Fig 1.
(A) Punch card programmable microfluidic system comprising of a paper punch card tape, plug-in microfluidic chip and a mechanical reader/actuator (inset depicts hand-crank powered device in action).
The punched tape moves through the device while being read sequentially. (B, C, D) Schematic depiction of device operation including (B) pumping achieved by rotating gear teeth interacting with a collapsible channel, (C) on-demand droplet generator using an impact-based jet formation (D) normally-closed microfluidic valves based on cantilever pins pushed against a chip. (E) All components including paper tape, mechanical reader/actuator, microfluidic chip and a hole-puncher for encoding the paper tape. (F) Top-down micrograph of the device with 15 active channels filled with colored fluids.
Fig 2.
Punch card controlled integrated multiplexed microfluidic pumps.
(A) A series of images of a single channel coupled to the rotating gear disc during one pumping cycle. (B) To characterize the flow pattern with each actuation, fluorescent polystyrene beads (2 μm) were used in de-ionized water. (C) Pumping in each cycle revealed a characteristic asymmetric pulsatile oscillatory flow depicted above as a kymograph. The amplitude of directed unidirectional flow depends on actuation height (h) and the angular velocity (ω) from the hand-crank. (D) Top-down view of the microfluidic chip with simultaneous operation of six punch card controlled integrated micro-pumps. Net flow rate in a fluidic line is a function of exact pattern of punched hole (number of holes punched and spacing between the same, an example pattern depicted above). (E) Effective flow rate characterized as a function of h and ω, easily achieving typical values demonstrated by integrated micro-pumps.
Fig 3.
Enhanced mixing is achieved using a zig-zag pattern of punched holes.
(A) Photomicrograph of six punch card controlled pumps driven by a zig-zag pattern (right inset). Left inset depicts the same device run through a traditional syringe pump (at the same flow rate) to highlight the striking difference in fluid mixing at the end of the channel (200 μm wide). (B) Mixing is quantified by mean-shift clustering approach (see methods for details) comparing four regions in the micro-channel marked a, b, c, d along the outflow. Six identified clusters merge into two. (C) Photomicrographs from video data reveal the mechanism for mixing. Pulsatile nature of flow induces increased folding of neighboring flow lines (and hence net interface length) thus enhancing diffusion and mixing.
Fig 4.
Integrated punch card controlled normally-closed valves.
(A) Schematic of normally-closed valves depicting mechanism of operation. (B) 3D printed cantilever beam array with spaced pins (2 mm apart), utilized for implementing 15 independent normally-closed valves. (C, D) Micrograph from video of ten normally-closed valves under operation (side view), all of which are independently actuated based on the punch card tape. (E) Normally-closed valve in action, at a single instance of opening and closing depicting the time duration for a single cycle (0.54 seconds). The image depicts the entire region of PDMS deformation with a completely collapsed channel.
Fig 5.
Demonstration of an impact based on-demand droplet generator.
(A) Schematic of droplet generator operation. A cantilever beam plucked by a gear tooth induces a pin to impact the channel, in correspondence to punched holes. (B) Photomicrographs of on-demand impact droplet generator at a flow-focusing geometry. Water droplets (green food coloring in DI water) were dispensed in mineral oil (viscosity 15cP, surfactant 2%v/v Tween 20). (C) Timing control between arrival of punched hole, corresponding impact of the pin and the resultant single droplet formation (inset depicts magnified view with time delay between the three events). (D) High-speed imaging of droplet generation reveals an impact jet that forms in the first 2ms of the impact. The jet is quickly destabilized with formation of a narrow thread that breaks into a single droplet. Sequence of images depicts the entire operation ending with a single droplet formation over a short period of only 55ms.
Fig 6.
(A) One-to-one mapping demonstrated for the punched code and sequence of droplets generated.
A binary code was implemented (every alphabet assigned a 5 bit code, example “U” = 10101) spelling “PUNCHCARD MICROFLUIDICS”. The presence of a hole in punch card tape (top) results in a single droplet representing a binary value of “1” while the absence of a hole results in no droplet representing a binary value of “0”. Vertical height of each plug represents droplet volume, which is approximately 2.5 nL. (B) Results of a qualitative colorimetric assay to test pH, ammonia, nitrates and nitrites in three samples: deionized water, pond water and seawater. Photographs compare bulk reactions (left image) with microfluidic outlet (right image); (1) pH readings with deionized water having a pH of 7.8, pond water at 8.2 and seawater at 8.8, (2) Ammonia levels in parts per million with deionized water at 0 ppm, pond water at 0.25 ppm and seawater at 0 ppm, (3) Nitrite levels with the deionized and sea water samples showing none and pond water at 2 ppm, (4) Nitrate levels in the water samples with pond water at 160 ppm and the deionized water and sea water samples having none.