Thermodynamically controlled multiphase separation of heterogeneous liquid crystal colloids

Phase separation is a universal physical transition process whereby a homogeneous mixture splits into two distinct compartments that are driven by the component activity, elasticity, or compositions. In the current work, we develop a series of heterogeneous colloidal suspensions that exhibit both liquid-liquid phase separation of semiflexible binary polymers and liquid crystal phase separation of rigid, rod-like nanocellulose particles. The phase behavior of the multicomponent mixture is controlled by the trade-off between thermodynamics and kinetics during the two transition processes, displaying cholesteric self-assembly of nanocellulose within or across the compartmented aqueous phases. Upon thermodynamic control, two-, three-, and four-phase coexistence behaviors with rich liquid crystal stackings are realized. Among which, each relevant multiphase separation kinetics shows fundamentally different paths governed by nucleation and growth of polymer droplets and nanocellulose tactoids. Furthermore, a coupled multiphase transition can be realized by tuning the composition and the equilibrium temperature, which results in thermotropic behavior of polymers within a lyotropic liquid crystal matrix. Finally, upon drying, the multicomponent mixture undergoes a hierarchical self-assembly of nanocellulose and polymers into stratified cholesteric films, exhibiting compartmentalized polymer distribution and anisotropic microporous structure.

Magnetic Quincke rollers with tunable single-particle dynamics and collective states

Electrohydrodynamically driven active particles based on Quincke rotation have quickly become an important model system for emergent collective behavior in nonequilibrium colloidal systems. Like most active particles, Quincke rollers are intrinsically nonmagnetic, preventing the use of magnetic fields to control their complex dynamics on the fly. Here, we report on magnetic Quincke rollers based on silica particles doped with superparamagnetic iron oxide nanoparticles. We show that their magnetic nature enables the application of both externally controllable forces and torques at high spatial and temporal precision, leading to several versatile control mechanisms for their single-particle dynamics and collective states. These include tunable interparticle interactions, potential energy landscapes, and advanced programmable and teleoperated behaviors, allowing us to discover and probe active chaining, anisotropic active sedimentation-diffusion equilibria, and collective states in various geometries and dimensionalities.

Magnetic field-driven particle assembly and jamming for bistable memory and response plasticity

Unlike classic synthetic stimulus-responsive and shape-memory materials, which remain limited to fixed responses, the responses of living systems dynamically adapt based on the repetition, intensity, and history of stimuli. Such plasticity is ubiquitous in biology, which is profoundly linked to memory and learning. Concepts thereof are searched for rudimentary forms of "intelligent materials." Here, we show plasticity of electroconductivity in soft ferromagnetic nickel colloidal supraparticles with spiny surfaces, assembling/disassembling to granular conducting micropillars between two electrodes driven by magnetic field B. Colloidal jamming leads to conduction hysteresis and bistable memory upon increasing and subsequently decreasing B. Abrupt B changes induce larger conduction changes than gradual B-changes. Periodic B pulsing drives to frequency-dependent facilitation or suppression of conductivity compared to exposing the same constant field. The concepts allow remotely controlled switching plasticity, illustrated by a rudimentary device. More generally, we foresee adaptive functional materials inspired by response plasticity and learning.

Electroferrofluids with nonequilibrium voltage-controlled magnetism, diffuse interfaces, and patterns

It has been recognized that driving matter to nonequilibrium states can lead to emergent behaviors and functionalities. Here, we show that uniform colloidal dispersions can be driven into dissipative nonuniform states with emerging behaviors. We experimentally demonstrate this with electrically driven weakly charged superparamagnetic iron oxide nanoparticles in a nonpolar solvent. The driving leads to formation of nonequilibrium concentration gradients that further translate to nonequilibrium magnetism, including voltage-controlled magnetization and susceptibility. The concentration gradients also serve as diffuse interfaces that respond to external magnetic fields, leading to novel dissipative patterns. We identify the closest nondissipative analogs, discuss the differences, and highlight the ability to directly quantify the dissipation and link it to the pattern formation. Beyond voltage-controlled magnetism, we foresee that the concept can be generalized to other functional colloids to create, e.g., optical, electrical, catalytic, and mechanical responses that are not possible in thermodynamic equilibrium.

Magnetic Field-Driven Deformation, Attraction, and Coalescence of Nonmagnetic Aqueous Droplets in an Oil-Based Ferrofluid

Stimuli-responsive compartments are attracting more and more attention through the years motivated by their wide applications in different fields including encapsulation, manipulation, and triggering of chemical reactions on demand. Among others, magnetic responsive compartments are particularly attractive due to the numerous advantages of magnetic fields compared to other external stimuli. In this article, we used an oil-based ferrofluid where the magnetic nanoparticles have been coated with different polymers to increase their amphiphilic character and surface activity, consequently rendering the interface magnetically responsive. Microliter aqueous nonmagnetic droplets dispersed in the oil-based ferrofluid were used as a model of microreactors. A comprehensive experimental and theoretical study of the deformation, attraction, and coalescence processes of the nonmagnetic water droplets coated with the magnetic nanoparticles under an applied magnetic field in the continuous oil-based ferrofluid phase is provided. To manipulate the packing of the nanoparticles at the water/oil interface, the ionic strength of the aqueous droplets was varied using different NaCl concentrations, and its effect on modulating the coalescence of the droplets was probed. Our results show that the water droplets deform along the magnetic field depending on the magnetic properties of the ferrofluid itself and on the surface properties of the interface, attract in pairs under the action of the magnetic dipole force, and coalesce by the action of the same force with a stochastic behavior. We have studied all of these phenomena as a function of the magnetic field applied, evaluating in each case the forces and/or pressures acting on the droplets with particular attention to roles of magnetic attraction, interface properties, and viscosity in the system. This work offers an overall set of tools to understand and predict the behavior of multiple water droplets in an oil-based ferrofluid for lab-on-a-chip applications.

Division of Ferrofluid Drops Induced by a Magnetic Field

We report a comprehensive study of the division of ferrofluid drops caused by their interaction with a permanent magnet. As the magnet gradually approaches the sessile drop, the drop deforms into a spiked cone and then divides into two daughter droplets. This process is the result of a complex interplay between the polarizing effect caused by the magnetic field and the magnetic attraction due to the field gradient. As a first attempt to describe it, during each scan we identify two characteristic distances between the magnet and the drop: z_max, corresponding to the drop reaching its maximum height, and z_saddle, corresponding to the formation of a saddle point on the drop peak identifying the beginning of the drop breakup. We have investigated the location of these two points using sessile drops of ferrofluid water solutions at various concentrations and volumes, deposited on four surfaces of different wettability. An empirical scaling law based on dimensionless variables is found to accurately describe these experimental observations. We have also measured the maximum diameter of the drops right before the division and found that it is very close to a critical size, which depends on the magnetic attraction.

Dynamics of Ferrofluid Drops on Magnetically Patterned Surfaces

The motion of liquid drops on solid surfaces is attracting a lot of attention because of its fundamental implications and wide technological applications. In this article, we present a comprehensive experimental study of the interaction between gravity-driven ferrofluid drops on very slippery oil-impregnated surfaces and a patterned magnetic field. The drop speed can be accurately tuned by the magnetic interaction, and more interestingly, drops are found to undergo a stick-slip motion whose contrast and phase can be easily tuned by changing either the strength of the magnetic field or the ferrofluid concentration. This motion is the result of the periodic modulation of the external magnetic field and can be accurately analyzed because the intrinsic pinning due to chemical defects is negligible on oil-impregnated surfaces.

Static Magnetowetting of Ferrofluid Drops

We report results of a comprehensive study of the wetting properties of sessile drops of ferrofluid water solutions at various concentrations deposited on flat substrates and subjected to the action of permanent magnets of different sizes and strengths. The amplitude and the gradient of the magnetic field experienced by the ferrofluid are changed by varying the magnets and their distance to the surface. Magnetic forces up to 100 times the gravitational one and magnetic gradients up to 1 T/cm are achieved. A rich phenomenology is observed, ranging from flattened drops caused by the magnetic attraction to drops extended normally to the substrate because of the normal traction of the magnetic field. We find that the former effect can be conveniently described in terms of an effective Bond number that compares the effective drop attraction with the capillary force, whereas the drop's vertical elongation is effectively expressed by a dimensionless number S, which compares the pressure jump at the ferrofluid interface because of the magnetization with the capillary pressure.

Pterygium inversum unguis. Report of 19 cases and review of the literature

BACKGROUND

Pterygium inversum unguis is a rare abnormality of the nail bed that remains adherent to the ventral surface of the nail plate, resulting in a subungual extension of the hyponychium and obliteration of the distal groove.

OBJECTIVE

The aim of our article is to illustrate the cases of pterygium inversum unguis that we observed in the last 20 years and to discuss them according to a broad review of the literature.

RESULTS

Nineteen new cases of pterygium inversum unguis have been observed: one congenital idiopathic form, five acquired idiopathic forms, and 13 secondary forms.

CONCLUSION

Our study and the review of the literature demonstrate that the most common forms of pterygium inversum unguis are the acquired secondary ones. They are generally related to systemic connective tissue diseases and, in particular, to progressive systemic sclerosis and systemic lupus erythematosus.

Unusual features of pyoderma gangrenosum: two atypical cases

Two cases of pyoderma gangrenosum are described that are atypical in the appearance of their skin lesions and their association with intestinal diseases.

Experience with tretinoin therapy in temperate regions

In a previously reported study on the anti-photoageing effects of topical tretinoin, the following regimen produced good patient compliance: 0.01% for 1 month, 0.025% for 1 month; and 0.05% for 4 months. The majority of patients (60/89) enrolled in the initial study continued to apply the cream to the face, and a further 140 patients were enrolled for a long-term study (mean duration 2 years). The prolonged study showed that 91.4% of patients used tretinoin in an attempt to slow down skin aging, and 8.6% sought subjective skin benefits. Of the 163 patients who completed the study, 58.8% sought an improvement of wrinkles, 30.1% skin trophism and 14.7% reduced pigmentation. The product was used throughout the year by 66.9% of patients, but 8.0% stopped using it during the summer. A daytime moisturizing cream was required by 77.9% of patients, and 82.8% used a sunscreen in the summer. Tretinoin was applied to other areas of the body by 63.8% of patients.

[Efficacy and cardiovascular tolerability of minotricon in the treatment of seborrheic alopecia]

The paper reports the results of local treatment using minoxidil 2% in a watery solution at a dose of 2 ml/day in 50 patients affected by androgenetic alopecia. The results were analysed statistically using Wilcoxon's non-parametric test and Mac Nemar's test.

Pityriasis lichenoides in children: a long-term follow-up of eighty-nine cases

Pityriasis lichenoides is usually classified into an acute and a chronic form. From a review of 89 cases of the disease seen since 1974 it seems that a more realistic classification into three main groups, according to the distribution of pityriasis lichenoides lesions, could be made, namely, a diffuse, a central, and a peripheral form, each characterized by a different clinical course. Conversely, no correlations were detected in our series between the severity of skin lesions and their distribution or the overall course of the disease. None of our cases suggests the possible evolution of pityriasis lichenoides into lymphomatoid papulosis. Although no infectious causative agent has been identified, a viral origin seems likely in some cases. Most patients responded favorably to UVB irradiation. Our conclusions are (1) that pityriasis lichenoides is probably a clinical disorder with a diverse etiology and (2) that its classification by distribution seems more useful than its subdivision into an acute and a chronic form.

The treatment of visible signs of senescence: the Italian experience

An open clinical study was undertaken to evaluate the anti-photoageing efficacy of topical tretinoin. A length of cream of approximately 1 cm was applied to the face daily in the evening for 6 months: during month 1 of therapy 0.01% tretinoin cream was administered; 0.025% was given during month 2; and 0.05% was given in months 3-6. The clinical symptoms of photoageing (coarse wrinkling, fine wrinkling, skin thinning, mottled hyperpigmentation, laxity and xerosis) were evaluated before and after therapy. A total of 19.1% of patients withdrew from the study; only 5.6% were for treatment-related reasons. At the end of the treatment period all the clinical parameters, except xerosis, were improved. The amount of improvement varied, but only 4.2% of patients failed to show any improvement. Tolerability was excellent in 51.4% of patients, good in 44.4% and fair in 4.2%, and compliance was excellent in 47.0% of patients, good in 48.5% and fair in 4.5%. Tolerability and compliance were improved by applying the same amount of cream each day but increasing the concentration of tretinoin over the 6-month period. Silicone skin replicas of the same area of skin taken before and after treatment, analysed by scanning electron microscopy, profilometry and computer image analysis, showed a decrease in the width of wrinkles, and an improvement in skin texture and follicle density.

[1% econazole hair-shampoo in the treatment of pityriasis capitis; a comparative study versus zinc-pyrithione shampoo]

On the basis of the assumption that Pityrosporum ovale is an important pathogenic factor in the aetiology of Pityriasis simplex capitis (dandruff), the Authors intended to evaluate the efficacy and tolerability of econazole (1% hair-shampoo) in the treatment of this scalp disease. Dandruff could be considered a problem more from a cosmetic than from a medical point of view; for this reason a conventional anti-dandruff hair-shampoo containing zinc-pyrithione was selected as a control. In this open controlled study, seventy patients suffering from different forms of Pityriasis simplex capitis were enrolled at the 1th Dermatological Institute, University of Milan, and randomly assigned to the econazole and zinc-pyrithione treatment groups, respectively. At the end of the four-weeks treatment (two applications/week) a marked decrease in signs (scaling, seborrhea, erythema) and symptoms (burning, itching) was observed in both groups. Regarding the antifungal efficacy, econazole hair-shampoo was slightly better than control. General evaluation on tolerability and cosmetical patterns was favourable for both formulations.

[Treatment of histamine-dependent allergic dermatoses with a 120-mg terfenadine tablet once a day]

Terfenadine, an anti-H1-selective antihistaminic drug has been used in an experimental clinical study. The effectiveness and tolerance of the compound in the treatment of pruritic dermatitis such as urticaria, atopic dermatitis and topical dermatitis, have been evaluated. Terfenadine, administered in 120 mg tablets in a single daily dose in 30 patients demonstrated a fully satisfactory therapeutic activity and reliability of use.

[Use of a cream based on 20% azelaic acid in the treatment of melasma]

A 20% azelaic acid base cream (Skinoren-Schering) known in the treatment of acne has been used in melasma. The statistically processed results refer to 39 patients treated for 6 months with 2 applications/die. The reduction in melasma intensity was obtained in all patients bar two whose basal pigmentation situation was already compromised. Overall assessment on a graduated scale in cm evidences, after 6 months of treatment, a mean reduction in pigmentation of 51.3% understood as intensity and surface. The overall judgment of physician and patient on the preparation coincide with some 79% excellent and good on the part of the physician and 85% on the part of the patient. Noteworthy is the absolute absence of sensitisation or leukoderma or any of the other typical side-effects of the other depigmentants available thus far.