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Physics - Advanced Engineering Materials Metallic Glasses

Modern Engineering Materials

   Posted On :  03.12.2016 10:12 pm

1 Introduction 2 Metallic Glasses 3 Shape Memory Alloys 4 Nano Materials 5 Properties of Nanoparticles 6 Applications of Nanoparticles 7 Non linear materials (NLO materials) 8 Biomaterials

Modern Engineering Materials

 

1 Introduction

2 Metallic Glasses

2.1 Glass transition temperature

2.2 Methods of production of Metallic Glasses

2.3 Types of Metallic Glasses

2.4 Properties of Metallic glasses

2.5 Applications of Metallic glasses

3 Shape Memory Alloys

3.1 Definition

3.2 Working Principle of SMA

3.3 Characteristics of SMA

3.4 Properties of Ni – Ti alloy

3.5 Advantages of SMA’s

3.6 Disadvantages of SMA’s

3.7 Applications of SMA’s

4 Nano Materials

4.1 Introduction

4.2 Definitions

4.3 Synthesis of Nanomaterials

4.4 Chemical Vapour Deposition (CVD)

5 Properties of Nanoparticles

6 Applications of Nanoparticles

7 Non linear materials (NLO materials)

7.1 Higher Harmonic Generation

7.2 Experimental Proof

7.3 Optical mixing

8 Biomaterials

8.1 Biomaterials Classifications

8.2 Conventional implant devices

8.3 Biomaterials Properties

8.4 Modern Engineering MaterialsBiomaterials Applications

 

1  INTRODUCTION

 

There have been a number of science fields which have helps to producing new engineering materials. Some of the fields are the nano engineering and the forensic engineering. Hundreds and hundreds of scientists and inventors are working and experimenting continuously to make this world a better place to live.

These new inventions have gradually changed the course of living of people, these New engineering materials are not a result of single engineering technology but these are obtained or produced from a blend of different technologies.

 

Some of the Modern Engineering Materials like Metallic glasses, Shape memory alloys, Nano materials are discussed here.

 

2  METALLIC GLASSES

 

Metallic glasses are the amorphous metallic solids which have high strength, good metallic properties and between corrosion resistance and will possess both the properties of metals and glasses.

 

Example: Alloys of Fe, Ni, Al, Mn, Cu.

 

2.1  Glass transition temperature

 

It is an important parameter for the preparation of metallic glasses. It is defined as a temperature at which the liquid like atomic structure is obtained into a solid.

 

The value of glass transition temperature for metallic alloys is about 20OC to 30OC.

2.2  Methods of production of Metallic Glasses

 

Metallic glasses are manufactured by the following methods. They are,

 

          Twin roller technique

 

          Melt extraction technique

 

          Melt spinning technique

 

          Twin roller system

 

In this technique, the molten alloy is passed through two rollers rotating in opposite directions.

 

2. Melt extraction technique

 

In this technique, the fast moving roller sweeps off molten droplet into a strip from a solid rod.

 

3. Melt spinning technique

 

Principle

 

Quenching is a technique used to from metallic glasses. Quenching means Rapid Cooling. Due to rapid cooling, atoms are arranged irregularly and from metallic glasses.

 

Construction

 

It consists of a refractory tube with fine nozzle at the bottom. The refractory tube is placed over the rotating roller. The roller is rotated at a higher speed to generate a velocity of more than 50 ms 1 . An induction heater is wounded over the refractory tube to heat the alloy to very high temperature.


Fig. 5.1 Melt spinning technique

Working

 

The alloy is put into the refractory tube and induction heater is switched on. This heats the alloy to very high temperature, hence the super heated molten alloy ejected through the nozzle on the rotating roller and is suddenly made to cool. The ejection rate may be increased by increasing the inert helium gas pressure inside the refractory tube. Thus due to rapid quenching a glassy alloy ribbon called metallic glass is formed over the rotating roller.

 

2.3  Types of Metallic Glasses

 

The metallic glasses are classified into two types.

 

          Metal – Metalloid Glasses

 

Example: Fe, Co, Ni – Ge, Si, B, C.

 

          Metal – Metal Glasses Example: Ni, Mg, Cu – Zn, Zr.

 

            Metal – Metalloid Glasses

 

The first class of metallic glasses is from transition metals (Fe, Co, Ni) Metalloid (B, Si, C & P) so they are called metal – metalloid glasses.

 

2. Metal – Metalloid Glasses

 

          Nickel – Niobium (Ni – Nb)

 

          Magnesium – Zinc (Mg – Zn)

 

          Copper – Zirconium (Cu – Zr)

 

          Hafnium – Vanadium (Hf – V) alloys

 

2.4 Properties of Metallic glasses

 

          Metallic glasses have very high strength and are stronger than metals because the absence of grain boundaries and dislocations.

 

          The structure of metallic glass is Tetrahedral Close Packing (TCP).

 

          These are having very high corrosion resistance.

 

          They have high workability and ductility.

 

          The electrical resistivity is found to be high (greater than 100)/ due to this eddy current loss is very small.

 

          Metallic glasses have both soft and hard magnetic properties.

 

          These are highly reactive and stable.

 

          It can also act as a catalyst.

 

Structural Properties

 

          They do not have any crystal defects such as grain boundaries and dislocations.

 

          They have tetrahedral packed structure. These materials do not passes long range anisotropy

 

Mechanical Properties

 

        Metallic glasses are stronger than metals and alloyes because they are free from defects and dislocations.

 

        They have high corrosion resistance due to random ordering.

 

        They have high elasticity and ductility.

 

Electrical Properties

 

         Electrical resistivity of metallic glasses is high and it does not vary with temperature.

 

        Eddy current loss is very small due to high resistivity.

 

        The Hall co-efficient of metallic glasses is found to have both positive and negtive signs.

 

Magnetic Properties

 

        It obeys both soft and hard magnetic properties.

 

        The core losses of metallic glasses are very small.

 

Chemical Properties

 

        They have high corrosion reistance.

 

        They have catalytic properties.

         

        They are highly reactive and stable.

 

2.5 Applications of Metallic glasses

 

          Metallic glasses are used as reinforcing elements in concrete, plastic and rubber.

 

          Metallic glasses are used to make pressure vessels and to construct larger fly wheels for energy storage.

 

          They are used to make accurate standard resistors, Magnetic resistance sensors and computer memories.

 

          These are used in tape recorder heads, cores of high power transformers and magnetic shields.

 

          Metallic glasses are used as core in motors.

 

          These are used to make razor blades and different kinds of springs.

 

          Metallic glasses can be used as superconductor for producing high magnetic fields and magnetic levitation effect.

 

          Metallic glasses are used to make containers for nuclear waste disposal and magnets for fusion reactors.

 

          Metallic glasses are used in marine cables, chemical filters, inner surfaces of reactor vessels, etc.,

 

10.Metallic glasses are very useful to make surgical instruments.

 

11.Superconducting mettalic glasses are used to produce high magnetic fields and magnetic levitation effect.

 

Appendix

 

The reasons for choosing metallic glasses are transformer core

 

Metallic glasses are available in thin sheets therefore the size and weight of the transformer is reduced. Hysteresis loss is directly proportional to the area of the hysteresis loop. The loop area of the metallic glasses is very small and also has high initial permeability. So, the hysteresis loss is almost zero… The eddy current in the core is inversely proportional to the resistivity of the core material and directly proportional to the thickness of the lamination of the core.

 

Since the resistivity of the metallic glasses is high and the thickness of the core laminated core material due to small thickness, smaller area, less weight, high resistivity, soft magnet with low hysteresis and eddy current losses.

 

3  SHAPE MEMORY ALLOYS

 

Share memory alloys (SMA’s) are metals, which exhibit two very unique properties, pseudo-elasticity and the shape memory effect. Arne Olander first observed these unusual properties in 1938 (Oksuta and Wayman 1998), but not until the 1960’s were any serious research advances made in the field of shape memory alloys. The most effective and widely used alloys include NiTi (Nickel – Titanium), CuZnA1 and CuA1Ni.

 

3.1  Definition

The ability of the metallic alloys to retain to their original shape when heating or cooling is called as Shape Memory Alloys (SMA).

These metallic alloys exhibit plastic nature when they are cooled to very low temperature and they return to their original nature when they are heated. This effect is known as Shape Memory Effect.

 

It is also called as smart materials or intelligent materials or Active materials. There are two types of shape memory alloys,

 

          One way shape memory – It returns to its memory only when heating

 

          Two way shape memory – It returns to its memory on both heating and Cooling.

 

Classification

 

          Piezo electric SMA materials.

 

          Electrostrictive SMA materials.

 

          Magnetostrictive SMA materials.

 

          Thermo elastic SMA materials.

 

Examples : Ni-Ti (Nickel – Titanium), Cu Zn A1, Cu A1 Ni, Au – Cd, Ni-Mn-Ga and Fe based alloys.

3.2  Working Principle of SMA

 

The shape memory effect occurs in alloys due to change in the crystalline structure of the materials with the change in temperature and stress.

 

The shape memory effect occurs between two temperature states known as Martensite and Austenite. The Martensite structure is a low temperature phase and is relatively soft, It has platelet structure the Austenite is a high temperature phase and is hard it has needle like structure.

 

Martensite is the relatively soft and easily deformed phase of shape memory alloys which exists at lower temperatures. It has two molecular structures namely, twinned Martensite and deformed Martensite. Austenite is the stronger phase of shape memory alloys which occurs at higher temperatures, the shape of the Austenite structure is cubic.

 

When we apply a constant load on a shape memory alloy and cool it, its shape changes due to produced strain. During the deformation, the resistivity, thermal conductivity, Young’s modulus and yield strength are decreased by more than 40%.

 

Twinned Martensite state alloy becomes deformed Martensite when it is loaded. The deformed Martensite becomes Austenite when it is heated, the Austenite transformed to original twinned Martensite state when it is cooled.


Fig.5.2 Material crystalline arrangement during shape memory effect

 

3.3  Characteristics of SMA

 

1. Hysteresis

 

Hysteresis of a SMA is defined as the difference between the temperatures at which the material is 50% transformed to austenite when heating and 50% transformed to martensite when cooling.

 

When the temperature is decreased in a metallic material, the phase transformation takes place from austenite to martensite. This transformation takes place not only at a single temperature, but over a range of temperatures.

 

The hysteresis curve for a shape memory alloy is shown below.


 

Fig.5.3 Hysteresis curve for SMA’s

 

2. Pseudo elasticity

 

When a metallic material is cooled from a temperature T to a lower temperature TC it deforms and changes its shape. On reheating the material to Temperature (T) the shape change is received so that the material returns to its original state. This effect is known as pseudo elasticity or thermo elastic property.

 

3. Super elasticity

 

Super elasticity is a property of SMA. When a material is deformed at a temperature slightly greater than its transformation temperature super elasticity property appears (Rubber like property).

 

3.4  Properties of Ni – Ti alloy

 

Ni – Ti is a compound of Nickel and Titanium and it finds many applications in the field of engineering due to the following properties.

 

          It has greater shape memory strain.

 

          It has more thermal stability and excellent corrosion resistance.

 

          It has higher ductility and more stable transformation temperatures.

 

          It has better bio-compatibility and it can be electrically heated.

 

3.5 Advantages of SMA’s

 

        They ahve good bio-Compatibility.

 

        They have simplicity, Compactness and high safety mechanism.

 

        They have good mechanical properties and strong corrosion-resistance.

 

        They have high power and weigh ratio.

 

3.6 Disadvantages of SMA’s

 

        They have poor fatigue properties.

 

        They are expensive and difficult to preparing in a machine.

 

        They have low energy efficiency.

 

        They have limited band with due to heating (or) cooling.

 

3.7 Applications of SMA’s

 

          Eye glass frames : We know that the recently manufactured eye glass frames can be bent back and forth and can retain its original shape within fraction of time.

 

          Toys : We might have seen toys such as butterflies, snakes etc., which are movable and flexible.

 

          Helicopter blades: The life time of helicopter blades depends on vibrations and their return to its original shape. Hence shape memory alloys are used in helicopter blades.

          Coffee Valves : Used to release the hot milk and the ingredients at a certain temperature

 

          Medical Applications of SMA’s

 

          It is used as Micro – Surgical instruments.

 

          It is used as dental arch wires.

 

          It is used as flow control devices.

 

          It is used as ortho – dentil implants.

 

          It is used for repairing of bones.

 

          They are used to correct the irregularities in teeth.

 

          Engineering Applications of SMA’s

 

          It is used as a thermostat valve in cooling system.

 

          It is used as a sealing plug for high pressure.

 

          It is used as a fire safety valve.

 

          It is used for cryofit hydraulic pipe couplings.

 

          It is used for eye glass frame, toys, liquid safety valve.

 

          It is used to make microsurgical instruments, orthopedic implants.

 

          It is used as blood clot filter and for fracture pulling.

 

          It is used to make antenna wires in cell phones.

 

          It can be used as circuit edge connector.

 

4 NANO MATERIALS

 

4.1  Introduction

 

Nanomaterials (nanocrystalline materials) are materials possessing grain sizes of the order of a billionth of a meter. They manifest extremely fascinating and useful properties, which can be exploited for a variety of structural and non structural applications.

 

All materials are composed of grains, which in turn comprise many atoms. These grains are usually invisible to the naked eye, depending on their size. Conventional materials have grains varying in size anywhere from 100’s of microns ( m ) to millimeters (mm). A micron ( m ) is a micrometer or a millionth (10–6) of a meter. An average human hair is about 100 m in diameter. A nanometer (nm) is even smaller a dimension than a m and is a billionth (10–9) of a meter. A nanocrystalline material has grains on the order of 1-100 nm. The average size of an atom is on the order of 1 to angstroms ( Ao ) in radius.

 

      nanometer comprises 10 Ao , and hence in one nm, there may be 3-5 atoms, depending on the atomic radii. Nanocrystalline materials are exceptionally strong, hard, and ductile at high temperatures, wear-resistant, corrosion-resistant, and chemically very active. Nanocrystalline materials, or Nanomaterials, are also much more formable than their conventional, commercially available counterparts.

 

4.2  Definitions

 

Nanotechnology

 

Nanotechnology is a field of applied science and technology which deals with the matter on the atomic and molecular scale, normally 1 to 100 nanometers, and the fabrication of devices with critical dimensions that lie within that size range.

 

Nanomaterials

Nano materials are the materials with grain sizes of the order of nano meter (10 9 m) i.e., (1-100 nm). It may be a metal, alloy, inter metallic (or) ceramic.

Nanomaterials are the materials with atoms arranged in nano sized clusters which become the building block of the material. Any Material with a size between 1 and 100 nm [ 10 9 m to 10 7 m] is also called

Nanomaterials.

 

4.3  Synthesis of Nanomaterials

 

The Nano mateirals can be synthesized by two processes, they are

 

          Top – down approach

           

          Bottom – up approach

 

1. Top – down approach

 

The removal or division of bulk material or the miniaturization of bulk fabrication processes to produce the desired nanostructure is known as top-down approach. It is the process of breaking down bulk material to Nano size.


 

Fig.5.4 Synthesis of Nanomaterials for Top – down approach

 

Types of Top – down Methods

 

          Milling

 

          Lithographic

 

          Machining

 

          Bottom – up approach

 

Molecules and even nano particles can be used as the building block for producing complex nanostructures. This is known as Bottom – up approach. The Nano particles are made by building atom by atom.


 

Fig.5.5 Synthesis of Nanomaterials for Bottom – up approach

 

Types of Bottom up Methods

 

          Vapour phase deposition Method

 

          Molecular beam epitaxy Method

 

          Plasma assisted deposition Method

 

          Metal Organic Vapour Phase Epitaxy [MOVPE]

 

          Liquid phase process [Colloidal method and Sol – Gel method]

 

4.4  Chemical Vapour Deposition (CVD)

 

It is method in which the reaction or thermal decomposition of gas phase species at higher temperatures [500 – 1000OC] and then deposition on a substrate takes place, in CVD method carbon nanotubes are grown from the decomposition of hydrocarbons at temperature range of 500 to 1200OC. In this process, the substrate is placed inside a reactor to which a number of gases are supplied. The fundamental principle of the process is that a chemical reaction takes place between the source gases. The produce of that reaction is a solid material with condenses on all surfaces inside the reactor.

 


 

Fig.5.6 CVD method

 

Example of CVD technique

 

An aerosol spray pyrolysis (Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen or any other reagents) is the example of CVD technique, in which high aqueous metal salts are sprayed in the form of fine mist and then passed into a hot flow tube. In the hot flow tube pyrolysis converts the salts into the final products on the substrate, in this method the materials are mixed in a solution, homogeneous mixing is obtained to the atomic level. They pyrolysis at low temperature gives the particles in the size range 5 – 500 nm, in this CVD method catalysts are used for better chemical reactions, when the catalyst is in nanosize, dispersion of particles is happened due to templating effect. In the Production of carbon nanotubes using the decomposition of ethane with hydrogen, Fe, Co or Ni based catalysts are used. The size and distribution of the catalyst particles determine the internal diameter of the nanotubes.

 

5  PROPERTIES OF NANOPARTICLES

 

A Bulk materials is reduced to a nano size, the following changes are occurred

 

          Large fraction of surface atoms

 

          High surface energy

 

          Spatial confinement

 

          Reduced imperfections

 

The surface area effects, quantum effects can begin to dominate the properties of matter as size is reduced to the nano scale. These can affect the optical, electrical and magnetic behavior of materials.

 

Due to their small dimensions, nano materials have extremely large surface area to volume ratio, which makes a large fraction of atoms of the materials to be the surface or interfacial atoms, resulting in more “surface” dependent material properties.

 

When the size of their structural components decreases, there is much greater interface area within the material this can greatly affect both mechanical and electrical properties, ie., the interface area within the material greatly increases, which increases its strength. Reduced imperfections are also an important factor in determination of the properties of the nano materials

 

1. Electrical Properties of Nanomaterials

 

Nanomaterials can store more electrical energy than the bulk material, because of their large grain boundary (surface) area.

The energy band structure and charge carried density in the nano materials can be modified quite differently form their bulk size in turn will modify the electronic properties of the materials.

 

In nano size an optical absorption band can be introduced, or an existing band can be altered by the passage of current or by the application of an electric field.

2. Optical Properties of Nanomaterials

 

The quantum confinement of electrical carriers within nanoparticles makes efficient energy and charge transfer over nanoscale distances in nano devices.

 

The linear and nonlinear optical properties of nanomaterials can be finely modified by controlling the crystal dimensions

 

The color of nanomaterials is changed when the surface plasmon size is reduced. A surface plasmon is a natural oscillation of the electron gas inside a given nano sphere.

 

3. Chemical Properties of Nanomaterials

 

The increased surface area of nano particle increases the chemical activity of the material. Metallic nanoparticles can be used as very active catalysts. Chemical sensors from nanoparticles and nano wires enhanced the sensitivity and sensor selectivity

 

4. Mechanical Properties of Nanomaterials

 

The mechanical properties such as hardness and elastic modulus, fracture toughness, scratch resistance, fatigue strength, tensile strength, strain-to-failure, Young’s modulus, impact strength and increased at the nanometer scale

 

Energy dissipation, mechanical coupling and mechanical nonlinearities are also influenced at the nanometer scale.

 

The strength of the material at nanosize approaching the theoretical limit due to the absence of internal Structural imperfections such as dislocations, micro twins, and impurities.

 

5. Magnetic Properties of Nanomaterials

 

The strength of a magnet is measured in terms of coercivity and saturation magnetization values. These values increase with a decrease in the grain size and an increase in the specific surface area (surface area per unit volume) of the grains.

 

6. Thermal Properties of Nanomaterials

 

Photon transport within the materials will be changed significantly due the photon confinement and quantization of photon transport, resulting in modified thermal properties. For example, nano wires from silicon have a much smaller thermal conductivities compared to bulk silicon.

 

The nanomaterials structures with high interfaces densities would reduce the thermal conductivity of the materials. There are several effects being considered for the reduction of thermal conductivities: interfacial roughness, phonon band gaps, dispersion mismatch, doping, structural defects, processing conditions, etc.

 

6  APPLICATIONS OF NANOPARTICLES

 

          Though nano – particles are very small, they are the important materials to built future world. They have applications almost in all engineering fields as follows Mechanical Engineering

 

          Since they are stronger, lighter etc., they are used to make hard metals.

 

          Smart magnetic fluids are used in vacuum seals, magnetic separators etc.

 

          They are also used in Giant Magneto Resistant (GMR) spin valves.

 

          Nano- MEMS (Micro-Electro Mechanical Systems) are used in ICs, optical switches, pressure sensors, mass sensors etc.

 

          Electrical, Electronics and Communication Engineering

 

          Orderly assembled nanomaterials are used as quantum electronic devices and photonic crystals.

          Some of the nanomaterials are used as sensing elements. Especially the molecular nanomaterials are used to design the robots, assemblers etc.

          They are used in energy storage devices such as hydrogen storage devices, magnetic refrigeration and in ionic batteries.

          Dispersed nanomaterials are used in magnetic recording devices, rocket propellant, solar cells, fuel cells, etc.

          Recently nano-robots were designed, which are used to remove the damaged cancer cells and also to modify the neutron network in human body.

          Computer Science Engineering and IT

 

          Nano-materials are used to make CD’s and semiconductor laser.

 

          These materials are used to store the information in smaller chips.

 

          They are used in mobiles, lap – tops etc

 

          Further they are used in chemical / Optical computers.

 

          Nano – dimensional photonic crystals and quantum electronic devices plays a vital role in the recently developed computers.

 

          Bio–Medical and Chemical Engineering

 

          Consolidated state nanoparticles are used as catalyst, electrodes in solar and fuel cells.

          Bio-sensitive nanoparticles are used in the production of DNA –chips, bio-sensors etc.

          Nano-structed ceramic materials are used in synthetic bones.

 

          Few nanomaterials are also used in adsorbents, self –cleaning glass, fuel additives, drugs, ferrofluids, paints etc.

 

          Nano –metallic colloids are used as film precursors.

 

7  NON LINEAR MATERIALS (NLO MATERIALS)

 

The change in optical properties due to electrical and magnetic field associated with light is called non linear effects and those materials which possess these effects are those materials possess these effects are called non-linear materials.

 

Example:

 

         Lithium tantalate

 

         Lithium iodate (LiO3)

 

         Barium Sodum niobate

 

         Ammonium-dihydrophosphate (ADO)

 

         Potassium-dyhydrophosphate (KDP)

 

7.1  Higher Harmonic Generation

 

Higher (second) Harmonic generation represents the generation of new frequencies with the help of the crystals such as quartz, LiO3, etc.

 

Explanation

 

          In a linear medium, Polarization (P) is proportional to the electric field E that induces it


When light of higher intensity is passed through dielectric medium, the electric field has larges amplitude and the oscillation of dipoles are distorted. Therefore, some nonlinearity is observed beteen P and E and hence the higher fields are written as


with increase of higher order terms come into play. Let us assume that the field is strong enough to give rise to χ2.


This non linear polarization shows that it contains the second harmonic of (III term) as well as an average term (I term) called optical rectification. It can be shown that only in the crystals lacking inversion symmetry, second harmonic generation (SHG) is possible.

 

7.2  Experimental Proof

 

When the fundamental radiation from a laser is sent through SHG crystal, due to SHG, conversion to double the frequency ie. half the wave length takes place. For example 1.064 m radiation from Nd-YAG laser gets converted to 0.532 m on passing through crystals like KDP, ADP, etc.


 

Fig. 5.7 Experiment arrangement for SHG

 

If the incident radiation from the laser is intense enough such that the polarization needs to be represented by three terms.


The last term in the above equation represents third harmonic generation at frequency 3ω . Likewise one can account for higher harmonic generation.

 

7.3  Optical mixing

 

We are familiar with ariving at a new colour by mixing of two colours in paints using non linear phenomena, called optical mixing, generation new frequencies are possible. Suppose two coherent waves of unequal frequencies 1 and 2 are traversing the material, then



8  BIOMATERIALS

 

Biomaterials are used to make devices to replace a part or a function of the body in safe, reliably economically, and physiologically acceptable manner. A variety of devices and materials are used in the treatment of disease or injury. Commonplace examples include suture needles, plates, teeth fillings, etc. (or)

 

A biomaterial is a synthetic material used to replace part of a living system or to function in intimate contact with living tissue of a human body. Alone or as part of a complex system, is used to direct, by control of interactions with components of living systems, the course of any therapeutic or diagnostic procedure.

8.1  Biomaterials Classifications

 

When a synthetic material is placed within the human body, tissue reacts towards the implant in a variety of ways depending on the material type. The mechanism of tissue interaction depends on the tissue response to the implant surface. In general, there are three terms in which a biomaterial may be described in or classified into representing the tissues responses. These are bioinert, bioresorbable, and bioactive.

 

1. Bioinert Biomaterials

 

The term bioinert refers to any material that once placed in the human body has minimal interaction with its surrounding tissue. Examples of these are stainless steel, titanium, alumina, partially stabilised zirconia, and ultra high molecular weight polyethylene. Generally a fibrous capsule might form around bioinert implants hence its bio functionality relies on tissue integration through the implant.

 

2. Bioactive Biomaterials

 

Bioactive refers to a material, which upon being placed within the human body interacts with the surrounding bone and in some cases, even soft tissue. This occurs through a time - dependent kinetic modification of the surface, triggered by their implantation within the living bone. An ion - exchange reaction between the bioactive implant and surrounding body fluids - results in the formation of a biologically active carbonate apatite (CHAp) layer on the implant that is chemically and crystallographically equivalent to the mineral phase in bone. Prime examples of these materials are synthetic hydroxyapatite [Ca10 (PO4)6(OH)2], glass ceramic A-W and bioglass.

 

3. Bioresorbable Biomaterials

 

Bioresorbable refers to a material that upon placement within the human body starts to dissolve (resorbed) and slowly replaced by advancing tissue (such as bone). Common examples of bioresorbable materials are tricalcium phosphate [Ca3 (PO4)2] and polylactic-polyglycolic acid copolymers. Calcium oxide, calcium carbonate and gypsum are other common materials that have been utilised during the last three decades.

 

8.2  Conventional implant devices

 

1. Ceramics

 

Inorganic compounds that contain metallic and non-metallic elements, for which inter-atomic bonding is ionic or covalent, and which are generally formed at high temperatures.

 

Example: aluminum oxide, zirconia, calcium phosphates.

Uses of Ceramics

 

Structural components

 

         Joint replacements, hip and knee

 

         Spinal fusion devices

 

         Dental crowns, bridges, implants, ect

 

Other applications

 

         Inner ear and cochlear implants

 

         Tissue engineering

 

         Coatings for heart valves

 

          Metals

 

Materials containing only metallic atoms either as single elements or in combination in a closely packed crystal structure.

 

Example: stainless steel, cobalt alloys, titanium alloys.

 

Uses of Metals

 

Structural components

 

         Joint replacements

 

         Bone fracture pins, plates

 

         Dental implants

 

Other applications

 

         Leads, wires, tubing

 

         Cardiac devices

 

        Polymers

 

From Greek - 'poly' meaning many and 'mer' meaning unit or part Low density structures of non-metallic elements Often in the form of macromolecules - chains, branched chains or cross linked networks Poor thermal and electrical conductors due to the affinity of the elements to attract or share valence electrons

 

Example: Silicones, poly (ethylene), poly (vinyl chloride), polyurethanes, polylactides

 

Uses of Polymers

 

Many applications

 

         Valves, ducts, catheters

 

         Joint replacement

 

         Coatings, encapsulates

 

         Tissue engineering scaffolds

 

8.3 Biomaterials Properties

 

         Mechanical properties of the various tissues in the human body are well established, and it is important that the in-vivo environment of an implant be considered during implant design. Mechanical performance of an implanted device is influenced by the inherent properties of the chosen biomaterial grades and by the processing method used to convert them into their finished forms.

 

         Degradation properties of chosen biomaterials can play a pivotal role in determining tissue healing dynamics and thus clinical outcome. Timescales involved in the tissue regeneration process are increasingly well understood. Through transferring functional requirement back to the native tissue during its regeneration, clinically superior results may be achieved. Furthermore, resorption of the implant can reduce both lifetime procedural cost and incidence of post-operative complications.

 

         Surface properties of a biomaterial, determined by both its chemical composition and conversion processes, affect the local tissue response at the biomaterial-tissue interface on a cellular level. Consideration is therefore given to the desired cellular response to a biomaterial surface, during medical implant design.

8.4  Biomaterials Applications

 

        Drug delivery

 

         Cancer detection, therapy and prevention.

 

         Biomaterial-cell interactions in applications such as tissue engineering, advanced stem-cell culture, biosensors, and targeted drug delivery via the blood.

 

         Advanced drug delivery, ranging from polymeric aerosols that carry life-saving drugs to cationic polymer/DNA self-assembled nanocomplexes that deliver DNA to specific tissues for in vivo gene therapy.

 

         Genetically-engineered polymers for tissue engineering and drug delivery applications.

 

         Cellular biopolymers and their role in cell migration and cancer metastasis.

 

        Other important applications

 

         Heart- pacemaker, artificial valve, artificial heart

 

         Eye -contact lens, intraocular lens

 

         Ear -artificial stapes, cochlea implant

 

         Bone -bone plate, intramedullary rod, joint prosthesis, bone cement, bone defect repair

 

         Kidney- dialysis machine

 

         Bladder- catheter and stent

 

         Muscle sutures- muscle stimulator

 

         Circulation- artificial blood vessels

 

         Skin burn- dressings, artificial skin

 

         Endocrine -encapsulated pancreatic islet cells.

 

 

Tags : Physics - Advanced Engineering Materials Metallic Glasses
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