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Polysaccharides like hyaluronan (HA) and chondroitin sulfate (CS) are native of the brain's extracellular matrix crucial for myelination and brain maturation. Despite extensive research on HA and CS as drug delivery systems (DDS), their high water solubility limits their application as drug carriers. This study introduces an injectable DDS using aldehyde-modified hyaluronic acid (HAOX) hydrogel containing polyelectrolyte complexes (PEC) formed with calcium, gelatin, and either CS or aldehyde-modified CS (CSOX) to deliver minocycline for Multiple Sclerosis therapy. PECs with CSOX enable covalent crosslinking to HAOX, creating immobilized PECs (HAOX_PECOX), while those with CS remain unbound (HAOX_PECS). The in situ forming DDS can be administered via a 20 G needle, with rapid gelation preventing premature leakage. The system integrates into an implanted device for minocycline release through either Fickian or anomalous diffusion, depending on PEC immobilization. HAOX_PECOX reduced burst release by 88 %, with a duration of 127 h for 50 % release. The DDS exhibited an elastic modulus of 3800 Pa and a low swelling ratio (0-1 %), enabling precise control of minocycline release kinetics. Released minocycline reduced IL-6 secretion in the Whole Blood Monocytes Activation Test, suggesting that DDS formation may not alter the biological activity of the loaded drug., Competing Interests: Declaration of competing interest Vladimír Velebný has a financial interest in the company Contipro a.s., Dolní Dobrouč, Czech Republic, the commercial producer of hyaluronic acid, Martin Pravda is employee of Contipro a.s., (Copyright © 2024 Contipro a.s. Published by Elsevier Ltd.. All rights reserved.)

Hyaluronan, a linear glycosaminoglycan comprising D-N-acetylglucosamine and D-glucuronic acid, is the main component of the extracellular matrix. Its influence on cell proliferation, migration, inflammation, signalling, and other functions, depends heavily on its molecular weight and chemical modification. Unsaturated HA oligosaccharides are available in defined length and purity. Their potential therapeutic utility can be further improved by chemical modification, e. g., reduction. No synthesis of such modified oligosaccharides, either stepwise or by hyaluronan cleavage, has been reported yet. Here we show a three-step synthesis (esterification, depolymerization and reduction) of unsaturated even numbered hyaluronan oligosaccharides with carboxylates and the reducing terminus reduced to an alcohol. Particular oligosaccharides were synthesised. The modified oligosaccharides are not cleaved by mammalian or bacterial hyaluronidase and do not affect the growth of mouse and human fibroblasts. Further, MTT and NRU viability tests showed that they inhibit the growth of human colon carcinoma cells HT-29 by 20-50 % in concentrations 500-1000 μg/mL. Interestingly, this effect takes place regardless of CD44 receptor expression and was not observed with unmodified HA oligosaccharides. These compounds could serve as enzymatically stable building blocks for biologically active substances., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

A mild and efficient reduction of negatively charged glucuronate units of hyaluronic acid (HA) into less polar glucose units has not been reported yet. However, this modification could significantly affect physical and chemical properties. Here we show a one-pot procedure where HA is converted into its derivate with carboxyl groups reduced to primary alcohols (HA-Red) without severe polymer degradation. Optimized synthesis aimed at aqueous solutions allowed the preparation of polysaccharides with molecular weights up to 1000 kDa. The chemical structure of HA-Red was proved by 2-dimensional NMR methodologies, FT-IR, LC-MS and SECMALLS. The final materials were exposed to a higher temperature or digested with bovine testicular hyaluronidase (BTH). Obtained data proved higher stability of HA-Red compared to HA, and significant dependence of stability on the degree of modification was observed in most cases. Preliminary in vitro studies showed no negative effects of HA-Red on the growth of 3T3 fibroblasts, which may be promising for applications requiring biodegradable and biocompatible HA derivatives with increased resistance to degradation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Popularity of hyaluronan (HA) in the cosmetics and pharmaceutical industries, led to the investigation and development of new HA-based materials, with enzymes playing a key role. Beta-D-glucuronidases catalyze the hydrolysis of a beta-D-glucuronic acid residue from the non-reducing end of various substrates. However, lack of specificity towards HA for most beta-D-glucuronidases, in addition to the high cost and low purity of those active on HA, have prevented their widespread application. In this study, we investigated a recombinant beta-glucuronidase from Bacteroides fragilis (rBfGUS). We demonstrated the rBfGUS's activity on native, modified, and derivatized HA oligosaccharides (oHAs). Using chromogenic beta-glucuronidase substrate and oHAs, we characterized the enzyme's optimal conditions and kinetic parameters. Additionally, we evaluated rBfGUS's activity towards oHAs of various sizes and types. To increase reusability and ensure the preparation of enzyme-free oHA products, rBfGUS was immobilized on two types of magnetic macroporous bead cellulose particles. Both immobilized forms of rBfGUS demonstrated suitable operational and storage stabilities, and their activity parameters were comparable to the free form. Our findings suggest that native and derivatized oHAs can be prepared using this bacterial beta-glucuronidase, and a novel biocatalyst with enhanced operational parameters has been developed with a potential for industrial use., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The research was supported by projects of Charles University (SVV 260636 and Cooperatio 207032-3 Immunity and Infection), (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The ability of hyaluronan as a dietary supplement to increase skin moisture and relieve knee pain has been demonstrated in several clinical studies. To understand the mechanism of action, determining hyaluronan's bioavailability and in vivo fate is crucial. Here, we used 13 C-hyaluronan combined with LC-MS analysis to compare the absorption and metabolism of oral hyaluronan in germ-free and conventional wild-type mice. The presence of Bacteroides spp. in the gut was crucial for hyaluronan absorption. Specific microorganisms cleave hyaluronan into unsaturated oligosaccharides (<3 kDa) which are partially absorbed through the intestinal wall. The remaining hyaluronan fragments are metabolized into short-chain fatty acids, which are only metabolites available to the host. The poor bioavailability (~0.2 %) of oral hyaluronan indicates that the mechanism of action is the result of the systematic regulatory function of hyaluronan or its metabolites rather than the direct effects of hyaluronan at distal sites of action (skin, joints)., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

A cascade of reactions known as the foreign body response (FBR) follows the implantation of biomaterials leading to the formation of a fibrotic capsule around the implant and subsequent health complications. The severity of the FBR is driven mostly by the physicochemical characteristics of implanted material, the method and place of implantation, and the degree of immune system activation. Here we present an in vitro model for assessing new materials with respect to their potential to induce a FBR in the peritoneum. The model is based on evaluating protein sorption and cell adhesion on the implanted material. We tested our model on the free-standing films prepared from hyaluronan derivatives with different hydrophobicity, swelling ratio, and rate of solubilization. The proteomic analysis of films incubated in the mouse peritoneum showed that the presence of fibrinogen was driving the cell adhesion. Neither the film surface hydrophobicity/hydrophilicity nor the quantity of adsorbed proteins were decisive for the induction of the long-term cell adhesion leading to the FBR, while the dissolution rate of the material proved to be a crucial factor. Our model thus helps determine the probability of a FBR to materials implanted in the peritoneum while limiting the need for in vivo animal testing., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Hyaluronan is being investigated extensively as a biocompatible and biodegradable material for use in biomedical applications. While the derivatization of hyaluronan broadens its potential therapeutic use, the pharmacokinetics and metabolization of the derivatives must be thoroughly investigated. The fate of intraperitoneally-applied native and lauroyl-modified hyaluronan films with varying degrees of substitution was investigated in-vivo employing an exclusive stable isotope-labelling approach and LC-MS analysis. The materials were gradually degraded in peritoneal fluid, lymphatically absorbed, preferentially metabolized in the liver and eliminated without any observable accumulation in the body. Hyaluronan acylation prolongs its presence in the peritoneal cavity depending on the degree of substitution. The safety of acylated hyaluronan derivatives was confirmed via a metabolic study that revealed its degradation into non-toxic metabolites, i.e. native hyaluronan and free fatty acid. Stable isotope-labelling with LC-MS tracking comprises a high-quality procedure for the investigation of the metabolism and biodegradability of hyaluronan-based medical products in-vivo., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This work reveals the growing potential of novel electrochemical methods that are applicable for polysaccharides. It was shown for the first time that the molecules of hyaluronic acid (HA) exhibit electrochemical response using phase-sensitive alternating current (AC) voltammetry in phase-out mode. Adsorption and desorption processes of HA fragments at a charged interface of mercury electrode were observed in buffered HA solutions. Electrostatic and hydrophobic manners of interactions were distinguished for native hyaluronan fragments in a wide electric potential range. The AC voltammetry response depended on the temperature, concentration, and length of HA chains. Results of this work open possibilities for further structural characterization of widely used HA fragments and understanding manners of interactions with charged hydrophobic surfaces that could be useful in the future for understanding HA interactions at biological levels., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Nanofibrous materials produced from natural polymers have wide range of potential uses in regenerative medicine. This paper focuses on preparation of nanofibrous layers produced from intentionally hydrophobized derivatives of hyaluronan, which is known for its ability to promote wound healing. This structural modification of hyaluronan expands the range of potential uses of this promising material, which is otherwise limited due to the hydrophilic nature of hyaluronic acid. The aim of this research was preparation of nanofibrous material that would retain its fibrous structure and dimensional stability even after getting into contact with an aqueous medium, which is impossible to achieve with layers composed solely of native hyaluronan. As a result, such material would be able to retain its breathability and good mechanical properties when both dry and wet. Furthermore, all prepared materials were proved non-toxic for cells. This self-supporting nanofibrous matrix can be used as a scaffold, or porous wound dressing., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Due to their large active surface, high loading efficiency, and tunable dissolution profiles, nanofibrous mats are often cited as promising drug carriers or antimicrobial membranes. Hyaluronic acid has outstanding biocompatibility, but it is hydrophilic. Nanofibrous structures made from hyaluronan dissolve immediately, making them unsuitable for controlled drug release and longer applications. We aimed to prepare a hyaluronan-based antimicrobial nanofibrous material, which would retain its integrity in aqueous environments. Self-supporting nanofibrous mats containing octenidine dihydrochloride or triclosan were produced by electrospinning from hydrophobized hyaluronan modified with a symmetric lauric acid anhydride. The nanofibrous mats required no cross-linking to be stable in PBS for 7 days. The encapsulation efficiency of antiseptics was nearly 100%. Minimal release of octenidine was observed, while up to 30% of triclosan was gradually released in 72 h. The nanofibrous materials exhibited antimicrobial activity, the fibroblast viability was directly dependent on the antiseptic content and its release., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this work, low molecular weight hyaluronan was chemically modified by oleoyl moieties utilising mixed anhydrides methodology. The activation of oleic acid with benzoyl chloride in organic solvents miscible with water was followed by NMR spectroscopy. The product selectivity correlates with the solvent's Hildebrand solubility parameter. Furthermore, the effect of the solvent for the mixed anhydride formation was elucidated by density functional theory (DFT) and showed that the reactions are faster in acetonitrile or alcohols than in hexane. Furthermore, the solvent demonstrated to control the substituent distribution pattern along HA chain during esterification. An even distribution of substituents was observed in reactions performed in water mixed with ethers. The substituent distribution pattern clearly influenced the aggregation behaviour of amphiphilic HA, controlling the stability of the delivery system, while increasing the encapsulation capacity., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

There is inconsistent information regarding the size effects of exogenously given hyaluronan on its in vivo fate. The data are often biased by the poor quality of hyaluronan and non-ideal labelling strategies used for resolving exogenous/endogenous hyaluronan, which only monitor the label and not hyaluronan itself. To overcome these drawbacks and establish the pharmacokinetics of intravenous hyaluronan in relation to its M w , 13 C-labelled HA of five M w s from 13.6-1562 kDa was prepared and administered to mice at doses 25-50 mg kg -1 . The elimination efficiency increased with decreasing M w . Low M w hyaluronan was rapidly eliminated as small hyaluronan fragments in urine, while high M w hyaluronan exhibited saturable kinetics and complete metabolization within 48 h. All tested M w s exhibited a similar uptake by liver cells and metabolization into activated sugars. 13 C-labelling combined with LC-MS provides an excellent approach to elucidating in vivo fate and biological activities of hyaluronan., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Electron-deficient chlorine covalently immobilised on an amido group of hyaluronic acid (HA) can be potentially exceptional for applications requiring biodegradable and biocompatible polymers with enhanced antibacterial or antiviral activity. This expectation is supported by the assumption that a small amount of HA chloramide (HACl) is formed in the extracellular matrix under inflammatory conditions by a reaction of endogenous HA with hypochlorous acid (HClO) generated by a myeloperoxidase/H 2 O 2 /Cl - system. HACl synthesis optimisation showed significant limitations of HClO as an oxidative agent where only lower degrees of substitution (DS) was achieved. Commercially available oxidative agents based on chlorinated isocyanuric acid were successfully tested, producing the HA chain with almost entirely chlorinated amidic groups. The structure of the final HACl was thoroughly studied using advanced 2-dimensional NMR methodologies and LC/MS. Stability of HACl at different temperatures was monitored over 12 months. Preliminary antimicrobial and antiviral tests demonstrated the potential of HACl for applications in biomedicine., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

N-Deacetylated hyaluronan (daHA) has been widely investigated as a starting material to develop biomaterials with unique composition and performance. However, its structure elucidation remains a challenging task due to its polysaccharide nature. After the brief mention of its properties and preparation, this review critically evaluates different analytical methods and approaches to characterize this promising polysaccharide. A special attention is paid to the determination of the degree of deacetylation. Besides, the analysis of its molecular weight, primary structure, and deacetylation pattern is also described. The older procedures are compared with the advanced techniques to provide reliable description of daHA., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

All-trans retinoic acid (ATRA) was grafted to hyaluronan (HA) via esterification. The reaction was mediated by mixed anhydrides. A perfect control of the degree of substitution (0.5-7.5%) was obtained by varying the molar ratio of retinoic acid in the feed. The degree of substitution plays a significant role in the long-term stability. The photodegradation of HA-ATRA upon UVA irradiation resulted in β-ionone, β-cyclocitral and 5,6-epoxy-(E)-retinoic acid. The photostability of the conjugate had increased with the combination with morin. The chemical structure of HA-ATRA and its degradation products was elucidated using NMR spectroscopy, SEC-MALLS, and gas chromatography-mass spectrometry (GC-MS). ATRA did not loss its biological activity after conjugation, as demonstrated by gene expression. The derivative was able to penetrate across the stratum corneum. Besides, HA-ATRA downregulated the expression of anti-inflammatory interleukins 6 and 8. HA-ATRA would be expected to be used for transdermal drug delivery or cosmetics., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Deacetylated hyaluronan (daHA) containing reactive free amino groups is an important intermediate for further modification. Comparing direct and indirect NMR and HPLC to characterize the degree of HA deacetylation (DD), direct NMR approach using area ratio of anomeric CH and CH-NH 2 groups was the most precise one. To describe the substitution pattern, daHA was selectively cleaved by nitrous acid generated in situ or hyaluronan lyase from Streptococcus pneumoniae. The resulting oligomers were identified by LC-ESI-MS. The experimental distribution of these oligomers was compared with theoretically expected random oligomer distribution. Independently on the starting HA molecular weight and deacetylation conditions, the experimental data differed from the random distribution model and suggested that deacetylation of certain N-acetyl-d-glucosamine had reduced the probability of deacetylation at the neighbouring disaccharide. This phenomenon was explained by conformational changes of HA caused by intra- and intermolecular interactions between positively charged amino and negatively charged carboxylic groups., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hyaluronan (HA) films exhibit properties suitable for medical applications, but the solubility of HA limits their use in aqueous environments. This can be overcome by modifying HA with hydrophobic side groups that enable physical cross-linking. In this work, we present water insoluble free-standing films from lauroyl modified HA as novel biomaterials with properties tuneable by the degree of HA substitution. The films are homogeneous, mechanically strong, and flexible and can be sterilized by ethylenoxide. To characterize the films, we measured their thickness, dry mass, content of residual organic solvent, mechanical properties, swelling and enzymatic degradation. The safety and biodegradability of the films were tested both in-vitro and in-vivo, showing that the films are safe and that their degradation can be tailored by the degree of HA substitution., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

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.)

A better understanding of in vivo behavior of nanocarriers is necessary for further improvement in their development. Here we present a novel approach, where both the matrix and the drug can be analyzed by LCMS/MS after one sample handling. The developed method was applied for the comparison of pharmacokinetic profile of free and encapsulated doxorubicin (DOX) in oleyl hyaluronan (HA-C18:1) polymeric micelles. The results indicated that nanocarriers were rapidly dissociated upon in vivo administration. Despite this fact, the administration of encapsulated DOX led to its longer circulation time and enhanced tumor targeting. This effect was not observed injecting blank HA-C18:1 micelles followed by unencapsulated DOX. Biodistribution studies and molecular weight estimation of the carrier matrix indicated relatively high stability of HA-C18:1 ester bond in bloodstream and complete elimination of the derivative within 72 h. The proposed methodology provides a novel strategy to elucidate the pharmacokinetic behavior of polysaccharide-based drug delivery systems., (Copyright © 2019. Published by Elsevier Ltd.)

Development of delivery systems which allow real-time visual inspection of tumors is critical for effective therapy. Near-infrared (NIR) fluorophores have a great potential for such an application. To overcome NIR dyes short blood circulation time and increase tumor accumulation, a NIR dye, cypate, was associated with oleyl hyaluronan, which can self-assemble into polymeric aggregates. The cypate association with oleyl hyaluronan was performed either by a covalent linkage, or physical entrapment. The two systems were compared for tumor targeting and contrast enhancement using BALB/c mice bearing 4T1 breast cancer tumors. Independently on the way of cypate association, it took more than 24 h from intravenous administration to detect NIR signal in tumors and the tumors were clearly visualized for 2 following weeks without substrate reinjection. Covalently linked cypate generated 2-3 fold stronger fluorescence signal than physically loaded cypate. This study demonstrates the potential of HA matrix to be used as carrier of contrast agents for non-invasive long-term tumor visualization., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Acyl derivatives of hyaluronan (acyl-HA) are promising materials for biomedical applications. Depending on the acyl length and the degree of substitution, these derivatives range from self-assembling water-soluble polymers to materials insoluble in aqueous environments. The behaviour of acyl-HA was studied in solution, but little attention was paid to the solid state, despite its importance for applications such as medical device fabrication. We thus used X-ray scattering and electron microscopy to explore the solid-state nano-structure of acyl-HA. The set of samples included various substituents, substitution degrees and molecular weights. The obtained data showed that all studied acyl-HA materials contained structures with dimensions on the order of nanometres that were not present in unmodified HA. The size of the nanostructures increased with the acyl length, while the degree of substitution and molecular weight had negligible effects. We suggest that the observed nanostructure corresponds to a distribution of hydrophobic domains in a hydrophilic matrix of unmodified HA segments., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In this work, amphiphilic hyaluronic acid (HA) was synthesized by the chemical bonding of steroids. Particularly, succinyl cholesterol (SCH), cholic acid (CA), deoxycholic acid (DOCA), and 18β-glycyrrhetinic acid (GA) were activated by benzoyl chloride towards the esterification reaction of HA in water. The degree of substitution can be controlled by varying the feed ratio of mixed anhydride to HA and up to 25% (mol/mol) can be obtained. Due to mild reaction conditions, no degradation of the polysaccharide was observed. The prepared amphiphilic polymers were characterized by NMR, infrared spectroscopy (FT-IR) and SEC/MALLS, as well as turbidity and size of the aggregates. The developed system is proposed for the delivery of hydrophobic drugs; for this purpose, curcumin, vitamin E and coenzyme Q10 were used as hydrophobic models; these molecules were loaded into the conjugates with high efficiency. The loading capacity was a function of degree of substitution. Furthermore, the biocompatibility of the derivatives and the cellular uptake of the delivery system enabled us to demonstrate the potential of the prepared delivery systems., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Chondroitin sulfate (CS) was regio-specifically modified to an unsaturated derivative (ΔCS) with a double bond in positions 4 and 5 of N-acetyl-d-galactosamine. The structure of ΔCS was elucidated in detail by two dimensional nuclear magnetic resonance, ultraviolet spectroscopy and mass spectrometry. The introduction of a nucleophilic CC double bond into a polymer backbone had no influence on biocompatibility of CS, which was demonstrated by MTT live-dead assay and enzymatic degradation in vitro. On the other hand the chemical modification significantly enhanced the reactivity of ΔCS towards numerous oxidizing agents, which might be promising for a variety of biomedical and cosmetic applications., (Copyright © 2018 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.)

This work reports the synthesis and characterisation of new amphiphilic hyaluronan (HA) grafted with poly(3-hydroxyalkanoates) (PHAs) conjugates. Hydrolytic depolymerisation of PHAs was used for the synthesis of defined oligo(3-hydroxyalkanoates)-containing carboxylic terminal moieties. A kinetic study of the depolymerisation was followed to prepare oligomers of required molecular weight. PHAs were coupled with hydroxyl groups of HA mediated by N, N'-carbonyldiimidazole (CDI) or HSTU Tetramethyl-O-(N-succinimidyl) uronium hexafluorophosphate. For the first time, the covalent bonding of oligo derivatives of P(3-hydroxybutyrate), P(3-hydroxyoctanoate), P(3-hydroxyoctanoate-co-3-hydroxydecanoate) and P(3-hydroxyoctanoate-co-3-hydroxydecanoate-co-3-hydroxydodecanoate) and HA was achieved by "grafting to" strategy. Achieved grafting degree was a function of hydrophobicity of PHA, Mw and polarity of the solvent. The most suitable reaction conditions were observed for oligo (3-hydroxybutyrate) grafted to HA (grafting degree of 14%). Graft copolymers were characterized by FT-IR, NMR, DSC and SEC-MALLS. Graft copolymers can be physically loaded with hydrophobic drugs and may serve as drug delivery system., (Copyright © 2017 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.)

A new photopolymerizable derivative of hyaluronan (methacrylhydrazide-HA, MAHA) was prepared by carbodiimide chemistry. The reaction conditions were optimized for molecular weight (M w ), reaction time and amount of reagents with a degree of methacrylation (DM) ranging from 2% to 58%. Methacrylhydrazide-HA was hydrolytically stable (PBS, 7days, 37°C) in contrast to commonly used methacrylester analoque (23% hydrolyzed). MAHA readily photopolymerized into densely crosslinked hydrogels under physiological conditions. The varied DM, M w , irradiation time (t exp ) and macromer concentration in photocrosslinking afforded hydrogels with different physical (swelling ratio, degradation rate) and mechanical properties (stiffness, toughness). Three-dimensional fabrication and surface patterning of MAHA hydrogels were demonstrated by photolithography and light mediated micromolding. A live-dead assay with skin fibroblasts showed convenient biocompatibility of MAHA (16%, 116kDa) for potential scaffolding applications in tissue engineering and regenerative medicine., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The physicochemical properties and biological functions of hyaluronan (HA) are closely related to its molecular weight (MW) and molecular weight distribution (MWD). Therefore, it is crucially important to provide a reliable characterization of these parameters for proper use of HA and its degradation products in both chemical and clinical fields. In this study, we present a novel method for the preparation of HA fragments of defined size with narrow molecular weight distribution. The HA fractionation was performed using an anion-exchange chromatography and is applicable either after enzymatic or chemical hydrolysis of polymeric HA. Isolated fractions with a molecular weight ranging from 3000-420,000gmol -1 were analyzed by size exclusion chromatography with multi-angle laser light scattering (SEC-MALLS). Hundred-milligram scale HA fragments were obtained from 5g hyaluronan starting material. Independently on weight-average molecular weight (M w ), the polydispersity index (PDI) of the HA fractions was less than 1.23. The fractionation methodology can be easily up-scaled and is applicable on any negatively charged polymers. We have also found that PDI is insufficient to characterize almost monodisperse fractions and for proper material characterization we proposed a new characteristic termed "distribution angle", calculated from the slope of the cumulative molecular weight distribution curve. Compared to PDI, the distribution angle reflects more efficiently changes in size distribution and thus is highly recommended to be used along with M w determination of any polymer., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Nanosized materials offer promising strategy for topical drug delivery due to their enhancing effect on drug percutaneous transport across the stratum corneum barrier. In this work, polymeric micelles made from hydrophobized hyaluronic acid (HA) were probed for skin delivery. Compared to non-polymeric micelle solutions containing similar drug amount, in vitro skin penetration analysis indicated 3 times larger deposition of drug in the epidermis and 6 times larger drug deposition in the dermis after 5h of topical treatment in Franz diffusion cells. The drug deposition was further increased with prolonged time of topical treatment. Laser confocal microscopy revealed the accumulation of both, the HA forming the vehicle and the payload, in the epidermis and dermis. Although fluorescent labeling of the HA would suggest co-transport of the HA and the drug, loading FRET pair dyes in the micellar core clearly demonstrated gradual micelle disruption with increasing skin depth. Transcellular penetration was the predominant pathway for the loaded drug. The HA polymeric micelles also demonstrated increased bioactivity of loaded compound in vitro and in vivo. In addition, the loaded micelles were found to be stable in cream formulations and thus they have great potential for topical applications for cosmetic and pharmaceutical purposes., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, hyaluronan (HA) was grafted with alpha-linolenic acid (αLNA) by benzoyl mixed anhydrides methodology, which allowed the derivatization of HA under mild reaction conditions. The reaction was optimized and transferred from laboratory to semi-scale production. The derivative revealed an unexpected cytotoxicity after oven drying and storage at 40°C. For this reason, the storage conditions of sodium linolenyl hyaluronate (αLNA-HA) were optimized in order to preserve the beneficial effect of the derivative. Oven, spray dried and lyophilized samples were prepared and stored at -20°C, 4°C and 25°C up to 6 months. A comprehensive material characterization including stability study of the derivative, as well as evaluation of possible changes on chemical structure and presence of peroxidation products were studied by Nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS), thermogravimetric analysis (TGA) and complemented with assessment of in vitro viability on mouse fibroblasts NIH-3T3. The most stable αLNA-HA derivative was obtained after spray drying and storage at ambient temperature under inert atmosphere. The choice of inert atmosphere is recommended to suppress oxidation of αLNA supporting the positive influence of the derivative on cell viability. The encapsulation of hydrophobic drugs of αLNA-HA were also demonstrated., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Novel hydrophobized hyaluronan (HA) derivatives, containing ω-phenylalkanoic acids (ω-PAA, 4-phenylbutyric acid, 6-phenylhexanoic, 8-phenyloctanoic or 11-tolylundecanoic acids) were prepared by esterification. Mixed anhydrides obtained after reaction of the carboxyl acid moiety and benzoyl chloride were found to be active acylating agents, affording hydrophobized HA in good yield and under mild conditions. The reactivity of the aromatic fatty acids towards esterification has decreased with the increasing length of the aliphatic spacer between the aromatic substituent and carboxylic acid moiety. The novel HA derivatives self-assembled from very low concentrations and were found to be non-cytotoxic. The potential use of ω-phenylalkanoic acids grafted-HA towards drug delivery applications was demonstrated by hydrophobic drugs (resveratrol and retinyl palmitate) encapsulation. The drug loading capacity of the novel HA derivatives was significantly improved most likely because of π⋯π interactions between the micelle core and loaded hydrophobic aromatic compound., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Hyaluronan (HA) films exhibit properties suitable for various biomedical applications, but the solubility of HA limits their use in aqueous environments. Therefore, we developed water insoluble films based on palmitoyl esters of HA (pHA). Films were prepared from pHA samples with various degrees of substitution (DS) and molecular weights and their mechanical properties and swelling were characterized. Additionally, scanning electron microscopy and atomic force microscopy were used for visualization. Despite being prepared by solution casting, the films had a very smooth surface and were homogeneous in thickness. The film properties were in accordance with the polymer DS and molecular weight, enabling to tailor them for future applications by choosing a suitable pHA material. The behavior of the films toward cells was assessed in vitro. All films were non-cytotoxic and showed no adhesion of cells. These results show that the developed films are suitable candidates for various biomedical applications such as tissue engineering or wound healing., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this work, hyaluronan (HA) was grafted by a novel and an efficient mixed anhydrides methodology with (hetero)-aryl and aliphatic acrylic moieties suitable for cross-linking. A precise control of stoichiometry was achieved. Derivatives with degree of substitution (DS) below 20% did not show self-crosslinking. Due to mild reaction conditions, a negligible degradation of the polysaccharide was obtained. The influence of the feed components on the reaction efficiency and DS were studied up to 200 g/batch. The structure of the modified HA was characterized by Infrared Spectroscopy, Nuclear Magnetic Resonance, SEC-MALS and chromatographic analyses. Enzymatic degradation of derivatives was performed and isolated dimers demonstrated to be non-cytotoxic. The feasibility of the grafted HA for electrospinning with subsequent photo-crosslinking to avoid nanofibers water dissolution was demonstrated. The biocompatibility of the material, its degradation products, and the formation of honeycomb porous structures also proved the potential of the material for future in vivo applications., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Chondroitin sulfate (CS) was chemoselectively oxidized by Tempo/NaClO to C-6 aldehyde of a D-galactosamine subunit (GalNAc). The subsequent, spontaneous desulfatation of oxidized CS gave rise to α,β-unsaturated aldehyde. A new derivative of CS was fully characterized and a degree of oxidation was determined by spectroscopic analysis. The optimization of reaction conditions showed a proportional degree of oxidation to an amount of sodium hypochlorite. The utility of α,β-unsaturated aldehyde for crosslinking and conjugation was demonstrated by a seamless condensation with various N-nucleophiles. We also demonstrated pH-dependent release of biologically active agents from oxidized CS. A live-dead assay in the presence of α,β-unsaturated aldehyde revealed unaffected viability of NIH 3T3 fibroblasts, which made this precursor promising for several biomedical applications including drug delivery and tissue engineering., (Copyright © 2015 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.)

Hyaluronan (HA) was chemically modified to a photocurable derivative by the acylation with a mixed anhydride of trans-cinnamic acid and characterized by UV, IR and 2D NMR spectroscopy. Photocurable HA was processed to a microfibrous structure by wet-spinning technology. Water solubility of otherwise water-soluble HA microfibres was reduced significantly by the solid-state photocrosslinking. We also investigated that the nature of polymer structure had a great impact to a final crosslink ratio. The analysis of the mechanical properties showed higher ultimate tensile strength and increased rigidity of the photocrosslinked fibres in comparison to the untreated ones. Moreover all tested materials are regarded as biocompatible according to the tests of cell viability, phototoxicity and enzymatic degradability, which make them suitable candidates for numerous biomedical applications., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The present work describes a novel and efficient method of synthesis of amphiphilic hyaluronan (HA) by esterification with alkyl fatty acids. These derivatives were synthesized under mild aqueous and well controlled conditions using mixed aliphatic aromatic anhydrides. These anhydrides characterized by the general formula RCOOCOC6H2Cl3 can be easily prepared by the reaction of the corresponding fatty acid (R) with 2,4,6-trichlorobenzoyl chloride (TCBC) in the presence of triethylamine. The aliphatic aromatic anhydrides RCOOCOC6H2Cl3 then react with the polysaccharide and enable the synthesis of aliphatic acid esters of HA in good yields. No hydrolytic degradation of hyaluronic acid could be observed. Parameters controlling the degree of esterification were systematically studied. Fatty acids with different chain lengths can be introduced applying this methodology. The degree of substitution was decreasing with increasing length of hydrophobic chain. The reaction products were fully characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), SEC-MALLS and chromatographic analyses. Although the esterified HA products exhibited aggregation in solution as demonstrated by NMR, microscopy and rheology, they were still water-soluble., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Hyaluronan (HA) based hydrogels have been synthesized combining chemical modification of the polysaccharide by partial oxidation, reductive amination and 'click chemistry'. HA was oxidized by 4-acetamido-TEMPO-mediated reaction, using sodium hypochlorite as primary oxidant and NaBr in buffered pH, so that the produced aldehyde moieties (hemiacetals) were trapped in situ by adding primary amines containing azide or alkyne-terminal groups. The structure of the reaction products, oxidized-HA and primary amines bonded to HA, was elucidated using 2D NMR spectroscopy. SEC-MALLS analysis of the modified substrates showed a negligible degradation of the polysaccharide using this procedure. Furthermore, azido- and alkynyl derivatives underwent cross-linking by click chemistry into hydrogels, which were characterized by NMR, FT-IR, swelling degree and mechanical properties. Possible application of the material as scaffold for tissue engineering was tested by seeding and proliferation of chondrocytes for up to 15 days., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Hyaluronan (Na(+) salt of hyaluronic acid, HA) was extensively depolymerised by HCl-catalyzed hydrolysis at pH 3 for up to 500min under temperature-controlled microwave irradiation. The effects of microwave heating on the hydrodynamic properties of the polysaccharide were determined by SEC-MALLS and viscometry. The weight-average molecular mass (Mw) of HA decreased from 1.44×10(6) to ∼5000, reaching the region of higher oligosaccharides. The scission of HA chains was found to proceed randomly during the whole degradation process. Treatment of the Mw and intrinsic viscosity data according to the Mark-Houwink equation, [η]=k×Mw(α) suggested three relationships with α1=0.46 for Mw>500,000, α2=0.84 for Mw between 500,000 and 50,000, and α3=1.13 for Mw<50,000. The results revealed that HA with Mw>10,000 adopts a stiffish coil conformation in solution. As monitored by FT-IR and NMR spectroscopic techniques, the primary structure of the HA chains was maintained during the microwave-assisted hydrolysis at pH 3 at 105°C. At reaction times larger than 240min, uv spectroscopy suggested the depolymerisation of HA was accompanied by formation of by-products produced by side reaction., (Copyright © 2008 Elsevier Ltd. All rights reserved.)