Effect of sodium chloride on the mechanical and osmotic properties of silicone matrices

Abstract

Sodium chloride has been suggested as a hydrophilic osmotic additive for controlling drug release from silicone polymers. In this study, the effect of sodium chloride on the mechanical and osmotic properties of silicone matrices and release of model drug from these matrices was evaluated. The addition of sodium chloride reduced the tensile strength of the matrices, shortened their elongation at break and increased the elastic modulus. Although the matrices became less flexible and brittle, their mechanical properties were acceptable for controlled release systems. In the beginning of sodium chloride release the crystals on the surface of the matrix dissolved rapidly. Then water was osmotically imbibed into the matrix and a continuous network of water channels was formed. This process was dependent on the amount and size of sodium chloride particles in the matrix. Sodium chloride was released at a constant rate when fixed osmotic pressure was maintained inside the network. When the sodium chloride particles in the matrix had dissolved, the release rate decreased until sodium chloride had diffused from the matrix. Corresponding phases were noticed during swelling of the matrices. The rates of matrix swelling and sodium chloride release were lower in vivo on the skin surface than they were in vitro. This was due to the smaller amount of water available.