Research progress on the performance of expandable systems for long-term gastric retention.

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Gastroretentive systems have gained attention due to their prolonged retention time in the human body, and they have the potential to improve treatment effects, simplify treatment regimens, and improve patient compliance. Among these systems, expandable gastroretentive systems (EGRSs) have emerged as an important type of carrier that can reside in the stomach for a desired period through on-demand expansion for drug delivery, obesity intervention, and medical diagnosis. As the physiological environment significantly influences the performance of EGRSs, here, the physiological factors such as the stomach's physiological structure and activity pattern, and the character of gastric juice are summarized. Following this, the research progress of EGRSs from ingestion to removal for long-term gastric retention is discussed with respect to the influencing factors and reinforcement strategies in mechanics. Additionally, as the duration of gastric retention increases, safety concerns arise. As such, safety issues in terms of removal after retention or in an emergency are also analyzed. Finally, the biomedical application of EGRSs as diagnostic and therapeutic tools and the potential direction for further research are discussed. STATEMENT OF SIGNIFICANCE: Expandable gastroretentive systems (EGRSs) resist gastric emptying due to their size exceeding the pylorus diameter, offering promising advantages for obesity intervention, drug delivery, and carrying sensors. However, a long gastroretentive time only by such a size mismatch is hard to be achieved due to the uninterrupted stomach contraction and gastric juice erosion. Recent studies indicate that the retention time and stability of EGRSs can be regulated by adjusting their mechanical properties. Hence, this review summarizes the state-of-art progress of EGRSs for long-term gastric retention from a mechanical perspective for the first time, focuses on material components and synthesis methods, and the reinforcement strategies, and suggests the required mechanical property parameters of EGRSs.