Effect of the Dianhydride/Branched Diamine Ratio on the Architecture and Room Temperature Healing Behavior of Polyetherimides.

Traditional polyetherimides (PEIs) are commonly synthesized from an aromatic diamine and an aromatic dianhydride (e.g., 3,4'-oxidianiline (ODA) and 4,4'-oxidiphtalic anhydride (ODPA)) leading to the imide linkage and outstanding chemical, thermal and mechanical properties yet lacking any self-healing functionality. In this work, we have replaced the traditional aromatic diamine by a branched aliphatic fatty dimer diamine (DD1). This led to a whole family of self-healing polymers not containing reversible chemical bonds, capable of healing at (near) room temperature yet maintaining very high elastomeric-like mechanical properties (up to 6 MPa stress and 570% strain at break). In this work, we present the effect of the DD1/ODPA ratio on the general performance and healing behavior of a room temperature healing polyetherimide. A dedicated analysis suggests that healing proceeds in three steps: (i) an initial adhesive step leading to the formation of a relatively weak interface; (ii) a second step at long healing times leading to the formation of an interphase with different properties than the bulk material and (iii) disappearance of the damaged zone leading to full healing. We argue that the fast interfacial adhesive step is due to van der Waals interactions of long dangling alkyl chains followed by an interphase formation due to polymer chain interdiffusion. An increase in DD1/ODPA ratio leads to an increase in the healing kinetics and displacement shift of the first healing step toward lower temperatures. An excess of DD1 leads to the cross-linking of the polymer thereby restricting the necessary mobility for the interphase formation and limiting the self-healing behavior. The results here presented offer a new route for the development of room temperature self-healing thermoplastic elastomers with improved mechanical properties using fatty dimer diamines.

Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber.

Broadband dielectric spectroscopy (BDS) is introduced as a new and powerful technique to monitor network and macroscale damage healing in an elastomer. For the proof of concept, a partially cured sulfur-cured natural rubber (NR) containing reversible disulfides as the healing moiety was employed. The forms of damage healed and monitored were an invisible damage in the rubber network due to multiple straining and an imposed macroscopic crack. The relaxation times of pristine, damaged, and healed samples were determined and fitted to the Havriliak-Negami equation to obtain the characteristic polymer parameters. It is shown that seemingly full mechanical healing occurred regardless the type of damage, while BDS demonstrates that the polymer architecture in the healed material differs from that in the original one. These results represent a step forward in the understanding of damage and healing processes in intrinsic self-healing polymer systems with prospective applications such as coatings, tires, seals, and gaskets.

Biodegradable PCL scaffolds with an interconnected spherical pore network for tissue engineering.

A technique for producing controlled interconnected porous structures for application as a tissue engineering scaffold is presented in this article. The technique is based on the fabrication of a template of interconnected poly(ethyl methacrylate) (PEMA) microspheres, the introduction of a biodegradable polymer, poly-epsilon-caprolactone (PCL), and the elimination of the template by a selective solvent. A series of PCL scaffolds with a porosity of 70% and pore sizes up to 200 microm were produced and characterized (both thermally and mechanically). Human chondrocytes were cultured in monolayer on bulk PCL disks or seeded into porous PCL scaffolds. Cell adhesion, viability, proliferation, and proteoglycan (PG) synthesis were tested and compared with monolayer cultures on tissue-treated polystyrene or pellet cultures as reference controls. Cells cultured on PCL disks showed an adhesion similar to that of the polystyrene control (which allowed high levels of proliferation). Stained scaffold sections showed round-shaped chondrocyte aggregates embedded into porous PCL. PG production was similar to that of the pellet cultures and higher than that obtained with monolayer postconfluence cultures. This shows that the cells are capable of attaching themselves to PCL. Furthermore, in porous PCL, cells maintain the same phenotype as the chondrocytes within the native cartilage. These results suggest that PCL scaffolds may be a suitable candidate for chondrocyte culture.

Temporal relationship between lens protein oxidation and cataract development in streptozotocin-induced diabetic rats.

We compared the progression of lens opacification with the time course of oxidation of lens proteins under conditions of streptozotocin-induced experimental diabetes in rats. By the end of the 17th week, approx. 50% of the diabetic animals developed mature cataracts. During the following month, 95% of the eyes in the diabetic group became cataractous. In the course of lens opacification we observed a time-dependent increase in the content of protein carbonyls and decrease in the concentration of protein sulfhydryls in the lenses of diabetic animals. Significantly higher protein carbonyl (p<0.01) and lower protein sulfhydryl (p<0.001) content was found in lenses with the advanced stage of cataract when compared with the diabetic lenses still transparent. We showed that the values of protein carbonyls exceeding 1.2 nmol/mg protein and of sulfhydryls falling below 60 nmol/mg protein corresponded to an approximately 50% incidence of mature cataract development. At the end of the 34th week, when all lenses of diabetic rats became cataractous, the corresponding values of protein carbonyls and sulfhydryls were 2.5 nmol/mg protein and 27 nmol/mg protein, respectively. The main finding of this study is the disclosure of quantitative relationship between the degree of protein oxidation and the rate of advanced cataract development in the widely used model of streptozotocin-induced experimental diabetes in rats.

Does the developmental neurotoxicity of chlorpyrifos involve glial targets? Macromolecule synthesis, adenylyl cyclase signaling, nuclear transcription factors, and formation of reactive oxygen in C6 glioma cells.

The widespread use of chlorpyrifos (CPF) has raised major concerns about its potential to cause fetal or neonatal neurobehavioral damage, even at doses that do not evoke acute toxicity. CPF has been shown to inhibit replication of brain cells, to elicit alterations in neurotrophic signaling governing cell differentiation and apoptosis, and to evoke oxidative stress. However, the specific cell types targeted by CPF have not been clarified, an issue of vital importance in establishing the boundaries of the critical period in which the developing brain is vulnerable. In the current study, we evaluated the effects of CPF on C6 glioma cells, a well-established glial model. In undifferentiated C6 cells, CPF inhibited DNA synthesis in a concentration-dependent manner, with greater potency than had been seen previously with neuronal cell lines. Just as found after in vivo CPF treatment or with neuronal cell lines, the effects on cell replication were independent of cholinergic stimulation, as cholinergic antagonists did not block CPF-induced inhibition. CPF interfered with cell signaling mediated through adenylyl cyclase at the level of G-protein function; the effects again were greater in undifferentiated C6 cells but were still detectable in differentiating cells. In contrast, differentiation enhanced the ability of CPF to elicit the formation of reactive oxygen species and to evoke deficits in Sp1, a nuclear transcription factor essential for differentiation. These results indicate that glial-type cells are targeted by CPF through the same multiple mechanisms that have been demonstrated for the effects of CPF on brain development in vivo. Because glial development continues long after the conclusion of neurogenesis, and given that CPF targets events in both glial cell replication and the later stages of differentiation, the vulnerable period for developmental neurotoxicity of CPF is likely to extend well into childhood.

Beta-adrenoceptor signaling and its control of cell replication in MDA-MB-231 human breast cancer cells.

MDA-MB-231 human breast cancer cells express high beta-adrenoceptor levels, predominantly the beta2 subtype. Receptor stimulation by isoproterenol evoked immediate reductions in DNA synthesis which were blocked completely by propranolol and were of the same magnitude as effects elicited by high concentrations of 8-Br-cAMP. Isoproterenol-induced inhibition of DNA synthesis was maintained throughout several days of exposure, resulting in a decrement in total cell number, and the effects were augmented by cotreatment with dexamethasone; an even greater effect was seen when cAMP breakdown was inhibited by theophylline, with or without addition of isoproterenol. Despite the persistent effect of isoproterenol, receptor downregulation was evident with as little as 1 h of treatment, and over 90% of the receptors were lost within 24 h. Receptor downregulation was paralleled by homologous desensitization of the adenylyl cyclase response to beta-adrenoceptor stimulation. Dexamethasone augmented the effects of isoproterenol on DNA synthesis but did not prevent receptor downregulation or desensitization. These results indicate that beta-adrenoceptors are effectively linked, through cAMP, to the termination of cell replication in MDA-MB-231 human breast cancer cells, and that activation of only a small number of receptors is sufficient for a maximal effect. Novel pharmacologic strategies that focus on cell surface receptors operating through adenylyl cyclase may offer opportunities to combat cancers that are unresponsive to hormonal agents, or that have developed multidrug resistance.

Neonatal chlorpyrifos exposure alters synaptic development and neuronal activity in cholinergic and catecholaminergic pathways.

After routine home application of chlorpyrifos (CPF), infant and child exposures can exceed acceptable levels. We treated neonatal rats daily on postnatal days (PN) 1-4 (1 mg/kg) or days 11-14 (5 mg/kg), treatments that evoked no overt signs of toxicity. Effects on the development of cholinergic neuronal function were assessed using choline acetyltransferase (ChAT) activity and hemicholinium-3 (HC-3) binding as indices of synaptic proliferation and synaptic activity, respectively. In the forebrain, early CPF treatment caused a decrease in ChAT without affecting HC-3 binding; late treatment decreased HC-3 binding without affecting ChAT. In the brainstem, early treatment had no effect on either parameter but late treatment decreased both ChAT and HC-3 binding. Effects of CPF were not limited to development of cholinergic synapses but also involved catecholamine pathways. For norepinephrine or dopamine, either early or late CPF treatment evoked an increase in synaptic activity (transmitter turnover). The cerebellum, a region with sparse cholinergic innervation, was affected the most. Effects on catecholamine systems were unrelated to the magnitude or temporal pattern of cholinesterase inhibition. Our results suggest that CPF exposure during the postnatal period of synaptogenesis elicits widespread disruption of cholinergic and catecholaminergic pathways. As this is the period in which patterns of synaptic responsiveness is programmed by neural input, the period of developmental vulnerability to CPF is likely to extend into childhood.

Transport, metabolism, and DNA interaction of melphalan in lymphocytes from patients with chronic lymphocytic leukemia.

We investigated the transport of [chloroethyl-14C]melphalan with lymphocytes from three groups of patients with chronic lymphocytic leukemia (untreated, treated sensitive, and treated resistant). There was no significant difference in the Km or Vmax of melphalan transport in lymphocytes from the three groups. In addition, there were no significant differences in intracellular melphalan levels after a 35-min incubation with 5.4 microM melphalan among the three groups. There was no evidence of intracellular metabolism of melphalan to dihydroxymelphalan except in lymphocytes from one treated sensitive patient. DL-2-Aminobicyclo[2,2,1]heptane-2-carboxylic acid, a specific analogue of the sodium-independent leucine-preferring amino acid transport system, inhibited the uptake of melphalan to a greater extent in lymphocytes from resistant patients than in those of untreated patients. Glutathione levels were not significantly different in lymphocytes from resistant patients as compared to those of untreated patients. The percentage of DNA cross-links as determined by an ethidium bromide fluorescence assay was 2-5-fold greater in lymphocytes from untreated patients than in those of resistant patients. These results suggest that resistance to the nitrogen mustards in patients with chronic lymphocytic leukemia is secondary to neither a transport defect nor alteration in intracellular melphalan levels but rather due to some other mechanism responsible for decreased DNA cross-links.

Phosphatidate phosphatase activity in isolated rod outer segment from bovine retina.

Phosphatidate phosphohydrolase (EC 3.1.3.4) was detected in isolated bovine rod outer segments and its properties investigated. The enzyme activity was assayed using aqueously dispersed 1,2-diacyl-sn-[2-3H]glycerol 3-phosphate as substrate. The phosphatidic acid concentration was optimal at 1 mM and the estimated Km value was 6.7 X 10(-4) M. The activity was linear for 60 min with a protein concentration of 0.3 mg. A clear pH optimum was observed at 7.5. When the enzyme activity was measured using a substrate phosphatidic acid containing 15% lyso compound, the production of diacylglycerols was inhibited by about 70-75% at all concentrations studied. In rod outer segment preparations containing 0.2 mM Mg2+, further additions of the ion (0.2-2.5 mM) only produced a slight inhibition of the activity at 2.5 mM. F- (50 mM), Ca2+ (1 mM) and EDTA (50 mM) inhibited the dephosphorylation of the substrate by 80, 10 and 70%, respectively. The aqueously dispersed phosphatidic acid-dependent activity present in rod outer segments was stimulated by Triton X-100 and taurocholate. Similar values were observed in the enzyme activity of entire rod outer segments and in that of disks obtained from them, showing the enzyme to be associated with disk membrane. The [3H]diacylglycerol production from [3H]phosphatidic acid was analyzed in synaptosomal-mitochondrial and microsomal fractions and in a crude pigment epithelium preparation. The degree of dephosphorylation of phosphatidic acid in these subcellular fractions was as follows: microsomes greater than synaptosomal-mitochondrial fraction greater than rod outer segment greater than crude pigment epithelium. The present report is the first evidence of phosphatidic acid phosphohydrolase activity associated with rod outer segment membranes.

Biosynthesis of molecular species of inositol, choline, serine, and ethanolamine glycerophospholipids in the bovine retina.

The distribution of radioactivity among molecular species of inositol, choline, serine, and ethanolamine glycerophospholipids was studied in whole bovine retinas and in microsomes from retinas incubated with [3H]glycerol, [3H]inositol, or [3H]serine, in the presence and absence of propranolol. Most of the labeled glycerol was incorporated into docosahexaenoate-containing molecular species (hexaenes and dipolyunsaturates), which suggests that they are synthesized de novo. The largest accumulation of label in these species occurred in phosphatidylinositol, although they were only a minor component of this phospholipid. At short incubation times, these species, as well as monoenes and saturates, incorporated higher percentages of both [3H]glycerol and [3H]inositol than did the tetraenes. Labeling of tetraenes increased thereafter, suggesting that they are produced by acyl-exchange reactions from less unsaturated species. Propranolol was shown to stimulate phosphatidylinositol and polyphosphoinositide synthesis by preferentially enhancing first the labeling of monoenoic and saturated phosphatidylinositols, and subsequently tetraenes. Labeled glycerol was not redistributed among species of phosphatidylcholine with time. Propranolol inhibited the synthesis of monoenes and saturates to a greater extent than other species of phosphatidylcholine. The labeling of diglycerides was first inhibited, and then stimulated by propranolol; tetraenoic diglycerides were the major product accumulated. Propranolol stimulated [3H]serine incorporation into phosphatidylserine and phosphatidylethanolamine, with no alteration in distribution of radioactivity among species; [3H]glycerol incorporation in phosphatidylethanolamine was inhibited, and its incorporation into phosphatidylserine was stimulated. Labeled serine and glycerol were concentrated largely in docosahexaenoate-containing species of phosphatidylethanolamine and phosphatidylserine.

Asessment of fetal gestational age in high-risk pregnancies by amniotic fluid analyses and ultrasound mensuration.

Maturity studies are reported on 204 women with high-risk pregnancies. Estimates of fetal maturity were made prenatally by the use of ultrasonic measurements, the lecithin/sphingomyelin (L/S) ratio, and a gestational index based on amniotic fluid creatinine, urea nitrogen, and cytology. These estimates were compared with the neonatal pediatric estimate of maturity. The gestational score agreed with pediatric maturity to within 14 days in 95 per cent of the cases. Estimates of L/S ratio distinguished between mature and immature infants in 86 per cent of the cases. Ultrasound could estimate gestational age only to within 14 days in 75 per cent of the cases, and the disagreements were greatest where either growth retardation or macrosomia was present. However, ultrasound is more useful in estimating fetal size and abnormalities of growth pattern. An estimate of gestational age by gestational score aids management, particularly where growth retardation is present, enabling a decision about delivery to be made even though the infant is very small and has an immature L/S ratio.