Biocompatibility and enzymatic degradation studies on sulphated hyaluronic acid derivatives

Synthesis of Novel Hyaluronic Acid Sulfonated Hydrogels Using Safe Reactants: A Chemical and Biological Characterization

Here, we present a one-pot procedure for the preparation of hyaluronic acid (HA) sulfonated hydrogels in aqueous alkaline medium. The HA hydrogels were crosslinked using 1,4-butanedioldiglycidyl ether (BDDE) alone, or together with N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (Bes), as a safe sulfonating agent. Conditions for the simultaneous reaction of HA with BDDE and Bes were optimized and the resulting hydrogels were characterized under different reaction times (24, 72, and 96 h). The incorporation of sulfonic groups into the HA network was proven by elemental analysis and FTIR spectroscopy and its effect on water uptake was evaluated. Compared with the non-sulfonated sample, sulfonated gels showed improved mechanical properties, with their compressive modulus increased from 15 to 70 kPa, higher stability towards hyaluronidase, and better biocompatibility to 10T1/2 fibroblasts, especially after the absorption of collagen. As main advantages, the procedure described represents an easy and reproducible methodology for the fabrication of sulfonated hydrogels, which does not require toxic chemicals and/or solvents.

Thermogels containing sulfated hyaluronan as novel topical therapeutics for treatment of ocular surface inflammation

The development of long lasting therapeutic agents is critically important for efficient treatment of chronic diseases. We herein report a rational strategy to develop a therapeutic thermogel featured with prolonged anti-inflammatory and corneal-protective effects. Specifically, a hyaluronic acid with different sulfation degrees and an amine-terminated poly(N-isopropylacrylamide) are conjugated to achieve the thermogels. In vitro studies reveal that the thermogels are highly biocompatible to statens seruminstitut rabbit cornea cells and their anti-inflammatory properties are strongly dependent on the sulfation degree. In a rabbit model of ocular inflammation, single-dose topical administration of a thermogel formulation could repair defects in corneal epithelium (∼99% thickness restored), prevent corneal cell apoptosis (∼68.3% cells recovered), and suppress ocular surface inflammation (∼4-fold decrease) for a follow-up period of 7 days. This high treatment efficacy of the thermogel can be attributed to its potent inhibition in selectin-mediated leukocyte infiltration as well as effective corneal protection. These findings show a great promise for topical treatment of ocular inflammation and advancement of ophthalmic formulations using the bioactive thermogel as a therapeutic component that is not rapidly cleared from the eye and thus considerably reduces administration times.

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Sulfated hyaluronan thermogels served as intrinsic therapeutic agents.

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Thermogels exert inhibitory effects on selectin-mediated leukocyte infiltration.

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Sulfation degree is a key to achieve superior therapeutic thermogels.

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Highly sulfated agent reveals potent anti-inflammatory/corneal-protective effects.

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Single dose reduces corneal inflammation by 4-folds at 7 days post-instillation.

Quantitative proteomics reveals altered expression of extracellular matrix related proteins of human primary dermal fibroblasts in response to sulfated hyaluronan and collagen applied as artificial extracellular matrix

Fibroblasts are the main matrix producing cells of the dermis and are also strongly regulated by their matrix environment which can be used to improve and guide skin wound healing processes. Here, we systematically investigated the molecular effects on primary dermal fibroblasts in response to high-sulfated hyaluronan [HA] (hsHA) by quantitative proteomics. The comparison of non- and high-sulfated HA revealed regulation of 84 of more than 1,200 quantified proteins. Based on gene enrichment we found that sulfation of HA alters extracellular matrix remodeling. The collagen degrading enzymes cathepsin K, matrix metalloproteinases-2 and -14 were found to be down-regulated on hsHA. Additionally protein expression of thrombospondin-1, decorin, collagen types I and XII were reduced, whereas the expression of trophoblast glycoprotein and collagen type VI were slightly increased. This study demonstrates that global proteomics provides a valuable tool for revealing proteins involved in molecular effects of growth substrates for further material optimization.

Polygalacturonic acid hydrogel with short-chain hyaluronate cross-linker to prevent postoperative adhesion

The purpose of this study was to develop a poly(galacturonic acid) (PGA)-based hydrogel using a short-chain hyaluronate (sHA) cross-linker for medical applications. PGA was grafted with adipic acid dihydrazide (ADH) to yield PGA–ADH, an amine-containing PGA derivative. This PGA–ADH formed a water-insoluble hydrogel by reacting with 1,1′-carbonyldiimidazole (CDI)–grafted sHA (sHA–CDI) in aqueous solution. The sHA–cross-linked PGA hydrogel has a water content of about 94%–97% and compressive modulus of 10.7–26.9 kPa. The in vitro data indicated that the sHA–cross-linked PGA hydrogel is degradable and noncytotoxic, thus suitable for biomedical applications. Animal implant studies showed that the sHA–cross-linked PGA hydrogel membrane exhibited antiadhesion potency, significantly higher than that found in untreated rats and has great potential for future clinical applications.

Role of mesenchymal stem cells in tissue engineering of meniscus

Tissue engineering is a promising approach for the treatment of tissue defects. Mesenchymal stem cells are of potential use as a source of repair cells or of important growth factors for tissue engineering. The purpose of this study was to examine the role of mesenchymal stem cells in meniscal tissue repair. This was tested using several cell and biomaterial-based treatment options for repair of defects in the avascular zone of rabbit menisci. Circular meniscal punch defects (2 mm) were created in the avascular zone of rabbit menisci and left empty or filled with hyaluronan-collagen composite matrices without cells, loaded with platelet-rich plasma, autologous bone marrow, or autologous mesenchymal stem cells. In some experiments, matrices with stem cells were precultured in chondrogenic medium for 14 days before implantation. Rabbits were then allowed free cage movement after surgery for up to 12 weeks. Untreated defects and defects treated with cell-free implants had muted fibrous healing responses. Neither bone marrow nor platelet-rich plasma loaded in matrices produced improvement in healing compared with cell-free implants. The implantation of 14 days precultured chondrogenic stem cell-matrix constructs resulted in fibrocartilage-like repair tissue, which was only partially integrated with the native meniscus. Non-precultured mesenchymal stem cells in hyaluronan-collagen composite matrices stimulated the development of completely integrated meniscus-like repair tissue. The study shows the necessity of mesenchymal stem cells for the repair of meniscal defects in the avascular zone. Mesenchymal stem cells seem to fulfill additional repair qualities besides the delivery of growth factors.

Enhancing action by sulfated hyaluronan on connexin-26, -32, and -43 gene expressions during the culture of normal human astrocytes

Astrocyte proliferation is strictly controlled during development and in the adult nervous system. In this study, we examined the role of sulfated hyaluronan (SHya) in the proliferation and differentiation of normal human astrocytes (NHAs). Cells were cultured with different concentrations of SHya for 7 days, and the number of viable cells and the presence of neural cell-specific genes were determined to assess their proliferation and development, respectively. With SHya, cell proliferation increased nonsignificantly. Furthermore, remarkable enhancing action by SHya on connexin-26, -32, and -43 gene expressions were observed during the culture of NHAs. It has been suggested that a fraction of NHAs have neural precursor activity that gives rise to astrocytes themselves, oligodendrocytes, and neurons. Our results clearly demonstrated that the expression of specific genes for neural precursor cells, astrocytes, neurons, and oligodendrocytes was significantly increased to 50 mug/mL in SHya-treated cultures when compared with that of the control culture. These findings suggest that SHya plays an important role in the proliferation and differentiation of NHAs and in the production of a novel material for tissue engineering.

Coagulation property of hyaluronic acid-collagen/chitosan complex film

Biomacromolecule has been widely used as biomedical material. Because different biomacromolecules possess different properties, how to exhibit the respective advantages of different components on one type of biomaterial becomes the hot spot in the field of biomaterial studying. This work reported a type of complex film that consisted of hyaluronic acid (HA), type I collagen (Col-I), and chitosan (CS) (HA-Col-I/CS, HCC). Then, a series of experiments were performed, such as inverted microscopic observation, atomic force microscopic (AFM) imaging, flow cytometry (FCM) measurement, MTT assay, and MIC assay. In the present work, we observed the growing condition of 3T3 fibroblasts on the surface of the HCC complex film, visualized the morphological changes of platelets during the coagulation process, and discovered microparticles on the platelet membrane. Moreover, we confirmed the microparticles are the platelet-derived microparticles (PMPs) using the FCM. In addition, the minimal inhibitory concentration (MIC) of HCC against Escherichia coli (E. coli) 8099 was 0.025 mg/ml, against Staphylococcus aureus (S. aureus) ATCC 6538 was 0.1 mg/ml. The results together indicated that the HCC film possessed promising coagulation property, cell compatibility and anti-bacteria property, and the potential in future clinical application such as wound healing and bandage.

Synthesis, characterization and chondroprotective properties of a hyaluronan thioethyl ether derivative

Hyaluronan (HA), a non-sulfated glycosaminoglycan, is widely used in the clinic for viscosurgery, viscosupplementation, and treatment of osteoarthritis. Four decades of chemical modifications of HA have generated derivatives in which the biophysical and biochemical properties, as well as the rates of enzymatic degradation in vivo have been manipulated and tailored for specific clinical needs. One earlier modification adds multiple thiol groups to HA through hydrazide linkages, leading to a readily crosslinkable material for adhesion prevention and wound healing. We now describe the synthesis and chemical characterization of a novel thioethyl ether derivative of HA, HA-sulfhydryl (HASH), with a minimal tether between the HA and the thiol group. Unlike earlier thiol-modified HA derivatives, HASH cannot be readily crosslinked to form a hydrogel using either oxidative or bivalent electrophilic conditions, thus offering a unique polymeric polythiol that remains soluble. Moreover, HASH showed no cytotoxicity towards primary human fibroblasts and reduced the apoptosis rates of primary chondrocytes exposed to hydrogen peroxide in vitro. These properties foreshadow the clinical potential of HASH to moderate inflammation and to act as a chondroprotective agent in vivo.

Hyaluronic acid hydrogel immobilized with RGD peptides for brain tissue engineering

In this paper, hyaluronic acid hydrogels with open porous structure have been developed for scaffold of brain tissue engineering. A short peptide sequence of arginine-glycine-aspartic acid (RGD) was immobilized on the backbone of the hydrogels. Both unmodified hydrogels and those modified with RGD were implanted into the defects of cortex in rats and evaluated for their ability to improve tissue reconstruction. After 6 and 12 weeks, sections of brains were processed for DAB and Glees staining. They were also labeled with GFAP and ED1 antibodies, and observed under the SEM for ultrastructral examination. After implanting into the lesion of cortex, the porous hydrogels functioned as a scaffold to support cells infiltration and angiogenesis, simultaneously inhibiting the formation of glial scar. In addition, HA hydrogels modified with RGD were able to promote neurites extension. Our experiments showed that the hyaluronic acid-RGD hydrogel provided a structural, three-dimensional continuity across the defect and favoured reorganization of local wound-repair cells, angiogenesis and axonal growth into the hydrogel scaffold, while there was little evidence of axons regeneration in unmodified hydrogel.

Silicone based polyurethane materials: a promising biocompatible elastomeric formulation for cardiovascular applications

The biocompatibility of a new material for cardiovascular applications constituted by a poly(ether)urethane (PEtU) and a silicone [polydimethylsiloxane (PDMS)] was evaluated. The achieved material shows properties similar to both polyurethanes and silicones. The material was transformed into porous membranes by a spray-deposition technique. Since any material preparation and manufacturing procedure may introduce some toxicity, in vitro cytotoxicity screening tests were carried out. Human umbilical vein endothelial cells (HUVECs) and a mouse fibroblasts cell line (L929) were cultivated with extracts obtained from materials containing 10, 40 and 100% (w/w) of PDMS. The commercially available Estane 5714-F1 and Cardiothane 51 were used as controls. Extracts were incubated up to 72 hours with HUVECs and L929 cells. The cytotoxic effect was evaluated by light microscopy, cell viability (MTT reduction and neutral red uptake) and proliferation (5-bromo-2'-deoxyuridine incorporation) tests. In vivo studies were carried out using materials containing the same PDMS percentages as for in vitro experiments. The same commercial controls were used. Results obtained with cell culture studies agreed with those obtained in the in vivo experiments and showed that the material preparation and manufacturing procedure do not introduce any toxicity in the products at each PDMS concentration investigated.

Biocompatibility and stability of disulfide-crosslinked hyaluronan films

Hyaluronan (HA) can be chemically modified to engineer robust materials with pre-selected mechanical properties and resorption rates that can be dictated by the intended clinical use. Disulfide-crosslinked HA films were prepared by air oxidation of thiol-modified HA, followed by treatment with 0.3% hydrogen peroxide. The degradation of the disulfide-crosslinked films in vitro was very slow (<10% in 7 days) in buffer alone and shorter (t1/2=3-5 days) in the presence of hyaluronidase (HAse). The cytocompatibility of the disulfide-crosslinked HA films was determined using two separate conditions: (i) in vitro culture of mouse fibroblasts in indirect contract with the films, and (ii) in vitro culture of fibroblasts directly on films coated with poly d-lysine. Excellent cytocompatibility was observed in murine fibroblasts that were cultured in indirect contact with thiolated HA films. Although cells were unable to attach and spread on thiolated HA films, pre-coating the thiolated HA films with poly D-lysine resulted in attachment and spreading equivalent to that observed on polystyrene. Rates of resorption in vivo were obtained by subcutaneous implantation of disulfide-crosslinked HA films into the backs of Wistar rats. Biocompatibility in vivo was determined in both subcutaneous flank and peritoneal cavity implantation of the films in Wistar rats. The disulfide-crosslinked HA films were less than 30% resorbed after 42 days in vivo, and histochemical and cytochemical analysis indicated that the films were well-tolerated with mild inflammatory response at both sites of implantation.

The use of hyaluronan and its sulphated derivative patterned with micrometric scale on glass substrate in melanocyte cell behaviour

Surface microfabrication techniques were widely utilised for the spatial control of in vitro cell behaviour. A photo-immobilisation procedure was utilised to create micropatterned surfaces: four different stripe patterns (100, 50, 25 and 10 microm) of hyaluronan (Hyal) and its sulphated derivative (HyalS) on silanised glass substrate were obtained.The morphological analysis showed that the surface topography showed regular stripes of 100, 50, 25 and 10 microm wide and ranging from 300 nm up to 1 microm in thickness. They reproduced the exact photo-mask pattern: glass stripes alternating with polysaccharide ones. On the contrary, Hyal microstructures showed just a topographic pattern as the glass stripes appeared to be covered by a thin layer of the macromolecule by TOF-SIMS. Cell adhesion studies demonstrated that melanocytes adhered and oriented within the first 2h of culture on HyalS microdomains and not on Hyal microstructures where they spread on glass substrate around the patterned area. Double photo-immobilised samples characterised by a 100 microm stripe pattern of Hyal or HyalS on the top of a continuous layer of the two polysaccharides were also created in order to investigate the effect of the topography on cell behaviour. The obtained results demonstrated that melanocytes adhered on HyalS stripes while on the Hyal micropatterned surfaces they spread on silanised glass substrate around the structured area, resulting in the exclusion of the topographic pattern.

Outcomes of hyaluronan therapy in diabetic foot wounds

The purpose of this study was to evaluate outcomes of persons with neuropathic diabetic foot wounds treated with a hyaluronan-containing dressing. Data were abstracted for 36 patients with diabetes, 72.2% male, aged 60.0+/-10.7 years and a mean glycated hemoglobin (HbA(1c)) of 9.5+/-2.5% presenting for care at two large, multidisciplinary wound care centers. All patients received surgical debridement for their diabetic foot wounds and were placed on therapy consisting of hyaluronan dressing (Hyalofill, Convatec, USA) with dressing changes taking place every other day. Outcomes evaluated included time to complete wound closure and proportion of patients achieving wound closure in 20 weeks. Hyalofill therapy was used until the wound bed achieved 100% granulation tissue. Therapy was then followed by a moisture-retentive dressing until complete epithelialization. In total, 75.0% of wounds measuring a mean 2.2+/-2.2 cm(2) healed in the 20-week evaluation period. Of those that healed in this period, healing took place in a mean 10.0+/-4.8 weeks. The average duration of Hyalofill therapy in all patients was 8.6+/-4.2 weeks. Deeper (UT Grade 2A) wounds were over 15 times less likely to heal than superficial (1A) wounds (94.7 vs. 52.9%, Odds Ratio=15.9, 95% Confidence Interval=1.7-142.8, P=0.006). We conclude that a regimen consisting of moist wound healing using hyaluronan-containing dressings may be a useful adjunct to appropriate diabetic foot ulcer care. We await the completion of a multicenter randomized controlled trial in this area to either support or refute this initial assessment.

Attachment of hyaluronan to metallic surfaces

Metal implants are in general not compatible with the tissues of the human body, and in particular, blood exhibits a severe hemostatic response. Herein we present results of a technique to mask the surface of metals with a natural biopolymer, hyaluronan (HA). HA has minimal adverse interactions with blood and other tissues, but attachment of bioactive peptides can promote specific biological interactions. In this study, stainless steel was cleaned and then surface-modified by covalent attachment of an epoxy silane. The epoxy was subsequently converted to an aldehyde functional group and reacted with hyaluronan through an adipic dihydrazide linkage, thus covalently immobilizing the HA onto the steel surface. Fluorescent labeling of the HA showed that the surface had a fairly uniform covering of HA. When human platelet rich plasma was placed on the HA-coated surface, there was no observable adhesion of platelets. HA derivatized with a peptide containing the RGD peptide sequence was also bound to the stainless steel. The RGD-containing peptide was bioactive as exemplified by the attachment and spreading of platelets on this surface. Furthermore, when the RGD peptide was replaced with the nonsense RDG sequence, minimal adhesion of platelets was observed. This type of controlled biological activity on a metal surface has potential for modulating cell growth and cellular interactions with metallic implants, such as vascular stents, orthopedic implants, heart valve cages, and more.

Hyaluronate-heparin conjugate gels for the delivery of basic fibroblast growth factor (FGF-2)

The stability and activity of recombinant growth factors administered locally for the repair of damaged tissue can be directly influenced by the physical structure and chemical composition of the delivery matrix. This study describes a novel basic fibroblast growth factor-2 (FGF-2) delivery system synthesized by the conjugation of a structure-stabilizing polymer, hyaluronate (HA), with a sulfated glycosaminoglycan, heparin (HP), that has inherent specific binding sites for members of the FGF family. The biopolymers were formed via stable amine or labile imine bonds by coupling amine-modified HA with oxidized heparin. The addition of recombinant human FGF-2 resulted in the rapid binding of FGF-2 to the heparin segment of the hyaluronate-heparin (HAHP) conjugate. The FGF-2 was released in vitro from the imine-bonded (HAHPi) gels in the form of FGF-2-heparin complexes through the hydrolysis of the imine bonds. In contrast, the release of growth factor from the more stable amine-bonded (HAHPa) gels required treatment with free heparin or enzymatic digestion of the hyaluronate segment. Functional analysis of the released FGF-2 showed that the HAHP conjugate gels increased both the stability and activity of the growth factor.

Micropatterned surfaces for the control of endothelial cell behaviour

Micropatterned materials were synthesised by photoimmobilising the sulphated hyaluronic acid, adequately functionalised with a photoreactive moiety, on glass substrates. Four different patterns (10, 25, 50 and 100 microns) were obtained. The spectroscopic and microscopic analysis of the microstructured surfaces revealed that the photoimmobilisation process was successful, demonstrating that the photomask was well reproduced on the sample surface. Analysis of endothelial cell behaviour on these micropatterned materials was performed in terms of adhesion, locomotion and orientation. Decreasing the stripe dimensions a more fusiform shape of the adhered endothelial cells was observed. At the same time the cell locomotion and orientation were increased. Furthermore, a photoimmobilisation of stripes of HyalS (10 and 100 microns) was performed on a continuous HyalS layer, in turn immobilised on glass substrate. Being excluded a different chemistry between the stripe and the substrate, the influence of topography on the behaviour of endothelia cells was thus envisaged.

In vitro study of blood-contacting properties and effect on bacterial adhesion of a polymeric surface with immobilized heparin and sulphated hyaluronic acid

The blood-contacting properties and the effect on bacterial adhesion of a material based on polyurethane and poly(amido-amine) (PUPA), both in its native form and with the anticoagulant molecules heparin or sulphated hyaluronic acid (HyalS3.5) electrostatically bonded to its surface, were evaluated and compared in vitro. The presence of the biological molecules on the surface was revealed by a dye test and ATR/FTIR analysis. Bound heparin was found to maintain its physiological action, in terms of thrombin inactivation, as well as did free heparin. Moreover, it reduced the degree of platelet adhesion. On the contrary, bound HyalS3.5 lost its anticoagulant activity, though it reduced platelet adhesion. The number of platelets on both modified surfaces was low. Their shape distribution, as determined by SEM, did not differ significantly on the two modified surfaces or with respect to the bare PUPA surface. HyalS3.5 and heparin also inhibited adhesion of Staphylococcus epidermidis to the material. A possible relationship between the platelet and bacterial adhesion is ascribed to the mediating role of plasma proteins.

Synthesis, chemical and rheological characterization of new hyaluronic acid-based hydrogels

New hyaluronic acid-based hydrogels have been synthesized. The carboxylate groups of hyaluronan were activated in order to bind the amino terminal groups of the di-amine cross-linking reagent. Different hydrogels were obtained according to the different di-amine cross-linking agents (1,3-diaminepropane, 1.6-diaminohexane, PEG500 di-amine. and PEG800 di-amine). The cross-linked polymer (C.L.Hyal) was then sulphated (C.L.HyalS) by a heterogeneous reaction using sulphur trioxide pyridine complex (SO3-Py). The thermo-mechanical properties and swelling degree were evaluated and are discussed in relation to the chemical structure and the hydrophilic character of the gels. The different behaviours of C.L.Hyal and C.L.HyalS indicate the important role of sulphated groups.

Cu(II) and Zn(II) complexes with hyaluronic acid and its sulphated derivative. Effect on the motility of vascular endothelial cells

With the aim of improving the compatibility of biomaterials to be used for the construction of cardiovascular prosthesis, we have designed bioactive macromolecules resulting from chemical modifications of hyaluronic acid (Hyal). The stability constants of Cu(II) and Zn(II) complexes with the sulphated derivative of hyaluronic acid (HyalS3.5) were evaluated. Two different complexes have been found for each metal ion, CuL, Cu(OH)2L and ZnL, Zn(OH)2L (L means the disaccharide unit of the ligands) in aqueous solution at 37 degrees C. The dihydroxo Cu(II) complex was present in high percentage at pH=7.4. On the contrary, the Zn(II) ion was present with a relatively low percentage of both complexes. The ability to stimulate endothelial cell adhesion and migration was evaluated for Hyal, HyalS3.5 and their complexes with Cu(II) and Zn(II) ions. The results revealed that Hyal and [Cu(OH)2HyalS3.5](4.5)- induced cell adhesion, while [ZnHyalS3.5](2.5)- and [Zn(OH)2HyalS3.5](4.5)- inhibited the process. The chemotactic activity of increasing concentrations of the above complexes was also evaluated, demonstrating that [Cu(OH)2HyalS3.5](4.5)- complex at 1 microM concentration was the most active in inducing cell migration. These results have been also strengthened by analysing adherent cell migration in agarose. In conclusion, sulphated hyaluronic acid coordinated to Cu(II) seems to be a promising matrix molecule for the construction of cardiovascular prosthesis.

Immobilisation of sulphated hyaluronan for improved biocompatibility

Hyaluronan (Hyal) was modified by the insertion of sulphate to hydroxyl groups. A series of heparin-like compounds with controllable properties was obtained. The physicochemical and biological behaviours of all these sulphated hyaluronan acids (HyalSx) and their complexes with heavy metal ions (Cu2+ and Zn2+) were investigated. HyalS, derivatives showed a good anticoagulant activity and low platelet aggregation which increased with increasing degree of sulphation. Moreover HyalSx and their Cu2+ complexes were demonstrated to favour the growth of human endothelial cells. However, the utilisation of HyalSx as a material is hindered by its high solubility in physiological solution. Our approach to improve its stability was directed to the synthesis of new HyalSx-based hydrogels and on the preparation of new biocompatible polymeric surfaces obtained through covalent photoimmobilisation of HyalSx. The reaction of primary ovine chondrocytes and B10D2 endothelial cells was studied on both matrices in terms of cell number, F-actin and CD44 receptor immunostaining. Analysis of cell movement showed that the cells respond to HyalSx showing good adhesion and spreading. These results suggest that HyalSx containing materials could be used as biomaterials to aid cartilage repair and vessel endothelisation.