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Conjugates of hyaluronic acid (HA) with biologically active molecules showed great potential in many applications. Oligomers of hyaluronic acid (oliHA) as possible regulators of biological processes and potential anti-cancer therapeutics, were reversibly attached via covalent bond on HA modified with an aldehyde group (HA-CHO) using bis-hydrazido or bis-oxyamino spacers. The structure of the final conjugates (HA-spacer-oliHA) was studied by advanced 2-dimensional NMR techniques in detail. The suggested synthetic strategy is simple, straightforward and can be used for the synthesis of various types of HA or oliHA conjugates. in vitro cytotoxicity assays showed selective activity of HA-spacer-oliHA conjugates against cancer cell lines in comparison with standard human fibroblasts., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The effect of hydrazide linkers on the formation and mechanical properties of hyaluronan hydrogels was intensively evaluated. The reaction kinetics of hydrazone formation was monitored by NMR spectroscopy under physiological conditions where polyaldehyde hyaluronan (unsaturated: ΔHA-CHO, saturated: HA-CHO) was reacted with various hydrazides to form hydrogels. Linear (adipic, oxalic dihydrazide) and branched (N,N´,N´´-tris(hexanoylhydrazide-6-yl)phosphoric triamide and 4-arm-PEG hydrazide) hydrazides were compared as crosslinking agents. The mechanical properties of hydrogels were also modified by attaching a hydrophobic chain to HA-CHO; however, it was found that this modification did not lead to an increase in hydrogel stiffness. Cytotoxicity tests showed that all tested hydrazide crosslinkers reduced the viability of cells only slightly, and that the final hyaluronan hydrogels were non-toxic materials., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hyaluronic acid (HA) modified with an aldehyde group (HA-CHO) has enormous potential for the covalent attachment of the amino compounds and for the crosslinking of HA with bis or multi-functional amino linkers under physiological conditions. Modification of HA-CHO to its α,β-unsaturated analogue (ΔHA-CHO) generally increases the stability of the reversible imino-attachment due to conjugation of the imine moiety with the adjacent CC double bound. Conjugation of a wide range of structurally different amines including the amines with enhanced biological activity were studied in detail. Results showed that the stabilities of the final conjugates ΔHACHNR significantly depend on the chemical structure of the amine and on the pH value., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Hyaluronic acid (HA) containing CC double bond in positions 4 and 5 of N-acetyl-glucosamine ring (ΔHA) is an unique material, which could be used for biomedical applications and cosmetics. The main advantage of the CC double bond is its ability to react with a wide range of oxidation agents. Location of the CC double bond directly on the glucopyranose ring allows to change the chemical capabilities and simultaneously to mimic the intrinsic physical properties of HA without introduction of linkers or other substances. The synthesis, structural analysis and basic chemical and biological characteristics of this novel biopolymer are described in details. In vitro cytotoxicity assays showed selective activity of ΔHA against cancer cell lines in comparison with standard human fibroblasts so this material has great potential in the field of anticancer drugs., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Hyaluronic acid (HA) modified with an aldehyde group (HA-CHO or HA-aldehyde) has been extensively used for various biomedical applications. The main advantage of the aldehyde moieties is the ability to react with a wide range of amino compounds under physiological conditions. Reactions of aldehydes with primary amines in water are reversible and equilibrium is thoroughly shifted towards starting aldehyde and amine. This work presents an unique modification of HA: α,β-unsaturated aldehyde of HA (4,5-anhydro-6(GlcNAc)-oxo HA or ΔHA-CHO), which allows the primary amines to be attached to HA more effectively in comparison to the saturated HA-CHO. Higher hydrolytic stability is caused by the conjugation of imine with an adjacent --C=C-- double bond. Two strategies for the preparation of unsaturated HA-aldehyde were developed and chemical structures were studied in details. Cross-linked materials prepared from this precursor are biocompatible and suitable for applications in drug delivery and regenerative medicine., (Copyright © 2015 Elsevier Ltd. All rights reserved.)