Thermal,Mechanical, and Acoustic Properties of Polydimethylsiloxane Filled with Hollow Glass Microspheres

Polydimethylsiloxane (PDMS) is the most widely used silicon-based polymer due to its versatility and its various attractive properties. The fabrication of PDMS involves liquid phase cross-linking to obtain hydrophobic and mechanically flexible material in the final solid form. This allows to add various fillers to affect the properties of the resulting material. PDMS has a relatively low Thermal Conductivity (TC), in the order of 0.2 W/mK, which makes it attractive for thermal insulation applications such as sealing in construction. Although a further decrease in the TC of PDMS can be highly beneficial for such applications, most research on the thermal properties of PDMS composites have focused on fillers that increase the TC rather than decrease it. In the present work, we propose a simple and reliable method for making a PDMS-based composite material with significantly improved thermal insulation properties, by adding hollow glass microspheres (HGMs) to the mixture of the liquid base and the cross-linker (10:1 ratio), followed by degassing and heat-assisted crosslinking. We obtained a 31% reduction of thermal conductivity and a 60% increase in the elastic modulus of samples with HGM content of 17% by weight. At the same time, the sound insulation capacity of the PDMS-HGM composite is slightly decreased in comparison to pure PDMS, as a result of its lower density. Finally, the wettability of the samples had no dependence on HGM content.     

Secretory Otitis Media and Allergy

This study is an investigation on whether allergy, and especially food allergy, is more common in patients with secretory otitis media (SOM) than in others. At the same time, the effectiveness of the cytotoxic leucocyte test (CLT) as an aid in the diagnosis of food allergy was also studied. The material comprised 90 patients: 69 suffering from secretory otitis media and 21 without the disease as controls. Patients were studied using allergy history, ear status, tests for nasal and blood eosinophilic cells, total IgE, skin tests for 20 allergens, RAST for milk and wheat, immunoglobulin A, G and M, precipitating antibodies for milk and gluten, Mantoux test, and the CLT for 23 allergens. Allergy was found in 20% of the SOM patients and 10% of the control patients; the difference was not statistically significant. The best methods for verifying allergy were history, skin tests, and tests for nasal eosinophilic cells. Laborartory tests could not verify objectively that food allergy was more common among SOM patients than controls, although 16% of the SOM patients compared with none of the controls had a history of food allergy. Of the tests used, the CLT correlated best with a history of allergy, but the results of the different tests were not in accordance with each other.     

No improvement in the overall survival of 194 patients with chondrosarcoma in Finland in 1971–1990

We describe the clinicopathologic profile and survival of 306 patients with chondrosarcoma reported to the Finnish Cancer Registry in 1971–1990. 218 cases were available for reevaluation. Owing to their various clinicopathologic characteristics, we excluded the histologic variants of chondrosarcoma. Therefore, the final study population included 194 patients. The minimum follow-up was 9 years. The study population included 69 grade 1 tumors, 114 grade 2 tumors, and 11 grade 3 tumors. The commonest tumor sites were the chest, pelvis and femur. A local recurrence developed in 25% of the patients and metastatic lesions in 18%. The patients were treated in 31 hospitals (in 22 hospitals during the 1970s and in 26 in the 1980s), and the number of patients biopsied before the referral remained about the same from the 1970s (15%) to the 1980s (18%). The 5-and 10-year disease-specific survival rates were 70% and 57%, respectively. Multivariate analysis showed that the most important independent predictors of shortened survival were high histologic grade, age 50 years or older, and a diagnosis in the 1980s, as compared to the 1970s.

Most findings accorded with reports from specialist treatment centers, but to our surprise, the survival rate declined among patients diagnosed in the 1980s versus the 1970s. The failure to improve patient survival is probably due to treatment of the patients in 31 hospitals rather than in a few centers dealing with treatment of cancer.     

Studies on the Role of Lipid Peroxidation in the Acute Toxicity of TCDD in Rats*

Lipid peroxidation has been shown to be enhanced following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but its role in TCDD toxicity is unclear. The present study was undertaken to further elucidate the relations between lipid peroxidation and TCDD lethality. A time course and dose-response experiment in Long-Evans (L-E; LD50 ca. 10 μg/kg) and Han/Wistar (H/W; LD50 > 3000 μg/kg) rats showed that hepatic lipid peroxidation, measured as the amount of thiobarbituric acid-reactive substances (TBA-RS), was induced by TCDD dose-dependently in L-E, but not in H/W rats. Hepatic glutathione peroxidase activity was suppressed in much the same manner in both strains. Lipid peroxidation correlated with body weight loss in L-E rats alone. When 500 μg/kg of TCDD was given to L-E rats, lipid peroxidation increased about 3-fold on Day 11 in the liver, while no change was seen in cardiac or renal TBA-RS. The pair-fed controls did not survive the 11-day test period and exhibited gastrointestinal hemorrhages. At 6 days, liver atrophy and elevated (over 2-fold) TBA-RS values were recorded in pair-fed controls but not in their TCDD-treated counterparts. TCDD decreased hepatic glutathione peroxidase activity by almost 50% at 6 days, while pair-feeding was without effect. Liver morphology was different between TCDD-treated and pair-fed rats. Moreover, the livers of TCDD-treated L-E rats contained much higher concentrations of probably peripheral fat-derived fatty acids than did the livers of pair-fed or ad libitum control rats. Restricted feeding over 6 days induced hepatic lipid peroxidation more in H/W than in L-E rats. Endotoxin increased liver TBA levels similarly in both strains having an additive effect with high doses of TCDD in H/W rats. Added as a 0.5% concentration in chow, butylated hydroxyanisole (BHA), but not ethoxyquin, tended to increase survival rate and time in L-E rats exposed to 20 μg/kg of TCDD; at 50 μg/kg the only survivor was again in the BHA group. However, neither antioxidant had any effect on initial body weight loss. It is concluded that lipid peroxidation mainly arises as a secondary phenomenon in TCDD toxicity, is not the cause of the typical histopathological liver lesion, but may contribute to lethality.     

Pathogenesis of primary central nervous system lymphoma: invasion of malignant lymphoid cells into and within the brain parenchyme

Summary The pattern of invasion of lymphoid cells to the central nervous system (CNS) was analyzed for malignant lymphocytes in 19 primary CNS lymphomas (PCNSL) and six intracerebral metastatic lymphomas, and for reactive lymphocytes in four encepphalitides and three astrocytomas. The identical spreading pattern in both primary and metastatic lymphomas suggests that even in the so-called primary CNSL the malignant transformation has occurred outside the CNS. The compact perivascular cuffs of both malignant and reactive lymphocytes were never seen around the smallest capillaries, and they were most common around vessels larger than 15 m in diameter. Perivascular lymphocytes resided within the reticulin network, which was immunopositive for collagen type III and IV, laminin and fibronectin. These findings imply that lymphocytes extravasate at the level of arterioles and venules and spread along the enlarged perivascular space. When the outer boundary of the perivascular network was broken, malignant lymphocytes spread diffusely into the CNS parenchyme; a pattern which is different from that of other CNS metastases. The widespread immunopositivity for the homing cell adhesion molecule CD44 in the CNS vessels and parenchyme, especially in the white matter which is the predilection site of PCNSL, suggest that this adhesion molecule and its ligands participate in spreading of malignant lymphocytes within the CNS parenchyme.Supported by a grant from the Finnish Cancer Foundation     

The morphology of the vestibular nerve in a patient with normal vestibular function and in patients with Ménière's disease

Summary The morphology of the vestibular nerve was studied in three fresh nerve specimens obtained by surgery from two patients with Ménière's disease and one patient with tinnitus after an attack of sudden deafness.The number of nerve fibres appeared light microscopically normal. The vestibular ganglion cells of the Ménière-specimens showed, as a characteristic finding advanced vesiculation of the cytoplasm. This change was confirmed by electron microscopy and the vacuoles appeared to consist of widened endoplasmic reticulum cisternae. Numerous primary lysosomes and lipofuscin granules were observed in all vestibular ganglion cells but their number appeared increased in the specimens from Ménière-patients. Some of the vestibular ganglion cells of these patients showed a filamentous appearance and the number of glycogen granules seemed reduced in all of them. All vestibular ganglion cells observed were unmyelinated. The degenerative changes observed might explain the typical elevation of the threshold for vestibular stimulation in Ménière's disease.We thank Miss Pirkko Leikas for skillful technical assistance.