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Study on a novel copper-containing composite for contraception
Contraception 79 (2009) 439 – 444
Original research article
Study on a novel copper-containing composite for contraception☆ Juan Lia , Jinping Suoa,⁎, Xunbin Huangb , Lintao Jiaa a
State Key Laboratory of Mould Technology, College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China b Family Planning Research Institute, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, PR China Received 21 November 2008; revised 31 December 2008; accepted 4 January 2009
Abstract Background: The copper-containing intrauterine devices (Cu-IUDs) are being increasingly used worldwide as an effective contraception for family planning. To avoid abnormal bleeding, pain, partial and complete expulsion, which are associated with the burst release of cupric ions during the first few days, a novel cross-linked composite based on polyvinyl alcohol (PVA) that contained cupric ions, but not metallic copper, was developed by our research team. Study Design: As a logical extension of our previous work, the corrosion products and release behavior of this composite after immersing in simulated body fluid (SBF) for 1 year were studied by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and atomic absorption spectrophotometry (AAS). Results: No other new elements, such as P, Cl and Ca, appeared on the surface of the composite, and no Cu2O was formed after immersing in SBF for 1 year, indicating that the effectiveness of copper can be greatly improved. Furthermore, no significant change on time dependence was found for the release rates of cupric ions in the composite compared with that of metallic copper, suggesting the absent burst release of cupric ions in the composite. Conclusion: The present in vitro long-term data suggest that this novel copper-containing composite has potential as a substitute for conventional materials used in the manufacture of IUDs. Crown Copyright © 2009 Published by Elsevier Inc. All rights reserved. Keywords: PVA; Metallic copper; Cu-IUDs; Long-term release behavior; Corrosion products
1. Introduction Among reversible birth control methods, the coppercontaining intrauterine device (Cu-IUD) is one of the most cost-effective devices to prevent pregnancy, especially for long-term use [1]. However, two major problems related to Cu-IUD have not been solved. On the one hand, there still exist side effects such as abnormal bleeding, pain, partial and complete expulsion associated with the burst release of copper in the first few days of usage [2]. On the other hand, the effectiveness of cupric ions in the Cu-IUD is low, i.e., the cupric ions trapped in the corrosion product and deposited there was about 30–40% of the total cupric ions released, indicating that one-third of the copper released is ineffective from the standpoint of contraception [3]. ☆
The authors are grateful for the financial support from the National Support Project (Grant No. 2006BA103B03) and Committee of Family Planning of Hubei Province. ⁎ Corresponding author. Tel.: +86 2787544307; fax: +86 2787559105. E-mail address: [email protected] (J. Suo).
To overcome these disadvantages, great efforts have been made to improve the Cu-IUDs and to investigate corrosion behaviors of copper in vivo and in vitro [4,5]. However, these improvements, which mainly focused on bulk copper in shape and size, have not settled these inherent disadvantages of Cu-IUDs. Cai et al. [6] first introduced a polymer and copper nanoparticles for IUDs, i.e., low-density polyethylene (LDPE) employed as the matrix material for IUDs and the sample was produced by mixing LDPE powders and copper nanoparticles. However, the problems related to Cu-IUD remained unsolved since the corrosion mechanism of copper nanoparticle is identical with that of bulk copper [7]. To address these inherent disadvantages of copper, whether in bulk or nanoparticles, a novel cross-linked composite based on polyvinyl alcohol (PVA)-containing cupric ions, but not metallic copper, was developed in our laboratory. This design is based on the following analysis: First, a copper-containing IUD is effective as a result of the formation of cupric ions, which leads to the inactivation
0010-7824/$ – see front matter. Crown Copyright © 2009 Published by Elsevier Inc. All rights reserved. doi:10.1016/j.contraception.2009.01.002
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of sperm and the suppression of myometrial contractions [8–10]. The study of Wildemeersch et al. [11] indicates that a minimal amount of copper is sufficient to provide a high contraceptive effect. Hagenfeldt [12] reported that the release of copper from T120 and T135 was 10.3 mg/year (range 7.4–13.5 mg/year), and for T200, a daily release of 45 mcg, about 17 mg/year. Therefore, if certain copper is loaded in the polymer matrix, which can release cupric ions that are effective for contraception, this copper-containing polymer composite might be used for Cu-IUD. Second, polymer composites are used as the matrix material because of their superior performance in controlled release of drug and continuous matrix phase [13]. The nondegradable polymers did not exhibit the initial high burst release in vitro and greatly increased the length of time of the drug release [14,15], which is highly desirable for contraception. In the past, PVA-controlled release application has been extensively investigated. Suzuki et al. [16] reported that the PVA derivative hydrogel was safe for clinical use due to its biocompatibility, and it allows gentamicin to be released at specific times and locations. Some other researchers also found that the drug released from PVA could be controlled by the rate of crystal dissolution and the degree of crosslinking of the polymer [17,18]. Lee [19] reported that PVA can provide a prolonged constant rate of release and exhibits good stability in the presence of saturated solutions of chlorinated isocyanurates due to the semicrystalline nature of PVA. Moreover, the results of our previous work showed that the burst release of cupric ions could be avoided and the effective utility of copper could be improved in this novel copper-containing composite [20]. These encouraging results suggested its potentiality as a substitute for conventional materials used in IUDs. As a long-term implanted medical material, however, short-term evaluation is far from enough for clinical application. In the present study, the composition and release behavior of the composite after soaking in simulated body fluid (SBF) for different time spans which extended to 1 year were studied. As a logical extension of our work, the main purposes of the present work were as follows: (1) To examine the composition of PVA composite before and after immersing in SBF. It is hypothesized that the use of this kind of composite would greatly reduce the formation of Cu2O, the major cause of lower copper utility and side effects of conventional metallic Cu-IUD. (2) To understand the longterm release behaviors of cupric ions in this novel composite, which may potentially be a substitute for conventional materials making up IUDs. 2. Materials and methods 2.1. Materials The PVA used in the study was supplied by Shanxi Sanwei Group Co. Ltd., China (polymerization ∼2400 and degree of hydrolysis ∼99%). Silica sol is a colloid solution
where colloid particles are dispersed homogeneously in water, provided by the Secondary Chemical Factory of Wuhan, China. The content of silica is 30 wt% and the particle size is about 10 nm. CuCl2·2H2O, NaCl, NaHCO3, KCl, K2HPO4·3H2O, MgCl2·6H2O, HCl, CaCl2 and Na2SO4 were provided by Shanghai Kechuang Chemicals Co., Ltd. NH2C(CH2OH)3 was supplied by Guangzhou Bio-key Science-tech Co., Ltd. 2.2. Samples preparation Samples were prepared as films in the following steps. (1) The preparation of PVA solution: aqueous 10 wt% PVA solutions were prepared by soaking preweighed quantities of dry PVA in de-ionized water for 6 h and heating at 90°C for 1 h. (2) The modification of PVA: silica sol was then mixed with the previously prepared PVA solution by stirring at 80°C for 1 h to obtain a homogeneous solution. PVA was modified by silica to decrease its solubility and enhance its mechanical properties [21]. (3) The introduction of cupric ions: saturated copper chloride solution was added into the previously mixed solution and the contents of copper chloride were 4 wt% in the total weight of PVA, SiO2 and CuCl2. The mixture was continuously stirred at 50°C for 0.5 h. After that, the mixture was poured into a clean and slick glass plate and placed in the ventilation cupboard for about 2 days to allow the solvent to evaporate. Finally, films with thickness of about 120 μm were obtained from the glass plate. 2.3. Immersion procedure A piece of film sample was soaked in a container with 500 mL SBF. The SBF was prepared by dissolving AR-grade NaCl, NaHCO3, KCl, K2HPO4·3H2O, MgCl2·6H2O, CaCl2 and NaSO4 into deionized water in a glass beaker. This mixture was then transferred to a 1000-mL volumetric flask. The chemical composition of the fluid is as follows: NaCl: 7.996 g/L; NaHCO3: 0.35 g/L; KCl: 0.24 g/L; K2HPO4·3H2O: 0.228 g/L; MgCl2·6H2O: 0.305 g/L; 1 mol/L HCl: 40 g/L; CaCl2: 0.278 g/L; Na2SO4: 0.071 g/L; and NH2C(CH2OH)3: 6.057 g/L. Finally, the solution was buffered at pH 7.2 with 0.5 mol/L NaOH or HCl. The container was then placed in a constant temperature (37±0.1°C) bath. Each experiment was performed in quadruplicate and SBF was refreshed every week. Four pieces of films were taken out from four different containers after immersing in SBF for 0, 3, 6 and 12 months, and then measured by various instruments. 2.4. Elemental composition analysis The elemental composition of corrosion product in composite was confirmed by X-ray fluorescence spectroscopy (XRF), Eagle III (EDAX, Inc.). This equipment is provided with an Rh target X-ray tube producing a focused and high-intensity beam with a 100-μm spot size. The X-ray beam is generated with an Rh X-ray tube at an accelerating voltage of 40 kV with a current of 1 mA. X-ray emission from the irradiated samples is detected with an energy-
J. Li et al. / Contraception 79 (2009) 439–444
dispersive X-ray spectrometer equipped with a liquid nitrogen-cooled high-purity Si detector. 2.5. Corrosion products analysis To understand the corrosion products of the composite, Xray diffraction (XRD) patterns of film specimens were measured with an X'Pert PRO diffractometer. The Cu Kα line of a conventional X-ray source powered at 40 kV and 40 mA was used.
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90, 120, 150, 180, 210, 240, 270, 300, 330 and 360 days, and analyzed by atomic absorption spectrophotometer (AA-300, Perkin Elmer, detection limit of cupric ion is 0.077 ppm) to determine the concentration of cupric ions. All experiments were performed in triplicate, showing a reproducibility of more than 93%. 3. Results
2.6. Studies of cupric ion release
3.1. Analysis of deposition elements on the surface of composite
The glass containers, which contain samples and SBF, were placed in a constant temperature (37±0.1°C) bath. An apparatus with constant mixing was used to accurately control the temperature. To compare the release behavior of metallic copper and copper-containing composite, the release rate of metallic copper and composite was studied in the same condition. A piece of film and metallic copper were separately soaked in the container with 500 ml SBF. Samples of 10 mL were taken after 1, 2, 4, 7, 10, 20, 30, 60,
XRF is a multielemental analysis method, which is very powerful in the detection of trace elements [22]. Compared with scanning electron microscopy–X-ray energy dispersive spectroscopy (SEM-EDX), the XRF technique is a nondestructive method for elementary analysis. The elements contained in the sample are excited by a primary source of white radiation, and the emission of the wavelengths characteristic of each element (fluorescent X-ray) is detected by an adequate detector. These wavelengths and
Fig. 1. X-ray fluorescent patterns of the composite (4% CuCl2/20% SiO2/PVA) with different soaking times: (A) 0 month, (B) 3 months, (C) 6 months, (D) 12 months.
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4. Discussion
Fig. 2. X-ray diffraction patterns of the composite (4% CuCl2/20% SiO2/ PVA) with different soaking times: (a) 0 month, (b) 3 months, (c) 6 months, (d) 12 months.
In the study of corrosion products of conventional CuIUD, it was found that new peaks of Cu, P, Cl and Ca were identified on the surface of metallic copper [23]. The release rate of cupric ions decreased or the release channels were obstructed due to the deposition of compounds which are composed of these elements. However, XRF and XRD results showed that no other new elements appeared on the surface of this novel composite after immersing in SBF for 12 months. The absence of these elements on the sample excluded the possibility of obstructing release channels. Also, this jamming up of release channels in metallic copper had successfully been overcome by the use of copper/LDPE nanocomposites [7]. The reason for this is that no polar group exists on the surface of the nanocomposites, resulting in no bonding between pollutant and composite. This is also true for this new copper-containing composite since the polar hydroxyl groups were lessened due to the condensation between PVA and silanol groups of silica and coordination
their associated energies are measured, and the elements can be identified. Fig. 1A–D shows the XRF spectra of the surface of 4 wt% CuCl2/20 wt% SiO2/PVA composite before and after being soaked in SBF for different time spans, respectively. A comparison of Fig. 1A to D pointed out that no other new elements appeared on the surface of the composite after immersing in SBF for 12 months. 3.2. Analysis of deposition compounds X-ray spectra provide semiquantitative analysis together with a qualitative measure of specific elements. To study the phase of corrosion products, X-ray diffraction was employed and patterns of the composite after soaking in SBF for different time spans are presented in Fig. 2. One peak around 2θ=19.44° appeared, corresponding to the (101) plane of PVA semicrystalline in pure PVA membrane [23]. This crystalline peak of PVA increased with the increase of soaking time. Moreover, no peaks representing compound of calcium and phosphorous appeared in the spectra. This result agrees well with that of XRF. 3.3. Release behavior of cupric ions in SBF Fig. 3 presents the data on the relationship between release amount of cupric ions and time in SBF at a temperature of 37°C. The release amount of cupric ions in the composite is 0.45 mcg/mm2 for the first day, 0.825 mcg/mm2 for 30 days and 2.37 mcg/mm2 for 360 days. For metallic copper, the amounts are 2.36, 26.4 and 136 mcg/mm2, respectively. It can be observed that Cu2+ release amounts of metallic copper increased with increasing soaking time. Nevertheless, there seems to be no significant change in the release amounts of cupric ions in composite compared with metallic copper, indicating the absence of burst release of copper in the composite.
Fig. 3. Release amount of cupric ions from metal copper and composite in SBF.
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reactions between PVA and cupric ions [24,25]. Moreover, strong intermolecular hydrogen bonding existed in PVA molecular with high hydrolysis. As for conventional metallic copper, however, a hydrogen bond formed between the oxygen in cuprous oxide and calcium carbonate (CaCO3), cupric subcarbonate (Cu2(OH)2CO3), during the corrosion of metallic copper [26]. Although the calcium carbonate, cupric subcarbonate deposition has been successfully avoided by adding nanocopper in LDPE [27], a trace of copper oxide phases can be observed on X-ray diffraction patterns of the nanocomposites due to high activity of the nanocopper surface. In this novel composite, however, no peaks of Cu oxide can be found. In our previous work, even the content of copper chloride increased to 20 wt%; there is still no copper oxide [20]. All of this evidence suggested that no Cu2O formed in the composite during the immersion. Meanwhile, this can also be explained by comparing the release mechanisms of metallic copper and copper-containing composite. In the former, the corrosion of metallic copper either in bulk or nanoparticles undergoes the following reactions [2,23]: 8Cu + O2 + 2H2 OY4Cu2 O + 4H + + 4e 2Cu + 4H + + O2 Y2Cu2 + + 2H2 O It is obvious that, during corrosion, metallic copper either in bulk or nanoparticle generates soluble ions together with Cu2O films on its surface. As far as the Cu-IUD is concerned, only soluble species of copper are desirable for antifertility [9,28]. It has been reported that the amount of cupric ions trapped in the corrosion product and deposited was about 30–40% of the total cupric ions released, indicating that onethird of the copper released is ineffective from the standpoint of contraception [3]. Furthermore, the deposition could also interact with the endometrium, resulting in side effects and incompatibility of the Cu-IUD. It could also be concluded that the release rate of cupric ions depends on oxygen partial pressure and pH. In places with higher pressure such as the exposure of the surface of Cu-IUD, copper wires or sleeves might be broken or fragmented after long-term corrosion, resulting in the failure of Cu-IUD [29]. From the release mechanism of metallic copper, to improve the effectiveness of copper and overcome the side effects of covered deposition, the use of metallic copper should be avoided. Therefore, the cupric ions rather than copper were added into the PVA matrix. PVA, as a chelating resin, has recently drawn considerable attention for its capability to chelate hydroxyl groups to retain metal ions [30]. Moreover, cupric ions' coordination to PVA is well known in the literature [25,31]. In the composite, the release of cupric ions depended on the chelated equilibrium, which is quite different from the corrosion of metallic copper. By avoiding the formation of cupric oxide, the effectiveness of copper can be greatly improved and the
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side effects caused by these compounds could also be eliminated. This is very important whether for trace element control or for Cu-IUD usage.
From the cupric ions release study, there seems to be no significant change in the release amounts of cupric ions in composite compared with metallic copper, indicating the absent burst release of cupric ions. The reason for this slight increase in the release amount of cupric ions is the chelated equilibrium of the composite. In other words, further release of cupric ions was inhibited by the concentration of cupric ions in the solution. Therefore, if enough copper is loaded in composite, and the release of cupric ions is at a constant rate, then a long-term effective contraception can be realized. 5. Conclusion In summary, the corrosion products and long-term release behavior of the novel composite after soaking in SBF for different time spans were studied. It was shown that there were no other new elements, such as P, Cl and Ca, appearing on the surface of the composite and no Cu2O formed after immersing in SBF for 1 year, indicating the release channels would not be obstructed by the deposition of these composites and the effectiveness of copper could be improved significantly. Release results indicated that there was no significant change in release rate of cupric ions from the composites compared with metallic copper. Thus, burst release of cupric ion could be markedly diminished. In view of the above results, this novel copper-containing composite might serve as a potential substitute for conventional materials of IUDs in the future. Acknowledgments Thanks go to the analytical and testing center of HUST for useful characterizations. The assistance in the measurement of cupric ions by Lihua Zhao, technician of the chemistry department of HUST, is highly appreciated. References [1] Avecilla-Palau A, Moreno V. Uterine factors and risk of pregnancy in IUD users: a nested case-control study. Contraception 2003;67: 235–9. [2] Zhang C, Xu N, Yang B. The corrosion behavior of copper in simulated uterine fluid. Corros Sci 1996;38:635–41.
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[3] Mora N, Cano E, Mora EM, Bastidas JM. Influence of pH and oxygen on copper corrosion in simulated uterine fluid. Biomaterials 2002;23: 667–71. [4] Xue HS, Xu NX, Zhang CD. Corrosion behavior of copper in a copper bearing intrauterine device in the presence of indomethacin. Contraception 1998;57:49–53. [5] Bastidas JM, Pinilla P, Cano E, Polo JL, Miguel S. Copper corrosion inhibition by triphenylmethane derivations in sulphuric acid media. Corros Sci 2003;45:427–9. [6] Cai SZ, Xia XP, Xie CS. Corrosion behavior of copper/LDPE nanocomposites in simulated uterine solution. Biomaterials 2005;26: 2671–6. [7] Cai SZ, Xia XP, Xie CS. Research on Cu2+ transformations of Cu and its oxides particles with different sizes in the simulated uterine solution. Corros Sci 2005;47:1039–47. [8] Bastidas JM, Mora N, Cano E, Polo JL. Characterization of copper corrosion products originated in simulated uterine fluids and on packaged intrauterine devices. J Mater Sci Mater M 2001;12:391–7. [9] Zhu JJ, Xu NX, Zhang CD. Characteristics of copper corrosion in simulated uterine fluid in the presence of protein. Adv Contracept 1999;15:179–90. [10] Xue H, Xu N, Zhang C. Effect of stainless steel on corrosion behavior of copper in a copper-bearing intrauterine device. Adv Contracept 1998;14:153–60. [11] Wildemeersch D, Cao XM, Zhang WH, et al. Efficacy of a mini version of the frameless GynexFix intrauterine system (IUS) with effective copper surface area of 200 mm2. Contraception 2002;66:237–41. [12] Hagenfeldt K. Intrauterine contraception with the copper-T device: 1. Effect on trace elements in the endometrium, cervical mucus and plasma. Contraception 1972;6:37–54. [13] Xu T, He B. Mechanism of sustained drug release in diffusioncontrolled polymer matrix-application of percolation theory. Int J Pharm 1998;170:139–49. [14] Brannon-Peppas L. Recent advance on the use of biodegradable microparticles and nanoparticles in controlled drug delivery. Int J Pharm 1995;116:1–13. [15] Liu LS, Ng CK, Thompson AY, et al. Hyaluronate–heparin conjugate gels for the delivery of basic fibroblast growth factor (FGF-2). J Biomed Mater Res 2002;62:128–35. [16] Suzuki Y, Tanihara M, Nishimura Y, Suzali K, Kakimaru Y, Shimizu Y. A new drug delivery system with controlled release of antibiotic only in the presence of infection. J Biomed Mater Res 1998;2:112–6.
[17] Kim SY, Lee YM. Drug release behavior of electrical responsive poly (vinyl alcohol)/poly (acrylic acid) IPN hydrogels under an electric stimulus. J Appl Polym Sci 1999;74:1752–61. [18] Mallapragada SK, Peppas NA, Colombo P. Crystal dissolutioncontrolled release systems: II. Metronidazole release from semicrystalline poly(vinyl alcohol) systems. J Biomed Mater Res 1997;36:125–30. [19] Lee PI. Poly (vinyl alcohol) membrane systems for the controlled release of chlorinated isocyanurates. J Appl Polym Sci 1993;50: 941–7. [20] Li J, Suo JP, Huang XB, Ye C, Wu XW. Release behavior of copper ion in a novel contraceptive composite. Contraception 2007;76:233–7. [21] Li J, Suo JP, Deng RZ. Structure, mechanical and swelling behaviors of Poly (vinyl alcohol)/SiO2 hybrid membranes. J Reinf Plast Comp [in press]. [22] Calzolai G, Chiari M, Lucarelli F, et al. PIXE and XRF analysis of particulate matter samples: an inter-laboratory comparison. Nucl Instru Meth B 2008;266:2401–4. [23] Bastidas JM, Cano E, Mora N. Copper corrosion-simulated uterine solutions. Contraception 2000;61:395–9. [24] Xu Y, Li ZH, Fan WH, et al. Density fluctuation in silica-PVA hybrid gels determined by small-angle X-ray scattering. Appl Sur Sci 2004; 225:116–23. [25] Tomita H. Solution spinning of high Tc oxide superconductor: 1. Effect of propionic acid on the interaction between poly (vinyl alcohol) and copper (II) acetate. Polymer 1992;34:2277–81. [26] Johnson AB, Maness RF, Wheeler RG. Calcareous deposits formed on IUDs in human exposures. Contraception 1976;14:507–16. [27] Cai SZ, Xia XP, Xie CS. Corrosion behavior of copper/LDPE nanocomposites in simulated uterine solution. Biomaterial 2005;26: 2671–6. [28] Bastidas JM, Mora N, Cano E, Polo JL. Characterization of copper corrosion products originated in simulated uterine fluids and on packaged intrauterine devices. J Mater Sci Mater M 2001;12:391–7. [29] Xia XP, Cai SZ, Hu JH, Xie CS. Water absorption characteristics of novel/LDPE nanocomposite for use in intrauterine devices. J Biomed Mater Res B 2006;79B:345–52. [30] Lin H, Watanabe Y, Kimura M, Hanabusa K, Shirai H. Preparation of magnetic poly (vinyl alcohol) (PVA) materials by in situ synthesis of magnetite in a PVA matrix. J Appl Polym Sci 2003;87:1239–47. [31] Murugesan R, Subramanian E. The effect of Cu(II) coordination on the structure and electric properties of polyaniline-poly(vinyl alcohol). Mater Chem Phys 2002;7:860–7.
Original research article
Study on a novel copper-containing composite for contraception☆ Juan Lia , Jinping Suoa,⁎, Xunbin Huangb , Lintao Jiaa a
State Key Laboratory of Mould Technology, College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China b Family Planning Research Institute, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, PR China Received 21 November 2008; revised 31 December 2008; accepted 4 January 2009
Abstract Background: The copper-containing intrauterine devices (Cu-IUDs) are being increasingly used worldwide as an effective contraception for family planning. To avoid abnormal bleeding, pain, partial and complete expulsion, which are associated with the burst release of cupric ions during the first few days, a novel cross-linked composite based on polyvinyl alcohol (PVA) that contained cupric ions, but not metallic copper, was developed by our research team. Study Design: As a logical extension of our previous work, the corrosion products and release behavior of this composite after immersing in simulated body fluid (SBF) for 1 year were studied by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and atomic absorption spectrophotometry (AAS). Results: No other new elements, such as P, Cl and Ca, appeared on the surface of the composite, and no Cu2O was formed after immersing in SBF for 1 year, indicating that the effectiveness of copper can be greatly improved. Furthermore, no significant change on time dependence was found for the release rates of cupric ions in the composite compared with that of metallic copper, suggesting the absent burst release of cupric ions in the composite. Conclusion: The present in vitro long-term data suggest that this novel copper-containing composite has potential as a substitute for conventional materials used in the manufacture of IUDs. Crown Copyright © 2009 Published by Elsevier Inc. All rights reserved. Keywords: PVA; Metallic copper; Cu-IUDs; Long-term release behavior; Corrosion products
1. Introduction Among reversible birth control methods, the coppercontaining intrauterine device (Cu-IUD) is one of the most cost-effective devices to prevent pregnancy, especially for long-term use [1]. However, two major problems related to Cu-IUD have not been solved. On the one hand, there still exist side effects such as abnormal bleeding, pain, partial and complete expulsion associated with the burst release of copper in the first few days of usage [2]. On the other hand, the effectiveness of cupric ions in the Cu-IUD is low, i.e., the cupric ions trapped in the corrosion product and deposited there was about 30–40% of the total cupric ions released, indicating that one-third of the copper released is ineffective from the standpoint of contraception [3]. ☆
The authors are grateful for the financial support from the National Support Project (Grant No. 2006BA103B03) and Committee of Family Planning of Hubei Province. ⁎ Corresponding author. Tel.: +86 2787544307; fax: +86 2787559105. E-mail address: [email protected] (J. Suo).
To overcome these disadvantages, great efforts have been made to improve the Cu-IUDs and to investigate corrosion behaviors of copper in vivo and in vitro [4,5]. However, these improvements, which mainly focused on bulk copper in shape and size, have not settled these inherent disadvantages of Cu-IUDs. Cai et al. [6] first introduced a polymer and copper nanoparticles for IUDs, i.e., low-density polyethylene (LDPE) employed as the matrix material for IUDs and the sample was produced by mixing LDPE powders and copper nanoparticles. However, the problems related to Cu-IUD remained unsolved since the corrosion mechanism of copper nanoparticle is identical with that of bulk copper [7]. To address these inherent disadvantages of copper, whether in bulk or nanoparticles, a novel cross-linked composite based on polyvinyl alcohol (PVA)-containing cupric ions, but not metallic copper, was developed in our laboratory. This design is based on the following analysis: First, a copper-containing IUD is effective as a result of the formation of cupric ions, which leads to the inactivation
0010-7824/$ – see front matter. Crown Copyright © 2009 Published by Elsevier Inc. All rights reserved. doi:10.1016/j.contraception.2009.01.002
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of sperm and the suppression of myometrial contractions [8–10]. The study of Wildemeersch et al. [11] indicates that a minimal amount of copper is sufficient to provide a high contraceptive effect. Hagenfeldt [12] reported that the release of copper from T120 and T135 was 10.3 mg/year (range 7.4–13.5 mg/year), and for T200, a daily release of 45 mcg, about 17 mg/year. Therefore, if certain copper is loaded in the polymer matrix, which can release cupric ions that are effective for contraception, this copper-containing polymer composite might be used for Cu-IUD. Second, polymer composites are used as the matrix material because of their superior performance in controlled release of drug and continuous matrix phase [13]. The nondegradable polymers did not exhibit the initial high burst release in vitro and greatly increased the length of time of the drug release [14,15], which is highly desirable for contraception. In the past, PVA-controlled release application has been extensively investigated. Suzuki et al. [16] reported that the PVA derivative hydrogel was safe for clinical use due to its biocompatibility, and it allows gentamicin to be released at specific times and locations. Some other researchers also found that the drug released from PVA could be controlled by the rate of crystal dissolution and the degree of crosslinking of the polymer [17,18]. Lee [19] reported that PVA can provide a prolonged constant rate of release and exhibits good stability in the presence of saturated solutions of chlorinated isocyanurates due to the semicrystalline nature of PVA. Moreover, the results of our previous work showed that the burst release of cupric ions could be avoided and the effective utility of copper could be improved in this novel copper-containing composite [20]. These encouraging results suggested its potentiality as a substitute for conventional materials used in IUDs. As a long-term implanted medical material, however, short-term evaluation is far from enough for clinical application. In the present study, the composition and release behavior of the composite after soaking in simulated body fluid (SBF) for different time spans which extended to 1 year were studied. As a logical extension of our work, the main purposes of the present work were as follows: (1) To examine the composition of PVA composite before and after immersing in SBF. It is hypothesized that the use of this kind of composite would greatly reduce the formation of Cu2O, the major cause of lower copper utility and side effects of conventional metallic Cu-IUD. (2) To understand the longterm release behaviors of cupric ions in this novel composite, which may potentially be a substitute for conventional materials making up IUDs. 2. Materials and methods 2.1. Materials The PVA used in the study was supplied by Shanxi Sanwei Group Co. Ltd., China (polymerization ∼2400 and degree of hydrolysis ∼99%). Silica sol is a colloid solution
where colloid particles are dispersed homogeneously in water, provided by the Secondary Chemical Factory of Wuhan, China. The content of silica is 30 wt% and the particle size is about 10 nm. CuCl2·2H2O, NaCl, NaHCO3, KCl, K2HPO4·3H2O, MgCl2·6H2O, HCl, CaCl2 and Na2SO4 were provided by Shanghai Kechuang Chemicals Co., Ltd. NH2C(CH2OH)3 was supplied by Guangzhou Bio-key Science-tech Co., Ltd. 2.2. Samples preparation Samples were prepared as films in the following steps. (1) The preparation of PVA solution: aqueous 10 wt% PVA solutions were prepared by soaking preweighed quantities of dry PVA in de-ionized water for 6 h and heating at 90°C for 1 h. (2) The modification of PVA: silica sol was then mixed with the previously prepared PVA solution by stirring at 80°C for 1 h to obtain a homogeneous solution. PVA was modified by silica to decrease its solubility and enhance its mechanical properties [21]. (3) The introduction of cupric ions: saturated copper chloride solution was added into the previously mixed solution and the contents of copper chloride were 4 wt% in the total weight of PVA, SiO2 and CuCl2. The mixture was continuously stirred at 50°C for 0.5 h. After that, the mixture was poured into a clean and slick glass plate and placed in the ventilation cupboard for about 2 days to allow the solvent to evaporate. Finally, films with thickness of about 120 μm were obtained from the glass plate. 2.3. Immersion procedure A piece of film sample was soaked in a container with 500 mL SBF. The SBF was prepared by dissolving AR-grade NaCl, NaHCO3, KCl, K2HPO4·3H2O, MgCl2·6H2O, CaCl2 and NaSO4 into deionized water in a glass beaker. This mixture was then transferred to a 1000-mL volumetric flask. The chemical composition of the fluid is as follows: NaCl: 7.996 g/L; NaHCO3: 0.35 g/L; KCl: 0.24 g/L; K2HPO4·3H2O: 0.228 g/L; MgCl2·6H2O: 0.305 g/L; 1 mol/L HCl: 40 g/L; CaCl2: 0.278 g/L; Na2SO4: 0.071 g/L; and NH2C(CH2OH)3: 6.057 g/L. Finally, the solution was buffered at pH 7.2 with 0.5 mol/L NaOH or HCl. The container was then placed in a constant temperature (37±0.1°C) bath. Each experiment was performed in quadruplicate and SBF was refreshed every week. Four pieces of films were taken out from four different containers after immersing in SBF for 0, 3, 6 and 12 months, and then measured by various instruments. 2.4. Elemental composition analysis The elemental composition of corrosion product in composite was confirmed by X-ray fluorescence spectroscopy (XRF), Eagle III (EDAX, Inc.). This equipment is provided with an Rh target X-ray tube producing a focused and high-intensity beam with a 100-μm spot size. The X-ray beam is generated with an Rh X-ray tube at an accelerating voltage of 40 kV with a current of 1 mA. X-ray emission from the irradiated samples is detected with an energy-
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dispersive X-ray spectrometer equipped with a liquid nitrogen-cooled high-purity Si detector. 2.5. Corrosion products analysis To understand the corrosion products of the composite, Xray diffraction (XRD) patterns of film specimens were measured with an X'Pert PRO diffractometer. The Cu Kα line of a conventional X-ray source powered at 40 kV and 40 mA was used.
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90, 120, 150, 180, 210, 240, 270, 300, 330 and 360 days, and analyzed by atomic absorption spectrophotometer (AA-300, Perkin Elmer, detection limit of cupric ion is 0.077 ppm) to determine the concentration of cupric ions. All experiments were performed in triplicate, showing a reproducibility of more than 93%. 3. Results
2.6. Studies of cupric ion release
3.1. Analysis of deposition elements on the surface of composite
The glass containers, which contain samples and SBF, were placed in a constant temperature (37±0.1°C) bath. An apparatus with constant mixing was used to accurately control the temperature. To compare the release behavior of metallic copper and copper-containing composite, the release rate of metallic copper and composite was studied in the same condition. A piece of film and metallic copper were separately soaked in the container with 500 ml SBF. Samples of 10 mL were taken after 1, 2, 4, 7, 10, 20, 30, 60,
XRF is a multielemental analysis method, which is very powerful in the detection of trace elements [22]. Compared with scanning electron microscopy–X-ray energy dispersive spectroscopy (SEM-EDX), the XRF technique is a nondestructive method for elementary analysis. The elements contained in the sample are excited by a primary source of white radiation, and the emission of the wavelengths characteristic of each element (fluorescent X-ray) is detected by an adequate detector. These wavelengths and
Fig. 1. X-ray fluorescent patterns of the composite (4% CuCl2/20% SiO2/PVA) with different soaking times: (A) 0 month, (B) 3 months, (C) 6 months, (D) 12 months.
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4. Discussion
Fig. 2. X-ray diffraction patterns of the composite (4% CuCl2/20% SiO2/ PVA) with different soaking times: (a) 0 month, (b) 3 months, (c) 6 months, (d) 12 months.
In the study of corrosion products of conventional CuIUD, it was found that new peaks of Cu, P, Cl and Ca were identified on the surface of metallic copper [23]. The release rate of cupric ions decreased or the release channels were obstructed due to the deposition of compounds which are composed of these elements. However, XRF and XRD results showed that no other new elements appeared on the surface of this novel composite after immersing in SBF for 12 months. The absence of these elements on the sample excluded the possibility of obstructing release channels. Also, this jamming up of release channels in metallic copper had successfully been overcome by the use of copper/LDPE nanocomposites [7]. The reason for this is that no polar group exists on the surface of the nanocomposites, resulting in no bonding between pollutant and composite. This is also true for this new copper-containing composite since the polar hydroxyl groups were lessened due to the condensation between PVA and silanol groups of silica and coordination
their associated energies are measured, and the elements can be identified. Fig. 1A–D shows the XRF spectra of the surface of 4 wt% CuCl2/20 wt% SiO2/PVA composite before and after being soaked in SBF for different time spans, respectively. A comparison of Fig. 1A to D pointed out that no other new elements appeared on the surface of the composite after immersing in SBF for 12 months. 3.2. Analysis of deposition compounds X-ray spectra provide semiquantitative analysis together with a qualitative measure of specific elements. To study the phase of corrosion products, X-ray diffraction was employed and patterns of the composite after soaking in SBF for different time spans are presented in Fig. 2. One peak around 2θ=19.44° appeared, corresponding to the (101) plane of PVA semicrystalline in pure PVA membrane [23]. This crystalline peak of PVA increased with the increase of soaking time. Moreover, no peaks representing compound of calcium and phosphorous appeared in the spectra. This result agrees well with that of XRF. 3.3. Release behavior of cupric ions in SBF Fig. 3 presents the data on the relationship between release amount of cupric ions and time in SBF at a temperature of 37°C. The release amount of cupric ions in the composite is 0.45 mcg/mm2 for the first day, 0.825 mcg/mm2 for 30 days and 2.37 mcg/mm2 for 360 days. For metallic copper, the amounts are 2.36, 26.4 and 136 mcg/mm2, respectively. It can be observed that Cu2+ release amounts of metallic copper increased with increasing soaking time. Nevertheless, there seems to be no significant change in the release amounts of cupric ions in composite compared with metallic copper, indicating the absence of burst release of copper in the composite.
Fig. 3. Release amount of cupric ions from metal copper and composite in SBF.
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reactions between PVA and cupric ions [24,25]. Moreover, strong intermolecular hydrogen bonding existed in PVA molecular with high hydrolysis. As for conventional metallic copper, however, a hydrogen bond formed between the oxygen in cuprous oxide and calcium carbonate (CaCO3), cupric subcarbonate (Cu2(OH)2CO3), during the corrosion of metallic copper [26]. Although the calcium carbonate, cupric subcarbonate deposition has been successfully avoided by adding nanocopper in LDPE [27], a trace of copper oxide phases can be observed on X-ray diffraction patterns of the nanocomposites due to high activity of the nanocopper surface. In this novel composite, however, no peaks of Cu oxide can be found. In our previous work, even the content of copper chloride increased to 20 wt%; there is still no copper oxide [20]. All of this evidence suggested that no Cu2O formed in the composite during the immersion. Meanwhile, this can also be explained by comparing the release mechanisms of metallic copper and copper-containing composite. In the former, the corrosion of metallic copper either in bulk or nanoparticles undergoes the following reactions [2,23]: 8Cu + O2 + 2H2 OY4Cu2 O + 4H + + 4e 2Cu + 4H + + O2 Y2Cu2 + + 2H2 O It is obvious that, during corrosion, metallic copper either in bulk or nanoparticle generates soluble ions together with Cu2O films on its surface. As far as the Cu-IUD is concerned, only soluble species of copper are desirable for antifertility [9,28]. It has been reported that the amount of cupric ions trapped in the corrosion product and deposited was about 30–40% of the total cupric ions released, indicating that onethird of the copper released is ineffective from the standpoint of contraception [3]. Furthermore, the deposition could also interact with the endometrium, resulting in side effects and incompatibility of the Cu-IUD. It could also be concluded that the release rate of cupric ions depends on oxygen partial pressure and pH. In places with higher pressure such as the exposure of the surface of Cu-IUD, copper wires or sleeves might be broken or fragmented after long-term corrosion, resulting in the failure of Cu-IUD [29]. From the release mechanism of metallic copper, to improve the effectiveness of copper and overcome the side effects of covered deposition, the use of metallic copper should be avoided. Therefore, the cupric ions rather than copper were added into the PVA matrix. PVA, as a chelating resin, has recently drawn considerable attention for its capability to chelate hydroxyl groups to retain metal ions [30]. Moreover, cupric ions' coordination to PVA is well known in the literature [25,31]. In the composite, the release of cupric ions depended on the chelated equilibrium, which is quite different from the corrosion of metallic copper. By avoiding the formation of cupric oxide, the effectiveness of copper can be greatly improved and the
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side effects caused by these compounds could also be eliminated. This is very important whether for trace element control or for Cu-IUD usage.
From the cupric ions release study, there seems to be no significant change in the release amounts of cupric ions in composite compared with metallic copper, indicating the absent burst release of cupric ions. The reason for this slight increase in the release amount of cupric ions is the chelated equilibrium of the composite. In other words, further release of cupric ions was inhibited by the concentration of cupric ions in the solution. Therefore, if enough copper is loaded in composite, and the release of cupric ions is at a constant rate, then a long-term effective contraception can be realized. 5. Conclusion In summary, the corrosion products and long-term release behavior of the novel composite after soaking in SBF for different time spans were studied. It was shown that there were no other new elements, such as P, Cl and Ca, appearing on the surface of the composite and no Cu2O formed after immersing in SBF for 1 year, indicating the release channels would not be obstructed by the deposition of these composites and the effectiveness of copper could be improved significantly. Release results indicated that there was no significant change in release rate of cupric ions from the composites compared with metallic copper. Thus, burst release of cupric ion could be markedly diminished. In view of the above results, this novel copper-containing composite might serve as a potential substitute for conventional materials of IUDs in the future. Acknowledgments Thanks go to the analytical and testing center of HUST for useful characterizations. The assistance in the measurement of cupric ions by Lihua Zhao, technician of the chemistry department of HUST, is highly appreciated. References [1] Avecilla-Palau A, Moreno V. Uterine factors and risk of pregnancy in IUD users: a nested case-control study. Contraception 2003;67: 235–9. [2] Zhang C, Xu N, Yang B. The corrosion behavior of copper in simulated uterine fluid. Corros Sci 1996;38:635–41.
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