Adapted nano-carriers for gastrointestinal defense components: surface strategies and challenges

Nano-carriers (NCs) provide drugs with protective and oriented strategies. Despite their success in parenteral administration, NCs still need to be optimized to meet the more serious obstacles encountered in the gastrointestinal tract (GIT). The main defense mechanisms include renewing mucus, epithelial obstacles and digestion by GIT segments. These hurdles pose challenges even before NCs target molecules or proteins, which has often led to unsatisfactory delivery efficiency. Therefore, a critical focus is the exemption from negative effects of GIT. A series of adapted NCs have been designed based on surface strategies to form an expected distribution and increase gastrointestinal utilization. In this paper, we review the strategies and efforts of NCs to adapt to gastrointestinal defense components, including the mucus, epithelium and gastrointestinal segments; the related gastrointestinal mechanisms and functions are also summarized synchronously. Last, we discuss the delivery challenges in terms of physiopathological GIT and surface properties of the NCs.