The invention discloses a biocompatible polymeric matrix which is functionalized through the reaction with a functionalizing agent including protonated carboxylic acid groups. There is also disclosed a method of preparation of the polymeric matrix and a pharmaceutical composition including the matrix as a carrier for controlled release of a bioactive agent. The pharmaceutical composition is suitable for immobilizing and protecting the bioactive agent from denaturing factors, and can take various forms such as tablets, spheres, films, hydrogels, and emulsions.