rheological and tensile properties of sodium hyaluronate hydrogels ...

RHEOLOGICAL AND TENSILE PROPERTIES OF SODIUM HYALURONATEHYDROGELS AND FILMSCalles J.A. 1 , Ressia J.A. 1,2 , Llabot J.M. 3 , Allemandi D.A. 3 , Palma S.D. 3 , Vallés E.M. 1,#1 Planta Piloto de Ingeniería Química (UNS-CONICET), Cam. La Carrindanga, Km. 7, Bahía Blanca,Argentina.2 Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC), La Plata, Argentina.3 Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba,Córdoba, Argentina.INTRODUCTIONThe hyaluronic acid sodium salt, also called hyaluronan (HA), is a naturally occurring high molecular masslinear polysaccharide, consisting of alternating units of N-acetyl-β-D-glucosamine (GlmNAct) and β-Dglucuronicacid (GlcAc). HA is distributed in the human body forming part of synovial fluid, skin, umbilicalcord and vitreous humor; and widely used in medical practice in many pathological conditions such asosteoarthritis, wound repair and eye surgery (1-5). Several studies related to biocompatibility andbiodegradability (6) have suggested the use of HA as a promising biomaterial to design modified drugdelivery systems with ophthalmic applications. In this work we present preliminary studies in order toevaluate rheological and mechanical properties of hydrogels and films based on HA prior to further structuralmodification needed to improve the biomechanical properties of HA.MATERIALS AND METHODSHA solutions were prepared at 1, 2 and 4% w/w concentrations using distilled water as solvent. Additionalsolutions were also prepared containing 2% w/w HA and different concentrations - 0.25, 0.5 and 1% w/w - ofpolyethyleneglycol 400 (PEG) (Merk). The solutions have pH near 6, avoiding polymer degradation (7,8).Hydrogel films from the 2% w/w HA and 2% w/w HA/PEG solutions were prepared by casting at roomtemperature. The rheological characterization of the different solutions was carried out in small-amplitudeoscillatory shear flow using a rotational rheometer from TA Instruments (AR-G2) 25°C. Stress-strain plotswere obtained in an Instron 3369 tester in traction mode at 2 mm/min at room conditions (23°C and 40%relative humidity).RESULTSBoth storage (G´) and loss (G´´) modules values increase with HA concentration. In all cases, the module G´´at low frequencies is higher than G´ to certain point where the crossover of the G´and G” curves occurs.Increasing HA concentration moves the crossover point toward lower frequencies indicating an earliertransition from viscous-like towards elastic behavior. This shift is less significant in HA/PEG solutions. Theincorporation of PEG slightly increases the magnitude of G´ and G´´ on the whole frequency range, althoughno significant difference was observed with different PEG concentrations used in this work.Table 1 shows elongational properties for the pure HA films and those containig 11, 20 and 33% w/w ofPEG. Multiple dog-bone shaped probes for each sample were tested in order to obtain mean values for eachproperty. Increasing PEG content diminish the elastic modulus inducing a change from fragile to ductilebehavior characterized by a yield zone at low deformations followed by drawing with no significant changesin the nominal stress up to the rupture point.Future adhesion assays will be performed to complete preliminary studies.ACKNOWLEDGMENTSThe authors thank financial support from Universidad Nacional de Sur (UNS), the Consejo Nacional deInvestigaciones Científicas y Técnicas (CONICET), and the Comisión de Investigaciones Científicas de laProvincia de Buenos Aires (CIC) .REFERENCES# Corresponding author. Tel +54 291 4861700, fax +54 291 4861600; e-mail: valles@plapiqui.edu.ar

(1) L. Ambrosio, A. Borzacchiello, P.A. Netti and L. Nicolais. Properties of new materials: Rheological studyon hyaluronic acid and its derivative solutions. J. Macromol. Sci. – Pure Appl. Chem 1999; 36: 991–1000.(2) E.A. Balazs and J.L. Denlinger, Viscosupplementation: A new concept in the treatment of osteoarthritis, J.Rheumatol. Suppl. 1993; 39: 3–9.(3) A. Borzacchiello, L. Mayol, O. Garskog, A. Dahlqvist and L. Ambrosio, Evaluation of injectionaugmentation treatment of hyaluronic acid based materials on rabbit vocal folds viscoelasticity, J. Mater. Sci.– Mater. Med. 2005; 16: 553–557.(4) M. Brown and S. Jones, Hyaluronic acid: a unique topical vehicle for the localized delivery of drugs to theskin, J. Eur. Acad. Dermatol. Venereol. 2005; 19: 308–318.(5) W.Y.J. Chen and G. Abatangelo, Functions of hyaluronan in wound repair, Wound Repair Regen. 1999; 7:79-89.(6) Teresio Avitabile, Filippo Marano, Francesco Castiglione, Claudio Bucolo, Melina Cro, Luigi Ambrosio,Carmelo Ferrauto and Alfredo Reibaldi, Biocompatibility and biodegradation of intravitreal hyaluronanimplants in rabbits. Biomaterials. 2001; 22: 195-200.(7) Atoosa Maleki, Anna-Lena Kjøniksen, Bo Nyström, Effect of pH on the behavior of hyaluronic acid indilute and semidilute aqueous solutions, Macromol. Symp. 2008; 274: 131–140.(8) Iuliana Gatej, Marcel Popa, and Marguerite Rinaudo. Role of the pH on Hyaluronan Behavior in AqueousSolution. Biomacromolecules 2005, 6, 61-67.Table 1. Elongational propertiesSampleThickness Elastic modulus Maximum Tensile Yield Stress (MPa)(m)(MPa)Strain (%)2% HA 38 ± 3 2564 ± 165 10.9 ± 2.3 77.9 ± 2.72% HA – 0.25% PEG 42 ± 3 2061 ± 282 17.1 ± 0.7 65.3 ± 4.52% HA – 0.5% PEG 47 ± 3 1593 ± 158 29.7 ± 2.6 48.1 ± 4.92% HA – 1.0% PEG 59 ± 5 853 ± 91 50.9 ± 4.9 26.4 ± 2.4