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Editor's Notes

• #2: Good morning everyone. I¡¯m__________. Today I¡¯m going to talk about the topic ¡°molded biocompatible and disposable pdms/su8 inkjet dispenser.¡± This paper is from the university of British Columbia.
• #3: This is the outline of my presentation. First, I¡¯m going to give some introduction about the inkjet dispenser. Then, show the device fabrication process and the fabrication result. And then show the result when we use the kind of inkjet dispenser. Finally, conclusions.
• #4: As we know, in microfluidic chip we can use sheath flow to do a droplet generator or flow focusing and then use in cell sorting and flow cytometry. 3D printing is very popular these days, we can use 3D printer to build whatever we want. If we combine these two technology and then use in bio, is that possible? Can we build a bio-printer to print a hydrogel structure? And this can be used in dispensing small amounts of ?uids in biotechnology applications such as microarrays, cell dispensing, protein crystallization, and drug delivery.
• #5: Microdispensers are type of micropumps that are used to inject or spray a certain volume of fluid. A variety of methods exists in microdroplet dispensing, and comprehensive details on microdroplet generation modes, actuation methods, and their applications were widely discussed. The key operating issues for droplet generators, such as actuation method, satellite droplets, hydraulic crosstalk, size controllability, and priming. In drop on demand device, droplets are generated when needed. Drop on demand dispensing mechanisms can be divided into two categories: contact and noncontact. Contact type dispensing is like the right upper figure: In contact droplet dispensing, properties of the dispensing surface become factors affecting droplet generation. The possibility of contamination of the dispensing is increased because of this contact with another material. Noncontact-type dispensing uses actuators to dispense droplets, such as pneumatic, electrostatic, acoustic and piezoelectric actuation methods. The red color animation is the piezoelectric actuation use in Epson inkjet printer. Compared with contact-type dispensing, noncontact dispensing has less variability between spots, which is suitable for biological applications. Because in biomedical or biochemical experiments we need the volume of every droplet to be the same.
• #6: The formation of microfluidic systems out of PDMS is a well-established and widely used technology that easily allows for the integration of different flow control components, such as mixers, pumps, and valves. These integrated microfluidic systems have applications in different fields, including biochemical analysis and cell-based assays. Combining such integrated PDMS-based microfluidic systems, that can manipulate and characterize suspensions, with a biocompatible and disposable inkjet dispensing system enables a broad range of applications that require accurate dispensing and patterning of various materialss. Conventional inkjet dispenser units are reusable, and the relatively high cost of each cartridge makes it tempting to use different inks with the same unit. However, this involves a risk of cross-contamination, which may be a significant issue with biological materials. In this paper, they present a biocompatible and disposable inkjet dispenser, with a modular design, made from PDMS and a photo-curable polymer, SU-8. Their design enables easy integration with other PDMS-based microfluidic systems.
• #7: The device is combined with a hydrophobic SU-8 micro-nozzle bonded to a PDMS microfluidic chip and an external piezoelectric stack actuator. The PDMS microfluidic chip was molded using a 3D-printed polymer mold, and then bonded to a molded PDMS cuboid such that the vertical guiding channel for the actuator of the cuboid is aligned with the chip¡¯s actuation membrane. To fabricate the SU-8 micro-nozzles, 300-400 ?m long inward tapered SU-8 pillars on a 1 mm-thick glass substrate were fabricated in a process.
• #8: These are the cross-sectional view of the fabrication process steps: First, SU-8 film is spin-coated on the glass substrate and exposed under UV light through a mask. Then SU-8 film is developed and leaving the SU-8 pillar. Another thin layer of SU-8 is spin-coated and a thin layer of PDMS is spin-coated and cured; Applied plasma treatment to improve the wettability; An aqueous 2% PVA solution was deposited and dried on the substrate to provide a sacrificial layer. PVA is easily dissolved in water and after water evaporation leaves a thin sacrificial film of PVA; SU-8 is cast onto the substrate and then form the nozzle; The sacrificial layer of PVA is dissolved and the nozzle is peeled off; A PDMS microfluidic chip is bonded to the SU-8 nozzle after PDMS treatment with nitrogen plasma.
• #9: These are the upside down complete fabricated inkjet dispenser: In the left figure, the left side is the fluid inlet and right side is the outlet. The right figure is a 3D drawing of the device layers. The red dashed arrows show the fluid flow direction and the blue solid arrow shows the tip vibration direction. The thick pdms cuboid at the bottom is vertical guiding channel, and the middle is the pdms chip with ejection cavity and fluid channel. The upper layer is the SU8 inkjet nozzle. And finally we can get a disposable PDMS/SU8 dispenser.
• #10: This is the experimental setup. The actuator holder is fixed on XY stage The device and the actuator are carried on the XYZ stage. The plastic tip attached to the piezoelectric stack actuator. To visualize droplet formation, a stroboscopic imaging system comprised of a LED synchronized with a CMOS camera was used. The delay times for the CMOS camera and LED relative to the waveform applied to the piezoelectric stack actuator were controlled by a computer to observe the different droplet formation stages. In order to print arbitrary patterns, the device was mounted on a computer-controlled XY-stage.
• #11: The device successfully dispenses droplets with diameters ranging from 80-130 microns at rates of 2-1000 droplets per second, depending on the orifice diameter and the applied waveform. In order to print complex 3D hydrogel constructs for biological applications, the dispenser must be capable of printing hydrogel without satellite droplet formation. To demonstrate this, an aqueous 2 percent low viscosity alginate solution was printed. The structure is sprayed with CaCl2 solution after printing every other layer to gel the material. A ¡°UBC¡± pattern was printed on paper demonstrate the device¡¯s capability to print arbitrary patterns without satellite droplets. In addition to the fabrication advantages, the ejection nozzle proposed here consists of a hydrophobic polymer, which they have found to be advantages in droplet breakup and in preventing ink accumulation on the tip.
• #12: In this paper, they presented an inkjet dispenser and demonstrated its capability of printing hydrogel structures and arbitrary patterns. The device is designed and fabricated to allow for the integration with other PDMS microfluidic modules, is based on low-cost materials and fabrication processes allowing for it to be disposed after use, and allows for the use of reusable external actuators. This technology has the potential for printing more complex 3D hydrogel structures that may include living cells, and it can be used for printing multiple materials. These capabilities make this technology suitable for applications such as drug testing and other biochemical analysis and cell-based assays.