Effect of the Structure of Reactor Poly(propylene‐co‐ethylene) Blends on the Diffusion Coefficient and Activation Energy of a Conventional Antioxidant

The diffusion of a thermal stabilizer, i.e., Irganox 1010, has been studied in three different reactor poly(propylene‐co‐ethylene) blends, namely HecoQ, ExpSS, and Super Soft. The diffusion experiments were carried out by using Roe's method based on a stack of several polymer films where each of them had 60–70 μm thickness. The concentration profile of the stabilizer in every film has been monitored by the absorbance at 282 nm of the recorded UV spectra. Under our experimental conditions, the diffusion of Irganox 1010 for all polymer materials can be correctly interpreted by using Fick's second law resolved under certain boundary conditions. Best‐fitting the experimental data with the equation model also allows calculation of the diffusion coefficient, D, for these polymer materials at 40, 70 and 80 °C. By applying an Arrhenius‐type equation to the calculated D coefficients, an estimation of activation energies of the diffusion process has been achieved. An interpretation, in terms of free volume theory, has been applied to explain the observed variation of D which depends mostly on the amount of amorphous phase of the blends.

Arrhenius plots of ln D versus 1/(RT) for the polymers given in legend.     

Propylene Polymerization with rac‐SiMe2(2‐Me‐4‐PhInd)2ZrMe2/MAO: Polymer Characterization and Kinetic Models

Poly(propylene)s were prepared with metallocene catalyst rac‐SiMe₂(2‐Me‐4‐PhInd)₂ZrMe₂/MAO (rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)dimethylzirconium/methylaluminoxane) in heptane solution at temperatures from 50 to 80 °C with varying concentrations of monomer, hydrogen, triisobutylaluminium (TIBA) and MAO. Polymer molar mass depended on the monomer, MAO, TIBA, and hydrogen concentrations and on polymerization temperature. The isotacticity was very high (mmmm > 95%), and only a slight decrease was detected at high temperatures. Regio selectivity was also high; the total amount of 2,1‐ and 3,1‐insertions was less than 0.4 mol‐%. Lowering the monomer concentration and raising the temperature increased the amount of 3,1 defects over the amount of 2,1 defects. End‐group analysis by ¹³C NMR spectroscopy revealed isobutyl and allyl end‐groups. Chain transfer to aluminium and β‐CH₃ elimination were concluded to be the dominating chain‐termination mechanisms. The importance of β‐CH₃ elimination increased with temperature. Hydrogen addition changed both the initiation and termination mechanisms as indicated by the presence of propyl, butyl and 2,3‐dimethylbutyl end‐groups. According to modeling studies, the molar mass follows a first‐order relationship with propylene and hydrogen concentrations, and a half‐order relationship with MAO concentration. Arrhenius‐type activation energy coefficients were 125 kJ · mol^?1 for β‐CH₃ elimination, 66 kJ · mol^?1 for chain transfer to aluminium, and 53 kJ · mol^?1 for chain transfer to hydrogen. A value of 45 kJ · mol^?1 was used for the propagation.

     

Development of silicone rubber hollow fiber membrane oxygenator for ECMO

Silicone rubber hollow fiber membrane produces an ideal gas exchange for long-term ECMO due to nonporous characteristics. The extracapillary type silicone rubber ECMO oxygenator having an ultrathin hollow fiber membrane was developed for pediatric application. The test modules were compared to conventional silicone coil-type ECMO modules. In vitro experiments demonstrated a higher O2 and CO2 transfer rate, lower blood flow resistance, and less hemolysis than the conventional silicone coil-type modules. This oxygenator was combined with the Gyro C1E3 centrifugal pump, and three ex vivo experiments were conducted to simulate pediatric V-A ECMO condition. Four day and 6 day experiments were conducted in cases 1 and 2, respectively. Case 3 was a long-term experiment up to 2 weeks. No plasma leakage and stable gas performances were achieved. The plasma free hemoglobin was maintained within a normal range. This compact pump-oxygenator system in conjunction with the Gyro C1E3 centrifugal pump has potential for a hybrid total ECMO system.     

Intense Inflammatory Reaction to Heparin Polymer Coated Intravascular Palmaz Stents in Porcine Arteries Compared to Uncoated Palmaz Stents

The objective of this study was to evaluate the efficacy of heparin-polymer-coated intravascular stents in the reduction of vessel stenosis. Three types of coatings for Palmaz stents were tested: 1) heparin covalently bound to a polyethylene oxide (Hp-PEO) tether; 2) heparin copolymerized with ethylene vinyl acetate (Hp-Elvax) and 3) Elvax alone. Polymer-coated stents and uncoated controls were deployed in the external iliac arteries following endothelial injury in 18 swine. The animals were maintained on an atherogenic diet and examined by angiography at 6 and 12 weeks. The stented segments were then harvested for histopathologic analysis. Both types of heparin-coated stents resulted in increased luminal narrowing as compared to the contralateral uncoated stents. At 6 weeks, average luminal stenosis was 48% for Hp-PEO stents vs 35% for uncoated stents (p < 0.05). At 12 weeks, average luminal stenosis was 36% for Hp-PEO stents vs 26% for uncoated stents (p = NS). For Hp-Elvax stents, the average stenosis was 58% vs 33% for uncoated controls (p < 0.05) at 6 weeks and 47% vs 19% for uncoated controls (p < 0.05) at 12 weeks. There was no significant difference between Hp-Elvax stents and Elvax stents (p = NS). Increased luminal narrowing in coated stents was primarily secondary to a marked inflammatory response. Heparin-polyethylene oxide and heparin-ethylene vinyl acetate-coated stents resulted in increased luminal narrowing as compared with uncoated stents, due to a marked inflammatory response.     

In vitro evaluation of ultrasound Doppler strain rate imaging: modification for measurement in a slowly moving tissue phantom

Doppler strain rate imaging (SRI) was evaluated in vitro using a silicone strip phantom mimicking slowly moving tissue. A test apparatus was developed that enabled controlled strain experiments with variable strain and strain rate to be performed. SRI strain was measured at eight different calculated strains (range 5.7 to 63.4 %) at three different pump speeds with tissue velocity 0.1, 0.5 and 1.0 mm/s. The effect of varying tissue velocity and strain sample size on the measured SRI strain was elaborated. SRI strains agreed well with calculated values for strain when SRI strain was measured as the average over the whole strip cross-section and the strain sample size was 1.9 mm (mean DIFFERENCE = 2.78%, limits of agreement ± 9.97% for tissue velocity 1.0 mm/s, n = 8). The variance was substantial if single central samples were used, especially for strain sample size of 0.8 mm (mean DIFFERENCE = −7.47%, limits of agreement ± 20.90 for tissue velocity 0.5 mm/s, n = 24). Increasing the strain sample size to 1.9 mm removed some of the underestimation (giving mean difference of −4.46%, n = 24). We found low intra- and interobserver variation. This study indicates that, for the SRI method to give accurate estimates of strain, strain sample size should be in the region of 2 mm. Averaging over several ultrasound (US) beams increased the accuracy further.(E-mail: Knut.Matre@med.uib.no)     

Experimental exposure to propylene glycol mist in aviation emergency training: acute ocular and respiratory effects

OBJECTIVES—Propylene glycol (PG) (1-2 propanediol; CAS No 57-55-6) is a low toxicity compound widely used as a food additive, in pharmaceutical preparations, in cosmetics, and in the workplace—for example, water based paints, de-icing fluids, and cooling liquids. Exposure to PG mist may occur from smoke generators in discotheques, theatres, and aviation emergency training. Propylene glycol may cause contact allergy, but there is sparse information on health effects from occupational exposure to PG.
METHODS—Non-asthmatic volunteers (n=27) were exposed in an aircraft simulator to PG mist over 1 minute, during realistic training conditions. Geometric mean concentration of PG was 309 mg/m³ (range 176-851 mg/m³), with the highest concentrations in the afternoon. The medical investigation was performed both before and after the exposure (within 15 minutes). It included an estimate of tear film stability break up time, nasal patency by acoustic rhinometry, dynamic spirometry, and a doctor's administered questionnaire on symptoms.
RESULTS—After exposure to PG mist for 1 minute tear film stability decreased, ocular and throat symptoms increased, forced expiratory volume in 1 second/forced vital capacity (FEV₁/FVC) was slightly reduced, and self rated severity of dyspnoea was slightly increased. No effect was found for nasal patency, vital capacity (VC), FVC, nasal symptoms, dermal symptoms, smell of solvent, or any systemic symptoms. Those exposed to the higher concentrations in the afternoon had a more pronounced increase of throat symptoms, and a more pronounced decrease of tear film stability. In four subjects who reported development of irritative cough during exposure to PG, FEV₁ was decreased by 5%, but FEV₁ was unchanged among those who did not develop a cough. Those who developed a cough also had an increased perception of mild dyspnoea.
CONCLUSION—Short exposure to PG mist from artificial smoke generators may cause acute ocular and upper airway irritation in non-asthmatic subjects. A few may also react with cough and slight airway obstruction.


Keywords: acoustic rhinometry; aviation medicine; propylene glycol; respiratory symptoms; tear film stability break up time     

藻酸双酯钠的超滤分级及分级产物抗凝血活性的比较研究

 目的利用膜分离超滤技术对藻酸双酯钠(PSS)及其分级产物进行抗凝血活性的比较研究。方法利用超滤膜对PSS原料进行分级,得到不同相对分子质量(M_r)及窄分散度的分级产物;对分级产物进行常规抗凝血活性PT/APTT/TT检测。结果超滤法分级产物M_r不同,分散度降低,各产物磺化度基本相同;抗凝血实验结果显示,随着糖链的减小,抗凝血活性显著降低。结论超滤法分级多糖药物PSS是一种可行的物理分级方法,PSS抗凝血活性强度与Mr显著相关。     

Improved topical treatment of lamellar ichthyosis: a double-blind study of four different cream formulations

Lamellar ichthyosis (LI) is characterized by generalized scaling of the skin and is often resistant to ordinary emollients. Recently, Locobase(R) fatty cream containing a mixture of 5% lactic acid and 20% propylene glycol (LPL) was found to be markedly effective in a pilot study. To consolidate this finding, a double-blind study comparing LPL with the corresponding mixture in Essex(R) (Diprobase(R)) cream (LPE) and Locobase(R) fatty cream containing either 5% urea or 20% propylene glycol was conducted in 20 patients with LI. Before and after applying the creams twice daily on each of the four extremities for 4 weeks, the following investigations were performed: scoring of xerosis, scaling and erythema, measurements of skin hydration (capacitance) and transepidermal water loss (TEWL), and moulding of the skin surface (replicas). Xerosis was reduced by all four creams, but significantly more so by LPL (P < 0.001) and LPE (P < 0.01). Scaling was only reduced by LPL (P < 0.001) and LPE (P < 0.01), which also caused a slight increase in the erythema score (P < 0.05 for both). The patients' weekly evaluation of symptoms showed that LPL produced the most rapid effect: the response rate after 4 weeks was 63%. Skin hydration and TEWL were both significantly increased by LPL and LPE, whereas skin roughness was reduced most by LPL. Fourteen patients preferred LPL over the other cream formulations. Ten patients continued using LPL for up to 8 weeks with good results and no side-effects other than occasional irritation in the skin folds. LPL is a major advance in the topical treatment of LI that suits most patients. Some patients, however, seem to prefer the more hydrophilic LPE formulation. Both formulations effectively reduce hyperkeratosis and xerosis, but may cause slight irritation and adversely affect the epidermal barrier function.