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Controlled release of IFC-305 encapsulated in silica nanoparticles for liver cancer synthesized by sol–gel
Colloids and Surfaces A: Physicochem. Eng. Aspects 384 (2011) 131–136
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Controlled release of IFC-305 encapsulated in silica nanoparticles for liver cancer synthesized by sol–gel León Albarran a,b , Tessy López a,b , Patricia Quintana c,∗ , Victoria Chagoya d a
Universidad Autónoma Metropolitana–Xochimilco, Calzada del Hueso 1100, Col. Villa Quietud, Coyoacán, C.P. 04960, D.F. México, Mexico National Neurology and Neurosurgery Institute Nanotechnology for Medicine Laboratory, Av. Insurgentes Sur 3877, Col. La Fama, Tlalpan, 14269, D.F. México, Mexico Departmento de Física Aplicada, CINVESTAV-IPN, Unidad Mérida, A.P. 73, Cordemex, C.P. 97310, Mérida, Yucatán, México, Mexico d Departmento de Biología Celular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Coyoacán, CP 04510, D.F. México, Mexico b c
a r t i c l e
i n f o
Article history: Received 29 September 2010 Received in revised form 10 March 2011 Accepted 18 March 2011 Available online 26 March 2011 Keywords: IFC-305 Silica sol–gel FTIR BET Drug release UV-Vis
a b s t r a c t IFC-305 was encapsulated into nanostructured silica and functionalized with OH groups by the sol–gel process using tetraethoxysilane (TEOS), to be used for a drug delivery system for the treatment of liver cancer. Synthesis was carried out at different molar hydrolysis ratios: 4, 8, 16 and 24 mol of water and drug concentrations of 10, 20 and 30%. Characterization of IFC-silica reservoirs by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal analysis (DTA-TGA), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms (BET), confirms that IFC-305 was trapped and stabilized in the SiO2 –OH matrix. Drug release was determined by UV spectrophotometry over a period of 1000 h. Results showed that the morphology and specific surface area are controlled by the amount of loaded drug and water content for the different synthesized reservoir systems. However, the in vitro analysis of drug discharge showed that the rate of drug release was independent of the amount of hydrolyzed water, although it was affected by the quantity of drug loaded. The mechanism of drug release is a combination of dissolution and diffusion processes. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Chronic liver diseases are a major health issue world-wide [1]. In Mexico, the mortality rate due to cirrhosis ranks among the highest in the world, being the third cause of death in the general population and the second in young adults in 2005 [2]; in that year, patients died due to liver cirrhosis and other chronic liver diseases at a rate of 25.9/100,000 inhabitants, and a steady rise in the number of cases is expected to occur in the following years [2,3]. Cirrhosis is a chronic degenerative disease in which normal liver cells are damaged and are then replaced by scar tissue; therefore, it reduces the liver’s ability to manufacture proteins and process hormones, nutrients, medications and the normal biochemical processes. In recent years, application of nanotechnology for the treatment of human diseases holds great promise. In particular, the use of SiO2 nanoparticles has been extended to biomedical and biotechnological fields, since it has a unique matrix that allows the incorporation of different types of molecules. It has been applied as biosensors and biomarkers [4], as well as for cellular imaging applications [5]. For controlled release applications, it has been shown that silica is able to store and gradually release therapeutically relevant drugs like antibiotics [6–8], or drugs for treating neurological diseases
∗ Corresponding author. Tel.: +52 999 9429442; fax: +52 999 9812917. E-mail address: [email protected] (P. Quintana). 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.03.042
as such as dopamine, valproic acid and sodium phenytoin [9–12]. Furthermore, silica nanoparticles have been used to enhance the biocompatibility of several drug delivery systems for cancer therapy and catalysis [8,13–15]. Amorphous, sol–gel derived SiO2 is known to be a biocompatible and bioresorbable material that has potential applications as implants or injectable matrices in the controlled delivery of biologically active agents in living tissues [16,17]. The sol is produced through hydrolysis and polycondensation reaction [18] from an alkoxide precursor. Due to the mild processing conditions, high concentrations of many types of biologically active agent can be incorporated in the liquid (sol) and, afterwards, is embedded in the matrix (gel), which after condensation and drying becomes a porous solid material [5–11]. It is also well known that release is dependent on synthesis parameters such as the molar ratio of silica precursor to water, type of precursor and the concentration of bioactive drug [8,12,19–21]. A promising therapeutic alternative to treat liver cirrhosis disease is the use of a novel drug called IFC-305, a derivative of 6-aminoribofuranosil purine, which has been tested to revert cirrhosis and liver dysfunction in rats, however, it shows a very short half-life due to its rapid metabolism in the liver [22]. In this work, silica nanoparticles were synthesized to encapsulate IFC-305, and to provide a stable reservoir to target the delivery of the drug to the liver in order to improve the metabolic stability and to achieve the appropriate dosage, needed to result in an efficient treatment. The
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drug molecule and both empty and loaded reservoirs were characterized to understand the linking mechanism, to verify the IFC-305 stabilization and to analyze in vitro the drug release behavior, with variation in the amount of water and drug content. 2. Materials and methods 2.1. Synthesis IFC-305 occluded into silica sol–gel was prepared with three different drug concentrations 10, 20 and 30%. SiO2 matrix was synthesized adding 70 mL of tetraethoxysilane (TEOS) to a drug aqueous solution, with a certain amount of water in order to have four different molar hydrolysis ratios, corresponding to 4, 8, 16 and 24 mol of water. Therefore, 12 samples were obtained with different ratios and were named as xIFC–ySi (x = drug concentration and y = amount of water). Afterwards, the samples were dried at room temperature (∼30 ◦ C). 2.2. Characterization techniques Powder X-ray diffraction measurements were performed on a ˚ Siemens X-ray diffractometer using CuK␣ radiation ( = 1.5416 A). The samples were placed in a glass sample holder and measured from 5 to 65◦ (2), with a step time of 3 s and a step size of 0.02◦ (2). Thermal analysis tests were made in a STA 409 EP Netzsch equipment. The samples were heated from 20 up to 800 ◦ C with a heat rate of 10 ◦ C/min in a static air atmosphere without a reference material. The amount used for this experiment was 100 mg of each sample. FTIR spectra were recorded mixing 5 mg of the sample with 195 mg of KBr (previously heated at 100 ◦ C for 2 h, to avoid external water presence) using a Thermo Nicolet Nexus 670 FTIR spectrophotometer. The wave number range was 4000–450 cm−1 . The particle shape was observed with a transmission electron microscope, TEM (Zeiss EM910), operated at 100 kV, with a side entry goniometer with a 0.4 nm point-to-point resolution attached to a CCD camera (Megavission III image processor). Bright field techniques were applied in order to characterize the morphology of the samples by means of mass-thickness contrast since the materials were amorphous. The surface properties such as BET specific surface area, total pore volume (Vp ), and mean radius pore (r) were determined from N2 adsorption isotherms determined at 77 K with a Micrometrics ASAP2020. Specific surface areas were calculated with the BET equation [23] and pore size distribution with the BJH method [24,25]. The total pore volume was taken from the desorption branch of the isotherm at P/P0 = 0.95, assuming complete pore saturation. To evaluate the controlled IFC-305 liberation in vitro, sample pellets of 50 mg and 1 cm in diameter were prepared in a hydraulic press and were immersed in 50 mL of distilled and deionized water at 25 ◦ C. At selected times, aliquots of xIFC–yTi were removed and the released drug was analyzed using UV spectroscopy. A characteristic peak centered at 240 nm (Varian Cary III Spectrophotometer) was selected in order to obtain the concentration of the drug. The concentration was determined using a calibration curve (Lambert–Beer Law) from 2.8 × 10−3 up to 25.9 × 10−3 g. 3. Results 3.1. X-ray diffraction and thermal stability The X-ray diffractograms of silica matrices with different water contents show mainly a wide peak with the highest intensity centered at 22◦ (2), assigned to the characteristic reflection of
amorphous silica. When the drug is incorporated to a SiO2 matrix, the powder patterns were similar even with 30% of drug; therefore, no crystalline phases are obtained during the sol–gel synthesis. In order to study the thermal stability of the system IFC/SiO2 , samples were analyzed by DTA/TGA. From TGA three steps of weight losses were observed on pure IFC. A strong exothermic peak at 231 ◦ C with a loss of 50% is related to a drug evaporation process, then a loss of 10% due to soft degradation at 440 ◦ C, and finally an endothermic 40% weight loss due to complete drug decomposition at 566 ◦ C. The curve profiles for the decomposition of as-prepared silica xerogel with variation of water exhibits a similar shape to that reported elsewhere [9,21,26]. Two weight drops were observed, the first one between room temperature and 180 ◦ C, related to water loss (dehydration) and the beginning of dehydroxylation due to the condensation of OH groups in the silica particles, with a weight loss of 17%. At higher temperature from 200 ◦ C up to about 600 ◦ C, a continuous weight loss of 7% was related to silane groups of the xerogel that were condensed to siloxanes. With a higher amount of water the behavior is similar; however, the weight loss percentage increases in the first step. DTA analysis showed a strong endothermic signal at 140 ◦ C and two small exothermic peaks at 240 ◦ C and 320 ◦ C, representing respectively, desorbed water, dehydroxylation and decomposition of the organic remains from the xerogel. When the drug is loaded, a weight loss of 18% at 140 ◦ C related to an endothermic peak at 150 ◦ C, is due to water evaporation. The signal decreased since the hydrolysis process was inhibited when higher drug content was incorporated in the system. On the other hand, if the drug concentration maintains constant and water content increases, a loss of weight step of 17% occurs at 210 ◦ C due to water elimination. The DTA results show a sharp exothermic peak that shifts to higher temperature from 100 ◦ C up to 150 ◦ C when the water content increases, which can be ascribed to the variation in the amount of hydroxyl groups surrounding the silicon atoms. A small exothermic peak at 320 ◦ C and an endothermic peak at 410 ◦ C, are due to elimination of organic molecules from silica xerogel and drug decomposition, respectively. Finally, a second signal of weight loss of 8% at 650 ◦ C corresponds to the matrix xerogel condensation. 3.2. FTIR analysis The IR spectra for the silica matrix (Fig. 1a) show in the high energy region a wide band from 4000 up to 2700 cm−1 due to vibrations of OH from silanol groups, Si–OH and from water. In the medium and lower energy region, 1700–450 cm−1 , small vibrational modes at 1639 and 1386 cm−1 are related to C–H stretching characteristic of CH2 /CH3 , indicating the presence of remaining methoxy groups. The following bands are well established to specific molecular motions that can be taken as the silica fingerprint [27]. The signals at 1220 and 1083 cm−1 belong to Si–O stretching. The band centered at 954 cm−1 is associated with the stretching mode of non-bridging oxide bands as Si–OH and Si–O− . The band around at 795 cm−1 is assigned to the symmetric stretching of the Si–O–Si mode. The lowest frequency modes (550 and 470 cm−1 ) are associated with the rocking motions perpendicular to the Si–O–Si plane, of the oxygen bridging two adjacent Si atoms that formed the tetra or trisiloxane rings [21,27]. The intensity of the bands diminishes when the water concentration increases (Fig. 1a), mainly those related to OH vibrations coming from the xerogel and from free or adsorbed water at 3700–3000 cm−1 , as well as the band attributed to asymmetric stretching vibrations of Si–O–Si at 1083 cm−1 , which includes the vibrations from the silica–alcoxy compound SiO–CO. This band appears always accompanied by an intense shoulder at the high frequency side (1220 cm−1 ) due to the interactions of transversal–longitudinal optical modes, which has been detected for several derived silica-TEOS xerogel materials [27]. The concen-
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Fig. 1. Infrared spectra of (a) pure silica synthesized with different amounts of water and (b) pure IFC-305.
tration of TEOS remains constant when the water content is raised, consequently, the hydrolysis and condensation kinetics increase, causing a reduction in the time of gelation; therefore, the formation of hydrogen bridges are not favored [28]. The infrared spectrum of IFC-305 shows several bands (Fig. 1b). In the high energy region from 4000 up to 1800 cm−1 , the appearance of absorption bands correspond to stretching vibrations of OH, NH and CH2 groups. The signals at 3328 and 3174 cm−1 are assigned to NH and OH modes from the ring and the amino groups. Several small bands between 2900 and 2600 cm−1 together with 1926 cm−1 , belong to aromatic and aliphatic CH modes. The broad band between 2700 and 2300 cm−1 has been assigned to an associated N–H mode, intermolecular hydrogen bonded in the form of N–H· · ·N hydrogen bonds. The bands below 1800 cm−1 are attributed to chains and ring skeletal vibrations of H–C–H, C O, H–N–H, C–N. The strong signal at 1665 cm−1 is related to an in-plane deformation mode of NH2 group, and the ones at 1604 and 1571 cm−1 to N–H vibration inplane and C O stretching. Angell [29] has pointed out a series of five fairly strong absorptions between 1500 and 1300 cm−1 assigned to ring vibrations CN single and double bonds, and also to a deformation mode of CH groups. At lower frequencies the absorptions bands at 1210, 1111, 1071, 1058 and 1012 cm−1 are related to C–N, CC and CH stretching and deformation modes, the bands at 979, 903 and 844 cm−1 belong to the skeletal ring, the bands at 794 and 768 cm−1 are attributed to CH, and finally the vibrations at 643 595 and 564 cm−1 correspond to a deformation mode of NH, COO− , and CH2 [30,31]. When the drug is incorporated into the matrix some spectral features of the xerogel are observed. The appearance of the spectra suggests that the system of IFC/SiO2 gels, either with or without
the drug, was well hydrolyzed and polymerized. The spectra for two drug concentrations (10 and 30%) and with different amounts of water are analyzed (Fig. 2a and b). In the high energy region, the band from 3600 up to 3200 cm−1 is attributed to H bonded to Si–OH in chains (Si–OH stretching), the highest band centered at 3450 cm−1 (O–H stretching) is assigned to silanol Si–OH groups linked to molecular H2 O through hydrogen bridges [27]. A sharp signal at 3740 cm−1 is assigned to free, Si–OH silanols on the surface of the xerogel, and a shoulder at 3660 cm−1 is due to a pair of surface Si–OH groups mutually linked by hydrogen bond or internal Si–OH bonds (isolated OH and terminal OH). The intensity of these bands changes due to the interaction between the drug and the matrix. The free Si–OH silanols band at 3740 cm−1 and the vibrational mode associated to isolated and terminal OH at 3660 cm−1 are bigger when a low amount of drug is incorporated (10%). The broad band below 2700 cm−1 corresponds to N–H mode, which is forming hydrogen bonds N–H· · ·N intermolecularly within the organic compounds associated to the drug and with silanol groups which are interacting through hydrogen bonds associated to molecularly adsorbed water. These bands predominate in those systems with 16 and 24 mol of water for both loaded drug amounts, indicating that a large number of OH groups and H2 O molecules are present on the surface, which play an important role in bonding [SiO4 ] ions with IFC molecules. The absorption bands observed below 2000 cm−1 belong to the silica matrix, which is overlapping IFC signals, however, the appearance of small bands within the range of 1690–1390 cm−1 indicates the presence of the drug organic groups. Special features can be detected when a comparison is made between the infrared spectra of the silica matrix with the system IFC–ySi. Some bands shifts to a lower energy region when the
Fig. 2. Infrared spectra of silica prepared with different hydrolysis ratios (y = mol of H2 O) and drug concentration. (a) 10% of IFC and (b) 30% of IFC.
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Fig. 3. N2 adsorption–desorption isotherms and pore distribution with different water contents, y = 4, 8, 16, 24 mol: (a) functionalized SiO2 matrix and (b) IFC/SiO2 system with 10% of drug.
drug is incorporated into the xerogel and when the water content increases. The absorption band of the xerogel at 3467 cm−1 in Fig. 1, shifts up to 3328 and 3311 cm−1 for 10% and 30% of IFC (Fig. 2), respectively. The strong band at 1083 cm−1 with a shoulder at 1220 and the band at 954 cm−1 increase their intensity and shift to 1080, 1202 and 935 cm−1 for lower IFC, and 1076, 1166 and 942 cm−1 for higher drug content. The displacement of the bands is due to the formation of weak hydrogen bond interactions O–H· · ·O, within the OH of Si–O· · ·H of silica and the NH and OH groups of the IFC organic compounds. 3.3. N2 adsorption–desorption isotherms and morphology The N2 adsorption isotherms and pore distribution for the pure silica matrix with different amounts of water are presented in Fig. 3a. All isotherms exhibit type I behavior with a small adsorption at low relative pressures, which is considered to be indicative of adsorption in micropores, since the isotherm levels off below the relative pressure of 0.1. However, the pore diameter is less than 15 nm (inset Fig. 3a), therefore, it can be classified as a mesoporous solid close to the micropore range. The shape of the hysteresis loop is H4, remaining horizontal and parallel over a wide range of P/P0 , associated to adsorption–desorption in narrow slit-like pores [13]. From BET analysis, no large differences in specific surface area with variation of water content can be seen, the values range from 132 up to 168 m2 /g, being the highest for 4 mol of water; however, the mean volume pore remains constant at 0.08 cm3 /g, with pore width values of 1.68 and 4.81, for 4 and 24 mol of water, respectively. When 10% of drug is loaded into the reservoirs, the profiles of the physisorption isotherms change with water content (Fig. 3b). For the lowest amount (4 mol of water) an isotherm type IV associated with adsorption on mesoporous solids via multilayer adsorption followed by capillary condensation is observed, where the limiting uptake occurs at high P/P0 . The pore width range of the mesoporous material is 4-14 nm (inset Fig. 3b). The desorption hysteresis is type H1, and is associated with porous materials with approximately spherical particles arranged in a uniform way with a relatively high pore size and pore connectivity [13]. This correlates well with BET analysis since the obtained mean pore volume of 0.6 cc/g and a pore width of 1.64 nm increase and also the specific surface area increases to 316 m2 /g. Isotherm adsorption behavior for higher water content are similar, they show a concave shape to the P/P0 axis characteristics of type I, which is related to microporous solids with a limiting uptake controlled by the accessible micropore volume, since the relative pressure levels off below 0.1. However, the hysteresis loop for intermediate water content (8 and 16 mol) is type H4 since it remains horizontal and parallel over a wide range of P/P0 , and is associated with narrow slit-like pores; meanwhile, for 24 mol of water the isotherm shows a hysteresis loop type
H2 attributed to a condensation–evaporation processes occurring in uniform channel-like pores, since the adsorption–desorption branches are located at intermediate relative pressures [13]. BET results of the silica matrix loaded with 10% of IFC in comparison with the unloaded system, for intermediate amount of water, illustrate that the specific surface area and the mean volume area decrease to 76 m2 /g and 0.05 cc/g, respectively. On the other hand, for the highest amount of water, the specific surface area and the mean volume increase to 487 m2 /g and 0.4 cc/g, respectively; meanwhile, the pore width maintains constant at 1.21 nm. The isotherms profile and BET data for the systems where the drug content increases are not shown since the specific surface area diminishes to 64 m2 /g. TEM analysis shows the production of a variety of shapes depending on the amount of water and in all cases the aggregation of particles is observed; however, the presence of small particles inside a bigger structure can be detected (Fig. 4). The material is constituted of small nanoparticles of less than 2 nm, except for the system with 16 mol of water, which shows multiple layered bigger aggregates (>100 nm), and the coalescence favors the cluster formation with smooth surfaces [12]. These morphologies can be well correlated to the obtained BET results, for loosely compacted submicrometer sized particles the microporosity increases therefore a higher superficial area and mean pore volume are obtained for the lowest and highest amount of water, and when a compact structure is obtained, the BET parameters diminish [12]. The gel agglomeration may be due to the differences in the hydrolysis reaction rate, since IFC itself has acid groups and can act as an acidic catalyst [31]. 3.4. In vitro drug release The behavior of drug release for the mixture of silica with different concentrations of IFC-305 and water content are presented in Fig. 5. With 10%, a remarkable slow discharge response is obtained with a continuous increasing release rate after 1000 h, being 3% and 10% the amount of drug for the low and high water content, respectively. When the drug load increases (20%) no significant changes are detected with the variation of water, the drug delivery range during the first 96 h is from 45 to 70%, then the release rate slows down, discharging almost 25% of IFC at the end of the experiment. Finally, for reservoirs with 30% of IFC, a fast delivery rate response is obtained between 75 and 93%, during 168 h, except the sample with 24 mol of water which showed the same behavior as the 20% of IFC systems, initially 75% of drug is released at 48 h and then 10% during the following 850 h. With a low drug content, the release rate is controlled by the drug–matrix interactions due to the formation of two hydrogen bond types, O–H· · ·O and O–H· · ·N, within the OH groups of silica and the NH and OH groups of the drug [32,33], which occurs inside the micro- and mesoporous matrix. However, at higher drug con-
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Fig. 4. Transmission electron microscopy of IFC/silica system synthesized with different hydrolysis ratios and 20% of drug concentration: (a) 4 mol of water; (b) 8 mol of water; (c) 16 mol of water and (d) 24 mol of water.
centration the release rate is controlled by the molecules bonded on the matrix surface showing a fast drug release during a short period of time, afterwards, only a small amount of molecules inside the micropores are discharged. It has been reported that, when drugs with organic acids are incorporated into the silica surface in the presence of amino groups, they are acting as strong anchoring points during the impregnation in the xerogel matrix, suppressing the release rate due to the strong carboxylic acid–amine interactions [34,35]. On the other hand, the diffusion of molecules inside of microporous solids is much slower than inside a mesoporous
gel, and the release rate is even smaller when gels are synthesized under acidic conditions [14]. Therefore, increasing the drug content and decreasing the gel-particle size, enhance the release rate. Also it has been observed that IFC/silica reservoirs upon contact with water show a strong swelling and erosion, favoring the drug dissolution and steeply increasing the delivery rate when the drug concentration is higher (Fig. 5b) [36]. Therefore, the release mechanism is probably a combination of diffusion and dissolution processes [14]. The latter is visually observed since swelling and erosion occurs when IFC/silica reservoirs are in contact with water.
Fig. 5. Release profiles with 10, 20 and 30% of IFC-305 encapsulated into TiO2 matrix synthesized at different water contents (4, 8, 16 and 24 mol).
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4. Conclusions In the present work, silica nanoparticles loaded with IFC-305, a promising therapeutic drug for the treatment of the cirrhotic liver, were functionalized with OH groups by the sol–gel method using different molar hydrolysis ratios of water and drug concentrations. The results show that the drug is stabilized into the silica xerogel, since the corresponding molecular vibrations of the functional groups from IFC-305 remain while incorporated in the xerogel structure. For the samples synthesized with low water content, a stronger interaction between the drug and SiO2 matrix is favored, generating free OH loose on the nanoparticle surface. With high water content, the band intensity of free OH is lower indicating that IFC-305 could have a better release behavior due to the formation of hydrogen bonds between the xerogel surface and IFC. Therefore, some absorption bands shift to a lower energy due to drug–matrix interaction since it favors the formation of hydrogen bonds within the OH of silica and the NH and OH groups of the drug. It has been observed that the drug release behavior under in vitro conditions was independent of the amount of hydrolyzed water, although it was affected by the drug content. Upon incorporating a low amount of drug, a micro/mesoporous IFC/silica system is produced, due to the presence of organic acid and amino groups that can be incorporated to silica matrix, therefore, a slow release rate is obtained due to the strong carboxylic acid–amine interactions. However, increasing IFC content, microporous solids are obtained, therefore, fast drug release is obtained during a short period of time since the drug molecules are mainly bonded on the matrix surface. It is proposed that the rate of drug release is a combination of dissolution and diffusion processes, and the release rates can be controlled by the internal structure of the particles for a desired diffusion profile. The results suggest that these materials can be used for liver targeted drug delivery reservoirs. Acknowledgements The authors thank to the Universidad Autónoma Metropolitana, to the Instituto Nacional de Neurología y Neurocirugía in México and to CONACYT-FONCICYT Project 96095 and FOMIX-108160, for financially and technically supporting this research, also to P. Castillo, E. Ortiz and D.H. Aguilar for technical support. Authors gratefully acknowledge the corrections made to the manuscript by Dr. G. Oskam. References [1] C. Bosseti, F. Levi, F. Lucchini, W.A. Zatonski, E. Negri, C. La Vecchia, Worldwide mortality from cirrhosis: an update to 2002, J. Hepatol. 46 (2007) 827–839. [2] Main general mortality causes, 2005 report. http://sinais.salud.gob. mx/mortalidad/mortalidad.htm. [3] N. Mendez-Sanchez, A.R. Villa, N.C. Chavez-Tapia, G. Ponciano-Rodriguez, P. Almeda-Valdes, D. Gonzalez, M. Uribe, Trends in liver disease prevalence in Mexico from 2005 to 2050 through mortality data, Ann. Hepatol. 4 (2005) 52–55. [4] R. Liang, J. Qiu, P. Cai, A novel amperometric immunosensor based on threedimensional sol–gel network and nanoparticle self-assemble technique, Anal. Chim. Acta 534 (2005) 223–229. [5] S. Santra, D. Dutta, B.M. Moudgil, Functional dye-doped silica nanoparticles for bioimaging, diagnostics and therapeutics, Trans. IChemE. Part C 83 (2005) 136–140. [6] D. Halamova, M. Badanicova, V. Zelenak, T. Gondova, U. Vainio, Naproxen drug delivery using periodic mesoporous silica SBA-15, Appl. Surf. Sci. 256 (2010) 6489–6494. [7] S. Radin, T. Chen, P. Ducheyne, The controlled release of drugs from emulsified, sol–gel processed silica microspheres, Biomaterials 30 (2009) 850–858. [8] M. Prokopowicz, Correlation between physicochemical properties of doxorubicin-loaded silica/polydimethylsiloxane xerogel and in vitro release of drug, Acta Biomater. 5 (2009) 193–207.
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Controlled release of IFC-305 encapsulated in silica nanoparticles for liver cancer synthesized by sol–gel León Albarran a,b , Tessy López a,b , Patricia Quintana c,∗ , Victoria Chagoya d a
Universidad Autónoma Metropolitana–Xochimilco, Calzada del Hueso 1100, Col. Villa Quietud, Coyoacán, C.P. 04960, D.F. México, Mexico National Neurology and Neurosurgery Institute Nanotechnology for Medicine Laboratory, Av. Insurgentes Sur 3877, Col. La Fama, Tlalpan, 14269, D.F. México, Mexico Departmento de Física Aplicada, CINVESTAV-IPN, Unidad Mérida, A.P. 73, Cordemex, C.P. 97310, Mérida, Yucatán, México, Mexico d Departmento de Biología Celular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Coyoacán, CP 04510, D.F. México, Mexico b c
a r t i c l e
i n f o
Article history: Received 29 September 2010 Received in revised form 10 March 2011 Accepted 18 March 2011 Available online 26 March 2011 Keywords: IFC-305 Silica sol–gel FTIR BET Drug release UV-Vis
a b s t r a c t IFC-305 was encapsulated into nanostructured silica and functionalized with OH groups by the sol–gel process using tetraethoxysilane (TEOS), to be used for a drug delivery system for the treatment of liver cancer. Synthesis was carried out at different molar hydrolysis ratios: 4, 8, 16 and 24 mol of water and drug concentrations of 10, 20 and 30%. Characterization of IFC-silica reservoirs by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal analysis (DTA-TGA), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms (BET), confirms that IFC-305 was trapped and stabilized in the SiO2 –OH matrix. Drug release was determined by UV spectrophotometry over a period of 1000 h. Results showed that the morphology and specific surface area are controlled by the amount of loaded drug and water content for the different synthesized reservoir systems. However, the in vitro analysis of drug discharge showed that the rate of drug release was independent of the amount of hydrolyzed water, although it was affected by the quantity of drug loaded. The mechanism of drug release is a combination of dissolution and diffusion processes. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Chronic liver diseases are a major health issue world-wide [1]. In Mexico, the mortality rate due to cirrhosis ranks among the highest in the world, being the third cause of death in the general population and the second in young adults in 2005 [2]; in that year, patients died due to liver cirrhosis and other chronic liver diseases at a rate of 25.9/100,000 inhabitants, and a steady rise in the number of cases is expected to occur in the following years [2,3]. Cirrhosis is a chronic degenerative disease in which normal liver cells are damaged and are then replaced by scar tissue; therefore, it reduces the liver’s ability to manufacture proteins and process hormones, nutrients, medications and the normal biochemical processes. In recent years, application of nanotechnology for the treatment of human diseases holds great promise. In particular, the use of SiO2 nanoparticles has been extended to biomedical and biotechnological fields, since it has a unique matrix that allows the incorporation of different types of molecules. It has been applied as biosensors and biomarkers [4], as well as for cellular imaging applications [5]. For controlled release applications, it has been shown that silica is able to store and gradually release therapeutically relevant drugs like antibiotics [6–8], or drugs for treating neurological diseases
∗ Corresponding author. Tel.: +52 999 9429442; fax: +52 999 9812917. E-mail address: [email protected] (P. Quintana). 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.03.042
as such as dopamine, valproic acid and sodium phenytoin [9–12]. Furthermore, silica nanoparticles have been used to enhance the biocompatibility of several drug delivery systems for cancer therapy and catalysis [8,13–15]. Amorphous, sol–gel derived SiO2 is known to be a biocompatible and bioresorbable material that has potential applications as implants or injectable matrices in the controlled delivery of biologically active agents in living tissues [16,17]. The sol is produced through hydrolysis and polycondensation reaction [18] from an alkoxide precursor. Due to the mild processing conditions, high concentrations of many types of biologically active agent can be incorporated in the liquid (sol) and, afterwards, is embedded in the matrix (gel), which after condensation and drying becomes a porous solid material [5–11]. It is also well known that release is dependent on synthesis parameters such as the molar ratio of silica precursor to water, type of precursor and the concentration of bioactive drug [8,12,19–21]. A promising therapeutic alternative to treat liver cirrhosis disease is the use of a novel drug called IFC-305, a derivative of 6-aminoribofuranosil purine, which has been tested to revert cirrhosis and liver dysfunction in rats, however, it shows a very short half-life due to its rapid metabolism in the liver [22]. In this work, silica nanoparticles were synthesized to encapsulate IFC-305, and to provide a stable reservoir to target the delivery of the drug to the liver in order to improve the metabolic stability and to achieve the appropriate dosage, needed to result in an efficient treatment. The
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drug molecule and both empty and loaded reservoirs were characterized to understand the linking mechanism, to verify the IFC-305 stabilization and to analyze in vitro the drug release behavior, with variation in the amount of water and drug content. 2. Materials and methods 2.1. Synthesis IFC-305 occluded into silica sol–gel was prepared with three different drug concentrations 10, 20 and 30%. SiO2 matrix was synthesized adding 70 mL of tetraethoxysilane (TEOS) to a drug aqueous solution, with a certain amount of water in order to have four different molar hydrolysis ratios, corresponding to 4, 8, 16 and 24 mol of water. Therefore, 12 samples were obtained with different ratios and were named as xIFC–ySi (x = drug concentration and y = amount of water). Afterwards, the samples were dried at room temperature (∼30 ◦ C). 2.2. Characterization techniques Powder X-ray diffraction measurements were performed on a ˚ Siemens X-ray diffractometer using CuK␣ radiation ( = 1.5416 A). The samples were placed in a glass sample holder and measured from 5 to 65◦ (2), with a step time of 3 s and a step size of 0.02◦ (2). Thermal analysis tests were made in a STA 409 EP Netzsch equipment. The samples were heated from 20 up to 800 ◦ C with a heat rate of 10 ◦ C/min in a static air atmosphere without a reference material. The amount used for this experiment was 100 mg of each sample. FTIR spectra were recorded mixing 5 mg of the sample with 195 mg of KBr (previously heated at 100 ◦ C for 2 h, to avoid external water presence) using a Thermo Nicolet Nexus 670 FTIR spectrophotometer. The wave number range was 4000–450 cm−1 . The particle shape was observed with a transmission electron microscope, TEM (Zeiss EM910), operated at 100 kV, with a side entry goniometer with a 0.4 nm point-to-point resolution attached to a CCD camera (Megavission III image processor). Bright field techniques were applied in order to characterize the morphology of the samples by means of mass-thickness contrast since the materials were amorphous. The surface properties such as BET specific surface area, total pore volume (Vp ), and mean radius pore (r) were determined from N2 adsorption isotherms determined at 77 K with a Micrometrics ASAP2020. Specific surface areas were calculated with the BET equation [23] and pore size distribution with the BJH method [24,25]. The total pore volume was taken from the desorption branch of the isotherm at P/P0 = 0.95, assuming complete pore saturation. To evaluate the controlled IFC-305 liberation in vitro, sample pellets of 50 mg and 1 cm in diameter were prepared in a hydraulic press and were immersed in 50 mL of distilled and deionized water at 25 ◦ C. At selected times, aliquots of xIFC–yTi were removed and the released drug was analyzed using UV spectroscopy. A characteristic peak centered at 240 nm (Varian Cary III Spectrophotometer) was selected in order to obtain the concentration of the drug. The concentration was determined using a calibration curve (Lambert–Beer Law) from 2.8 × 10−3 up to 25.9 × 10−3 g. 3. Results 3.1. X-ray diffraction and thermal stability The X-ray diffractograms of silica matrices with different water contents show mainly a wide peak with the highest intensity centered at 22◦ (2), assigned to the characteristic reflection of
amorphous silica. When the drug is incorporated to a SiO2 matrix, the powder patterns were similar even with 30% of drug; therefore, no crystalline phases are obtained during the sol–gel synthesis. In order to study the thermal stability of the system IFC/SiO2 , samples were analyzed by DTA/TGA. From TGA three steps of weight losses were observed on pure IFC. A strong exothermic peak at 231 ◦ C with a loss of 50% is related to a drug evaporation process, then a loss of 10% due to soft degradation at 440 ◦ C, and finally an endothermic 40% weight loss due to complete drug decomposition at 566 ◦ C. The curve profiles for the decomposition of as-prepared silica xerogel with variation of water exhibits a similar shape to that reported elsewhere [9,21,26]. Two weight drops were observed, the first one between room temperature and 180 ◦ C, related to water loss (dehydration) and the beginning of dehydroxylation due to the condensation of OH groups in the silica particles, with a weight loss of 17%. At higher temperature from 200 ◦ C up to about 600 ◦ C, a continuous weight loss of 7% was related to silane groups of the xerogel that were condensed to siloxanes. With a higher amount of water the behavior is similar; however, the weight loss percentage increases in the first step. DTA analysis showed a strong endothermic signal at 140 ◦ C and two small exothermic peaks at 240 ◦ C and 320 ◦ C, representing respectively, desorbed water, dehydroxylation and decomposition of the organic remains from the xerogel. When the drug is loaded, a weight loss of 18% at 140 ◦ C related to an endothermic peak at 150 ◦ C, is due to water evaporation. The signal decreased since the hydrolysis process was inhibited when higher drug content was incorporated in the system. On the other hand, if the drug concentration maintains constant and water content increases, a loss of weight step of 17% occurs at 210 ◦ C due to water elimination. The DTA results show a sharp exothermic peak that shifts to higher temperature from 100 ◦ C up to 150 ◦ C when the water content increases, which can be ascribed to the variation in the amount of hydroxyl groups surrounding the silicon atoms. A small exothermic peak at 320 ◦ C and an endothermic peak at 410 ◦ C, are due to elimination of organic molecules from silica xerogel and drug decomposition, respectively. Finally, a second signal of weight loss of 8% at 650 ◦ C corresponds to the matrix xerogel condensation. 3.2. FTIR analysis The IR spectra for the silica matrix (Fig. 1a) show in the high energy region a wide band from 4000 up to 2700 cm−1 due to vibrations of OH from silanol groups, Si–OH and from water. In the medium and lower energy region, 1700–450 cm−1 , small vibrational modes at 1639 and 1386 cm−1 are related to C–H stretching characteristic of CH2 /CH3 , indicating the presence of remaining methoxy groups. The following bands are well established to specific molecular motions that can be taken as the silica fingerprint [27]. The signals at 1220 and 1083 cm−1 belong to Si–O stretching. The band centered at 954 cm−1 is associated with the stretching mode of non-bridging oxide bands as Si–OH and Si–O− . The band around at 795 cm−1 is assigned to the symmetric stretching of the Si–O–Si mode. The lowest frequency modes (550 and 470 cm−1 ) are associated with the rocking motions perpendicular to the Si–O–Si plane, of the oxygen bridging two adjacent Si atoms that formed the tetra or trisiloxane rings [21,27]. The intensity of the bands diminishes when the water concentration increases (Fig. 1a), mainly those related to OH vibrations coming from the xerogel and from free or adsorbed water at 3700–3000 cm−1 , as well as the band attributed to asymmetric stretching vibrations of Si–O–Si at 1083 cm−1 , which includes the vibrations from the silica–alcoxy compound SiO–CO. This band appears always accompanied by an intense shoulder at the high frequency side (1220 cm−1 ) due to the interactions of transversal–longitudinal optical modes, which has been detected for several derived silica-TEOS xerogel materials [27]. The concen-
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Fig. 1. Infrared spectra of (a) pure silica synthesized with different amounts of water and (b) pure IFC-305.
tration of TEOS remains constant when the water content is raised, consequently, the hydrolysis and condensation kinetics increase, causing a reduction in the time of gelation; therefore, the formation of hydrogen bridges are not favored [28]. The infrared spectrum of IFC-305 shows several bands (Fig. 1b). In the high energy region from 4000 up to 1800 cm−1 , the appearance of absorption bands correspond to stretching vibrations of OH, NH and CH2 groups. The signals at 3328 and 3174 cm−1 are assigned to NH and OH modes from the ring and the amino groups. Several small bands between 2900 and 2600 cm−1 together with 1926 cm−1 , belong to aromatic and aliphatic CH modes. The broad band between 2700 and 2300 cm−1 has been assigned to an associated N–H mode, intermolecular hydrogen bonded in the form of N–H· · ·N hydrogen bonds. The bands below 1800 cm−1 are attributed to chains and ring skeletal vibrations of H–C–H, C O, H–N–H, C–N. The strong signal at 1665 cm−1 is related to an in-plane deformation mode of NH2 group, and the ones at 1604 and 1571 cm−1 to N–H vibration inplane and C O stretching. Angell [29] has pointed out a series of five fairly strong absorptions between 1500 and 1300 cm−1 assigned to ring vibrations CN single and double bonds, and also to a deformation mode of CH groups. At lower frequencies the absorptions bands at 1210, 1111, 1071, 1058 and 1012 cm−1 are related to C–N, CC and CH stretching and deformation modes, the bands at 979, 903 and 844 cm−1 belong to the skeletal ring, the bands at 794 and 768 cm−1 are attributed to CH, and finally the vibrations at 643 595 and 564 cm−1 correspond to a deformation mode of NH, COO− , and CH2 [30,31]. When the drug is incorporated into the matrix some spectral features of the xerogel are observed. The appearance of the spectra suggests that the system of IFC/SiO2 gels, either with or without
the drug, was well hydrolyzed and polymerized. The spectra for two drug concentrations (10 and 30%) and with different amounts of water are analyzed (Fig. 2a and b). In the high energy region, the band from 3600 up to 3200 cm−1 is attributed to H bonded to Si–OH in chains (Si–OH stretching), the highest band centered at 3450 cm−1 (O–H stretching) is assigned to silanol Si–OH groups linked to molecular H2 O through hydrogen bridges [27]. A sharp signal at 3740 cm−1 is assigned to free, Si–OH silanols on the surface of the xerogel, and a shoulder at 3660 cm−1 is due to a pair of surface Si–OH groups mutually linked by hydrogen bond or internal Si–OH bonds (isolated OH and terminal OH). The intensity of these bands changes due to the interaction between the drug and the matrix. The free Si–OH silanols band at 3740 cm−1 and the vibrational mode associated to isolated and terminal OH at 3660 cm−1 are bigger when a low amount of drug is incorporated (10%). The broad band below 2700 cm−1 corresponds to N–H mode, which is forming hydrogen bonds N–H· · ·N intermolecularly within the organic compounds associated to the drug and with silanol groups which are interacting through hydrogen bonds associated to molecularly adsorbed water. These bands predominate in those systems with 16 and 24 mol of water for both loaded drug amounts, indicating that a large number of OH groups and H2 O molecules are present on the surface, which play an important role in bonding [SiO4 ] ions with IFC molecules. The absorption bands observed below 2000 cm−1 belong to the silica matrix, which is overlapping IFC signals, however, the appearance of small bands within the range of 1690–1390 cm−1 indicates the presence of the drug organic groups. Special features can be detected when a comparison is made between the infrared spectra of the silica matrix with the system IFC–ySi. Some bands shifts to a lower energy region when the
Fig. 2. Infrared spectra of silica prepared with different hydrolysis ratios (y = mol of H2 O) and drug concentration. (a) 10% of IFC and (b) 30% of IFC.
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Fig. 3. N2 adsorption–desorption isotherms and pore distribution with different water contents, y = 4, 8, 16, 24 mol: (a) functionalized SiO2 matrix and (b) IFC/SiO2 system with 10% of drug.
drug is incorporated into the xerogel and when the water content increases. The absorption band of the xerogel at 3467 cm−1 in Fig. 1, shifts up to 3328 and 3311 cm−1 for 10% and 30% of IFC (Fig. 2), respectively. The strong band at 1083 cm−1 with a shoulder at 1220 and the band at 954 cm−1 increase their intensity and shift to 1080, 1202 and 935 cm−1 for lower IFC, and 1076, 1166 and 942 cm−1 for higher drug content. The displacement of the bands is due to the formation of weak hydrogen bond interactions O–H· · ·O, within the OH of Si–O· · ·H of silica and the NH and OH groups of the IFC organic compounds. 3.3. N2 adsorption–desorption isotherms and morphology The N2 adsorption isotherms and pore distribution for the pure silica matrix with different amounts of water are presented in Fig. 3a. All isotherms exhibit type I behavior with a small adsorption at low relative pressures, which is considered to be indicative of adsorption in micropores, since the isotherm levels off below the relative pressure of 0.1. However, the pore diameter is less than 15 nm (inset Fig. 3a), therefore, it can be classified as a mesoporous solid close to the micropore range. The shape of the hysteresis loop is H4, remaining horizontal and parallel over a wide range of P/P0 , associated to adsorption–desorption in narrow slit-like pores [13]. From BET analysis, no large differences in specific surface area with variation of water content can be seen, the values range from 132 up to 168 m2 /g, being the highest for 4 mol of water; however, the mean volume pore remains constant at 0.08 cm3 /g, with pore width values of 1.68 and 4.81, for 4 and 24 mol of water, respectively. When 10% of drug is loaded into the reservoirs, the profiles of the physisorption isotherms change with water content (Fig. 3b). For the lowest amount (4 mol of water) an isotherm type IV associated with adsorption on mesoporous solids via multilayer adsorption followed by capillary condensation is observed, where the limiting uptake occurs at high P/P0 . The pore width range of the mesoporous material is 4-14 nm (inset Fig. 3b). The desorption hysteresis is type H1, and is associated with porous materials with approximately spherical particles arranged in a uniform way with a relatively high pore size and pore connectivity [13]. This correlates well with BET analysis since the obtained mean pore volume of 0.6 cc/g and a pore width of 1.64 nm increase and also the specific surface area increases to 316 m2 /g. Isotherm adsorption behavior for higher water content are similar, they show a concave shape to the P/P0 axis characteristics of type I, which is related to microporous solids with a limiting uptake controlled by the accessible micropore volume, since the relative pressure levels off below 0.1. However, the hysteresis loop for intermediate water content (8 and 16 mol) is type H4 since it remains horizontal and parallel over a wide range of P/P0 , and is associated with narrow slit-like pores; meanwhile, for 24 mol of water the isotherm shows a hysteresis loop type
H2 attributed to a condensation–evaporation processes occurring in uniform channel-like pores, since the adsorption–desorption branches are located at intermediate relative pressures [13]. BET results of the silica matrix loaded with 10% of IFC in comparison with the unloaded system, for intermediate amount of water, illustrate that the specific surface area and the mean volume area decrease to 76 m2 /g and 0.05 cc/g, respectively. On the other hand, for the highest amount of water, the specific surface area and the mean volume increase to 487 m2 /g and 0.4 cc/g, respectively; meanwhile, the pore width maintains constant at 1.21 nm. The isotherms profile and BET data for the systems where the drug content increases are not shown since the specific surface area diminishes to 64 m2 /g. TEM analysis shows the production of a variety of shapes depending on the amount of water and in all cases the aggregation of particles is observed; however, the presence of small particles inside a bigger structure can be detected (Fig. 4). The material is constituted of small nanoparticles of less than 2 nm, except for the system with 16 mol of water, which shows multiple layered bigger aggregates (>100 nm), and the coalescence favors the cluster formation with smooth surfaces [12]. These morphologies can be well correlated to the obtained BET results, for loosely compacted submicrometer sized particles the microporosity increases therefore a higher superficial area and mean pore volume are obtained for the lowest and highest amount of water, and when a compact structure is obtained, the BET parameters diminish [12]. The gel agglomeration may be due to the differences in the hydrolysis reaction rate, since IFC itself has acid groups and can act as an acidic catalyst [31]. 3.4. In vitro drug release The behavior of drug release for the mixture of silica with different concentrations of IFC-305 and water content are presented in Fig. 5. With 10%, a remarkable slow discharge response is obtained with a continuous increasing release rate after 1000 h, being 3% and 10% the amount of drug for the low and high water content, respectively. When the drug load increases (20%) no significant changes are detected with the variation of water, the drug delivery range during the first 96 h is from 45 to 70%, then the release rate slows down, discharging almost 25% of IFC at the end of the experiment. Finally, for reservoirs with 30% of IFC, a fast delivery rate response is obtained between 75 and 93%, during 168 h, except the sample with 24 mol of water which showed the same behavior as the 20% of IFC systems, initially 75% of drug is released at 48 h and then 10% during the following 850 h. With a low drug content, the release rate is controlled by the drug–matrix interactions due to the formation of two hydrogen bond types, O–H· · ·O and O–H· · ·N, within the OH groups of silica and the NH and OH groups of the drug [32,33], which occurs inside the micro- and mesoporous matrix. However, at higher drug con-
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Fig. 4. Transmission electron microscopy of IFC/silica system synthesized with different hydrolysis ratios and 20% of drug concentration: (a) 4 mol of water; (b) 8 mol of water; (c) 16 mol of water and (d) 24 mol of water.
centration the release rate is controlled by the molecules bonded on the matrix surface showing a fast drug release during a short period of time, afterwards, only a small amount of molecules inside the micropores are discharged. It has been reported that, when drugs with organic acids are incorporated into the silica surface in the presence of amino groups, they are acting as strong anchoring points during the impregnation in the xerogel matrix, suppressing the release rate due to the strong carboxylic acid–amine interactions [34,35]. On the other hand, the diffusion of molecules inside of microporous solids is much slower than inside a mesoporous
gel, and the release rate is even smaller when gels are synthesized under acidic conditions [14]. Therefore, increasing the drug content and decreasing the gel-particle size, enhance the release rate. Also it has been observed that IFC/silica reservoirs upon contact with water show a strong swelling and erosion, favoring the drug dissolution and steeply increasing the delivery rate when the drug concentration is higher (Fig. 5b) [36]. Therefore, the release mechanism is probably a combination of diffusion and dissolution processes [14]. The latter is visually observed since swelling and erosion occurs when IFC/silica reservoirs are in contact with water.
Fig. 5. Release profiles with 10, 20 and 30% of IFC-305 encapsulated into TiO2 matrix synthesized at different water contents (4, 8, 16 and 24 mol).
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4. Conclusions In the present work, silica nanoparticles loaded with IFC-305, a promising therapeutic drug for the treatment of the cirrhotic liver, were functionalized with OH groups by the sol–gel method using different molar hydrolysis ratios of water and drug concentrations. The results show that the drug is stabilized into the silica xerogel, since the corresponding molecular vibrations of the functional groups from IFC-305 remain while incorporated in the xerogel structure. For the samples synthesized with low water content, a stronger interaction between the drug and SiO2 matrix is favored, generating free OH loose on the nanoparticle surface. With high water content, the band intensity of free OH is lower indicating that IFC-305 could have a better release behavior due to the formation of hydrogen bonds between the xerogel surface and IFC. Therefore, some absorption bands shift to a lower energy due to drug–matrix interaction since it favors the formation of hydrogen bonds within the OH of silica and the NH and OH groups of the drug. It has been observed that the drug release behavior under in vitro conditions was independent of the amount of hydrolyzed water, although it was affected by the drug content. Upon incorporating a low amount of drug, a micro/mesoporous IFC/silica system is produced, due to the presence of organic acid and amino groups that can be incorporated to silica matrix, therefore, a slow release rate is obtained due to the strong carboxylic acid–amine interactions. However, increasing IFC content, microporous solids are obtained, therefore, fast drug release is obtained during a short period of time since the drug molecules are mainly bonded on the matrix surface. It is proposed that the rate of drug release is a combination of dissolution and diffusion processes, and the release rates can be controlled by the internal structure of the particles for a desired diffusion profile. The results suggest that these materials can be used for liver targeted drug delivery reservoirs. Acknowledgements The authors thank to the Universidad Autónoma Metropolitana, to the Instituto Nacional de Neurología y Neurocirugía in México and to CONACYT-FONCICYT Project 96095 and FOMIX-108160, for financially and technically supporting this research, also to P. Castillo, E. Ortiz and D.H. Aguilar for technical support. Authors gratefully acknowledge the corrections made to the manuscript by Dr. G. Oskam. References [1] C. Bosseti, F. Levi, F. Lucchini, W.A. Zatonski, E. Negri, C. La Vecchia, Worldwide mortality from cirrhosis: an update to 2002, J. Hepatol. 46 (2007) 827–839. [2] Main general mortality causes, 2005 report. http://sinais.salud.gob. mx/mortalidad/mortalidad.htm. [3] N. Mendez-Sanchez, A.R. Villa, N.C. Chavez-Tapia, G. Ponciano-Rodriguez, P. Almeda-Valdes, D. Gonzalez, M. Uribe, Trends in liver disease prevalence in Mexico from 2005 to 2050 through mortality data, Ann. Hepatol. 4 (2005) 52–55. [4] R. Liang, J. Qiu, P. Cai, A novel amperometric immunosensor based on threedimensional sol–gel network and nanoparticle self-assemble technique, Anal. Chim. Acta 534 (2005) 223–229. [5] S. Santra, D. Dutta, B.M. Moudgil, Functional dye-doped silica nanoparticles for bioimaging, diagnostics and therapeutics, Trans. IChemE. Part C 83 (2005) 136–140. [6] D. Halamova, M. Badanicova, V. Zelenak, T. Gondova, U. Vainio, Naproxen drug delivery using periodic mesoporous silica SBA-15, Appl. Surf. Sci. 256 (2010) 6489–6494. [7] S. Radin, T. Chen, P. Ducheyne, The controlled release of drugs from emulsified, sol–gel processed silica microspheres, Biomaterials 30 (2009) 850–858. [8] M. Prokopowicz, Correlation between physicochemical properties of doxorubicin-loaded silica/polydimethylsiloxane xerogel and in vitro release of drug, Acta Biomater. 5 (2009) 193–207.
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