peptides, evaluation of release mechanism and comparison of release rate of cefalexin antibiotic under different conditions Mahsima Zeraaty m.zeratishamsabadi@ce.iut.ac.ir Date of submission: July 3, 2019 Department of chemical engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Farsi Supervisor: Prof.seyyed Mohammad Ghoreishi, ghoreshi@cc.iut.ac.ir Today, due to the growing need to use antibiotics as an agent for the elimination of infections and bacteria and besides, existence of side effects such as: long-term drug resistance and sudden release of drug at high concentrations during using, demand for using controlled drug release system is increasing. Drug delivery systems, as the name implies, are systems in which drug is delivered at a specified amount and rate at a specific location, so this controlled release automatically cause reducing consumables dose and increasing effectiveness of drug. Among drug carrier nanostructures, peptide – based nanostructures have received more attention because of their easy structure and synthesis. So for this purpose, diphenylalanine peptide was used for synthesizing nanostructure hydrogel and cephalexin was used as a drug model. Initially, the hydrogel structures were synthesized by a combination of different solvents, among which, according to the results of FESEM and FTIR analyzes, the hydrogel structure was combined with 25% Ethanol + 75% Toluene based on formation of better hydrogel structure was selected for experiment. ubsequently, 20, 40 60 ppm concentrations of the drug were loaded into hydrogel and then by spectrophotometric analysis, due to loading 99% of the 20 ppm concentration into the hydrogel structure, this concentration was selected as an optimum concentration (the concentration where the highest percentage of loading occurs). It was also found that the percentage of drug was loaded into hydrogel structure was decreased when drug concentration was increased. In the following, at two steps, released drug from selected hydrogel sample was examined. At first step, three concentrations of 20, 40 60 ppm of drug were loaded into hydrogel structure and after that the percentage of drug was released based on time and delivery mechanism were determined. During this step, by interprenting the results were obtained with Korsmeyer –Pepas equation and n values ( release power) obtained for the three concentrations of 20,40 and 60 ppm respectively are 0.7, 0.67 0.75 (all are larger than 0.5) was observed that the mechanism of drug delivery was non-ficken (penetration with dissolution of polymeric network) and also according to drug delivery percentage diagram based on time, it was found that drug delivery has been explosive at first 2 hours, which is very useful for releasing antibiotics to speed up the elimination of infection and bacteria. At final step, the percentage drug delivery from hydrogel structure with optimum concentration (20ppm) at two pH = 1.2 7.4 was investigated that percentage of drug released was increased with pH increasing