The primary function of the cell membrane is to protect cells from their surroundings. This entails a strict regulation on controlling the exchange of matter between the cell and its environment. A key factor when considering potential biological applications of a particular chemical structure has to do with its ability to internalize into cells. Molecules that can readily cross cell membranes are frequently needed in biological research and medicine, since most therapeutic entities are designed to modulate intracellular components. However, the design of molecules that do not penetrate cells is also relevant toward, for example, extracellular contrast agents, which are most widely used in clinical diagnosis.

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纳米颗粒与小分子的细胞吸收：大小问题

细胞膜的主要功能是保护细胞免受周围环境的侵害。这需要严格控制细胞及其周围环境之间的物质交换。在考虑特定化学结构的潜在生物学应用时，一个关键因素与其内在进入细胞的能力有关。在生物学研究和医学中，经常需要能容易地穿过细胞膜的分子，因为大多数治疗实体被设计为调节细胞内成分。但是，不渗透细胞的分子的设计也与例如细胞外造影剂有关，细胞外造影剂是临床诊断中最广泛使用的。