Rheological and tensile properties of sodium hyaluronate hydrogels and films

CALLES JAVIER; RESSIA JORGE; LLABOT JUAN MANUEL; ALLEMANDI DANIEL; PALMA SANTIAGO; VALLES ENRIQUE

Córdoba

Congreso; 1era Reunión Internacional de Ciencias Farmacéuticas; 2010

Facultad de Ciencias Químicas - UNC

INTRODUCTION The hyaluronic acid sodium salt, also called hyaluronan (HA), is a naturally occurring high molecular mass linear polysaccharide, consisting of alternating units of N-acetyl-2-D-glucosamine (GlmNAct) and 2-Dglucuronic acid (GlcAc). HA is distributed in the human body forming part of synovial fluid, skin, umbilical cord and vitreous humor; and widely used in medical practice in many pathological conditions such as osteoarthritis, wound repair and eye surgery (1-5). Several studies related to biocompatibility and biodegradability (6) have suggested the use of HA as a promising biomaterial to design modified drug delivery systems with ophthalmic applications. In this work we present preliminary studies in order to evaluate rheological and mechanical properties of hydrogels and films based on HA prior to further structural modification needed to improve the biomechanical properties of HA. MATERIALS AND METHODS HA solutions were prepared at 1, 2 and 4% w/w concentrations using distilled water as solvent. Additional solutions were also prepared containing 2% w/w HA and different concentrations - 0.25, 0.5 and 1% w/w - of polyethyleneglycol 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 room temperature. The rheological characterization of the different solutions was carried out in small-amplitude oscillatory shear flow using a rotational rheometer from TA Instruments (AR-G2) 25°C. Stress-strain plots were obtained in an Instron 3369 tester in traction mode at 2 mm/min at room conditions (23°C and 40% relative humidity). RESULTS Both 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 earlier transition from viscous-like towards elastic behavior. This shift is less significant in HA/PEG solutions. The incorporation of PEG slightly increases the magnitude of G´ and G´´ on the whole frequency range, although no 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 of PEG. Multiple dog-bone shaped probes for each sample were tested in order to obtain mean values for each property. Increasing PEG content diminish the elastic modulus inducing a change from fragile to ductile behavior characterized by a yield zone at low deformations followed by drawing with no significant changes in the nominal stress up to the rupture point. Future adhesion assays will be performed to complete preliminary studies.