Administration of methylene blue in septic shock: pros and cons.

Septic shock typically requires the administration of vasopressors. Adrenergic agents remain the first choice, namely norepinephrine. However, their use to counteract life-threatening hypotension comes with potential adverse effects, so that non-adrenergic vasopressors may also be considered. The use of agents that act through different mechanisms may also provide an advantage. Nitric oxide (NO) is the main driver of the vasodilation that leads to hypotension in septic shock, so several agents have been tested to counteract its effects. The use of non-selective NO synthase inhibitors has been of questionable benefit. Methylene blue, an inhibitor of soluble guanylate cyclase, an important enzyme involved in the NO signaling pathway in the vascular smooth muscle cell, has also been proposed. However, more than 25 years since the first clinical evaluation of MB administration in septic shock, the safety and benefits of its use are still not fully established, and it should not be used routinely in clinical practice until further evidence of its efficacy is available.

The pulmonary artery catheter.

PURPOSE OF REVIEW: To review recently published data on pulmonary artery catheter (PAC) use in critically ill patients and consider optimal use of the PAC in personalized clinical practice. RECENT FINDINGS: Although PAC use has decreased considerably since the mid-1990s, PAC-derived variables can still have an important role in elucidating hemodynamic status and directing management in complex patients. Recent studies have suggested benefit, notably in patients having cardiac surgery. SUMMARY: Only a small number of acutely ill patients require a PAC and insertion should be individualized based on clinical context, availability of trained staff, and the possibility that measured variables will be able to help guide therapy.

Ultrasound Elastography Detects Age-Related Changes in Adult False Vocal Folds.

PURPOSE: To investigate the feasibility of ultrasound elastography for assessing the symmetry in stiffness values and movements of both false vocal folds (FVFs). METHODS: After Institutional Review Board's approval and written informed consent obtained, we measured ultrasound strain and shear wave velocity (SWV) of the bilateral FVF in vocal fold abduction and adduction in 30 participants using a linear array transducer (4-10 MHz). Twenty-eight participants met inclusion criteria as healthy subjects for analysis. Mean strain of FVF produced by FVF movement from abduction to adduction was analyzed using 2D speckle-tracking software offline. A SWV ratio ([SWVadduction - SWabduction ]/SWabduction ) was developed to test the contractibility of FVF. Statistical analysis included one-way ANOVA to test the difference in mean strain, SWV (adduction and abduction), and SWV ratio among the three age groups; linear regression to analyze correlations of stiffness and movement between the right and left FVF; and intraclass correlation coefficient (ICC) to examine intra- and interobserver reliability in performing shear wave elastography (SWE) of FVF. RESULTS: The 28 healthy participants were divided into 3 age groups (10 of young 20-44 years; 9 of mid-age 45-64 years; and 9 of senior ≥65 years). The SWV in FVF abduction was higher and the SWV ratio was lower in seniors compared to young participants (P < .05). Good to excellent correlation of mean strain and SWV between both FVFs (R2 > 0.89). The reliability of performing SWE of FVF was moderate to excellent. CONCLUSION: Ultrasound elastography is feasible to assess the stiffness, dynamic movement, and symmetry of adult FVF, and healthy seniors may exhibit increased FVF stiffness.

Perfil epidemiológico de la infección por Enterococcus SPP en un hospital regional / Epidemiological profile of enterococcus SPP infection in a regional hospital

Introducción: los enterococos son responsables de múltiples infecciones y por su creciente patrón de resistencia se ha vuelto de interés en el país y en el mundo. Objetivo: caracterizar las infecciones por Enterococcus spp. Metodología: estudio descriptivo, retrospectivo observacional transversal desde enero 2015 hasta enero 2018 en un hospital regional. Resultados: la prevalencia de las infecciones por Enterococcus spp. fue de 0,154%. El E. faecalis fue el más aislado, seguido del E. faecium. La resistencia a ampicilina fue de 19% y a vancomicina de 10%; 32% de los pacientes tuvieron terapia empírica con vancomicina y 22% con piperacilina tazobactam, la mediana de antibioticoterapia fue de 10 días. Discusión: el interés por los Enterococcus spp. se ha incrementado debido a que representan una carga importante en las infecciones asociadas con la atención en salud (IAAS). La mayoría se dan en hombres con una edad mediana de 40 a 60 años, hospitalizados en UCI, con infecciones urinarias y comorbilidades como inmunosupresión y cirugías previas. Conclusión: como ha venido reportándose aumento en las tasas de resistencia a vancomicina y ampicilina, se recomienda el uso responsable de la terapia antibiótica, con la finalidad de erradicar en forma eficaz al patógeno y prevenir nuevas resistencias.

Introduction: enterococci can cause multiple infections and due to their increasing resistance to antibiotics they have become of national and global concern. Objective: to characterize infections caused by Enterococcus spp.Methodology: descriptive, retrospective observational cross-sectional study conducted from January 2015 to January 2018 in a regional hospital. Results: the prevalence of Enterococcus spp. infections was 0.154%. E. faecalis was the most commonly isolated, followed by E. faecium. Antibiotic resistance was 19% and 10% for ampicillin and vancomycin respectively, 32% of patients received empirical therapy with vancomycin and 22% with piperacillin tazobactam. The median duration of antibiotic therapy was 10 days. Discussion: interest in Enterococcus spp. has increased for they are recognized as an important burden in healthcare-associated infections (HAIs). Enterococcal infection occurs mainly among men, median age 40 to 60 years, hospitalized in the ICU, with urinary tract infections and comorbidities such as immunosuppression and previous surgeries. Conclusion: as an increased rate of vancomycin and ampicillin resistance in enterococci has been reported, a responsible use of antibiotic therapy is recommended in order to effectively eradicate the pathogen and prevent the emergence of new bacterial resistances.

The medical treatment of cardiogenic shock: cardiovascular drugs.

PURPOSE OF REVIEW: To discuss the use of vasopressors and inotropes in cardiogenic shock. RECENT FINDINGS: The classic form or cardiogenic shock requires administration of inotropic and/or vasopressor agents to try to improve the impaired tissue perfusion. Among vasopressors various alpha-adrenergic agents, vasopressin derivatives and angiotensin can be used. The first-line therapy remains norepinephrine as it is associated with minimal adverse effects and appears to be associated by the best outcome in network meta-analyses. On the contrary, epinephrine is associated with an increased incidence of refractory shock and observational studies suggest an increased risk of death. Vasopressin may be an excellent alternative in tachycardiac patients or in the presence of pulmonary hypertension. Concerning inotropic agents, dobutamine is the first-line agent but levosimendan is an excellent alternative or additional agent in cases not responding to dobutamine. The impact on outcome of inotropic agents remains controversial. SUMMARY: Recent studies have refined the position of the various vasopressor and inotropic agents. Norepinephrine is recommended as first-line vasopressor agent by various guidelines. Among inotropic agents, selection between the agents should be individualized and based on the hemodynamic response.

Predifferentiated Gingival Stem Cell-Induced Bone Regeneration in Rat Alveolar Bone Defect Model.

Cleft alveolus, a common birth defect of the maxillary bone, affects one in 700 live births every year. This defect is traditionally restored by autogenous bone grafts or allografts, which may possibly cause complications. Cell-based therapies using the mesenchymal stem cells (MSCs) derived from human gingiva (gingiva-derived mesenchymal stem cells [GMSCs]) is attracting the research interest due to their highly proliferative and multilineage differentiation capacity. Undifferentiated GMSCs expressed high level of MSC-distinctive surface antigens, including CD73, CD105, CD90, and CD166. Importantly, GMSCs induced with osteogenic medium for a week increased the surface markers of osteogenic phenotypes, such as CD10, CD92, and CD140b, indicating their osteogenic potential. The objective of this study was to assess the bone regenerative efficacy of predifferentiated GMSCs (dGMSCs) toward an osteogenic lineage in combination with a self-assembling hydrogel scaffold PuraMatrix™ (PM) and/or bone morphogenetic protein 2 (BMP2), on a rodent model of maxillary alveolar bone defect. A critical size maxillary alveolar defect of 7 mm × 1 mm × 1 mm was surgically created in athymic nude rats. The defect was filled with either PM/BMP2 or PM/dGMSCs or the combination of three (PM/dGMSCs/BMP2) and the bone regeneration was evaluated at 4 and 8 weeks postsurgery. New bone formation was evaluated by microcomputed tomography and histology using Hematoxylin and Eosin staining. The results demonstrated the absence of spontaneous bone healing, either at 4 or 8 weeks postsurgery in the defect group. However, the PM/dGMSCs/BMP2 group showed significant enhancement in bone regeneration at 4 and 8 weeks postsurgery, compared with the transplantation of individual material/cells alone. Apart from developing the smallest critical size defect, results showed that PM/dGMSCs/BMP2 could serve as a promising option for the regeneration of bone in the cranio/maxillofacial region in humans.

Evaluación de la respuesta sostenida en pacientes con dolor crónico de la pared abdominal tratados con infiltración de anestesia local / Evaluation of sustained responses to infiltration of local anesthetic in patients with chronic abdominal wall pain

Resumen Introducción: el dolor abdominal crónico es frecuente en consulta externa. El enfoque tradicional es investigar patologías viscerales. El 50 % de esos pacientes finalmente tiene dolor crónico de la pared abdominal (DCPA), generalmente secundario a atrapamiento del nervio cutáneo anterior. Esta entidad se identifica con el signo de Carnett. El tratamiento de elección es infiltrar con lidocaína los puntos dolorosos. Con una postinfiltración hay una mejoría significativa en el 85 %-90 % de los pacientes. Se desconoce la duración de la mejoría postinfiltración. El objetivo de este trabajo es determinar la respuesta sostenida en seguimientos a 1 y 2 años. Materiales y métodos: estudio de cohorte, retrospectivo, realizado en la unidad de gastroenterología de la Clínica Fundadores. Se incluyeron pacientes adultos mayores de 18 años que hubieran recibido tratamiento con inyección local con lidocaína al 2 % sin epinefrina y que hubieran respondido una encuesta telefónica para evaluar la intensidad del dolor en una escala análoga. Resultados: se identificaron 360 elegibles y, finalmente, atendieron la entrevista telefónica 324 pacientes (90 %). El 87 % era de sexo femenino. La edad promedio de la población era de 57 años. En la preinfiltración el dolor promedio era 8,7 puntos. En la postinfiltración los pacientes tuvieron una mejoría con una intensidad promedio de 2,38 (p < 0,05). En el 71 % de los pacientes la intensidad del dolor en el seguimiento hasta 2 años tuvo una intensidad promedio de 1,65 (p < 0,05), que representa una mejoría del 81 % en la intensidad (p = 0,001). La fibromialgia tuvo una asociación positiva con la mejoría sostenida del dolor (p = 0,008). Conclusiones: en los pacientes con DCPA, la infiltración de la pared con anestesia local produce una respuesta sostenida hasta 2 años después del tratamiento.

Abstract Introduction: Chronic abdominal pain is frequently encountered at outpatient clinics where the traditional approach is to investigate visceral pathologies. Fifty percent of these patients are finally found to have abdominal wall pain which is generally secondary to entrapment of the anterior cutaneous nerve. This entity is identified by Carnett's sign. The treatment of choice is to infiltrate the painful points with lidocaine following which there is significant improvement in 85% to 90% of these patients. The duration of post-infiltration improvement is unknown. The objective of this work is to determine sustained response in one and two-year follow-up examinations. Materials and Methods: This is a retrospective cohort study conducted in the gastroenterology unit of the Clínica Fundadores. We included adult patients over 18 years of age who had received local injection treatment with 2% lidocaine without epinephrine and who had answered a telephone survey to assess the intensity of pain on an analogous scale. Results: Of the 360 eligible patients identified, 324 patients (90%) were interviewed by telephone. The average age of those interviewed was 57 years, and 87% were women. The average pain level prior to infiltration was 8.7 points. Following infiltration, the average intensity was 2.38 points (p <0.05). In 71% of patients, average pain intensity at a two year follow-up examination was 1.65 points (p <0.05), an 81% improvement in intensity (p = 0.001). Fibromyalgia had a positive association with sustained improvement in pain (p = 0.008). Conclusions: Infiltration of the abdominal wall with a local anesthetic produces a sustained response for up to two years in patients with chronic abdominal wall pain.

Quantifying Flabby Ridge Tissue Displacement During Impression-Making for Patients With Combination Syndrome.

Patients with Combination syndrome present with early bone loss and flabby hyperplastic tissues in the anterior maxilla caused by functional loads exerted by mandibular anterior teeth on maxillary complete dentures. Use of conventional mucocompressive impression techniques captures flabby maxillary anterior ridge tissue in a distorted state, and dentures made from such impressions could displace flabby tissues when loaded and become loose when unloaded. In this study, which examined two patients diagnosed with Combination syndrome, computer-aided design/computer-aided manufacturing (CAD/CAM) technology was used to determine the degrees of displacement when six impression materials were used for making final impressions for complete dentures.

Engineered nanoceria cytoprotection in vivo: mitigation of reactive oxygen species and double-stranded DNA breakage due to radiation exposure.

Cerium oxide nanomaterials are known to absorb ionizing radiation energy, as well as to neutralize free radicals in solution, by undergoing redox changes. We, therefore, proposed that ceria nanoparticles could be used in biomedical applications as an injectable, radio-protectant material. In this study, we examine the effectiveness of engineered nanoparticles in protecting germ cells from the damaging effects of irradiation-induced cell death, in vivo. C57BL/6J male mice were used as a model and irradiation was localized to the scrotal region at 2.5, 5, and/or 10 Gy intensities. Ceria nanoparticles were introduced as 100 µL injections at 100 nM and 100 µM via tail vein injections, weekly, for one month. Following this, the animals were sacrificed and their organs (heart, brain, kidneys) were harvested. Tissues were fixed, sectioned, and stained for instances of cell death, DNA damage (TUNEL assay), and ROS (nitro-tyrosine evolution). Tissues from mice treated with ceria nanoparticles showed significantly less (∼13% decrease; *P < 0.05) tissue damage (per immunohistochemistry) over controls at up to 5 Gy radiation. DNA damage and ROS also decrease substantially with ceria treatment, confirming ceria's capacity as an injectable, radio-protectant material. The study also highlights the ability of ceria nanoparticles to protect cells/tissues from both direct and indirect effects of ionizing radiation.

Modulating the Catalytic Activity of Cerium Oxide Nanoparticles with the Anion of the Precursor Salt.

In this work, we tested our hypothesis that surface chemistry and antioxidant properties of cerium nanoparticles (CNPs) are affected by presence of counterions. We first employed various precursor cerium (III) (Ce(III)) salts with different counterions (acetate, nitrate, chloride, sulfate) to synthesize CNPs following the same wet chemical methodology. Electron spin resonance (ESR) studies provided evidence for the formation of radicals from counterions (e.g., NO3•2- from reduction of NO3- in CNPs synthesized from Ce(III) nitrate). Physicochemical properties of these CNPs, e.g., dispersion stability, hydrodynamic size, signature surface chemistry, SOD-mimetic activity, and oxidation potentials were found to be significantly affected by the anions of the precursor salts. CNPs synthesized from Ce(III) nitrate and Ce(III) chloride exhibited higher extent of SOD-mimetic activities. Therefore, these CNPs were studied extensively employing in-situ UV-Visible spectroelectrochemistry and changing the counterion concentrations affected the oxidation potentials of these CNPs. Thus, the physicochemical and antioxidant properties of CNPs can be modulated by anions of the precursor. Furthermore, our ESR studies present evidence of the formation of guanine cation radical (G•+) in 5'-dGMP via UV-photoionization at 77 K in the presence of CNPs synthesized from Ce(III) nitrate and chloride and CNPs act as the scavenger of radiation-produced electrons.

Tissue deposition and toxicological effects of commercially significant rare earth oxide nanomaterials: Material and physical properties.

Rare earth oxide (REO) materials are found naturally in earth's crust and at the nanoscale these REO nanoparticles exhibit unique thermal, electrical, and physicochemical properties. REO nanoparticles are widely used in different industrial sectors for ceramics, glass polishing, metallurgy, lasers, and magnets. Recently, some of these REO nanoparticles have been identified for their potential application in medicine, including therapy, imaging, and diagnostics. Concurrent research into the REO nanomaterials' toxicities has also raised concern for their environmental impacts. The correlation of REO nanoparticles mediated toxicity with their physiochemical properties can help to design nanoparticles with minimal effect on the environment and living organisms. In vitro assay revealed toxicity toward Human squamous epithelial cell line (CCL30) and Human umbilical vascular endothelial cells (HUVEC) at a concentration of 100 µM and higher. In vivo results showed, with the exception of CeO2 and Gd2 O3 , most of the naoparticles did not clear or had minimum clearance (10-20%) from the system. Elevated levels of alanine transferase were seen for animals given each different nanoparticle, however the increases were not significant for CeO2 and Dy2 O3 . Nephrotoxicity was only seen in case of Dy2 O3 and Gd2 O3 . Lastly, histological examination revealed presence of swollen hepatocytes which further confirms toxicity of the commercial REO nanomaterials. The in vivo toxicity is mainly due to excessive tissue deposition (70-90%) due to the commercial REO nanoparticles' poor physical properties (shape, stability, and extent of agglomeration). Therefore, optimization of nanoparticles physical properties is very important. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 904-917, 2017.

Reporte de Caso Clínico y discusión de tema: Síndrome del opérculo Torßcico / Descrição do caso clínico e discussão do tema: síndrome do desfiladeiro torßcico / Report and discussion of a study case: Thoracic Outlet Syndrome

Introdución: El síndrome del Opérculo Torßcico (SOT) es un grupo heterogéneo y potencialmente disfuncional de síndromes relacionados con compresión extrínseca de estructuras neurovasculares a su paso, desde el cuello hacia el miembro superior, por diferentes estructuras anatómicas congénitas o adquiridas, siendo mßs frecuente la compresión neurológica, ocasionando una variedad de sintomatología que varía según grado de compresión y estructura afectada, que en algunos casos hacen difícil su diagnóstico. Es una entidad mal diagnosticada teniendo en cuenta que no hay criterios diagnósticos establecidos; por eso, el examen físico es primordial para su sospecha clínica. El tratamiento inicial es conservador, siendo el tratamiento quirúrgico, una opción con múltiples procedimientos personalizados para cada tipo de paciente, según etiología. Objetivo: El propósito del artículo es realizar una discusión del caso clínico basada en la evidencia, para permitir un conocimiento general de esta patología, y comprender que hace parte de las causas de dolor en miembro superior, para así orientar al profesional de la salud a realizar un diagnóstico oportuno y un tratamiento efectivo que disminuya el riesgo de complicaciones irreversibles.

Introduction: Thoracic Outlet Syndrome - TOS - is a heterogeneous and potentially dysfunctional group of syndromes related to extrinsic compression of neurovascular structures from the neck to the upper limb for different congenital or acquired anatomical structures, being more frequent the neurological compression, causing a variety of symptoms that vary according to the degree of compression and affected structure that in some cases make it difficult to diagnose. Due to the lack of established diagnostic criteria, the physical exam is the most important element used to formulate a diagnosis. The initial treatment is conservative. The surgical treatment becomes an option with multiple personalized procedures for each type of patient according to the etiology. Objective: The purpose of the article is to discuss the clinical case based on the evidence allowing general knowledge of that pathology, and understanding the causes of pain in the upper limb, to therefore guide medical staff to perform a timely diagnosis and effective treatment that decreases the risk of irreversible complications.

Introdução: A Síndrome do desfiladeiro Toraxico (SOT) é um grupo heterogéneo e potencialmente disfuncional de síndromes relacionadas à compressão extrínseca de estruturas neurovasculares da passagem do pescoço para o membro superior por diferentes estruturas anatômicas congênitas ou adquiridas, sendo a compressão neurológica mais frequente, sua varieda sintomatología depende do grau de compressão e da estrutura afectada, o que em alguns casos podem dificultar o seu diagnóstico. É uma doença mal diagnosticada porque não hß criterios estabelecidos para o diagnóstico; por esta razão o exame físico é fundamental na suspeita clínica. O tratamento inicial é conservador, sendo a opção cirúrgico uma intervenção com múltiplos procedimentos personalizados acordo com a etiologia do paciente. Objetivo: O objetivo deste artigo é realizar uma discussão do caso clínico com base em provas, que permita um conhecimento geral da doença, e entender que faz parte das causas de dor no membro superior permitindo orientar o profissional de saúde a fazer um diagnóstico oportuno e um tratamento eficaz a fim de reduzir o risco de complicações irreversíveis. (au)

Myocardial dysfunction during H1N1 influenza infection.

PURPOSE: The purpose of the study is to evaluate the incidence and hemodynamic consequences of right ventricular (RV) and left ventricular (LV) dysfunction in critically ill patients with H1N1 infection. PATIENTS AND METHODS: This is a retrospective analysis of all patients admitted to the intensive care unit of an academic hospital between October 2009 and March 2011 with severe H1N1 infection. Hemodynamic measurements and respiratory conditions were noted daily during the intensive care unit stay. RESULTS: Forty-six patients were admitted with severe H1N1 infection. Echocardiography was obtained in 39 patients on admission: 28 (72%) had abnormal ventricular function, of whom 13 (46%) had isolated LV abnormalities, 11 (39%) had isolated RV dysfunction, and 4 (14%) had biventricular dysfunction. Echocardiography was repeated in 19 of the 39 patients during their hospitalization: RV function tended to worsen with time, but LV function tended to normalize. The ventricular abnormalities were not associated with history, severity of the respiratory failure, or hemodynamic status. However, patients with ventricular dysfunction needed more aggressive therapy, including more frequent use of vasopressor and inotropic agents and of rescue ventilatory strategies, such as inhaled nitric oxide, prone positioning, and extracorporeal membrane oxygenation. CONCLUSIONS: These observations emphasize the high incidence of cardiac dysfunction in patients with H1N1 influenza infections.

Microcirculatory effects of angiotensin II inhibitors in patients with severe heart failure.

CONTEXT: The renin-angiotensin system is activated in patients with acute severe heart failure, and increased levels of angiotensin II could contribute to microcirculatory defects in these patients. OBJECTIVE: To evaluate the microcirculatory effects of angiotensin II antagonists in critically ill patients with severe heart failure. METHODS: After Ethics Committee approval and signed consent, we conducted a prospective observational study using sidestream darkfield (SDF) imaging to evaluate changes in the sublingual microcirculation of 25 adult patients with severe heart failure (ejection fraction < 40% or cardiac index < 2.5 L/min.m2) who received angiotensin inhibitors during their ICU stay. SDF images and global hemodynamic data were obtained immediately before and 4 h, 24 h, and 48 h after the first administration of the drug. RESULTS: Already 4 h after administration, there was a significant improvement in the proportion of perfused small (<20 µm) vessels (PPV) (from 78 [72-84] to 89 [82-94]%, P < 0.05) and the microvascular flow index (MFI) (from 2.25 [1.95-2.50] to 2.80 [2.39-2.95] points, P < 0.05), which persisted over subsequent hours. Large vessel perfusion remained constant. There was no correlation between changes in the PPV and changes in the mean arterial pressure (R2 0.02, P = 0.50), cardiac output (R2 0.004, P = 0.85), or central or mixed venous oxygen saturation (R2 0.03, P = 0.53). CONCLUSIONS: In patients with severe heart failure, introduction of angiotensin antagonist therapy was associated with an early improvement in the microcirculation that persisted over subsequent hours. The microcirculatory effects were independent of global hemodynamic variables. The improvement in microcirculatory perfusion observed with angiotensin inhibitors in patients with severe heart failure may partially explain the beneficial clinical effects of this intervention in such patients.

La mujer y el liderazgo empresarial / Women and business leadership

El objetivo de este estudio fue describir la situación actual de la mujer en el mundo laboral y analizar las circunstancias que le han impedido alcanzar altas posiciones en las compañías. El núcleo de la discusión giró en torno a las barreras del liderazgo femenino y cómo estas pueden ser superadas a través del reconocimiento de las diferencias. Se argumenta que el principal problema relacionado con la participación inequitativa en cargos de alta gerencia se debe principalmente a los estereotipos femeninos, los cuales suelen ser contrarios a los roles de liderazgo aceptados por la mayoría de las culturas. Se resalta la necesidad de que las mujeres ejerzan el liderazgo desde sus propias características, en vez de imitar el tradicional rol de liderazgo masculino.

The aim of this paper was to describe the current leadership situation from the gender perspective and to analyze the circumstances that deter women from achieving high leadership positions in companies. The core of the discussion turned around women's leadership barriers and how these can be overcome through the recognition of the difference of being a woman. We argued that the main issue related to this unequal participation as CEOs is mainly due to stereotypes concerning women's roles, which in many cases are contrary to the leadership roles accepted in most cultures. We point out that women should find their own leadership capacity, according to their own characteristics rather than to imitate the traditional male leadership role.

Slow dynamics of stress and strain relaxation in randomly crumpled elasto-plastic sheets.

Stress and strain relaxation in randomly folded paper sheets under axial compression is studied both experimentally and theoretically. Equations providing the best fit to the experimental data are found. Our findings suggest that, in an axially compressed ball folded from an elastic or elasto-plastic material, the relaxation dynamics is ruled by activated processes of an energy foci rearrangement in the crumpling network. The dynamics of relaxation is discussed within a framework of Edwards's statistical mechanics. The functional forms of the activation barrier between admissible jammed folding configurations of the crumpling network under axial compression are derived. It is shown that relaxation kinetics can be mapped to activated dynamics of depinning and creep of elastic interface in a disordered medium.

Fractal topology of hand-crumpled paper.

We study the statistical topology of folding configurations of hand folded paper balls. Specifically, we are studying the distribution of two sides of the sheet along the ball surface and the distribution of sheet fragments when the ball is cut in half. We found that patterns obtained by mapping of ball surface into unfolded flat sheet exhibit the fractal properties characterized by two fractal dimensions which are independent on the sheet size and the ball diameter. The mosaic patterns obtained by sheet reconstruction from fragments of two parts (painted in two different colors) of the ball cut in half also possess a fractal scale invariance characterized by the box fractal dimension DBF=1.68 ± 0.04 , which is independent on the sheet size. Furthermore, we noted that DBF, at least numerically, coincide with the universal fractal dimension of the intersection of hand folded paper ball with a plane. Some other fractal properties of folding configurations are recognized.