Page 320 - IJB-10-5

International Journal of Bioprinting Amphiphobic encap. for transient devices

(up to 8%) and stomach (up to 40%) ; and large angular supraspinatus tendon (10–20 kPa Young’s modulus), and
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displacement or flexion in the spinal cord or skin. Figure 2 gland muscles (30–45 kPa Young’s modulus) or stomach
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presents the stress–strain curve and summarizes the (≈40% strain). Moreover, the increased toughness of
differences between SP/500 and 3P/500, in terms of strain, 3D-printed PBTPA (≈290.59 %) supports this possibility.
Young’s modulus, and toughness. The tensile test of PBTPA
layers was conducted according to the ASTM-D1708 3.2. 3D-printed amphiphobic encapsulation
standard (Figure S6, Supporting Information). The strain/ The 3D printing process enables the formation of
elongation of the 3D-printed PBTPA was approximately amphiphobic encapsulation structures using binary
186.01% higher compared to the screen-printed PBTPA hydrophobic polyanhydride. This unique membrane
(45.39% vs. 15.87%); Young’s modulus of the 3D-printed structure has been fabricated utilizing two types of
PBTPA was approximately 50.16% lower compared to the PBTPA solutions, i.e., with 1:1:2.5 and 1:4:7 of 4PA, TTT,
screen-printed PBTPA (30.75 kPa vs. 61.69 kPa) (Figure and BDT. The 1:1:2.5 and 1:4:7 PBTPA solutions were
S7, Supporting Information). These improvements are alternatively dispensed onto the 3D printer substrate to
comparable to or even exceed the impact of changing the ensure alternate stacking between the two unit layers
molar composition ratio of the PBTPA layer to obtain (Figure S8, Supporting Information). A similar strategy
softer PBTPA. The different molar composition ratio for stacking materials of different properties to establish
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of 4PA, TTT, and BDT (1:4:7–1:1:2.5) resulted in a slight a water barrier has been studied in the development of
increase in elongation (15.14%) and a decrease in Young’s organic LEDs (OLEDs). Encapsulation films made of a
modulus (79.28%), based on previous research. Therefore, single material cannot maintain the desired water-barrier
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the 3D printing method, yielding 186.01% increased strain effect if they exceed the critical thickness. This has led to
and 50.12% reduced Young’s modulus, could be used to the development of multi-material water barriers. 48,49 This
adjust the mechanical and waterproofing properties in at- effect is also applicable in the 3D-printed amphiphobic
once UV curing processes. Soft materials typically allow encapsulation of transient electronics (Figure 3A).
more frequent water diffusion through the film, but the The binary hydrophobic polyanhydrides, i.e., less
homogenous polymerization by 3D printing enhances hydrophobic 1:1:2.5 PBTPA and more hydrophobic 1:4:7
both waterproofing and mechanical characteristics. Hence, PBTPA, form a thick bulk membrane via layer-by-layer
the 3D-printed polymer membrane can better stabilize 3D printing, which increases the diffusion length of water
implanted devices and enable robust and longer operation, from decoupled defects in the unit layer. In addition,
particularly in dynamic tissues. Specifically, 3D-printed amphiphobic PBTPAs interact with water molecules
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membranes further extend the application of transient in two distinctive ways: water trapping and water
devices to more diverse physiological environments, such repulsion. These distinctive interactions are attributed
as the human intestine (20–40 kPa Young’s modulus), to the small size of defects (pore or pinhole) on PBTPA
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Figure 2. Enhanced mechanical properties of the 3D-printed polyanhydride encapsulation layer. (A) Stress–strain curve comparison between SP/500 and
3P/500. (B) Comparison between SP/500 and 3P/500, in terms of strain, Young’s modulus, and toughness. Abbreviations: 3P/500, 3D-printed 500-μm-
thick film; SP/500, screen-printed 500-μm-thick film.

Volume 10 Issue 5 (2024) 312 doi: 10.36922/ijb.3871