Analysis of Reactive Injection Compression Molding by Numerical Simulations and Experiments

Injection compression molding is an injection molding process with the addition of a compression stage after the injection. This process is useful for the injection molding of precision parts. A stable and controlled manufacturing process is needed to guarantee reliability of complex products, and usually process optimization is achieved by experimental and time consuming approaches. However, for being competitive a minimal market time is a very important requirement and computer simulations can help to optimize the process at the only expense of computational time. This paper reports and discusses for the first time the results of a 3D finite element simulation of reactive injection compression molding (RICM) by commercial software for the production of rubber diaphragms. In particular, the stages of mold filling dynamics and material curing are analyzed and the results verified with experimental tests. To get an accurate representation of the process, the rheological behavior, thermal properties, and kinetic behavior during curing of the real rubber compound were described by mathematical models. A differential scanning calorimeter (DSC) and a capillary rheometer are employed to characterize the rubber material in order to achieve an appropriate curing reaction and viscosity models, respectively. The computations are found to be in good agreement with the experimental results, indicating that reliable information on material viscosity and curing kinetics can play a key role in making well-founded predictions and avoiding trial and error methods

Designing Viscoelastic Gelatin-PEG Macroporous Hybrid Hydrogel with Anisotropic Morphology and Mechanical Properties for Tissue Engineering Application

The mechanical properties of scaffolds play a vital role in regulating key cellular processes in tissue development and regeneration in the field of tissue engineering. Recently, scaffolding material design strategies leverage viscoelasticity to guide stem cells toward specific tissue regeneration. Herein, we designed and developed a viscoelastic Gel-PEG hybrid hydrogel with anisotropic morphology and mechanical properties using a gelatin and functionalized PEG (as a crosslinker) under a benign condition for tissue engineering application. The chemical crosslinking/grafting reaction was mainly involved between epoxide groups of PEG and available functional groups of gelatin. FTIR spectra revealed the hybrid nature of Gel-PEG hydrogel. The hybrid hydrogel showed good swelling behavior (water content > 600%), high porosity and pore interconnectivity suitable for tissue engineering application. Simple unidirectional freezing followed by a freeze-drying technique allowed the creation of structurally stable 3D anisotropic macroporous architecture that showed tissue-like elasticity and was capable of withstanding high deformation (50% strain) without being damaged. The tensile and compressive modulus of Gel-PEG hybrid hydrogel were found to be 0.863 MPa and 0.330 MPa, respectively, which are within the range of normal human articular cartilage. In-depth mechanical characterizations showed that the Gel-PEG hybrid hydrogel possessed natural-tissue-like mechanics such as non-linear and J-shaped stress-strain curves, stress softening effect, high fatigue resistance and stress relaxation response. A month-long hydrolytic degradation test revealed that the hydrogel gradually degraded in a homogeneous manner over time but maintained its structural stability and anisotropic mechanics. Overall, all these interesting features provide a potential opportunity for Gel-PEG hybrid hydrogel as a scaffold in a wide range of tissue engineering applications

Regulation of amino acid catabolism in rats fed diets with different protein content

[eng] Current lifestyle with high-energy diets and characterized by sedentary is triggering an alarming growth in obesity. Obesity along with metabolic syndrome- related co-morbidities (i.e. insulin resistance, atherosclerosis, sleep apnea, depression, asthma, hypertension and the alteration of blood lipid transport) are the most apparent consequence of the excess energy. Under conditions of excess dietary energy, the body cannot easily dispose of the excess amino-N against the evolutively-adapted schemes that prevent its wastage; thus ammonia and glutamine formation and urea excretion are decreased. High lipid and energy availability limit the utilization of glucose, and high glucose spares the production of ammonium from amino acids, decreasing the synthesis of glutamine and its utilization by the intestine and kidney. In contrast, high protein diets enhance protein synthesis and growth, and the synthesis of non-protein-N-containing compounds. But these outlets are not enough; consequently, less- conventional mechanisms are activated, such as increased synthesis of NO∙ followed by higher nitrite (and nitrate) excretion and changes in the microbiota. In this study we studied how the initial phase of development of metabolic syndrome can affects the function of liver as main site of amino-N metabolism, and to determine whether doubling the protein content in the diet induced significant changes in enzyme of amino acids metabolism along intestine and on liver. The common result obtained by these studies is that, both in case of hyperlipidic or hyperproteic diets, elimination of excess N is necessary but cannot be easily carried out through the metabolic pathways/tissues we evaluated, although possible alternative pathways have been taken into consideration.[cat] L’estil de vida actual amb les dietes d'alt contingut energètic, i caracteritzat pel sedentarisme, està provocant un creixement alarmant de l'obesitat. L'obesitat, juntament amb les comorbiditats relacionades amb la síndrome metabòlica (és a dir, resistència a la insulina, aterosclerosi, apnea del son, depressió, asma, la hipertensió i l'alteració del transport de lípids en la sang) són la conseqüència més evident de l'excés d’energia. En condicions d'excés d'energia de la dieta, el cos no pot eliminar ràpidament l'excés d'amino-N contra els esquemes adaptats evolutivament i que impedeixin el seu deteriorament; així, la formació d'amoníac i de glutamina i l'excreció d'urea disminueixen. Els elevats nivells de lípids i de la disponibilitat d'energia limiten la utilització de la glucosa, i nivells elevats de glucosa estalvia la producció d'amoni a partir dels aminoàcids, disminuint la síntesi de glutamina i la seva utilització per l'intestí i el ronyó. En contrast, les dietes d’elevat contingut en proteïnes incrementen la síntesi de proteïnes i el creixement, i la síntesi de compostos que contenen N i no són proteïnes. Però aquests mecanismes no són suficients i en conseqüència, s'activen mecanismes menys convencionals, com ara augment de la síntesi de NO ∙ seguides per l’augment del nitrit (i nitrat) i la seva excreció, juntament amb canvis en la microbiota. En aquest treball es va estudiar com la fase inicial de desenvolupament de la síndrome metabòlica pot afectar la funció del fetge com lloc principal del metabolisme d'amino-N, i per determinar si la duplicació del contingut de proteïnes en la dieta induïa canvis significatius en els enzims del metabolisme d'aminoàcids al llarg intestí i al fetge. El resultat genèric obtingut per aquests estudis és que, tant en el cas de que la dieta sigui hiperlipídica o hiperproteica, l'eliminació de l'excés de N és necessària, però no es pot dur a terme fàcilment a través de les vies metabòliques / teixits que avaluem, tot i les possibles vies alternatives s'han tingut en consideració

Dynamic Freedom: Substrate Stress Relaxation Stimulates Cell Responses

An elastic substrate stores cell-induced forces, while a viscoelastic substrate dissipates these forces through matrix reorganization and facilitates cell proliferation and differentiation

Effects of sex and site on amino acid metabolism enzyme gene expression and activity in rat white adipose tissue

Podeu consultar dades primàries associades a l'article a: http://hdl.handle.net/2445/66872Background and Objectives.White adipose tissue (WAT) shows marked sex- and diet-dependent differences.However, our metabolic knowledge ofWAT, especially on amino acid metabolism, is considerably limited. In the present study, we compared the influence of sex on the amino acid metabolism profile of the four mainWAT sites, focused on the paths related to ammonium handling and the urea cycle, as a way to estimate the extent ofWAT implication on body amino-nitrogen metabolism. Experimental Design. Adult female and male rats were maintained, undisturbed, under standard conditions for one month. After killing them under isoflurane anesthesia. WAT sites were dissected and weighed. Subcutaneous, perigonadal, retroperitoneal and mesentericWAT were analyzed for amino acid metabolism gene expression and enzyme activities. Results. There was a considerable stability of the urea cycle activities and expressions, irrespective of sex, and with only limited influence of site. Urea cycle was more resilient to change than other site-specialized metabolic pathways. The control of WAT urea cycle was probably related to the provision of arginine/citrulline, as deduced from the enzyme activity profiles. These data support a generalized role of WAT in overall amino-N handling. In contrast, sex markedly affected WAT ammonium-centered amino acid metabolism in a site-related way, with relatively higher emphasis in males' subcutaneousWAT. Conclusions. We found that WAT has an active amino acid metabolism. Its gene expressions were lower than those of glucose-lipid interactions, but the differences were quantitatively less important than usually reported. The effects of sex on urea cycle enzymes expression and activity were limited, in contrast with the wider variations observed in other metabolic pathways. The results agree with a centralized control of urea cycle operation affecting the adipose organ as a whole

White adipose tissue urea cycle activity is not affected by one-month treatment with a hyperlipidic diet in female rats.

Under high-energy diets, amino acid N is difficult to dispose of, as a consequence of the availability of alternative substrates. We found, recently, that WAT contains a complete functional urea cycle, we analyzed the possible overall changes in the WAT urea cycle (and other-related amino acid metabolism gene expressions) in rats subjected to a cafeteria diet. Adult female Wistar rats were fed control or simplified cafeteria diets. Samples of WAT sites: mesenteric, periovaric, retroperitoneal and subcutaneous, were used for the estimation of all urea cycle enzyme activities and gene expressions. Other key amino acid metabolism gene expressions, and lactate dehydrogenase were also measured. Subcutaneous WAT showed a differentiated amino acid metabolism profile, since its cumulative (whole site) activity for most enzymes was higher than the activities of the other sites studied. After one month of eating an energy rich cafeteria diet, and in spite of doubling the size of WAT, the transforming capacity of most amino acid metabolism enzymes remained practically unchanged in the tissue. This was not only due to limited changes in the overall enzyme activity, but also a consequence of a relative decrease in the expression of the corresponding genes. Overall, the results of this study support the consideration of WAT as an organ, disperse but under uniform control. The metabolic peculiarities between its different sites, and their ability to adapt to different energy availability conditions only add to the variable nature of adipose tissue. We have presented additional evidence of the significant role of WAT in amino acid metabolism

Master curves for the mechanical reinforcement of diene elastomers with sp2 carbon allotropes

sp2 carbon allotropes are efficient reinforcing fillers for polymer melt and elastomers: carbon black (CB) has been used since early 1900’s and nanofillers such as carbon nanotubes (CNT), graphene and graphene related materials (GRM) have increased their importance over the last decades. Nanofillers can definitely establish larger interfacial area with the polymer matrix than CB and great impact on material properties is thus expected. However, it is widely acknowledged that they will not be able to completely replace CB. Hence, increasing research efforts are on hybrid systems based on CB-CNT and CB-GRM [1]. Research objective is to identify common features and behaviour of nano (CNT, GRM) and nanostructured (CB) sp2 carbon allotropes. In this work, initial modulus was determined by means of dynamic-mechanical shear measurements of composites based on either poly(1,4-cis-isoprene) or poly(styrene-co-butadiene) as the rubber and either CB or CNT or GRM or hybrid systems as the reinforcing fillers. Filler-polymer interfacial area (i.a.), calculated as the product of filler surface area, density and volume fraction, was used to establish a common correlation with the composite initial modulus. A sort of master curve was derived, able to fit all the points up to interfacial area of about 27 μm-1, corresponding to remarkable filler content. Much better efficiency was shown by carbon fillers, when composites were prepared through latex blending. To allow easy dispersion in rubber latex, sp2 carbon allotropes were functionalized with a serinol derivative: 2-(2,5-dimethyl- 1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP) [2, 3], shown in Figure 1

Secular trends in age at menarche in relation to body mass index

OBJECTIVE: To evaluate the secular trend of menarche according to body mass index (BMI). SUBJECTS AND METHODS: Six hundred and eighty five girls (7-18 years) assessed in 2001 were compared with 750 evaluated in 2010. They were grouped by BMI Z-score: (thin + normal) and (overweight + obese). Menarche was reported by status quo and age at menarche estimated by a logit model. We used the Qui-square test, Mann-Whitney test, and Logistic Regression, at a 5% significance level. RESULTS: Menarche advanced 3.24 months. There was an increase in obesity, and a decrease of the prevalence of normal girls. Menarche was anticipated by 1.44 month in the thin + normal group and by 5.76 months in the overweight + obese group. There was no interaction between the effects determined by the evaluated period and nutritional diagnosis. CONCLUSIONS: Although both the period and BMI influence the menarche, one cannot attribute this advance only to changes in the nutritional profile of the sample. Other factors that were not tested may also contribute to this finding.OBJETIVO: Avaliar a tendência secular da menarca de acordo com o índice de massa corporal (IMC). SUJEITOS E MÉTODOS: Seiscentos e oitenta e cinco meninas (7-18 anos) avaliadas em 2001 foram comparadas a 750 avaliadas em 2010. Elas foram agrupadas pelo Z-escore do IMC em: (magreza + eutrofia) e (sobrepeso + obesidade). A menarca foi relatada pelo status quo e a idade, estimada pelo logito. Foram utilizados os testes Qui-quadrado, Mann-Whitney e a Regressão logística, com significância de 5%. RESULTADOS: A menarca adiantou 3,24 meses entre 2001 e 2010. Houve aumento da obesidade e diminuição de eutróficas. O evento antecipou 1,44 mês no grupo magreza + eutrofia e 5,76 meses no sobrepeso + obesidade. Não houve interação entre os efeitos determinados pelo período avaliado e diagnóstico nutricional. CONCLUSÕES: Embora tanto o período quanto o IMC tenham influenciado a menarca, não se pode atribuir essa antecipação só à mudança do perfil nutricional da amostra. Outros fatores não testados podem estar contribuindo também para isso.Pontifícia Universidade Católica de Campinas (PUC-Campinas) Faculdade de MedicinaUniversidade Estadual de Campinas (Unicamp) Faculdade de Ciências Médicas Departamento de PediatriaUniversidade Federal de São Paulo (UNIFESP)UNIFESPSciEL

Evidences of basal lactate production in the main white adipose tissue sites of rats. Effects of sex and a cafeteria diet.

Female and male adult Wistar rats were fed standard chow or a simplified cafeteria diet for one month. Then, the rats were killed and the white adipose tissue (WAT) in four sites: perigonadal, retroperitoneal, mesenteric and subcutaneous (inguinal) were sampled and frozen. The complete WAT weight in each site was measured. Gene expression analysis of key lipid and glucose metabolism enzymes were analyzed, as well as tissue and plasma lactate and the activity of lactate dehydrogenase. Lactate gradients between WAT and plasma were estimated. The influence of sex and diet (and indirectly WAT mass) on lactate levels and their relationships with lactate dehydrogenase activity and gene expressions were also measured. A main conclusion is the high production of lactate by WAT, practically irrespective of site, diet or sex. Lactate production is a direct correlate of lactate dehydrogenase activity in the tissue. Furthermore, lactate dehydrogenase activity is again directly correlated with the expression of the genes Ldha and Ldhb for this enzyme. In sum, the ability to produce lactate by WAT is not directly dependent of WAT metabolic state.We postulate that, in WAT, a main function of the lactate dehydrogenase path may be that of converting excess available glucose to 3C fragments, as a way to limit tissue self-utilization as substrate, to help control glycaemia and/or providing short chain substrates for use as energy source elsewhere. More information must be gathered before a conclusive role of WAT in the control of glycaemia, and the full existence of a renewed glucose-lactate-fatty acid cycle is definitely established