Corrosion Behavior And Controlled Release Of Cupric Ion Of Copper/LDPE Nanocomposites In The Simulated Uterine Solution

Being safe, effective, economic, reversible and simple, intrauterine device (IUD) is one of the most popular contraceptive methods that are used all around the world. IUD can be divided into two categories, namely, the inert and the active one. Owing to its weak effect of contraceptive, the inert IUD has been replaced gradually with the active one. The active IUD covers copper-containing IUD (Cu-IUD) and drug slow-release IUD. Recently, Cu-IUD has been widely investigated and employed due to great contraceptive effect of copper. During the employment of more than thirty years, the conventional Cu-IUD exhibited some inherent disadvantages as follows. Firstly, effective utility ratio of copper contained in IUD is rather low. Secondly, burst release of Cu²⁺ in the first few months after insertion occurs. Finally, release rate of Cu²⁺ cannot be controlled. These defects may bring about several complications such as bleeding, expulsion and pelvic infections. To overcome the limitations of conventional materials of Cu-IUD, a novel IUD material, namely, low density polyethylene (LDPE) matrix nanocomposite filled with copper nanoparticles were successfully designed and prepared. The corrosion behavior and Cu²⁺ release property of this composite in the simulated uterine solution were investigated systemically. Cu²⁺ transformations of Cu and its oxide particles with different sizes in the simulated uterine solution were investigated by absorbance measurement. The corrosion intermediate of copper nanoparticles in the simulated uterine solution was determined by using X-ray diffraction (XRD) technique. The results show that, when compared with copper microparticles and bulk copper, copper nanoparticles can increase Cu²⁺ transformation ratio greatly in the simulated uterine solution with the maximum being over 98 %. Moreover, nanoparticles of CuO and Cu2O can be further transformed into Cu²⁺ with transformation ratio over 90 %. The reason for high transformation ratio together with the transformation mechanism of nanoparticles was discussed. The fact that copper nanoparticles displayed high Cu²⁺ transformation rate in the simulated uterine solution has created a good condition for preparation of novel IUD material, which solves the problem of low effective utility ratio of Cu and provides practical evidence for copper nanoparticles to be applied in contraceptive in future. Given that the metal particles are enwrapped by polymer, the corrosion rate of the particles in media would be slow down and the release of soluble corrosion products could be controlled. In view of this, Copper/LDPE nanocomposite was prepared with copper nanoparticles and low density polyethylene. Distribution of copper nanoparticles in Copper/LDPE nanocomposite, composition of corrosion products and release of Cu2+ in the simulated uterine solution were studied by absorbance measurement, scanning electron microscopy (SEM) and XRD. The results indicate that Cu2+ release rate of Copper/LDPE nanocomposite in the simulated uterine solution can be controlled through modifying the copper nanoparticle mass fraction. The results of volume resistivity and Cu2+ release behavior confirm that continuous network of copper nanoparticles can be obtained in composites when the mass fraction of copper nanoparticles ranges from 30 % to 35 %. It is found out by comparison that nanocomposite is superior to microcomposite in respect of Cu2+ release behavior and composite composition adjustment. Cu2+ release rate of nanocomposite decreases with the increasing of pH value of the simulated uterine solution. In the simulated uterine solution, the corrosion mechanism of composite is almost the same as that of copper nanoparticles only. As for Copper/LDPE nanocomposite, the change of matrix structure during incubation and morphology of composite surface after incubation were investigated by DSC,XRD and EDX/SEM. The results demonstrate that, during incubation in the simulated uterine solution at 37℃, polyethylene matrix transforms gradually to lamellar stacking structure, and the crystallinity degree increases due to structural relaxation. Simultaneously, the bulge of polyethylene lattice due to water absorption annihilated the original microscopic cavities in composite. Furthermore, Copper/LDPE nanocomposite has component self-cleaning effect, which facilitates the steady release of Cu2+ and eliminates the detriment to endometrium that is caused by the inorganic deposit on the surface of conventional Cu-IUD in usage. Copper/LDPE nanocomposite and microcomposite after 280 days of incubation were investigated for comparison by using internal standard method in XRD. The resultssuggest that, in the simulated uterine solution, the Cu2+ release behavior controlled by nanocomposite is superior to that by microcomposite. The reason is that, during incubation of nanocomposite in the simulated uterine solution, clusters composed of copper nanoparticles are firstly oxidized into large amount of Cu2O phase, which congregates in the composite and produces high concentration grade,finally facilitating the Cu2+ steady release. The oxide membrane on surface of copper microparticles in microcomposite retards the further oxidization of the Cu in the inner part of particles. As a result, no concentration grade of Cu2O in microcomposite can form, leading to unsteady release of Cu2+. In the end of this dissertation, the property parameters of two types of novel IUD were put forward according to the Cu2+ release behavior controlled by Copper/LDPE nanocomposite in the simulated uterine solution. When compared with the conventional Cu-IUD in the same shape, the two novel IUDs have less mass than the Cu-IUD, which will alleviate the patient's uncomfortable feeling. Besides, the Cu2+ release rate of the novel IUDs can be modified within a rather wide range, which makes it possible for the patients to select IUD with various release rates according to different conditions of individuals.