Biomimic preparation of highly dispersible silica nanoparticles based polymer nanocomposites

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CERAMICS INTERNATIONAL

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Biomimic preparation of highly dispersible silica nanoparticles based polymer nanocomposites Chunning Henga,b, Meiying Liub, Ke Wangc, Fengjie Dengb, Hongye Huangb, Qing Wanb, Junfeng Huia,n, Xiaoyong Zhangb,n,1, Yen Weic,n,2 a

Department of Shaanxi Key Laboratory of Degradable Biomedical Materials, Shaanxi R&D Center of Biomaterials and Fermentation Engineering, School of Chemical and Engineering, Northwest University, Xi’an, 710069, PR China b Department of Chemistry and Jiangxi Provincial Key Laboratory of New Energy Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, PR China c Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing 100084, PR China Received 9 July 2015; received in revised form 10 July 2015; accepted 16 August 2015

Abstract Silica nanoparticles (SiO2 NPs) have been widely applied in a number of domains because of their inodorous, non-pollution, optical transparency, chemical inert and good biocompatibility. However, to achieve better performance, surface modification of SiO2 NPs to enhance their dispersibility is generally required. In this paper, a simple, facile and environmental friendly procedure was developed for surface modification of SiO2 NPs with a biocompatible polymer (polyPEGMA) via combination of mussel inspired chemistry and Michael addition reaction for the first time. Firstly, monodisperse SiO2 NPs were prepared by using a slightly modified Stöber process. Secondly, SiO2 NPs were coated with polydopamine (PDA), which was formed through self-polymerization of dopamine in an alkaline aqueous solution. Lastly, the PDA coated SiO2 NPs were facilely conjugated with polyPEGMA, which were synthesized through chain transfer free radical polymerization using cysteamine hydrochloride as chain transfer agent and poly(ethylene glycol) methyl ether methacrylate as the monomer. The successful preparation of these composites was confirmed by a number of characterization techniques including transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis and X-ray photoelectron spectroscopy. This method obviously enhance the dispersion of SiO2 NPs in different organic solvents and aqueous solution. This synthetic method is convenient, effective and environmental friendly, that can be also extended to modify SiO2 NPs with other functional polymers because of the features of mussel inspired chemistry and chain transfer living polymerization. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: Silica nanoparticles; Mussel inspired chemistry; Dispersibility; Michael addition reaction; PEGylation

1. Introduction Silica nanoparticles (SiO2 NPs) are an interesting class of nanomaterials [1–3], which possess remarkable physicochemical properties and have been mass producted for a number of n

Corresponding author. E-mail addresses: [email protected] (J. Hui), [email protected] (X. Zhang), [email protected] (Y. Wei). 1 Tel.: +86 791 8396 9553. 2 Tel.: +86 10 6277 2674; fax: +86 10 6277 1149.

engineering applications [4–7]. It has been demonstrated that SiO2 NPs showed great potential for different applications including photovoltaic, catalysis, electronic information industry, fillers of nanocomposites, environmental protection, chromatography and biomedical applications etc. [8–13]. However, for most of these applications, surface modification of SiO2 NPs is generally required to enhance their performance and endow novel functions. To date, a number of surface modification strategies have been developed and different functional components have been integrated with SiO2 NPs. Among them, surface modification of SiO2 NPs with polymers have attracted the most attention because of their

http://dx.doi.org/10.1016/j.ceramint.2015.08.072 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Please cite this article as: C. Heng, et al., Biomimic preparation of highly dispersible silica nanoparticles based polymer nanocomposites, Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.08.072

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Scheme 1. Schematic representation for the preparation of SiO2-PDA-poly(PEGMA) nanomaterials via combination of mussel inspired chemistry and Michael addition reaction. One step shows the preparation of polymers (poly(PEGMA)) using poly(ethylene glycol) methyl methacrylate (PEGMA) as monomer and ammonium persulfate as initiator by free radical polymerization. The second step represents that amino-terminated polymers further react with monodisperse SiO2 NPs with PDA (SiO2-PDA) in deionized water for 8 h at room temperature.

excellent performance and well designability of polymers. A general adopted route for introduction of polymers to SiO2 NPs is first surface linkage of the bare SiO2 NPs with functional silicates (such as 3-Aminopropyl-trimethoxysilane) through sol–gel methods, and then the functional groups on the SiO2 NPs can be further used for immobilization of polymers through different polymerization methods and conjugation reactions. For example, Yuan et al. have demonstrated that pH and thermo-responsive polymers PDAEMA can be used for surface modification of SiO2 NPs through atom transfer radical polymerization (ATRP) [14]. In this work, amino groups should be first immobilized on the bare SiO2 NPs by reacted with 3-Aminopropyl-trimethoxysilane at 115 1C for 24 h. And then the ATRP initiator (2-Bromo-propionyl bromide) can be further reacted with amino groups on SiO2 NPs, that can introduced the PDAEMA through ATRP. On the other hand, they also demonstrated that magentic silica nanoparticles can be modified with β-cyclodextrin through (ATRP) and utilized for the catalysis and adsorption applications [15]. However, most of these strategies involved the expensive functional silicates, complex experiment procedure and long reaction time. Therefore, the development of novel and effecient strategies for surface modification of SiO2 NPs under mild experimental conditions is of great importance. Mussels, a kind of aquatic organisms, that can attach themselves onto most of the inorganic and organic materials through their byssuses threads. Inspired by mussel adhesion properties, Messersmith et al. found dopamine, which is similar to a kind of adhesive components in mussel proteins, could self-assemble in alkaline circumstance and formed a thin layer film on the surface of inorganic and organic materials, such as precious metals, oxides, polymers, semiconductors, ceramics [16–21]. After that, mussel-inspired chemistry has aroused great research attention of scientists from the biology, chemistry, materials and medicine, that has been rapidly applied in various fields, including surface coating, adhesives, sealants, environmental protection, energy coversion and storage, biological imaging and cancer photothermal treatment [22–24]. Because of the versatility of mussel inspired chemistry, surface modification of silica based nanomaterials have also been demonstrated by Lee and these mussel inspired modified silica nanoparticles showed enhanced performanace

for energy storage capability [25]. On the other hand, Zhou et al. have demonstrated that PDA could be coated on SiO2 NPs through mussel inspired chemistry, and PDA functionalized SiO2 NPs were served as precursors for preparation of polymer microcapasules [26]. However, to the best of our knowledge, the surface modification of SiO2 NPs through combination of mussel inspired chemistry and chain transfer free radical polymerization has not been reported thus far. In this work, we introduce a simple and efficient method to modify SiO2 NPs with PPEGMA through integration of mussel inspired chemistry and Michael addition reaction. Firstly, highly-dispersed SiO2 NPs were sythesized using a slightly modified Stöber process in aqueous and organic solutions. Secondly, SiO2 NPs were then coated with PDA films by the self-polymerization of dopamine at room temperature in aqueous solution. The last is polymer PPEGMA from chain transfer free radical polymerization were conjugated with PDA films via the Michael addition reaction (Scheme 1). 2. Experimental procedure 2.1. Materials All chemicals were of analytical grade and were used as received without any further purification. All aqueous solutions were prepared with distilled water. Tetraethyl orthosilicate and Ammonia (28%) were purchased from Sino Nanotech Ltd. (Beijing, China). Dopamine hydrochloride (DA, MW:189.64 Da, 498%) were supplied from company of Sangon Biotech. Tris (hydroxymethyl) aminomethane (Tris) is obtained from Sinopharm Chemical Reagent Co., Ltd. cysteamine hydrochloride (MW: 113.61, 98%), Ammonium persulfate (MW: 228.2, 98%) and poly(ethylene glycol) methyl ether methacrylate (PEGMA, 60 MW:950 Da, 98%) were supplied by Aladdin (Shanghai, China). 2.2. Characterization Transmission electron microscopy (TEM) images were recorded on a Hitachi 7650B microscope operated at 80 kV;

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stirrer at room temperature. After the polymerization, the SiO2 NPs coated with PDA were separated by centrifugation at 8000 rpm for 10 min and washed with deionized water and ethanol three times and dried in vacuum drying oven 40 1C to yield SiO2-PDA. 2.5. Synthesis of polyPEGMA

Fig. 1. Representative 1H NMR spectrum of poly(PEGMA) dissolved in D2O.

the TEM specimens were made by placing a drop of the nanoparticle ethanol suspension on a carbon-coated copper grid. The Fourier transform infrared (FT-IR) spectra were obtained by using a Nicolet 380 Fourier transform spectrometer with a resolution of 2 cm
1. The samples were pressed with KBr into a pellet before measuring the infrared absorption spectra. Thermal gravimetric analysis (TGA) was conducted on a TA instrument Q50 with a heating rate of 20 1C min
1. Samples weight between 10 mg were heated from 25 to 600 1C in air flow (60 mL min
1), N2 as the balance gas (40 mL min
1). Each sample was ultrasonicated for 30 min prior to analysis. The reported values are the mean values of three measurements. The X-ray photoelectron spectra (XPS) were performed on a VGESCALAB 220-IXL spectrometer using an Al Kα X-ray source (1486.6 eV). The energy scale was internally calibrated by referencing to the binding energy (Eb) of the C1s peak of a carbon contaminant at 284.6 eV. The size distribution of PEGylated SiO2 NPs in water was determined using a zeta Plus apparatus (ZetaPlus, Brookhaven Instruments, Holtsville, NY). 2.3. Synthesis of monodisperse SiO2 nanoparticles Monodisperse SiO2 nanoparticles 100–150 nm in diameter were prepared by using a slightly modified Stöber process. In a typical synthesis of 150 nm SiO2 nanoparticles, 2.5 mL of TEOS was rapidly added into a mixture of 27.5 mL of ethanol, 22.5 mL of H2O, and 7.5 mL of ammonium. By fixing the concentration of TEOS and H2O, and varying the concentration of ammonium, the resulting particle sizes can be easily adjusted. 2.4. Synthesis of SiO2-PDA Solution A: 100 mg of SiO2 NPs was dispersed in 50 ml Tris buffer solution (10 mM, pH ¼ 8.5). Solution B:100 mg of dopamine hydrochloride was dissolved in 50 mL Tris buffer solution (10 mM, pH ¼ 8.5). A and B combined ultrasonic treatment for 10 min, and stirring for 8 h on the magnetic

The amino-terminated polyPEGMA was synthesized by free radical polymerization using cysteamine hydrochloride as the chain transfer agent and PEGMA as monomer. In this experiment, PEGMA (10 mM, 9.5 g), cysteamine hydrochloride (0.1 mM, 20 mg), ammonium persulphate (1.0 mM, 223 mg), and deionized water (30 mL) were introduced in a polymerization bottle with a magnetic stir bar and purged by nitrogen flow at 40 1C for 24 h. The products with deionized water and methanol dialysis for 24 h, and dried in vacuum drying oven. 2.6. Preparation of SiO2-PDA-poly(PEGMA) The process for synthesis of SiO2-PDA-poly(PEGMA) through Michael addition reaction is described following. First, 100 mg of SiO2-PDA was dispersed in 60 mL of Tris buffer solution (10 mM, pH ¼ 8.5), and then 100 mg of polyPEGMA was added into above solution, and stirring for 8 h on the magnetic stirrer at room temperature. These assynthesized SiO2-PDA-poly(PEGMA) nanocomposites were collected by repeated centrifugation and washing to remove unreacted polymers and dried at 50 1C for 12 h. 3. Results and discussion The results of 1H NMR (δ, D2O) spectra could provide evidence of successfully synthesis functional polymers poly (PEGMA) by free radical polymerization. As shown in Fig. 1, the result could be clearly described as follows: 1H NMR (D2O, δ, ppm): –O–CH2–(4.05), NH2–CH2–(3.24), –CH2– CH2–(2.58), CH3–(1.79), –CH2–(2.08), –CH3(0.92), –O– CH3(3.38), –CH2–O–(3.59). Preparation of monodisperse SiO2 NPs is the precondition for the preparation of high quality SiO2 composites [27]. In 1968, Stöber et al. [28] repeated Kolbe experimental results successfully and that is known as Stöber method. Traditional Stöber method of the reaction developed rapidly in the initial stage, however, the short nucleation process resulted in the difficulty in controlling the initial stage of the reaction, which is the core influencing factor of the final SiO2 microspheres particle size. As is known to all, the SiO2 microspheres morphology depends on the initial density and the concentration of silicon source, which can make the preparation consequence a considerable difference [29–33]. The actual particle size and particle size deviation sometimes is expected to more than 50%, under different reaction conditions of preparation of SiO2 NPs. In order to get the controllable preparation process and gain the strict requirements of SiO2 NPs, improving the traditional Stöber method is necessary [34–36]. Surface modification of SiO2 NPs is one valid way to

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Fig. 2. TEM images of original SiO2 NPs (A and B), SiO2-PDA (C) and SiO2-PDA-poly(PEGMA) (D). Thin polymer films coated on SiO2 NPs were clearly observed by TEM observation after they were functionalized with PDA and polymers. The TEM images confirmed the successful modification of PEGMA through mussel inspired chemistry and Michael addition reaction.

Fig. 3. FT-IR spectra of SiO2 and PEGMA functionalized SiO2. Characteristic IR peaks located at 1654.9, 2949.0 and 3465.9 cm
1 were observed in SiO2PDA-poly(PEGMA), suggesting that the functional groups such as C¼ O, C–H and C–O were existed in SiO2-PDA-poly(PEGMA).

enhance the SiO2 surface properties, such as its hydrophobicity, optical ability, biotechnological application and adsorption ability [37–43]. However, this depends on the modifier types or functional groups and the modification methods. The modification of the surface of the SiO2 NPs can be easily functionalized by different chemical procedures, such as heat treatment and polymer grafting [44]. Recently, silica surface modification method is emerging in endlessly with polymers. For example, a developed effective method to small Ag particles were embedded

in SiO2 glass thin films by a multi-target sputtering method [45]. Helmut Schlaad et al. presented a simple and facile method to fabricate thermoresponsive polymer-grafted silica particles by directing surface-initiated photopolymerization of Nisopropylacrylamide (NIPAM) [46]. The macroscopic features of SiO2, SiO2-PDA and SiO2PDA-poly(PEGMA) samples have been characterized by TEM (Fig. 2). Firstly, the diameter of ungroomed SiO2 NPs between 100 and 200 nm can be clearly identified. SiO2, with PDA and PEGMA modified, was covered with a layer of thin layer, and can be clearly observed, proved that the SiO2 NPs are modified by PDA and poly(PEGMA) successfully (Fig. 2C and D). More importantly, compared with the unmodified SiO2 NPs, the morphology of these modified SiO2 NPs has not obvious changes, but the particle size seems larger than the ratio of original materials. On the other hand, this method is quite effective and simple in this work. It is therefore this method could be more suitable for surface modification of SiO2 NPs as compared with the covalent methods. The FTIR spectrum of silica particles shows two strong Si–O–Si stretching vibration bands at 1084 and 950.9 cm
1 because the Si–C bond disrupts the symmetry of Si–O–Si structure in the hybrid silica (Fig. 3). The broad band closed to 3465.9 cm
1,which can be attributed to N–H or O–H stretching vibration mode was observed in SiO2-PDA, evidencing the successful modification of SiO2 NPs by PDA. Furthermore, weak peaks range from 3000 to 2850 cm
1 are likely as a result of C–H stretches observed in the sample of SiO2-PDA. The characteristic stretching vibration of the C¼ O group is quite weak but can be discerned at 1654.9 cm
1, which was observed

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Fig. 4. TGA curves of SiO2, SiO2-PDA and SiO2 -PDA-poly(PEGMA). Significant mass decrease was observed in the samples of SiO2-PDA- poly(PEGMA) when the temperature is located at 180–290 1C, indicating the PEGMA was successfully attached on SiO2 NPs via Michael addition reaction.

in the sample of SiO2-PDA-poly(PEGMA). The results further confirmed that poly(PEGMA) from chain transfer free radical polymerization can be effectively immobilized on the surface of SiO2-PDA through Michael addition reaction. TGA was further used to characterize the SiO2 samples. As shown in Fig. 4A, the weight loss of pristine SiO2 NPs is about 5.9% when the temperature was 600 1C. After modification with PDA, the weight loss of SiO2-PDA from the temperature 114 to 600 1C is about 10%, suggesting that PDA was successfully coated on the surface of SiO2 NPs via mussel inspired chemistry. Therefore, the weight percentage of PDA coated on the surface of SiO2 could calculate about 4.1% based on the TGA results. After further modification of SiO2-PDA with PEGMA, much more weight loss was observed in SiO2-PDA-PEGMA as compared with SiO2-PDA. It can be seen that weight loss of SiO2-PDAPEGMA was increased to 72.8%. It is therefore, the mass percentage of polymer grafted to the SiO2-PDA was calculated to be 18.8%. All of these above results demonstrated that PEGMA was indeed conjugated to the SiO2-PDA. The DTA data of SiO2 NPs were shown in Fig. 4B. It can be seen that a gentle “single peak’’ was observed around 200 1C. The DTA consequences are well agreed with the TGA curve of SiO2 NPs. After surface coated with PDA, the weight loss of SiO2-PDA below 200 1C was decreased in some extent. The weight loss of SiO2-PDA in the second stage of was just about 5%. This is possibly attributed to the PDA is much stable than the hydroxyl

group of SiO2 (Fig. 4C). As shown in Fig. 4D, a new endothermic peak is appeared due to the PEGMA graft onto SiO2-PDA. The TGA and DTA results powerfully demonstrated that PDA and PEGMA was successfully coated on the SiO2 NPs through internalization of mussel inspired chemistry and Michael addition reaction. XPS spectra were further utilized to characterize the chemical components of SiO2 samples. The elements including Silicon (Si), carbon (C), nitrogen (N) and oxygen (O) were detected from XPS curves (Fig. 5). On the basis of spectra, it can be seen that only C, Si and O were existed in the sample of prisitine SiO2. However, the signal of N1s was emerged in the samples of SiO2-PDA and SiO2-PDA-poly(PEGMA), indicating that SiO2 was modified with PDA and PEGMA successfully. The high-resolution O1s, N1s, C1s and Si2p XPS spectra were shown in Fig. 6A–D. It can be seen that the binding energy peak of Si in the pristine SiO2 NPs is located at 103.17 eV, which can be assigned to Si on SiO2 (Fig. 6A). After surface coated with PDA, shoulder peaks shifted to the high binding energy between 286.65 and 286.88 eV were emerged in the samples of SiO2PDA, SiO2-PDA-poly(PEGMA). The emerged peaks can be attributed to the C–O and C¼ O bonds of PDA and polyPEGMA. More importantly, the signal of SiO2-PDA-poly (PEGMA) of C1s at high binding energy is much stronger as compared with SiO2-PDA, indicating that polyPEGMA can be conjugated with SiO2-PDA through Michael addition reaction.

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Fig. 6B shows the N1s spectra of SiO2 samples. Obvious N1s peak located at 396.2–405.2 eV can be found in the sample of SiO2-PDA, suggesting that PDA was successfully coated on SiO2 NPs. After further conjugated SiO2-PDA with polyPEGMA, the signals of N1s decreased correspondingly in the samples of SiO2-PDA-poly(PEGMA). From O1s spectra (Fig. 6C), we found that signals of O1s located at 528.0– 540.0 eV in the samples of SiO2-PDA and polyPEGMA functionalized SiO2 are much less than that of pristine SiO2, which is well consistent with the results of C1s and N1s (Fig. 6D).

Fig. 5. The representative XPS spectra of SiO2, SiO2-PDA and SiO2-PDApoly(PEGMA).

Furthermore, based on XPS spectra, the mass percentages of C, N, O, Si were also calculated (Table 1). Two elements Si (17.03%), C (18%) and O (64.97%) were found in pristine SiO2 NPs. After surface coating with PDA, the weight percentages of Si, C and O were changed to 12.54%, 41.43% and 42.68%, respectively. There is a focus on that a new element N (3.35%) was found in the sample of SiO2PDA. These results evidenced the successful coating SiO2 NPs with PDA. After further conjugation of SiO2-PDA with polyPEGMA, the oxygen contents were further decreased to 40.7% for the sample of SiO2-PDA-poly(PEGMA). Well consistent with the above results, the percentages of N was decreased from 3.35% for SiO2-PDA to 2.49% for SiO2-PDApoly(PEGMA). These results further demonstrated that these aminated polyPEGMA can be used for surface modification of SiO2 NPs through combination of mussel inspired chemistry and Michael addition reaction. As is well known, SiO2 NPs can be prevented from aggregation after modified with polymers due to the strong steric hindrance of macromolecular chains and the sharp decrease of hydrogen bonds related to the consumption of hydroxyl groups. The dispersibility of SiO2 samples in water was further evaluated. As shown in Fig. 7, pristine SiO2 NPs were quickly precipitated within 10 min in deionized water (Fig. 7A). As compared with pristine SiO2 NPs, the dispersibility of SiO2-PDA in deionized water was improved in some extent, which will be also precipitated within 1 h (Fig. 7B). After SiO2-PDA was further modified with polyPEGMA, the

Fig. 6. XPS Spectra of (A) Si2p, (B) C1s, (C) N1s, and (D) O1s.

Please cite this article as: C. Heng, et al., Biomimic preparation of highly dispersible silica nanoparticles based polymer nanocomposites, Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.08.072

C. Heng et al. / Ceramics International ] (]]]]) ]]]–]]] Table 1 Element contents (%) of SiO2 nanoparticles based on XPS analysis. Sample

Si

C

N

O

SiO2 SiO2-PDA SiO2-PDA-poly(PEGMA)

17.03 12.54 11.32

18 41.43 44.99

0 3.35 2.49

64.97 42.68 41.2

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modify the SiO2 NPs using the same procedure. Finally, this method described in this work can be also extended for surface modification of other nanomaterials and surface for the versality and strong adhesion of PDA to various materials and surface. Therefore, this method should be a novel and universal method for surface modification of nanomaterials and will find potential applications in various fields. Acknowledgments This research was supported by the National Science Foundation of China (Nos. 21134004, 21201108, 51363016 and 21474057), and the National 973 Project (Nos. 2011CB935700).

References

Fig. 7. Dispersion of SiO2 samples (Bottles from left to right are the samples of SiO2 NPs, SiO2-PDA, SiO2-PDA-poly(PEGMA)) in deionized water for different times. (A) 10 min, (B) 1 h, (C) 12 h and (D) 24 h.

dispersibility of SiO2-PDA-poly(PEGMA) is obviously enhanced. No perceivable precipitation was found in the sample of SiO2-PDA-poly(PEGMA) even they were deposited for 24 h. It is well known that PDA can effectively responsed to the near-infrared light and therefore potential useful for cancer photothermal treatment. In this work, the SiO2 NPs were facilely modified by a biocompatible and hydrophilic polymer (polyPEGMA) via combination of mussel inspired chemistry and chain transfer free radical polymerization [47]. Given the desirable biological properties of PEG, the obtained SiO2 NPs based nanocomposites are expected highly potential for photothermal treatment of cancer and many other biomedical applications. 4. Conclusion In summary, surface modification of SiO2 NPs with polyPEGMA by combination of mussel-inspired chemistry and Michael addition reaction was reported for the first time. The successful conjugation of polyPEGMA with SiO2 NPs was proved by a series of characterization techniques including FTIR spectroscopy, TGA and XPS spectroscopy. Thus obtained SiO2-PDA-poly(PEGMA) showed remarkable enhanced dispersibility in aqueous solution. As compared with conventional methods for surface modification of SiO2 NPs, the method described in this work is rather simple, effective and environmental friendly. On the other hand, apart from poly(PEGMA), many other functional polymers could also be facilely used to

[1] J.S. Chang, K.L.B. Chang, D.F. Hwang, Z.L. Kong, In vitro cytotoxicitiy of silica nanoparticles at high concentrations strongly depends on the metabolic activity type of the cell line, Environ Sci Technol. 41 (6) (2007) 2064–2068. [2] L.D. Bonifacio, B.V. Lotsch, D.P. Puzzo, F. Scotognella, G.A. Ozin, Stacking the nanochemistry deck: structural and compositional diversity in one‐dimensional photonic crystals, Adv Mater. 21 (16) (2009) 1641–1646. [3] J. Lee, S. Mahendra, P.J. Alvarez, Nanomaterials in the construction industry: a review of their applications and environmental health and safety considerations, ACS Nano 4 (7) (2010) 3580–3590. [4] J. García Barrasa, J.M. López de Luzuriaga, M. Monge, Silver nanoparticles: synthesis through chemical methods in solution and biomedical applications, Cent. Eur. J. Chem. 9 (1) (2011) 7–19. [5] P. Yang, S. Gai, J. Lin, Functionalized mesoporous silica materials for controlled drug delivery, Chem. Soc. Rev. 41 (9) (2012) 3679–3698. [6] C.O. Hendren, X. Mesnard, J. Dröge, M.R. Wiesner, Estimating production data for five engineered nanomaterials as a basis for exposure assessment, Environ. Sci. Technol. 45 (7) (2011) 2562–2569. [7] S.W. Hwang, G. Park, C. Edwards, E.A. Co rbin, S.K. Kang, H. Cheng, et al., Dissolution chemistry and biocompatibility of single-crystalline silicon nanomembranes and associated materials for transient electronics, ACS Nano 8 (6) (2014) 5843–5851. [8] Y. Wang, Z. Li, D. Hu, C.T. Lin, J. Li, Y. Lin, Aptamer/graphene oxide nanocomplex for in situ molecular probing in living cells, J. Am. Chem. Soc. 132 (27) (2010) 9274–9276. [9] Y. Liu, C. Lou, H. Yang, M. Shi, H. Miyoshi, Silica nanoparticles as promising drug/gene delivery carriers and fluorescent nano-probes: recent advances, Curr. Cancer Drug Target 11 (2) (2011) 156–163. [10] M.L. Chen, Y.J. He, X.W. Chen, J.H. Wang, Quantum-dot-conjugated graphene as a probe for simultaneous cancer-targeted fluorescent imaging, tracking, and monitoring drug delivery, Bioconjugate Chem. 24 (3) (2013) 387–397. [11] X. Kang, Z. Cheng, C. Li, D. Yang, M. Shang, M.a. Pa, et al., Core–shell structured up-conversion luminescent and mesoporous NaYF4: Yb3+/Er3 +@ n SiO2@ m SiO2 nanospheres as carriers for drug delivery, J. Phys. Chem. C 115 (32) (2011) 15801–15811. [12] S. Zhang, Z. Chu, C. Yin, C. Zhang, G. Lin, Q. Li, Controllable drug release and simultaneously carrier decomposition of SiO2-drug composite nanoparticles, J. Am. Chem. Soc. 135 (15) (2013) 5709–5716. [13] F. Erogbogbo, K.T. Yong, R. Hu, W.C. Law, H. Ding, C.W. Chang, et al., Biocompatible magnetofluorescent probes: luminescent silicon quantum dots coupled with superparamagnetic iron (III) oxide, ACS Nano 4 (9) (2010) 5131–5138. [14] L. Zhou, W. Yuan, J. Yuan, X. Hong, Preparation of double-responsive SiO2-g-PDMAEMA nanoparticles via ATRP, Mater. Lett. 62 (8) (2008) 1372–1375.

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[15] Y. Kang, L. Zhou, X. Li, J. Yuan, β-Cyclodextrin-modified hybrid magnetic nanoparticles for catalysis and adsorption, J. Mater. Chem. 21 (11) (2011) 3704–3710. [16] S.A. Mian, L.M. Yang, L.C. Saha, E. Ahmed, M. Ajmal, E. Ganz, A fundamental understanding of catechol and water adsorption on a hydrophilic silica surface: exploring the underwater adhesion mechanism of mussels on an atomic scale, Langmuir 30 (23) (2014) 6906–6914. [17] Y.S. Choi, D.G. Kang, S. Lim, Y.J. Yang, C.S. Kim, H.J. Cha, Recombinant mussel adhesive protein fp-5 (MAP fp-5) as a bulk bioadhesive and surface coating material, Biofouling 27 (7) (2011) 729–737. [18] C.E. Brubaker, P.B. Messersmith, The present and future of biologically inspired adhesive interfaces and materials, Langmuir 28 (4) (2012) 2200–2205. [19] B.J. Sparks, E.F. Hoff, L.P. Hayes, D.L. Patton, Mussel-inspired thiolene polymer networks: influencing network properties and adhesion with catechol functionality, Chem. Mater. 24 (18) (2012) 3633–3642. [20] J. Wu, L. Zhang, Y. Wang, Y. Long, H. Gao, X. Zhang, et al., Musselinspired chemistry for robust and surface-modifiable multilayer films, Langmuir 27 (22) (2011) 13684–13691. [21] X. Jia, M.a. Zy, Zhang Gx, H.u. Jm, L.i.u. Zy, Wang Hy, et al., Polydopamine film coated controlled-release multielement compound fertilizer based on mussel-inspired chemistry, J. Agric. Food Chem. 61 (12) (2013) 2919–2924. [22] H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Mussel-inspired surface chemistry for multifunctional coatings, Science 318 (5849) (2007) 426–430. [23] S.M. Kang, S. Park, D. Kim, S.Y. Park, R.S. Ruoff, H. Lee, Simultaneous reduction and surface functionalization of graphene oxide by musselinspired chemistry, Adv. Funct. Mater. 21 (1) (2011) 108–112. [24] Y. Cao, X. Zhang, L. Tao, K. Li, Z. Xue, L. Feng, et al., Mussel-inspired chemistry and michael addition reaction for efficient oil/water separation, Acs Appl. Mater. Inter. 5 (10) (2013) 4438–4442. [25] M.-H. Ryou, J. Kim, I. Lee, S. Kim, Y.K. Jeong, S. Hong, et al., Musselinspired adhesive binders for high-performance silicon nanoparticle anodes in lithium-ion batteries, Adv. Mater. 25 (11) (2013) 1571–1576. [26] B. Yu, D.A. Wang, Q. Ye, F. Zhou, W. Liu, Robust polydopamine nano/ microcapsules and their loading and release behavior, Chem. Commun. 44 (2009) 6789–6791. [27] S. Gai, C. Li, P. Yang, J. Lin, Recent progress in rare earth micro/ nanocrystals: soft chemical synthesis, luminescent properties and biomedical applications, Chem. Rev. 114 (4) (2013) 2343–2389. [28] W. Stöber, A. Fink, E. Bohn, Controlled growth of monodisperse silica spheres in the micron size range, J Colloid and Interf Sci. 26 (1) (1968) 62–69. [29] A.D. Duong, S. Sharma, K.J. Peine, G. Gupta, A.R. Satoskar, E. M. Bachelder, et al., Electrospray encapsulation of toll-like receptor agonist resiquimod in polymer microparticles for the treatment of visceral leishmaniasis, Mol. Pharm. 10 (3) (2013) 1045–1055. [30] A. Nykänen, A. Rahikkala, S.P. Hirvonen, V. Aseyev, H. Tenhu, R. Mezzenga, et al., Thermally sensitive block copolymer particles prepared via aerosol flow reactor method: morphological characterization and behavior in water, Macromolecules 45 (20) (2012) 8401–8411. [31] N. Sharma, H. Ojha, A. Bharadwaj, D.P. Pathak, R.K. Sharma, Preparation and catalytic applications of nanomaterials: a 66 (5) (2015) 53381–53403.

[32] S.M. Wells, I.A. Merkulov, Kravchenko II, N.V. Lavrik, M.J. Sepaniak, Silicon nanopillars for field-enhanced surface spectroscopy, ACS Nano 6 (4) (2012) 2948–2959. [33] X. Wang, Z. He, S. Xiong, X. Wu, Synthesis of crystalline pyramidal εFeSi and morphology-and size-dependent ferromagnetism, J. Phys. Chem. C 118 (4) (2014) 2222–2228. [34] S. Santra, R. Tapec, N. Theodoropoulou, J. Dobson, A. Hebard, W. Tan, Synthesis and characterization of silica-coated iron oxide nanoparticles in microemulsion: the effect of nonionic surfactants, Langmuir 17 (10) (2001) 2900–2906. [35] S.W. Bian, I.A. Mudunkotuwa, T. Rupasinghe, V.H. Grassian, Aggregation and dissolution of 4 nm ZnO nanoparticles in aqueous environments: influence of pH, ionic strength, size, and adsorption of humic acid, Langmuir 27 (10) (2011) 6059–6068. [36] E. Marie, R. Rothe, M. Antonietti, K. Landfester, Synthesis of polyaniline particles via inverse and direct miniemulsion, Macromolecules 36 (11) (2003) 3967–3973. [37] W. Yuan, J. Yuan, S. Zheng, X. Hong, Synthesis, characterization, and controllable drug release of dendritic star-block copolymer by ringopening polymerization and atom transfer radical polymerization, Polymer 48 (9) (2007) 2585–2594. [38] T. Meng, X. Gao, J. Zhang, J. Yuan, Y. Zhang, J. He, Graft copolymers prepared by atom transfer radical polymerization (ATRP) from cellulose, Polymer 50 (2) (2009) 447–454. [39] G. Han, J. Yuan, G. Shi, F. Wei, Electrodeposition of polypyrrole/ multiwalled carbon nanotube composite films, Thin Solid Films 474 (1) (2005) 64–69. [40] W. Yuan, J. Yuan, F. Zhang, X. Xie, Syntheses, characterization and in vitro degradation of ethyl cellulose-graft-poly (ε-caprolactone)-blockpoly (l-lactide) copolymers by sequential ring-opening polymerization, Biomacromolecules 8 (4) (2007) 1101–1108. [41] X. Sui, J. Yuan, M. Zhou, J. Zhang, H. Yang, W. Yuan, et al., Synthesis of cellulose-graft-poly (N, N-dimethylamino-2-ethyl methacrylate) copolymers via homogeneous ATRP and their aggregates in aqueous media, Biomacromolecules 9 (10) (2008) 2615–2620. [42] S. Yang, J. Li, D. Shao, J. Hu, X. Wang, Adsorption of Ni (II) on oxidized multi-walled carbon nanotubes: effect of contact time, pH, foreign ions and PAA, J. Hazard Mater. 166 (1) (2009) 109–116. [43] Q. Yan, J. Yuan, Z. Cai, Y. Xin, Y. Kang, Y. Yin, Voltage-responsive vesicles based on orthogonal assembly of two homopolymers, J. Am. Chem. Soc. 132 (27) (2010) 9268–9270. [44] S. Laurent, D. Forge, M. Port, A. Roch, C. Robic, L. Vander Elst, et al., Magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization, physicochemical characterizations and biological applications, Chem. Rev. 108 (6) (2008) 2064–2110. [45] J.A. Jiménez, M. Sendova, M. Sendova-Vassileva, Real-time monitoring of plasmonic evolution in thick Ag: SiO2 films: nanocomposite optical tuning, ACS Appl. Mater. Inter. 3 (2) (2011) 447–454. [46] H. Zou, H. Schlaad, Thermoresponsive PNIPAM/silica nanoparticles by direct photopolymerization in aqueous media, J. Polym. Sci. Pol. Chem. 53 (10) (2015) 1260–1267. [47] Y. Liu, K. Ai, J. Liu, M. Deng, Y. He, L. Lu, Dopamine-melanin colloidal nanospheres: an efficient near-infrared photothermal therapeutic agent for in vivo cancer therapy, Adv. Mater. 25 (9) (2013) 1353–1359.

Please cite this article as: C. Heng, et al., Biomimic preparation of highly dispersible silica nanoparticles based polymer nanocomposites, Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.08.072