Wetting on silicone surfaces.

Silicone is frequently used as a model system to investigate and tune wetting on soft materials. Silicone is biocompatible and shows excellent thermal, chemical, and UV stability. Moreover, the mechanical properties of the surface can be easily varied by several orders of magnitude in a controlled manner. Polydimethylsiloxane (PDMS) is a popular choice for coating applications such as lubrication, self-cleaning, and drag reduction, facilitated by low surface energy. Aiming to understand the underlying interactions and forces, motivated numerous and detailed investigations of the static and dynamic wetting behavior of drops on PDMS-based surfaces. Here, we recognize the three most prevalent PDMS surface variants, namely liquid-infused (SLIPS/LIS), elastomeric, and liquid-like (SOCAL) surfaces. To understand, optimize, and tune the wetting properties of these PDMS surfaces, we review and compare their similarities and differences by discussing (i) the chemical and molecular structure, and (ii) the static and dynamic wetting behavior. We also provide (iii) an overview of methods and techniques to characterize PDMS-based surfaces and their wetting behavior. The static and dynamic wetting ridge is given particular attention, as it dominates energy dissipation, adhesion, and friction of sliding drops and influences the durability of the surfaces. We also discuss special features such as cloaking and wetting-induced phase separation. Key challenges and opportunities of these three surface variants are outlined.

Effectiveness and Safety of Antiobesity Medications in Patients With Obesity and Inflammatory Bowel Disease.

INTRODUCTION: Limited data exist evaluating antiobesity medications (AOM) in patients with inflammatory bowel disease (IBD). METHODS: We performed a case-control study evaluating the effectiveness and safety of AOM in patients with IBD with obesity, matched to non-IBD controls. RESULTS: After 12 months, the case (n = 36) and control (n = 36) groups achieved similar percent total body weight loss of -6.9 ± 8.3 and -8.1 ± 7.0 (P = 0.30), respectively. Side effect profiles were similar between groups. Seven patients experienced an IBD flare, all managed medically. DISCUSSION: AOM use in patients with IBD demonstrated similar effectiveness and safety when compared with that observed in the non-IBD population.

Phase Separation in Wetting Ridges of Sliding Drops on Soft and Swollen Surfaces.

Drops in contact with swollen, elastomeric substrates can induce a capillary mediated phase separation in wetting ridges. Using confocal microscopy, we visualize phase separation of oligomeric silicone oil from a cross-linked silicone network during steady-state sliding of water drops. We find an inverse relationship between the oil tip height and the drop sliding speed, which is rationalized by competing transport timescales of the oil molecules: separation rate versus drop-advection speed. Separation rates in highly swollen networks are as fast as diffusion in pure melts.

Capillary detachment of a microparticle from a liquid-liquid interface.

The attachment and detachment of microparticles at a liquid-liquid interface are common in many material systems, from Pickering emulsions and colloidal assemblies to capillary suspensions. Properties of these systems rely on how the particles interact with the liquid-liquid interface, including the detachment process. In this study, we simultaneously measure the capillary detachment force of a microparticle from a liquid-liquid interface and visualize the shape of the meniscus by combining colloidal probe microscopy and confocal microscopy. The capillary behavior is studied on both untreated (hydrophilic) and fluorinated (hydrophobic) glass microparticles. The measured force data show good agreement with theoretical calculations based on the extracted geometric parameters from confocal images of the capillary bridge. It is also evident that contact line pinning is an important aspect of detachment for both untreated and fluorinated particles.

Cronkhite-Canada syndrome: treatment responses and improved overall survival.

BACKGROUND: Cronkhite-Canada syndrome (CCS) is considered a relentlessly progressive disease with high mortality rates. Although disease understanding and treatment options have greatly improved, the prognosis from these advancements has not been well documented. This study aimed to evaluate treatment outcomes and overall survival of CCS. METHODS: Seventeen patients who were diagnosed and treated over a 20-year period at Mayo Clinic (Rochester, Minnesota) were included. Data were abstracted, which included clinical and endoscopic manifestations, treatment course, and survival outcomes. RESULTS: The median (interquartile range) duration of follow-up was 8.3 (3.7-15.8) years. All patients received an initial prednisone dose equivalence of 30-80 mg daily, and five patients required steroids at the time of the last follow-up. Twelve patients trialed thiopurine therapy, and ten patients continued with a thiopurine until the last follow-up. Fifteen patients achieved clinical complete remission, and eleven patients achieved endoscopic complete remission after pharmacotherapy initiation. Seven patients required gastrointestinal surgeries during their disease course. The 5-year overall survival was 93.3% (95% confidence interval (CI): 81.5-100%), and the 3-year relapse-free survival was 82.4% (95% CI: 66.1-100%). CONCLUSION: The prognosis and overall survival of patients with CCS have markedly improved with advancement in disease understanding and therapies. Pharmacotherapy, including corticosteroids and immunomodulators, is effective in inducing and maintaining remission, and gastrointestinal surgery is commonly needed as an adjunct for managing CCS disease complications.

Visualizing Penetration of Fluorescent Dye through Polymer Coatings.

Understanding how small molecules penetrate and contaminate polymer films is of vital importance for developing protective coatings for a wide range of applications. To this end, rhodamine B fluorescent dye is visualized diffusing through polystyrene-polydimethylsiloxane block copolymer (BCP) coatings using confocal microscopy. The intensity of dye inside the coatings grows and decays non-monotonically, which is likely due to a combination of dye molecule transport occurring concurrently in different directions. An empirical fitting equation allows for comparing the contamination rates between copolymers, demonstrating that dye penetration is related to the chemical makeup and configuration of the BCPs. This work shows that confocal microscopy can be a useful tool to visualize the transport of a fluorophore in space and time through a coating.

Temperature-dependent soft wetting on amorphous, uncrosslinked polymer surfaces.

The wetting of polymer melts at high temperatures is studied by placing a glycerol drop on a poly(n-butyl methacrylate) film and measuring the wetting ridge. The height of the wetting ridge grows continuously over time. These wetting ridge growth rates can be explained by polymer chain dynamics occurring at the molecular level, determined using oscillatory shear rheology of the polymer melt. The shape of wetting ridge profile can be modeled using an equation previously used for elastomers, with a simple modification that incorporates the time-dependent storage modulus of the uncrosslinked melts.

Capillary-driven indentation of a microparticle into a soft, oil-coated substrate.

Small scale contact between a soft, liquid-coated layer and a stiff surface is common in many situations, from synovial fluid on articular cartilage to adhesives in humid environments. Moreover, many model studies on soft adhesive contacts are conducted with soft silicone elastomers, which possess uncrosslinked liquid molecules (i.e. silicone oil) when the modulus is low. We investigate how the thickness of a silicone oil layer on a soft substrate relates to the indentation depth of glass microspheres in contact with crosslinked PDMS, which have a modulus of <10 kPa. The particles indent into the underlying substrate more as a function of decreasing oil layer thickness. This is due to the presence of the liquid layer at the surface that causes capillary forces to pull down on the particle. A simple model that balances the capillary force of the oil layer and the minimal particle-substrate adhesion with the elastic and surface tension forces from the substrate is proposed to predict the particle indentation depth.

Quantitative CT Predictors of Portal Venous Intervention in Uncontrolled Variceal Bleeding.

OBJECTIVE. The purpose of this study was to quantify abdominal CT predictors of endoscopically refractory, uncontrolled variceal hemorrhage requiring portal venous intervention. MATERIALS AND METHODS. From 2009 to 2018, 64 patients with endoscopically refractory variceal hemorrhage requiring portal venous intervention (variceal hemorrhage group) and 67 patients without hemorrhage but with symptomatic, pressure gradient-proven portal hypertension (control group) underwent CT. CT scans were retrospectively reviewed for the following: varix size, variceal intraluminal protrusion, liver and spleen volumes, and portal vein diameter. RESULTS. Gastric variceal protrusion was found to be a strong CT parameter associated with refractory hemorrhage (mean depth, 0.75 mm in variceal hemorrhage group vs -2.91 mm in control group; p = 0.001). Gastric varix size was also associated with variceal hemorrhage (mean diameter, 8.03 vs 6.51 mm; p = 0.001). However, this trend was not observed in the sizes of the esophageal varices (mean diameter, 6.28 vs 6.43 mm; p = 0.370). Larger spleen volume (mean, 1312 vs 1152 cm3; p = 0.029) and liver volume (mean, 1514 vs 1143 cm3; p = 0.004) were also found to be predictors of variceal hemorrhage. Significant CT threshold findings included gastric variceal protrusion depth more than 0 mm (odds ratio [OR], 6.44), gastric varix size more than 6 mm (OR, 3.89), spleen volume more than 1000 cm3 (OR, 2.63), and liver volume more than 1000 cm3 (OR, 2.82). CONCLUSION. Quantitative imaging parameters on abdominal CT, such as intraluminal protrusion of gastric varices, gastric varix size, and larger spleen and liver volumes, were predictive of portal venous intervention, whereas esophageal varix size was not.

Stick-Slip Friction of PDMS Surfaces for Bioinspired Adhesives.

Friction plays an important role in the adhesion of many climbing organisms, such as the gecko. During the shearing between two surfaces, periodic stick-slip behavior is often observed and may be critical to the adhesion of gecko setae and gecko-inspired adhesives. Here, we investigate the influence of short oligomers and pendent chains on the stick-slip friction of polydimethylsiloxane (PDMS), a commonly used material for bioinspired adhesives. Three different stick-slip patterns were observed on these surfaces (flat or microstructured) depending on the presence or absence of oligomers and their ability to diffuse out of the material. After washing samples to remove any untethered oligomeric chains, or after oxygen plasma treatment to convert the surface to a thin layer of silica, we decouple the contributions of stiffness, oligomers, and pendant chains to the stick-slip behavior. The stick phase is mainly controlled by the stiffness while the amount of untethered oligomers and pendant chains available at the contact interface defines the slip phase. A large amount of oligomers and pendant chains resulted in a large slip time, dominating the period of stick-slip motion.

Stretching of assembled nanoparticle helical springs.

Hybrid materials that possess high inorganic fractions of nanoscale particles can be advantageous for a wide range of functions, from optoelectronic or electronic devices to drug delivery. However, many current nanoparticle (NP) based materials lack the necessary combination of simple fabrication and robust mechanical properties that span across length scales greater than tens of microns. We have developed a facile, evaporative assembly method called flow coating to create NP based ribbons that can subsequently form helical structures. Here we analytically examine the stretching properties of these helical ribbons which are nanometers thick, microns wide, and arbitrarily long. We find that the force-extension behavior is well described by the elastic and surface energies, which can be used as a guideline for their design. In addition, we show that the properties may be tuned by changing the ribbon dimensions or material composition to yield a different stiffness. These macroscale mechanical properties, along with properties inherent to the nanometer length scale of the particles can provide tunable multifunctionality for a number of applications.

Controlling Anti-Penetration Performance by Post-Grafting of Fluorinated Alkyl Chains onto Polystyrene-block-poly(vinyl methyl siloxane).

Polydimethylsiloxane (PDMS) has been widely used as a surface coating material, which has been reported to possess dynamic omniphobicity to a wide range of both polar and nonpolar solvents due to its high segmental flexibility and mobility. However, such high flexibility and mobility also enable penetration of small molecules into PDMS coatings, which alter the chemical and physical properties of the coating layers. To improve the anti-penetration properties of PDMS, a series of fluorinated alkyl segments are grafted to a diblock copolymer of polystyrene-block-poly(vinyl methyl siloxane) (PS-b-PVMS) using thiol-ene click reactions. This article reports the chemical characterization of these model fluorosilicone block copolymers and uses fluorescence measurements to investigate the dye penetration characteristics of polymer thin films. The introduction of longer fluorinated alkyl chains can gradually increase the anti-penetration properties as the time to reach the maximum fluorescence intensity (tpeak) gradually increases from 11 s of PS-b-PVMS to more than 1000 s of PS-b-P(n-C6F13-VMS). The improvement of anti-penetration properties is attributed to stronger inter-/intrachain interactions, phase segregation of ordered fluorinated side chains, and enhanced hydrophobicity caused by the grafting of fluorinated alkyl chains.

Large deformation and adhesive contact studies of axisymmetric membranes.

A model membrane contact system consisting of an acrylic copolymer membrane and a PDMS substrate was utilized to evaluate a recently developed nonlinear large-deformation adhesive contact analysis. Direct measurements of the local membrane apex strain during noncontact inflation indicated that the neo-Hookean model provides an accurate measure of membrane strain and supports its use as the strain energy function for the analysis. Two membrane contact geometries, exhibiting significantly different strain distributions during withdrawal, were investigated. The first examines the wet contact of an air pressurized membrane. The second looks at the dry contact of a fluid deformed membrane in which a stepper motor controls membrane-substrate separation. A time-dependent modulus emerges from the analysis, with principal tensions obtained from a comparison of predicted and experimental membrane profiles. The applicability of this numerical analysis for determining membrane tension, however, is limited by wrinkling instabilities and viscoelasticity. For this reason, a conceptually simpler method, based on the direct measurement of the membrane tension and contact angle, was also utilized. The traditional peel energy defined with this direct measurement accurately described the membrane/substrate adhesive interactions, giving well-defined peel energies that were independent of the detailed strain state of the membrane.

Creasing in microscale, soft static friction.

Utilizing colloidal probe, lateral force microscopy and simultaneous confocal microscopy, combined with finite element analysis, we investigate how a microparticle starts moving laterally on a soft, adhesive surface. We find that the surface can form a self-contacting crease at the leading front, which results from a buildup of compressive stress. Experimentally, creases are observed on substrates that exhibit either high or low adhesion when measured in the normal direction, motivating the use of simulations to consider the role of adhesion energy and interfacial strength. Our simulations illustrate that the interfacial strength plays a dominating role in the nucleation of a crease. After the crease forms, it progresses through the contact zone in a Schallamach wave-like fashion. Interestingly, our results suggest that this Schallamach wave-like motion is facilitated by free slip at the adhesive, self-contacting interface within the crease.

Synchronous melanosis of upper and lower urinary tract.

Urothelial melanosis is an exceptionally rare diagnosis, with less than 25 cases being reported in the literature. Melanosis of the urothelium is characterized by abnormal melanin deposition within tissues, producing a black, velvety appearance to the urothelial mucosa. We present a 67-year-old male undergoing cystoscopy during a routine percutaneous nephrolithotomy (PCNL), who was found to have diffuse bladder melanosis extending up the ureter and into the renal pelvis. To our knowledge, this is the first reported case of synchronous melanosis of upper and lower urinary tract.

27-year trends in incidence rates for testis cancer across a large statewide registry.

PURPOSE: To review 27-years of testicular cancer (TC) incidence data (1990-2017) within the state of Pennsylvania to better define incidence, geographic distribution, and trends over time. METHODS: The Pennsylvania Cancer Registry was reviewed for statewide and component county age-adjusted TC incidence rates and stage distribution. We reported annual percent changes (APCs) in age-adjusted rates. Maps plotting county-level incidence rates across the state in five-year time intervals were created. RESULTS: In Pennsylvania, 9,933 TC cases were recorded between 1990-2017. Over two-thirds of patients were < 40 years of age and 95% were White. Approximately 89% presented as local and regional disease. Age-adjusted annual rates of total TC increased from 4.80 to 7.20 patients per 100,000 with an APC of 0.94 (95% Confidence Interval (CI) = (0.59, 1.29), P < 0.01) over the study interval. Annual rates of local disease increased from 3.20 to 5.00 patients per 100,000 with an APC of 1.07 (95% CI = (0.67, 1.46), P < 0.01). Annual rates of distant disease were stable and ranged from 0.50 to 0.80 patients per 100,000 with an APC of 0.69 (95% CI = (-0.02, 1.40), P = 0.06). Geospatial investigation noted increased incidence in urban centers. CONCLUSIONS: Although TC is rare, incidence is rising. Rates of TC in Pennsylvania almost doubled over the past two decades. Fortunately, this rising trend is primarily attributed to increases in local and regional disease. Counties with higher incidence rates cluster in urban centers which may reflect exposure risk, access to care, or reporting bias.

Engineering ligand reactivity enables high-temperature operation of stable perovskite solar cells.

Perovskite solar cells (PSCs) consisting of interfacial two- and three-dimensional heterostructures that incorporate ammonium ligand intercalation have enabled rapid progress toward the goal of uniting performance with stability. However, as the field continues to seek ever-higher durability, additional tools that avoid progressive ligand intercalation are needed to minimize degradation at high temperatures. We used ammonium ligands that are nonreactive with the bulk of perovskites and investigated a library that varies ligand molecular structure systematically. We found that fluorinated aniliniums offer interfacial passivation and simultaneously minimize reactivity with perovskites. Using this approach, we report a certified quasi-steady-state power-conversion efficiency of 24.09% for inverted-structure PSCs. In an encapsulated device operating at 85°C and 50% relative humidity, we document a 1560-hour T85 at maximum power point under 1-sun illumination.

Hydrophobic surface patterning with soft, wax-infused micro-stamps.

HYPOTHESIS: Waxy hydrocarbons diffuse freely in polydimethylsiloxane (PDMS), and this capability can be leveraged to generate inexpensive surface micropatterns that modify adhesion and wetting. EXPERIMENTS: Patterns are created by placing a waxy Parafilm sheet on the back of a PDMS stamp containing microscale surface features. When heated, the paraffin liquefies and diffuses through the stamp, creating a thin liquid layer on the micropatterned stamp surface; when placed in contact with a target surface, the layer solidifies and is retained on the target when the stamp is removed. Micropatterns were generated on different materials and surface topographies; pattern geometry was evaluated using optical profilometry and changes in wetting were evaluated using contact angle goniometry. Diffusion of paraffin through PDMS was evaluated using XPS. FINDINGS: Wax micropatterns have submicron lateral resolution and thickness ranging from 85 to 380 nm depending on contact time. By using XPS analysis to track paraffin diffusion within the PDMS stamp during this process, we estimate the diffusion coefficient to be 5.3 × 10-7 cm2/s at 65 °C. This means that the paraffin layer at the stamp surface replenishes in less than a second after stamping, so it can be used multiple times without re-inking to deposit complex, multi-layer paraffin patterns.

Shaping Nanoscale Ribbons into Microhelices of Controllable Radius and Pitch.

We report fabrication of highly flexible micron-sized helices from nanometer-thick ribbons. Building upon the helical coiling of such ultrathin ribbons mediated by surface tension, we demonstrate that the enhanced creep properties of highly confined materials can be leveraged to shape helices into the desired geometry with full control of the final shape. The helical radius, total length, and pitch angle are all freely and independently tunable within a wide range: radius within ∼1-100 µm, length within ∼100-3000 µm, and pitch angle within ∼0-70°. This fabrication method is validated for three different materials: poly(methyl methacrylate), poly(dimethylaminoethyl methacrylate), and transition metal chalcogenide quantum dots, each corresponding to a different solid-phase structure: respectively a polymer glass, a cross-linked hydrogel, and a nanoparticle array. This demonstrates excellent versatility with respect to material selection, enabling further control of the helix mechanical properties.

Erodible thermogelling hydrogels for localized mitochondrial transplantation to the spinal cord.

We developed a thermal-gelling, erodible hydrogel system for localized delivery of viable mitochondria in vivo, as well as labeled transplanted mitochondria with specific dyes and/or genetically modified mitochondria tagged with red fluorescence protein (RFP). We also employed cell lines to optimize a hydrogel composed of methylcellulose and hyaluronic acid designed to preserve bioenergetics while facilitating mitochondrial release. We further investigated how transplantation of allogeneic or xenogeneic mitochondria into respective cell lines affects host cellular metabolism, as measured by MTS assay. We found that 70% of mitochondria are released from the hydrogel within 20 min at 37 °C, that the respiratory capacity of hydrogel-released mitochondria over 60 min was greater than those without gel, and that MTR-labeling of mitochondria is not indelible. RFP-tagged transgenic mitochondria isolated from modified SH-SY5Y human neuroblastoma cells showed effective uptake into both naïve SH-SY5Y cells and rat PC-12 cells, notably when released from hydrogel. The hydrogel both protected the mitochondria at physiological conditions in vitro while solidifying and diffusing within 60 min locally in situ. To assess metabolic effects, both cell lines were transplanted with different concentrations of SH-SY5Y or PC-12 cell line-derived mitochondria and all resulted in significant increases in metabolism at 6- and 24-hour after transplantation. Alternatively, transplanted mitochondria at highest concentration from rat brain and spinal cord tissues reduced metabolic activities after 24-hour. Along with hydrogel refinements, we are further investigating whether such metabolic changes are due to alterations in cell proliferation or the number of exogenous mitochondria incorporated into individual host cells.