Drug Adsorption And Release Pattern From Mesoporous Silicas

The primary objective of this research is to examine the feasibility of using a new kind of anionic-templated mesoporous silica (AMS) as a drug delivery system, and to characterize the factors affecting adsorption and release into and from this material. AMS possesses a series of unique characteristics such as large surface area, uniform and designable pore size and pore type, functionalized pore channel surface and nontoxicity. These features offer a series of facts for rational design of AMS as drug delivery carriers. In this article, we used the AMS with amino-group modified, to load model drug with carboxylic groups, aiming at studying how these amino groups and pore size affect drug adsorption and release pattern.Cephalexin was chosen as the model drug in this article. Cephalexin was loaded in the channel of AMS through mechanical mixing. Pore size and surface properties were modified to study their influences on drug loading amounts and release rates. Nitrogen adsorption/desorption data showed that the pore size, pore volume and surface area of AMS all decreased after drug adsorption, while drug-loading amounts increased with pore size. It was found through XRD analysis that drug adsorption did not destroy the crystal structure of AMS. As the amino groups in the AMS-ex samples were retained through extraction, AMS-ex samples displayed good selectivity in adsorbing cephalexin as they adsorbed more cephalexin than AMS-cal samples that were obtained through calcination. It was found through FTIR analysis that AMS-cal samples adsorb cephalexin physically, while AMS-ex samples adsorbed cephalexin both physically and chemically. Both AMS-cal and AMS-ex samples showed controlled release pattern in the in-vitro experiments, while AMS-ex samples showed longer release period due to the existence of amino groups. Pore sizes were also crucial in the release experiments as the release rates and release amounts were both proportional to the pore diameters of AMS. In the third chapter of this article, we changed release temperature to study the release solution from AMS/cephalexin samples: with high performance liquid chromatography and mass spectrometry, we reached a conclusion that standard cephalexin water solution was stable in the range of 25℃to 47℃, however the cephalexin released from AMS-ex in 47℃broke down after 24 hours while kept unchanged before 24hrs; meanwhile the 24hrs 25℃released drug was also unchanged. This means that the chemical adsorption into AMS-ex would probably cause break down of cephalxin. However, AMS-cal/cephalexin preparation would maintain drug structure as cephalexin was adsorbed physically.From our experiments results, it could be concluded that the pore size and surface properties were the major factors that influenced drug adsorption and desorption. The non-toxic AMS performed rather high drug loading amount and controlled release pattern, which enabled it as a potential candidate for drug carrier.