Glycerol

Insulatard Penfil (INS) 100 IU/mL (human insulin, isophane, long-acting; excipients: zinc chloride, glycerol, metacresol, phenol, disodium phosphate dihydrate, sodium hydroxide, hydrochloric acid, protamine sulphate, water for injection) was purchased from Novo Nordisk (Bagsværd, Denmark). Sepineo™ P 600 and Sepineo™ PHD 100 were donated by Seppic (Paris, France). glycerol 85% was purchased from Galfarm (Krakow, Poland). Phosphate-buffered saline (PBS) pH = 7.4 was purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). All chemicals used in the study were of analytical grade. The Strat-M^® membrane was purchased from Merck Millipore (Burlington, MA, USA).

Insulin Actrapid Penfill 100 j.m./mL (the other ingredients were zinc chloride, glycerol, metacresol, sodium hydroxide, hydrochloric acid, and water for injections) was purchased from Novo Nordisk (Bagsværd, Denmark). Carbopol^® Ultrez^TM 10 (INCI: Carbomer) and Carbopol^® Ultrez^TM 30 (INCI: Carbomer) were purchased from Lubrizol (Cleveland, OH, USA). Carbopol^® Ultrez™ 10 and Carbopol^® Ultrez^TM 30 were cross-linked polyacrylic acid polymers. Methyl cellulose was purchased from Fluka Chemie, Buchs, Switzerland. Wheat starch was purchased from PPH Galfarm (Kraków, Poland). glycerol was purchased from Pharma Cosmetic, Poland. Ethanol was purchased from Alpinus Chemia, Poland. Triethanolamine (TEA) was purchased from Chempur, Śląskie, Poland. Sodium chloride was purchased from POCH, Gliwice, Poland. All chemicals and solvents used for the study were of analytical grade.