Macro-to-micro interfacing to microfluidic channels using 3D-printed templates: application to time-resolved secretion sampling of endocrine tissue

Abstract

Employing 3D-printed templates for macro-to-micro interfacing, a passively operated polydimethysiloxane (PDMS) microfluidic device was designed for time-resolved secretion sampling from primary murine islets and epidiymal white adipose tissue explants. Interfacing in similar devices is typically accomplished through manually punched or drilled fluidic reservoirs. We previously introduced the concept of using hand fabricated polymer inserts to template cell culture and sampling reservoirs into PDMS devices, allowing rapid stimulation and sampling of endocrine tissue. However, fabrication of the fluidic reservoirs was time consuming, tedious, and was prone to errors during device curing. Here, we have implemented computer-aided design and 3D printing to circumvent these fabrication obstacles. In addition to rapid prototyping and design iteration advantages, the ability to match these 3D-printed interface templates with channel patterns is highly beneficial. By digitizing the template fabrication process, more robust components can be produced with reduced fabrication variability. Herein, 3D-printed templates were used for sculpting millimetre-scale reservoirs into the above-channel, bulk PDMS in passively-operated, eight-channel devices designed for time-resolved secretion sampling of murine tissue. Devices were proven functional by temporally assaying glucose-stimulated insulin secretion from <10 pancreatic islets and glycerol secretion from 2 mm adipose tissue explants, suggesting that 3D-printed interface templates could be applicable to a variety of cells and tissue types. More generally, this work validates desktop 3D printers as versatile interfacing tools in microfluidic laboratories.

Figure 1

Microfluidic device design and interfacing for endocrine tissue stimulation and sampling. A) 8 channel microfluidic design. For clarity, only one channel output (green) is labelled. B) PDMS microfluidic chip with 3D-templated fluidic reservoir, cell trap, and PDMS plug-to-tubing interfaces. C) Disassembled and D) assembled 8-strip sample collection device. Each tube was interfaced with both a vacuum line and a sample line from the microchip to facilitate sequential temporal sampling.

Figure 2

Fabrication of tissue and fluidic interfaces using 3D-printed templates. A) Image of a 3D-printed alignment container and a 6-well template for sculpting PDMS central reservoirs above SU-8 patterned microchannels. B) Cross-section of PDMS cured around an untreated 3D template and C) a template treated with THF vapours for 1 min. D) Cross-section of a typical PDMS microdevice. For clarity, only one microchannel sampling path is labelled.

Figure 3

Channel crosstalk during time resolved sampling was determined as insignificant using fluorescein as a flow tracer (n = 5 devices). 50 nM fluorescein was added to the large central reservoir. 0.5 μL of 100 μM fluorescein was spiked into the smaller, cell-trap reservoir at the start of the 20 min sampling time to mimic cellular release. Inset channel design is labelled with channel numbers.

Figure 4

Adipose tissue buoyancy was counteracted using 3D-printed trapping accessories. A) Explant traps sized for microfluidic devices (leftmost two) and 96-well plates (middle two). B) 3D rendering of explant traps, with parallel beams of PLA (0.50 mm widths) designed to hold adipose explants. C) A 2 mm explant was sequestered well below solution level and into the smaller inlet port near microchannel inlets.

Figure 5

3D-printed templates were used for microfluidic interfacing of two types of endocrine tissue for stimulation and temporal sampling. A) The insulin secretion rate from primary murine islets was clearly increased (p<0.05 for all points) in the presence of higher glucose levels, and the expected initial spike of insulin was observed. Five groups of <10 islets were assayed at high glucose, and two groups were assayed at low glucose (total of 7 microdevices used). B) Buoyant eWAT explants (2 mm) were trapped with 3D-printed accessories and interfaced to a 3D-templated device. After 30 min of treatment in HGHI solution, the explants were switched to LHLI solution, and the glycerol secretion rate was observed to increase, as expected. Three eWAT explants were evaluated on three separate microdevices.