Page 163 - IJB-9-4

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

Figure 7. (i) Schematic showing the design of the sweat sensors. (ii) Schematic showing the fabrication steps of the sweat sensors. (iii) Graphs showing the
[58]
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detection Na , K and Ca ions and the selectivity of the sensors. (Reprinted with permission from . Copyright (2021) from John, Wiley and Sons Inc.)
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attempted the fabrication of CNT-based resistive pH function adequately with heat treatment at only 60°C [113] .
sensor via AJP and IJP, respectively [73,78,84] . The pH- Graphene–PLA-based electrodes, on the other hand,
responsive property of CNT allows the detection of pH are usually used to produce enzymatic glucose sensors.
through the monitoring of electrical resistance of the CNT- The fabrication of these sensors involves certain post-
based pH sensing electrodes. On the other hand, Fan et al. processing steps such as polishing, cleaning, and surface
demonstrated the fabrication of organic electrochemical activation, and enzyme immobilization. The oxygenated
transistor (OECT) that is pH-sensitive on a 3D-printed groups from the nanocomposite material provides suitable
PLA substrate . The OECT has a multi-layered conditions for the enzyme (glucose oxidase) to immobilize
[69]
architecture and contains multiple materials, such as silver on its surface via crosslinkers such as glutaraldehyde [60,61] .
conductor and PEDOT:PSS, and it is fabricated through Other than 3D-printed microheater, temperature
DIW technique. They found that the performance of the sensors, pH sensors and glucose sensors, there are other
sensor is comparable to other devices that are fabricated types of 3D-printed sensors, such as sweat sensor ,
[58]
using microfabrication techniques. biomolecule sensor , and DNA sensor [115] for other
[60]
Glucose sensor is an essential component of glucose physiological parameters. For instance, Kim et al.
monitoring for diabetic patients. It enables on-demand fabricated a 3D-printed wearable bioelectronic patch that
triggering of insulin release whenever the glucose level of allows in situ sweat electrolyte monitoring purposes .
[58]
the patients is at an unhealthy level. So far, there are many The sweat sensing relies on the DIW-printed ion-selective
works that have demonstrated using 3D-printed sensors electrodes to detect the concentrations of Na , K , and
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for glucose level detection [60,61,113,114] . Interestingly, most of Ca ions in the sweat electrolyte (Figure 7). The main
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these works involve the use of FFF 3D printing techniques ingredients of the ion-selective electrodes are sodium
to fabricate the 3D electrodes. The electrode materials ionophore, potassium ionophore, and calcium ionophore,
that have been attempted include copper filament [114] , which are the lipophilic complexing agents that reversibly
graphene–PLA nanocomposite filament [60,61] , and copper- bind ions. These ingredients are usually incorporated into
zinc oxide-PVDF nanocomposite filament [113] . Redondo a membrane before binding to the 3D-printed electrodes.
et al. found that the 3D-printed copper electrode is very Other than ions, there is another work that describes
suitable for non-enzymatic glucose sensing due to their the detection of biologically-produced molecules such
high conductivity and high catalytic activity resulting from as uric acid and nitrite using 3D-printed graphene–PLA
the porous structure [114] . However, it should be noted that electrode [116] . They have tested the 3D-printed sensor
the drawback of the 3D-printed copper electrode is the with saliva and urine and shown that the sensor exhibits
high energy consumption as it requires a high sintering satisfactory linear range, sensitivity, limit of detection.
temperature of greater than 1000°C. In contrast, Kumar Another interesting example of 3D-printed sensor is
et al. demonstrated that the use of copper–zinc oxide- on DNA sensing. Loo et al. used selective laser melting
reinforced PVDF as nonenzymatic glucose electrode can printing technology to fabricate a helical-shape stainless

Volume 9 Issue 4 (2023) 155 https://doi.org/10.18063/ijb.725