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1.
Int J Mol Sci ; 23(13)2022 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-35806437

RESUMO

Type 2 diabetes (T2D) has been considered a relentlessly worsening disease, due to the progressive deterioration of the pancreatic beta cell functional mass. Recent evidence indicates, however, that remission of T2D may occur in variable proportions of patients after specific treatments that are associated with recovery of beta cell function. Here we review the available information on the recovery of beta cells in (a) non-diabetic individuals previously exposed to metabolic stress; (b) T2D patients following low-calorie diets, pharmacological therapies or bariatric surgery; (c) human islets isolated from non-diabetic organ donors that recover from "lipo-glucotoxic" conditions; and (d) human islets isolated from T2D organ donors and exposed to specific treatments. The improvement of insulin secretion reported by these studies and the associated molecular traits unveil the possibility to promote T2D remission by directly targeting pancreatic beta cells.


Assuntos
Diabetes Mellitus Tipo 2 , Células Secretoras de Insulina , Diabetes Mellitus Tipo 2/metabolismo , Humanos , Insulina/metabolismo , Secreção de Insulina , Células Secretoras de Insulina/metabolismo
2.
Biochem Biophys Res Commun ; 564: 86-91, 2021 07 30.
Artigo em Inglês | MEDLINE | ID: mdl-32747088

RESUMO

At first glance, plants seem relatively immobile and, unlike animals, unable to interact with the surroundings or escape stressful environments. But, although markedly different from those of animals, movement pervades all aspects of plant behaviour. Here, we focused our investigation on the approaching movement of climbing plants, that is the movement they perform to reach-to-climb a support. In particular, we examined whether climbing plants evolved a motor accuracy mechanism as to improve the precision of their movement and how this eventually differs from animal species. For this purpose, by means of three-dimensional kinematical analysis, we investigated whether climbing plants have the ability to correct online their movement by means of secondary submovements, and if their frequency production is influenced by the difficulty of the task. Results showed, not only that plants correct their movement in flight, but also that they strategically increase the production of secondary submovements when the task requires more precision, exactly as humans do. These findings support the hypothesis that the movement of plants is far cry from being a simple cause-effect mechanism, but rather is appropriately planned, controlled and eventually corrected.


Assuntos
Movimento/fisiologia , Pisum sativum/fisiologia
3.
Int J Mol Sci ; 22(22)2021 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-34829980

RESUMO

Arginase 2 (ARG2) is a manganese metalloenzyme involved in several tissue specific processes, from physiology to pathophysiology. It is variably expressed in extra-hepatic tissues and is located in the mitochondria. In human pancreatic beta cells, ARG2 is downregulated in type 2 diabetes. The enzyme regulates the synthesis of polyamines, that are involved in pancreas development and regulation of beta cell function. Here, we discuss several features of ARG2 and polyamines, which can be relevant to the pathophysiology of type 2 diabetes.


Assuntos
Arginase/genética , Diabetes Mellitus Tipo 2/genética , Células Secretoras de Insulina/metabolismo , Poliaminas/metabolismo , Diabetes Mellitus Tipo 2/metabolismo , Diabetes Mellitus Tipo 2/patologia , Humanos , Células Secretoras de Insulina/patologia , Mitocôndrias/metabolismo , Mitocôndrias/patologia
4.
Biomacromolecules ; 18(12): 3978-3991, 2017 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-29131607

RESUMO

In this work, carbon papers and aerogels based on graphene layers and chitosan were prepared. They were obtained by mixing chitosan (CS) and a high surface area nanosized graphite (HSAG) in water in the presence of acetic acid. HSAG/CS water dispersions were stable for months. High resolution transmission electron microscopy revealed the presence of few graphene layers in water suspensions. Casting or lyophilization of such suspensions led to the preparation of carbon paper and aerogel, respectively. In X-ray spectra of both aerogels and carbon paper, peaks due to regular stacks of graphene layers were not detected: graphene with unaltered sp2 structure was obtained directly from graphite without the use of any chemical reaction. The composites were demonstrated to be electrically conductive thanks to the graphene. Chitosan thus makes it possible to obtain monolithic carbon aerogels and flexible and free-standing graphene papers directly from a nanosized graphite by avoiding oxidation to graphite oxide and successive reduction. Strong interaction between polycationic chitosan and the aromatic substrate appears to be at the origin of the stability of HSAG/CS adducts. Cation-π interaction is hypothesized, also on the basis of X-ray photoelectron spectroscopy findings. This work paves the way for the easy large-scale preparation of carbon papers through a method that has a low environmental impact and is based on a biosourced polymer, graphene, and water.


Assuntos
Carbono/química , Quitosana/química , Grafite/química , Acetatos/química , Liofilização/métodos , Microscopia Eletrônica de Varredura/métodos , Microscopia Eletrônica de Transmissão/métodos , Nanocompostos/química , Oxirredução , Óxidos/química , Papel , Tamanho da Partícula , Espectroscopia Fotoeletrônica/métodos , Polímeros/química , Água/química
5.
EMBO J ; 31(6): 1405-26, 2012 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-22293752

RESUMO

In addition to genetic predisposition, environmental and lifestyle factors contribute to the pathogenesis of type 2 diabetes (T2D). Epigenetic changes may provide the link for translating environmental exposures into pathological mechanisms. In this study, we performed the first comprehensive DNA methylation profiling in pancreatic islets from T2D and non-diabetic donors. We uncovered 276 CpG loci affiliated to promoters of 254 genes displaying significant differential DNA methylation in diabetic islets. These methylation changes were not present in blood cells from T2D individuals nor were they experimentally induced in non-diabetic islets by exposure to high glucose. For a subgroup of the differentially methylated genes, concordant transcriptional changes were present. Functional annotation of the aberrantly methylated genes and RNAi experiments highlighted pathways implicated in ß-cell survival and function; some are implicated in cellular dysfunction while others facilitate adaptation to stressors. Together, our findings offer new insights into the intricate mechanisms of T2D pathogenesis, underscore the important involvement of epigenetic dysregulation in diabetic islets and may advance our understanding of T2D aetiology.


Assuntos
Metilação de DNA , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/metabolismo , Ilhotas Pancreáticas/metabolismo , Idoso , Animais , Linhagem Celular , Ilhas de CpG , Impressões Digitais de DNA/métodos , Epigênese Genética , Loci Gênicos , Glucose/metabolismo , Humanos , Regiões Promotoras Genéticas , Ratos , Transcrição Gênica
6.
Dermatology ; 229(4): 279-87, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25472035

RESUMO

Several studies report the usefulness of different biological therapies in the management of a difficult-to-treat pathology such as hidradenitis suppurativa (HS). However, there are little data on this, which shows the great difficulty in the management of this disease. We will report herein our experience of the treatment of four complex cases of HS. We will also review previous cases published in the literature in order to further assess the results obtained with different biological drugs in terms of efficacy and safety. We conclude that, in the near future, biological therapy could become an essential tool in the management of cases of HS who have not previously responded to classical treatment.


Assuntos
Anti-Inflamatórios não Esteroides/uso terapêutico , Anticorpos Monoclonais Humanizados/uso terapêutico , Terapia Biológica , Fármacos Dermatológicos/uso terapêutico , Hidradenite Supurativa/tratamento farmacológico , Fator de Necrose Tumoral alfa/antagonistas & inibidores , Adalimumab , Adulto , Anti-Inflamatórios não Esteroides/administração & dosagem , Anticorpos Monoclonais/uso terapêutico , Anticorpos Monoclonais Humanizados/administração & dosagem , Fármacos Dermatológicos/administração & dosagem , Etanercepte , Feminino , Hidradenite Supurativa/cirurgia , Humanos , Imunoglobulina G/uso terapêutico , Infliximab , Masculino , Pessoa de Meia-Idade , Receptores do Fator de Necrose Tumoral/uso terapêutico , Retratamento , Falha de Tratamento , Adulto Jovem
7.
Endocr Pract ; 20(10): 1022-31, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-24793923

RESUMO

OBJECTIVE: The use of metformin in pregnant women is still controversial, despite the increasing reports on metformin's safety and effectiveness. We aimed to evaluate the maternal and neonatal safety of metformin in subjects with gestational diabetes mellitus (GDM). METHODS: We retrospectively reviewed the clinical records of 186 pregnancies complicated with GDM surveilled at Hospital de Santa Maria, Lisboa, between 2011 and 2012. The maternal and neonatal outcomes of 32 females who took metformin during pregnancy were compared with 121 females controlled with diet and 33 insulin-treated females. RESULTS: Of the 186 GDM subjects, 32 (17.2%) received metformin during pregnancy. No statistical differences between the diet and metformin groups were found with regard to the rates of abortion, prematurity, preeclampsia, macrosomy, small-for-gestational-age (SGA) or large-for-gestational-age (LGA) newborns, cesarean deliveries, neonatal intensive care unit (NICU) admissions, and birth malformations or neonatal injuries. Similarly, there were no differences between the metformin and insulin groups with regard to the referred outcomes. No abortions or perinatal deaths were recorded in the metformin group. Ten out of 32 metformin patients required additional insulin. CONCLUSION: This retrospective study suggests that metformin is a safe alternative or additional treatment to insulin in females with GDM. Metformin was not associated with a higher risk of maternal or neonatal complications when compared to the insulin or diet groups.

8.
Biology (Basel) ; 13(7): 502, 2024 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-39015821

RESUMO

Structural and functional asymmetries are traceable in every form of life, and some lateralities are homologous. Functionally speaking, the division of labour between the two halves of the brain is a basic characteristic of the nervous system that arose even before the appearance of vertebrates. The most well-known expression of this specialisation in humans is hand dominance, also known as handedness. Even if hand/limb/paw dominance is far more commonly associated with the presence of a nervous system, it is also observed in its own form in aneural organisms, such as plants. To date, little is known regarding the possible functional significance of this dominance in plants, and many questions remain open (among them, whether it reflects a generalised behavioural asymmetry). Here, we propose a comparative approach to the study of handedness, including plants, by taking advantage of the experimental models and paradigms already used to study laterality in humans and various animal species. By taking this approach, we aim to enrich our knowledge of the concept of handedness across natural kingdoms.

9.
Theor Exp Plant Physiol ; 36(3): 423-437, 2024 Jan 29.
Artigo em Inglês | MEDLINE | ID: mdl-39132627

RESUMO

Motor cognition involves the process of planning and executing goal-directed movements and recognizing, anticipating, and interpreting others' actions. Motor cognitive functions are generally associated with the presence of a brain and are ascribed only to humans and other animal species. A growing body of evidence suggests that aneural organisms, like climbing plants, exhibit behaviors driven by the intention to achieve goals, challenging our understanding of cognition. Here, we propose an inclusive perspective under motor cognition to explain climbing plants' behavior. We will first review our empirical research based on kinematical analysis to understand movement in pea plants. Then, we situate this empirical research within the current theoretical debate aimed at extending the principles of cognition to aneural organisms. A novel comparative perspective that considers the perception-action cycle, involving transforming perceived environmental elements into intended movement patterns, is provided.

10.
Plant Signal Behav ; 19(1): 2355739, 2024 Dec 31.
Artigo em Inglês | MEDLINE | ID: mdl-38837041

RESUMO

Previous studies on the kinematics of pea plants' ascent and attach behavior have demonstrated that the signature of their movement varies depending on the kind of support. So far, these studies have been confined to artificial supports (e.g. wooden sticks). Little is known regarding the conditions under which pea plants could rely on biological supports (e.g. neighboring plants) for climbing toward the light. In this study, we capitalize on the 3D kinematic analysis of movement to ascertain whether pea plants scale their kinematics differently depending on whether they aim for artificial or biological support. Results suggest that biological support determines a smoother and more accurate behavior than that elicited by the artificial one. These results shed light on pea plants' ability to detect and classify the properties of objects and implement a movement plan attuned to the very nature of the support. We contend that such differences depend on the augmented multisensory experience elicited by the biological support.


Assuntos
Pisum sativum , Pisum sativum/fisiologia , Fenômenos Biomecânicos , Movimento
11.
AoB Plants ; 16(1): plad088, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-38192569

RESUMO

In life, it is common for almost every kind of organism to interact with one another. In the human realm, such interactions are at the basis of joint actions, when two or more agents syntonize their actions to achieve a common goal. Shared intentionality is the theoretical construct referring to the suite of abilities that enable such coordinated and collaborative interactions. While shared intentionality has become an important concept in research on social cognition, there is controversy surrounding its evolutionary origins. An aspect still unexplored but promising to bring new insights into this open debate is the study of aneural organisms. To fill this gap, here we investigate whether climbing plants can act jointly to achieve a common goal, i.e. reaching the light. We examined Pisum Sativum plants growing intertwined when there is a need to climb but a potential support is not present in the environment. Three-dimensional kinematic analysis of their movement revealed a coordinated and complementary behaviour. They tend to coordinate their movement in time and space to achieve a joint climbing. By deliberately extending the context in which a joint action takes place, we pay tribute to the complex nature of this social phenomenon. The next challenge for the field of joint action is to generate a perspective that links coordination mechanisms to an evolutionary framework across taxa.

12.
Plants (Basel) ; 13(10)2024 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-38794459

RESUMO

Pea plants (Pisum sativum L.) can perceive the presence of potential supports in the environment and flexibly adapt their behavior to clasp them. How pea plants control and perfect this behavior during growth remains unexplored. Here, we attempt to fill this gap by studying the movement of the apex and the tendrils at different leaves using three-dimensional (3D) kinematical analysis. We hypothesized that plants accumulate information and resources through the circumnutation movements of each leaf. Information generates the kinematical coordinates for the final launch towards the potential support. Results suggest that developing a functional approach to grasp movement may involve an interactive trial and error process based on continuous cross-talk across leaves. This internal communication provides evidence that plants adopt plastic responses in a way that optimally corresponds to support search scenarios.

13.
Dermatol Online J ; 19(1): 5, 2013 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-23374947

RESUMO

Primary cutaneous adenoid cystic carcinoma (PCACC) is an uncommon adnexal skin tumor. It is usually located on the head or neck of people over 50 years of age, affecting men and women equally. The etiology is unclear; the source used to be considered the eccrine glands, but more recent hypotheses defend this carcinoma as originating in the apocrine glands or modified apocrine glands. The tumor may clinically appear as a normal skin-colored nodule with ill-defined edges and slow growth. Histologically, a proliferation of neoplastic cells appears, which could present in a tubular, cribriform, or solid pattern. Perineural invasion is characteristic for this tumor. For diagnosis of PCACC it is essential to exclude metastasis, especially in the salivary glands. Treatment involves surgical excision. We present a case of primary adenoid cystic carcinoma in a young woman located on the skin of the upper limb, which is an unusual place.


Assuntos
Carcinoma Adenoide Cístico/patologia , Neoplasias Cutâneas/patologia , Neoplasias das Glândulas Sudoríparas/secundário , Adulto , Braço/patologia , Carcinoma Adenoide Cístico/cirurgia , Diagnóstico Diferencial , Feminino , Humanos , Neoplasias das Glândulas Salivares/secundário , Neoplasias Cutâneas/cirurgia , Neoplasias das Glândulas Sudoríparas/patologia
14.
Prim Care Diabetes ; 17(5): 524-525, 2023 10.
Artigo em Inglês | MEDLINE | ID: mdl-37353465

RESUMO

AIM/HYPOTHESIS: Efficiency in controlling chronic diseases, especially in the primary care setting, is associated with reduced rates of hospitalizations. Poorly controlled diabetes is associated with severe diabetic decompensation, such as diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS). It is hypothesized that, in addition to the SARS-CoV2 pandemic, there was a parallel increase in decompensation of previously controlled chronic diseases, such as diabetes. In this work, the impact of the SARS-CoV2 pandemic on hospitalizations for severe diabetic decompensation in a Portuguese hospital was assessed. METHODS: A retrospective study by hospital clinical file consultation was performed and a cohort of 177 patients admitted to a Portuguese hospital with a diagnosis of DKA or hyperosmolar hyperglycemic state HHS, excluding SARS-CoV2 infected patients, between 2019 and 2020 was analysed. RESULTS: In the population not infected by SARS-CoV2, statistically significant differences were found in the relative number of hospitalizations (5.59 vs 3.79 hospitalizations for DKA/HHS per 1000 patients not infected with SARS-CoV2, p = 0.0093) and lethality due to DKA/HHS (0941 vs 0337 deaths from DKA/HHS per 1000 patients not infected with SARS-CoV2, p = 0.0251). This increase in hospitalizations and lethality was accompanied by a statistically significant increase in newly type 2 diabetes diagnosis in DKA/HHS hospital admissions (p = 0.0156) and by a statistically significant increase in average age of patients (56.3 ± 22.4 vs 69.1 ± 17.6, p < 0.001). DISCUSSION AND CONCLUSIONS: These results show the empirical perspective that the consequences of the pandemic also had a considerable impact on the control of chronic diseases such as diabetes, with a higher percentage of hospitalizations due to severe decompensation, especially in the elderly population.


Assuntos
COVID-19 , Diabetes Mellitus Tipo 2 , Cetoacidose Diabética , Coma Hiperglicêmico Hiperosmolar não Cetótico , Humanos , Idoso , Coma Hiperglicêmico Hiperosmolar não Cetótico/diagnóstico , Coma Hiperglicêmico Hiperosmolar não Cetótico/epidemiologia , Coma Hiperglicêmico Hiperosmolar não Cetótico/terapia , Diabetes Mellitus Tipo 2/diagnóstico , Diabetes Mellitus Tipo 2/epidemiologia , Diabetes Mellitus Tipo 2/terapia , RNA Viral , Estudos Retrospectivos , Pandemias/prevenção & controle , COVID-19/epidemiologia , COVID-19/complicações , SARS-CoV-2 , Cetoacidose Diabética/diagnóstico , Cetoacidose Diabética/epidemiologia , Cetoacidose Diabética/prevenção & controle , Diagnóstico Precoce , Doença Crônica , Atenção Primária à Saúde , Teste para COVID-19
15.
Plants (Basel) ; 12(8)2023 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-37111821

RESUMO

Finding a suitable support is a key process in the life history of climbing plants. Those that find a suitable support have greater performance and fitness than those that remain prostrate. Numerous studies on climbing plant behavior have elucidated the mechanistic details of support-searching and attachment. Far fewer studies have addressed the ecological significance of support-searching behavior and the factors that affect it. Among these, the diameter of supports influences their suitability. When the support diameter increases beyond some point, climbing plants are unable to maintain tensional forces and therefore lose attachment to the trellis. Here, we further investigate this issue by placing pea plants (Pisum sativum L.) in the situation of choosing between supports of different diameters while their movement was recorded by means of a three-dimensional motion analysis system. The results indicate that the way pea plants move can vary depending on whether they are presented with one or two potential supports. Furthermore, when presented with a choice between thin and thick supports, the plants showed a distinct preference for the former than the latter. The present findings shed further light on how climbing plants make decisions regarding support-searching and provide evidence that plants adopt one of several alternative plastic responses in a way that optimally corresponds to environmental scenarios.

16.
Biology (Basel) ; 12(2)2023 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-36829607

RESUMO

Many daily activities involve responding to the actions of other people. However, the functional relationship between the motor preparation and execution phases still needs to be clarified. With the combination of different and complementary experimental techniques (i.e., motor excitability measures, reaction times, electromyography, and dyadic 3-D kinematics), we investigated the behavioral and neurophysiological signatures characterizing different stages of a motor response in contexts calling for an interactive action. Participants were requested to perform an action (i.e., stirring coffee or lifting a coffee cup) following a co-experimenter's request gesture. Another condition, in which a non-interactive gesture was used, was also included. Greater corticospinal inhibition was found when participants prepared their motor response after observing an interactive request, compared to a non-interactive gesture. This, in turn, was associated with faster and more efficient action execution in kinematic terms (i.e., a social motor priming effect). Our results provide new insights on the inhibitory and facilitatory drives guiding social motor response generation. Altogether, the integration of behavioral and neurophysiological indexes allowed us to demonstrate that a more efficient action execution followed a greater corticospinal inhibition. These indexes provide a full picture of motor activity at both planning and execution stages.

17.
Plants (Basel) ; 12(4)2023 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-36840313

RESUMO

Climbing plants require an external support to grow vertically and enhance light acquisition. Climbers that find a suitable support demonstrate greater performance and fitness than those that remain prostrate. Support search is characterized by oscillatory movements (i.e., circumnutation), in which plants rotate around a central axis during their growth. Numerous studies have elucidated the mechanistic details of circumnutation, but how this phenomenon is controlled during support searching remains unclear. To fill this gap, here we tested whether simulation-based machine learning methods can capture differences in movement patterns nested in actual kinematical data. We compared machine learning classifiers with the aim of generating models that learn to discriminate between circumnutation patterns related to the presence/absence of a support in the environment. Results indicate that there is a difference in the pattern of circumnutation, depending on the presence of a support, that can be learned and classified rather accurately. We also identify distinctive kinematic features at the level of the junction underneath the tendrils that seems to be a superior indicator for discerning the presence/absence of the support by the plant. Overall, machine learning approaches appear to be powerful tools for understanding the movement of plants.

18.
J Comp Psychol ; 137(4): 228-237, 2023 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-37166943

RESUMO

"How" an action is performed is not solely determined by biomechanical constraints, but it depends on the agent's intention, that is, "why" the action is performed. Recent findings suggest that intentions can be specified at a tangible and quantifiable level in the kinematics of movements; that is, different motor intentions translate into different kinematic patterns. In the present study, we used 3D kinematical analysis to investigate whether the organization of climbing plants' approach-to-grasp action is sensitive to the kind of intention driving their movement toward potential support, namely individual or social. For the individual condition, a plant in isolation acted upon the support. For the social condition, two plants were located in the same pot opposite to each other with a support in the middle. Results indicate differences in kinematics depending on the context within which the plant is acting. In the presence of neighbors, climbing plants are able to modify their behaviors to maximize their long-term gains, including the grasping of a potential support. Overall, these data suggest that the organization of climbing plants' kinematics is sensitive to the "intention" driving their movement toward a potential support. To discuss this phenomenon, we capitalize on the concept of motor intentionality in plants and on available theories concerned to motor cognition. We suggest how they could be revisited to explain the intentionality component inherent in plant life and other brainless organisms. (PsycInfo Database Record (c) 2023 APA, all rights reserved).


Assuntos
Intenção , Movimento , Cognição , Fenômenos Biomecânicos , Força da Mão
19.
Rev Bras Ginecol Obstet ; 45(5): 273-280, 2023 May.
Artigo em Inglês | MEDLINE | ID: mdl-37339647

RESUMO

Pituitary apoplexy refers to a rare clinical syndrome consisting of signs and symptoms that occur due to rapid expansion of the contents of the sella turcica. It can occur spontaneously or associated with pituitary tumors. It can have a broad clinical spectrum, but usually presents with severe headache, visual impairment and hypopituitarism. Sudden onset of symptoms associated to imagiologic confirmation makes the diagnosis. Surgical treatment is advised when there is important compression of the optic tract. We present a case report and a review of the literature on pituitary apoplexy in pregnancy. The cases were reviewed to obtain information on maternal characteristics, clinical presentation, diagnostic studies, therapeutic modalities and maternal and fetal outcomes. Our review found 36 cases of pituitary apoplexy in pregnancy. Most of the cases occurred in the second trimester of pregnancy and headache was the most frequent symptom at presentation. Surgical therapy was required in more than half of the patients. In what respect maternal and fetal outcomes, there were 3 cases of preterm delivery and one case of maternal death. Our clinical case and literature review reinforces the importance of an early diagnosis to avoid potential adverse consequences.


Assuntos
Morte Materna , Apoplexia Hipofisária , Neoplasias Hipofisárias , Gravidez , Feminino , Recém-Nascido , Humanos , Apoplexia Hipofisária/diagnóstico , Apoplexia Hipofisária/terapia , Apoplexia Hipofisária/complicações , Neoplasias Hipofisárias/complicações , Neoplasias Hipofisárias/patologia , Neoplasias Hipofisárias/cirurgia , Cuidado Pré-Natal , Cefaleia/complicações , Cefaleia/terapia
20.
Polymers (Basel) ; 14(14)2022 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-35890695

RESUMO

Sulfur vulcanization is the most used method for curing of natural and synthetic rubbers. The crosslinking degree achieved is usually controlled by adding proper quantities of accelerants, activators, co-activators, retardants, and inhibitors, and influences the hardness, elasticity, hysteresis of elastomers and, consequently, the properties and behavior of the materials that incorporate them. Despite the fine tuning pursued over the years, sulfur crosslinking is still difficult to control both in terms of degree and homogeneity of cross-link. Addition of thermally activable bifunctional reagents able to crosslink the polymer matrix through covalent bonds could be a strategy to modulate and control finely the reticulation grade of elastomers. Tetrazoles can form highly reactive nitrilimines by thermal treatment at appropriate temperature, which can react with the vinyl double bonds present in the rubber. In this work a set of bis-tetrazoles were synthesized and those with the right activation temperatures were used for the curing of styrene-butadiene rubber, acting both as single crosslinkers and together with classic sulfur-based ones. The addition of bistetrazoles simplified and made more efficient the compounding process, allowing to prolong the mixing until optimum dispersion and homogeneity were obtained. Moreover, they led to an improvement in the hysteretic properties of the compound and to the reduction of the non-linearity of the dynamic behavior (Payne effect).

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