Page 159 - IJB-9-4

International Journal of Bioprinting 3D printing and 3D-printed electronics in smart drug delivery devices

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Figure 3. Schematics showing the various 3D printing processes, namely (a) fused filament fabrication (FFF) , (b) direct ink writing (DIW) , (c) inkjet
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printing (IJP) , (d) aerosol jet printing (AJP) , and (e) stereolithography .
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techniques. These techniques are widely used for 3D onto the substrate (Figure 3d) . AJP process consists of
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electronic printing to manufacture high-performance and several stages, which are the atomization, aerosol delivery,
advanced electronics components and devices. Typically, aerosol focusing, and deposition [77,78] . The atomization of the
these printing techniques produce thin-film electronic inks can be performed by means of pneumatic atomization
architectures that conform to the surface of the substrate. or ultrasonic atomization, depending on the viscosity of
IJP technique is a process that deposit the ink by ejecting the ink. Typically, the working ranges of ink’s viscosity
a series of droplets through a nozzle using an appropriate for the pneumatic atomizer and ultrasonic atomizer are
droplet ejecting mechanism (Figure 3c) . Generally, there 1–1000 cP and <10 cP, respectively. The formed aerosols
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are two main ejecting mechanisms, namely piezoelectric will then be transported to the printhead by the carrier gas
actuation and thermal actuation. IJP techniques tend through a tubing. Once the aerosols reach the printhead, a
to have strict requirements on the ink properties, such sheath flow is used to aerodynamically focus the ink flow
as surface tension, viscosity, and particle size due to the into a fine jet before exiting the nozzle. Due to the high exit
small nozzle size and the dominating surface tension effect velocity of the aerosols, the standoff distance between the
that can affect the printability of the ink significantly . nozzle and the substrate can be as far as 5 mm which makes
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Typically, the particle size has to be at least one-tenths or it very suitable for conformal printing as the alignment
smaller than the nozzle size to prevent nozzle clogging of part becomes less critical compared to other contact
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issues and to ensure successful and continuous printing. printing processes like the DIW techniques . Besides,
IJP techniques are more commonly used for printing 2D another advantage of AJP technique is that the process
circuits and sensors that are structurally flat. To date, many can achieve a line resolution as high as 20 µm which could
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works have used IJP techniques to fabricate physiological be useful for high-performance electronic applications .
sensors that can be applied to drug delivery devices, such Unlike IJP technique, AJP technique is less prone to nozzle
as CNT-based pH sensor for wound monitoring , silver clogging issue due to the presence of sheath flow to prevent
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nanowire-based transparent strain sensor and heater for the ink from coming in contact directly with the inner wall
human wearables , just to name a few . of the nozzle. Similar to IJP, AJP technique also works with
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many kinds of nanomaterials, such as nanoparticle ,
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AJP technique, on the other hand, uses inert gas flows nanowires , and 2D nanomaterials . So far, AJP
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like nitrogen gas to direct and deposit the droplets of ink technique has been used to develop and fabricate sensors,
Volume 9 Issue 4 (2023) 151 https://doi.org/10.18063/ijb.725