Novel Nanostructured Coating on PDMS Substrates Featuring High Resistance to Urine

Abstract

Artificial urinary devices are commonly employed to restore the lost functionalities of the urinary system, due to diseases, disfunctions or organ resections. However, the long-term operation of these devices in the urinary system is affected by encrustations. In this paper, three different nanostructured coatings, based on diamondlike carbon (DLC), molybdenum disulfide (MoS2) and Tungsten disulfide (WS2), were deposited on polydimethylsiloxane substrates, an elastomer suitable for coating different kinds of urinary devices, and tested in terms of resistance to urinary encrustations. DLC coatings were deposited using plasma enhanced-chemical vapor deposition (T < 180 °C), whereas MoS2 and WS2 coatings were achieved through self-assembly at room temperature. All coatings showed good adhesion and stability on PDMS substrate over one month, relatively small roughness, a strongly hydrophobic behavior, and low surface energy. After immersion in artificial urine formulations and continuous mechanical agitation for 4 weeks, WS2 coating resulted the most resistant to encrustations. This material had been never investigated in the urinary context. Our results pave the way to the adoption of WS2 coatings for developing long-lasting stable urinary devices.

PDMS and DLC‐coated unidirectional valves for artificial urinary sphincters: Opening performance after 126 days of immersion in urine

“…The slight decrease in contact angle values due to the DLC coating confirms previous findings 13 . Differently, the marked increase in surface roughness values does not reflect the results obtained in previous studies 19,20 .…”

“…Because the urine parameters such as pH and protein content are subjected to a considerable variability depending on the subject and his/her overall conditions, three different urine solutions were considered. This allowed testing standard as well as altered precipitation conditions in which the encrustations are more favored 13,18 . The used formulations were (i) sterile artificial urine (Sterile); (ii) artificial urine with the addition of the urease enzyme, to simulate the presence of a bacterial infection (Urease); and (iii) artificial urine with the addition of the urease enzyme and the albumin protein (Albumin) to evaluate the role of the protein component in the encrustation process.…”

“…In this work, we demonstrated that PDMS-based valves, whose constitutive material typically undergoes massive encrustation after a few weeks, in both sterile and urease-enriched urine, 13 have unchanged performance over time, in terms of opening pressure. The polymeric valves made of such a material, in this study, outperformed even the long-term indwelling catheters (that after 12 weeks fail), demonstrating that the periodical mechanical opening of the valve (multiple times per day) is effective in "resetting" the chain of events that bring from the first small crystalline deposit to the large struvite, apatite, or calcium oxalate crystals, not giving them the time they need to form.…”

“…Cardona et al investigated the behavior of PDMS samples in terms of formation of encrustations, also testing the effect of urine‐resistant coatings (nanostructured diamond‐like carbon [DLC], MoS 2 nanoparticles, and WS 2 nanoparticles) in comparison with the bare polymer 13 . However, in this study, the materials were maintained in static conditions (without opening the valve) for 4 weeks.…”

Future Directions for Ureteral Stent Technology: From Bench to the Market

“…[49,50] Other novel materials also recently considered include molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) nanostructured coatings. [51] Apart from the abovementioned strategies, many other materials, especially those belonging to the class of metals (as gold) and oxides (silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 )) are rising as potential candidates for the fabrication of inorganic coatings with improved functionalities. [52,53] These materials show very interesting physical and chemical properties, which are tunable once externally activated.…”