Analysis of the diffusion process by pH indicator in microfluidic chips for liposome production

In recent years, the development of nano- and micro-particles has attracted considerable interest from researchers and enterprises, because of the potential utility of such particles as drug delivery vehicles. Amongst the different techniques employed for the production of nanoparticles, microfluidic-based methods have proven to be the most effective for controlling particle size and dispersity, and for achieving high encapsulation efficiency of bioactive compounds. In this study, we specifically focus on the production of liposomes, spherical vesicles formed by a lipid bilayer encapsulating an aqueous core. The formation of liposomes in microfluidic devices is often governed by diffusive mass transfer of chemical species at the liquid interface between a solvent (i.e., alcohol) and a non-solvent (i.e., water). In this work, we developed a new approach for the analysis of mixing processes within microfluidic devices. The method relies on the use of a pH indicator, and we demonstrate its utility by characterizing the transfer of ethanol and water within two different microfluidic architectures. Our approach represents an effective route to experimentally characterize diffusion and advection processes governing the formation of vesicular/micellar systems in microfluidics, and can also be employed to validate the results of numerical modelling

The accumulation of particles in ureteric stents is mediated by flow dynamics: Full-scale computational and experimental modeling of the occluded and unoccluded ureter

Ureteric stents are clinically deployed to restore urinary drainage in the presence of ureteric occlusions. They consist of a hollow tube with multiple side-holes that enhance urinary drainage. The stent surface is often subject to encrustation (induced by crystals-forming bacteria such as Proteus mirabilis) or particle accumulation, which may compromise stent's drainage performance. Limited research has, however, been conducted to evaluate the relationship between flow dynamics and accumulation of crystals in stents. Here, we employed a full-scale architecture of the urinary system to computationally investigate the flow performance of a ureteric stent and experimentally determine the level of particle accumulation over the stent surface. Particular attention was given to side-holes, as they play a pivotal role in enhancing urinary drainage. Results demonstrated that there exists an inverse correlation between wall shear stress (WSS) and crystal accumulation at side-holes. Specifically, side-holes with greater WSS levels were those characterized by inter-compartmental fluid exchange between the stent and ureter. These "active " side-holes were located either nearby ureteric obstructions or at regions characterized by a physiological constriction of the ureter. Results also revealed that the majority of side-holes (> 60%) suffer from low WSS levels and are, thus, prone to crystals accumulation. Moreover, side-holes located toward the proximal region of the ureter presented lower WSS levels compared to more distal ones, thus suffering from greater particle accumulation. Overall, findings corroborate the role of WSS in modulating the localization and extent of particle accumulation in ureteric stents. (C) 2022 Author(s)

Fluid mechanical modeling of the upper urinary tract

The upper urinary tract (UUT) consists of kidneys and ureters, and is an integral part of the human urogenital system. Yet malfunctioning and complications of the UUT can happen at all stages of life, attributed to reasons such as congenital anomalies, urinary tract infections, urolithiasis and urothelial cancers, all of which require urological interventions and significantly compromise patients' quality of life. Therefore, many models have been developed to address the relevant scientific and clinical challenges of the UUT. Of all approaches, fluid mechanical modeling serves a pivotal role and various methods have been employed to develop physiologically meaningful models. In this article, we provide an overview on the historical evolution of fluid mechanical models of UUT that utilize theoretical, computational, and experimental approaches. Descriptions of the physiological functionality of each component are also given and the mechanical characterizations associated with the UUT are provided. As such, it is our aim to offer a brief summary of the current knowledge of the subject, and provide a comprehensive introduction for engineers, scientists, and clinicians who are interested in the field of fluid mechanical modeling of UUT

Latest advancements in ureteral stent technology

Urological diseases such as tumours, kidney stones, or strictures in the ureter can lead to a number of health consequences, including life-threatening complications. Ureteral stents have been widely used as a valid solution to restore compromised urological function. Despite their clinical success, stents are subject to failure due to encrustation and biofilm formation, potentially leading to urinary tract infection. The current review focuses on recent advancements in ureteral stent technology, which have been reported in recent scientific journals or patents. Web of Science and Google Scholar have been used as a search engine to perform this review, using the keywords “Ureteral + Stent + Design”, “Ureteral + Stent + Material + Coating”, “Ureteric + Stent” and “Ureteral + Stent”. A significant proportion of technological developments has focused on innovating the stent design to overcome migration and urinary reflux, as well as investigating novel materials and coatings to prevent biofilm formation, such as poly(N,N-dimethylacrylamide) (PDMMA) and swellable polyethylene glycol diacrylate (PEGDA). Biodegradable ureteral stents (BUS) have also emerged as a new generation of endourological devices, overcoming the “forgotten stent syndrome” and reducing healthcare costs. Moreover, efforts have been made to develop pre-clinical test methods, both experimental and computational, which could be employed as a screening platform to inform the design of novel stent technologies

A microfluidic-based investigation of bacterial attachment in ureteral stents

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these complications, ureteral stents are often deployed clinically in order to temporarily re-establish urinary flow. Despite their clinical benefits, stents are prone to encrustation and biofilm formation that lead to reduced quality of life for patients; however, the mechanisms underlying the formation of crystalline biofilms in stents are not yet fully understood. In this study, we developed microfluidic-based devices replicating the urodynamic field within different configurations of an occluded and stented ureter. We employed computational fluid dynamic simulations to characterise the flow dynamic field within these models and investigated bacterial attachment (Pseudomonas fluorescens) by means of crystal violet staining and fluorescence microscopy. We identified the presence of hydrodynamic cavities in the vicinity of a ureteric occlusion, which were characterised by low levels of wall shear stress (WSS < 40 mPa), and observed that initiation of bacterial attachment occurred in these specific regions of the stented ureter. Notably, the bacterial coverage area was directly proportional to the number of cavities present in the model. Fluorescence microscopy confirmed that the number density of bacteria was greater within cavities (3 bacteria•mm-2) when compared to side-holes of the stent (1 bacterium•mm-2) or its luminal surface (0.12 bacteria•mm-2). These findings informed the design of a novel technological solution against bacterial attachment, which reduces the extent of cavity flow and increases wall shear stress over the stent's surface

Laser-based printing and patterning for biological applications

We present the use of pulsed lasers as patterning and printing tools for the end applications of micro-contact printing and paper-based fluidics. A fs-laser was used with a digital multi-mirror device (DMD) to structure a mould via ablation or photo-polymerisation. The patterns in this mould were then cast into polydimethlysiloxane (PDMS)-mould which was used for micro-contact printing. With the end-goal of producing a microfluidic diagnostic sensor on paper, a ns-laser was used for laser-induced forward transfer (LIFT) of proteins onto a paper substrate, whose viability was validated by a colorimetric detection assa

Engineering solutions to ureteral stents: Material, coating and design

Introduction: An ideal stent would offer simple insertion and removal with no discomfort and/or migration, it would have no biofilm formation or encrustation and would also maintain the patient's quality of life. Material and methods: In this mini-review, we outlined the engineering developments related to stent material, design and coating. Results: There have been a wide variety of in-vitro, model-based, animal-based and clinical studies using a range of commercial and non-commercial stents. Ureteric stents have evolved since their first usage with a wider range of stent design, material and coating available for laboratory and clinical use. Conclusions: While engineering innovations have led to the evolution of stents, more work needs to be done to address the issues relating to stent encrustation and biofilm formation