Self-directed Learning through Creative Activity of Students

Teaching a foreign language is associated with the development of thinking, emotions and other areas of the personality. The importance and the need to include motivational and emotional spheres of the individual student in the study of a foreign language are stressed in the article. Self-directed learning means various types of individual and group activity of students that they have undertaken in the classroom and extracurricular activities at home without the direct participation of the teacher. The authors discuss the problem of independent work skills development of students learning a foreign language, assert that the effect of independent work is possible only when it is implemented in the educational process as a whole system that runs through all stages of foreign language teaching, and pay special attention to the tasks that students develop themselves

Исследование влияния дождевых осадков на радиационный фон приземной атмосферы

Объектом исследования являются поля β- и γ-излучений в синхронном эксперименте во время ливневых осадков. В процессе работы выполнен статистический анализ осадков и всплесков в β- и γ- фонах. Проведен регрессионный анализ зависимостей плотности потока β-излучения и мощности дозы амбиентного эквивалента γ-излучения от интенсивности осадков. Исследовано влияние дождевых осадков на радиационный фон приземной атмосферы.The objects of research are the field β- and γ-radiation in the synchronous experiment during heavy rainfall. The statistical analysis of rainfall and splashes in the β- and γ- backgrounds was carried out. A regression analysis of dependencies β-flux density and dose ambient equivalent γ-radiation on the intensity of precipitation was carried out. The influence of rainfall on the background radiation of surface atmosphere was invesigate

Biodegradable Polydepsipeptides

This paper reviews the synthesis, characterization, biodegradation and usage of bioresorbable polymers based on polydepsipeptides. The ring-opening polymerization of morpholine-2,5-dione derivatives using organic Sn and enzyme lipase is discussed. The dependence of the macroscopic properties of the block copolymers on their structure is also presented. Bioresorbable polymers based on polydepsipeptides could be used as biomaterials in drug controlled release, tissue engineering scaffolding and shape-memory materials

Electrospun Poly(lactide-co-glycolide-co-3(S)-methyl-morpholine-2,5-dione) Nanofibrous Scaffolds for Tissue Engineering

Biomimetic scaffolds have been investigated in vascular tissue engineering for many years. Excellent biodegradable materials are desired as temporary scaffolds to support cell growth and disappear gradually with the progress of guided tissue regeneration. In the present paper, a series of biodegradable copolymers were synthesized and used to prepared micro/nanofibrous scaffolds for vascular tissue engineering. Poly(lactide-co-glycolide-co-3(S)-methyl-morpholine-2,5-dione) [P(LA-co-GA-co-MMD)] copolymers with different l-lactide (LA), glycolide (GA), and 3(S)-methyl-2,5-morpholinedione (MMD) contents were synthesized using stannous octoate as a catalyst. Moreover, the P(LA-co-GA-co-MMD) nanofibrous scaffolds were prepared by electrospinning technology. The morphology of scaffolds was analyzed by scanning electron microscopy (SEM), and the results showed that the fibers are smooth, regular, and randomly oriented with diameters of 700 ± 100 nm. The weight loss of scaffolds increased significantly with the increasing content of MMD, indicating good biodegradable property of the scaffolds. In addition, the cytocompatibility of electrospun nanofibrous scaffolds was tested by human umbilical vein endothelial cells. It is demonstrated that the cells could attach and proliferate well on P(LA-co-GA-co-MMD) scaffolds and, consequently, form a cell monolayer fully covering on the scaffold surface. Furthermore, the P(LA-co-GA-co-MMD) scaffolds benefit to excellent cell infiltration after subcutaneous implantation. These results indicated that the P(LA-co-GA-co-MMD) nanofibrous scaffolds could be potential candidates for vascular tissue engineering

Synthese und Charakterisierung von bioabbaubaren Polymeren auf der Basis von Polydepsipeptiden

The thesis deals with the synthesis and characterization of bioresorbable polymers based on polydepsipeptides. Four different types of polydepsipeptide-polyether block copolymers were synthesized via ring-opening polymerization of morpholine-2,5-dione derivatives. The dependence of the macroscopic properties of the block copolymers on their structure is discussed. A new method for the synthesis of polydepsipeptides, i.e. the enzyme-catalyzed ring-opening polymerization of morpholine-2,5-dione derivatives, is presented. Synthesis and characterization of new block copolymers based on polydepsipeptides ABA block copolymers with polydepsipeptides (A) and poly(ethylene oxide) ( = 6000, PEO, B) blocks were synthesized via ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione or 3(S)-isobutyl-morpholine-2,5-dione in the presence of hydroxytelechelic poly(ethylene oxide) with stannous octoate as a catalyst. of the resulting copolymers increases with increasing amount of morpholine-2,5-dione derivatives. No racemization of the isoleucine or leucine residue takes place during both homopolymerization and polymerization of morpholine-2,5-dione derivatives in the presence of PEO and Sn(oct)2. The melting temperature of the poly(Glc-Leu) segments in poly(Glc-Leu)-PEO-poly(Glc-Leu) block copolymers increases with increasing length of the poly(Glc-Leu) blocks. The poly(Glc-Leu) block crystallizes first upon cooling from the melt. This leads to imperfect crystallization or no crystallization of the PEO block. The melting temperature of the PEO block is lower than that of the homopolymer, and the crystallinity of the PEO block decreases with increasing length of the polydepsipeptide blocks in both triblock copolymers. Static contact angle measurement with water clearly reveal that the hydrophilicity of the resulting copolymers increases greatly with increasing PEO content in the copolymers. Four different types of polydepsipeptide-polyether block copolymers were synthesized via ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione or 3(S)-isobutyl-morpholine-2,5-dione in the presence of poly(ethylene oxide) with one, two, three and four terminal OH-groups with stannous octoate as a catalyst, i.e., an AB block copolymer, an ABA block copolymer, an (A)2B star shaped block copolymer and an (A)2B(A)2 star shaped block copolymer, respectively, where A is a polydepsipeptide and B a PEO block. The molar ratio of depsipeptide to PEO was varied to obtain copolymers with different weight fractions of polydepsipeptide blocks ranging from 47 to 97.5 wt%. The crystallinity of the PEO block decreases in the following order: AB > (A)2B > ABA > (A)2B(A)2. The static contact angle q with water decreases with increasing PEO content in the block copolymers. Polydepsipeptides with protected functional groups were obtained by ring-opening copolymerization of DLLA with morpholine-2,5-dione derivatives having protected functional substituents. The copolymerization was carried out in the bulk at 140°C in the presence of Sn(oct)2 as a catalyst. Polyester amides with pendant carboxylic acid groups were prepared by catalytic hydrogenation of the protected copolymers. Copolymers with a PEO8000 center block and two arms of random lactide/depsipeptides copolymers were synthesized and characterized. Increasing proportion of PEO results in a decrease in molecular weight of the block copolymer and higher crystallinity in PEO block. The block copolymers having a high fraction of PEO (> 40%) are brittle. The block copolymers based on depsipeptides, DLLA and PEO have much higher elongation at break and lower Young's modulus than the corresponding block copolymers based on depsipeptides, LLA and PEO. The mechanical properties are mainly influenced by the crystallinity of copolymer blocks, when the block copolymers were prepared from the same depsipeptide and with the same molar ratio, but different lactide, i.e., DLLA or LLA. Hydrolytic degradation of block copolymers based on polydepsipeptides In vitro degradation experiments reveal that the block copolymers based on depsipeptides, DLLA and PEO lose their weight faster than the block copolymers based on depsipeptides, LLA and PEO. The weight loss rates depend on the weight fraction of PEO in the block copolymers and the starting molecular weight. The molecular weight decreases quickly, while the molecular weight distribution increases up to a polydispersity from 1.63 to 4.29 with increasing degradation time. CaH2 as a co-initiator for the ring-opening polymerization of Cyclo(Glc-Val) Block copolymers with poly(Glc-Val) and PEO6000 blocks were synthesized via the ring-opening polymerization of 3(S)-isopropyl-morpholine-2,5-dione in the presence of PEO with CaH2 as a co-initiator at 140°C for 24 h or 96 h. of the resulting copolymers increases with increasing 3(S)-isopropyl-morpholine-2,5-dione content in the feed and reaction time. According to 1H NMR analysis, racemization of valine residue takes place during the polymerization. About 40% of 3(S)-isopropyl-morpholine-2,5-dione is racemized in 96 h at 140°C during polymerization, while about 12% is racemized in 24 h. The glass transition temperature of the poly(Glc-Val) segments in the triblock copolymers is about 74°C. The melting temperature of the PEO block upon first heating is lower than that of the homopolymer, and disappears with increasing length of the poly(Glc-Val) blocks. Enzyme-catalyzed ring-opening polymerization of morpholine-2,5-diones The enzymatic ring-opening polymerization of 6-membered cyclic depsipeptides, 3(S)-isopropyl-morpholine-2,5-dione, 3(R)-isopropyl-morpholine-2,5-dione, 3(R,S)-isopropyl-morpholine-2,5-dione, (3S, 6R,S)-3-isopropyl-6-methyl-morpholine-2,5-dione, 3(S)-isobutyl-morpholine-2,5-dione, 3(S)-sec-butyl-morpholine-2,5-dione, 6(S)-methyl-morpholine-2,5-dione and 6(R,S)-methyl-morpholine-2,5-dione in the bulk, was investigated by using the lipase PPL as a catalyst. In the absence of the enzyme, the monomers were recovered, indicating that the present polymerization proceeds through enzymatic catalysis. During the polymerization of morpholine-2,5-diones racemization of both the amino acid and the S-lactic acid moiety takes place. Enzymatic polymerization produces polydepsipeptides with a carboxylic acid group at one end and a hydroxyl group at the other one. Selected commercial lipases were screened as catalysts for the polymerization of 3(S)-isopropyl-morpholine-2,5-dione at 100°C in bulk. Polymerizations catalyzed with lipases PPL, PS and CR result in conversions of about 50%, and in molecular weights ranging from 3500 to 17500. Lipase PPL was selected for further studies. The apparent rate of polymerization increases with PPL concentration. When the PPL concentration is 5 wt% and 10 wt% with respect to the monomer, a conversion of about 70% is reached after 5 d and 7 d, respectively, while for PPL concentrations of 1 wt% and 0.5 wt% the conversion is less than 15% even after 11 d. High concentrations of PPL (10 wt%) result in high values (< 4 d); with decreasing concentration of PPL poly(Glc-Val) of lower molecular weight is obtained. The highest molecular weight poly(Glc-Val), = 30000 resulted from a polymerization conducted at 130°C. Increasing polymerization time (and conversion) leads for high PPL concentration (10 wt%) first to an increase in and later to a decrease. The general trends observed by variation of the polymerization temperature are the following: (i) increasing monomer conversion and with increasing reaction temperature from 100 to 130°C,.(ii) increasing reaction temperature leads to a bimodal molecular weight distribution. Water is an important factor that controls not only the conversion but also the molecular weight. With increasing water content, enhanced polymerization rates are achieved while the molecular weight of poly(Glc-Val) decreases. Polymerizations of 6(S)-methyl-morpholine-2,5-dione catalyzed with 10 wt% lipases PPL, PC and CR result in conversions of about 75% in 3 d, and in molecular weights ranging from 8200 to 12100. MJ showed lower catalytic activity for the polymerization. The apparent rate of polymerization increases with increasing PPL concentration when the temperature is 100°C. When the PPL concentration is 5 wt% and 10 wt% with respect to the monomer, a conversion of about 70% is reached after 6 d and 1 d, respectively, while for PPL concentration of 1 wt% the conversion is less than 20% even after 6 d. High concentrations of PPL (10 wt%) result in high values (< 3 d); with lower concentration of PPL poly(Lac-Gly) of lower molecular weight is obtained. The reaction temperature (100 - 130°C) affects monomer conversion and slightly. The effect of water on the conversion and the molecular weight is similar to that in the ring-opening polymerization of 3(S)-isopropyl-morpholine-2,5-dione in the presence of PPL. The lipase-catalyzed ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione was also studied in detail. Copolymerization of 3(S)-isopropyl-morpholine-2,5-dione and D,L-lactide was carried out in the presence of PPL as a catalyst at 100°C for 168 h. Copolymers of various compositions were obtained. The enzymatic polymerization of DLLA and 3(S)-isopropyl-morpholine-2,5-dione produces copolymers with a carboxylic acid group at one end and a hydroxyl group at the other end

Synthese und Charakterisierung von bioabbaubaren Polymeren auf der Basis von Polydepsipeptiden

The thesis deals with the synthesis and characterization of bioresorbable polymers based on polydepsipeptides. Four different types of polydepsipeptide-polyether block copolymers were synthesized via ring-opening polymerization of morpholine-2,5-dione derivatives. The dependence of the macroscopic properties of the block copolymers on their structure is discussed. A new method for the synthesis of polydepsipeptides, i.e. the enzyme-catalyzed ring-opening polymerization of morpholine-2,5-dione derivatives, is presented. Synthesis and characterization of new block copolymers based on polydepsipeptides ABA block copolymers with polydepsipeptides (A) and poly(ethylene oxide) ( = 6000, PEO, B) blocks were synthesized via ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione or 3(S)-isobutyl-morpholine-2,5-dione in the presence of hydroxytelechelic poly(ethylene oxide) with stannous octoate as a catalyst. of the resulting copolymers increases with increasing amount of morpholine-2,5-dione derivatives. No racemization of the isoleucine or leucine residue takes place during both homopolymerization and polymerization of morpholine-2,5-dione derivatives in the presence of PEO and Sn(oct)2. The melting temperature of the poly(Glc-Leu) segments in poly(Glc-Leu)-PEO-poly(Glc-Leu) block copolymers increases with increasing length of the poly(Glc-Leu) blocks. The poly(Glc-Leu) block crystallizes first upon cooling from the melt. This leads to imperfect crystallization or no crystallization of the PEO block. The melting temperature of the PEO block is lower than that of the homopolymer, and the crystallinity of the PEO block decreases with increasing length of the polydepsipeptide blocks in both triblock copolymers. Static contact angle measurement with water clearly reveal that the hydrophilicity of the resulting copolymers increases greatly with increasing PEO content in the copolymers. Four different types of polydepsipeptide-polyether block copolymers were synthesized via ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione or 3(S)-isobutyl-morpholine-2,5-dione in the presence of poly(ethylene oxide) with one, two, three and four terminal OH-groups with stannous octoate as a catalyst, i.e., an AB block copolymer, an ABA block copolymer, an (A)2B star shaped block copolymer and an (A)2B(A)2 star shaped block copolymer, respectively, where A is a polydepsipeptide and B a PEO block. The molar ratio of depsipeptide to PEO was varied to obtain copolymers with different weight fractions of polydepsipeptide blocks ranging from 47 to 97.5 wt%. The crystallinity of the PEO block decreases in the following order: AB > (A)2B > ABA > (A)2B(A)2. The static contact angle q with water decreases with increasing PEO content in the block copolymers. Polydepsipeptides with protected functional groups were obtained by ring-opening copolymerization of DLLA with morpholine-2,5-dione derivatives having protected functional substituents. The copolymerization was carried out in the bulk at 140°C in the presence of Sn(oct)2 as a catalyst. Polyester amides with pendant carboxylic acid groups were prepared by catalytic hydrogenation of the protected copolymers. Copolymers with a PEO8000 center block and two arms of random lactide/depsipeptides copolymers were synthesized and characterized. Increasing proportion of PEO results in a decrease in molecular weight of the block copolymer and higher crystallinity in PEO block. The block copolymers having a high fraction of PEO (> 40%) are brittle. The block copolymers based on depsipeptides, DLLA and PEO have much higher elongation at break and lower Young's modulus than the corresponding block copolymers based on depsipeptides, LLA and PEO. The mechanical properties are mainly influenced by the crystallinity of copolymer blocks, when the block copolymers were prepared from the same depsipeptide and with the same molar ratio, but different lactide, i.e., DLLA or LLA. Hydrolytic degradation of block copolymers based on polydepsipeptides In vitro degradation experiments reveal that the block copolymers based on depsipeptides, DLLA and PEO lose their weight faster than the block copolymers based on depsipeptides, LLA and PEO. The weight loss rates depend on the weight fraction of PEO in the block copolymers and the starting molecular weight. The molecular weight decreases quickly, while the molecular weight distribution increases up to a polydispersity from 1.63 to 4.29 with increasing degradation time. CaH2 as a co-initiator for the ring-opening polymerization of Cyclo(Glc-Val) Block copolymers with poly(Glc-Val) and PEO6000 blocks were synthesized via the ring-opening polymerization of 3(S)-isopropyl-morpholine-2,5-dione in the presence of PEO with CaH2 as a co-initiator at 140°C for 24 h or 96 h. of the resulting copolymers increases with increasing 3(S)-isopropyl-morpholine-2,5-dione content in the feed and reaction time. According to 1H NMR analysis, racemization of valine residue takes place during the polymerization. About 40% of 3(S)-isopropyl-morpholine-2,5-dione is racemized in 96 h at 140°C during polymerization, while about 12% is racemized in 24 h. The glass transition temperature of the poly(Glc-Val) segments in the triblock copolymers is about 74°C. The melting temperature of the PEO block upon first heating is lower than that of the homopolymer, and disappears with increasing length of the poly(Glc-Val) blocks. Enzyme-catalyzed ring-opening polymerization of morpholine-2,5-diones The enzymatic ring-opening polymerization of 6-membered cyclic depsipeptides, 3(S)-isopropyl-morpholine-2,5-dione, 3(R)-isopropyl-morpholine-2,5-dione, 3(R,S)-isopropyl-morpholine-2,5-dione, (3S, 6R,S)-3-isopropyl-6-methyl-morpholine-2,5-dione, 3(S)-isobutyl-morpholine-2,5-dione, 3(S)-sec-butyl-morpholine-2,5-dione, 6(S)-methyl-morpholine-2,5-dione and 6(R,S)-methyl-morpholine-2,5-dione in the bulk, was investigated by using the lipase PPL as a catalyst. In the absence of the enzyme, the monomers were recovered, indicating that the present polymerization proceeds through enzymatic catalysis. During the polymerization of morpholine-2,5-diones racemization of both the amino acid and the S-lactic acid moiety takes place. Enzymatic polymerization produces polydepsipeptides with a carboxylic acid group at one end and a hydroxyl group at the other one. Selected commercial lipases were screened as catalysts for the polymerization of 3(S)-isopropyl-morpholine-2,5-dione at 100°C in bulk. Polymerizations catalyzed with lipases PPL, PS and CR result in conversions of about 50%, and in molecular weights ranging from 3500 to 17500. Lipase PPL was selected for further studies. The apparent rate of polymerization increases with PPL concentration. When the PPL concentration is 5 wt% and 10 wt% with respect to the monomer, a conversion of about 70% is reached after 5 d and 7 d, respectively, while for PPL concentrations of 1 wt% and 0.5 wt% the conversion is less than 15% even after 11 d. High concentrations of PPL (10 wt%) result in high values (< 4 d); with decreasing concentration of PPL poly(Glc-Val) of lower molecular weight is obtained. The highest molecular weight poly(Glc-Val), = 30000 resulted from a polymerization conducted at 130°C. Increasing polymerization time (and conversion) leads for high PPL concentration (10 wt%) first to an increase in and later to a decrease. The general trends observed by variation of the polymerization temperature are the following: (i) increasing monomer conversion and with increasing reaction temperature from 100 to 130°C,.(ii) increasing reaction temperature leads to a bimodal molecular weight distribution. Water is an important factor that controls not only the conversion but also the molecular weight. With increasing water content, enhanced polymerization rates are achieved while the molecular weight of poly(Glc-Val) decreases. Polymerizations of 6(S)-methyl-morpholine-2,5-dione catalyzed with 10 wt% lipases PPL, PC and CR result in conversions of about 75% in 3 d, and in molecular weights ranging from 8200 to 12100. MJ showed lower catalytic activity for the polymerization. The apparent rate of polymerization increases with increasing PPL concentration when the temperature is 100°C. When the PPL concentration is 5 wt% and 10 wt% with respect to the monomer, a conversion of about 70% is reached after 6 d and 1 d, respectively, while for PPL concentration of 1 wt% the conversion is less than 20% even after 6 d. High concentrations of PPL (10 wt%) result in high values (< 3 d); with lower concentration of PPL poly(Lac-Gly) of lower molecular weight is obtained. The reaction temperature (100 - 130°C) affects monomer conversion and slightly. The effect of water on the conversion and the molecular weight is similar to that in the ring-opening polymerization of 3(S)-isopropyl-morpholine-2,5-dione in the presence of PPL. The lipase-catalyzed ring-opening polymerization of 3(S)-sec-butyl-morpholine-2,5-dione was also studied in detail. Copolymerization of 3(S)-isopropyl-morpholine-2,5-dione and D,L-lactide was carried out in the presence of PPL as a catalyst at 100°C for 168 h. Copolymers of various compositions were obtained. The enzymatic polymerization of DLLA and 3(S)-isopropyl-morpholine-2,5-dione produces copolymers with a carboxylic acid group at one end and a hydroxyl group at the other end

Biodegradable Polymers for Medical Applications

Biodegradable polymers have a long history which, however, is difficult to be traced as some of them are natural products. The concept of synthetic biodegradable polymers, the topic of this special issue, was introduced in the 1980s. Since then the field has experienced a steady and stable growth as its outcomes are potentially relevant to the majority of population. This interdisciplinary field encompasses elements of materials science, biology, chemistry, medicine, tissue engineering, and others