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Natural materials such as collagen and alginate have promising applications as dural graft substitutes. These materials are able to restore the dural defect and create optimal conditions for the development of connective tissue at the site of injury. A promising material for biomedical applications is chitosan-a linear polysaccharide obtained by the deacetylation of chitin. It has been found to be nontoxic, biodegradable, biofunctional and biocompatible in addition to having antimicrobial characteristics. In this study we designed new chitin-chitosan substitutes for dura mater closure and evaluated their effectiveness and safety. Chitosan films were produced from 3 % of chitosan (molar mass-200, 500 or 700 kDa, deacetylation rate 80-90%) with addition of 20% of chitin. Antimicrobial effictively and cell viability were analysed for the different molar masses of chitosan. The film containing chitosan of molar mass 200 kDa, had the best antimicrobial and biological activity and was successfully used for experimental duraplasty in an in vivo model. In conclusion the chitin-chitosan membrane designed here met the requirements for a dura matter graft exhibiting the ability to support cell growth, inhibit microbial growth and biodegradade at an appropriate rate. Therefore this is a promising material for clinical duroplasty.

Acid-modified halloysite nanotubes were used for the first time as a stereoselective catalyst for synthesis of oxygen-containing heterocycles applying of allyl alcohol (À)-isopulegol condensation with aldehydes to the octahydro-2H-chromenol (4R-and 4S-diastereomers) as an example. The catalysts were characterized by XRF, XRD, N 2 -adsorption, FTIR with pyridine and MAS NMR methods. A high ratio of 4R/4S diastereomers (7.6-14.5) under mild conditions in cyclohexane was considerably exceeding previously reported results. Unprecedented selectivity (79-83 %) to 4R isomer of thiophenyl-substituted chromenol exhibiting high analgesic activity was achieved. An increase in stereoselectivity with a decrease in the halloysite drying temperature and catalyst acidity clearly indicates formation of 4R diastereomer on the weak Brønsted sites. This work is an example that control of the stereoselectivity of acid-catalyzed organic reactions can be effectively carried out by varying water content on the aluminosilicate surface. Modified halloysite nanotubes can be considered as extremely promising catalysts for stereoselective synthesis of heterocyclic compounds.

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