A statistical theory of polymer network degradation

A statistical theory was proposed for the degradation (random scission of chains) of a network having f-functional nodes in the case where all chains contain equireactive groups and a chain scission event does not create new groups or suppress more than one group. Closedform relations were established between the conversion ratio of the degradation process and the crosslink density. Emphasis was put on the value of the conversion ratio for which the gel disappears. Some limited cases already considered in the literature were recovered, but a general solution was proposed for networks having any number of reactive groups per chain, be it uniform or not, and for conversion ratios up to the degelation point. The results were applied successfully to recent experiments regarding the hydrolysis of a polyester

Thermooxidative aging of polydicyclopentadiene in glassy state

Thermal aging of thin films of unstabilized polydicyclopentadiene (pDCPD) at several temperatures ranging from 120 to 30 C was investigated by means of carbonyl build up by FTIR with ammonia derivatization, double bond titration, mass uptake measurement, hydroperoxides titration by iodometry and DSC coupled with sulfur dioxide treatment. In the temperature range under investigation, pDCPD is in glassy state and it oxidizes faster than common polymers oxidized at rubbery state (e.g. polydienic elastomers). Using the kinetic analysis, these results were ascribed to increased initiation rate due to catalyst residues, some possible intramolecular processes favoring propagation, or a very low termination rate of oxidation radical chains because of the control of termination reactions by macroradical diffusion

Degarelix versus Goserelin plus Bicalutamide in the short-term relief of lower urinary tract symptoms in prostate cancer patients: results of a pooled analysis

Objective In patients with prostate cancer (PCa), prostate enlargement may give rise to lower urinary tract symptoms (LUTS); many patients suffer from moderate-to-severe symptoms. We compare the efficacy of degarelix and goserelin plus bicalutamide in improving LUTS in PCa patients. Methods Data were pooled from three Phase 3, randomized clinical trials of once-monthly treatment for 12 weeks with degarelix (240/80 mg; n = 289) or goserelin (3.6 mg) plus bicalutamide (50 mg; n = 174) for initial flare protection. LUTS at weeks 4, 8, and 12 were compared to baseline. Clinically relevant LUTS relief was a ≥3-point International Prostate Symptom Score (IPSS) decrease. Adverse events were assessed throughout the trials. Results Patients receiving degarelix had significantly greater decreases in IPSS vs. goserelin at week 12 (adjusted difference: −1.24; 95% CI −2.33 to −0.14, P = 0.03). Clinically relevant LUTS relief with degarelix was especially pronounced in patients with moderate-to-severe LUTS (baseline IPSS ≥13) (odds ratio; OR 2.31; 95% CI 1.19–4.47, P = 0.01) and advanced PCa (OR 2.36; 95% CI 1.10–5.04, P = 0.03). A twofold higher OR for early (week 4) LUTS relief was seen with degarelix vs. goserelin (OR 2.03; 95% CI 1.14–3.60, P = 0.02). No difference in total prostate volume or urinary tract infection-related adverse events (2%) was seen between treatment groups. Conclusion An early, significant and clinically more pronounced improvement of LUTS, especially in patients with moderate-to-severe LUTS or advanced PCa, was seen with degarelix vs. goserelin plus bicalutamide

Radiochemical 'degelation' of polymethyl methacrylate networks

Methyl methacrylate-ethylene glycol dimethacrylate networks were synthetized and submitted to radiochemical degradation, with ageing monitored by means of sol-gel analysis. The networks were shown to undergo chain scission predominantly, which leads to their degelation, i.e., the recovery of a thermoplastic-like behavior with loss of all elastically active chains. The degelation dose was shown to increase with crosslink density and the corresponding critical conversion ratio was discussed regarding a recent and general statistical theory that covers radiochemical as well as chemical chain scissions

The Pkn22 Ser/Thr kinase in Nostoc PCC 7120: role of FurA and NtcA regulators and transcript profiling under nitrogen starvation and oxidative stress

International audienceBackground: The filamentous cyanobacterium Nostoc sp. strain PCC 7120 can fix N2 when combined nitrogen is not available. Furthermore, it has to cope with reactive oxygen species generated as byproducts of photosynthesis and respiration. We have previously demonstrated the synthesis of Ser/Thr kinase Pkn22 as an important survival response of Nostoc to oxidative damage. In this study we wished to investigate the possible involvement of this kinase in signalling peroxide stress and nitrogen deprivation. Results: Quantitative RT-PCR experiments revealed that the pkn22 gene is induced in response to peroxide stress and to combined nitrogen starvation. Electrophoretic motility assays indicated that the pkn22 promoter is recognized by the global transcriptional regulators FurA and NtcA. Transcriptomic analysis comparing a pkn22-insertion mutant and the wild type strain indicated that this kinase regulates genes involved in important cellular functions such as photosynthesis, carbon metabolism and iron acquisition. Since metabolic changes may lead to oxidative stress, we investigated whether this is the case with nitrogen starvation. Our results rather invalidate this hypothesis thereby suggesting that the function of Pkn22 under nitrogen starvation is independent of its role in response to peroxide stress. Conclusions: Our analyses have permitted a more complete functional description of Ser/Thr kinase in Nostoc. We have decrypted the transcriptional regulation of the pkn22 gene, and analysed the whole set of genes under the control of this kinase in response to the two environmental changes often encountered by cyanobacteria in their natural habitat: oxidative stress and nitrogen deprivation

Thermal stability of polymethacrylic based ELIUM® resin: Effect of comonomers, antioxidants and aluminum trihydrate filler

This paper presents the study of the thermal degradation of methyl methacrylate resin based materials known as ELIUM® resin. Samples under investigation were made from MMA based resin (ELIUM® V1), ELIUM® V1 with a dimethacrylate comonomer (ELIUM® V2), and ELIUM® V2 with a stabilizer package (ELIUM® V3). They were used for trying to discuss the degradation mechanisms. Blocks differing by their thickness made from ELIUM® formulation filled with aluminum TriHydrate used as flame retardant were also investigated in order to better match some industrial materials. Degradation was observed to be mainly driven by unzipping, consistent with the methacrylic nature of ELIUM® resin. Occurrence of oxidation is also discussed depending on materials formulation and temperature. A blend of antioxidants was inefficient for limiting mass loss. At 200 °C, both ATH and ELIUM® degrade, which contributes to overall mass loss. At temperatures below 180 °C, ATH does not seem to induce new degradation mechanisms but would increase oxygen diffusivity. Finally, a first simple kinetic model is proposed to predict mass loss in thick composite blocks aged under air

Thermal stability OF elium® resin and its composites

This paper deals with the thermal ageing of ELIUM® based composites filled with mineral fillers (aluminium trihydrate in particular) and corresponding matrices. The ageing of thin films and thick blocks was investigated by gravimetry. The comparison of matrices with an incremental complexity highlighted the effect of comonomers and thermal stabilizers. In all cases, unzipping was shown to be the predominant source of mass loss but oxidation seems also to be involved in the case of ageing under air. The existence of this latter was confirmed by the existence of a brown surface layer. This oxidized layer was shown to be deeper for filled composites than unfilled matrices, suggesting that fillers favor the oxygen diffusion into the bulk

Radiochemical 'degelation' of polymethyl methacrylate networks

Methyl methacrylate-ethylene glycol dimethacrylate networks were synthetized and submitted to radiochemical degradation, with ageing monitored by means of sol-gel analysis. The networks were shown to undergo chain scission predominantly, which leads to their degelation, i.e., the recovery of a thermoplastic-like behavior with loss of all elastically active chains. The degelation dose was shown to increase with crosslink density and the corresponding critical conversion ratio was discussed regarding a recent and general statistical theory that covers radiochemical as well as chemical chain scissions

Thermal oxidation of poly(dicyclopentadiene) - Effect of phenolic and hindered amine stabilizers

The thermal oxidation of stabilized polydicyclopentadiene was deeply studied here for the first time. Three kinds of antioxidants (phenolic antioxidant BHT, monomeric hindered amine in alkoxylated form Tinuvin 123 and oligomeric hindered amine Chimassorb 2020) were compared at the same concentrations. Tinuvin 123 was observed to me more efficient than Chimassorb 2020 because of the “activated” nature of alkoxyamine in Tinuvin 123. Results were simulated using a completed version of previously established kinetic model for thin PDCPD films in order to be able to make reliable lifetime prediction of stabilized PDCDP.Mr Christiano Santos is acknowledged for his help for experimental work. Agence Nationale de la Recherche is gratefully acknowledged for having funded this study (Project VRPOM Vieillissement des Réseaux Polymérisés par Metathèse 2016-2019)

1st INEXO Symposium: Alternative models in vitro, ex ovo and organisms: From research to applications in pathologies and aging

International audience123 gation and subsequent differentiation into complex tissue-like structures with reproducible ratios of neurons, astrocytes and oligodendrocytes. The generated neurons elicit spontaneous calcium transients and stimuli-induced neurotransmitter release. Whole-cell current-and-voltage clamp recordings show polarized neurons and voltage-dependent ion currents. Differentiated glial cells present astrocytic functions. Moreover, expression of genes involved in synaptic and ion transport machinery and the accumulation of neural proteoglycans suggests that this 3D differentiation strategy mimics the neural tissue microenvironment better than other differentiation methods. These models have applications as tools for preclinical assessment and in disease modelling. In the next session on reconstituted tissues and 3D bioprint-ing, Dr Christian Pellevoisin (Episkin Academy, Lyon, France) spoke about reconstructed skin, which is a powerful and highly versatile technology already used at all stages of cosmetic product development (toxicology, UV sensitivity, skin allergy, skin aging, skin microbiome, etc). The ability to reproduce several functions of human skin in vitro broadens the scope for industrial applications. He demonstrated that it is now possible to predict positive or negative effects of cosmetics early in their development process using in vitro skin models instead of animal testing. Reconstructed human skin is also used for screening and assessing the efficacy of new active ingredients, deciphering their mechanism of action, and optimizing the composition of formulations