Education and Human Sciences, College of (CEHS)


Date of this Version

Spring 3-2009


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy; Major: Human Sciences. Under the Supervision of Professor Yiqi Yang
Lincoln, Nebraska: May, 2009
Copyright (c) 2009 Weijie Xu.


Drug release and its relationship with kinetic and thermodynamic parameters of drug sorption onto biodegradable and biocompatible fibers made of polylactic acid (PLA), starch acetate (SA), wheat gluten (WG) and soy protein (SP) have been studied using Diclofenac, 5 Fluorouracil (5-Fu) and Metformin as drug models. To understand drug release from these four fibers using sorption, kinetic and thermodynamic parameters, such as the diffusion coefficient, activation energy for diffusion, affinity, and sorption enthalpy and entropy, have been investigated. Quantitative relationship between drug release and drug loading concentration, affinity, and activation energy for diffusion was established to predict initial bursts and later drug release. In addition, the dissolution method was used to compare with the sorption method.

The study showed that high temperature led to high diffusion coefficient for three drugs and Diclofenac had the lowest diffusion coefficient on four different fibers. WG and SP fibers had fast drug sorption rates, followed by SA and PLA fibers. The results also showed that increasing temperature increased the sorption amount for all three drugs onto PLA and SA fibers and increased Diclofenac and Metformin sorption amount onto WG and SP fibers, while increasing temperature decreased 5-Fu sorption amount onto WG and SP fibers. It also has been found that the sorption method has at least similar drug release rates with the dissolution method.

The research showed that drug loaded PLA fibers had the lowest initial bursts and the most constant drug release rates, followed by SA, WG and SP. The results also showed that lower drug loading concentration led to the lower initial burst and more constant subsequent release. Diclofenac had the most constant release from PLA and SA fibers. It has been found that high drug loading temperature leads to the most constant release from PLA and SA fibers. Diclofenac and Metformin had high initial bursts in phosphorous buffered saline (PBS) but more constant release in artificial gastric juice (AGJ). It also has been found that drugs with lower activation energy for diffusion and higher affinity (especially van der Waals force) on fibers are more suitable for sorption loading to achieve higher loading capacity and more constant releasing rate.