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Nanobotany pp 67-82 | Cite as

Nanofibers and Nanowires

  • Aneeqa Sabah
  • Gabour Loius Hornyak
Chapter

Abstract

Nanomaterials having 2-dimensions confined to nanoscale <100 nm and one dimension can go more than μm scale in length. For example, the nanowire, nanotubes, nano fibers etc. Different types of nanowires are introduced on the basis of shapes, textures and geometrical pattern of nano structure obtained.Nanowires exhibited enhanced and unique mechanical, electrical and optical properties different from bulk due to quantum confinement. Templated based, precipitation and sol-gel techniques provide the best control on dimension confinement in comparison to sol-gel, self-assembly and radiation based methods.Carbon nanofibers are the formed by stacking of graphene layers into platelets of approximately 80–100 nm, much larger than a nanotube even. The CNFs possess higher disorder degree than CNTs (the synthesis of CNTs carries out at higher temperatures). The combination of high-specific surface area, flexibility, and significantly directional strength made the fiber a preferred material for various applications ranging from clothing to aerospace structures. Nano-fibers scaffolds are more suitable and favorable for tissue engineering and bio-sensing applicationsdue to high surface area. As increased surface area results in the easy attachment or release of functional groups, absorbed molecules, ions, catalysts, and nanoparticlesfor cell adhesion and migration.

4.1 Fundamentals of Nanomaterials

Nanomaterials can be categorized into three main types on the basis of dimensions that cannot be confined to nano scale (<100 nm). zero-dimensional (0-D) quantum dots, one- dimensional (1-D) nano wires, nanofibers and tubes, two- dimensional (2-D) super lattices and thin films. This classification of having one or more small and confined dimensions small of nanostructured materials in comparison of bulk, exhibit special properties. In 0-D materials, all three dimensions are restricted to nanometer scale. For example, the nanoparticles in any form, can be amorphous, crystalline, single or poly crystalline, exist in various shapes and sizes. 2-D nanomaterials have two unconfined dimensions and only one is restricted to nanometer scale. 2- D materials include nano plating, nano disks, nano coating, nanolayers and films. They can also be either metallic or crystalline. 2-D materials are formed by depositing some specified thickness of specimen on substrate. Finally, the 1-D materials are those having one dimension out of nanoscale and other two are confined to nano scale with negligible crystallite size. For example, the nano rods, nano wires and fibers and nanotubes are 1-D nanomaterials. Electrons and holes exhibited quantum confinement within two dimensions and free to travel in third one.

4.2 Introduction to Nano Fibers and Nanowires

The term fiber comes from Latin fibra: meaning: an elongated thread like structure. It is essential to understand first, the viewpoint of various researchers and scientist about fibers. Botanist consider the fibers as elongated, thick walled cells that give support and strength to plant tissues. Fibers are defined as natural and synthetic filaments in textile industry such as cotton and nylon to made different functional materials. Biochemist and physiologist identify the term fiber as indigestible plant matter having cellulose to stimulate intestinal peristalsis.

The term “nano” comes from Greek word,“nannas” meaning “dwarf” small, little entity. Technically the nano defines as a physical quantity of one billionth of meter (10−9 m). In nano-bio engineering and research, naturally existing nanofibers are frequently in use to reconstruct the functional nanostructures and devices. Nano and micro wires provide recent breakthrough in fabricating the flexible electronic device by aligning the organic wires on substrate under controlled conditions like flexible displays in computers, transistors, smart phones etc [Queens University Report].

Nanowires are the structures with the length to width ratio (aspect ratio) being greater than 1000. The diameter of wires is restricted to tens of nanometer scale but unconstrained length. Nanofibers are highly preferable materials for variety of applications ranging from textile industry to air-craft structures due to high surface area, flexibility and specific directional strength.

4.3 One-Dimensional Nanomaterials

Nanofibers geometrically (according to shape, size and dimensions) falls into the category of 1-D nanomaterials. Nano rods, nanotubes, nano wires all comes within nanofibers. Rather, nanofibers are much more flexible as can be aligned with highly flexible nano elements like globular proteins e.g. DNA helix strands. One of the best example of nanowires and nanorods is carbon nanotubes also termed as quantum wire (as quantum effect become prominent at nano scale, electron behave like wave.) having two dimensions restricted to exciton Bohr radius (electron and hole pair distance within the conduction and valence band respectively).

4.4 Types of Nanowires

Different types of nanowires and fibers exist including metallic, semiconducting, insulating, molecular either organic or inorganic, bio-templated within the range of few 100 of nm in diameter and exceeding the length over 100 μm. Basically the diameter depicts the dimensions and homogeneous nucleation establish the suitable wire length (Gabor et al. 2008).

Biomimetic Nanofibers/wires : Naturally occurring biological structures exhibit attractive properties that can be implanted within metallic nanoparticles to design biomimetic complex structures. Fungal species occurs in variety of geometrical shapes, patterns, textures as well as colors that is very motivating for engineers, scientists and researchers to be used as templates. The hard surfaces of microorganisms are found to be the best template for self-organization of nanoparticles into uniform nanofiber arrays with advanced functional properties. These bio-nano fibers composites may lead to cost-effective, small size and reliable architecture in comparison to complex and trendy techniques in market. Tip Fungal hyphae tip growth is sensitive to the variety of physical, chemical and environmental factor (Gow 1994). The influence of external stimuli such as light, heat, radiations, nutrients, flow sensing, external fields and gravity to control the direction of growing tip can produce the directed mesh of wires for potential application, specifically in electric circuits. Dimensions of nano and micro wires can be well controlled by tropism of microorganisms towards external stimuli for their survival and reproduction. Cellular tip extension and orientation is controlled by vesicles released by micro-tubules and actin (Alexandra and Gow 2009).

Helical Nanofibers, Dumbbell-shaped molecules self-assembled into helical cylinders of ~ diameter of 8 nm and pitch length of 5.6 nm in an aqueous solution. These elementary helical fibers further assembled into super-helical fibers having length of several micrometers. Such 1-D biomimetic nanofibers may introduce new era in flexible electronic and photonic fields (Bae et al. 2005).

Branched and Bundled Nanofiber, Bundled and branched nanofibers were fabricated by self-assembly of conjugated amphiphilic block co-polymers of polythiophene (PHT) and polyethylene glycol (PEG). The shape, length and density of bundled and branched nanofibers were controlled by the length, ratio block co-polymer and homopolymer and quality of solvent. Self-assembled amphilic polymers can be transformed

into isolated, bundled, and branched nanofibers (Kamps et al. 2012). Branched and porous carbon nanofibers are frequently used in electrochemical double-layer capacitors (Tao et al. 2006), Hollow and composite (McCann et al. 2005; Li and Xia 2004).

Ribbon like nanofibers were also reported (Chang et al. 2011).

4.5 Properties of Nanofibers and Nanowires

Nanowires and nanofibers exhibit many different and interesting properties in comparison of bulk due to quantum confinement.

4.5.1 Mechanical Properties

Nanowires are frequently in use as connecting wires in electronic circuits and devices as well. The use of carbon nanotube as probe tip in AFM or STM is termed as nanostructure but if used in some electronic circuit as connecting conducting wire than referred to working as device. Young’s modulus of gold nanowires as nanomechanically measured by AFM tip is found to be independent of diameter and yield strength and provide 100 times better strength than bulk one (Wu et al. 2005). Self-twisting and flexibility of nanofibers is quite impressive for advancement in flexible electronics. Greater tensile strength, flexibility and bending of polymer nano-fibers composite is improved to extensive level by surface functionalizing). Nanofiber may exist as single nanofiber, nanofiber yarn, nanofiber membrane. Fiber diameter, porosity, and pore size, surface contact angle measurementscorrespond to mechanical strength of nano-fibers (Cassie and Baxter 1994).

4.5.2 Optical Properties

Optical properties of nanowires are anisotropic, as orientation play the role. Nanowires can be aligned in the presence of electromagnetic field accordingly. Confined population of electrons is affected by the restoring force the depolarization field. This depolarization effect is caused by surface plasmon of curved surface. The degree of effect is dependent on aspect ratio of synthesized nanoparticles (Pérez-Juste et al. 2005). Longitudinal and transvers, two plasmon modes are observed in absorption spectrum for gold nanorods (Hornyak 1997). Addition of organic materials to nanowires alters their optical response as absorption maxima in UV-visible spectrum shifted to lower energies, the red shifts (Gabor et al. 2008). If the additive one is an insulating material, then polarization is diffuse toward red shift.

4.5.3 Electrical Properties

In nanowires, electrons are free to move without any collisions with impurities, hence no energy loss occur. This effect will become prominent, when the wire width is below the mean free path of electron. For example, the ballistic conduction (electrons are free to move from one electrode to another) or diffusive, depending on elastic scattering and electron tunnelingin single walled carbon nanotubes SWCNT as reported. The nanotubes can withstand with high value of current ~ 1 mA (Chappel and Zabau 2002). Unlike the ballistic transport in CNT, nanowires also exhibit the conductivity strongly dependent on edge effect. Atoms lies on the nanowires surface are loosely bound with neighboring atoms. This dangling bonding creates the defects that may cause the nanowires to conduct electricity. For small size nanowires and nanofibers, the edge effect becomes prominent. Bacterial nanowires with electrical conductivity comparable to semiconductor wires and elasticity are similar to typical polymeric material. These protein-nature bacterial nanowires may provide potential application for bio-fuel cell and bio-nano flexible electronic area.

4.6 Nano Fibers and Nanowires Synthesis Techniques

Processing techniques for nanofibers and nanowires fabrications and manufacturing broadly falls into two categories: top down and bottom up. Top down is defined as the breaking of large entities into smaller ones to nano- range. Bottom up is an assembly of small building blocks, atoms or molecules or even smaller things to design and fabricate hierarchies and complex systems by various wet chemical or physical methods. Nature stands behind the bottom up approaches as shapes, textures, sizes and designing of plant tissues, human cells and crystals all reflects the bottom up processing quite well. Bottom up approaches includes wet chemical methods like sol-gel, precipitation, co-precipitation, hydrothermal, solvothermal, template oriented, radiation based (sono chemical and microwaves), self-assembly, CVD (chemical vapor depositions), carbon-arc discharge, laser pyrolysis and much more to go. Template based synthesis, precipitation and sol-gel techniques provide good control on nanofiber dimensions in comparison to self-assembly and radiation based methods (Leung et al. 2011; Niraj 2005) (Table 4.1).
Table 4.1

Advantages and disadvantages of synthesis techniques for nanowires and nanofibers

Techniques

Advantages

Disadvantages

Template synthesis

Fibers of various shapes and sizes can be fabricated by using different template living or non-living

Hard (non-living) template are difficult to remove. A complex and especially designed process is required in many cases.

Phase separation

Minimum equipment requirement, direct fabrication of nanofibers matrix, mechanical properties can be controlled by varying the polymer concentration

Limited to types of specific polymers

Self-assembly

Good to get small nanofibers and composites without requiring any external glimpse

Complex process

Electro-spinning

Cost- effective, elongated and continuous nanofibers can be obtained

Jet instability

Adjustment of voltage for spinning.

Still hallmark to fabricate 3-dimensional structure

Precipitation and sol-gel

Easy to handle for fiber fabrication

Difficult to obtain excellent fibers without controlled conditions on large scale

Template free polymerization

Pure and uniform poly-nano fibers in large quantity.

Handling and choice of suitable polymer is difficult.

Hydrothermal synthesis

Cost effective and controlled environment at suitable temperature and pressure.

Nano-fibers and Nanowires formed with low crystallinity

Vapor-liquid-solid growth followed by the chemical vapor deposition.

Uni-directional and hybrid nano-wires having no defects are obtained

Choice of catalyst , must be inert

4.6.1 Template Based Growth

Bio-templating self-organized nano wires attracting a lot of attention for nano-micro scaled complex structures. Instead of typical and tedious physical and chemical processing techniques, the use of unique and interesting natural entities as template is now being explored. Template based nanotubes, nanowires (NWs), by using biological entities such as micro-organisms like fungus, bacteria, virus, spider silk, chitin fibers, collagen, cotton and bamboo etc., as soft templateis now in common practice (Sabah 2013). Among all alumina membranes are quite suitable to be used as hard template for fiber fabrication. Basically, template method is used to control the geometric features of nano-wires such as density and diameter by colloidal dispersion. The drawback islong time polarization effect and non-uniform pore filling for high aspect-ratio of nanorods and tubes cause template degeneration. Appropriate selection of template provide controlled and desired size, structure morphology, uniformity and density of the pores. Sol-gel technique is quite common for fabrication of well-ordered mesoporous metal oxidesfor sensing and energy applications by using surfactant as templates. The obtained nanofibers have uniform diameters within the range of roughly 25–120 nm (Zhao et al. 2007). Bio-oriented methods are simpler, versatile, environment-friendlyfor producing nanofibers and wires at industrial scales.

4.6.2 Phase Separation

Porous polymer templateswere employed by thermally induced phase separation in old era that are suitable for implantation due to their porous structure and interconnected spaces. Suitable attachment and migration of cells through interconnecting mechanical strength by such continuous three-dimensionalfibrous network make it an effective approach. This method involves following steps (i) polymer dissolution (synonymous), (ii) phase separation and gelation, (iii) solvent extraction through water (iv) freezingand drying under vacuum. The proper solvent selection is critical step or the formation nanofibrous structure. Thesemicroporous fibers provide three in one action to cell, first is nutrient absorption, second, the signals receiving and transmission, finally the waste disposal. This combination of nano- and macro-structures at the nanofiber level provides uniform cellular distribution and better response.

4.6.3 Self-Assembly

Self-assembly is highly promising bottom-up approachof spontaneously assembled smaller molecules into well-organized nanothreads. Variety of interactions are involved in the formation of these nano-structures like hydrophobic forces, dipole/dipole interactions, non-specific van der Waals interactions p–p stacking, hydrogen bonds, electrostatic interactions, and repulsive steric forces. Peptide amphiphiles chains consist of hydrophobic tails (dialkyle chain) and hydrophilic head (N-a-amino) group scan be self-assembled reversibly into nanofibers and can be applied for variety of materials fabrication. Many reagents such as acid, divalent ion and covalent moieties are responsible for the self-assembling of peptides. It produced low poly disperse nanofibers with high yield. Such nano fibers can develop “smart” biomaterial scaffolds for effective tissue regeneration in future. Briefly, the physical functionality of nanoparticles combined with bio-functioning of living cells as scaffold without any involvement of external entity and intermolecular bond breaking or making, entropic contributions and small enthalpy (∆H) also play the prominent role in such self-assembled process (Fredric 2002).

4.6.4 Electrospinning

In this process, electrostatic forces fabricate continuous nanofiber assemblies. By applying high voltage to the droplet in solution, the molecules get charged and create an electrostatic repulsion, which counteracts the surface tension of the droplet. Variety of fibrous architectures was created based on this principle as electrospinning setups and collectors etc. The morphology of the fibers was strongly influenced by the surface tension, viscosity, and density like properties. Poly lactic acid (PLA) and tetra ethyl benzyl ammonium chloride (TEBAC) are used to fabricate fibers having low diameter by using electrospinning technique. Surface tension and electrical conductivity of the solution is controlled by an amount of TEBAC. These electrospinning nanofibers can be used as drug delivery reservoirs for controlled and timely release of drugs, proteins, antioxidants, and other molecules to the malfunctioning area in tissues. Electrospinning technique has plenty of benefits but it is still a challenge to fabricate a three-dimensional (3D) scaffold by electrospinning. Nanofibers have great capacity for the attachment or release of functional groups, absorbed molecules, ions, catalysts, and nanoparticles due to remarkably high surface area. As a result, these nanofiber assemblies can be used as highly active bio-scaffolds for cells migration and adhesion in the field of tissue engineering and sensing. Nanofibers of different materials as prepared by electrospinning are displayed in Fig. 4.1.
Fig. 4.1

SEM images of different types of nanofibers fabricated by electrospinning (a) random-oriented ribbons (b) aligned hollow tubes, (c) spider-web-shaped, (d) densed network -wires (e) rice grain-shaped (f) multi-channal entagled tubular (g) tubes in tubes (h) Needle -like wires mesh (l) vertically-aligned flattend ribbons (Jeong et al. 2015)

4.6.5 Template-Free (Interfacial Polymerization)

It is a template free technique to synthesize pure and uniform polyaniline nanofibers in bulk. Type and concentration of an aciddecide the dimensions, quality and uniformity of the nanofibers. High acid concentration results in the highproportion of nanofibers in the final product.

Rapidly initiated polymerization is an alternative technique to surface-interface polymerization (Abdolahi et al. 2012). Generally, an initiator solution containing ammonium peroxydisulfate in HCl is poured into a monomer solution containing aniline in HCl all at once. The size of the polyaniline nanofibers formed is influenced by the choice of an acid used, whilethe quality of nano-wires is effected the polarity of the reaction medium; more polar the solvent, more good the nanofibers. Reaction temperature and reactant concentration have no effect on nanofibers morphology of nano-wires is not affected by temperature and concentration of reactants.

4.6.6 Vapor-Liquid-Solid (VLS) Growth

One-dimensional (1D) nanostructures without defects can be synthesized by this technique. Growth of hybrid and doped form of nano-wires and nano-fibers based on the formation of metal nanodroplets from gaseous precursors is crucial pint for this method. At first the metallic nanocrystals are melted in a tube furnace on a single stub. Saturation of molten metal nano droplets occur during melting process by introducing the different gases. These droplets act as catalysts to synthesize single crystalline and uni-directional nano-fibers . The interface energy plays an important role for deciding the droplet size and shape. If contact angle between solid surface and droplet results in larger growth area whereas, small contact angles give wires and whiskers of small radius.

4.6.7 Hydrothermal Synthesis

In this technique, the growth of the nanofibers and nanowires occur by chemical decomposition of thermally agitated reactive ions of precursors; in an autoclave under pressure of 1 atm and temperature of about 100–300 °C. Appropriate catalysts are used to enhanced the growth rate. Temperature, precursor concentration, and pH, etc. are the key parameters to control the fibers growth. Low level of crystalline structure of the grown nanofibers is one of the major drawback of this method. Among various nanofibers fabrication methods like self-assembly, phase separation, hydrothermal template based etc., electrospinning is the solely method to fabricate 1D ceramic nanofibers in a cost-effective and controlled environment.

4.6.8 Sol-Gel Synthesis

Sol-gel is one of the simple and flexible technique for 1-D nanowires synthesis. Initially the chemical solution as sol is used as precursor to precede final consolidated gel like network of either individual particles or polymers. Homogeneous polymer-embedded cellulose nanofiber composites were obtained by sol-gel process (Fig. 4.2). Cellulose whiskers are produced by the formation of homogeneous dispersed whisker as sol and thus followed by gel via exchange of water molecules with solvent. Acetone was routinely used in the procedure. Gels with a whisker content of 1.0–1.8% w/w were explored. This method is widely applicable for the fabrication of nanocomposites having unique properties of individual components. These ‘whiskers’ exhibits high mechanical strength and can be obtained from naturally occurring bio-entities like wood and cotton, the safe and cost- effective (Jeffery et al. 2007).
Fig. 4.2

(a) Single –walled and (b) Multi-walled carbon nanotubes

4.7 Applications of Nanofibers

4.7.1 Carbon Nanotubes

As implantable sensors: Carbon nanotubes and their allotropes based sensors are frequently used as sensors for nanomedicineand nano-biotechnology due to their unique and enhanced properties. Properties such as surface area to mass ratio, retention time within tissues and body and the reactivity have greater impact in fuel cells, plasmonics, photovoltaic batteries, medical monitoring and diagnostics (Wujcik and Monty 2013). SWCNTs have a typical diameter of 0.5–1.5 nm, while that of MWCNTs are typically above 100 nm (Karimi et al. 2013).

CNTs are very promising for in vitro and in vivo sensing due to their unique properties such as an efficient entry into the cells, modification to get rid of toxic materials, enhanced intrinsic electronic, optical and magnetic properties that can be tuned and pertinent to life science applications. MWNTs are found to be encouraging scaffolds for orthopedic implantation, as well as provide skillful monitoring of bone growth through electrochemical sensing. Highly conductive surface area of MWNT’s provides high electric activity in orthopedic treatment. CNT’s can be prepared mainly by chemical vapor deposition (CVD), laser ablation etc. A remarkable surface area of SWNT’s is promising for single molecule detection due to NIR fluorescence, band gap sensitivity to local environment and the quenching capabilities of CNT’s. DNA modified SWNT causing red shift in band gap spectrum to modulate the transitions in blood, mammalians cells and tissues. Multi-walled and single walled CNTs are shown in Fig. 4.3. DNA and RNA strands can be detected very quickly by using CNT nano electrodes for molecular diagnosis. Well aligned multi-walled nano- tube arrays were embedded on SiO2 matrix by bottom up approach.
Fig. 4.3

Microlenses and fiber optical fabricated from protein scaffolds (Zhang 2003)

In future, carbon based nano tubes can provide fast and appropriate detection of metal ions, contaminants neuron-transmitters and pathogen detection in microfluidic devices (Li et al. 2003).

4.7.2 Difference in Carbon Nanotubes and Nanofibers

CNTs and CNF can be differentiated to some extent as CNT’s graphene layers are folded into hollow cylinders whereas in CNF, the graphene layers can be stacked as platelet, ribbon or rod like structure. CNFs can be termed as stacked-cup CNTs. The CNFs possess higher disorder degree than CNTs (the synthesis of CNTs carries out at higher temperatures). Difference can be examined by TEM and Raman analysis. The CNTs have lower diameter that CNFs. The diameter of CNFs can be higher than 80–100 nm. Tubes are the rolled graphene sheet. Fibers are all the carbon nano chips stacking on top of each other and form the fiber form. The diameter of CNF is larger than single-wall nanotubes.

4.7.3 Biological and Chemical Application of Nanofibers/Wires

Nanofibers enhanced the regeneration of many tissues and organs in medical applications for example, cell migration, infiltration, bio-compatibility and bio degradation with nano-fiber based scaffolds. Current challenges of tissues and organs failures can be accomplished by the use of nano fibers. High surface area to volume ratio of nano-fibers enhances the serum absorption by giving more binding sites to cells. Nanofibers also exhibit higher efficiency and flux in catalytic reactions (both hetro and homogeneous) chemical sensing and detection due to higher sensitivity in reactions in comparison to micro and nano-structures. Nano fibrous scaffolds facilitate skin regeneration, diabetic ulcer and normal wounds effectively in comparison to simple fibrous scaffolds. Nano-fibers are remarkably in use for investigating skeletal tissue engineering, both in absence and presence of growth factors. 3-D hierarchical nano-wires and fibers scaffolds are found to be mechanically strongwith controlled pore size and diameter for hard tissue regeneration (Nguyen et al. 2013).

ZnO nanorods grown on polyethylene fibers are used as antibacterial water purifier. Up to 99% of E. coli and S. aureus in spiked water containing about 1010 colony forming units (CFU) of bacterial cells were found to be immobilized under sunlight, while 80% of E. coli and 59% of S. aureus cells were inactivated. This water filter can be utilized in areas of drinking water scarcity. Formation of reactive oxygen contents through photo catalysis and release of Zn ions through dissolution of ZnO are responsible for antibacterial effect (Sunadan et al. 2012).

Living organisms at ambient temperature and low pressure can be used to fabricate composites. For example, fiber-optical spicule of Euplectella has the dimensions of a single human hair and can act as multimode waveguides. These optical fibers exhibit much more fracture resistance due to presence of organic ligands, high refractive indices and remarkable flexibility as compared with typical synthetic optical fibers. These microfibers act as multimode wave guides when light was coupled to free-standing spicules as depicted in Fig. 4.4 (Zhang 2003).
Fig. 4.4

A schematic representation of the virus-mimicking fiber fabrication process by wet-electro-spinning technique (Lee and Angela 2003)

Silver nano-fibers were reported by using bio-organisms extracts as reducing and stabilizing agents. Single crystalline Ag nano plates can be synthesized by the extract of unicellular green algae Chlorella vulgaris at standard temperature pressure conditions. Proteins in the extract act as reducing agent for Ag ions as well as stabilizing agent for controlling the shape of fibers. Basically the carboxyl groups in aspartic and glutamine residual and the hydroxyl groups in tyrosin residue of the proteins were the cause of Ag + ion reduction. Extracts from live plant alfalfa, the liquid broths of lemongrass, geranium leaves etc. are used as green reactants in Ag NF synthesis. A mushroom, vegetable like capsicum etc. can also produce Ag-protein (core–shell) NPs with an average size of 30.5 nm. Glutathione (γ-Glu-Cys-Gly-), a bio-organic act as reducing and stabilizing agent produce water-soluble and size tunable Ag NFs that can attached to protein, bovine serum albumin, dominant in bio-nano-medicine (Sharma et al. 2009).

M13 viruses were used to fabricate micro and nano sized fibers by following the electro and wet spinning techniques of the silk spideras depicted in Fig. 4.4. In capillary tubes (diameter ~micro-meter), virus suspension was properly shaped by cross linkage of glutaraldehyde solution. Spider-silk mimicking fibers were found to be 10–20 μm in diameter. After that mixing of polyvinyl pyrolidone (PVP) and M13 viruses produce continuous uniform virus blended PVP nano-fibers . These electro spun fibers are prominent in sensitive catalytic actions for biomedical field and biosensors in future (Lee and Angela 2003).

Polymer nano-fibers provided a proper route to a bio-mimetic approach . Surface features and topography display the important effects on to control cell adhesion, arrangement, orientation, activities etc. within all around nano and micro featured network. These polymer-based nano fibers and wires are used prominently in tissue engineering, drug attachment and delivery, wounds healings, medical implants, nano-composites for dental applications, molecular separation, biosensors and preservation of bioactive agents.

Actin and tubulin are naturally occurring filamentous protein structures can be used as template for nano and micro wires. The first use of such cytoskeleton proteins for building the nanostructure was the utilization of s7 nm thin actin filaments as templates for nanowires fabrication. Self-assembly of actin protein filaments was covalently modified by depositing gold nanoparticles using an amine-reactive agent (N-hydroxysuccinimide), results in continuous gold nano-wires. Actin fibers and ATP hydrolysis are used to give cytoskeleton modification that may lead to various nano-electromechanical system applications in mechanics, conductivity based on the bio-inorganic composites (Gazit 2006).

4.7.4 Metallic Nano-wires and Textile Industry

Metal-coated nano-wires embedded cloths are more durable for several washing cycles due to increased mechanical strength. Silver (Ag) deposited nano-wires coating in textile provides thermal insulation more than 21% due to less radiation loss. Briefly, the metallic nano-wires form a mesh of wires having empty spaces of 200–300 nm with nano-wires in neighborhood, so that visible light can be transmitted and majority of the human body radiations reflected back to body to enhance the thermal insulation. This spacing of 300 nm corresponds to ~97% of thermal reflectance (Hsu et al. 2014). It’s almost 70 years ago, that textile industry made a revolutionary impact to our society with dramatic changes from animal skin to leaves to yarns and now fabrics. In order to meet with increasing demands of consumers, new technologies are needed to apply to the trendy textile industry to develop the products with remarkable values to overcome the issues regarding with conventional finishing treatments. Growth of oriented hexagonal ZnO nanoparticles rod arrays (10–50 nm in diameter and 300 nm to 500 nm in length) onto various flexible fiber substrates by using dip-coating and self-assembly processes is reported.

ZnO dumb-bells shaped nanostructures provide a high UPF (UV protection factor) of 1000 and demonstrated a breakthrough of more complete blocking UV range (400–280 nm) as compared of ZnO nano-sols (352–280 nm), nano-rods (375–280 nm), and anatase Titania films (332–280 nm). Such unique shaped ZnO based architecture is not only prominent in textile field as well as showed great implication in vehicles, windscreens, glass windows, outdoor products, and aircrafts industry. A fabric functionalized by Alkyl silanes modified silica on oriented growth of ZnO crystals displayed increases water durability. The water contact angle was decreased to 128°, 120°, 114°, and 110°. Basically, the GPTS and F13 promoted the adhesive forces to cloth resulting in durable wetting even after repeated washing cycles. Finally, the chitosan fibers as core material (~50 nm to 5 μm) and gold shells as capped entity (~20–50 nm in depth) were used for fabricating organic and in-organic complexes (Wang 2007).

4.7.5 Nanowires and Nanofibers for Sensing Applications

Immobilization of antibodies and bacterial binding on nano-diamond and carbon nano-tubes is crucial for biosensor applications. Biosensors are the devices used to detect the biological changes in human body. High surface area, flexibility, increases mechanical strength and elasticity, and specifically directed growth, made the fiber a suitable material for various applications ranging from textile industry to air-crafts. One-dimensional nano-wires displayed great capacity for the attachment or release of functional groups, absorbed molecules, ions, catalysts, and nano-particles due to its remarkable increase in surface area per unit volume that is highly demanding for sensing and cell engineering as well (Wang 2006).

Sensors based on silicon nano-bio-wires SiNW, nano-arrays and complexes increases light absorption, charge transfer and separation, chemical and catalytic performances. SiNW FETs are used in biological interfacing with live cells and tissues for intracellular electrical measurements, and electrical diagnostic of biological and chemical species (Yanli et al. 2013).

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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Aneeqa Sabah
    • 1
  • Gabour Loius Hornyak
    • 2
  1. 1.Department of PhysicsLahore College for Women UniversityLahorePakistan
  2. 2.Asian Institute of TechnologyKhlong NuengThailand

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