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3D-Printing-Assisted EADs for Preventing VUR through DJ Stents
reflux along the stents was reported in 51.4% of patients fused deposition modeling (FDM)-type printing method
even after immediate insertion of ureteral stents . has been commonly used owing to its simplicity, low
[22]
Although VUR associated with DJ stents would not cost, and fast printing speed [37,38] . Moreover, products
require an immediate treatment or surgery to relieve the can be designed using computer-aided design (CAD)
symptoms, repetitive VUR may adversely affect patients software to create the desired shape. The FDM method
who require long-term placement of ureteral stents [21,23] . deposits a filament (e.g., polylactic acid or acrylonitrile
Thus, for the quality of patients’ life, the prevention of butadiene styrene) layer-by-layer; however, the resulting
VUR is significantly important, and therefore, anti-reflux product has a poor surface roughness [38,39] . Recent studies
medical devices compatible with the DJ stents must be have revealed that this drawback (i.e., rough surface)
developed; this remains as a challenge in urology. can be intentionally utilized for various applications
Once a DJ stent is inserted in the ureter, urine can such as (super) hydrophobic surfaces , micro-drilling
[40]
[43]
flow either through the inner wall or outer surface of devices , microchannels , and non-sticky surfaces .
[42]
[41]
the stent (more specifically, the space between the outer In this study, we fabricated and demonstrated
stent wall and the inner wall of the ureter) . Due to the attachable extraluminal anti-reflux diodes (EADs) based
[24]
dilated VUJ, reflux can flow not only in the intraluminal on an umbrella shape, which can effectively prevent
space but also in the extraluminal space [15,16] . To decrease extraluminal reflux from the bladder into the kidney
the VUR, various types of anti-reflux devices integrated while allowing urine drainage from the kidney into the
with DJ stents have been investigated for intraluminal bladder. The EADs were based on four different types of
reflux [15,21,23,25-27] . For example, polymeric flap valves and polygonal shapes and were fabricated by a casting process
collapsed valves have been demonstrated as intraluminal using an FDM-type 3D printer. The Ecoflex elastomer
anti-reflux devices [15,21,25,26] . For polymeric flap valve was utilized as the main body material due to its good
devices, in vitro experiments using hydrostatic pressure flexibility and biocompatibility [44,45] . To demonstrate the
indicated that volumetric backflow rates were decreased diode performance, the devices were characterized using
by up to 8 times under 50 cm-H O pressure compared an in vitro voiding (urination) model to measure the
2
to a bare DJ stent with no valve. The membrane-type maximum reflux height. In addition, the attached position
anti-reflux valves at distal end of the stent have also of the diode on the DJ stent and the number of diodes were
been studied and shown to reduce VUR degrees and considered to investigate the maximum performance. The
frequencies [23,27] . However, the valves were large, disadvantage of 3D printing (i.e., rough surface patterns)
inducing discomfort and irritation symptoms in patients was intentionally used to effectively attach the diode onto
during the insertion and therapeutic period. Although the stent, and the mechanical properties were compared to
the devices described in previous studies were effective those without rough surface patterns. To further investigate
in preventing intraluminal reflux, they could not prevent the health safety and durability of the devices in urine,
extraluminal reflux alongside the stent, which accounts Fourier transform infrared (FTIR) spectroscopy was
for the majority of the overall reflux. In addition, from conducted to observe changes in the chemical structures
a clinical point of view, there is also be a concern that of devices immersed in artificial urine for 4 weeks.
extraluminal reflux may occur [15,21] . To the best of our 2. Design and fabrication
knowledge, there is currently no published study about
the prevention of extraluminal reflux alongside the Figure 1A shows an overall schematic of the EAD,
stent. Therefore, the development of small, flexible, which is an anti-reflux device integrated with the DJ stent
biocompatible, and reliable anti-reflux devices with less in the ureter. Since the material of the EAD is Ecoflex,
irritation is still required to prevent extraluminal reflux which is flexible, its shape can be easily deformed by
alongside the stent. pressure. Figure 1B presents the operational mechanisms
In the last decade, additive manufacturing has been for the forward flow (urine drainage) and backward flow
widely used to develop various medical devices such as (urine reflux). The mechanism is based on the change in
bio-microfluidic chips , dental implants [29,30] , custom the cross-sectional area (internal area) of the EAD with
[28]
prosthetics [31,32] , and even ureteral stents . In particular, respect to the flow direction. During forward flow, the
[33]
casting processes using three-dimensional (3D)-printed urine flows and pushes the outer wall of the EAD. As the
molds have been utilized in a variety of fields because EAD is pushed toward the stent, the internal area decreases
they allow the use of diverse materials, which differ and the external area (i.e., the area between the outer
from 3D-printed materials. For example, in medical wall of the EAD and inner wall of the ureter) increases.
devices, flexible or biocompatible materials, such as Consequently, urine can readily flow along the external
silicone, epoxy, and polydimethylsiloxane, were utilized area in a forward direction. In contrast, during backward
as the casting material poured in 3D-printed molds [34-36] . flow, the urine flows and pushes the inner wall of the EAD.
Among the various types of 3D-printing methods, the Thus, the EAD expands and increases the internal area.

96 International Journal of Bioprinting (2022)–Volume 8, Issue 2