A composition comprising nanoparticles of a hydrolysable silicon-contain material for use as a delivery system for a bioactive ingredient, wherein surface of the silicon- containing material is associated with a stabilizing agent which modifies the rate of hydrolysis of the silicon-contain material and/or inhibits the rate of orthosilicic acid polymerisation and a method of promoting the controlled release of orthosilicic acid on degradation of a composition comprising nanoparticles of a hydrolysable silicon- contain material, the method involving the treatment of the surface of the silicon-containing material with a stabilizing agent to modify the rate of hydrolysis of the silicon-containing material and/or inhibit the rate of orthosilicic acid polymerisation.
