easily adapted for a workstation activity using conventional filter paper discs and wax crayons. By drawing a design directly onto the filter paper with a wax crayon and melting the wax into the paper on a hot plate, channel structures can be easily and rapidly formed that allow aqueous solutions to be directed along desired paths (Fig. 8(a)).
Multiple paper devices featuring three designs (Fig. 3) were prepared for the workshop activity. When the students sat down at the workstation, the demonstrator explained, with the help of a poster (Fig. S4 in the supplementary material)59 and the pre-prepared paper devices, the following: (1) the fact that water can travel through the pores between the fibres of paper; (2) that by introducing hydrophobic walls or borders, explicitly stated as being walls that water “does not like,” such as borders made from wax, channel structures can be drawn on paper that will control where water is able to move; (3) how this concept can be used to form paper-based microfluidic devices, μPADs, by employing wall designs that allow different liquids to be brought together. The students were also told of how “detection” chemicals can be added and dried onto the paper, and when a sample is added the chemical will change colour, indicating the presence of a certain species, for example, a disease or pollutant. At this point, the use of μPADs as low-cost, portable, point-of-care, disposable devices for the testing of diseases, particularly in poorer regions, was highlighted. (4) The concept of laminar flow assays was explained using the pre-prepared chip design that featured a straight channel, a bulb, and strips of pH paper (acting as a detection zone) and blue paper (acting as a control zone) taped across the channel on the underside of the device (Fig. 3(c)). In particular, the layout and operation of this chip could be described in relation to what is probably the most widely known laminar flow assay: the pregnancy test, although given the age range of the students, not all of them may have been aware of the principle of the test prior to this, but it is nonetheless the most relatable test for the general populace. (5) Taking these makeshift laminar flow assay paper devices, each student was invited to add a few drops of clear solution to the narrow end (i.e., not the bulb) of the channel via a plastic Pasteur pipette. Unbeknownst to the students, the clear solution contained either water or lemon juice. Some care had to be taken that too much solution was not added such that it was able to cross over the wax barrier, and it helped to have the device tilted just slightly so that gravity helped to direct the liquid through the channel. As the solution passed through the channel, it crossed the pH paper and blue paper before finishing in the bulb, with the wetting of the filter paper allowing visualisation of the pH and blue paper underneath (Fig. 8(b)). If a student's solution contained only water, the pH paper turned green, while if the solution was lemon juice, then the pH paper turned red, indicating “positive” and “negative” results, respectively. The blue paper remained blue and was explained as being a control channel that demonstrated that the device was working properly.
Following this first test, the students were given devices that featured either the Y-shaped channel design (Fig. 3(a)) or the gradient mixing channel design (Fig. 3(b)). Using plastic Pasteur pipettes, they simultaneously added aqueous solutions of yellow and blue food dyes to the two inlets in each device and observed the behaviour of the fluids as they passed through the channels. Again, it was found that tilting the paper devices downwards slightly helped to direct the fluid flow through the channel structure thanks to gravity. If performed correctly, the Y-shaped channel demonstrated how the yellow and blue dyes mixed in the straight channel to form a green colour (Fig. 8(c)). While the gradient design was more difficult to get right, it was arguably more rewarding as the two colours were split, mixed, and recombined twice to yield four outlets with a gradient of colour going from pure yellow, through different shades of green, to pure blue (Fig. 8(d)). Due to the speed and ease of operation of the activity, combined with the fact that multiple devices had been pre-prepared, students were invited to have extra attempts if they were not successful the first time.
Finally, students were given blank filter paper discs and wax crayons and asked to draw a design of their choice (Fig. 8(e)), which ranged from basic shapes, letters, their own names, animals (especially horses), somewhat abstract pieces, and figures from pop culture (the video game character, Pac-Man, proved particularly popular). The paper discs were collected from the students as they finished their drawings and were placed on a hot plate for a minute to melt the wax into the paper, after which they were returned to the students. The students were then allowed to pipette coloured food dye solutions onto their designs, with the wax confining liquids to defined locations that enabled the students to colour different parts of the paper as they wished. The coloured paper discs were then either allowed to dry on the desk or on the hot plate and given back to the student to take home with them.
The students enjoyed the workshop activity, and while they found the initial tests interesting, they were particularly excited to draw their own designs and decorate them as they desired.
D. Gradient formation by diffusive mixing: Oversized gradient microfluidic chips
Microfluidic devices relying on the repeated splitting, mixing, and recombination of two or more reagent streams to form a gradient of the reagents were introduced in the early 2000s by the group of Whitesides.60,61 Since then, the use of gradient chips has been successful for a number of biological applications,78–82 in particular, the ability to simultaneously expose a population of cells to a concentration gradient of stimuli (e.g., reagents, drugs) across a chamber (or in multiple chambers) in order to determine the effect from high-to-low concentrations. At the University of Hull, this has previously been employed to study the effect of different concentrations of a genotoxic chemical on magnetically functionalised yeast cells.63 Therefore, we intended to create an activity that demonstrated several aspects of gradient production, and flow regimes in general, in microfluidic channels.
As described in Section II E, two oversized gradient devices were prepared. The larger of the two (design 1, the “demo chip”) was connected to a syringe pump that continuously introduced red and blue food dye solutions into the device over the course of the day, demonstrating a stable flow regime and gradient to the students (Figs. 9(a) and 9(b)). With direct reference to this demo, and with the help of a poster (Fig. S5 in the supplementary material),59 an overview of flow characteristics commonly found in microfluidics was explained to the students, albeit in a “stripped back” manner devoid of depth, jargon, or equations. Specifically, the workstation was described thus: (1) laminar flow was described as being the way in which fluid streams, on a small-scale as in microfluidic devices, flow side-by-side; (2) diffusive mixing was discussed as being the way in which two such laminar streams containing chemicals slowly move into each other as they flow alongside each other, allowing their mixing; (3) gradient formation by the continuous splitting, recombining, and diffusive mixing of the laminar flow streams; (4) the use of such gradients for simultaneously observing the effects of drugs or other chemicals on cells within a chamber (or chambers), with examples stated as including the testing of different concentrations of cancer drugs on cancer cells. To aid in explaining this latter point, a glass microfluidic device used to perform research experiments at Hull63 was also presented to the students in order to relate the real device to the oversized platform.
Following these explanations, the students were separated into pairs and asked to perform an activity using device design 2 (the “juice chip”). The juice chip was set up such that a syringe containing yellow coloured fruit juice (e.g., orange juice or pineapple juice) was attached to one inlet of the device, while a syringe containing red coloured fruit juice (e.g., cranberry juice or blackcurrent juice) was attached to the other inlet. The two students in a pair took hold of one syringe each and were instructed to push the syringe plungers and try to form a gradient in the microfluidic channels (Fig. 9(c)), as was being demonstrated in device 1. The channels in the oversized juice chip had been milled with relatively large dimensions not only to allow good visualisation of the fluids within them but to produce little backpressure and so make it easier for the students to push the syringes and generate flow in the channels. As the outlet reservoirs became full, they would be emptied using a 20 ml disposable syringe (BD Plastipak) with a blunted syringe needle or cut-to-size pipette tip attached.
Although a simple-sounding task, the application of different pressures from the two students added a high degree of challenge to the proceedings that let them develop an understanding of laminar flow and of how small changes in pressure can have a large effect on the flow regime, with the gradient shifting to the left and right in the device. With time and patience, however, most student pairs were able to produce a fairly steady gradient across the chip, with the pair who produced the best gradient receiving a treat (a packet of sweets/candy), and the students generally enjoyed the hands-on activity and challenge it posed.
E. Tissue-on-a-chip: Oversized tissue chip
Microfluidic devices have become very popular for the study of biological tissues,83–86 and for the mimicry of tissues and organs,4,74,85–92 thanks to the ability to continuously flush nutrients through microchannels to the tissue. This better mimics the in vivo environment compared to conventional flask-based methods, and research is moving towards the development of a “human-on-a-chip” that allows fluidic contact between tissues or organ-mimicking cell structures in a microfluidic platform.62,90,93–95 The University of Hull has been working with tissue on-chip for many years now, having developed devices for the on-chip culture of tissue biopsies,64,96 toxicity studies,97–99 dissociation and detection of antibody-labelled cells from tumour cells,100 perfusion of viable heart tissue with electrochemical monitoring,101,102 and the study of radiation-induced cell death in tissue.103 With this established history in microfluidics-based tissue research, we were keen to demonstrate some of the basic concepts of the field to the school students.
The microfluidic devices employed at the University of Hull have largely followed a similar design concept,64 in that a chamber containing a tissue biopsy is situated in the path of a microchannel such that media or reagents can be flushed over the tissue, allowing the effect of stimuli to be observed on the tissue both visually (via microscopy and fluorescence microscopy) and by collecting effluent from the outlet of the chip for analysis of biomolecules released from the tissue. With this in mind, an oversized tissue chip was fabricated from PMMA for the workstation, featuring a lidded central chamber in the flow path of a single microchannel (see Section II F and Fig. 10(a)). The setup and the microfluidic procedures were explained to the school students in terms of drug studies for cancer treatment, with the help of a poster (see Fig. S6 in the supplementary material)59 and an actual glass microfluidic tissue chip that had been used to perform experiments at Hull.64 Specifically, the concept and setup was explained thus: (1) with the aid of the real chip and the oversized chips, it was explained how a piece of cancerous tissue, taken from a tumour biopsy, can be placed in the tissue chamber of the chip; (2) a solution containing cancer drugs can be pumped through the chip, thereby exposing the tumour to the drug; (3) how the effect on the tissue can be observed directly via a microscope, in terms of a positive result (i.e., cancerous tissue is killed) or negative result (i.e., there is no effect on the tissue, or the tissue even grows), and/or the solution can be collected from the outlet of the chip and analysed to determine whether any chemicals had been released by the tumour that would indicate a positive or negative result; and (4) the analogous experiment involving the oversized chip was explained, with pH paper representing tissue, and solutions of lemon juice and water representing different drugs.
To perform the experiment, the “tissue” chamber of the oversized device was opened and a piece of universal pH paper, mimicking a piece of tissue, would be placed in the microfluidic channel and then the lid closed. The inlet tubing would be placed in a beaker of either the lemon juice or water, and a student would then pull on the plunger of the 20 ml syringe attached to the outlet tubing, drawing the solution through the microchannel and so across the pH paper via negative pressure (to avoid the risk of spraying acidic lemon juice into someone's eyes, as could occur if positive pressure was applied and a seal burst somewhere in the chip or tubing) (Fig. 10(b)). Lemon juice would thus turn the pH paper red, indicating a negative effect of the “drug” on the “tissue,” while water would turn the pH paper green, indicating a positive effect of the drug (Fig. 10(c)). Whether the solution consisted of water or lemon juice was chosen at random, and between each test the chip would be flushed with air and the inside of the chamber dried with Kimwipe roll. The students generally enjoyed the activity, commenting that it was “interesting” and “well explained,” with one student writing in their feedback that “It has given me an insight into the treatments of cancer and testing on cancerous tissue.”
During the workshop, the level of engagement of the students with the activities and their enjoyment of them could be gauged to an extent, with a largely positive vibe present throughout. In order to better quantify their response to the event, the students were given a questionnaire that they filled in and submitted at the end of their session. The questionnaire, which can be found in the supplementary material,59 was designed to determine how the students found the event in general and the individual workstations, as well as whether they had previously heard of lab-on-a-chip and if they felt they had achieved a better understanding of the field by the end of the workshop. Responses were garnered from 51 students in total. Unfortunately, a couple of groups of students were unable to perform all of the activities during their session due to time constraints; hence, some answers were not given for individual activities, while some of the questions in the questionnaire were simply not answered. Returned questionnaires featuring questions that lacked answers have been eliminated from the following analysis and discussion, although the raw data from the 51 students can be found in Tables S1–S3 in the supplementary material.59
The results from the questionnaire were compiled and are presented here as graphs. Fig. 11(a) shows the response to the question “How did you find the workshop?,” with a choice of answers ranging from Very good to Very bad. On the whole, nearly half of the students found the workshop to be Very good and nearly half to be Good, with only one student judging it to be Okay and one student not providing an answer. Nobody found the workshop to be Bad or Very bad. Thus, response to the workshop was very positive, with a 98% satisfaction rating. The students were then asked to judge how well the individual activities were explained on the same Very good-to-Very bad scale, as shown in Fig. 11(b). On the whole, the workstation explanations were judged as being Very good or Good, though a portion of students thought they were only Okay. The tissue, chocolate, and gradient mixing explanations were considered to be bad by one student each, but on the whole the response was generally very positive, with a minimum satisfaction rating of 73% (based on Very good and Good responses) for any of the activity explanations. The chocolate moulding activity was considered to be the best explained (94% rating of Very good or Good), with the pantograph milling exercise also performing particularly strongly (94% rating of Very good or Good).
Fig. 11(c) indicates which workstation activity the students found to be their favourite. Perhaps unsurprisingly given the treat-based nature of the exercise, the chocolate moulding workstation was by far the most popular, with more than half (56.5%) of the students preferring this station above the others. The other stations' popularity each accounted for 8.7%–13.0% of the favourites among the students.
The students were further asked to state whether they had heard of lab-on-a-chip before attending the workshop, to which the response was a unanimous “No.” However, upon undertaking the various activities and explanations of lab-on-a-chip, 94% of students answered “Yes” the question “Do you feel you have a better understanding of what lab-on-a-chip is now?” This, combined with the fact that 100% of students who responded to the question “Did you find the workshop interesting?” answered “Yes,” demonstrated that the two main priorities of the workshop as a whole, to provide an interesting and exciting experience that introduced students to the field of lab-on-a-chip, had been realised.
The survey indicated that, on the whole, the workshop and the individual workstations were a rousing success. However, the largely multiple choice survey offered only limited feedback about specific aspects of the workshop. For example, it could have been anticipated that the students, who were unlikely to have heard of lab-on-a-chip or microfluidics before, would indicate that they now had a better understanding of what the field was. In later workshop events, an updated survey could be employed that asks more open-ended questions, forcing the students to write specific answers rather than simply tick a box, and even asking students to state in their own words what different terms were and what they had learned. It could even perhaps take the form of a short test, although this could potentially take some of the “fun factor” away from the overall event. Furthermore, such open-ended questions and short tests require more time, which was already very limited at the workshop; hence, a compromise between multiple choice questions and a few select open-ended questions would likely be more ideal. The same critique can also be applied to the questions about the workstations, since there was little information about why some activities were more popular than others. Further to this, the answers may have been influenced by factors other than the activity itself. For example, while the chocolate station was the favourite, this may have been swayed by the fact that the students received a chocolate treat; if there was no treat at the end, would the workstation still be rated so highly based purely on the actual activity? While an option was given for the students to explain why a specific workstation was their favourite, only a handful actually provided such feedback. As with the questions about lab-on-a-chip and the workshop in general, this would benefit from requiring specific feedback for each workstation, but again this would need to compromise with the need for a fast questionnaire that can be completed in the strict timeframe of the workshop. Alternatively, an agreement could be made with the students' teacher(s), such that the questionnaire can be taken away, completed by the students shortly after the workshop, and then returned to the workshop organisers at a later date. All of these aspects will need to be considered prior to the next version of the workshop.
In addition to the questionnaire, the experiences of the demonstrators and supervisors of the workshop, in addition to comments made by students and teachers during the event, can be used to gauge the attitudes towards how the workshop was run and to the individual workstations. Most of the children genuinely appeared to enjoy the workshop and participation in the various activities, though as is only natural, some students were more inquisitive and willing to engage than others. The ability of the demonstrators to gauge the response of the students actually led to the introductions provided for each workstation developing over the course of the day, based on overheard comments and by judging the expressions of the students. It soon became apparent that in many cases it was better to provide only an overview of the technique being described and to focus on “how a technique works” rather than “why a technique works in the way it does,” without going into much depth or theory. The impression gleaned by the demonstrators was that by approaching the description in such a way the students were largely able to understand the core concepts of each activity. For example, students performing the chocolate moulding activity seemed to come away with the idea of how injection moulding worked: melting a polymer, injecting it into a mould, and letting it cool to form the device, but without necessarily understanding how an actual injection moulding machine worked. The same can be said for the pantograph activity, where students understood that a cutting tool, controlled by a computer onto which a design is uploaded, is used to cut that design into a substrate/workpiece, but again without going into detail about how the actual CNC milling machine works. Thus, at each workstation the introduction and amount of detail had to be adapted until a level was reached such that the students could grasp the main concepts.
One instance was noted in which a researcher visited one of the workstations early in the day where, upon seeing a microfluidic device being described with which they had extensive experience, the researcher attempted to give a more in-depth understanding of the concepts behind the chip, only to end up using technical terms and concepts to which the students were unfamiliar. This particular student group subsequently left that workstation notably confused as to the purpose of the chip and how it worked. A similar scenario was observed at another workstation during a description of the applications of a microfluidic device, in which the teacher in charge of the students remarked that the demonstrator was using terms unfamiliar to the students. These examples reiterated the fact that descriptions and discussions needed to be stripped down to jargon-free overviews that stated only the core concepts without going into any great depth or technical detail.
The engagement of the students with the workstation activities was largely noted to be very successful. One thing that became apparent was that the more hands-on an activity was, the more enjoyable it appeared. For example, the students clearly engaged very well with the chocolate moulding activity, regardless of the chocolate treat. Likewise, the pantograph milling station also seemed particularly well-liked, and despite arguably being the most disconnected example in terms of the technique it purports to describe, the students nonetheless left with a good, basic understanding of how chips can be fabricated by milling. Perhaps it would be possible to develop a new workshop activity that describes in more detail how CNC milling actually works, but the pantograph actually represented an excellent example of bridging “fun and hands-on” with “educational.” Conversely, while an activity such as the oversized tissue chip offered a more accurate example of how a microfluidic device works, the hands-on component was quite limited. Interestingly, it could be noted how some of the students actually preferred to understand more about such techniques from an intellectual standpoint rather than the hands-on aspect. With over 50 students undertaking the workshop, however, the more hands-on activities were overall more popular; hence, the tissue activity would benefit from a more practical aspect, which could include collecting different “tissues” from different sources before testing them on the device with multiple reagents. A further problem encountered was that “rough handling” by students resulted, in one instance, in the tubing being pulled out of the chip, leading to one group missing this activity while the tubing was reattached. Robustness of apparatus is therefore an extra factor that must be considered, particularly for objects such as oversized chips which feature tubing and syringes that can become unattached.
It had been considered that the paper microfluidics station, which involved drawing on paper with wax crayons, may have been looked on as being “childish” by the students, but actually this example largely proved very popular, particularly when the students were asked to draw their own designs and apply the coloured liquids to them. The fluid manipulation and laminar flow assay examples helped to explain these concepts, but there is scope for improvement and the activity would perhaps benefit from a stronger link to actual μPADs, possibly incorporating reagents for analysing simple samples as described in the previously published articles.47–50 Furthermore, the recent acquisition of a wax printer means that more sophisticated devices could be fabricated for these demonstrations, but the procedures used here nonetheless provide a very useful, minimalist approach.
Students enjoyed the interesting patterns of the oversized gradient devices, and the challenge of attempting to generate their own gradient in the “juice chip,” but again this activity has scope for more of a link to some of the applications. This could be achieved by modifying the chip design to include a chamber across which the gradient can be applied, with cell substitutes (e.g., pH paper) incorporated into the chamber to demonstrate the effect of a gradient of “drug” on single “cells.” Furthermore, the channels in the juice chip exhibited very little backpressure, meaning that the system was very susceptible to slight differences in pressure from the inlets, thereby requiring very careful manipulation of the inlet syringes. For most students, this took a little getting used to but after some practice they could generate a gradient, and could observe the phenomena of laminar flow and diffusive mixing, while appreciating how small differences in inlet pressure can affect the system. Some more heavy-handed students, however, did struggle to obtain a “nice looking” gradient, but nevertheless appeared to enjoy their attempts.
While some aspects of the workshop and the activities could stand to be improved in later iterations based on the student responses and experiences of the demonstrators and supervisors, the event on the whole was very successful. To reiterate points commented on in the introduction of this paper, and discussed in the previous paragraphs, the engagement of the students (aged 13–14) with the activities and concepts increased with the more hands-on examples and with descriptions that avoided technical jargon or in-depth detail that went beyond core information. These experiences will help to plan future events, which we anticipate will utilise the same workstation activities, albeit updated in some cases.
We have developed a series of activities for introducing school students to the field of microfluidics and lab-on-a-chip, by using hands-on props that were analogous to various fabrication processes and applications. The workshop was produced as part of a larger Hull Science Festival 2015 event, taking place over several days. The lab-on-a-chip workstations were designed to highlight some of the facilities and research performed at the University of Hull, in particular, CNC micromilling (via the use of a pantograph), polymer injection moulding (via the moulding of molten chocolate), fabrication and operation of paper microfluidic devices (via wax crayon designs), gradient formation and flow regimes (via an oversized gradient chip), and on-chip tissue analysis (via an oversized tissue chip).
The students responded well to the workshop, and importantly their feedback indicated that they found it both interesting and informative. The feedback also indicated points that could be worked on and improved for subsequent workshops. As scientific outreach events become more popular, an increase in the number of microfluidics and lab-on-a-chip workshops being delivered is expected to increase, and we hope that the hands-on activities described here can help to provide ideas and inspiration for such events.
The authors acknowledge advice, suggestions, ideas, and assistance from Gary Kipling, Nathaniel J. Brown, Stephen J. Haswell, John Greenman, Charlotte Dyer, Ruth Bower, Alexander Iles, Ruchi Gupta, and Mark Lorch. Mike Park is thanked for the photographs taken during the workshop. Nigel Parkin and Chris Lloyd are thanked for the provision and fabrication of materials and apparatus.