PET/EPR blends properties in the presence of compatibilisers containing glycidyl methacrylite

Blends of PET with the different commercial co(ter)polymer compatibilisers were prepared and the effect of their glycidyl methacrylate (GMA) content and viscosity on the blend properties was determined. The efficiency of compatibilisation of the commercial co(ter)polymer in the ternary blends was examined and compared. For all the ternary blends (PET/EPR/co(ter)polymer, the PET content was fixed at 70 wt% of the total weight of the blends. Higher compatibilisation effect was found in PET/EPR blends compatibilised with the commercial copolymer ethylene glycidyl methacrylate (E-GMA8(5)) containing 8% GMA and MFI = 5 (g/10min) was achieved as reflected in the observed higher elongation at break when compared to corresponding blends compatibilised with the methyl acrylate containing terpolymer ethylene methyl acrylate glycidyl methacrylate EM-GMA8(6) containing 8% GMA and MFI = 6 (g/10min). The presence of methyl acrylate ester groups in the commercial terpolymer EM-GMA (containing similar amount of GMA and same MFI) resulted in low level of compatibilisation due to the possibility of a higher extent of branching and crosslinking resulting from the presence of the ester groups and this would be responsible for the observed lower elongation, and the less favourable morphology observed. Further, the more bulky structure of the terpolymer compared to the copolymer would give rise to a more difficult migration to the interface, thus lowering the efficiency of compatibilisation. However, the morphology of both blends compatibilised with either the terpolymer or the copolymer were not significantly different.

Studies on the neurotoxicity of 6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) in SH-SY5Y cells

We have studied the hypothesis that 6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) is neurotoxic. Salsolinol induced a significant time and dose related inhibition of 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide; thiazoyl blue (MTT) reduction, and increased lactate dehydrogenase release (LDH) release from human SH-SY5Y neuroblastoma cells, at concentrations within the range of 1-methyl-4-phenylpyridinium (MPP+) cytotoxicity, in vitro. Cytotoxicity was not inhibited by the addition of antioxidants, monoamine oxidase inhibitors or imipramine. In confluent monolayers, salsolinol stimulated catecholamine uptake with EC50 values of 17 muM and 11 muM, for noradrenaline and dopamine, respectively. Conversely, at concentrations above 100 muM, salsolinol inhibited the uptake of noradrenaline and dopamine, with IC50 values of 411 muM and 379 muM, respectively. The inhibition of catecholamine uptake corresponded to the increase displacement of [3H]nisoxetine from the uptake 1 site by salsolinol, as the Ki (353 muM) for displacement was similar to the IC50 (411 and 379 muM) for uptake. Salsolinol stimulated catecholamine uptake does not involve the uptake recognition site, or elevation of cAMP, cGMP, or inhibition of protein kinase C. Salsolinol also inhibited both carbachol (1 mM) and K+ (100 mM, Na+ adjusted) evoked released of noradrenaline from SH-SY5Y cells, with IC50 values of 500 muM and 120 muM, respectively. In conclusion, salsolinol appears to be cytotoxic to SH-SY5Y cells, via a mechanism that does not require uptake 1, bioactivation by monoamine oxidase, or membrane based free radical damage. The effects of salsolinol on catecholamine uptake, and the mechanism of toxicity require further investigation.

Subthalamic nucleus neurones in slices from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mice show irregular, dopamine-reversible firing pattern changes, but without synchronous activity

The loss of dopamine in idiopathic or animal models of Parkinson's disease induces synchronized low-frequency oscillatory burst-firing in subthalamic nucleus neurones. We sought to establish whether these firing patterns observed in vivo were preserved in slices taken from dopamine-depleted animals, thus establishing a role for the isolated subthalamic-globus pallidus complex in generating the pathological activity. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) showed significant reductions of over 90% in levels of dopamine as measured in striatum by high pressure liquid chromatography. Likewise, significant reductions in tyrosine hydroxylase immunostaining within the striatum (>90%) and tyrosine hydroxylase positive cell numbers (65%) in substantia nigra were observed. Compared with slices from intact mice, neurones in slices from MPTP-lesioned mice fired significantly more slowly (mean rate of 4.2 Hz, cf. 7.2 Hz in control) and more irregularly (mean coefficient of variation of inter-spike interval of 94.4%, cf. 37.9% in control). Application of ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2-amino-5-phosphonopentanoic acid (AP5) and the GABAA receptor antagonist picrotoxin caused no change in firing pattern. Bath application of dopamine significantly increased cell firing rate and regularized the pattern of activity in cells from slices from both MPTP-treated and control animals. Although the absolute change was more modest in control slices, the maximum dopamine effect in the two groups was comparable. Indeed, when taking into account the basal firing rate, no differences in the sensitivity to dopamine were observed between these two cohorts. Furthermore, pairs of subthalamic nucleus cells showed no correlated activity in slices from either control (21 pairs) or MPTP-treated animals (20 pairs). These results indicate that the isolated but interconnected subthalamic-globus pallidus network is not itself sufficient to generate the aberrant firing patterns in dopamine-depleted animals. More likely, inputs from other regions, such as the cortex, are needed to generate pathological oscillatory activity. © 2006 IBRO.

The role of tissue transglutaminase in 1-methyl-4-phenylpyridinium (MPP+)-induced toxicity in differentiated human SH-SY5Y neuroblastoma cells

Tissue transglutaminase (TG2) can induce post-translational modification of proteins, resulting in protein cross-linking or incorporation of polyamines into substrates, and can also function as a signal transducing G protein. The role of TG2 in the formation of insoluble cross-links has led to its implication in some neurodegenerative conditions. Exposure of pre-differentiated SH-SY5Y cells to the Parkinsonian neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+) resulted in significant dose-dependent reductions in TG2 protein levels, measured by probing Western blots with a TG2-specific antibody. Transglutaminase (TG) transamidating activity, on the other hand, monitored by incorporation of a polyamine pseudo-substrate into cellular proteins, was increased. Inhibitors of TG (putrescine) and TG2 (R283) exacerbated MPP+ toxicity, suggesting that activation of TG2 may promote a survival response in this toxicity paradigm.

Studies in the anionic polymerization of methyl methacrylate

A study has been made of the anionic polymerization of methyl methacrylate using butyllithium and polystyryl lithium as initiators and using aluminium triisobutyl as a cocatalyst. The aspects of the polymerization that were examined were the effect of changing the order of addition of reagents, the temperature at which polymerization takes place and the polarity of the solvent. Trends were assessed in terms of molecular weight, molecular weight distribution and tacticity. In addition, a second monomer addition test was carried out to verify that the polymerization was truly a living one, and a kinetic study was attempted. Studies to investigate the effect of changing the order of addition of reagents showed that polymer with similar polydispersities and tacticities are produced whether the pre-mixing (mixing initiator and cocatalyst before addition of monomer) or the post-mixing (mixing monomer and cocatalyst before addition of initiator) method were used. However, polymerizations using the post-mixing mixing method demonstrated lower initiator efficiencies, possibly indicating a different initiating species. Investigations into the effect of changing the polymerization temperature show the molecular weight distribution to narrow as the temperature decreases, although a small amount of low molecular weight tailing was also observed at low temperature. A clear relationship between tacticity and temperature was observed with syndiotacticity increasing with decreasing temperature. Changes in solvent polarity were achieved by using mixtures of the standard solvent, toluene, with varying amounts of cyclohexane, tetrahydrofuran or dichloromethane. Experiments at low solvent polarity (using toluene/cyclohexane mixtures) showed problems with initiator solubility but produced polymer with lower polydispersity and higher syndiotacticity than in toluene alone. Experiments using toluene/THF mixtures yielded no polymer, thought to be owing to a side reaction between THF and aluminium triisobutyl. Increased solvent polarity, achieved using toluene/dichloromethane mixtures produced polymer with higher polydispersity and at lower yields than the conventional system, but also with higher syndiotacticity. Second monomer addition reactions demonstrated that the polymerization was 'living' since an increase in molecular weight was observed with no increase in polydispersity. Kinetic studies demonstrated the high speed of the polymerization but yielded no useful data.

Novel high water content hydrogels

Hydrogels may be described as cross-linked hydrophilic polymers that swell but do not dissolve in water. The production of high water content hydrogels was the subject of investigation. Based upon copolymer compositions that had already achieved commercial success as biomaterials, new monomers were added or substituted in and the effects observed. The addition of N-isopropyl acrylamide to an acrylamide-based composition that had previously been designed to become a contact lens, produced materials that showed smart effects in that the water content showed dependence on the temperature of the hydrating solution. Such thermo-responsive materials have potential uses in drug delivery, ultrafiltration and cell culture surfaces. Proteoglycans in nature have an important role to play in structural support where a highly hydrophilic structure maintains lubricious surfaces. Certain functional groups that impart this hydrophilicity are present in certain sulphonate monomers, Bis(3-sulphopropyl ester) itaconate, dipotassium salt (SPI), 3-Sulphopropyl ester acrylate, potassium salt (SPA) and Sodium 2-(acrylamido)-2-methyl propane sulphonate (NaAMPS). These monomers were incorporated into a HEMA-based copolymer that had been designed initially as a contact lens and the resulting effects examined. Highly hydrophilic materials resulted that showed reduced protein deposition over the neutral core material. It is postulated that a sulphonate group would have a larger number of hydration shells around it than for example methacrylic acid, leading to more dynamic exchange and so reducing the adsorption of biological solutes. A cationic monomer was added to bring back the net anionic nature of the sulphonate hydrogels and the effects studied. Ionic interactions were found to cause a reduction in the water content of the resulting materials as the mobility of the network decreased, leading to stiffer but less extensible materials. The presence of a net dominant charge, whether negative or positive, appeared to act to reduce protein deposition, but increasing equivalence in the amount of both charges served to present a more 'neutral' surface and deposition subsequently increased. The grafting of hydrophilic hydrogel layers onto silicone elastomer was attempted and the results evaluated using dynamic contact angle measurements. Following plasma oxidation to reduce the surface energy barrier to aqueous grafting chemistry, it was found that the wettability of the modified elastomers could be significantly enhanced by such treatment. The SPA-grafted material in particular hinted at an osmotic drive for rehydration that may be exploited in biomaterials.

The metabolism of n-methyl compounds

The metabolism of compounds containing the N-methyl group is discussed with particular consideration being made to the possible role of the product of oxidative metabolism, the N-hydroxymethyl moiety, in the generation of potentially toxic, reactive electrophiles. Particular pathways which are considered are: (i), the production of formaldehyde; (ii), the generation of iminium ions or imines; and (iii), the formation of N-formyl compounds which might act as formylating agents. 4-Chloro-N-(hydroxymethyl)benzamide and 3-(4-chlorophenyl)-1-hydroxy-methyl-1-methylurea (the product of oxidative metabolism of 3-(4-chlorophenyl)-1,1-dimethylurea) are model carbinolamides which do not readily release formaldehyde. The electrophilic properties of these model carbinolamides were investigated: neither reacted with nucleophiles such as cyanide or glutathione under physiological conditions. In contrast, N-(acetoxymethyl)-4-chlorobenzamide yielded the cyanomethylamide with potassium cyanide and S-(4-chlorobenzamidomethyl)glutathione with glutathione. 4-Chloro-N-(hydroxymethyl)benzamide and 3-(4-chlorophenyl)-1,1-dimethylurea were not biotransformed to electrophilic moieties when incubated with mouse hepatic 9000 x g supernatant and Acetyl-CoA or PAPS-generating system. N-(Acetoxymethyl)-4-chlorobenzamide was non-mutagenic to Salmonella typhimurium in the short term bacterial assay; but toxicity to the bacteria was observed. 4-Chloro-N-(hydroxymethyl)benzamide and 3-(4-chlorophenyl)-1,1-dimethylurea showed no mutagenicity or toxicity in the mutagenicity assay including an Aroclor-induced rat hepatic 9000 x g supernatant. Addition of Acetyl-CoA or a PAPS-generating system did not produce a mutagenic response. 4-Chloro-N-formlbenzamide did not act as a formylating agent towards the weak nucleophile aniline. However, 4-chloro-N-formylbenzamide, N-formylbenzamide, 3-(4-chlorophenyl)-1-formyl-1-methylurea and 3-(4-chlorophenyl)-1-formylurea are all metabolised by mouse hepatic mirosomes and post-microsomal supernatant. The results demonstrate the potential for N-hydroxymethyl compounds to generate highly reactive species if these are substrates for conjugation with sulphate (or acetate). The model compounds employed here, apparently do not show any ability to be conjugated themselves, however, other N-hydroxymethyl compounds might be readily conjugated. The formation of N-formyl compounds does not appear to be toxicologically significant, as adjudged on limited experiments performed, but rather represent a detoxification pathway.

Polymer PCF Bragg grating sensors based on poly(methyl methacrylate) and TOPAS cyclic olefin copolymer

Fibre Bragg grating (FBG) sensors have been fabricated in polymer photonic crystal fibre (PCF). Results are presented using two different types of polymer optical fibre (POF); first multimode PCF with a core diameter of 50µm based on poly(methyl methacrylate) (PMMA) and second, endlessly single mode PCF with a core diameter of 6µm based on TOPAS cyclic olefin copolymer. Bragg grating inscription was achieved using a 30mW continuous wave 325nm helium cadmium laser. Both TOPAS and PMMA fibre have a large attenuation of around 1dB/cm in the 1550nm spectral region, limiting fibre lengths to no longer than 10cm. However, both have improved attenuation of under 10dB/m in the 800nm spectral region, thus allowing for fibre lengths to be much longer. The focus of current research is to utilise the increased fibre length, widening the range of sensor applications. The Bragg wavelength shift of a grating fabricated in PMMA fibre at 827nm has been monitored whilst the POF is thermally annealed at 80°C for 7 hours. The large length of POF enables real time monitoring of the grating, which demonstrates a permanent negative Bragg wavelength shift of 24nm during the 7 hours. This creates the possibility to manufacture multiplexed Bragg sensors in POF using a single phase mask in the UV inscription manufacturing. TOPAS holds certain advantages over PMMA including a much lower affinity for water, this should allow for the elimination of cross-sensitivity to humidity when monitoring temperature changes or axial strain, which is a significant concern when using PMMA fibre.

A sulphonate based hydrogel for nucleus pulposus repair

Introduction: Lower back pain treatment and compensation costs >$80 billion overall in the US. 75% of back pain is due to disc degeneration in the lumbar region of the spine. Current treatment comprises of painkillers and bed rest or as a more radical solution – interbody cage fusion. In the early stages of disc degeneration the patient would benefit from addition of an injectable gel which polymerises in situ to support the degenerated nucleus pulposus. This involves a material which is an analogue of the natural tissue capable of restoring the biomechanical properties of the natural disc. The nucleus pulposus of the intervertebral disc is an example of a natural proteoglycan consisting of a protein core with negatively charged keratin and chondroitin sulphate attached. As a result of the high fixed charge density of the proteoglycan, the matrix exerts an osmotic swelling pressure drawing sufficient water into support the spinal system. Materials and Methods: NaAMPs (sodium 2- acrylamido 2-methyl propane sulphonic acid) and KSPA (potassium 3- sulphopropyl acrylate) were selected as monomers, the sulphonate group being used to mimic the natural sulphate group. These are used in dermal applications involving chronic wounds and have acceptably low cytotoxicity. Other hydrophilic carboxyl, amide and hydroxyl monomers such as 2-hydroxyethyl acrylamide, ß-carboxyethyl acrylate, acryloyl morpholine, and polyethylene glycol (meth)acrylate were used as diluents together with polyethyleneglycol di(meth)acrylate and hydrophilic multifunctional macromers as cross-linker. Redox was the chosen method of polymerisation and a range of initiators were investigated. Components were packaged in two solutions each containing a redox pair. A dual syringe method of injection into the cavity was used, the required time for polymerisation is circa 3-7 minutes. The final materials were tested using a Bohlin CVO Rheometer cycling from 0.5-25Hz at 37oC to measure the modulus. An in-house compression testing method was developed, using dialysis tubing to mimic the cavity, the gels were swelled in solutions of various osmolarity and compressed to ~ 20%. The pre-gel has also been injected into sheep spinal segments for mechanical compression testing to demonstrate the restoration of properties upon use of the gel. Results and Discussion: Two systems resulted using similar monomer compositions but different initiation and crosslinking agents. NaAMPs and KSPA were used together at a ratio of ~1:1 in both systems with 0.25-2% crosslinking agent, diacrylate or methacrylate. The two initiation systems were ascorbic acid/oxone, and N,N,N,N - tetramethylethylenediamine (TEMED)/ potassium persulphate. These systems produced gelation within 3-7 and 3-5 minutes respectively. Storage of the two component systems was shown to be stable for approximately one month after mixing, in the dark, refrigerated at 1-4oC. The gelation was carried out at 37oC. Literature values for the natural disc give elastic constants ranging from 3-8kPa. The properties of the polymer can be tailored by altering crosslink density and monomer composition and are able to match those of the natural disc. It is possible to incorporate a radio-opaque (histodenz) to enable x-ray luminescence during and after injection. At an inclusion level of 5% the gel is clearly visible and polymerisation and mechanical properties are not altered. Conclusion: A two-pac injection system which will polymerise in situ, that can incorporate a radio-opaque, has been developed. This will reinforce the damaged nucleus pulposus in degenerative disc disease restoring adequate hydration and thus biomechanical properties. Tests on sheep spine segments are currently being carried out to demonstrate that a disc containing the gel has similar properties to an intact disc in comparison to one with a damaged nucleus.

Photosensitivity mechanism of undoped poly(methyl methacrylate) under UV radiation at 325 nm and its spatial resolution limit

In this Letter, we provide evidence suggesting that the main photosensitive mechanism of an undoped poly(methyl methacrylate)-based microstructured optical fiber under UV radiation at 325 nm is a competitive process of both photodegradation and polymerization. We found experimentally that increasing strain during photo-inscription leads to an increased photosensitivity, which is evidence of photodegradation. Likewise, refractive index change in the fiber was measured to be positive, which provides evidence for further polymerization of the material. Finally, we relate the data obtained to the spatial recording resolution of the samples. © 2014 Optical Society of America.

The nitric oxide-donating pravastatin derivative, NCX 6550 [(1S-[1α(βS*, δS*), 2α, 6α, 8β-(R*), 8aα]]-1,2,6,7,8,8a-hexahydro-β, δ, 6-trihydroxy-2-methyl-8-(2-methyl-1-oxobutoxy)-1-naphtalene-heptanoic acid 4-(nitrooxy)butyl ester)], reduces splenocyte adhesion and reactive oxygen species generation in normal and atherosclerotic mice

Statins possess anti-inflammatory effects that may contribute to their ability to slow atherogenesis, whereas nitric oxide (NO) also influences inflammatory cell adhesion. This study aimed to determine whether a novel NO-donating pravastatin derivative, NCX 6550 [(1S-[1∝(ßS*,dS*),2∝,6a∝,8ß-(R*),8a∝]]-1,2,6,7,8,8a-hexahydro-ß,δ,6-trihydroxy-2-methyl-8-(2-methyl-1-oxobutoxy)-1-naphthalene-heptanoic acid 4-(nitrooxy)butyl ester)], has greater anti-inflammatory properties compared with pravastatin in normal and atherosclerotic apolipoprotein E receptor knockout (ApoE-/-) mice. C57BL/6 and ApoE-/- mice were administered pravastatin (40 mg/kg), NCX 6550 (48.5 mg/kg), or vehicle orally for 5 days. Ex vivo studies assessed splenocyte adhesion to arterial segments and splenocyte reactive oxygen species (ROS) generation. NCX 6550 significantly reduced splenocyte adhesion to artery segments in both C57BL/6 (8.8 ± 1.9% versus 16.6 ± 6.7% adhesion; P < 0.05) and ApoE-/- mice (9.3 ± 2.9% versus 23.4 ± 4.6% adhesion; P < 0.05) concomitant with an inhibition of endothelial intercellular adhesion molecule-1 expression. NCX 6550 also significantly reduced phorbol 12-myristate 13-acetate-induced ROS production that was enhanced in isolated ApoE-/- splenocytes. Conversely, pravastatin had no significant effects on adhesion in normal or ApoE-/- mice but reduced the enhanced ROS production from ApoE-/- splenocytes. In separate groups of ApoE-/- mice, NCX 6550 significantly enhanced endothelium-dependent relaxation to carbachol in aortic segments precon-tracted with phenylephrine (-logEC50, 6.37 ± 0.37) compared with both vehicle-treated (-logEC50, 5.81 ± 0.15; P < 0.001) and pravastatin-treated (-logEC50, 5.57 ± 0.45; P < 0.05) mice. NCX 6550 also significantly reduced plasma monocyte chemoattractant protein-1 levels (648.8 pg/ml) compared with both vehicle (1191.1 pg/ml; P < 0.001) and pravastatin (847 ± 71.0 pg/ml; P < 0.05) treatment. These data show that NCX 6550 exerts superior anti-inflammatory actions compared with pravastatin, possibly through NO-related mechanisms.