Historia de la Enfermería Pediátrica en el Hospital Infantil de México Federico Gómez / History of Pediatric Nursing at the Children´s Hospital of Mexico Federico Gomez

El cuidado otorgado a los niños tiene un lugar importante para la historia de la enfermería en México; desde la cultura azteca, se les preparaba para sus actividades futuras en el calmecac, telpuchcalli y culcalli, mientras que durante la época precortesiana la principal figura era la tlamatqui-ticitl (partera), responsable de atender a las embarazadas y a sus niños durante los primeros meses.Posteriormente se funda el Hospital de la Inmaculada Concepción (hoy Hospital de Jesús), así como centros de protección para niños indígenas, mestizos y criollos a cargo de monjes agustinos, franciscanos, dominicos y jesuitas. Vasco de Quiroga fundó una casa cuna, motivo por el cual fue llamado "protector del niño indio de América", y el arzobispo Francisco de Lorenzana y Butrón fundó la Casa de Niños Expósitos de la ciudad de México. Durante el Imperio de Maximiliano de Habsburgo, la emperatriz Carlota logró el establecimiento de una "casa de maternidad e infancia". Tiempo después se planea el primer centro de higiene infantil y se funda la Casa Cuna de Coyoacán.El 30 de abril de 1943 se funda oficialmente el Hospital Infantil de México Federico Gómez (HIMFG) e inician los cursos de enfermería pediátrica, que con el tiempo cambian para constituir la especialidad en Enfermería infantil y dar origen a la especialidad en Neonatología y Oncología.

The care of children has a relevant place in Mexico nursing history; in Aztec culture, children were prepared for their future activities in the calmecac, telpuchcalli and culcalli; in the pre-Cortesian period the main figure was the tlamatqui-ticitl (midwife), who looked after pregnant women and their newborn during the first months.Subsequently, the Hospital de la Inmaculada Concepción (nowadays Hospital de Jesús) was founded, as well as protection centers for indigenous, mestizo and criollo children administered by Augustinian, Franciscan, Dominican and Jesuit monks. Vasco de Quiroga also founded an orphanage, that earned him the title of "protector of the Indian child of America". Archbishop Francisco de Lorenzana y Butrón founded as well the Casa de Niños Expósitos in Mexico City.During the Maximilian of Habsburg Empire, empress Carlota managed to establish a "maternity and childhood home". Eventually, the first child hygiene center was planned and the Casa Cuna de Coyoacán was founded.On April 30, 1943, the Hospital Infantil de México Federico Gómez (HIMFG) was officially founded, and its pediatric nursing courses were settled, which changed over time to constitute the specialty in pediatric nursing and give rise to the specialty in neonatology and oncology.

Caracterización de pacientes hospitalizados con sospecha de disfagia en el Hospital San Camilo de San Felipe, Chile / Characterization of hospitalized patients with suspected dysphagia at Hospital San Camilo, San Felipe

Resumen Introducción: El trastorno de la deglución, se denomina disfagia y presenta como complicaciones fundamentales la deshidratación, desnutrición y neumonía por aspiración, situaciones que condicionan desfavorablemente el estado de salud, incrementando la morbimortalidad. En Chile, existen escasas publicaciones a la fecha que den cuenta de antecedentes clínicos que permitan describir a los pacientes con sospecha de disfagia. Objetivo: Describir las características clínicas de pacientes hospitalizados con sospecha de disfagia en el Hospital San Camilo de San Felipe, Chile. Material y Método: Estudio descriptivo de 767 registros de pacientes, entre los años 2017 y 2019. Se revisó información demográfica y antecedentes clínicos. Para variables cualitativas, se utilizaron proporciones y distribuciones frecuenciales, para variables cuantitativas, se usaron medidas de tendencia central. Resultados: El 58,54% de los pacientes era de sexo masculino y el 79,4% correspondió a personas mayores (79,4%). Las patologías neurológicas representaron el diagnóstico de ingreso más frecuente (61,93%). El 14,73% presentó antecedentes de intubación endotraqueal, el 8,34% tenía traqueostomía y el 84,09% era edéntulo parcial o total. En la evaluación con alimentos, las degluciones múltiples y la presencia de tos correspondieron a las alteraciones de eficacia y seguridad más frecuentes. En el 82,01% se diagnosticó disfagia y la mayoría de etiología neurogénica (68,45%). Conclusión: El presente estudio permitió conocer las características clínicas de los pacientes con sospecha de disfagia hospitalizados. En este contexto los pacientes extubados, traqueostomizados y las personas mayores con trastornos neurológicos o patologías respiratorias se presentan como potenciales candidatos para la evaluación de deglución.

Abstract Introduction: The swallowing disorder is called dysphagia and presents complications such as dehydration, malnutrition and aspiration pneumonia, situations that unfavorably condition the state of health, increasing morbidity and mortality. In Chile, there are few publications to date that provide an account of clinical history that allow the description of patients with suspected dysphagia. Aim: To describe the clinical characteristics of hospitalized patients with suspected dysphagia at Hospital San Camilo de San Felipe, Chile. Material and Method: Descriptive study of 767 patient records, between the years 2017 and 2019. Demographic information and clinical history were reviewed. For qualitative variables, proportions and frequency distributions were used, for quantitative variables, measures of central tendency were used. Results: 58.54% of the patients were male and 79.4% corresponded to elderly people (79.4%). Neurological pathologies represented the most frequent admission diagnosis (61.93%). 14.73% had a history of endotracheal intubation, 8.34% had a tracheostomy, and 84.09% were partial or total edentulous. In the evaluation with food, multiple swallows and the presence of cough corresponded to the most frequent alterations in efficacy and safety. In 82.01%, dysphagia was diagnosed and the majority of neurogenic etiology (68.45%). Conclusion: The present study allowed us to describe the clinical characteristics of hospitalized patients with suspected dysphagia. In this context, extubated, tracheostomized patients and the elderly with neurological disorders or respiratory pathologies are presented as potential candidates for swallowing evaluation.

Resultados del programa nacional de implantes cocleares y garantías explícitas en salud en beneficiarios pertenecientes al servicio de salud Aconcagua / Results of the national program of cochlear implants and explicit health guarantees in beneficiaries belonging to the Aconcagua health service

Resumen Introducción: En Chile, desde la ejecución de políticas públicas vinculadas a la implementación de implantes cocleares, sólo existen estudios elaborados y publicados en la Región Metropolitana que han buscado describir los resultados que estas han alcanzado en la población. Objetivo: Describir los resultados del Programa Nacional de Implantes Cocleares y Garantías Explícitas en Salud en pacientes beneficiados pertenecientes al Servicio de Salud Aconcagua. Material y Método: Estudio de corte transversal. Se reportan los resultados de la totalidad de pacientes beneficiados implantados en el período 2003-2016 del Servicio de Salud Aconcagua. Resultados: Del total de personas postuladas a nivel nacional, el 3% (n = 17) fueron postuladas desde el Servicio de Salud Aconcagua, de las cuales, el 58,8% (n = 10), fueron beneficiadas con implante coclear. La totalidad de los beneficiados fueron pesquisados a través de consulta en policlínico de Otorrinolaringología. La mediana de diagnóstico auditivo fue 22 meses (Q1-Q3:16-24), implementación de audífonos 24 meses (Q1-Q3:17-25), implementación de implante coclear 50 meses (Q1-Q3:29-56) y encendido de 52 (Q1-Q3:33-57). La mediana de ganancia funcional con implante fue 58,4 dB (Q1-Q3:46-65); estadísticamente significativa (p < 0,05). Conclusión: Los resultados en pacientes usuarios de implante coclear son satisfactorios. Es necesario ampliar la cobertura de estas políticas en el valle del Aconcagua, en coherencia con la mejora de procesos vinculados al diagnóstico oportuno de hipoacusia y posterior implementación de ayudas auditivas en tiempos que la evidencia sugiere pertinentes.

Abstract Introduction: In Chile, since the implementation of public policies linked to the program of cochlear implants, the only published studies were prepared in the Metropolitan Region, that have sought to describe the results that these responses have obtained in the population. Aim: Describe the results of the National Cochlear Implants Program and explicit health guarantees in beneficiary patients belonging to Aconcagua health service. Material and Method: Cross-sectional study. The results of all the patients benefited implanted in the period 2003-2016 are reported. Results: Of the total number of people nominated nationwide, 3% (n = 17) were chosen from the Aconcagua health service, of which 58.8% (n = 10) were benefited with cochlear implants. All the benefited patients were investigated through consultation in the Otolaryngology polyclinic. The median auditory diagnosis was 22 months (Q1-Q3: 16-24), hearing aid implementation 24 months (Q1-Q3: 17-25), cochlear implant implementation 50-month (Q1-Q3: 29-56) and on of cochlear implant 52 months (Q1-Q3: 33-57). The median functional gain with implant was 58.4 dB (Q1-Q3: 46-65); statistically significant (p < 0.05). Conclusion: The results in patients using cochlear implants are satisfactory. It is necessary to expand the coverage of these public policies in the Aconcagua valley, consistent with the improvement of the processes related to the timely diagnosis of hearing loss and subsequent implementation of hearing aids in the times that the relevant evidence.

Torsión de pedículo de quiste anexial durante el embarazo: experiencia clínica de manejo conservador / Adnexal torsion in pregnancy: clinical experience of conservative management

Las masas anexiales en el embarazo oscilan entre el 2% a 10%; su torsión es causa rara de abdomen agudo durante el mismo. La conducta frente al diagnóstico fue, tradicionalmente, anexectomía sin detorsión del lado comprometido; posteriormente, detorsión y conservación del anexo torcido. OBJETIVO: describir el valor de la punción y aspiración bajo guía ecográfica como tratamiento, inicialmente temporal, en cuadro de torsión de pedículo de quiste anexial durante el embarazo. MÉTODOS: estudio observacional prospectivo de 9 casos clínicos con diagnóstico de torsión de pedículo de quiste anexial y embarazo sometidos al tratamiento de punción aspiración del quiste torcido bajo guía ecográfica entre el año 2014 a 2019. RESULTADOS: en todos los casos fue posible salvar en anexo comprometido; en dos casos hubo persistencia del quiste que se extirpó durante la cesárea; en el resto, la resolución fue completa. Hubo una pérdida de embarazo atribuible al cuadro clínico. CONCLUSION: la punción-evacuación del quiste simple torcido parece ser una buena alternativa en la resolución del cuadro agudo.

The adnexal masses in pregnancy range from 2% to 10%; the adnexal torsion is a rare cause of acute abdomen during pregnancy. Surgical management traditionally involved adnexectomy without detorsion of the compromised structure; recently conservative surgery was proposed which consists in detorsion and conservation of the affected annex. OBJETIVE: to describe the value of ultrasound guided fine needle puncture and aspiration as the initially treatment in pedicle torsion of adnexal cyst during pregnancy. METHODS: prospective observational study of 9 patients that had the diagnosis of pedicle torsion of adnexal cyst during pregnancy who underwent ultrasound guided fine needle aspiration as a treatment of the adnexal cyst torsion between 2014 and 2019. RESULTS: in all cases it was possible to save the compromised structure; in two cases we observed recurrence of the cyst, that was subsequently removed during a caesarean section in both cases; in the rest of the patient's resolution was complete. Spontaneous abortion was seen in one of the patients, this event was not related to the invasive procedure. CONCLUSION: ultrasound guided fine needle aspiration of an adnexal who has suffered of pedicle torsion seems to be a good alternative for the management of this acute condition.

Preoperative factors associated with technical difficulties of laparoscopic cholecystectomy in acute cholecystitis. / Factores prequirúrgicos asociados con dificultades técnicas de la colecistectomía laparoscópica en la colecistitis aguda.

OBJECTIVE: To identify preoperative factors associated with surgical time and conversion of the laparoscopic cholecystectomy (LC) to open surgery in subjects with acute cholecystitis (AC). METHOD: We developed a cross-sectional study that included 99 subjects older than 17 years with definitive diagnosis of AC who had undergone to LC. Preoperative variables such as clinical data, laboratory markers and ultrasound findings as wall thickness, the size of the major calculus and the presence of: perivesicular fluid, multiple cholelithiasis, biliary mud or microlithiasis were registered. We consider indirect measures of technical difficulties of LC the total surgical time and the need for conversion to open surgery. We used the square chi and Mann-Whitney U test to stablish the correlation between preoperative variables and the technical difficulties of LC. We build ROC curves of the variables with significant statistical association (p ≤0.05 and 95% confidence interval [95%CI]) to determine the cut-off points of better sensitivity and specificity to predict conversion of LC to open surgery. RESULTS: A gallbladder wall thickness ≥6mm detected by ultrasound has a sensitivity of 87.5% and a specificity of 62.6% with OR 11.71 (95%CI: 1.38-99; p = 0.008) for predict conversion to open surgery. There was no relationship between surgical time and the preoperative evaluated variables. CONCLUSION: The gallbladder wall thickness detected by the ultrasound is associated with the need of conversion of LC to open surgery in subjects with AC, furthermore this finding could warn the surgeon on the complexity with a particular patient.

In utero exposure to fluoride and cognitive development delay in infants.

The objective of this study was to evaluate the association between in utero exposure to fluoride (F) and Mental and Psychomotor Development (MDI and PDI) evaluated through the Bayley Scale of Infant Development II (BSDI-II) in infants. The sample included 65 mother-infant pairs. Environmental exposure to F was quantified in tap and bottled water samples and F in maternal urine was the biological exposure indicator; samples were collected during the 1st, 2nd and 3rd trimester of pregnancy. The mean values of F in tap water for the 1st, 2nd and 3rd trimester were 2.6±1.1mg/l, 3.1±1.1mg/l and 3.7±1.0mg/l respectively; above to 80% of the samples exceeded the reference value of 1.5mg/l (NOM-127-SSA1-1994). Regarding F in maternal urine, mean values were 1.9±1.0mg/l, 2.0±1.1mg/l and 2.7±1.1mg/l for the 1st, 2nd and 3rd trimester respectively. The infants with MDI and PDI scores less than 85 points were 38.5% and 20.9% respectively. After adjusting for potential confounding factors (gestational age, age of child, marginalization index and type of water for consumption), the MDI showed an inverse association with F levels in maternal urine for the first (ß=-19.05, p=0.04) and second trimester (ß=-19.34, p=0.01). Our data suggests that cognitive alterations in children born from exposed mothers to F could start in early prenatal stages of life.

Separating the effects of repulsive and attractive forces on the phase diagram, interfacial, and critical properties of simple fluids.

Molecular simulations in the canonical and isothermal-isobaric ensembles were performed to study the effect of varying the shape of the intermolecular potential on the phase diagram, critical, and interfacial properties of model fluids. The molecular interactions were modeled by the Approximate Non-Conformal (ANC) theory potentials. Unlike the Lennard-Jones or Morse potentials, the ANC interactions incorporate parameters (called softnesses) that modulate the steepness of the potential in their repulsive and attractive parts independently. This feature allowed us to separate unambiguously the role of each region of the potential on setting the thermophysical properties. In particular, we found positive linear correlation between all critical coordinates and the attractive and repulsive softness, except for the critical density and the attractive softness which are negatively correlated. Moreover, we found that the physical properties related to phase coexistence (such as span of the liquid phase between the critical and triple points, variations in the P-T vaporization curve, interface width, and surface tension) are more sensitive to changes in the attractive softness than to the repulsive one. Understanding the different roles of attractive and repulsive forces on phase coexistence may contribute to developing more accurate models of liquids and their mixtures.

Leptin and metabolic syndrome in patients with Duchenne/Becker muscular dystrophy.

OBJECTIVES: To determine whether patients with Duchenne/Becker muscular dystrophy (DMD/BMD) have components of metabolic syndrome (MetSy) and to evaluate whether leptin is associated with components of MetSy. METHODS: This study included 78 patients (nine, <6 years of age; 54, 6 to <16 years of age; and 15 patients, ≥16 years of age). Obesity and body fat mass were determined by waist circumference and dual-energy X-ray absorptiometry, respectively. A 12-h fasting blood sample was collected in the morning. Patients were categorized into four groups according to the number of criteria for MetSy: group 0: none; group 1: one; group 2: two and group 3: three or more criteria. RESULTS: All age groups showed components of MetSy. The concentration of these components was significantly higher in patients ≥16 years old. The prevalence of hypertriglyceridemia was from ~37% to 46% in all age groups. The prevalence of MetSy was 7.1% for patients from 6 to <16 years of age and 24% for patients ≥16 years of age. Serum leptin levels increased significantly (P < 0.05) with age; the highest (13.43 ± 9.4 ng/ml) value was observed in patients >16 years of age. Total leptin was correlated with the number of patients with MetSy (r = 0.383; P = 0.001). CONCLUSIONS: Components of MetSy are significant in patients with DMD/BMD. A high prevalence of hypertriglyceridemia was observed. Younger patients with DMD/BMD have risk factors for MetSy. Although leptin increased according to different degrees of MetSy, this relation disappeared when the body fat was corrected by leptin; therefore, the association could be caused by a common risk factor-fat.

Desarrollo y caracterización de micropartículas de ácido fólico formadas por secado por aspersión, utilizando goma arábiga y maltodextrina como materiales de pared / Development and characterization of folic acid microparticles formed by spray-drying with gum arabic and maltodextrin

El ácido fólico es una vitamina esencial, que participa en la biosíntesis de aminoácidos esenciales y en algunos procesos asociados al ADN. Es una vitamina con limitaciones en su estabilidad frente a factores como la luz, pH y oxígeno. Por esta razón se hace necesario desarrollar estrategias que permitan su estabilización sin afectar su actividad biológica. Así pues, se propone la obtención de micropartículas utilizando mezclas de goma arábiga y maltodextrina, con el método de secado por aspersión, que presenten características adecuadas para actuar como un reservorio del ácido fólico con potencialidades para su estabilización.En este estudio se obtienen micropartículas de ácido fólico utilizando cuatro mezclas diferentes de goma arábiga y maltodextrina, caracterizadas mediante los siguientes parámetros: distribución de tamaño de partícula, porcentaje de humedad, morfología, eficiencia de encapsulación y perfil de disolución. Los resultados de la caracterización muestran diferentes aspectos: la morfología de las micropartículas obtenidas por este método varía con la relación goma arábiga- maltodextrina, la eficiencia de encapsulación es elevada para los cuatro tipos de micropartículas estudiadas, la distribución de tamaño de partícula no cambia con la relación de los materiales de la pared y los perfiles de disolución muestran un porcentaje de disolución limitado, siendo el mejor el que corresponde a micropartículas con la relación goma arábiga- maltodextrina 70-30. La goma arábiga es efectiva para el atrapamiento del ácido fólico y cuando se mezcla con maltodextrina se mejoran las características de morfología, eficiencia y disolución de las micropartículas, lo cual sugiere que existe una mezcla óptima de los dos materiales de pared que optimizan las características de las micropartículas.

Exposure assessment of polybrominated diphenyl ethers (PBDEs) in Mexican children.

Flame retardants (FRs) constitute a group of compounds that are added to materials in order to suppress, reduce, or delay fire. At present the most used FRs are the polybrominated diphenyl ethers (PBDEs), and diverse studies have found individuals exposed to them. However, few studies have reported data in children. The objective of this report was to assess PBDEs levels in children of six communities in México. During the year 2006 we analyzed a total of 173 healthy children (aged 6-13 years old). Plasma samples were taken and quantified (gas chromatography/mass spectrometer) for PBDEs. Six PBDEs congeners (BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, and BDE-209) were quantified in blood serum. We detected exposure to PBDEs in all the communities. The total PBDEs levels ranged from no detectable (nd) to 43.4 ng g(-1) lipid, the dominant PBDE congener was BDE-47, followed by BDE-100, BDE-99 and BDE-153, whereas the levels of BDE-209 were below LOD. Children living in an industrial and urban area (Cd. Juarez, Chih) had the highest levels of PBDEs, approximately two times that of children living in El Refugio, S.L.P. (a rural area) or in Milpillas, S.L.P. (municipal landfill) and 4-5 times higher than levels found in children living in San Luis Potosi, S.L.P. (urban area), in Chihuahua, Chih. (urban area), and San Juan Tilapa, Edo. Mex. (municipal landfills). Results cannot be generalized since the communities selected are not representative of the Mexican population. However, they do indicate that Mexican children are exposed to PBDEs.

Madeleine Leininger: un análisis de sus fundamentos teóricos / Madeleine Leininger: an analysis of its theoretical foundations

El presente artículo tiene como propósito hacer un análisis de los fundamentos teóricos de la propuesta de Madeleine Leininger, que se sustenta en dos disciplinas; Antropología y Sociología. El trabajo contiene los antecedentes biográficos de la autora, planteamientos de la antropología filosófica, social y cultural, a partir de los cuales se hacen inferencias en relación a los constructos utilizados por Leininger. Finalmente se establece que la Enfermería requiere del conocimiento del ser humano que vive dentro de una estructura social donde la cultura determina el estado de bienestar/ salud.

The present article has like intention make an analysis of the theoretical foundations of the proposal of Madeleine Leininger, that is sustained in two disciplines; Anthropology and Sociology. The work contains the biographical antecedents of the author, expositions of the philosophical, social and cultural anthropology, from which inferences in relation to the constructos used by Leininger become. Finally one settles down that the nursing requires of the knowledge of the human being who lives within a social structure where the culture determines the well-being state health.

Evaluación de la calidad física de diferentes variedades de cebada (Hordeum sativum jess) cultivada en los estados de Hidalgo y Tlaxcala, México / Evaluation of physical quality from different barley varities (Hordeum sativum jess) produced in the states of Hidalgo and Tlaxcala from Mexico

La cebada es el cuarto cereal de mayor importancia a nivel mundial, así como también a nivel nacional en México. Hidalgo y Tlaxcala son dos de los estados de mayor producción de cebada en grano de temporal. Entre los cereales existen variaciones en sus características y propiedades físicas, aún siendo de la misma variedad. Es por eso que existen sistemas de clasificación, para darle al grano de cebada determinada calidad y grado. Con la finalidad de determinar la calidad de siete variedades de cebada producidas en Hidalgo y Tlaxcala, las muestras se sometieron a diferentes análisis: sensorial y temperatura, impurezas y sanidad, densidad, dureza y selectivo. De los análisis mencionados se determinó que sólo la variedad Pastor Ortiz tiene el grado México de acuerdo a la norma mexicana NMX-FF-043-SCFI-2003, las otras seis variedades obtienen el grado México no clasificado.

Barley is the fourth cereal of greater importance at world-wide level, as well as at national level in México. Hidalgo and Tlaxcala are two of the states of greater production of barley. Between cereals, physical variations in their characteristics and properties exist, even in those of the same variety. A classification systems exist to give to the grain from certain barley regarding quality and degree. With the purpose of determining the quality of seven produced varieties of barley in Hidalgo and Tlaxcala, samples were put under different analyses: sensorial and temperature, impurities and sanitary, density, hardness and selectivity. From the analyses mentioned it was determined that only the Pastor Ortiz variety has the Mexico degree according to Mexican norm NMX-FF-043-SCFI-2003, the other six varieties received the Mexico rank of none classified.

Attractive interactions between like-charged colloidal particles at the air/water interface.

In the past few years, measurements of the pair interaction potential have shown evidence of micrometer-range attractive interactions between colloidal particles trapped between glass plates. In these experiments it is believed that the glass walls play an important role in the observed attractions. Colloidal particles trapped at the air/water interface show the formation of different 2-D colloidal patterns such as foams, clusters, and chains, whose formation has been taken as evidence of micrometer-range attractive interaction. Here, we present measurements of the pair interaction potential between 0.5-microm colloidal particles at the air/water interface. Indeed, the pair potential shows an attractive secondary minimum at about 1.9sigma, where sigma is the particle's diameter. Surprisingly, the position and depth of the secondary well are similar to those found in colloidal systems trapped between glass plates. However, we do not have a clear explanation on the origin of the attractive component of the interaction potential.

Quenched disorder in a liquid-crystal biosensor: adsorbed nanoparticles at confining walls.

We analyze the response of a nematic liquid-crystal film, confined between parallel walls, to the presence of nanoscopic particles adsorbed at the walls. This is done for a variety of patterns of adsorption (random and periodic) and operational conditions of the system that can be controlled in experimental liquid-crystal-based devices. We compute simulated optical textures and the total optical output of the sensor between crossed polars, as well as the correlation function for the liquid-crystal tensor order parameter; we use these observables to discuss the gradual destruction of the original uniform orientation. For large concentrations of particles adsorbed in random patterns, the liquid crystal at the center of the sensor adopts a multidomain state, characterized by a small correlation length of the tensor order parameter, and also by a loss of optical anisotropy under observation through crossed polars. In contrast, for particles adsorbed in periodic patterns, the nematic at the center of the cell can remain in a monodomain orientation state, provided the patterns in opposite walls are synchronized.

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles.

Recent experiments indicate that liquid crystals can be used to optically report the presence of biomolecules adsorbed at solid surfaces. In this work, numerical simulations are used to investigate the effects of biological molecules, modeled as spherical particles, on the structure and dynamics of nematic ordering. In the absence of adsorbed particles, a nematic in contact with a substrate adopts a uniform orientational order, imposed by the boundary conditions at this surface. It is found that the relaxation to this uniform state is slowed down by the presence of a small number of adsorbed particles. However, beyond a critical concentration of adsorbed particles, the liquid crystal ceases to exhibit uniform orientational order at long times. At this concentration, the domain growth is characterized by a first regime where the average nematic domain size LD obeys the scaling law LDt approximately t1/2; at long times, a slow dynamics regime is attained for which LD tends to a finite value corresponding to a metastable state with a disordered texture. The results of simulations are consistent with experimental observations.

Polymer-particle mixtures: depletion and packing effects.

The structure of polymers in the vicinity of spherical colloids is investigated by Monte Carlo simulations and integral equation theory. Polymers are represented by a simple bead-spring model; only repulsive Lennard-Jones interactions are taken into account. Using advanced trial moves that alter chain connectivity, depletion and packing effects are analyzed as a function of chain length and density, both at the bond and the chain level. Chain ends segregate to the colloidal surface and polymer bonds orient parallel to it. In the dilute regime, the polymer chain length governs the range of depletion and has a negligible influence on monomer packing in dense polymer melts. Polymers adopt an ellipsoidal shape, with the larger axis parallel to the surface of the particle, as they approach larger colloids. The dimensions are perturbed within the range of the depletion layer.

Defect structure around two colloids in a liquid crystal.

This Letter investigates the defect structures that arise between two colloidal spheres immersed in a nematic liquid crystal. Molecular simulations and a dynamic field theory are employed to arrive at molecular-level and mesoscopic descriptions of the systems of interest. At large separations, each sphere is surrounded by a Saturn ring defect. However, at short separations both theory and simulation predict that a third disclination ring appears in between the spheres, in a plane normal to the Saturn rings. This feature gives rise to an effective binding of the particles. The structures predicted by field theory and molecular simulations are consistent with each other.