Self-Motility of an Active Particle Induced by Correlations in the Surrounding Solution.

Current models of phoretic transport rely on molecular forces creating a "diffuse" particle-fluid interface. We investigate theoretically an alternative mechanism, in which a diffuse interface emerges solely due to a nonvanishing correlation length of the surrounding solution. This mechanism can drive self-motility of a chemically active particle. Numerical estimates indicate that the velocity can reach micrometers per second. The predicted phenomenology includes a bilinear dependence of the velocity on the activity and a possible double velocity reversal upon varying the correlation length.

Active Janus colloids at chemically structured surfaces.

If catalytically active Janus particles are dispersed in certain liquid solutions, they can create a gradient in the chemical composition of this solution along their surfaces, as well as along any nearby confining surfaces. This gradient drives self-propulsion via a self-phoretic mechanism, while the compositional gradient along a wall gives rise to chemiosmosis, which additionally contributes to self-motility. In this study, we analyze theoretically the dynamics of an active colloid near chemically patterned walls. We use a point-particle approximation combined with a multipole expansion in order to discuss the effects of pattern geometry and chemical contrast on the particle trajectories. In particular, we consider planar walls patterned with chemical steps and stripes. We investigate in detail the changes in the topology of the corresponding phase portraits upon varying the chemical contrast and the stripe width.

Self-diffusiophoresis induced by fluid interfaces.

The influence of a fluid-fluid interface on self-phoresis of chemically active, axially symmetric, spherical colloids is analyzed. Distinct from the studies of self-phoresis for colloids trapped at fluid interfaces or in the vicinity of hard walls, here we focus on the issue of self-phoresis close to a fluid-fluid interface. In order to provide physically intuitive results highlighting the role played by the interface, the analysis is carried out for the case that the symmetry axis of the colloid is normal to the interface; moreover, thermal fluctuations are not taken into account. Similarly to what has been observed near hard walls, we find that such colloids can be set into motion even if their whole surface is homogeneously active. This is due to the anisotropy along the direction normal to the interface owing to the partitioning by diffusion, among the coexisting fluid phases, of the product of the chemical reaction taking place at the colloid surface. Different from results corresponding to hard walls, in the case of a fluid interface the direction of motion, i.e., towards the interface or away from it, can be controlled by tuning the physical properties of one of the two fluid phases. This effect is analyzed qualitatively and quantitatively, both by resorting to a far-field approximation and via an exact, analytical calculation which provides the means for a critical assessment of the approximate analysis.

Effective squirmer models for self-phoretic chemically active spherical colloids.

Various aspects of self-motility of chemically active colloids in Newtonian fluids can be captured by simple models for their chemical activity plus a phoretic-slip hydrodynamic boundary condition on their surface. For particles of simple shapes (e.g., spheres) --as employed in many experimental studies-- which move at very low Reynolds numbers in an unbounded fluid, such models of chemically active particles effectively map onto the well studied so-called hydrodynamic squirmers (S. Michelin and E. Lauga, J. Fluid Mech. 747, 572 (2014)). Accordingly, intuitively appealing analogies of "pusher/puller/neutral" squirmers arise naturally. Within the framework of self-diffusiophoresis we illustrate the above-mentioned mapping and the corresponding flows in an unbounded fluid for a number of choices of the activity function (i.e., the spatial distribution and the type of chemical reactions across the surface of the particle). We use the central collision of two active particles as a simple, paradigmatic case for demonstrating that in the presence of other particles or boundaries the behavior of chemically active colloids may be qualitatively different, even in the far field, from the one exhibited by the corresponding "effective squirmer", obtained from the mapping in an unbounded fluid. This emphasizes that understanding the collective behavior and the dynamics under geometrical confinement of chemically active particles necessarily requires to explicitly account for the dependence of the hydrodynamic interactions on the distribution of chemical species resulting from the activity of the particles.

Comparative efficacy of oral contraceptive versus local treatment versus intense pulsed light combined with vacuum in endocrine acne in women.

Acne is the most common affection of adolescents, although it can be also found in adult women. Our study was aimed at the comparative assessment of three different therapies over a three-month period, applied to women with moderate comedogenic and papulo-pustular endocrine acne. In the study 116 female patients with endocrine localized face acne were included and divided into three groups: group I with 42 patients was treated with a combination of contraceptive pill + local treatment + pulsed-vacuum light; group II with 38 patients was treated with contraceptives and pulsed-vacuum light and group III with 36 patients was treated only with local treatment. The acne evaluation was made using the Global Acne Grading System (GAGS). Statistical data processing was carried out using the STATA software. For the comedogenic form of acne, the good and very good results were superior in group I vs group II and III (83.33% vs 31.58% vs 5.56%) at the end of the three months of treatment. For the papulo-pustulous form of acne, good and very good results were similar in groups I and II (92.86% vs 73.68%) both after the first month of treatment and at the end of the study, well above the local treatment group (13.99%). Our study highlighted the superiority of laser treatment combined with hormonal treatment, compared to hormonal and local treatment in the comedogenic form of acne, and the superiority of hormonal treatment combined (or not) with laser treatment in the papulo-pustular form compared to local treatment.

Perils of ad hoc approximations for the activity function of chemically powered colloids.

Colloids can achieve motility by promoting at their surfaces chemical reactions in the surrounding solution. A well-studied case is that of self-phoresis, in which motility arises due to the spatial inhomogeneities in the chemical composition of the solution and the distinct interactions of the solvent molecules and of the reaction products with the colloid. For simple models of such chemically active colloids, the steady-state motion in an unbounded solution can be derived analytically in closed form. In contrast, for such chemically active particles moving in the vicinity of walls, the derivation of closed-form and physically intuitive solutions of the equations governing their dynamics turns out to be a severe challenge even for simple models. Therefore, recent studies of these phenomena have employed numerical methods as well as approximate analytical approaches based on multipolar expansions. We discuss and clarify certain conceptual aspects concerning the latter type of approach, which arise due to ad hoc truncations of the underlying so-called activity function, which describes the distribution of chemical reactions across the surface of the particle.

Effective Interaction between Active Colloids and Fluid Interfaces Induced by Marangoni Flows.

We show theoretically that near a fluid-fluid interface a single active colloidal particle generating, e.g., chemicals or a temperature gradient experiences an effective force of hydrodynamic origin. This force is due to the fluid flow driven by Marangoni stresses induced by the activity of the particle; it decays very slowly with the distance from the interface, and can be attractive or repulsive depending on how the activity modifies the surface tension. We show that, for typical systems, this interaction can dominate the dynamics of the particle as compared to Brownian motion, dispersion forces, or self-phoretic effects. In the attractive case, the interaction promotes the self-assembly of particles into a crystal-like monolayer at the interface.

Erratum: Effective Interaction between Active Colloids and Fluid Interfaces Induced by Marangoni Flows [Phys. Rev. Lett. 116, 078301 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.078301.

Guiding Catalytically Active Particles with Chemically Patterned Surfaces.

Catalytically active Janus particles suspended in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemiosmosis, providing an additional contribution to self-motility. Chemiosmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate "point-particle" approach, that by chemically patterning a planar substrate one can direct the motion of Janus particles: the induced chemiosmotic flows can cause particles to either "dock" at the chemical step between the two materials or follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.

Active colloids at fluid interfaces.

If an active Janus particle is trapped at the interface between a liquid and a fluid, its self-propelled motion along the interface is affected by a net torque on the particle due to the viscosity contrast between the two adjacent fluid phases. For a simple model of an active, spherical Janus colloid we analyze the conditions under which translation occurs along the interface and we provide estimates of the corresponding persistence length. We show that under certain conditions the persistence length of such a particle is significantly larger than the corresponding one in the bulk liquid, which is in line with the trends observed in recent experimental studies.

Collective dynamics of chemically active particles trapped at a fluid interface.

Chemically active colloids generate changes in the chemical composition of their surrounding solution and thereby induce flows in the ambient fluid which affect their dynamical evolution. Here we study the many-body dynamics of a monolayer of spherically symmetric active particles trapped at a fluid-fluid interface. To this end we consider a model for the large-scale spatial distribution of particles which incorporates the direct pair interaction (including also the capillary interaction which is caused specifically by the interfacial trapping) as well as the effect of hydrodynamic interactions (including the Marangoni flow induced by the response of the interface to the chemical activity). The values of the relevant physical parameters for typical experimental realizations of such systems are estimated and various scenarios, which are predicted by our approach for the dynamics of the monolayer, are discussed. In particular, we show that the chemically-induced Marangoni flow can prevent the clustering instability driven by the capillary attraction.

Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering.

Micron-sized particles moving through a solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry.

Rheotaxis of spherical active particles near a planar wall.

For active particles the interplay between the self-generated hydrodynamic flow and an external shear flow, especially near bounding surfaces, can result in a rich behavior of the particles not easily foreseen from the consideration of the active and external driving mechanisms in isolation. For instance, under certain conditions, the particles exhibit "rheotaxis", i.e., they align their direction of motion with the plane of shear spanned by the direction of the flow and the normal of the bounding surface and move with or against the flow. To date, studies of rheotaxis have focused on elongated particles (e.g., spermatozoa), for which rheotaxis can be understood intuitively in terms of a "weather vane" mechanism. Here we investigate the possibility that spherical active particles, for which the "weather vane" mechanism is excluded due to the symmetry of the shape, may nevertheless exhibit rheotaxis. Combining analytical and numerical calculations, we show that, for a broad class of spherical active particles, rheotactic behavior may emerge via a mechanism which involves "self-trapping" near a hard wall owing to the active propulsion of the particles, combined with their rotation, alignment, and "locking" of the direction of motion into the shear plane. In this state, the particles move solely up- or downstream at a steady height and orientation.

Efficacy of cetuximab in metastatic colon cancer - case report.

In recent years, targeted therapies have proved effective in the treatment of colon cancer, but even in these conditions,metastatic disease is generally considered incurable.Cetuximab is approved for the treatment of advanced colorectal cancer patients with KRAS wild-type, in order to increase survival and hinder progression of the disease. We report a case of a 55 year-old woman, diagnosed with stenosing sigmoid cancer and liver metastases, which underwent multimodal treatment: palliative surgery -Hartmann segmental colectomy, and adjuvant chemotherapy -second line monotherapy with cetuximab, according to standard protocols. After 6 months of XELOX chemotherapy,during which she showed progression of metastatic disease, she was switched to monotherapy with cetuximab, with favorable outcome. Comparing relevant literature, in which complete response to treatment with cetuximab is obtained in low percentages ( 3%) after 3 months of treatment with cetuximab the patient shows clinical and paraclinical complete response and increased quality of life. Proper selection of patients with metastatic colon cancer for treatment with anti-EGFR therapy may lead to prolonged survival and time to progression.

Activity tracker-based intervention to increase physical activity in patients with type 2 diabetes and healthy individuals: study protocol for a randomized controlled trial.

BACKGROUND: One relevant strategy to prevent the onset and progression of type 2 diabetes mellitus (T2DM) focuses on increasing physical activity. The use of activity trackers by patients could enable objective measurement of their regular physical activity in daily life and promote physical activity through the use of a tracker-based intervention. This trial aims to answer three research questions: (1) Is the use of activity trackers suitable for longitudinal assessment of physical activity in everyday life? (2) Does the use of a tracker-based intervention lead to sustainable improvements in the physical activity of healthy individuals and in people with T2DM? (3) Does the accompanying digital motivational intervention lead to sustainable improvements in physical activity for participants using the tracker-based device? METHODS: The planned study is a randomized controlled trial focused on 1642 participants with and without T2DM for 9 months with regard to their physical activity behavior. Subjects allocated to an intervention group will wear an activity tracker. Half of the subjects in the intervention group will also receive an additional digital motivational intervention. Subjects allocated to the control group will not receive any intervention. The primary outcome is the amount of moderate and vigorous physical activity in minutes and the number of steps per week measured continuously with the activity tracker and assessed by questionnaires at four time points. Secondary endpoints are medical parameters measured at the same four time points. The collected data will be analyzed using inferential statistics and explorative data-mining techniques. DISCUSSION: The trial uses an interdisciplinary approach with a team including sports psychologists, sports scientists, health scientists, health care professionals, physicians, and computer scientists. It also involves the processing and analysis of large amounts of data collected with activity trackers. These factors represent particular strengths as well as challenges in the study. TRIAL REGISTRATION: The trial is registered at the World Health Organization International Clinical Trials Registry Platform via the German Clinical Studies Trial Register (DRKS), DRKS00027064 . Registered on 11 November 2021.

Phoretic motion of spheroidal particles due to self-generated solute gradients.

We study theoretically the phoretic motion of a spheroidal particle, which generates solute gradients in the surrounding unbounded solvent via chemical reactions active on its surface in a cap-like region centered at one of the poles of the particle. We derive, within the constraints of the mapping to classical diffusio-phoresis, an analytical expression for the phoretic velocity of such an object. This allows us to analyze in detail the dependence of the velocity on the aspect ratio of the polar and the equatorial diameters of the particle and on the fraction of the particle surface contributing to the chemical reaction. The particular cases of a sphere and of an approximation for a needle-like particle, which are the most common shapes employed in experimental realizations of such self-propelled objects, are obtained from the general solution in the limits that the aspect ratio approaches one or becomes very large, respectively.

[Correlations between the occlusal plane angle and the risk of relapse after surgical orthodontic treatment of Angle Class III anomalies]. / Corelatii intre orientarea planului de ocluzie si riscul de recidiva in tratamentul chirurgical al anomaliilor dento-maxilare de clasa a III-a.

An important criterion in the diagnostic and therapeutic assessment of severe true mandibular prognathia (characterized by excessive growth of the mandible and hiperdivergent facial growth pattern) is the orientation of the occlusal plane compared with the facial benchmark represented by the Frankfurt horizontal line. This is because orthognatic surgery in this pathology (sagittal bilateral osteotomy) envisages not only the shortening of the mandible, but also the counterclockwise rotation of the mandible to restore facial and dento-alveolar harmony in the three planes (sagittal, transverse, vertical). The aim of the study is the analysis of the evolution of the maxillo-mandibular complex in relation to the occlusal plane after orthognatic surgery (sagittal osteotomy of the mandible and bilateral Le Fort I of the maxilla), in a group of 15 patients with a mean age 22+3 years diagnosed with skeletal class III malocclusion, hiperdivergent facial pattern, initial average value of the occlusal plane angle 130+0.60. t test applied for comparative statistical analysis for the linear and angular parameters considered in four therapeutic stages (initial presurgical, post surgical, one year post surgical) show statistically significant changes in parameters related to the mandibular length and rotation, without significant variations one year after the surgical phase.

Thyroid regional metastasis from a giant cell malignant fibrous histiocytoma of the larynx in a patient with history of trichinellosis and tuberculosis.

Sarcomas represent less than 1% of malignant laryngeal tumors and giant cell malignant fibrous histiocytoma is exceptionally rare. Diagnosis is histologically based and immunohistochemistry allows differentiation from other fibro-histiocytic neoplasms. We present the case of a 53-year-old male patient with positive medical history for trichinellosis and tuberculosis, and a laryngeal tumor invading the thyroid and causing respiratory distress by airway obstruction. Total laryngectomy and thyroidectomy were performed followed by thyroxine replacement therapy and radiotherapy. Histologically, the tumor consisted of spindle shaped cells with prominent mitoses, and abundant, osteoclast-like, multinucleated giant cells. Similar lesions were identified in the thyroid, adipose and muscular tissues. Parasitic elements were present in muscles. Tumoral cells showed positive immunostaining for Ki67 (40-50%) and vimentin and negative for AE1/AE3, CD31, S100 and myoglobin; the giant multinucleated cells were CD68-positive. Chronic infection might have had a pathogenic significance.

Axisymmetric spheroidal squirmers and self-diffusiophoretic particles.

We study, by means of an exact analytical solution, the motion of a spheroidal, axisymmetric squirmer in an unbounded fluid, as well as the low Reynolds number hydrodynamic flow associated to it. In contrast to the case of a spherical squirmer-for which, e.g. the velocity of the squirmer and the magnitude of the stresslet associated with the flow induced by the squirmer are respectively determined by the amplitudes of the first two slip ('squirming') modes-for the spheroidal squirmer each squirming mode either contributes to the velocity, or contributes to the stresslet. The results are straightforwardly extended to the self-phoresis of axisymmetric, spheroidal, chemically active particles in the case when the phoretic slip approximation holds.

Interface-mediated spontaneous symmetry breaking and mutual communication between drops containing chemically active particles.

Symmetry breaking and the emergence of self-organized patterns is the hallmark of complexity. Here, we demonstrate that a sessile drop, containing titania powder particles with negligible self-propulsion, exhibits a transition to collective motion leading to self-organized flow patterns. This phenomenology emerges through a novel mechanism involving the interplay between the chemical activity of the photocatalytic particles, which induces Marangoni stresses at the liquid-liquid interface, and the geometrical confinement provided by the drop. The response of the interface to the chemical activity of the particles is the source of a significantly amplified hydrodynamic flow within the drop, which moves the particles. Furthermore, in ensembles of such active drops long-ranged ordering of the flow patterns within the drops is observed. We show that the ordering is dictated by a chemical communication between drops, i.e., an alignment of the flow patterns is induced by the gradients of the chemicals emanating from the active particles, rather than by hydrodynamic interactions.