ENG223 Materials Engineering : About Magnetic Nanoparticles

Introduction

As the world population continues to increase, many diseases are catching up with human kind cancer being one of the most dangerous diseases today (Kumar, 2009). Scientists all over the world have come up with different methods to control cancer hence increase the life span of man (aju Francis, 2016). A number of methods such as therapeutic drugs, delivery of radionuclide and gene have been put up to control cancer cases (Paul K. Chu, 2008). Radio frequency is also a method used to catabolize tumours through hyperthermia (Wang, 2016). In recent research and surveys, it’s estimated that over 20.8 million people in the world are likely to suffer from cancer cases from now to the year 2030 and 13 million death is likely to occur by the year 2030 from cancer cases, but the treatment for cancer still intensely relies on radiation treatment, surgical operation or chemical therapy which leads to side effect or cases of sequela in most cases (Yun-Pei Zhu, 2014). And in most cases, if cancer is not detected early enough and treated death occurs (Abdelhamid Sayari, 2008). Early detection and effective treatment for cancer are essential in saving people who have cancer and other diseases. Catalysts play a significant role in current science and technology as they advance reaction yield, promote exact enantioselectivity in the unequal synthesis and reduce the temperature of chemical processes. Modern advancement in the morphology regulator and surface functionalization of mesoporous silica nanoparticles have boosted biocompatibility of the materials with opening volumes and large surface area (Mariela A. Agotegaray, 2017). Current reports have shown that the mesoporous silica particles can be resourcefully internalized by plants cells and animal tissues (María Vallet-Regí, 2015). Functionalization of Mesoporous silica nanoparticles with carbon-based nanostructure or moieties conveys measured discharge and molecular recognition abilities to this mesoporous material for drugs and gene transfer and detecting applications (Bengt Fadeel, 2012). Mesoporous silica nanoparticles materials with various apparatuses of measured discharge, along with the ability to accomplish null discharge in the nonexistence of stimuli, the overview of the fresh features to allow the use of non-selective molecules as displays for the construction of highly choosy sensor systems (Newnes, 2013).             

Literature review

Mesoporous silica was discovered in the early 1990s by a great scientist known as Koruda together with his co-workers at Oil Company known as Mobil Oil Company. The discovery came due to the need of extending zeolites (Chengtie Wu, 2013). The original materials with well-ordered pores of 2 to 10 mm in width were made to hold molecules that were large which could not fit into the micropores of the already existing zeolites.  Ever since, the magnetic materials have been considered as of great potential due to their properties and series of applications such as biomedical, data storage, energy storage, catalysts and environmental remediation. In recent years, porous materials have also been attracting considerable attention due to their unique morphology and properties including a large surface area, large pore volume, narrow pore size distribution, controllable wall composition and modifiable surface properties.  Accordingly, porous magnetic materials are anticipated to take advantages of not only magnetic property but also porous structure.

The Magnetism and irresistible materials

Magnetism is widely known from the youthful stage as a phenomenon by which some materials attract or repel depending on the materials used to make them e.g. loadstone, iron, and some steels. Attractive forces are engendered by moving charged particles which lead to the creation of the magnetic field.

In biomedical application

Magnetic materials are of great importance for biomedical applications for its ability to control magnetic materials remotely via the use of the non-invasive magnetic field. To be precise, applications of magnetic properties in the field of biomedical includes drug delivery, hyperthermia based cancer, and resonance imaging. Iron oxide is the most commonly used material for this application to prevent acute toxicity and anonymous fate and thereby restricts their applications. Another way of approach is to change magnetic ions into the biocompatible and biodegradable material to convey magnetic properties. The unique properties and utility of the porous magnetic materials are ascribed to high pore volume capable of storing drug, large functional surface reacting with biomolecules and controllability by a magnetic field. While porous metal oxides with high surface area can be used in energy storage application.  Supercapacitor, also known as electrochemical capacitor and ultra capacitor is one of the most interesting alternative clean energy sources which is widely used ranging from portable devices to hybrid vehicles.14 Thus, the utilization of magnetic materials with porous structure is expected as a great approach in both biomedical and energy application. Selection of precursor and structure in preparation step to synthesize functional porous and magnetic materials plays a key role in those applications. To date, plenty of approaches has been performed to prepare magnetic materials such as hydrothermal, sol-gel, sonochemical, coprecipitation, etc. In general; porous materials are categorized in three class according to IUPAC classification such as macroporous (> 50nm), mesoporous (2-50nm) and microporous materials Mesoporous and Microporous materials are also called nanoporous materials. Recently, considerable efforts to develop various porous materials have been devoted such as soft-templating methods, hard-templating Methods, and sacrificial templates as well as hybridization methods. The reparation of magnetic materials with these approaches is beneficial to fabricate advantageous nanostructure adapting to applications. Herein, the preparation of magnetic materials, porous materials and their biomedical and energy storage application are summarized.

Synthesis

This procedure is normally seen in the preparation of mesoporous silica microsphere. Silica and other metallic oxides with equal mesoscale pores which ranges from 2 to 10 mm channels are normally employed. The constant pore channels and thin size supply are the suitable properties when it comes to porous microsphere. Normally, inorganic materials is pressured and carbon based templates are synthesized to mesoporous materials. For common synthesis, BmimBF4, is added to Na2SiO3 . 9H2O solution, from there hydrochloric acid is added to the mixture while shaking for the solution to mix uniformly. The mixture is then left to rest for five hours under regulated temperature ( room temperature) under calm conditions and then the mixture is transferred to source of heat, where it is heated for 60 hours at 80⁰ C. The resulting product is then collected by centrifugal method and washed using deionized liquid and ethanol. The final step is to calcined the product at 550⁰C for 4 hours in order to remove all the impurities that the product may contain.            

Magnetic materials can classified in different ways depending on the strength and the materials used to enhance magnetic properties. Some of the classifications used to classify magnet materials includes. Ferromagnetic, diamagnetic, antiferromagnetic and paramagnetic. During the assortment of preparation methods, metal salt and solvent are used to determine desired materials and property of the magnetic. Considering the advantages of synthesis of Fe3O4 as an illustration, demonstrative methods are winded up in this section.

The most suitable and common method used is precipitation method which is used to synthesize magnetic nanoparticles in aqueous solution. In broad spectrum, the precursors firstly understanding hydroxide nature following dehydration to oxide state. Ammonium solution or sodium hydrate is often utilized as alkaline solution to induce hydroxide state. Through coprecipitation method, Fe3O4 nanoparticles are successfully synthesized at room temperature ( mascoplo et al). surprisingly, cation precursor is not required to synthesize Fe3O4. The report submitted by Chao Hui indicates that iron II oxide precursor is firstly reacted with the hydroxide giving out oxydroxide since it reacted with the oxygen from the air. The final step is to contrive Fe3O4  by dehydration. It is not easy to control size transportation of nanoparticles in this method.

 Templating methods

Template method has been widely investigated by many scientific researchers due to its simple design. Templating methods are commonly utilized to fabricate nanostructural materials. In general, template method requires three steps: The first step is fabrication of template followed by a common synthesis. The final step is the removal of template, resulting in porous materials. Template method is mainly classified two categories: one is soft-templating methods and the other is hard-templating methods. Soft template is relatively easier and simple to eliminate by heat treatment or dissolution in proper solution. In contrast, the main advantage of hard-templating methods is a stable controllability to obtain desired morphology. The selection of template is a key to prepare porous materials with target structure.

Diamagnetism

This is the weakest magnetism and is the essential property of all material. Diamagnetism is generally due to lack of cooperation behavior of orbital electrons resulting from external forces of magnetic fields. Diamagnetism is brought about because all the atoms have paired electrons hence there is no unpaired electrons in the shell. This is resulting to net magnetic moment of atom of diamagnetic constituent is zero. It is however noted that, when peripheral magnetic field is induced on these materials, the substances are magnetized on the opposite direction of the field resulting in negative magnetization.

Paramagnetism

In paramagnetsm, atoms and ions have partial unpaired electrons in orbitals. This would mean that each atom present in paramagnetic substance has at least little magnetic moment. However, it is realized that there is no relation between these atomic magnets. In presence of peripheral magnetic field, partial alignment of atomic magnetic moment is experienced in the direction of the applied field resulting in net positive magnetization unlike the case of diamagnetic and positive susceptibility. But, when the field is zero, magnetization also tends be zero.

Soft-templating methods

Soft-templating method is important to fabricate porous structural materials. In general, the materials for soft template is surfactants, polymer and biopolymer which form aggregation by means of intermolecular or intramolecular interaction force such as van der Waals force, hydrogen bonding, chemical bonding and static electricity. Removal of the soft template is relatively simple and facile process. Surfactant consists of hydrophilic and hydrophobic part and it forms versatile morphology such as spherical, cylindrical, and lamellar micelles. The surfactant becomes liquid crystal phase at high concentration in the aqueous media, based on surfactant geometry. In the solution, inorganic precursor interacts with surfactants. In the preparation process, the choice of proper condition plays a key role to determine desired morphology since the condition is directly affect the interaction between organic and inorganic interface. For example, the interaction between them is a weak hydrogen bonds in strong acidic solution, whereas, strong electrostatic force occurs in strong alkaline solution.27 In most case, porous materials using surfactant template are obtained by aqueous solution synthesis or EISA routes.29 Also, the removal of template is an important process so proper process should be selected in accordance with framework composition. There have been many reports for mesoporous materials using surfactant as soft template.

In recent years, various mesoporous transition metal oxides template by surfactants were reported. Pore size of these materials is usually small because the pore is obtained by low-molecular weight amphiphilic molecules, which has small hydrophilic heads and hydrophobic tails. Consequently, their short hydrophobic chains leads to small pore siz4. The diameter of pore size generally depends on hydrophobic part. Polymer template have been widely used to enrich pore volume and surface area. Polymer, especially block copolymer, is widely employed in the synthesis of mesoporous materials due to its advantages such as large molecular weight, stability and various molecular structures, leading to mesoporous structure. The structure and morphology are controllable by using different combination of blocks and should be adapted to application. Capucine et al reported mesoporous RuO2 film by using PS-b-PEO diblock copolymer.34 Furthermore, Bishnu et al successfully synthesized mesoporous silica with well-defined pore by using symmetric triblock copolymer. In recent year, the same group reported the synthesis of mesoporous metal oxide with various composition by using PS-b-PVP-b-PEO asymmetric triblock copolymer.36 it is clear that using polymer as template is beneficial to enlarge pore size compared with surfactant. However, it is still challenge to fabricate well crystallized materials because the wall composition tends to be collapsed at extremely high temperature, where polymer faces difficulty to preserve its morphology.

Biopolymer or Biomolecule is another promising soft-template to fabricate porous materials owing to their natural availability, various structures, less toxicity and facile process in removal of template. DNA, protein, virus etc. are commonly used as biopolymer template many reports have been published about porous materials template by biopolymer. Recently, cellulose is used in wide range as template because of natural abundant and many sources. Huang et al reported porous metal oxide templated by cellulose. Tobacco mosaic virus is well familiar as biomolecule template for synthesis porous inorganic materials. In those achievements, it is obvious that biopolymer/molecule is a great template to fabricate various kinds of structural materials though it might be difficult to find alternative template, which has same property and/or morphology in nature.

Ferromagnetism

Normally when we think of magnetic materials, the first thing that comes to our mind are nickel, iron and magnetite. The above mentioned are referred to as ferro magnetic materials. The force in between these substances are stronger than any other magnetic materials. The strong forces that exist in between the atomic magnets is due to lthe parallel arrangement of electrons to each other under the impact exchange forces. It is estimated that the magnitude of the forces that exists in between these atomic magnet is 1000 Tesla. The strength is 10⁸ stronger than that of the earth magnetic field.

Hard-templating method

Hard-templating method is an important strategy to fabricate porous metals, metal oxides and carbon in nanoscale since it directly gives the stable porous structure to the final products. Wide variety of hard template was previously reported such as polymeric microsphere42, anodic aluminum oxide (AAO) 43 and silica. Although polymer is well known as soft-template, polymer beads are also widely used as hard template because its capability of rigid structure. The particle size is controllable by the rate of polymerization in wide range. In the report by Xu et al., polymethyl methacrylate was successfully used as hierarchical ordered colloidal template to synthesize three-dimensionally ordered macroporous. In general, removal of template is carried out by dissolution in appropriate solvents, calcination or pyrolysis. Silica template is often employed to fabricate porous metal oxides as hard template because of its versatile morphology and adjustable size.47 (Figure 5) Functionalization on the surface of silica is helpful to achieve desired structure. Also, silica template has a good stability even under severe conditions such as vacuum, high temperature and strongly acidic environment48, which lead to better quality framework. Three-dimensional ordered macroporous materials have been synthesized by colloidal silica template.45 In recent years, mesoporous silica has been promoting research interest as template to fabricate mesoporous metal oxides framework. Bagheri et al reported mesoporous MgFe2O4 templated by the mesoporous silica (KIT6).

Advantages of nano magnetic materials

It has been found that nanoparticles have various advantages and applications put together when it comes to the field biology and medicine. First and foremost, nanoparticles can be easily controlled from limited nanometers to 10s of nanometers. The sizes are similar to those of the cell (10- 100µm), a protein (5- 50 nm), a virus (20- 450 nm) and gene (2 nm wide). Because of the ability and required sizes that these particles have enable them to be used with any given biological entity.

Application           

Biomedical applications

Magnetic materials are useful in biomedical application in not only diagnosis but also treatment in vivo and vitro. Particle size, surface functionalization, surface area and pore volume are important parameter, adaptingto applications. Although many approaches have been performed to each application, it is still challenge to develop magnetic materials for multiple applications. Herein, recent reports on biomedical application by magnetic materials are summarized. Magnetic resonance imaging. Magnetic resonance imaging (MRI) plays an important role in diagnosis. So as to obtain clear images, contrast agent is very helpful. Currently gadolinium chelate are used as contrast agent, which make images clearer in T1 (longitudinal relaxation time)-weighted images but the agents lead to make image dark because of short intravascular half-lives and rapid renal excretion.66 Magnetic materials, in particular superparamagnetic materials could be used to clarify clear image in T1, T2(transverse relaxation)- weighted images contrast agent.67 However, it is still hard to deliver magnetic materials to the targeting site since the magnetic materials are carried to targeting site by the reticuloendothelia system (RES) which result in less effective detection.68 Magnetic materials enable to be carried to the targeting site by magnetic fields and coating the magnetic materials by polymer, silica, gold, platinum could achieve the better detection and

Targeting as well as high biocompability. Biosensor. In recent years, magnetic materials have been used as biosensor to detect glucose, DNA, virus, bacteria and cancer cell.70,71 It is required that the materials for biosensor is superior in sensitivity, size, power consumption, stability, response, resistance to aggressive media, price, and automatization level. Also, functionalization on the surface of materials is advantageous in the detection for molecular interaction so nanostructural magnetic materials could meet these requirements because the large surface area allow materials to be functionalized more efficiently for interaction with targeting biomolecules. Immobilization of enzyme is of great importance in fabrication for biosensor to retain bioactivity by utilization of the magnetic materials. Plenty of efforts have been devoted to prepare materials for electrochemical biosensor by using magnetic materials with carbon and/or conductive polymers. Drug delivery System. The development of Drug delivery system (DDS) is crucial in order to reduce side effects and to enhance the effect of therapy in the treatment of disease. Considerable efforts have been devoted to develop DDS by many approaches such as stimuli-responsive polymeric nanoparticles76, liposomes, metals/metal oxides78, and exosomes79, but there have been still challenges to be overcome including bio toxicity, targeting, difficulty of fabrication in large scale and economical availability. In those systems, drug is entrapped, attached, absorbed or encapsulated into or onto the carrier agent. Magnetic materials are beneficial to carry drug to target tumor by magnetic fields. A key parameter in DDS is the rate of adsorption and release as well as delivery of drug to targeting site. Nanostructured materials play important roles as a drug vehicle, which is expected to store and release drug efficiently. Nanostructural materials, especially porous magnetic materials are great potential for development of DDS to overcome these challenges. Cheng et al demonstrated hollow Fe3O4 for anticancer drug delivery. The hollow Fe3O4 was functionalized to interact with cisplatin, which is typical anticancer drug. The adsorption and release were conducted and high magnetic property was efficient to control the particles to tumor site. Also, magnetic nanoparticles coated by mesoporous silica for DDS was repoted. The iron oxide core plays a role as controllable and silica shell is used as reaction site with biomolecule at tumor site and storage for drug. Furthermore, better controlled porous Fe3O4 was demonstrated by Mislav et al. Interestingly, both alternating and direct magnetic field assist efficient release of drug. Surface functionalization for targeting, pore volume to storage drug and magnetic property for better control as well as magnetic field are important factors to develop DDS by nanomaterials. Hyperthermia. Not only DDS but also magnetic hyperthermia is of great importance in the cancer treatment. In the system, magnetic materials are led to heat under the alternating magnetic field, caused by hysteresis loss. The heating temperature by hyperthermia depends on magnetic property, the strength of magnetic field and the blood flow at the target tumor.85 Typically, cells exhibits signal of apoptosis when elevating temperature from 41 to 47 ?and necrosis when above 50.86 However, there is also difficulty that the normal cell/tissue are damaged during heating tumor cell. Also, functionalization on the surface of magnetic materials is also important to target tumor site to minimize damage to healthy cell/tissue. Fe3O4 nanoparticles coated by oleic acid and polyethylene glycol was reported for magnetic hyperthermia, which showed Fe3O4 nanoparticles coated by oleic acid and polyethylene glycol indicate increasing killing of breast cancer cell at 35% and 65% respectively.88 In further approach, Jiang et al demonstrated the effectiveness of hyperthermia and MRI by Fe3O4 nanoparticles functionalized by folic acid to react with tumor cell, which achieve great biocompatibility, resulting in clear heating effect and good contrast change. Combination diagnosis with hyperthermia is superior approach to treat cancer cell since both diagnosis and treatment at the same time lead to less side effect and better efficacy.

Energy applications

Metal oxides are useful in both lithium ion battery and supercapacitor as anode and electrode materials, respectively. Although many approach have been reported, the result is still far from the theoretical value. Therefore, further development of electrode materials is a key to optimize properties of those energy storage applications.

Lithium-ion batteries. Lithium ion battery is one of the most reliable energy storage in portable electronic devices. Development of anode materials of lithium ion battery lead to better performance including higher power densities, enhanced safety, and longer cycle life. Carbon based materials, especially graphite is currently used as anode materials in commerce, but there is limitation in specific capacitance and safety. Novel approach to prepare anode materials is essential to overcome these problems. Metal oxides are often employed as alternative anode materials in lithium ion battery since it is well known to huge availability.

Application of magnetic material

 TEM bright field image of 16-nm Fe3O4 nanoparticles deposited from their dodecane dispersion on amorphous carbon surface and dried at 60 ? for 30 min: a monolayer assembly, a multilayerassembly, HRTEM image of a single Fe3O4 nanoparticle. Structure of surfactant (Spherical, revere spherical, bilayer vesicle, cylindrical micelle, lamellar phase).  Schematic phase diagram of the various morphologies formed by block copolymers, including spherical and cylindrical micelles, vesicles, spheres with face-centered cubic (space group: Fm3?m) and body-centered cubic (Im3?m) packing, hexagonally packed cylinders (p6m), bicontinuous gyroid (Ia3?d), surface (Fd3?m), P surfaces (Pm3?n, Pn3?m, or Pm3?m), and lamella. Adapted with permission Schematic illustration of the Nano casting pathway using mesoporous silica hard templates with

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