Diverse applications of fibers surface-functionalized with nano- and microparticles

Composites Science and Technology 79 (2013) 77–86

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Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech

Review

Diverse applications of fibers surface-functionalized with nano- and microparticles Young Gun Ko, Ung Su Choi ⇑ Center for Urban Energy Systems, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea

a r t i c l e

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Article history: Received 4 December 2012 Received in revised form 12 February 2013 Accepted 14 February 2013 Available online 28 February 2013 Keywords: A. Fibers A. Functional composites A. Hybrid composites A. Nanoparticles A. Smart materials

a b s t r a c t The study of particles on surfaces is extremely important in many area of human endeavor (ranging from microelectronics to optics to biomedical). However, the topics of review articles on nano- and microparticles are limited to the synthesis, applications and particles on the flat surface, although interest in nanoand microparticles/soft-fibrous template composites has increased because they have merits of low particle aggregation at high concentrations, good physicochemical properties, and highly mechanical strength. Here, we briefly review the recent applications of nano- and microparticles/soft-fibrous template composites such as fibrous scaffolds for bone tissue engineering, smart fibrous magnets, photoluminescence composites, and sequestration of toxic materials in water and air. Ó 2013 Elsevier Ltd. All rights reserved.

Contents 1. 2. 3. 4. 5. 6.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . Fibrous scaffolds for bone tissue engineering. Smart fibrous magnets. . . . . . . . . . . . . . . . . . . Photoluminescence composites. . . . . . . . . . . . Sequestration of toxic materials in water and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction The diverse structures and properties of nano- and microparticles make them useful tools for both fundamental studies and pragmatic applications in a range of disciplines [1–3]. However, particles should be often attached on the substrate for the applications without the particle aggregation and compromising the physicochemical properties [4–7]. Therefore, the study of particles on surfaces is extremely important in many areas of human endeavor (ranging from microelectronics to optics to biomedical). The statistical research reflects scientists and engineers’ interest on them. The number of published articles on the particle growth on the substrate has increased with the explosive growth of the number of their citations (Fig. 1).

⇑ Corresponding author. Tel.: +82 2 958 5657; fax: +82 2 958 5659. E-mail address: [email protected] (U.S. Choi). 0266-3538/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compscitech.2013.02.016

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Nano- and microparticles have been supported on diverse substrates such as carbon [8,9], polymers [10], metal or metal oxide [11], and silica [12], tailored to their potential usefulness as electronic [13,14], bio- [15], optical [16], sensor [17], and catalytic materials [18]. Strong interactions between a template and particles lead to the arrangement of particles in structures that are predefined by the shape of the template. Fibrous architectures are among the most abundant load-carrying materials in nature, encompassing molecular level peptide assemblies, supramolecular protein materials (e.g., collagen), nanoscale carbon nanotube, colloidal level native cellulose nanofibrils, through to macroscale spider silk [19,20]. Commonly, two types of hard templates (such as chemically functionalized carbon nanotubes or inorganic wires [21]) and soft templates (such as synthetic polymers [22], proteins [23], DNA molecules [24,25] or viruses [26]) are classified for the fibrous template [27]. There are several good review articles on nano- and microparticles [28–33]. To our knowledge, the topics of these review articles

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Fig. 1. The numbers of publications and citations related with particles growth on the substrate in the period of January 1980–December 2011. They were analyzed with topic keywords of ‘‘particle’’ and ‘‘growth’’ and ‘‘substrate’’ in Web of Science (Thomson Reuters).

are limited to the synthesis, applications and particles on the flat surface, although interest in nano- and microparticle/fibrous template composites has increased. The objectives of this article are to briefly review the applications of nano- and microparticles/soft-fibrous template composites such as fibrous scaffolds for bone tissue engineering, smart fibrous magnets, photoluminescence composites, and sequestration of toxic materials in water and air. Instead of the classic mixing of particles in a fibrous matrix, if a new approach of particles/soft-fibrous template composites is used, the range of their applications will widen without losses of physicochemical properties of particles and mechanical properties of fibrous matrix. The approach also gives a merit of low particle aggregation at high concentrations.

2. Fibrous scaffolds for bone tissue engineering Since tissue engineering came into the spotlight for the aimed repair and the regeneration of injured organs and tissues, various scaffolds mimicking the natural extracellular matrix have been developed to create the optimum environment for cell adhesion, growth, migration and differentiation [34]. The development of scaffolds capable of mimicking the structure and function of the natural extracellular matrix (ECM) is a rapidly growing research area [35]. Natural bone is mainly composed of collagen fibers and hydroxyapatite (HAp) nanocrystals [36]. To mimic the collagen fibers, biocompatible nanofibers have been fabricated using various methods such as electrospinning [37], phase separation [38], and self-assembly [39]. And due to their chemical similarity to the inorganic phase of bone, inorganic biomaterials such as calcium phosphate (CaP), e.g. hydroxyapatite (HAp), a- and b-tricalciumphosphate (TCP), have been more intensively investigated in respect to their possible application as bone scaffolds [40,41]. These materials are bioactive, osteoconductive and are able to bond directly to bone. Moreover, numerous in vitro and in vivo studies have shown that HAp and CaPs support the adhesion, differentiation and proliferation of osteogenesis related cells (e.g. osteoblasts, mesenchymal stem cells) [42,43]. Many groups have investigated the controlled nucleation and growth of crystals from organic templates in vitro such as poly(lactic acid) [44], reconstituted collagen [45], and many others. These studies suggest that the anionic groups on the surface of organic templates are nucleation sites of crystals. The anionic groups ex-

posed in solution tend to concentrate the inorganic cations resulting in local supersaturation followed by nucleation of crystals [46]. Stupp et al. used the pH-induced self-assembly of a peptideamphiphile to make a nanostructured fibrous scaffold reminiscent of extracellular matrix (Fig. 2a) [47]. These fibers can be crosslinked by formation of intermolecular disulfide bonds upon oxidation, which results in a chemically robust fiber, and the cross-links can be reversed by the reduction of the disulfides back to free thiol groups. After cross-linking, the fibers were able to direct mineralization of hydroxyl apatite to form a composite material in which the crystallographic c axes of hydroxyapatite are aligned with the long axes of the fibers. These mineralized nanofibers resemble the lowest level of hierarchical organization of bone. The mineralization process was conducted in an aqueous solution with CaCl2 and Na2HPO4 at the room temperature through the steps of nucleation and growth of crystal. The number of polymers that can be electrospun is vast, but for tissue engineering special care has to be taken to ensure biocompatibility. Obvious choices include natural polymers such as collagen, gelatin, elastin, chitosan, and silk among others, but there are some processing difficulties associated with protein denaturation. Synthetic polymers provide more processing flexibility but lack certain biological properties of the natural polymers. However, research is progressing toward hybrid polymers that include both natural and synthetic polymers in an effort to merge the advantage of both [48]. Li et al. functionalized electrospun poly(DL-lactic acid) fibers with carboxyl, hydroxyl and amino groups, and conducted HAp nucleation and growth on the fibers in simulated body fluid (SBF) (Fig. 2b) [49]. Higher contents of carboxyl groups, combination of hydroxyl and carboxyl groups, and combination of amino, hydroxyl and carboxyl groups were favorable for HAp nucleation and growth in SBF, resulting in higher content and lower crystal size of formed HAp. It was suggested that the formation of HAp on the surfaces of electrospun fibers was controlled by the charge density of groups on the fiber surface and the interaction intensities among corresponding ionic groups and/or polar groups. The biomineralization of apatite on a bioactive surface is considered to be a consequence of a ceramic surface reaction with interstitial blood plasma, of which the core cascade appears inorganic. Specifically in vitro, an acellular SBF with ion concentrations nearly equal to those in blood plasma could reproduce the formation of apatite on bioactive surface in vivo [50]. Fig. 2c schemati-

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Fig. 2. Nucleation and growth of hydroxyapatite crystals on (a) peptide amphiphile nanofiber [47] and (b) electrospun poly(DL-lactide) fibers for bone tissue engineering [49], and (c) schematic presentation of the origin of the negative charge on the surface and the process of bone-like apatite formation thereon in SBF (ACP: amorphous calcium phosphate) [51].

cally summarizes the mechanism of bone-like apatite formation on the fiber with negative charge in SBF, by indicating the processes of formation of the Ca-rich amorphous calcium phosphate (ACP) incorporating calcium ions, the Ca-poor ACP incorporating phosphate ions and the apatite incorporating both the calcium and phosphate ions [51]. Recently, the strategy of the mineralization of the scaffold for the bone tissue engineering has become more diversity. Huang et al. applied an approach of current-mediated ion diffusion (CMID), as a feasible means of 3D biomimetic mineralization (Fig. 3a) [52]. This approach can create a wide range of nanoscale single crystals of calcium phosphate within the scaffold having narrow pores (such as hydrogel, and woven fabric). During the 3D biomimetic mineralization, the cation Ca2+, and the anions, PO34 , HPO24 , and OH were focused to diffuse in reverse directions into the scaffold matrix from the respective ion reservoir. The cation and anion met inside the scaffold to form calcium phosphate minerals. A wide range of calcium phosphate crystals may be obtained by altering the current density, the pH of the reservoirs and the ionic strength of the scaffold. Other electric method to mineralize the scaffold is the electrodeposition. Nardecchia et al.

applied a ‘‘flow-through’’ electrodeposition process for the homogeneous mineralization of the internal structure of the 3D scaffold [53]. In contrast, Gungormus et al. designed peptide-based nanofibers that direct the formation of hydroxyapatite [54]. They described the development of an in situ forming, self-assembling peptide nanofibers that is capable of directing the mineralization of calcium phosphate. The peptide, MDG 1 (Mineral Directing Gelator), undergoes triggered intra-molecular folding into a conformation that subsequently self-assembles to form a fibrillar network where a mineral-directing peptides sequence was displayed from the fibrils (Fig. 3b). Aside these new fibrous scaffolds, new and various attempts have been tried to fabricate the mineralized fibrous scaffold for bone tissue engineering by mimicking the bone or nature.

3. Smart fibrous magnets Magnetic materials have played many important roles in our daily life over thousands of years [55]. They are classified by their response to an externally applied magnetic field. Five basic types of

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Fig. 3. (a) Schematic of 3D biomimetic mineralization of pHEMA type polymer via a current-mediated ion diffusion (CMID) approach [52] and (b) schematic representation of the folding, self-assembly, and resultant hydrogelation of MDG 1, cMDG 1, and MAX8 peptides [54].

magnetism can be described: diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism and ferrimagnetism. If a material does not have magnetic dipoles in the absence of an external field and has weak induced dipoles in the presence of a field, the material is referred to as diamagnetic (e.g., quartz SiO2 and calcite CaCO3). If a material has randomly oriented dipoles that can be aligned in an external field, it is paramagnetic (e.g., montmorillonite and pyrite). For a ferromagnetic material, the magnetic dipoles always exist in the absence and presence of an external field and exhibit long-range order (e.g., Fe, Ni and Co). For an antiferromagnetic material, the adjacent dipoles are antiparallel in the absence of an external field and cancel each other (e.g., troilite FeS and ilmenite FeTiO2). In a ferromagnetic material, there are always weaker magnetic dipoles aligned antiparallel to the adjacent, stronger dipoles in the absence of an external magnetic field (e.g., Fe3O4 and Fe3S4) [56]. Especially, small particles do not have permanent magnetic moments in the absence of an external field but can respond to an external magnetic field. They are referred to as superparamagnetic particles. Superparamagnetic behavior can be described as a combination of paramagnetic and ferromagnetic behavior. Superparamagnetic nano- and microparticles are of great interest for researchers from a broad range of disciplines, including magnetic fluids, data storage, catalysis, and bio-applications [57]. Polymer–magnetic nanoparticle composites have been attractive use in applications requiring multifunctional characteristics

[58–61]. In classical methods, magnetic nanoparticles are simply mixed with a polymer matrix. However, they aggregate in the matrix if the magnetic nanoparticle content is increased to improve material functionality [62]. The problem of aggregation worsens for magnetic nanoparticles and their nanocomposites because of interparticle dipolar forces [63]. Therefore, instead of the classic mixing of magnetic nanoparticles in a polymer matrix, the formation of the magnetic nanoparticles on the matrix have been tried to reduce the aggregation of the magnetic nanoparticles and the mechanical properties of the matrix. Olsson et al. demonstrated a facile template approach to constructing magnetic nanocomposites that enables tunability from highly porous, flexible, magnetically actuating aerogels to solid and stiff nanocomposites with high particle loading (Fig. 4a) [64]. The synthesis pathway is as follows: a bacterial cellulose hydrogel (step 1) is first freeze-dried into a porous cellulose nanofibril aerogel (step 2). The dried aerogel template is then immersed in aqueous FeSO4/CoCl2 solution at room temperature (step 3) before heating the system to 90 °C to thermally precipitate the non-magnetic metal hydroxides/oxides on the template. The precipitated precursors are converted into ferromagnetic cobalt ferrite nanoparticles (CoFe2O4) on immersion in NaOH/KNO3 solution at 90 °C (step 4). The fabricated magnetic aerogels can be magnetically actuated, absorb water, and behave as magnetically actuating ferrogels. Olsson et al. envisaged their use in aqueous biological, medical and fluidics applications.

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Fig. 4. (a) Synthesis of elastic aerogel magnets with cellulose nanofibrils and CoFe2O4 [64] and (b) magnetic nanofibrillated cellulose/CoFe2O4 hybrids [65].

The nanofibrillated cellulose (NFC) was suggested as a template for constructing magnetic nanocomposites by Walther et al. [65]. The NFC was prepared similar to TEMPO-mediated oxidation (2,2,6,6-tetramethylpiperidin-1-oxyl) of wood pulp and subsequent homogenization in a microfluidizer, which is known to yield high-aspect ratio nanofibrils with diameters down to a few nanometers and length up to several micrometers in aqueous suspensions that form strong hydrogels. The NFC-based macrofibers can be prepared by simple wet-extrusion of the NFC hydrogels into a coagulation bath of an organic solvent (e.g., ethanol, dioxane, or tetrahydrofuran). The magnetic NFC macrofibers that allow a response in external magnetic fields were prepared by attaching CoFe2O4 nanoparticles to form inorganic/organic hybrid fibers. The CoFe2O4 particles were synthesized by a simple aqueous coprecipitation reaction [66] of FeSO4 and CoCl2 in the presence of an already prepared macrofiber (Fig. 4b). The resulting magnetic NFC macrofibers demonstrated excellent mechanical properties combining stiffness and strength with toughness without the loss of magnetic properties. This combination of mechanical strength and high degree of functionality render the materials a versatile platform for applications in materials and bio/life sciences. Various applications of fibrous magnets have been suggested. Calcagnile et al. fabricated an oil absorber based on commercially available polyurethane foams functionalized with colloidal superparamagnetic iron oxide nanoparticles and submicrometer polytetrafluoroethylene (PTFE) particles, which can efficiently separate oil from water (Fig. 5a) [67]. The functionalized foams presented three important and desirable features: water-repellency, fast oil absorption, and magnetic actuation, attributed to both chemical and morphological features. The functionalized foams can be fabricated with the commercial fabrics using the simple attachment of PTFE and superparamagnetic nanoparticles. In the field industry, unwanted harmful-nanoparticles have been produced and caused serious problems in many parts of the world [68,69]. To remove them, the filtration system has been used. However, the filtration efficiency is not good due to their tiny size. Many of these nanoparticles, such as iron, can be attached to a

magnet. Therefore, the magnetic particles attached fabrics can be the more effective filter (Fig. 5b) [70]. Electromagnetic interference (EMI) has become a pollution problem due to the extensive utilization of electronic devices, local computer networks, mobile phones, and personal computers [71]. The electromagnetic wave is also very harmful to the human health. As a result, the demand for the microwave absorbers and electrcomagnetic shields in this frequency range is increasing. Magnetic particle are one of the effective materials which absorb the microwave [72–75]. The microwave absorbers can be used to minimize electromagnetic reflections from metal plates. Magnetic fabrics can be used more wide and convenient than particles or composite-panels forms (Fig. 5c). In the treatment of the cancer, the formation of new tissue is important together with the elimination of tumor cells. Huang et al. suggested new idea to solve the difficult problem [76]. They fabricated the mangetic-nanoparticles embedded fibrous-scaffold to treat cancer. The implanted scaffold into the cancer area kills the tumor cells by the magnetic heating. The magnetic-nanoparticles can kill only tumor cells selectively. The nanofibrous scaffold can be a good supporter for a new tissue formation by cells’ migration and proliferation (Fig. 5d).

4. Photoluminescence composites As light-emitting nanocrystals, quantum dots (QDs) have been a major focus of research and enormous development during over the past two decades [77]. QDs are semiconductor nanoparticles, which can emit narrow fluorescence covering the entire visible light spectra region under UV light excitation [78]. They fluoresce at progressively shorter wavelength as the particle size is decreased [79]. This is because the energy of the light emitted by electrons that drop back to the ground state depends directly on the size of the gap. The unique electro-optical properties of QDs arise from the combination of material and dimensionality, the latter known as ‘‘quantum confinement’’ [80]. Ma and Su summarized

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Fig. 5. (a) Removal of the oil by the magnetically driven PU/NPs/PTFE sample [67], (b) removal of heave metal nanoparticles from the air and aqueous solution, (c) microwave absorption fabric, and (d) magnetic fibrous scaffold for cancer therapy.

Fig. 6. (a) Fabrication of CdS nanoparticles coated butterfly wings [83] and (b) synthesis of PVK-co-PGMA/CdTe QDs composite nanofibers and its fluorescence confocal microscopy image (right bottom) [86].

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the comparison of character, modification strategy and application of QDs [81]. The size effect of QDs also has been studied well [82]. The relevant ideas to a combination of QDs and natural scaffold can inspire the investigation of photonic crystal (PhC) materials. Han et al. prepared the butterfly wings as natural photonic crystal scaffolds for controllable assembly of CdS nanoparticles [83]. Originally wings are activated via an EDTA/DMF treatment, then involved in the in situ synthesis of CdS seeds, followed by a solvothermal process (Fig. 6a). The assembly patterns of nanoCdS in the final nano-CdS/wing scales were successfully controlled at two levels: one is the PhC structures (>100 nm) that can be varied by taking diverse scales from specific parts of a butterfly or from different butterfly species as the scaffolds, the other is the nano-CdS small clusters (<100 nm) that can be controlled by adjusting procedure factors. The study is not for a specific application. However, a related investigation is currently under way which should illuminate new valuable applications. Much effort has been devoted to the construction of one-dimensional (1D) structures of nanoparticles, owing in part to their application as pivotal building blocks in fabricating a new generation of optoelectronic devices [84,85]. Yang et al. developed an interfacedirected synthesis pathway to polymer-encapsulated CdTe QDs [86]. Especially, CdTe nanocrystals have attracted increasing research interests as QD materials in recent years due to the advantage of its synthesis in an aqueous solution [87]. CdTe QDs were covalently grafted with poly(N-vinylcarbazole-co-glycidylmethacrylate) (PVK-co-PGMA) to form uniform fibrous fluorescent composites at the water/chloroform interface via the reaction between epoxy groups of PVK-co-PGMA and carboxyl groups on the surface of CdTe QDs (Fig. 6b). The microfibers have a propensity to form twisted morphology (Fig. 6b, right top), while their refined nanostructures still reveal relatively parallel character and confirm the microfibers are assembled form countless corresponding nanofibers. An individual microfiber exhibited strong and homogeneous green fluorescence at kex = 488 nm (Fig. 6b, right bottom). This interfacial assembly strategy offers a versatile route to incorporate QDs into a polymer host, forming uniform one-dimensional nanomaterials potentially useful in optoelectronic applications.

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The application of photoluminescence composites including QDs has been concentrated on the sensors. Under these circumstances, Fahmi et al. fabricated CdSe nanofibers for biomedical applications [88]. They synthesized the CdSe nanofibers in situ in aqueous solution by the self-assembly of elastin-like polymers (ELPs) [(VPGVG)2(VPGEG)(VPGVG)2]15 at room temperature (Fig. 7a). The experimental results on ELP–CdSe cytotoxicity demonstrated that the material represents a novel and promising class of non-toxic nanofibrous materials, which indeed are capable of crossing the cell membrane barriers. Fahmi et al. suggested these types of nanofibers could be introduced in future medicine nanotechnology and applied in the diagnosis and treatment of various diseases. Other useful application of the QDs embedded fiber is the detection of enzyme activity. He et al. developed a novel enzyme sensor based on CdSe QDs/polycaprolactone (PCL) composite porous fibers (Fig. 7b) [89]. In the biochemical reaction, Lactate dehydrogenase (LDH) catalyzes the interconversion of L-lactate (LL) and pyruvate with the coenzyme nicotinamide adenine dinucleotide (NAD). NAD is converted to its reduced from NADH. The prepared fluorescent fibrous films can be reversibly quenched by NAD due to the energy transfer process between NAD and CdSe QDs. Therefore, based on the films and the LDH-catalyzed reaction for converting NAD to NADH, He et al. fabricated a sensor for turnon fluorescence detection of the activity of LDH. The QD composite fluorescent-porous fibrous film can be developed as a facile, rapid, sensitive and stable enzyme activity detection platform.

5. Sequestration of toxic materials in water and air Because of their intrinsically persistent nature, heavy-metal ions are major contributors to pollution of the biosphere [90,91]. These metals, when discharged or transported into the environment, may undergo transformations and can have a large environmental, public health, and economic impact [92,93]. Adsorption is one of the methods commonly used to remove heavy-metal ions from various aqueous solutions with relatively low metal ion concentrations [94–96]. Ko and Choi suggested a unique idea for the sequestration

Fig. 7. (a) Schematic representation of the generation of self-assembled nanofibers of ELP–CdSe nanoparticle in situ [88] and (b) the principle for assay of the activity of LDH based on CdSe QD doped fluorescent-porous fiber and enzyme-catalyzed reactions [89].

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Fig. 8. (a) Nucleation and growth of Cu(OH)2 crystals on PADD under various pHs [97] and (b) MnO2/cellulose fiber composite for oxidative decomposition of formaldehyde [102].

of heavy metal ions in an aqueous solution [97]. They suggested the particle formation (crystal growth) of heavy metal ions on a chelating fiber to increase the removal capacity of ions in an aqueous solution. As the chelating fiber, poly(acryloamidino diethylenediamine) (PADD) was obtained via the heating of polyacrylonitrile fiber with diethylenetriamine and AlCl3
6H2O. After the adsorption of Cu(II) on the fabricated PADD fibers, the pinecone-like Cu(II) crystals covered the entire surfaces of chelating fibers. In the Cu(II) adsorption isotherm curves, adsorbed H+ on the amine groups blocks amineCu2+ complex formation at low pHs. With increase of pH, amineCu2+ complex forms well. And the complexed Cu2+s become Cu(OH)2 crystals finally (Fig. 8a). It is well-known that long exposure to indoor air with concentrations of formaldehyde (HCHO) that exceed safe limitations is greatly harmful to human health [98,99]. Catalytic oxidation has great potential to degrade HCHO, which yields CO2 and H2O as final products [100]. Sekine found that manganese dioxide (MnO2) was most effective for the removal of HCHO and that harmful byproducts were not released through the catalytic reaction [101]. Zhou et al. reported on facile in situ synthesis of manganese oxide nanosheets on porous cellulose fibers as a unique nano-reactor and template (Fig. 8b) [102]. The nanostructured MnO2/cellulose composites show excellent catalytic performance for the oxidative decomposition of HCHO. The HCHO conversion per milligram of MnO2 of 8.86 wt% MnO2/cellulose is about 9–17 times as high as that of birnessite MnO2 powder prepared by a hydrothermal method. The catalytic activity was found to be dependent not only on the content of MnO2, but also on the adsorption of HCHO on cellulose fibers as well. 6. Conclusions Recently, nano- and microparticle/fibrous template composites have received plenty of attention since they have merits of low

particle aggregation at high concentrations, good physicochemical properties, highly mechanical strength, and so on. Due to these merits, recently many studies have supported the nano- and microparticle/fibrous template composites as one of the key materials. Here, we briefly reviewed the recent applications of nanoand microparticles/soft-fibrous template composites. The applications were divided into four categories: (1) fibrous scaffolds for bone tissue engineering, (2) smart fibrous magnets, (3) photoluminescence composites, and (4) sequestration of toxic materials in water and air. More applications have been researched and developed at various researched fields. To widen applications of nanoand microparticles/soft-fibrous template composites, following requirements should be researched: (1) easy synthesis of particles in aqueous solution at low temperature, (2) strong attachment of particles on the fibrous template, (3) good physicochemical properties of particles on the fibrous template, (4) highly mechanical and optimized (flexible or stiff) properties of the fibrous template, (5) control of the state of particle aggregation and size on the fibrous template, (6) control of the average distance between nanoparticles, (7) low cost for synthesis of particles, and (8) investigation of the physicochemical interaction between particles and soft-fibrous matters. To date, new researches of nano- and microparticles have led the development of nano- and microparticles/soft-fibrous template composites. However, it is also expected that new materials can be developed through the optimized harmony of particles and soft-fibrous matters. We hope that this review paper will provide insights into the new use of nano- and microparticles/soft-fibrous template composites for researchers and engineers working for nano- and biotechnologies.

Acknowledgment This research was supported by the Converging Research Center Program funded by the Ministry of Education, Science and Technology (2012K001421).

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