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Bioactivity of PLGA-gel-derived bioglass composites

100%

Łączka M. , Maślanka E. , Pawlik J. , Dziadek M. , Zagrajczuk B. , Cholewa-Kowalska K.

tom Vol. 3, no. 2

27--34

A series of PLGA (poly L-lactide-co-glycolide) based composites modified with gel-derived glasses in the form of foils were obtained by solvent casting procedure. As a modifier, glass particles with different chemical compositions from the CaO–SiO2, CaO–P2O5–SiO2,and Al2O3–SiO2 systems were used. All glasses were synthesized by the sol-gel process. Evaluation of bioactive properties of obtained composites was made on the basis of surface changes occurring during contact with simulated body fluid. The changes of Ca, P and Si ions concentration in SBF after incubation of composites were also measured. The result showed that all composites with bioglasses (CaO–SiO2, CaO–P2O5–SiO2) exhibit formation of calcium phosphates layer after SBF test, however, kinetics of Ca, Si ion release and P uptake from SBF was dependent on bioglass chemical composition. The higher solubility, as well as faster consumption of phosphorus from SBF, was observed for materials from CaO–SiO2 (T1/PLGA, S1/PLGA) compared to composites with respective bioglass particles from the CaO–P2O5–SiO2(T2/PLGA, S2/PLGA). Our results showed that rate of Si and Ca release from the gel-derived glasses and P uptake from SBF are dependent on both: the concentration of respective ions in the materials and the presence of phosphates in their structure. For materials modified with gel-derived glasses from Al2O3–SiO2 system no significant surface changes during contact with SBF were observed, and it seems that their behavior in physiological solution indicate that they are bio-inert materials.

Insecticidal activity - a new bioactive property of the cyanobacterium Fischerella

51%

Becher P. G. , Juttner F.

nr 4

Cyanobacterial biofilms serve as food and shelter for benthic invertebrates, such as juvenile insects. Chironomids are often the most widely distributed and abundant insect larvae in freshwater ecosystems. As a consequence of high grazing pressure, effective defence mechanisms can be expected in biofilm-forming organisms. The presence of chemical defence was studied in 12 axenic and monoxenic cyanobacterial species. Flakes of cyanobacterial biofilms were offered to Chironomus riparius (Meigen) over a period of 8 days. Mortality and body-length of the surviving animals were used as indicators for the toxicity of the cyanobacteria and their suitability as food. Toxicity and inhibition of larval growth were found for several cyanobacteria tested. Fischerella sp. (ATCC 43239) was the most active and caused 100% mortality in Chironomus larvae within 24 h. Mortality was also high (87%) for larvae fed with Aphanothece sp. Moderate toxicity (40–60% mortality) was found for Calothrix sp. (PCC 7507), C. braunii Bornet et Flahault, C. thermalis (Schwabe) Hansgirg and a cyanobacterium of the LPP group designated JU 5. Mortality of 7–33% was observed for Calothrix parietina (Nägeli) Thuret, Oscillatoria brevis (Kützing) Gomont, Cylindrospermum sp., Nostoc sp., Calothrix anomala Mitra and a cyanobacterium of the LPP group designated 5 KB. Differences depending on the cyanobacterial food offered were also seen in the lengths of surviving larvae. Fischerella sp. (ATCC 43239) was studied in more detail to chemically characterise the observed insecticidal activity. The insecticidal activity could be extracted with 60% aq. methanol from the fresh biomass and caused 100% mortality in Chironomus. A literature survey was performed on the bioactive compounds so far isolated and characterised from Fischerella and related Stigonematales. It is noticeable that no insecticidal activity has been shown for any of these compounds yet. The newly found insecticidal property of Fischerella may lead to the identification of bioactive compounds which may be important as chemical defence against insect grazers.