Research Progress of Mesoporous Silica in Drug Delivery Systems

In recent years, the development of nanotechnology has brought about the dawn of overcoming many problems of traditional clinical drugs such as low solubility, weak selectivity, biodistribution and poor pharmacokinetics. Currently, a variety of nanomaterials such as silica, liposomes, carbon materials, layered hydroxides, and polymers have been reported as carriers for drug delivery. However, these new drug delivery systems still have many defects. For example, direct mixing of the silica sol and the drug results in heterogeneous dispersion of the drug, thereby causing the drug release rate to be affected by the sample batch. Liposomal carriers are less stable and are easily cleared by the reticuloendothelial system, resulting in fewer drugs reaching the lesion area. In addition, studies have shown that some cross-linked chitosan microspheres have poor biocompatibility. Therefore, the ideal nano drug carrier system should meet the basic conditions of good biosafety, stable structure and controlled release properties.

In 2001, Vallet-Regí et al. first proposed the use of mesoporous material MCM-41 (Mobil composition of matter-41) as a new drug delivery system, which led to the research boom of mesoporous silica as a drug delivery vehicle. Studies have shown that mesoporous silica has a variety of excellent physical and chemical properties, such as good biocompatibility in vivo and in vitro, and thermal stability, making it very suitable for pharmaceutical carriers. Its structural advantages, such as adjustable pore size, high pore volume and high specific surface area, ensure the payload and packaging of multiple drug molecules. In addition, by further functional modification of mesoporous silica, it can be responsive to certain external stimuli (such as pH, redox environment, temperature, light, and ultrasound.), thereby enabling drug loading of targeted release. However, mesoporous silica drug delivery systems also have some problems to be solved. First, although conventional PEGylation can reduce the non-specific uptake of mesoporous silica to some extent, its widespread accumulation in non-targeted organs such as the liver and spleen is still unavoidable. Therefore, it is necessary to explore new targeting ligands to modify mesoporous silica to enhance its accumulation in targeted cells and organs. Secondly, in order to achieve therapeutic purposes, it is usually necessary to continue administering the drug multiple times to achieve an effective drug concentration, so the degradation properties of mesoporous silica are particularly important. Although mesoporous silica can be metabolized to a cleavable silicate, in most cases it is biodegraded very slowly and, therefore, its degradation properties still need to be further improved. Finally, even though mesoporous silica has been proven to have good biocompatibility in some in vitro and in vivo studies, its biosafety is far from certain due to the complex physiological environment of the human body. It still has enormous challenges in clinical application. And in addition to acute toxicity, chronic toxicity (such as genetic toxicity) caused by mesoporous silica cannot be ignored, but studies on the effects of mesoporous silica on embryonic development are still rare. It is believed that as the research progresses further, the above problems can be solved in turn, so that the prospect of using mesoporous silica for drug delivery systems is broader.