Size, shape, charge and "stealthy" surface: Carrier properties affect the drug circulation time .

The present review sets out to discuss recent developments of the effects and mechanisms of carrier properties on their circulation time. For most drugs, sufficient circulation time is the basis of high bioavailability. Drug carrier plays an irreplaceable role in helping drug avoid being quickly recognized and cleared by mononuclear phagocyte system, to give drug enough time to arrive at targeted organ and tissue to play its therapeutic effect. The physical and chemical properties of drug carriers, such as size, shape, surface charge and surface modification, would affect their circulation time, metabolic behavior and biodistribution. The final circulation time of carriers is determined by the balance between macrophage recognitions, blood vessel penetration and urine excretion. Therefore, when designing the drug delivery system, we should pay much attention to the properties of drug carriers to get enough circulation time to arrive at target site eventually. This article mainly reviews the effect of carrier size, size, surface charge and surface properties on its circulation time , and discusses the mechanism of these properties affecting circulation time. This review has reference significance for the research of long-circulation drug delivery system.