Smart Material in Medicine

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Smart mater ials used in medical

applications


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Table of contents

1. General description of smart materials

2. Smart metallics used in medical applications

Intelligent titanium surfaces Nitinol (for Nickel Titanium Naval Ordnance Laboratory)

3. Smart ceramics used in medical applications

Hydroxyapatite Zirconia

4. Smart polymers used in medical applications

High-performance polyethylene Hydrogels Poly(methyl methacrylate) Polyglycolic acid LTL Color Compounders

5. Smart composites used in medical applications

Electrical resistance measurement in carbon-reinforced composites Piezo composites

6. New tendencies and ideas in smart materials used in medical applications

7. Conclusions

8. Bibliography


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1. General description of smart materials

1.1. What are smart materials?

Fig. 1.1. Evolution of materials

Science and technology have made amazing developments in the design of electronics and

machinery using standard materials, which do not have particularly special properties (i.e. steel,

aluminum, gold). Imagine the range of possibilities, which exist for special materials that have

properties scientists can manipulate. Some such materials have the ability to change shape or size

simply by adding a little bit of heat, or to change from a liquid to a solid almost instantly when near a

magnet; these materials are called smart materials.

Smart materials have one or more properties that can be dramatically altered. Most everyday

materials have physical properties, which cannot be significantly altered; for example if oil is heated

it will become a little thinner, whereas a smart material with variableviscositymay turn from a fluid
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which flows easily to a solid. A variety of smart materials already exist, and are being researched

extensively. These include piezoelectric materials, magneto-rheostatic materials, electro-rheostatic

materials, and shape memory alloys. Some everyday items are already incorporating smart materials

(coffeepots, cars, the International Space Station, eyeglasses) and the number of applications for

them is growing steadily.

Each individual type of smart material has a different property which can be significantly

altered, such as viscosity, volume, and conductivity. The property that can be altered influences what

types of applications the smart material can be used for.

There are a number of types of smart material, some of which are already common. Some examples

are as following:

Piezoelectricmaterials are materials that produce a voltage when stress is applied. Since thiseffect also applies in the reverse manner, a voltage across the sample will produce stress within

the sample. Suitably designed structures made from these materials can therefore be made that

bend, expand or contract when a voltage is applied.

Shape memory al loysandshape memory polymersare materials in which large deformationcan be induced and recovered through temperature changes or stress changes (pseudoelasticity).

The large deformation results due to martensitic phase change.

Magnetostrictivematerials exhibit change in shape under the influence of magnetic field andalso exhibit change in their magnetization under the influence of mechanical stress.

Magnetic shape memoryalloys are materials that change their shape in response to asignificant change in the magnetic field.

pH-sensiti ve polymersare materials that change in volume when the pH of the surroundingmedium changes.

Temperatur e-responsive polymersare materials which undergo changes upon temperature. Halochromicmaterials are commonly used materials that change their colour as a result of

changing acidity. One suggested application is for paints that can change colour to

indicatecorrosionin the metal underneath them.

Chromogeni c systemschange colour in response to electrical, optical or thermal changes.These includeelectrochromicmaterials, which change their colour or opacity on the application

of a voltage (e.g.liquid crystal displays),thermochromicmaterials change in colour depending

on their temperature, andphotochromicmaterials, which change colour in response to lightfor

example, light sensitivesunglassesthat darken when exposed to bright sunlight.

Ferrofluid
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Photomechanical materi alschange shape under exposure to light. Self -healing materialshave the intrinsic ability to repair damage due to normal usage, thus

expanding the material's lifetime

Dielectri c elastomers(DEs) are smart material systems which produce large strains (up to300%) under the influence of an external electric field.

Magnetocaloric materialsare compounds that undergo a reversible change in temperatureupon exposure to a changing magnetic field.

Thermoelectric materi alsare used to build devices that convert temperature differences intoelectricity and vice-versa.

Several well established and ongoing applications are today available for adaptive/active

materials in medicine that exploit the properties of shape memory and super elastic alloys, shape

memory polymers, active and resorbable bioceramics and bioglasses, biomimetic polymers and gels,

active (nano)particles, smart textiles, active optical fibers, etc.

Nevertheless, the continuously increasing capability to image and manage matter at the

atomic and molecular level enabled by a number of nanoscale tools such as scanning probes, self and

directed assembly, single molecule techniques, nanolithography and DNA-based technologies,

coupled with advanced theory, multiscale modeling and simulation approaches for nanophase and

nanostructured materials and smart nano/micro/meso-engineered devices and prostheses, is fuelling

relevant opportunities and entirely new perspectives to inbuilt smartness or intelligence in materials

and devices that would interject in a meaningful way with the body environment. These are opening

new frontiers in medical diagnostics, pharmaceuticals, therapies, and in implant and prostheses.

Specific areas of interest include new or creatively engineered materials, multi-scale cell

engineering for functional tissues and drug and gene delivery systems, new materials and systems for

medical diagnostics, implants and prostheses, and systemic interaction in the body environment

including biocompatibility and biofunctionality issues.

2. Smart metallics used in medical applications

2.1. Intelligent titanium surfaces

Researchers Say That Smart Metallic Surfaces May Lead to Better Prostheses

Researchers at the Universit de Montral with help from McGill University, the Institut National de

la Recherche Scientifique (INRS-EMT), Plasmionique Inc and the Universidade de So Paulo, have managed
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to chemically modify titanium to create so called intelligent surfaces. The new material can interact with

cells in the body and either promote healing or suppress their growth. It is believed that this research will lead

to smart prostheses that will help promote healing of tissue post implantation.

Dr. Nanci and colleagues applied chemical compounds to modify the surface of the common

biomedical metals such as titanium. Exposing these metals to selected etching mixtures of acids and oxidants

results in surfaces with a sponge-like pattern of nano (ultra small) pits. We demonstrated that some cells stick

better to these surfaces than they do to the traditional smooth ones, says Dr. Nanci. This is already an

improvement to the standard available biomaterial.

The researchers then tested the effects of the chemically-produced nanoporous titanium surfaces on

cell growth and development. They showed that the treated surfaces increased growth of bone cells, decreased

growth of unwanted cells and stimulated stem cells, relative to untreated smooth ones. In addition, expression

of genes required for cell adhesion and growth were increased in contact with the nanoporous surfaces.

Fig. 2.1. Control Ti-Uncontrolled growth of cells on a Titanium surface

Nano Ti-Controled growth of cells on a nanoporous Titanium surface

Uncontrolled growth of cells on an implant is not ideal. For example, when using cardiovascular

stents, it is important to limit the growth of certain cells in order not interfere with blood flow. Also, in some

cases, cells can form an undesirable capsule around dental implants causing them to fall. The scientists

demonstrated that treatment with specific etchants reduced the growth of unwanted cells.

2.2. Memory metal2.2.1. Introduction

In 1965, the first of a series of metal alloys of nickel and titanium was produced by the Naval

Ordnance Laboratory. These alloys are called Nitinol,

for Nickel Titanium Naval Ordnance Laboratory. Many of the alloys have a rather remarkable

property: they remember their shape. This "smart" property is the result of the substance's ability to

undergo a phase change - a kind of atomic ballet in which atoms in the solid subtly shift their


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positions in response to a stimulus like a change in temperature or application of mechanical stress. A

simple demonstation involves bending a sample, then exposing it to a source of heat like hot air or

hot water. The sample recovers its original shape as its temperature is raised above the temperature

corresponding to the phase change. This temperature may be tuned by varying the ratio of nickel to

titanium atoms in the solid by a few percent relative to a 1:1 ratio.

2.2.2. How it works

As noted above, Nitinol is an alloy of nearly equal numbers of nickel and titanium atoms,

with the exact amounts varied to match the temperature of the phase change to the application. The

alloy can exist in either of two structures (phases) at room temperature, depending on the exact ratio

of nickel to titanium atoms. The structure found above the temperature of the phase change possesses

the high symmetry of a cube and is called austenite; the structure found below the temperature of the

phase change is much less symmetric and is called martensite. In the martensite phase the material is

very elastic, while in the austenite phase the material is comparatively rigid.

Nitinol can be "trained" to have a new shape while in the austenite phase by deforming it into

the desired shape. As it then cools to below the phase transition temperature, the material enters the

martensite phase. In the martensite phase the shape can then be changed by mechanical stress: groups

of atoms that were "leaning" in one direction will accommodate the mechanical stress by "leaning" in

another direction, as allowed by the less symmetric structure. The sample will revert to the shape

enforced upon it while it was in the austenite phase by returning it to the austenite phase through an

increase in its temperature. The thermal energy acquired by the shape through heating it provides the

energy the atoms need to return to their original positions and the sample to its original shape.

Fig. 2.2. Phases of Nitinol in different treatment


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The transformation from austenite to martensite can be accomplished in 24 different ways.

These 24 ways of producing martensite from austenite are the result of the symmetric CsCl structure

having 6 equivalent face diagonal planes, each of which can shift in one of two directions and can

distort (shear) in one of two directions, 6 x 2 x 2 = 2.

Fig. 2.3. Modification of the crystal lattice during the transformation from Austenite to Martensite

Fig. 2.4. A spring made oshape memory metal in its

martensitephase.

Fig. 2.5. The same spring

stretched to a new shape.

Fig. 2.6. In warm water or

with a stream of hot air, the

spring returns to its

"trained" shape by heating it to

above the temperature of the

phase change into the more

rigid austenitephase.


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2.2.3. Applications

The biocompatibility of NiTi allows its use in many medical applications such as: vascular

stents, anchors for attaching tendons to bone, medical guidewires, medical guidepins, root canal files,

bendable surgical tools, and devices for closing holes in the heart.

Another important attribute of nitinol in medicine is itssuperelasticity.

Other shape memory materials include gold cadmium, copper-aluminum-nickel, copper-zinc-

aluminum, and iron-manganese-silicon alloys.

2.2.3.1. Orthodontic archwires.

The archwire of these braces used in orthodontia is made of memory metal to apply pressure

uniformly to the teeth.

Fig. 2.5. Braces of archwire made of memory metal

2.2.3.2. Flexible eyeglass frames.

Bending the memory metal eyeglass frames converts the metal from the rigid austenite

structure to the more flexible martensite structure. When this mechanical stress is removed, the

frames return to their original shape and austenite structure. See this exact pair of framesdistort

when exposed to liquid nitrogen.

Fig. 2.6. Eyeglass frames made of memory metal
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3. Smart ceramics used in medical applications

Ceramics are used as components of dental implants, hip implants, middle ear implants, and

heart valves. They are generally more chemically stable and inert than most metals due to their

chemical bonding.The most commonly used material are alumina, zirconia, bioglass, hydroxyapatite, and

tricalcium phosphate. These materials work well within the human body for several reasons. They are

inert, and because they are resorbable and active, the materials can remain in the body unchanged.

They can also dissolve and actively take part in physiological processes, for example, when

hydroxyapatite, a material chemically similar to bone structure, can integrate and help bone grow into

it. One proposed use for bioceramics is the treatment ofcancer. Two methods of treatment have been

proposed; treatment throughhyperthermia, and radiotherapy.

Fig. 3.1. Cell of hydroxyapatite

3.1. Classification of technical ceramics

Technical ceramics can also be classified into three distinct material categories:

Oxides: alumina, beryllia, ceria, zirconia Nonoxides: carbide, boride, nitride, silicide Composite materials: particulate reinforced, fiber reinforced, combinations

ofoxides and nonoxides.Each one of these classes can develop unique material properties because ceramics tend to be

crystalline.

3.2. Smart Biomaterials and their Applications

The range of applications of smart materials in the biomedical field has become increasingly

diverse over the past decade. The increasing complexity of modern smart biomaterials makes it
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difficult to identify broad application areas, or themes, where current research is providing, or has the

potential to provide, new or improved capabilities. A biomaterial may be defined as any natural or

synthetic substance or combination of substances (other than a drug) which can be used for any

period of time, as a whole or as a part of a system which treats, augments, or replaces any tissue,

organ, or function of the body . It is clear that biocompatibility is an essential requirement for any

implanted smart material or device. All other material requirements will depend on the particular

application. For permanent implants, resistance to abrasion and wear, fatigue strength, durability

(corrosion resistance), long-term dimensional stability and permeability to gases, water, and small

biomolecules can be critical. These include:

3.2.1. Hydroxylapatite, also called hydroxyapatite (HA), is a naturally

occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but is usually written

Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is

the hydroxyl endmemberof the complex apatite group. The OH- ion can be replaced

by fluoride, chloride orcarbonate, producing fluorapatite orchlorapatite. It crystallizes in

the hexagonal crystal system. Pure hydroxylapatite powder is white. Naturally occurring apatites can,

however, also have brown, yellow, or green colorations, comparable to the discolorations of dental

fluorosis.

Hydroxylapatite can be found in teeth and bones within the human body. Thus, it is

commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth

into prosthetic implants. Although many otherphases exist with similar or even identical chemical

makeup, the body responds much differently to them. Coral skeletons can be transformed into

hydroxylapatite by high temperatures; their porous structure allows relatively rapid ingrowth at the

expense of initial mechanical strength. The high temperature also burns away any organic molecules

such as proteins, preventing an immune response and rejection.

Fig. 3.2. Flexible hydrogel-HA composite, which has a mineral-to-organic matrix ratio

approximating that of human bone.
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3.2.2. Use of Zirconia in Restorative Dentistry

Zirconia is being used on the artificial femoral heads for hip replacements. This makes the

part stronger and the heads are smaller so the patient experiences less trauma during the operation.

Besides hip replacements, zirconia is being used in shoulders, knee joints, spinal implants and

phalangeal joints. This is an amazing use of ceramic materials and it is making great strides in the

medical field. Who knows what they will come up with next.

Though zirconia has been available for use in restorative dentistry for several years, there has

been an increased interest recently in these materials. Zirconia based restorations are quite versatile

and can be used for crowns,bridges, and implantabutments in a variety of clinical situations if the

appropriate guidelines are followed..

CRYSTAL Zirconia is a modern dental ceramic replacement for the metal substructures used

under porcelain crowns and bridges. CRYSTAL brand Dental Zirconia is also translucent, which

gives the overlaid procelain a brighter more natural look. Because of it's stronger-than-steel

properties, Zirconia has been used for decades on the space shuttle and on the new high-tech brakes

on German sports cars and other industrial applications.CRYSTAL Zirconia is a new formulation of

medical grade zirconia material, packed into blocks and ground to a custom fit using state-of-the-

art dental milling machines, and then sintered in 1500 C oven till it is virtually unbreakable. In the

past, dentists used to say that crowns or bridges need to be replaced every five or ten years, but while

the porcelain may chip or need repair, a crown or bridge substructure created with CRYSTAL

Zirconia should last a lifetime, and includes alifetimewarrantywhen milled by a certified dental

laboratory.

CRYSTAL Zirconia is 100% biocompatible and because the body does not reject zirconia,

this material is the preferred modern material for medical applications. Unlike amalgams and metal

alloys used in the dentistry in the past, the body accepts zirconia as a natural material, so you dont

have to worry about allergies or adverse reactions.

Fig. 3.3. Fixed partial denture Fig. 3.4. Crystal Zirconia
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3.2.3. Ceramics and Medicine help Liver Cancer

As most people know traditional treatment for cancer usually involves chemotherapy which

can be very difficult for individuals. Usually this means a hospital stay and they will become sick

afterwards with vomiting, nausea and hair loss. Most patients understand that this is the plight that

they have to deal with when they go through these treatments and some will, but others decide it's

just too much to bear.

Because of this researchers looked for a new way to do some type of treatment so that people

would not have to suffer so much. Glass microspheres are the answer that was found. These are very

tiny and very thin -- some have compared them to a human hair saying they are smaller -- and they

are approved by the FDA and currently in use in several hospitals across the United States.

This is a very simple treatment and the individual can have it done as an outpatient. The

microspheres are inserted into the tumor using a catheter and the radiation is centralized to the tumor.

The malignant tumor is then addressed and there is minimal damage to the other tissue. Because it is

done this way, the individual doesn't have the normal after therapy symptoms and will only

experience fatigue for several weeks while the radiation is working.

3.3. Discussions and Conclusions

Ceramics are difficult to form into complicated geometries using high-temperature processes

in a cost-effective manner in small dental laboratories. Other processes are well suited for custom

operations. Hot-isostatic-pressing (HIP) has great advantages for creating standard shapes in a

reusable mold, such as prepable zirconia abutments for implants. For custom prostheses (crowns and

bridges), it is currently more practical to rely on milling operations or molding operations to form

dental shapes. CAD/CAM ceramic materials provide a unique option to start with almost defect-free

material, but they don't provide flexibility to regionally customize esthetics or other properties for a

restoration. That is a large part of the reason that CAD/CAM has not replaced much of traditional

ceramic fabrication technology. No alternative yet competes with the esthetic result of dental

porcelain being layered by an artistic ceramic technician to fully characterize a restoration. While one

can speculate that this is possible, this is not currently an option. When this is true, then CAD/CAM

might have much grander appeal.

The detection of ceramic defects before oral inserting the prostheses allows all the corrections

in order to avoid the fracture of the ceramic component. The fractures that occur within the structure

of these prostheses were motivated by the elasticity module of the ceramics and by the defects within

the ceramic layers. Early detection of substance defects within these layers allows for optimal


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corrections before inserting them and applying masticatory stress together with reduction of fractures.

Also some of the defects are situated superficial enough and cervical, namely in the maximum

tension area recorded during mastication with high risks of fracture at this level.

4. Smart polymers used in medical applications

Fig. 4.1. Polyethylene chain picture

` A polymer is a large molecule (macromolecule) composed of repeating structural units.

These sub-units are typically connected covalent chemical bonds(sharing of pairs of

electrons between atoms).The polymer can be natural(as examples shellac,amber,natural rubber) or

synthetic(examples as synthetic rubber ,nylon ,PVC polystyrene,polyethylene,silicone,polypropylene

and many others).

What makes a polymer smart? Maybe because it can be used in various applications industry

,medicine , sports , agriculture and for his properties that makes him biodegradable , inert or bioactivif we refer to medicine.

For instance high-performance polyethylene (HPPE or ultra-high-molecular-weight polyethylene)

used in total or partial joint replacement implants, hydrogels used for scaffolds tissue engineering or

Poly(methyl methacrylate) (PMMA) for bone cement and of course many other polymers.

Fig. 4.2. Various polymers in their crude form


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4.1. High-performance polyethylene (HPPE or ultra-high-molecular-weight

polyethylene)

Is a subset of the thermoplastic polyethylene. It has extremely long chains, chains that makes

him transfer load more effectively from here result a very tough material, with the highest impact

strength of any thermoplastic presently made.

HPPE is a type ofpolyolefin. It is made up of extremely long chains of polyethylene, which

all align in the same direction. It derives its strength largely from the length of each individual

molecule (chain). Van der Waals bondsbetween the molecules are relatively weak.

It is highly resistant to corrosive chemicals with exception ofoxidizing acids; has extremely low

moisture absorption and a very low coefficient of friction; is self-lubricating; and is highly resistant

to abrasion, in some forms being 15 times more resistant to abrasion than carbon steel. Its coefficient

of friction is significantly lower than that ofnylon and acetal, and is comparable to that

ofpolytetrafluoroethylene (Teflon).

Fig. 4.3.Structure of HPPE, with n greater than 100,000 and knee implant

4.1.1. Medical applications

Used in total or partial joint replacement such as hip , knee or intervertrebal implants.

4.2. Hydrogels

Hydrogel (also called aquagel) is a network of polymer chains that are hydrophilic,

sometimes found as a colloidal gel in which wateris the dispersion medium. Hydrogels are

highly absorbent (they can contain over 99.9% water) natural or synthetic polymers. Hydrogels also

possess a degree of flexibility very similar to natural tissue, due to their significant water content.
http://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Polyethylenehttp://en.wikipedia.org/wiki/Impact_forcehttp://en.wikipedia.org/wiki/Impact_forcehttp://en.wikipedia.org/wiki/Polyolefinhttp://en.wikipedia.org/wiki/Van_der_Waals_bondinghttp://en.wikipedia.org/wiki/Oxidizing_acidhttp://en.wikipedia.org/wiki/Coefficient_of_frictionhttp://en.wikipedia.org/wiki/Wear#Abrasive_wearhttp://en.wikipedia.org/wiki/Carbon_steelhttp://en.wikipedia.org/wiki/Nylonhttp://en.wikipedia.org/wiki/Polyoxymethylenehttp://en.wikipedia.org/wiki/Polytetrafluoroethylenehttp://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Absorption_(chemistry)http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Absorption_(chemistry)http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Polytetrafluoroethylenehttp://en.wikipedia.org/wiki/Polyoxymethylenehttp://en.wikipedia.org/wiki/Nylonhttp://en.wikipedia.org/wiki/Carbon_steelhttp://en.wikipedia.org/wiki/Wear#Abrasive_wearhttp://en.wikipedia.org/wiki/Coefficient_of_frictionhttp://en.wikipedia.org/wiki/Oxidizing_acidhttp://en.wikipedia.org/wiki/Van_der_Waals_bondinghttp://en.wikipedia.org/wiki/Polyolefinhttp://en.wikipedia.org/wiki/Impact_forcehttp://en.wikipedia.org/wiki/Impact_forcehttp://en.wikipedia.org/wiki/Polyethylenehttp://en.wikipedia.org/wiki/Thermoplastic


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Fig. 4.4.Porous hydrogel structure

4.2.1. Applications

currently used as scaffolds in tissue engineering. When used as scaffolds, hydrogels maycontain human cells to repair tissue.

hydrogel-coated wells have been used for cell culture[2] environmentally sensitive hydrogels which are also known as 'Smart Gels' or 'Intelligent

Gels'. These hydrogels have the ability to sense changes of pH, temperature, or the

concentration of metabolite and release their load as result of such a change.

as sustained-release drug delivery systems hydrogels that are responsive to specific molecules, such as glucose , can be used

as biosensors

Fig. 4.5. Scaffold structures are built up from layers of cross-hatched hydrogel strands

used in disposable diapers where they absorb urine, or in sanitary napkins contact lenses (silicone hydrogels)
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EEG and ECG medical electrodes using hydrogels composed ofcross-linkedpolymers(polyethylene oxide)

dressings for healing ofburn or other hard-to-heal wounds. Wound gels are excellent forhelping to create or maintain a moist environment.

4.3. Poly(methyl methacrylate) (PMMA)

Poly(methyl methacrylate) is a transparent thermoplastic, often used as a light or shatter-

resistant alternative to glass.

PMMA is an economical alternative to polycarbonate (PC) when extreme strength is not

necessary. It is often preferred because of its moderate properties, easy handling and processing, and

low cost, but behaves in a brittle manner when loaded, especially under an impact force, and is more

prone to scratching compared to conventional inorganic glass.

PMMA is methyl methacrylate monomer polymerization. Presents high mechanical strength,

toughness.

Fig. 4.6. Structure of PMMA

4.3.1. Applications

PMMA has a good degree of compatibility with human tissue, and can be used forreplacement intraocular lenses in the eye

In orthopedic surgery, PMMA bone cement is used to affix implants and to remodel lostbone. It is supplied as a powder with liquid methyl methacrylate (MMA).Although PMMA

is biologically compatible, MMA is considered to be an irritant and a possible carcinogen

.Although sticky, it does not bond to either the bone or the implant, it primarily fills the

spaces between the prosthesis and the bone preventing motion. A big disadvantage to this

bone cement is that it heats to quite a high temperature.

Dentures are often made of PMMA, and can be color-matched to the patient's teeth
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In cosmetic surgery, tiny PMMA microspheres suspended in some biological fluid areinjected under the skin to reduce scars permanently

A large majority of white Dental filling materials (composites) have PMMA as their mainorganic component.

Fig. 4.7. Sacroplasty, a bone gluepolymethylmethacrylate (PMMA) is injected into the

fracture

4.4. Polyglycolic acid (PGA)

Fig. 4.8. Ring-opening polymerization of glycolide to polyglycolide

Polyglycolic acid (PGA) is a biodegradable, thermoplastic polymerand It can be prepared

starting from glycolic acidby means ofpolycondensation orring-opening polymerization.

Polyglycolide is characterized by hydrolytic instability and the degradation process is erosive

and appears to take place in two steps during which the polymer is converted back to its monomer

glycolic acid: first water diffuses into the amorphous (non-crystalline) regions of the polymer matrix;

the second step starts after the amorphous regions have been eroded, leaving the crystalline portion of

the polymer susceptible to hydrolytic attack.
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Silver ion AM does not kill microorganisms in the sense of a disinfectant such as chlorine

bleach. Instead the AM suppresses cellular reproduction by disrupting the energy production

mechanism of the cell, preventing DNA replication in the cell, and weakening the cell wall. Silver

ions bound in an inorganic matrix are incorporated into a plastic. The silver ions migrate to the

surface of the plastic in the presence of trace amounts of moisture and then move into the cell. As a

result the count of microorganisms decreases over a period of hours. As an indication of

effectiveness, standardized tests such as JIS Z 2801 utilize specific bacterial strains to determine the

reduction in bacteria count on treated surfaces over a 24 hour period. In this test very large reductions

of 99.9% or greater.

Fig. 4.10.ColorRx Antimicrobial (AM)

5. Smart composites used in medical applications

The composite materials considered here are solid objects with a macrostructure. The

constituents of these, solids can be observed with the naked eye. Solid objects are said to be smartif

they embody additional functionality capabilities beyond their inherent structural attributes. These

capabilities might be attributed to an embedded network of interconnected sensors, actuators and

computers, for example. Synthetic inhomogeneous materials with these capabilities comprise the

basis for a new generation of materials. These materials have the potential to revolutionize many

types of products, and usher into existence unforeseen manufactured goods.

Humankinds traditional quest for superior materials may be satisfied in the near future by

ideas furnished by Mother Nature. The design and manufacturing methodologies needed for creating

new generations of materials will come from a meticulous study of flora and fauna.

The future lies with the development of synthetic materials that mimic naturally occurring biological

materials.


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5.1. Cure monitoring

Today, engineering plastics and polymer matrix composites (PMCs) are widely used in

consumer and leisure products such as golf clubs, fishing rods, skis, and tennis rackets. Fiber-

reinforced plastics (FRPs), particularly, are the most promising composite materials for airplanes,

space structures, and military ships. Thermosetting and thermoplastic polymers are common

materials used in FRPs.

In the molding process for polymers, a liquid resin becomes solid. As for thermosetting

polymers, a monomeric liquid resin becomes a cross-linked rigid solid and a tightly bound three-

dimensional network is produced. This process is called cure. Thermoplastics do not need to

becured because they are not cross-linked. In these advanced engineering materials, the integrity of

the product is very important for certifying the performance. The quality of a product strongly

depends on the profiles of the control parameters such as the temperature and pressure in the molding

process. Therefore, many researchers have developed techniques for optimizing the molding process.

The monitoring technique is essential for the optimal control system of the molding process. The cure

monitoring technique, especially has been an important focus because the cure reaction of a

thermosetting FRP is too complicated to predict. Techniques for monitoring the molding process of

thermosetting FRPs are not discussed. However, it should be remembered that some of the

techniques that monitor the mechanical, optical, and electrical properties, can also be applied to

monitor the state of solidification in the process of molding thermoplastic polymers.

5.2. Electrical Resistance Measurement in Carbon-Reinforced Composites

The technique for health monitoring by measuring electrical resistance has become attractive

since the late 1980s for carbon-reinforced composites (90). This technique measures changes in

electrical resistance when strains or damages are applied to the composites. Like the tagging

technique, the advantage of this technique is that there is no need for embedded sensors for in situ

monitoring. In addition, the mechanical properties of the composites are not affected by using this

monitoring technique because the carbon reinforcements work as sensors. Recently, applications

have focused on three types of composites; carbonfiber- reinforced concrete, carbon-fiber-reinforced

polymers (CFRPs), and carbon fibercarbon matrix (C/C) composites (91). The self-monitoring

functions of carbon-reinforced composites are aimed at strain and damage monitoring. These

functions result from changes in the electrical paths and in the conductivity of carbon. Short carbon-

fiber-reinforced concrete consists of low conductive concrete and carbon fibers at a low volume

fraction. In continuous carbon-reinforced polymers, the electrical paths are composed of the carbon


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fibers due to the nonconductivity of polymers. A current flows overall in the C/C composite because

it has conductivity in the fiber and matrix. The electrical paths in the composites are changed by

damages such as fiber breaks, delaminations, matrix cracks, and debonding between the fiber and

matrix. The mechanism of the variation of electrical resistance differs among these composites due to

their different electrical paths.

5.3. Piezo Composites

1-3 Piezo Composites have become the material of choice for many high performance

ultrasound transducer since it was invented by R.E. Newnham and L.E. Cross in the late 1970's .A variety of piezo composite materials can be made by combining piezo ceramic elements with a

passive polymer such as epoxy or active polymer. Piezo-composites are classified according to their

connectivity (such as 2-2, 1-3, 0-3 etc.,). Connectivity is defined as the number of dimensions

through which the material is continuous. It is conventional for the first digit to refer to the

piezoelectrically active phase.

Prof. Newnham defined the family of interconnectivity of piezo electric composites as shown

in one of his drawn pictures below.

Today the most piezo composites on the market are with the 1-3 and 2-2 connectivity used in

ultrasound transducers, actuators and sensors.

1-3 piezo composites advantages over standard bulk piezo ceramics are in general:

lower acoustic impedance, 1-3 piezo composites are available with acoustic impedancebetween 8MRayl and 26MRayl

higher coupling coefficient of typically 0.63 to 0.70 compared with 0.54 of bulk material higher bandwidth and lower Qm

Disadvantages of piezo composites over bulk piezoceramic components are in general the

higher costs and the often limited temperature operating range.

The typical applications for 1-3 piezo composites are

Medical Diagnostic Ultrasound Non Destructive Testing NDT SONAR, mostly defense oriented for high performance Flow Control and Air Ultrasound

The biggest single market for the 1-3 piezo composite is the medical diagnostic ultrasound

market which is using more 1-3 piezo composite than the other markets combined. Today's medical


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ultrasound imaging systems would be not possible without the advancements in 1-3 piezo

composites.

Smart Material is manufacturing and distributing piezo composite material with 2-2

connectivity (theMFC) and

1-3 connectivity.

Smart Material is utilizing different manufacturing technologies to meet to meet the typical

requirements of the applications for 1-3 piezo composites as outlined above which are listed under

Types Available:

1-3 Fiber Composites with Random Pixel Distribution

1-3 Fiber Composites with Regular Pixel Distribution

1-3 Standard Dice&Fill Composites

Utilizing different manufacturing technologies for 1-3 piezo composites allows Smart

Material to provide 1-3 composites for frequencies ranging from 40kHz to 10 MHz, with fill factor

ranging from 25% to 80% and sizes up to 100mm by 100mm (4inches by 4 inches).

6. New tendencies and ideas in smart materials used in medical applications

There are two diverting ideas that define a direction in the research of new materials field:

Creating a universal material able to respond to all the requirements (this idea is purely sci-fifor now);

Creating the material needed in the place needed, with the structure needed, in the quantitiesneeded (this would be possible by manipulating the matter at an atom scale).

Implementing a system with an automated response in various fields present significant

advantages by monitoring certain signals and responding accordingly when it detects limit overruns.

Adding to the system the possibility of learning certain patterns, which is possible today using neural

networks, enhances the autonomy and efficiency. Applying these new findings from science and

technology in medicine requires miniaturization and keeping the interactions with the environment

strictly limited to the purpose these assemblies were created for.

Smart materials are exactley this, combining the sensing activity with the actuating one. The

disadvantage is that they usualy respond to only one type of signal and respond in only one way. By

combining in certain ways different types of smart materials there is a posibility of reducing this

disadvantage.
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Regenerative medicine, diagnostics and drug delivery could profit from intelligent

biomaterials. For example enzyme-responsive materials have the potential to detect, respond to, and

ultimately repair biological processes by injecting cell-scaffold that gels when triggered by tissue

fluid enzymes. Also the flow of molecules into (and out of) polymer particles can be controlled by

very specific enzyme switches - the first steps in making truly bio-responsive materials. The goal for

now is to mimic the in-vivo feed-back systems that control enzyme activity.

Carbon nanotubes is known to be highly electrically conductive, this being used to create a

connection with the neuronal cell membranes. Unlike the metal electrodes that are currently used in

research and clinical applications, the nanotubes can create shortcuts between the distal and proximal

compartments of the neuron, resulting in enhanced neuronal excitability. From a study conducted in

Switzerland resulted this finding is relevant for the emerging field of neuro-engineering and

neuroprosthetics, the nanotubes could be used as a new building block of novel "electrical bypass"

systems for treating traumatic injury of the central nervous system. Carbon nano-electrodes could

also be used to replace metal parts in clinical applications such as deep brain stimulation for the

treatment of Parkinson's disease or severe depression. And they show promise as a whole new class

of "smart" materials for use in a wide range of potential neuroprosthetic applications.

There are three fundamental obstacles to developing reliable neuroprosthetics:

1) stable interfacing of electromechanical devices with neural tissue,2) understanding how to stimulate the neural tissue, and3) understanding what signals to record from the neurons in order for the device to make an

automatic and appropriate decision to stimulate.

The new carbon nanotube-based interface technology discovered together with state of the art

simulations of brain-machine interfaces is the key to developing all types of neuroprosthetics -- sight,

sound, smell, motion, vetoing epileptic attacks, spinal bypasses, as well as repairing and even

enhancing cognitive functions.Near-infrared (NIR) light (which is just beyond what human can see) penetrates through the

skin and almost four inches into the body, with great potential for diagnosing and treating diseases.

Low-power NIR does not damage body tissues as it passes. A new smart polymer that responds to

low-power NIR light breaks apart into small pieces that seem to be nontoxic to surrounding tissue. A

hydrogel with the new polymer could release medications or imaging agents when hit with NIR. This

is the first example of a polymeric material capable of disassembly into small molecules in response

to harmless levels of irradiation.


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Fig. 6.1. Near-infrared light

Fig. 6.2. Molybdenum oxide wheel molecule

Working out how nano-particles are built is key to developing new intelligent materials,

electronic devices, and understanding the bio-machinery that operates in living cells. The ability to

control this self-assembly has profound consequences for the development of new technologies as

well as understanding the basis for complex chemistry, and for example, the origins of life.

A team of experts at Glasgow devised an experiment which enabled them to observe

molecules being constructed around what appeared to be a transient template cluster.

The experiment involved the construction a flow reactor system for the assembly of the nano-

particles under dynamic flowing conditions. This new experimental approach allows self-assembly

being examined in a new way at the nano-level, giving rise to unprecedented mechanistic information

unmasking the complexities of molecular self-assembly (the process by which objects form a

particular arrangement without any external manipulation).

During the experiment, the researchers observed the self-assembly of molybdenum oxidewheel molecules around an intermediate structure in the centre of the wheel which they found to be

the template or scaffold used to construct the larger molecule. Following completion of the

molybdenum oxide wheel molecule, which is just 3.6 nanometres in diameter, the template was

ejected, freeing it to repeat the process. The researchers were able to photograph this process and

the template using X-ray crystallography.
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Understanding the assembly process is vital if we are to create a new range of functional

nano-objects.

A tiny cage of gold covered with a smart polymer, it

responds to light, opening to empty its contents, and

resealing when the light is turned off.

The principle on which it is based on is fairly intuitive

described in the next few steps.

Attach a smart polymer to a gold nano-cage with thepores at the corners.

To load the cages, shake them in a solution of thedrug at a temperature above the polymer's critical

temperature.

Fig. 6.2. Nano cage polymer

Let the cages cool, so that the polymer chains stand up like brushes, sealing the cage's pores. To release the drug, expose the cages to laser light (the lightning bolt) at their resonant

frequency, heating them just enough to drive the polymer over its critical temperature.

The polymer chains will collapse, opening the pores, and releasing the drug. The cage can beresealed simply by turning off the light.

Medicines sometimes have to be administered in extremely small quantities. Just a few tenths

of a milliliter may be sufficient to give the patientthe ideal treatment. Micro-pumps greatly facilitate

the dosage of minute quantities.

The peristaltic pump is a highly complex

system. It contracts in waves in a similar way to the

human esophagus, and thus propels the liquid along

it changes shape of its own accord. To achieve

this, researchers had to use a whole range of

different materials and special material composites.

They used lead-zirconate-titanate (PZT) films that are joined in a suitable way with bending

elements made of carbon-fiber-reinforced plastic and a flexible tube.

PZT materials change their shape as soon as you apply an electric field to them. This makes it

possible to control the pump system electronically. Special adhesives additionally hold the various


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components of the pump system together. Thanks to the special control electronics, tiny quantities

can be pumped accurately through the system.

7. Conclusions

The most sophisticated class of smart materials in the foreseeable future will be that whichemulates biological systems. This class of multifunctional materials will possess the capability to

select and execute specific functions intelligently in order to respond to changes in the

local environment. Furthermore, these materials could have the ability to anticipate challenges based

on the ability to recognize, analyze, and discriminate. These capabilities should include self-

diagnosis, self-repair, selfmultiplication, self-degradation, self-learning, and homeostasis.

The intelligence to be imbued in a synthetic material developed by humankind should emulate

the intelligent attributes found in biological systems. These attributes do not require human

involvement, and they function autonomously, as evidenced by self-learning, selfdegradation, and

regeneration. Thus the rusting of iron in a humid environment could be considered to be a simple

form of self-degradation. Other functions could include the availability to recognize and subsequently

discriminate, redundancy, hierarchical control schemes, and the election of an appropriate action

based on sensory data.

Furthermore, a material that has been damaged and is undergoing a process of self-repair

would reduce its level of performance in order to survive. This intelligence should be inherent in

future generations of smart materials.

So, were looking forward to the future, waiting impatiently to see what wonderful discoveries will

appear in the materials domain.

8. Bibliography

Encyclopedia of Smart Materials by Mel Schwartz

http://accurx.net/Pharmacogel.html http://www.narang.com/laboratory-products/burets/index.php http://medgadget.com www.mrsec.wisc.edu.com www.wikipedia.com www.smart-material.com
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http://bme.usc.edu/UTRC/info/pubs/Electroceramics.pdf http://www.siemens.com/innovation/en/publikationen/publications_pof/pof_spring_2003/mat

erials_articles/bioengineering.htm

http://www.mdtmag.com/tags/Products/Materials/?page=2http://www.mdtmag.com/Products/2012/02/Antimicrobial-Grades-of-Polymer-Offering-Expanded/

http://www.natureasia.com/asia-materials/highlight.php?id=657 http://sciencenotes.ucsc.edu/1001/pages/hydrogel/hydrogel.html http://pmr.cuni.cz/Data/files/PragueMedicalReport/PMR%2007-01%20Pilathadka.pdf http://www.tmj.ro/article.php?art=8354908538128542 www.sciencedaily.com www.physorg.com www.design-technology.com www.rsc.org www.nitinol.com
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