3D-Printing-Assisted Extraluminal Anti-Reflux Diodes for Preventing Vesicoureteral Reflux through Double-J Stents.

This paper presents novel umbrella-shaped flexible devices to prevent vesicoureteral reflux along double-J stents, which is a backward flow of urine from the bladder to the kidney and is a critical issue in patients with urinary stones. The anti-reflux devices were designed to mechanically attach to the stent and were manufactured using three-dimensional (3D) printing and polymer casting methods. Based on the umbrella shapes, four different devices were manufactured, and the anti-reflux efficiency was demonstrated through in vitro experiments using a urination model. Consequently, penta-shaped devices exhibited the best anti-reflux performance (44% decrease in reflux compared to the stent without the device), and maximum efficiency occurred when the device was attached near the bladder-ureter junction. In addition, a disadvantage of 3D printing (i.e., unwanted rough surface) helped the device strongly adhere to the surface of the stent during the insertion operation. Finally, long-term soaking experiments revealed that the fabricated devices were mechanically robust and chemically stable (safe) even being soaked in urine for 4 weeks. The findings of this study support the use of additive manufacturing to make various flexible and biocompatible urological devices to mitigate critical issues in patients with urinary stones.

A biomimetic compound eye lens for photocurrent enhancement at low temperatures.

In this study, an artificial compound eye lens (ACEL) was fabricated using a laser cutting machine and polyvinyl alcohol (PVA) solution. A laser cutter was used to punch micro-sized holes (500 µm diameter-the smallest possible diameter) into an acrylic plate; this punched plate was then placed on the aqueous PVA solution, and the water was evaporated. The plate was used as the mold to obtain a polydimethylsiloxane (PDMS) micro lens array film, which was fixed to a dome-shaped three-dimensional-printed mold for further PDMS curing, and a hemispherical compound eye lens was obtained. Using a gallium nitride (GaN) photodetector, a light detection experiment was performed with the ACEL, bare lens, and no lens by irradiating light at various angles under low temperatures. The photodetector with the ACEL generated a high photocurrent under several conditions. In particular, when the light was irradiated at 0° and below -20 °C, the photocurrent of the GaN sensor with the ACEL increased by 61% and 81% compared with the photocurrent of the GaN sensor with the bare lens and without a lens, respectively. In this study, a sensor for detecting light with ACEL was demonstrated in low-temperature environments, such as indoor refrigerated storages and external conditions in Antarctica and Arctic.

Modeling and application of anisotropic hyperelasticity of PDMS polymers with surface patterns obtained by additive manufacturing technology.

Polydimethylsiloxane (PDMS) polymer has been widely used in the biomedical fields because of its bio-compatibility, being used as sensors, medical equipment and tissue implants. The present study aims to synthesize and characterize micro lane-type surface patterns of PDMS polymers and evaluate their effects on mechanical properties for various applications in the bio-engineering field. Fabrication of surface patterns is achieved using fused filament fabrication in additive manufacturing, and the mechanical properties of the polymer specimens with the surface patterns are measured using tensile test. The surface patterns are rotated at different angles and changed into different shapes to change the anisotropic material properties of the PDMS specimens. This is achieved by changing the raster angles and modifying the fused filament paths during the additive manufacturing process. In addition, the application of the printed pattern to medical soft robot is presented. Owing to the anisotropic material properties, in-plane and out-of-plane actuation can be realized by attaching polymer patches with different lane-type surface patterns. The results of this study support the implementation of additive manufacturing for the rapid manufacture of scalable structures with anisotropic material properties for various applications.