Hasan, I.; Paul, S.; Akhter, S.; Ayon, N. J.; Reza, M. S. Evaluation and Optimization of Influence of Permeability Property and Concentration of Polymethacrylic Polymers on Microspheres of Metformin HCl. Dhaka Univ. J. Pharm. Sci 2014, 12, 131-141.