Multifunctional Magnetic Cellulose Surface-Imprinted Microspheres for

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Multifunctional magnetic cellulose surface imprinted microsphere for highly selective adsorption of Artesunate Hailong Huang, Xianghui Wang, Hao Ge, and Min Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00386 • Publication Date (Web): 19 Apr 2016 Downloaded from http://pubs.acs.org on April 21, 2016

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ACS Sustainable Chemistry & Engineering

Multifunctional magnetic cellulose surface imprinted microsphere for highly selective adsorption of Artesunate Hailong Huang, Xianghui Wang, Hao Ge, Min Xu* Shanghai Key Laboratory of Magnetic Resonance, Department of physics, East China Normal University, No. 3663 North Zhongshan Road, Shanghai 200062, P R China

ABSTRACT: Molecularly imprinted magnetic composite microspheres（ MIP-MCM） of artesunate (Ars), is developed by a surface functional monomer-directing system. The MIP-MCM is obtained by coating a layer of MIP on the surface of the cellulose and Fe3O4 composite microspheres. The composite materials are characterized by Fourier transform infrared spectra (FTIR), X-ray powder diffraction (XRD), Vibrating Sample Magnetometry (VSM), UV-vis spectrophotometer (UV), Dynamic light scattering (DLS) and Magnetic Resonance Imaging (MRI). It is adsorption-selective to Ars with highly regenerate and keep stable in a wide pH and temperature range. The adsorption of Ars reaches equilibrium within 10h, and the maximum adsorption quantity is as high as 0.22mg/mg, much better than previous reports. Through the Langmuir Freundlich isotherm and pseudo-second-order kinetic model, the adsorption kinetics and thermodynamics of MIP-MCM were studied. The thermodynamic studies suggest that the adsorption of Ars on the MIP-MCM is a spontaneous process. MIP-MCM also shows rapid magnetic separation and high reusability (retained 90% after five cycles). Thus, it is an efficient

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method for Ars separation and purification. Furthermore, the MIP-MCM is also a good negative MRI contrast agent with good biocompatiblity. Due to these properties, this work offers a new potential application for MIP-MCM in aspects of drug delivery and tracking, disease diagnosis and therapy.

KEYWORDS: Molecularly imprinted polymers; magnetic composite microspheres; artesunate; imaging; releasing; Introduction Molecularly imprinted polymers (MIP) are receiving considerable attention as chemical and biochemical analyses materials for its featuring of high specificity and low cost nowadays[1,2]. Through designing binding sites, MIP recognize the specially given template and the functional groups of the molecule[3,4]. The MIP have been applied in various fields including chem/biosensors and artificial enzyme inhibitor/antibody[5-8]. However, there are some problems for MIP, such as poor site accessibility and irregularly shape. These limit the applications of MIP. Due to functionalities, nontoxic nature and quickly separation, the magnetic microspheres technology has received much attention[9-12]. Hence, it is greatly interesting to combination of the Molecularly imprinted technique and magnetic microspheres technology for developing highly specific recognition ability. In recent years, because of special selectivity toward target molecule and rapid magnetic separation, MIP functionalized magnetic composites materials have become a hotspot. Peng et al. developed magnetic cellulose-chitosan microsphere for Cu (II) adsorption. Li et al. fabricated surface protein imprinted for selective Lysozyme[13]. Wu et al. prepared specific glucose-to-SPR signal transduction at physiological pH by molecularly imprinted responsive hybrid micro gels[14]. All of these applications are based on the imprinted materials and separation. However, the magnetic molecularly imprinted polymers as separation, purity, drug


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recognition and carrier was few reported. In this work, we prepared a material MIP-MCM by surface imprinting technique. Considering that Cellulose is the most abundantly natural renewable polymer, chemical and thermal stability. Natural polymer cellulose is chosen as the microspheres to embed nano Fe3O4 particles. Thus, the MIP-MCM with magnetic property is attractive for easy controlling and fast separation. It is also a good negative MRI contrast agent. The cellulose based MIP microspheres have higher surface area, effective adsorption sites, and easy taking back from aqueous solution. The MIP-MCM also shows very good biocompatibility. The antimalarial drug artesunate (Ars) is used as template molecule[15]. The adsorption capacity of the magnetic cellulose microsphere surface molecularly imprinted is much higher than that of normal imprinting membranes[16-18]. The excellent selectivity toward Ars makes the MIP-MCM a good candidate for separation and purification of Ars. Moreover, the good biocompatibility, MRI imaging ability and responsive release indicate that the MIP-MCM could be used as a drug release system. Which may be a safe and effective method for rapid early diagnosis and targeted therapy. Experimental sections Materials Cellulose (Mn=8X104) was kindly provided by Wuhan University. Sodium hydroxide(98%), urea (98%), ferrous sulfate hetahydrate (FeSO4﹒7H2O, 98%), anhydrous ferric chloride (FeCl3), artesunate (Ars, 98%), artemisinin (Ari, 98%), ethylene glycol dimethacrylate (EDMA, 98%), acrylamide (AM, 99%), methacrylic acid (MA, 99%), methylene-bis-acrylamide (MBA, 99%), ammonium persulfate (APS, 99%), paraffin oils and Span 80 were purchased from Aladdin and used as received. The water used in all experiments was distilled water.


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Characterization Fourier transform infrared spectra

(FTIR) experiments

were recorded on

the

FTIR

spectrophotometer (Nicolet-Nexus 670). X-ray powder diffraction (XRD) experiments were recorded on X-ray diffractometer (Holland Panalytical PRO PW 3040/60, V = 30 kV, I = 25 mA, λ=1.5418 Å). The magnetic properties were examined by vibrating sample magnetometry (VSM, Lake Shore7404). The contents of Ars were determined by a UV-Vis spectrophotometer (CARY-100, Agilent). The pH values were measured on METTLER TOLEDO SevenEasy pH meter. The microspheres size was measured by Dynamic light scattering (DLS, LA-950V2). The relaxivity was measured by MRI scanner (VTMR20-010V-T, MesoMR23-060H-I, NIUMAG) Preparation of magnetic cellulose microspheres ( MCM ) Amounts of FeCl3 and FeSO4﹒7H2O (Fe3+ : Fe2+ = 2:1) were dissolved in deionized water under the protection of nitrogen. 2.0 M sodium hydroxide solution was slowly added into the mixture with 100 Hz ultrasonic. When pH was adjusted to 10, a certain amount of Fe3O4 nano particles were gained. The MCM was made by the following process. A solution with NaOH/urea/H2O of 7: 12: 81 by weight was cooled to -12 ℃. Cellulose (8g) and Fe3O4 fluid (1g) were dispersed in the cooled NaOH/urea/H2O solution (200g) with stirring. Subsequently, 20 mL mixed solution was dispersed in the solution containing 60 mL paraffin oils and 4g Span 80. The mixture was put into a reactor and agitated at 800 rpm for 5h. After stirring, hydrochloric acid (0.1mol/L) was added into the mixture to match the pH 7. After removal of the liquid paraffin and water-washing with deionized water, the MCMs were obtained and stored in alcohol at 5 ℃. Modification of activated MCM by the imprinted polymer ( MIP-MCM )


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MIP coated MCM ( MIP-MCM ) was prepared as follows: In a 100ml round-bottom flask equipped with a stirrer and a N2 gas inlet, artesunate (Ars, 0.025mmol), acrylamide (AM, 1.0mmol), methacrylic acid (MA, 0.5mmol), methylene-bis-acrylamide (MBA, 0.2 mmol), 20 mg of MCM were dispersed in 50 mL sodium hydroxide aqueous solution (0.2%). After 1h ultrasonic, the mixture was stirring for 8h to form a stable prepolymerization system. Then ammonium persulfate (APS, 0.6%) and EDMA (2%) were added into the complex system. The reaction system was purged by nitrogen through the solution for 15 min at room temperature. Then the polymerization procedure was carried out at 70℃ for 24h under stirring. Through this polymerization process, the molecularly imprinted microspheres (MIP-MCM) was obtained by the surface functional monomer covering. Then the MIP-MCM was washed with acetone and deionized water. The MIP-MCM was purified by soxhlet extraction with the mixture of methanol/acetic acid (9:1, V:V) to remove the template molecules Ars. Until no Ars could be detected by UV. Finally, the purified MIP-MCM was dried in a vacuum drying chamber at 60℃. The microspheres without imprinted molecular (NIP-MCM) were prepared by the same process without addition of template molecules. Adsorption Experiment To evaluate the adsorption capacity of MIP-MCM and NIP-MCM, 5 mg samples were dispersed in 5 mL of sodium hydroxide aqueous solution (0.2%), with Ars concentration ranging from 0.046 mg/mL to 0.332 mg/mL. The mixture was mixed at room temperature for 24 h and then separated by a magnet. The concentration of Ars in the solution was determined by UV[19] at 288nm.


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The adsorption kinetics studies were investigated as follows. 5 mg MIP-MCM was added into 5mL of Ars solution (0.0384 g/mL) with 0.2% sodium hydroxide at 25℃. And the samples were taken out at predetermined time ranging from 5 min to 24 h. The experimental adsorption capacity of Ars Qt (mg/mg) was calculated according to Equation(1) [20]: Selectivity experiments were studied by using Ars and Ari structural analogues. MIP-MCM (5 mg) was dispersed into 5 mL sodium hydroxide aqueous solution (0.2%) containing 0.0384 g/mL Ars and Ari, respectivily. The amounts of Ars and Ari in the solution were determined by UV after shaking at room temperature. The recognition ability of MIP-MCM was evaluated by the imprinting factor (a), which was calculated by following Equation (2)[21]: The effect of pH on the adsorption capacity of MIP-MCM toward Ars was evaluated with the Ars concentration of 0.0384 g/mL from pH=1.0 to pH=14.0 at 25℃. HCl and NaOH solutions were used to adjust solution pH. The effect of temperature on the adsorption capacity of MIP-MCM toward Ars was evaluated with Ars concentration of 0.0384 g/mL from 283k to 333K. To investigate the regenerate and stability character of MIP-MCM, adsorption/desorption experiments were performed. The MIP-MCM was first put into the Ars solution with concentration of 0.0384g/mL. After saturated adsorption, the MIP-MCM was then washed with the mixture of acetic acid and methanol (1:9) by Soxhlet extraction to remove the target molecules and used in second adsorption. The regenerate experiments were repeated for five times. The equilibrium adsorption capacity was measured each time. In vitro cytotoxicity


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The human amnion epithelial (FL) cell line was seeded in 96-well culture plate with the density of 4×104 cells/cm2. After exposed to MCM, NIP-MCM and MIP-MCM for 1 h at standard cell culture conditions, the supernatant of each well was collected and the lactate dehydrogenase (LDH) activity was measured in order to estimate the toxicity of MCM, NIP-MCM and MIP-MCM. Cell death rate (%) was determined by compare the LDH release of the samples to the standard curve. The influence of MCM, NIP-MCM and MIP-MCM on the proliferation property of FL cell line was determined by Cell Counting Kit-8 (CCK-8) assay. FL cell line was seeded in 96-well plates with the density of 0.625 cells/cm2. After 24 h of standard incubation, cells adhered and spread well on the bottom of the plate. Subsequently, the old cell culture medium was removed and the cells were rinsed in the phosphate buffer solution (PBS). After that, new medium with different concentration of MCM, NIP-MCM and MIP-MCM were added for a continue cell culture. 24 h, 48 h, and 72 h later, the CCK-8 assay was performed in a dark environment to quantify the amount of living cells [22]. Relaxivity measurement For MRI experiments, MIP-MCM was dissolved into PBS solution with different concentrations (10µg/mL, 50µg/mL, 100µg/mL). The transverse relaxation time T2 of each solution was measured by using a MRI scanner at a magnetic field strength of 0.5T. The relaxivity r2 was calculated through the curve fitting of 1/T2 relaxation time (s-1) vs the Fe concentration (mM)[23]. Artesunate releasing To investigate the Ars releasing property of MIP-MCM, the Ars releasing from the MIP-MCM were studied in vitro filled with 30 mL of PBS of three different pH values (pH=2.0, pH=4.0 and


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pH=7.4) at 37℃. After centrifugation, 5 mL of solution was collected. Then the same volume of fresh PBS solution was added to keep the volume of the solution no changed. All the adsorption experiments were performed in three repetitions to ensure the accuracy of data and the error bars were shown in correspond figures.

Results and discussion Preparation of MIP-MCM MIP-MCM samples were prepared by surface-imprinted polymerization technology. The micro size of solid support had a large surface to volume ratio which could provided abundant reaction sites for surface imprinting. The proposed process of the MCM and MIP-MCM were shown in Scheme 1. First, Fe3O4 nanoparticles were synthesized by co-precipitation method. Then, cellulose was coated on the Fe3O4 nanoparticles forming Fe3O4@cellulose microspheres. The cellulose was served not only as the matrix but also offered large amount of functional groups –OH. The Fe3O4 nanoparticles were stabilized in the cellulose microspheres through electrostatic adsorption and hydrogen bonding interactions[5]. After that, APS initiated the polymerization of AM, MA and MBA reacting with EDGA and Ars. Thus, the Ars@MIP was coated onto the surface of Fe3O4@cellulose. After removing the Ars, MIP-MCM with surface binding sites was obtained. FTIR Spectroscopy The FTIR spectra of Fe3O4, cellulose, MCM, NIP-MCM, MIP-MCM and Ars were displayed in Figure 1a. The characteristic peak of Fe3O4 was observed at 580cm-1[24]. The characteristic peaks of cellulose were at 3300 cm-1, 2880 cm-1 and 1150 cm-1, which were attributed to the stretching vibrations of -OH, -CH2 and -C-O-C-, respectively. In the MCM spectrum (Figure 1γ), both Fe3O4 and cellulose characteristic peaks were observed, which indicating the microspheres with


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magnetic core and cellulose were synthesized. In the spectrum of MIP-MCM, the characteristic absorption peak of Fe3O4 (around 590 cm-1) was appeared. While the –OH peak of MCM shifed from 3300 to 3450 cm-1 and became broader, which suggesting that the strong interaction between cellulose and Fe3O4 nanoparticles through hydrogen bonding existed in MCM[25]. At same time, the band at 1580cm-1 became weaker, which was also due to the strong hydrogen bonding between Fe3O4 and cellulose. This suggested the stability of Fe3O4 nanoparticles in cellulose microspheres was enhanced[26]. The high stability was very important for the application of the MCM. For NIP-MCM (Figure 1a, curve δ), and MIP-MCM (Figure 1a, curve ε), the band at 3400cm-1, 1700 cm-1, 1210 cm-1, and 1120 cm-1 can be assigned to the N-H , C=O and -O-C-O- group, which suggested the polymers were grafted on the MCM successfully. Compared with Ars (Figure 1a, curve ζ), the -OH peak at 3547 and 1120 cm-1 shifted to 3430 cm-1 and 1200 cm-1, respectivily. It could be attributed to hydrogen bonds between Ars and MIP-MCM[27]. These results indicated that the MIP-MCM was successfully synthesized. After the sample Ars@MIP-MCM was washed with the mixture of acetic acid/methanol (1:9 ) by Soxhlet extraction, no characteristic of Ars can be found in FTIR spectrum, indicating the template Ars molecules were removed thoroughly from MIP-MCM composites. It also could be proved by UV experiments. Crystalline Structure Analysis The powder X-ray diffraction patterns of Fe3O4 , cellulose, MCM and MIP-MCM were presented in Figure 1b. The characteristic peaks of cellulose microspheres showed at 2θ= 12.4, 20.2 and 22.2° for (110), (110), and (200) planes, which were characteristic peaks of cellulose II crystal. The characteristic XRD peaks of Fe3O4 (2θ= 30.1, 35.5, 43.1, 53.4, 57.0)[28], assigned to the (111), (220), (400), (422), and (511) planes of Fe3O4. The combination of MCM and Fe3O4


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made some crystal changes, suggesting that cellulose had been successfully coated onto the surface of Fe3O4[29]. The typical diffraction pattern of MCM changes were consistent with a transformation from cellulose Ι to cellulose II. The characteristic peaks of Fe3O4 could be hardly seen in the spectrum of MIP-MCM. It indicated the MCM surface had been successfully coated with MIP, which made the diffraction peak intensity weaken. Magnetic Properties The magnetic hysteresis loops of Fe3O4, MCM, and MIP-MCM were shown in Figure 1c. All of these samples exhibited low coercivity and small hysteresis loop, suggesting that the MIN-MCM was superparamagnetic particle[30]. The results indicated that all the samples possessed a sensitive magnetic responsiveness. The saturation magnetization of MIP-MCM was 7.07emu/g, which was lower than that of Fe3O4 (48.1emu/g) and MCM (46.7emu/g). This phenomenon indicated that the MIP had been successfully coated onto the surface of MCM. Thus, the saturation magnetization of MIP-MCM decreased. Though the saturation magnetization of MIP-MCM was lower, MIP-MCM still showed obvious sensitive magnetic responsiveness. Morphology Analysis Figure 2 showed SEM images of cellulose microspheres and MIP-MCM’s porous microspheres structure with average pore diameter 100nm. As shown in Figure 2b, the microporous of MCM-MIP was denser than that of cellulose microsphere. It indicated that the Fe3O4 nanoparticles was embedded into the cellulose microsphere. The particle size of MIP-MCM was determined by DLS (Figure 2c). The results showed that the averaged diameter of particles was about 22.79 µm. And the size distribution was as low as 1.64.


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The morphology of MIP-MCM was observed by Microscope (Figure 2d). The core-shell structure was clearly observed. Cellulose microspheres with lots of Fe3O4 nanoparticles formed the core. MIP coated on the surface of the core forming the shell. Most of the particles showed regular spherical shape. Adsorption properties of MIP-MCM To estimate the adsorption capability of the MIP-MCM and NIP-MCM, the adsorption experiments were conducted with different concentrations of Ars solution. Figure 3a showed the adsorption amount of MIP-MCM and NIP-MCM in different Ars concentrations at 25℃. The adsorption amount were calculated by the following Equation(3): It could be seen that for both MIP-MCM and NIP-MCM, the adsorption amount for Ars were increased with the increasing Ars concentration. The adsorption amount of Ars to the MIP-MCM was much higher than that to the NIP-MCM. The equation (1-2) was used to evaluate the adsorption ability of the MIP-MCM and NIP-MCM. The equilibrium adsorption of MIP-MCM was calculated to be 0.221±0.009mg/mg, an order of magnitude higher than that of NIP-MCM (0.022±0.003mg/mg). The adsorption capacity of MIP-MCM in this study was much higher than imprinted polymers previously reported[31]. The reported adsorption of Ars was only about 0.05 mg/mg. This strong adsorption ability of MIP-MCM could be attributed to the magnetic cellulose microspheres providing much more superficial area than that were reported imprinted membrane and other imprinted shape. It could provide large amount of selective recognition sites for Ars molecules. The surface imprinted sites could improve the template adsorption amount and rate[32]. Besides, it was reported that a specific interaction between Fe3O4 and Ars[33], which could increase the activity of Ars. We believe that the interaction might be one of the factors increasing the adsorption in this system.


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The Ars adsorption kinetic curves of MIP-MCM and NIP-MCM were shown in Figure 3b. In the first 10 h, the MIP-MCM exhibited an obvious rapidly adsorption of template molecules and reached nearly 90% of the equilibrium capacity. After 10 h, the adsorption amount increased slowly and reached the adsorption equilibrium within 12 h. In contrast with that of MIP-MCM, the kinetic curve of NIP-MCM increased slowly in the whole adsorption process. The results suggested an obvious rapid adsorption for Ars to compared with normal imprinting materials which usually needed more than 20 h to reach the adsorption equilibrium[34]. The rapidly adsorption might attribute to the microspheres structure, strong interaction between Ars and MIP-MCM, and plentiful empty imprinted sites at the surface of MIP-MCM. The porous structure of cellulose microspheres improved the adsorption dynamics rate by the physical adsorption interaction. The imprinted microspheres with rapid and amount adsorption is very useful and important as the chemical structure separation materials. To further study the adsorption rate of Ars on MIP-MCM, adsorption data was studied by the kinetic adsorption rate equation as following Equation(4-5)[35]: The adsorption rates fitted by pseudo-first-order rate equation and pseudo-second-order rate equation were listed in Table 1. The kinetic adsorption process met the characteristics of the pseudo-second-order, indicating the adsorption system could be controlled by chemical adsorption process[36,37]. It suggested the adsorption at the beginning was fast. For the Langmuir adsorption equilibrium of Ars on MIP-MCM surface suggested that the adsorption of Ars was a monolayer process. The Langmuir adsorption equation was calculated as following Equation(6)[38, 39]:


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The adsorption relationship between Ars and MIP-MCM also could be calculated by the Freundlich adsorption equation as following Equation(7)[40]: Figure 3a was the comparison of different isothermal adsorption curve for Ars adsorption on MIP-MCM. The parameters of Langmuir and Freundlich adsorption were shown in Table 2. The correlation coefficient R2 of Langmuir was 0.99, which suggested that the adsorption of Ars on the MIP-MCM was monolayer adsorption. The Freundlich constant (1/n) was the sorption intensity, if 1/n < 1, indicating adsorption capacity increased. The 1/n value of Ars on the MIP-MCM was calculated to be 0.457, indicating that the Ars could be easily adsorbed on the MCM. The correlation coefficients R2 for both Langmuir and Freundlich were close to 1, suggesting the adsorption of Ars on MIP-MCM was both physical adsorption and chemical adsorption[41-43]. Adsorption Specificity Molecular recognition ability of MIP-MCM was dependent on the interactions between MIP-MCM and template molecules. To investigate the special recognition ability of MIP-MCM, the competitive adsorption was carried out for Ars and Ari. In the selectivity experiments, Ars and Ari were coexisting in the same system with same concentration. As shown in Figure 3c, MIP-MCM exhibited a much higher adsorption capacity for Ars comparing with Ari, which suggested that the similar structure could hardly affect the specific recognition of MIP-MCM. In contrast, the adsorption ability of NIP-MCM toward target molecules was the same as that of competitive molecules. The structure of Ari molecule was similar to the NIP-MCM coating sites, but not matching with the recognition sites of MIP-MCM. Thus there was no specific adsorption between MIP-MCM and Ari. The selectivity factor in the competitive adsorption was 9.853,


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indicating a high specificity and adsorption selectivity of the MIP-MCM towards target molecules compared with NIP-MCM[44,45]. The Kinetic parameters of Ars and Ari were showed in Table 3. Compared with the adsorption of MIP-MCM and NIP-MCM for Ars and Ari molecules, the permeation flux J (mg/cm2﹒s), permeability coefficient P (cm3/s), and permselectivity factor βArs/Ari were obtained as followed Equation (8-10)[46,47]: The P value of Ars for MIP-MCM was much higher than that of Ari. The MIP-MCM also exhibited higher specificity recognition ability according to the values of βArs/Ari. The high selectivity for Ars could be attributed to the specific imprinted sites on the surface of the MIP-MCM[48-50]. Only Ars could match the adsorption sites. Ars molecule could be preferentially match with the cavities at the surface of MIP-MCM, while Ari could be hardly adsorbed onto the MIP-MCM. Effect of Solution pH The pH is an important parameter for the MIP’s adsorption ability. To study the adsorption capacity of the MIP-MCM toward Ars in different solution pH values, adsorption experiments were performed with pH ranging from 1 to 14. The results were shown in Figure 4a. It was clear that the MIP-MCM exhibited excellent adsorption toward Ars in a wild rang of pH (3~12). When pH12, the adsorption amount decreased sharply. The MIP-MCM kept stable adsorption in wide pH range from (3~12). The phenomena could be due to the charge of Ars and MIP-MCM at different pH solution. The charge of Ars was negative at pH12, because of the repulsive force by the negative charge of MIP-MCM and Ars, the adsorption of Ars


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was decreased. When pH

Multifunctional Magnetic Cellulose Surface-Imprinted Microspheres for

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