SEARCH Articles Figures Tables Controlled-release delivery systems gastrointestinal tract Gastrointestinal Drug Delivery Gastrointestinal delivery systems Gastrointestinal delivery systems chitosan Gastrointestinal tract drug delivery Gastrointestinal tract drug delivery absorption Gastrointestinal tract drug delivery forms Gastrointestinal tract drug delivery small intestine Gastrointestinal tract drug delivery stomach Gastrointestinal tract, oral drug delivery Local gastrointestinal delivery