Novel amphiphilic hyaluronic acid derivatives as injectable hydrogels for controlled drug release

摘要

Introduction: In the treatment of arthritis, drug delivery systems are of mayor interest since they ensure a controlled release of the active substance in the region of interest. Moreover one possible and often used treatment of osteoarthntis is by intra-articular injection of hyaluronic acid (MA) in order to restore the elastic and viscous properties of the synovial fluid. A significant research effort has been devoted to alter the HA physic-chemical and viscoelastic properties by chemical modification. The idea of this study was to combine viscosupplementation approach with the controlled delivery of an anti-inflammatory drug in situ. In this work we tested the potential use of chemically modified HA as viscosupplementation agent and at the same time able to control the release of an anti-inflammatory hydrophobic drug. To this aim, modified HA samples were characterized from a rheological point of view. The solubility of a hydrophobic drug was studied and its in vitro drug release kinetics was evaluated. Experimental Methods: A HA derivative bearing respectively ethylenediamino (EDA) and octadecyl pendant groups (HA-EDA-C18) was obtained as elsewhere reported. As anti-inflammatory drug dexamethasone (DM) (Sigma-Aldrich), was chosen. HA-EDA-C18 based samples were prepared at different polymer concentrations (1%, 3% and 5% w/v) in bidistilled water (DDW) and Dulbecco's Phosphate-Buffered Saline (DPBS). To improve the solubility of both HA-EDA-C18 and DM, also β-CD (Sigma-Aldrich), at different concentrations (1%, 2% w/v) were used. The viscoelastic properties of the samples were evaluated on a rotational rheometer (Mars HAAKE Ⅲ, Thermoscientific, Germany) at 25°C. HA-EDA-C18 samples were subjected to small amplitude frequency sweep tests to evaluate the dependence of the elastic and viscous moduli, G' and G" upon frequency. Solubility tests were carried out by dissolving DM (0.05%), HA-EDA-C18 and β-CD in DDW and DPBS. DM release from HA-EDA-C18 samples was studied by loading the gel in dialysis membranes (molecular cut off: 25 kDa), which were immersed in DPBS at 37 °C. At different time points, the release medium was withdrawn and analyzed by UV. Results and Discussion: HA-EDA-C18 samples showed a rheological behavior typical of a weak gel. The mechanical spectra was characterized by a elastic modulus G' greater than loss modulus G" in all frequency range. In particular for the sample characterized by HA-EDA-C18 concentration of 3% w/v and β-CD of 1% w/v, at a frequency of 1 Hz, G' was about 185 Pa and G" about 50 Pa. Furthermore the viscoelastic properties of HA-EDA-C18 samples were dependent upon polymer concentration. The increase in HA-EDA-C18 concentration leads to an increase of both G' and G". The drug solubility tests showed that the presence of hydrophobic groups on HA influenced the drug solubilization positively. The release tests have shown that the presence of HA-EDA-C18 leads to an increase of the percentage of drug released until reaching a plateau after one week. Conclusion: Amphiphilic HA derivative was able to solubilize hydrophobic drug and showed rheological properties of weak gel suitable for viscosupplementation applications. Moreover it was able to sustain the release of an anti-inflammatory drug for at least one week.