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International Journal of Bioprinting Amphiphobic encap. for transient devices

eliminate the risks associated with the secondary surgical fabrication (FFF), 34,35 and selective laser sintering (SLS).
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extraction process of implant devices, 10–12 leading to the This diversity of principles offers novel solutions to
development of bioresorbable drug-delivery systems, 13–15 address issues, such as incomplete crosslinking in transient
electrophysiological sensors, 16–18 mechanical sensors, 19–21 electronics. In this study, we utilized the DLP method,
nerve stimulators, 22–26 and pacemakers. Researchers are known for its high output speed and capability to produce
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also studying the fundamental chemistry of dissolution and sophisticated designs, to photo-cure PBTPA. In the DLP
strategies to trigger transience. 6,28,29 For clinical use in real- process of PBTPA, achieving the desired final polymer
world environments, transient devices should be designed membrane thickness involves dividing it into multiple
to bioresorb only after operating for a specified duration. layers and stacking them sequentially. This process relies
Therefore, the main challenge in transient electronics is on a fixed UV light source within a customized DLP
controlling and extending their operational lifetime. device, with the substrate containing the PBTPA precursor
solution moving vertically downward after each unit
A controllable encapsulation layer for transient
electronics could provide a feasible solution to this layer is photo-synthesized and stacked. Implementing a
50-μm layer-by-layer 3D printing method could improve
challenge. In the body’s environment, the hydrolysis of the polymeric lifetime and mechanical properties by
constituent materials can act as a primary trigger for ensuring complete crosslinking throughout the entire
transient device degradation. Therefore, the waterproof encapsulation layer. The waterproofing characteristic,
encapsulation layer is essential to enhance the lifetime of Young’s modulus, and toughness were selected as the
electronics. These encapsulation materials should be soft criteria for evaluating PBTPA as the encapsulation
and biocompatible to function effectively in vivo, ideally layer. Based on these criteria, we found that the physical
offering a long operational lifespan. The requirement properties of the polymer can be enhanced by changing
of these properties has driven extensive research in the the crosslinking degree via fine thickness-controlled 3D
development of new materials for encapsulation layers. printing and minimizing the light attenuation effect. In
Polymers (e.g., polybutanedithiol 1,3,5-triallyl-1,3,5- addition, introducing a unique amphiphobic structure
triazine-2,4,6[1H,3H,5H]-trione pentenoic anhydride using binary hydrophobic polyanhydride layers enhanced
[PBTPA], 30 polyurethane [PU], 24,31 poly[lactic-co- the application of 3D-printed polymer membranes, in
glycolic acid] [PLGA] 15,24 ), natural waxes, 28,32 and terms of waterproofing and mechanical properties. This
inorganic materials (e.g., SiO and Si N ) could serve amphiphobic encapsulation maximized the lifetime of
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2
3
4
as encapsulation materials. The common processes for transient devices through the unique interaction between
fabricating the encapsulation layer mainly include drop- layer-by-layer hydrophobic polymer layers. We believe that
casting (e.g., for PU and PLGA), mold-based techniques our 3D-printed multi-unit layers can provide alternatives
(e.g., for PBTPA), and screen-printing (e.g., for PBTPA). for versatile selections of encapsulation materials in
However, conventional methods have many limitations transient electronics.
when it comes to micro-processing and precise thickness
control. For example, PBTPA, a type of polyanhydride, 2. Materials and methods
is a photocurable and biodegradable polymer suitable
for use as an encapsulation layer in transient electronics 2.1. Materials
due to its hydrophobic chemistry and surface erosion The chemicals 4-pentenoic anhydride (4PA),
characteristics. The molding process and screen-printing 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione
followed by ultraviolet (UV) irradiation are frequently (TTT), 1,4-butanedithiol (BDT), and 2,2-dimethoxy-2-
used to fabricate the PBTPA encapsulation layers. 15,24 These phenylacetophenone were used to synthesize bioresorbable
simple fabrication methods have gained considerable polyanhydride (Sigma-Aldrich, United States of
attention due to their convenience and rapidity. However, America [USA]). Agarose and phosphate-buffered saline
they fail at precisely controlling the properties because (PBS) were obtained from Sigma-Aldrich (USA) for
of the nonuniform irradiation on PBTPA with different device-level demonstration.
thicknesses, leading to incomplete crosslinking.
2.2. Preparation and 3D printing of PBTPA solution
Three-dimensional (3D) printing has been applied in The 3D printer was fabricated by ourselves by installing a
various engineering fields, owing to its cost-effectiveness, light-emitting diode (LED; PRO4710; Wintech, USA) as
capability for personalization, and tunable mechanical an ultraviolet (UV) source into customized hardware. The
properties. The principles of 3D printing can vary customized hardware consisted of an Arduino board and
according to the specific requirements of each engineering a 200-angle motor to repeatedly move the substrate in the
field, such as digital light processing (DLP), fused filament vertical direction as the unit polymer layer is synthesized.

Volume 10 Issue 5 (2024) 308 doi: 10.36922/ijb.3871