Chitosan/chemistry; Drug Carriers; Glycerophosphates/chemistry; Hypoglycemic Agents/administration & dosage; Hypoglycemic Agents/pharmacokinetics; Metformin/administration & dosage; Metformin/pharmacokinetics; Adhesiveness; Administration, Oral; Animals; Area Under Curve; Biological Availability; Calorimetry, Differential Scanning; Chemistry, Pharmaceutical; Chitosan/analogs & derivatives; Delayed-Action Preparations; Gastric Mucosa/metabolism; Hypoglycemic Agents/chemistry; Intestinal Absorption; Intestinal Mucosa/metabolism; Liposomes; Male; Metformin/chemistry; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Rats; Rats, Wistar; Rheology; Solubility; Technology, Pharmaceutical/methods; X-Ray Diffraction