Preparation of ABCBA-type block copolymers by use of macro-initiators containing peroxy and azo groups

Some new macroinitiators ( 5 ) containing azo and peroxy groups were synthesized by transformation of esters of poly(ethylene glycol) ( 1 ) (PEG) of different molecular weight with hydroxyl end groups and an azo group in the middle into the corresponding polymers with tert-butylperoxycarbonyl end groups by reaction with terephthaloyl chloride and subsequently with tert-butyl hydroporoxide. Decomposition in the presence of styrene at 60°C or with 3,6,9-triazaun-decane-1,11-diamine in presence of methyl methacrylate gave the corresponding ABA block copolymer 6 and the ABBA block copolymer 7 , respectively. Both block copolymers were used as polymeric initiators. The ABCBA block copolymer 8 was synthesized from 6 and methyl methacrylate or from 7 and styrene by thermally induced polymerization at 80°C. The resulting block copolymers were separated from the homopolymers by selective solvent extraction and characterized by spectroscopic and fractional precipitation methods.     

Kinetics of the reaction of a glycol with a diisocyanate

The reaction between poly(ethylene oxide) glycol (α-hydro-ω-hydroxypoly(oxyethylene)) and methylenebis(1,4-cyclohexylene) diisocyanate was studied at 70, 80 and 90°C. The course of the reaction was followed by determining the isocyanate content of the reaction mixture at appropriate time intervals. The data thus obtained were analyzed by taking into consideration the glycol- and urethane-catalyzed reactions separately. It was found that although the urethane-catalyzed reaction was faster in the temperature range studied, its relative importance decreased with increasing temperature.     

Interpenetrating polymer networks of poly(dimethylsiloxane) with polystyrene,polybutadiene and poly(glycerylpropoxytriacrylate)

The synthesis of full and semi interpenetrating networks (IPNs) based on poly(dimethy1-siloxane) (PDMS)/polystyrene, PDMS/polybutadiene and PDMS/poly(glycerylpropoxytriacry-late) 1

1 Glycerylpropoxytriacrylate (GFTA):

is described. PDMS was used as host polymer in most cases. PDMS networks were prepared with two prepolymers having different number-average molecular weights between junctions, M?_c = 15 · l0³ and M?_c = 75 · l0³. Physical properties of IPN samples such as stress-strain behaviour, swelling and glass transition temperature (T_g) were examined. IPNs of both PDMS/polystyrene and PDMS/poly(glycerylpropoxytriacrylate) exhibit superior mechanical and elastomeric properties with respect to pure PDMS network. Most of the IPN systems studied in this work display two T_gs and indicate phase separation.     

A new model for the induction of tumours in the forestomach of rats by N-methyl-N-nitrosourea

BACKGROUND AND AIM: Experimental carcinogenesis models provide a useful tool in the study of the aetiopathogenesis and treatment of gastric cancer. We developed a model based on the administration of N-methyl-N-nitrosourea (NMU) in Wistar rats for the induction of maximal yield of gastric carcinomas with a short latency period, and being exclusively localized at the gastric level. METHODS: A gastric antiperistaltic fistula was performed in 90 Wistar rats classified into eight different groups. Fifteen days after surgery 5, 10, 15 or 20 mg of NMU/100 g were administered through the fistula once a week for a 3- to 5-week period. Before the administration of NMU, a pyloric blockade was made in order to obtain a temporary isolation of the stomach. At 20 weeks, animals were sacrificed and organs were removed for histological study. RESULTS: All rats treated with 15 mg NMU/100 g once a week for 5 weeks, after pyloric blockade maintained for 1 h, developed well-differentiated carcinomas in the forestomach. Carcinomas were multiple in 11% of cases and appeared with papillomatous lesions in 33% of rats. No tumours were observed in any other organs. In the other groups, no gastric carcinomas were diagnosed. CONCLUSION: The high incidence of carcinomas in the forestomach, the absence of tumours in other organs and the short latency period represent valuable criteria for the use of our model in chemotherapeutic investigations, as well as in the study of cancer evolution without interferences caused by tumour development in other organs.     

Monoamine oxidase inhibitory activities of the scorpion Mesobuthus gibbosus (Buthidae) venom peptides.

In the present study, crude venom of Mesobuthus gibbosus (Buthidae), a scorpion distributed all over Anatolia was isolated and purified by the Sephadex G-50 gel filtration and high pressure liquid chromatographic (HPLC) separation. Two of the five fractions (fractions 4 and 5) obtained from the Sephadex G-50 filtration and detected as lethal on mice and Musca domestica larvae in in vivo toxicity tests, were independently subjected to the HPLC separation. Only one of seven fractions (fraction 5.5*) obtained from the HPLC separation of the fraction 5 was found to be extremely lethal. Sodium dodecylsulfate polyacrylamide gel electrophoretic (SDS-PAGE) analysis of the crude venom and its chromatographic fractions demonstrated that crude venom consisted of peptides with molecular weights of 6500-210,000 Da. The neurotoxic fraction 5.5* appeared as a single band of 28,000 Da and two bands of 6200 and 22,000 Da in SDS-PAGE under non-reducing and reducing conditions, respectively, suggesting that it might consist of two chains attached by a disulfide bridge. Fractions 5 and 5.5* inhibited monoamine oxidase A (MAO-A) of rat liver reversibly and non-competitively, in a concentration-dependent manner. Fraction 5.5* appeared as a potent and specific MAO-A inhibitor with a Ki value of 0.12 mg venom proteinml(-1). The inhibitory effect of venom peptide 5.5* on MAO-A was found to be dependent on the preincubation time suggesting that the peptide binds to some site other than the substrate-binding site. Results of the present study demonstrated that M. gibbosus venom contains a peptide with specific MAO-A inhibitory activity which may be responsible for the anxiogenic effects of the scorpion venoms on animals and humans.     

Collagen for brain repair:therapeutic perspectives

Biomaterials have increasingly become a focus of research on neuroprotection and neuroregeneration.Collagen,in terms of brain repair,presents many advantages such as being remarkably biocompatible,biodegradable,versatile and non-toxic.Collagen can be used to form injectable scaffolds and micro/nano spheres in order to:(i) locally release therapeutic factors with the aim of protecting degenerating neurons in neurodegenerative conditions such as Alzheimer's or Parkinson's diseases,(ii) encapsulate stem cells for safe delivery,(iii) encapsulate genetically modified cells to provide a long term source of trophic factors,(iv) fill in the voids from injury to serve as a structural support and provide a permissive microenvironment to promote axonal growth.This mini-review summarizes different applications of collagen biomaterial for central nervous system protection and repair,as well as the future perspectives.Overall,collagen is a promising natural biomaterial with various applications which has the potential to progress the development of therapeutic strategies in central nervous system injuries and degeneration.     

Factors Predicting Iliac Metastasis and Overall Survival in Malignant Melanoma of the Lower Extremities

Background : To analyse the patient-related, disease-related and treatment-related factors in a group of melanoma patients to assess their impact on iliac metastasis and on overall survival.

Methods : Medical records of thirty nine patients with lower extremity malignant melanoma were retrospectively reviewed to confirm all of the clinical data. Age and gender were recorded as patient-related factors. Tumor location, size, histology, ulceration status, and TNM stage, Breslow thickness, Clark level, presence of inguinal LN metastases, and locoregional metastases (local recurrences, in transit metastases and regional LN metastases) were evaluated as disease-related factors. Type of surgery (en block excision of primary tumor, en block excision of primary tumor and inguinal lymph node dissection, en block excision of primary tumor and ilioinguinal lymph node dissection) and postoperative chemotherapy were taken into account as treatment-related factors.

Results : The presence of inguinal lymph node metastases was significantly associated with iliac metastasis (p = 0.015). Tumor size (p = 0.046), tumor TNM stage (p = 0.009), Breslow thickness (p = 0.033), Clark level (p = 0.029), presence of in transit metastases (p = 0.010) and postoperative chemotherapy (p = 0.002) has been related to impaired overall survival rate.

Conclusions : Therapeutic lymph node dissection appears to carry a small but definite therapeutic benefit. Selection of appropriate patients for the more extensive procedure would be ideal, but at present there are no well proven selection criteria. The authors advocate therapeutic dissection when the inguinal lymph nodes are involved.     

Effects of impacted maxillary canines on root resorption of lateral incisors

Objectives

The aim of this study was to analyze the amount of root resorption of maxillary lateral incisors by relating the position, location, and angulation of the impacted canine using cone-beam computed tomography (CBCT).

Materials and methods

The study sample consisted of panoramic and CBCT radiographs of 46 patients with a unilateral impacted canine (16 males and 30 females; mean age: 19.53 ± 6.66 and 19.44 ± 5.77 years, respectively). Sector location and canine angulation were measured in panoramics. All tomographs were obtained using CBCT (NewTom 5G, QR, Verona, Italy) and three-dimensional (3D) reconstructions of the maxillary laterals assessed by Mimics 14.01 image analysis software.

Results

Upper lateral incisor volume was smaller on the impacted side (401.95 ± 83.69 mm³) than on the nonimpacted side (433.54 ± 92.6 mm³, P < 0.05). There were no significant differences of lateral root resorption volume when comparing the impacted canines being on the labial or palatal sides (P > 0.05), but impacted canine angulation was significantly steeper on the labial side (70.85°) than on the palatal side (46.09°, P < 0.05). The volume of root resorption of laterals when comparing the various positions of the canine in different sectors or canine angulation in 30^o intervals was not statistically significantly different (P > 0.05).

Conclusions

The impacted canines caused root resorption of lateral incisors. The angulation of the canine was steeper on the labial side than on the palatal side but root resorption of adjacent laterals was not different. There were no statistically significant differences in the amount of root resorption of the laterals when the canine was evaluated according to localization and angulation.