Comparison of Cross-Pin Versus Cortical Button Femoral Fixation in Anterior Cruciate Ligament Reconstruction With Hamstrings Autograft: A Long-Term Clinical Study and Review of the Literature

Background Anterior cruciate ligament reconstruction (ACLR) is a common operative procedure and many options regarding the type of the selected graft and fixation technique have been described to date. Although many studies have addressed the issue of the optimal femoral fixation device during ACLR with a hamstring tendon (HT) autograft, no clear evidence to indicate one technique over another has been found. Objective The purpose of this study was to compare the long-term postoperative outcomes and complication rates between transfemoral Cross-pin (CP) and Endobutton-Cortical Button (CB) fixation techniques in patients undergoing ACLR with an HT autograft. Methods One hundred and seven consecutive patients underwent ACLR by using a quadruple HT autograft that was stabilized with either a CP (CP Group: 52 patients) or a CB (CB Group: 55 patients) fixation technique. The Lachman test (LT), the Pivot-shift test (PST), the side-to-side difference in anterior translation of the tibia, the International Knee Documentation Committee (IKDC), and the Lysholm knee scoring systems were evaluated before surgery and during long-term follow up. The femoral and tibial tunnel diameter was measured in the anteroposterior (AP) and lateral radiographs after surgery and at the final follow-up. A review of the literature was also carried out to identify any differences between both techniques. Results Study groups were comparable in terms of patient demographics. The mean follow-up was 10.4 ± 1.3 and 10.6 ± 1.3 years in the CP and CB Groups, respectively (p = 0.47). In the CP Group, improvements after surgery in LT and PST from grade 2 (n=34) or 3 (n=18) to grade 0 (n = 41) or 1 (n = 11) and from grade 2 (n=36) or 3 (n = 16) to grade 0 (n = 44) or 1 (n = 8), respectively, were observed. In the CB Group, similar improvements in LT and PST scores from grade 2 (n = 40) or 3 (n = 15) to grade 0 (n = 46) or 1 (n = 9) and from grade 2 (n = 41) or 3 (n = 14) to grade 0 (n = 47) or 1 (n = 8), respectively, were observed. However, no differences between the groups (p = 0.53 for LT and p = 0.90 for PST) were noted. The mean Lysholm scores were 89.7 ± 6.8 and 90.2 ± 7.2 in the CP and CB groups, respectively (p = 0.59). Side-to-side difference improved from 9.1 ± 2.8 to 1.7 ± 1.5 mm and from 8.6 ± 2.5 to 1.6 ± 1.4 mm in the CP and CB groups, respectively (p = 0.89 between groups). According to IKDC grades, 92.1% and 91.4% of knees in the CP and CB groups, respectively were reported to be Grade A (Normal) or B (Nearly Normal) with a p = 0.7. Femoral and tibial tunnel widening was found in the last follow-up in both groups. However, there was no difference in the degree of tunnel widening among the two techniques. With respect to LT, PST, anterior drawer test, and IKDC score, none of the 15 published comparative studies demonstrated any significant differences between the two techniques and only one study detected a difference regarding the Lysholm score in favor of CP fixation. Conclusion In the long term, both CB and CP femoral stabilization techniques were shown to be associated with similar functional outcomes and low complication rates. Further large multicenter random clinical trials are still required to identify the most effective method of femoral fixation for HT autograft during ACLR surgery.

Satisfactory Short-Term Outcomes of Reverse Shoulder Arthroplasty for Complex Three- and Four-Part Fractures of the Humeral Head in Octogenarians

BACKGROUND

Proximal humeral fractures with severe comminution and poor bone quality are among the most common injuries in the elderly population. Reverse shoulder arthroplasty (RSA) has been widely used to manage complex three- and four-part humeral head fractures. The purpose of the present study was to report the result of this technique in the demanding population of octogenarians.

MATERIALS AND METHODS

 Twenty-six patients above the age of 80 years were included in the study and followed for a minimum of one-year follow-up. To assess the functional outcomes the postoperative range of motion (ROM), the Constant score, the visual analog scale for pain, and the disability of the arm and shoulder score (DASH) were measured at 6 and 12 months. Radiological assessment and potential complications were also recorded.

RESULTS

The mean age of the study population was 81.9 years (81-86) at the time of surgery. There was a statistically significant improvement in all outcomes over the follow-up intervals. Shoulder ROM was 125.7o for flexion, 98.2o for abduction, 42.2o for internal rotation, and 43.2o for external rotation at 12 months. The mean Constant, DASH, and VAS scores at the last follow-up were 61.3, 31.9, and 0.5, respectively. Reported complications include one superficial surgical site infection.

CONCLUSION

RSA is a safe and reliable surgical option with satisfactory outcomes to manage complex three- and four-part fractures of the humeral head as it can provide prompt pain relief and function in octogenarians.

Application of the method of parallel trajectories on modeling the dynamics of COVID-19 third wave

In this paper, we present a new method for successfully simulating the dynamics of COVID-19, experimentally focusing on the third wave. This method, namely, the Method of Parallel Trajectories (MPT), is based on the recently introduced self-organized diffusion model. According to this method, accurate simulation of the dynamics of the COVID-19 infected population evolution is accomplished by considering not the total data for the infected population, but successive segments of it. By changing the initial conditions with which each segment of the simulation is produced, we achieve close and detailed monitoring of the evolution of the pandemic, providing a tool for evaluating the overall situation and the fine-tuning of the restrictive measures. Finally, the application of the proposed MPT on simulating the pandemic's third wave dynamics in Greece and Italy is presented, verifying the method's effectiveness.

Stemless reverse total shoulder arthroplasty: a systematic review of contemporary literature

PURPOSE

Reverse shoulder prostheses are increasingly used for treatment of rotator cuff tear arthropathy and other degenerative shoulder diseases. In recent years, aiming for bone stock preservation has led to the design of metaphyseal humeral components without a stem. The aims of this study were to evaluate the complication and reintervention rates, as well as the clinical and radiographic outcomes in patients who underwent reverse shoulder arthroplasty (RSA) with stemless implants.

METHODS

A systematic review of the literature was completed until May 2020 using PubMed, EMBASE, CINAHL and Cochrane databases, according to PRISMA guidelines.

RESULTS

The literature search revealed 2942 studies, of which 13 were included in this review, with a total of 517 patients and a mean follow-up between 6.4 and 101.6 months. The total complication rate was 6.5%, while 3.3% were humeral associated complications. Finally, the rate of shoulders that underwent a reintervention was 6.7%, with 1.4% relating to a humeral component reason. Stemless RSA led to substantial improvements in patient reported outcome measures and range of motion across all studies. Scapular notching was reported in 15.2%, and lucencies around humeral component were reported in 0.8% of shoulders.

CONCLUSION

Stemless RSA resulted in low complication and reintervention rates at the mid-term follow-up. The reported clinical and radiological outcomes showed that these prostheses have at least equivalent outcomes with their stemmed counterparts. Further studies are required to investigate the long-term longevity and performance of the stemless humeral implants.

LEVEL OF EVIDENCE

Level IV; Systematic Review.

Impact of substrate elasticity on contact angle saturation in electrowetting

The electrostatically assisted wettability enhancement of dielectric solid surfaces, commonly termed as electrowetting-on-dielectric (EWOD), facilitates many microfluidic applications due to simplicity and energy efficiency. The application of a voltage difference between a conductive droplet and an insulated electrode substrate, where the droplet sits, is enough for realizing a considerable contact angle change. The contact angle modification is fast and almost reversible; however it is limited by the well-known saturation phenomenon which sets in at sufficiently high voltages. In this work, we experimentally show and computationally support the effect of elasticity and thickness of the dielectric on the onset of contact angle saturation. We found that the effect of elasticity is important especially for dielectric thickness smaller than 10 μm and becomes negligible for thickness above 20 μm. We attribute our findings on the effect of the dielectric thickness on the electric field, as well as on the induced electric stresses distribution, in the vicinity of the three phase contact line. Electric field and electric stresses distribution are numerically computed and support our findings which are of significant importance for the design of soft materials based microfluidic devices.

Criticality in epidemic spread: An application in the case of COVID19 infected population

Recently, it has been successfully shown that the temporal evolution of the fraction of COVID-19 infected people possesses the same dynamics as the ones demonstrated by a self-organizing diffusion model over a lattice, in the frame of universality. In this brief, the relevant emerging dynamics are further investigated. Evidence that this nonlinear model demonstrates critical dynamics is scrutinized within the frame of the physics of critical phenomena. Additionally, the concept of criticality over the infected population fraction in epidemics (or a pandemic) is introduced and its importance is discussed, highlighting the emergence of the critical slowdown phenomenon. A simple method is proposed for estimating how far away a population is from this "singular" state, by utilizing the theory of critical phenomena. Finally, a dynamic approach applying the self-organized diffusion model is proposed, resulting in more accurate simulations, which can verify the effectiveness of restrictive measures. All the above are supported by real epidemic data case studies.

Salvinia-like slippery surface with stable and mobile water/air contact line

Superhydrophobic surfaces are widely used in many industrial settings, and mainly consist of rough solid protrusions that entrap air to minimize the liquid/solid area. The stability of the superhydrophobic state favors relatively small spacing between protrusions. However, this in turn increases the lateral adhesion force that retards the mobility of drops. Here we propose a novel approach that optimizes both properties simultaneously. Inspired by the hydrophobic leaves of Salvinia molesta and the slippery Nepenthes pitcher plants, we designed a Salvinia-like slippery surface (SSS) consisting of protrusions with slippery heads. We demonstrate that compared to a control surface, the SSS exhibits increased stability against pressure and impact, and enhanced lateral mobility of water drops as well as reduced hydrodynamic drag. We also systematically investigate the wetting dynamics on the SSS. With its easy fabrication and enhanced performance, we envision that SSS will be useful in a variety of fields in industry.

Microdroplet Contaminants: When and Why Superamphiphobic Surfaces Are Not Self-Cleaning

Superamphiphobic surfaces are commonly associated with superior anticontamination and antifouling properties. Visually, this is justified by their ability to easily shed off drops and contaminants. However, on micropillar arrays, tiny droplets are known to remain on pillars' top faces while the drop advances. This raises the question of whether remnants remain even on nanostructured superamphiphobic surfaces. Are superamphiphobic surfaces really self-cleaning? Here we investigate the presence of microdroplet contaminants on three nanostructured superamphiphobic surfaces. After brief contact with liquids having different volatilities and surface tension (water, ethylene glycol, hexadecane, and an ionic liquid), confocal microscopy reveals a "blanket-like" layer of microdroplets remaining on the surface. It appears that the phenomenon is universal. Notably, when placing subsequent drops onto the contaminated surface, they are still able to roll off. However, adhesion forces can gradually increase by up to 3 times after repeated liquid drop contact. Therefore, we conclude that superamphiphobic surfaces do not warrant self-cleaning and anticontamination capabilities at sub-micrometric length scales.

Wetting of soft superhydrophobic micropillar arrays

Superhydrophobic surfaces are usually assumed to be rigid so that liquids do not deform them. Here we analyze how the relation between microstructure and wetting changes when the surface is flexible. Therefore we deposited liquid drops on arrays of flexible micropillars. We imaged the drop's surface and the bending of micropillars with confocal microscopy and analyzed the deflection of micropillars while the contact line advanced and receded. The deflection is directly proportional to the horizontal component of the capillary force acting on that particular micropillar. In the Cassie or "fakir" state, drops advance by touching down on the next top faces of micropillars, much like on rigid arrays. In contrast, on the receding side the micropillars deform. The main force hindering the slide of a drop is due to pinning at the receding side, while the force on the advancing side is negligible. In the Wenzel state, micropillars were deflected in both receding and advancing states.

Detaching Microparticles from a Liquid Surface

The work required to detach microparticles from fluid interfaces depends on the shape of the liquid meniscus. However, measuring the capillary force on a single microparticle and simultaneously imaging the shape of the liquid meniscus has not yet been accomplished. To correlate force and shape, we combined a laser scanning confocal microscope with a colloidal probe setup. While moving a hydrophobic microsphere (radius 5-10  μm) in and out of a 2-5  μm thick glycerol film, we simultaneously measured the force and imaged the shape of the liquid meniscus. In this way we verified the fundamental equations [D. F. James, J. Fluid Mech. 63, 657 (1974)JFLSA70022-112010.1017/S0022112074002126; A. D. Scheludko, A. D. Nikolov, Colloid Polymer Sci. 253, 396 (1975)] that describe the adhesion of particles in flotation, deinking of paper, the stability of Pickering emulsions and particle-stabilized foams. Comparing experimental results with theory showed, however, that the receding contact angle has to be applied, which can be much lower than the static contact angle obtained right after jump in of the particle.

Shape of a sessile drop on a flat surface covered with a liquid film

Motivated by the development of lubricant-infused slippery surfaces, we study a sessile drop of a nonvolatile (ionic) liquid which is embedded in a slowly evaporating lubricant film (n-decane) on a horizontal, planar solid substrate. Using laser scanning confocal microscopy we imaged the evolution of the shape of the liquid/liquid and liquid/air interfaces, including the angles between them. Results are compared to solutions of the generalized Laplace equations describing the drop profile and the annular wetting ridge. For all film thicknesses, experimental results agree quantitatively with the calculated drop and film shapes. With the verified theory we can predict height and volume of the wetting ridge. Two regimes can be distinguished: for macroscopically thick films (excess lubrication) the meniscus size is insensitive to changes in film thickness. Once the film is thin enough that surface forces between the lubricant/air and solid/lubricant interfaces become significant the meniscus changes significantly with varying film thickness (starved lubrication). The size of the meniscus is particularly relevant because it affects sliding angles of drops on lubricant-infused surfaces.

Energy Dissipation of Moving Drops on Superhydrophobic and Superoleophobic Surfaces

A water drop moving on a superhydrophobic surface or an oil drop moving on a superoleophobic surface dissipates energy by pinning/depinning at nano- and microprotrusions. Here, we calculate the work required to form, extend, and rupture capillary bridges between the protrusions and the drop. The energy dissipated at one protrusion W_S is derived from the observable apparent receding contact angle Θ_r^app and the density of protrusions n by W_s = γ(cos Θ_r^app + 1)/n, where γ is the surface tension of the liquid. To derive an expression for W_s that links the microscopic structure of the surface to apparent contact angles, two models are considered: A superhydrophobic array of cylindrical micropillars and a superoleophobic array of stacks of microspheres. For a radius of a protrusion R and a receding materials contact angle Θ_r, we calculate the energy dissipated per protrusion as W_s = πγR²[A - ln(R/κ)]f(Θ_r). Here, A = 0.60 for cylindrical micropillars and 2.9 for stacks of spheres. κ is the capillary length. f(Θ_r) is a function which depends on Θ_r and the specific geometry, f ranges from ≈0.25 to 0.96. Combining both equations above, we can correlate the macroscopically observed apparent receding contact angle with the microscopic structure of the surface and its material properties.

Nonlinear control of high-frequency phonons in spider silk

Spider dragline silk possesses superior mechanical properties compared with synthetic polymers with similar chemical structure due to its hierarchical structure comprised of partially crystalline oriented nanofibrils. To date, silk's dynamic mechanical properties have been largely unexplored. Here we report an indirect hypersonic phononic bandgap and an anomalous dispersion of the acoustic-like branch from inelastic (Brillouin) light scattering experiments under varying applied elastic strains. We show the mechanical nonlinearity of the silk structure generates a unique region of negative group velocity, that together with the global (mechanical) anisotropy provides novel symmetry conditions for gap formation. The phononic bandgap and dispersion show strong nonlinear strain-dependent behaviour. Exploiting material nonlinearity along with tailored structural anisotropy could be a new design paradigm to access new types of dynamic behaviour.

Long-Term Repellency of Liquids by Superoleophobic Surfaces

Applications of superoleophobic surfaces depend on the stability of the air cushion formed under liquid drops. To analyze the longevity of air cushions we used reflection-interference contrast microscopy (RICM) for drops on a porous fractal-like structure of sintered nanoparticles. RICM permits us to monitor the height of the air cushion with nanometer resolution. Whereas the air cushion under all investigated liquids was stable on a time scale of a few seconds to minutes and liquids rolled off, liquids with low surface tension penetrated the coating on the time scale of hours and longer. The penetration speed showed a power law dependence on time, dz/dt∼t^{p}, the exponent p varying from -0.5 to -1.2. Thus, penetration is qualitatively different from the Lucas-Washburn law that governs spontaneous capillary filling of porous structures.

Understanding the Formation of Anisometric Supraparticles: A Mechanistic Look Inside Droplets Drying on a Superhydrophobic Surface

Evaporating drops of nanoparticle suspensions on superhydrophobic surfaces can give anisotropic superaparticles. Previous studies implied the formation of a stiff shell that collapses, but the exact mechanism leading to anisotropy was unclear so far. Here we report on a new experiment using confocal laser scanning microscopy for a detailed characterization of particle formation from droplets of aqueous colloidal dispersions on superhydrophobic surfaces. In a customized setup, we investigated droplets of fumed silica suspensions using two different fluorescent dyes for independently marking silica and the water phase. Taking advantage of interfacial reflection, we locate the drop-air interface and extract normalized time-resolved intensity profiles for dyed silica throughout the drying process. Using comprehensive image analysis we observe and quantify shell-like interfacial particle accumulation arising from droplet evaporation. This leads to a buildup of a stiff fumed silica mantle of ∼20 μm thickness that causes deformation of the droplet throughout further shrinkage, consequently leading to the formation of solid anisometric fumed silica particles.

Synthesis of Mesoporous Supraparticles on Superamphiphobic Surfaces

A method for mesoporous supraparticle synthesis on superamphiphobic surfaces is designed. Therefore, supraparticles assembled with nanoparticles are synthesized by the evaporation of nanoparticle dispersion drops on the superamphiphobic surface. For synthesis, no further purification is required and no organic solvents are wasted. Moreover, by changing the conditions such as drop size and concentration, supraparticles of different sizes, compositions, and architectures are fabricated.

Super liquid-repellent layers: The smaller the better

Super liquid-repellent layers need to have a high impalement pressure and high contact angles, in particular a high apparent receding contact angle. Here, we demonstrate that to achieve both, the features constituting the layer should be as small as possible. Therefore, two models for super liquid-repellent layers are theoretically analyzed: A superhydrophobic layer consisting of an array of cylindrical micropillars and a superamphiphobic layer of an array of pillars of spheres. For the cylindrical micropillars a simple expression for the apparent receding contact angle is derived. It is based on a force balance rather than a thermodynamic approach. The model is supported by confocal microscope images of a water drop on an array of hydrophobic cylindrical pillars. The ratio of the width of a pillar w to the center-to-center spacing a is a primary factor in controlling the receding angle. Keeping the ratio w/a constant, the absolute size of surface features should be as small as possible, to maximize the impalement pressure.

Functional superhydrophobic surfaces made of Janus micropillars

We demonstrate the fabrication of superhydrophobic surfaces consisting of micropillars with hydrophobic sidewalls and hydrophilic tops, referred to as Janus micropillars. Therefore we first coat a micropillar array with a mono- or bilayer of polymeric particles, and merge the particles together to shield the top faces while hydrophobizing the walls. After removing the polymer film, the top faces of the micropillar arrays can be selectively chemically functionalised with hydrophilic groups. The Janus arrays remain superhydrophobic even after functionalisation as verified by laser scanning confocal microscopy. The robustness of the superhydrophobic behaviour proves that the stability of the entrapped air cushion is determined by the forces acting at the rim of the micropillars. This insight should stimulate a new way of designing super liquid-repellent surfaces with tunable liquid adhesion. In particular, combining superhydrophobicity with the functionalisation of the top faces of the protrusions with hydrophilic groups may have exciting new applications, including high-density microarrays for high-throughput screening of bioactive molecules, cells, or enzymes or efficient water condensation. However, so far chemical attachment of hydrophilic molecules has been accompanied with complete wetting of the surface underneath. The fabrication of superhydrophobic surfaces where the top faces of the protrusions can be selectively chemically post-functionalised with hydrophilic molecules, while retaining their superhydrophobic properties, is both promising and challenging.

Direct observation of drops on slippery lubricant-infused surfaces

Water droplet resting on a slippery surface.

Magnetically actuated micropatterns for switchable wettability

Arrays of actuated magnetic micropillars that can be tilted, twisted, and rotated in the presence of a magnetic field gradient were obtained. The type and extent of the movements are dependent on the distribution (isotropic, anisotropic) of the magnetizable particles inside the pillars and the strength and the direction of the magnetic field gradient. Independent motion of groups of pillars in the same or opposite directions or homogeneous motion of the whole pattern has been realized. Changing the pattern geometry causes changes in the roll-off angle (ROA) of water droplets on the surface. We show magnetically induced changes in the ROA and direction-dependent ROAs as a consequence of the anisotropy of tilted patterns. We also demonstrate transfer of microparticles between magnetically actuated neighboring pillars.

Acute partial passive stretching increases range of motion and muscle strength

AIM

The purpose of this study was to investigate the effects of partial passive stretching (PPS) on peak torque (PT) and joint range of motion (ROM) in healthy subjects.

METHODS

Twenty-two males (mean age 20.4±1.0 yrs, height 181.1±4.2 cm and weight 75.8±6.8 kg) participated in the study. Quadriceps and hamstrings PT at different angular velocities was obtained on an isokinetic dynamometer. Standing leg method hop was tested for the stretched and unstretched leg. Each subject performed PPS for 20 seconds. The stretching procedure was repeated 5 times for each muscle group. The whole stretching program lasted for 6 minutes and 20 seconds followed by 5 seconds resting period.

RESULTS

Directly after the stretching procedure significant increases were observed of PT in quadriceps and hamstrings, however, only at 300o.s⁻¹ (P<0.05). Joint ROM was increased in all subjects (P<0.05). The distance in single length hop was increased significantly in the stretched leg following stretching (P<0.05). No changes were observed in the unstretched leg.

CONCLUSION

Our results indicated that the PPS altered ROM, maximal concentric isokinetic strength at high angle velocities and single length hop only for the stretched leg. These findings suggest that PPS may be an effective technique for enhancing muscle performance.

Optimization of superamphiphobic layers based on candle soot

Liquid repellent layers can be fabricated by coating a fractal-like layer of candle soot particles with a silicon oxide layer, combusting the soot at 600 °C and subsequently silanizing with perfluoroalkylsilanes. Drops of different liquids deposited on these so called “superamphiphobic” layers easily roll off thanks to the low liquid-solid adhesion. The lower value of the surface tension of liquids that can be repelled depends on details of the processing. Here, we analyze the influence of the soot deposition duration and height with respect to the flame on the structure and wetting properties of the superamphiphobic layer. The mean diameter of the soot particles depends on the distance from the wick. Close to the wick, the average diameter of the particles varies between 30 and 50 nm as demonstrated by scanning electron microscopy (SEM). Close to the top of the flame, the particles size decreases to 10–20 nm. By measuring the mass of superamphiphobic layers and their thickness by laser scanning confocal microscopy (LSCM) in reflection mode, we could determine that the average porosity is 0.91. The height-dependent structural differences affect the apparent contact and roll-off angles. Lowest contact angles are measured when soot is deposited close to the wick due to wax that is not completely burnt, smearing out the required overhanging structures. The small particle size close to the top of the flame also reduces contact angles, again due to decreasing size of overhangs. Sooting in the middle of the flame led to optimal liquid repellency. Furthermore, for sooting times longer than 45 s the properties of the layer did not change with sooting time, verifying the self-similarity of the layer.

Superamphiphobic particles: how small can we go?

Water and oil repellent coatings--so-called superamphiphobic coatings--greatly reduce the interaction between a liquid and a solid. So far, only flat or weakly curved superhydrophobic and superamphiphobic surfaces have been designed. This raises the question of whether highly curved structures or microspheres are feasible. Therefore, we coated microspheres with a superamphiphobic layer and measured the force between the spheres and a liquid. A qualitatively different dependence of the adhesion force on the applied load for superamphiphobic and smooth spheres is detected. Furthermore, we demonstrate both experimentally and theoretically that superamphiphobicity fails below a critical particle radius, depending on topological details and type of liquid. Therefore, this study sets a fundamental physical limit to the application of superamphiphobic layers for small objects with high curvature.

Liquid drops impacting superamphiphobic coatings

The dynamics of liquid drops impacting superamphiphobic coatings is studied by high-speed video microscopy. Superamphiphobic coatings repel water and oils. The coating consists of a fractal-like hydrophobized silica network. Mixtures of ethanol-water and glycerin-water are chosen to investigate the influence of interfacial tension and viscosity on spreading and retraction dynamics. Drop spreading is dominated by inertia. At low impact velocity, the drops completely rebound. However, the contact time increases with impact velocity, whereas the restitution coefficient decreases. We suggest that the drop temporarily impales the superamphiphobic coating, although the drop completely rebounds. From an estimate of the pressure, it can be concluded that impalement is dominated by depinning rather than sagging. With increasing velocity, the drops partially pin, and an increasing amount of liquid remains on the coating. A time-resolved study of the retraction dynamics reveals two well-separated phases: a fast inertia-dominated phase followed by a slow decrease of the contact diameter of the drop. The crossover occurs when the diameter of the retracting drop matches the diameter of the drop before impact. We suggest that the depth of impalement increases with impact velocity, where impalement is confined to the initial impact zone of the drop. If the drop partially pins on the coating, the depth of impalement exceeds a depth, preventing the whole drop from being removed during the retraction phase.

How superhydrophobicity breaks down

A droplet deposited or impacting on a superhydrophobic surface rolls off easily, leaving the surface dry and clean. This remarkable property is due to a surface structure that favors the entrainment of air cushions beneath the drop, leading to the so-called Cassie state. The Cassie state competes with the Wenzel (impaled) state, in which the liquid fully wets the substrate. To use superhydrophobicity, impalement of the drop into the surface structure needs to be prevented. To understand the underlying processes, we image the impalement dynamics in three dimensions by confocal microscopy. While the drop evaporates from a pillar array, its rim recedes via stepwise depinning from the edge of the pillars. Before depinning, finger-like necks form due to adhesion of the drop at the pillar's circumference. Once the pressure becomes too high, or the drop too small, the drop slowly impales the texture. The thickness of the air cushion decreases gradually. As soon as the water-air interface touches the substrate, complete wetting proceeds within milliseconds. This visualization of the impalement dynamics will facilitate the development and characterization of superhydrophobic surfaces.

Dynamic measurement of the force required to move a liquid drop on a solid surface

We measured the forces required to slide sessile drops over surfaces. The forces were measured by means of a vertical deflectable capillary stuck in the drop. The drop adhesion force instrument (DAFI) allowed the investigation of the dynamic lateral adhesion force of water drops of 0.1 to 2 μL volume at defined velocities. On flat PDMS surfaces, the dynamic lateral adhesion force increases linearly with the diameter of the contact area of the solid-liquid interface and linearly with the sliding velocity. The movement of the drop relative to the surfaces enabled us to resolve the pinning of the three-phase contact line to individual defects. We further investigated a 3D superhydrophobic pillar array. The depinning of the receding part of the rim of the drop occurred almost simultaneously from four to five pillars, giving rise to peaks in the lateral adhesion force.

Electrokinetics on superhydrophobic surfaces

On a superhydrophobic surface a liquid is exposed to a large air-water interface. The reduced wall friction is expected to cause a higher electro-osmotic mobility. On the other hand, the low charge density of a superhydrophobic surface reduces the electro-osmotic mobility. Due to a lack of experimental data it has not been clear so far whether the reduced wall friction or the reduced charge density dominate the electrokinetic mobilities. To separate the relative contributions of electrophoresis and electro-osmosis, the mobilities of colloids on a negatively charged hydrophilic, a superhydrophobic (Cassie) and a partially hydrophilized superhydrophobic (Cassie composite) coating were measured. To vary the charge density as well as its sign with respect to those of the colloids the partially hydrophilized surfaces were coated with polyelectrolytes. We analyzed the electrokinetic mobilities of negatively charged polystyrene colloids dispersed in aqueous medium on porous hydrophilic and superhydrophobic surfaces by confocal laser scanning electron microscopy. In all cases, the external electric field was parallel to the surface. The total electrokinetic mobilities on the superhydrophobic (Cassie) and negatively charged partially hydrophilized (Cassie composite) surfaces were similar, showing that electro-osmosis is small compared to electrophoresis. The positively charged Cassie composite surfaces tend to 'trap' the colloids due to attracting electrostatic interactions and rough morphology, reducing the mobility. Thus, either the charge density of the coatings in the Cassie composite state or its slip length is too low to enhance electro-osmosis.

Ultrasound evaluation of the distal migration of the long head of biceps tendon following tenotomy in patients undergoing arthroscopic repair of tears of the rotator cuff

This study evaluates the position of the long head of biceps tendon using ultrasound following simple tenotomy, in patients with arthroscopically repaired rotator cuff tears.

In total, 52 patients with a mean age of 60.7 years (45 to 75) underwent arthroscopic repair of the rotator cuff and simple tenotomy of the long head of biceps tendon. At two years post-operatively, ultrasound revealed that the tendon was inside the bicipital groove in 43 patients (82.7%) and outside in nine (17.3%); in six of these it was lying just outside the groove and in the remaining three (5.8%) it was in a remote position with a positive Popeye Sign. A dynamic ultrasound scan revealed that the tenotomised tendons had adhered to the surrounding tissues (autotenodesis).The initial condition of the tendon influenced its final position (p < 0.0005). The presence of a Popeye sign was statistically influenced by the pre-operative co-existence of supraspinatus and subscapularis tears (p < 0.0001).

It appears that the natural history of the tenotomised long head of biceps tendon is to tenodese itself inside or just outside the bicipital groove, while its pre-operative condition and coexistent subscapularis tears play a significant role in the occurrence of a Popeye sign.

Effect of nanoroughness on highly hydrophobic and superhydrophobic coatings

The effect of nanoroughness on contact angles and pinning is investigated experimentally and numerically for low-energy surfaces. Nanoroughness is introduced by chemical vapor deposition of tetraethoxysilane and was quantified by scanning force microscopy. Addition of a root-mean-square roughness of 2 nm on a flat surface can increase the contact angle after fluorination by a semifluorinated silane by up to 30°. On the other hand, nanoroughness can improve or impair the liquid repellency of superhydrophobic surfaces that were made from assembled raspberry particles. Molecular dynamics simulations are performed in order to gain a microscopic understanding on how the length and the surface coating density of semifluorinated silanes influence the hydrophobicity. Solid-liquid surface free energy computations reveal that the wetting behavior strongly depends on the density and alignment of the semifluorinated silane. At coating densities in the range of experimental values, some water molecules can penetrate between the semifluorinated chains, thus increasing the surface energy. Combining the experimental and numerical data exhibits that a roughness-induced increase of the contact angle competes with increased pinning caused by penetration of liquid into nanopores or between neighboring semifluorinated molecules.

Wetting on the microscale: shape of a liquid drop on a microstructured surface at different length scales

Describing wetting of a liquid on a rough or structured surface is a challenge because of the wide range of involved length scales. Nano- and micrometer-sized textures cause pinning of the contact line, reflected in a hysteresis of the contact angle. To investigate contact angles at different length scales, we imaged water drops on arrays of 5 μm high poly(dimethylsiloxane) micropillars. The drops were imaged by laser scanning confocal microscopy (LSCM), which allowed us to quantitatively analyze the local and large-scale drop profile simultaneously. Deviations of the shape of drops from a sphere decay at two different length scales. Close to the pillars, the amplitude of deviations decays exponentially within 1-2 μm. The drop profile approached a sphere at a length scale 1 order of magnitude larger than the pillars' height. The height and position dependence of the contact angles can be understood from the interplay of pinning of the contact line, the principal curvatures set by the topography of the substrate, and the minimization of the air-water interfaces.

Arthroscopic removal of impinging cement after unicompartmental knee arthroplasty

Complications following unicompartmental knee arthroplasty (UKA) include aseptic loosening, polyethylene wear, arthritis progression and periprothetic fractures. We report on a patient with a firmly fixed, sizeable cement extrusion into the posteromedial aspect of the knee after a UKA causing impingement and pain in full extension. Cement extrusion is an extremely rare but potentially disabling complication that may occur despite care to remove all cement following implantation of the prosthesis. Removing a cement fragment, especially when this is firmly fixed to difficult-to-visualise and access parts of the prosthesis, is challenging. We believe the patient we report is the first one where a firmly fixed, sizeable cement extrusion was removed arthroscopically from the posterior aspect of the knee. This was achieved via an anterolateral portal with trans-notch view, combined with a posteromedial portal used both for viewing and instrument insertion. Arthroscopic removal of the impinging cement with the technique described above is a safe and effective option for the treatment of this difficult albeit rare problem.

Prostate sarcomatoid carcinoma as accidental finding in transurethral resection of prostate specimen. A case report and systematic review of current literature

BACKGROUND

Sarcomatoid carcinoma of the prostate is an extremely rare and highly aggressive neoplasm that accounts for less than 0.1% of primary prostate malignancies. Long-term survival rates for adult patients with prostate sarcomatoid carcinoma are poor. Surgical treatment seems to be the most effective therapeutic approach. In contrast radiation therapy alone has shown limited efficacy.

AIM

The purpose of the study is to present a case of sarcomatoid carcinoma of the prostate treated with a combination of radiotherapy and TURP.

CASE REPORT

A 76-year-old man treated with TURP due to acute urinary retention was finally diagnosed with sarcomatoid carcinoma upon pathology examination of the surgical specimen. Patient was initially treated with external beam radiotherapy. Six months later, he presented with urinary retention suggesting extension of the tumor into the bladder neck. Pathology report diagnosed prostate sarcomatoid carcinoma containing also large areas of necrosis. Patient underwent an extensive TURP and he received a second round radiotherapy. One year after the initial diagnosis of sarcomatoid carcinoma, patient is free of symptoms and follow up investigation shows no evidence of metastatic disease.

CONCLUSIONS

Radiation therapy in combination with extensive TURP may delay disease progression.

Ionic concentration- and pH-dependent electrophoretic mobility as studied by single colloid electrophoresis

Optical tweezers are employed to measure separately the complex electrophoretic mobility of a single colloid and the complex electroosmotic response of the surrounding medium in a specially designed microfluidic cell. Using the very same colloid both quantities are determined in dependence on the concentration of the aqueous salt solution (10 (- 5)-10 (- 1) mol l (- 1)), the valence of the ions (K (+) , Ca(2 +) ) and the pH (2.5-8.5). A pronounced effect is observed for all these examined parameters. The dependence on ion concentration agrees qualitatively-for the monovalent case-with the predictions of the standard electrokinetic model.