1

1. INTRODUCTION

Plastic and polymeric products are now being a part of our life and living

without them is almost beyond thoughts. Plastic products got popularized

and widely being accepted because of many reasons mainly light in weight,

moldability in any shape, non-corrosive in nature, variety of colors, save the

use of plant woods for house hold furniture and above all reusability etc.

plastics are polymeric in nature, so in general inert in nature and suppose to

cause no intracellular reachability and reactivity. The applications of plastic

are rapidly increasing all over the world. Glance of their usages pattern in

daily life indicates that we are approximately surrounded by 70-80% of

them ranging from packaging materials, automobiles, kitchenware and

children toys to the components of the designed products, aircrafts or the

biomedical devices.

Plastics are used in a variety of other consumer and industrial products viz.

textile, fibers, packaging, paints, automobiles, alternate building materials

etc. Due to their versatile properties, plastics are also used in the electronics

such as television, refrigerators, air conditioners, agricultures etc. In

hospital, plastic medical devices are being used for storage and transfusion

of life saving fluids, syringes, blood bags, biomedical implants, tubing and

heart valves for the cardiac patients.

In the present scenario, we find the plastic usage pattern such as in various

sectors. The 33% of plastic is being used for the packaging purpose, 20% in

building construction, 10% in electrical and electronic items, 7% in

automobiles, 5% in agriculture and 25% in the other sectors such as medical

2

and leisure. Plastic use is dominated by single use or short term use, and at

the same time most plastics are extremely persistent in the environment.

―Plastics are important in our society and offer many benefits for human

health and the environment, for instance.‖1, 2

Plastic packaging protects food and goods from getting wasted and/or

contaminated and thereby saves resources.

The light weight packaging material saves fuel and decreases

emissions during transportation.

Plastic water supply systems and storage containers/tanks provide

clean water.

Light plastic materials in cars and aircraft save fuel and decreases

emissions.

Plastic protective clothing and safety equipment (e.g. fire proof

materials, helmets, air bags) protects from injury.

Plastic products for medical applications are very important and

contribute to improved heath (e.g. blood pouches, tubings, disposable

syringes, prosthesis).

The plastic industries in India started with the introduction of products like-

cellulose acetate, acrylics and vinyl. The newer plastics, such as

polyethylene, polypropylene, polystyrene, polycarbonate, polymethyl

methacrylate, polyurethane, polyester and silicones joined polystyrene and

PVC in wide applications. Plastics have increasingly provided the desired

performance characteristics that fulfill consumer requirements at all levels.

They are used in such a wide range of applications because they are capable

of offering desired properties that offer consumer benefits unsurpassed by

any other material. More recently, because of a better understanding of the

3

importance of surface, avoidance of contamination, and control of

molecular weight and molecular weight distribution, the use of synthetic

polymers in the biomedical sciences is increasing.

―Polymers are viewed as important biomedical materials for a number of

reasons, some of which appear contradictory-but only because of different

uses require different properties. Some of the important properties are the

ability to tailor make structures, surface control, strength, flexibility,

rigidity, inertness/reactivity, lightweight, ease of fabrication, ability to

achieve a high degree of purity, compatibility, and the ability of some of

them to withstand long term exposure to the human body a truly hostile

environment. Surface hydrophobicity / hydrophilicity, presence/absence of

ionic groups, chemical and physical surface are all important considerations

as one design a material for a specific application. In 1997, Dow introduced

syndiotactic polystyrene under the trade name Questra. Targeted areas

include medical, automotive, and electronic applications. Index, an

ethylene-styrene interpolymer, was introduced in 1998 and is intended to

compete with block copolymers such as styrene-butadiene, flexible PVC,

polyurethanes and polyolefins. It is being used as a modifier for polystyrene

and polyethylene. A number of new materials have been developed because

of the health fears associated with the monomer Bisphenol A, which is the

comonomer for most polycarbonates. The replacement should possess

similar properties to polycarbonates and also be available in large quantity

and inexpensive. One material that has become available is copolymer

polyester developed by Eastman. The structure for this material, Tritan, is

proprietary but is believed to be based on the diol tetramethylcyclo-

4

butanediol. The ring system contributes the necessary stiffness and the

methylenes supply the flexibility.‖ 3

OHOH

CH3H3C

H3C CH3

Tritan

―The global medical device industry is estimated to be between U.S. $ 220

and 250 x 109 in value. This industry continues to show a healthy growth

rate overcoming many economic slowdowns. It is projected to grow from

about U.S. $ 100 billion to almost U.S. $ 300 x 109 in 2015. Figure 1.1

shows the growth from 2000 projected to 2013.‖ 4

Year

Figure1.1 Global medical device markets

0

50

100

150

200

250

300

2000 2005 2008 2009 2010 2013

Val

ue

US

$ B

illio

n

5

―The U S has about 40% of the global market share, followed by Europe,

Japan, and the rest of the world (Figure 1.2). Germany is the largest market

in Europe followed by France, Italy, and the United Kingdom. Japan is the

second largest country by market share next to the U. S. The rest of the

world comprises regions like China, India, and Latin America. These

regions are seeing 10-15% annual growth rates in the medical device

market. One of the reasons for this growth is the population increases in

these regions compared to the United States and Europe. The demand for

health care and medical devices as a result continues to increase for these

regions and globally as well.‖ 4

Figure1.2. Global medical device market share by region

―Medical devices range from simple devices like tongue depressors,

syringes, and bandages to highly sophisticated imaging machines and long

term surgical implants. Medical devices include surgical instruments,

catheters, tubing‘s, coronary stents, pacemakers, MRI machines, X-ray

machines, prosthetic limbs, artificial hips, knees, surgical gloves, and

bandages. Medical device as defined by the U.S. FDA is anything used for

United States, 40%

Europe, 25%

Japan, 15%

Rest of the World, 20%

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therapeutic and/or diagnostic purposes in humans or animals, which is not a

drug. In the European Medical Device Directive a medical device is defined

as a product with a medical intended purpose, whether for diagnosis,

treatment, or alleviation of a medical condition in humans and is not a drug.

Devices are classified into three classes: Class I, Class II, and Class III

depending upon their risk and criticality. Examples of Class I devices are

tongue depressors, bandages, gloves, and simple surgical devices. Class II

devices are wheel-chairs, X-ray machines, MRI machines, surgical needles,

catheters, and diagnostic equipment. Class III devices are used inside the

body. Most implants are Class III devices. Examples include heart valves,

stents, implanted pacemakers, silicone implants, and hip and bone

implants.‖ 4

1.1 Types of Devices

Medical devices can be classified into two major categories- disposables

and non-disposables. Disposable devices include bandages, gloves, blood

bags, colostomy bags, catheters, syringes, IV kits, and tubing.

There is a wide spectrum of requirements that apply to materials used in

medical device applications. It is important to understand these

requirements and design the right part with the right material that fits the

intended use and the processing and assembly of the finished device.

Materials used in the design, production, and assembly of medical devices

include metals, ceramics, glass, and plastics. The use of plastics continues to

grow especially with the growth in disposable products (Figure 1.3).

7

Year

Figure1.3 Global plastics volume in medical devices

―Plastics have superior design flexibility compared to metals, ceramics, and

glass. They can be processed into different shapes, sizes, thickness, and

colors. Their properties can be tailored to meet a wide spectrum of physical,

mechanical, chemical, and biocompatibility requirements.‖ 4

Table 1.1 Summary of Plastics in Medical Device Applications

Property Commodity Plastics Engineering

Thermoplastics

High Temp.

Engineering

Thermoplastics and

other polymers

Percent usage in

medical device

Applications

70% of all plastics

20% of all plastics

10% of all plastics

Types of

Plastics

Polyethylene

Polypropylene

Polystyrene

Polyamides

Polyesters

Polycarbonates

Polyimides

Polyether imides

Polysulfones

0

1

2

3

4

5

6

7

8

1985 1994 2000 2010

Mill

ion

Met

ric

Ton

nes

8

Polyvinyl chloride

Polyurethanes

Acrylics

Acetals

Polyether ether

ketones

Polyphenylene sulfide

Fluoropolymers

Liq. Crystalline

Polymers

Biopolymers

Thermosets and

adhesives

Medical Device

Applications

Tubing

Films

Packaging

Connectors

Labware

I V bags

Catheters

Pacemakers

Drug delivery

components

Membranes

Sutures

Syringes

Surgical instruments

Balloons

Blood set

Components

Blood bowls

Blood oxygenators

Syringes

Catheters

Surgical instruments

Surgical trays

Syringes

Implants

Dental implants

Bone implants

Moving part and

components

Bioresorbable sutures

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1.2 Types of Plastics

There are three major classes of plastics – thermoplastics, thermosets, and

elastomers.

Thermoplastics are those, which once shaped can be softened by the

application of heat and can be reshaped repeatedly, till it loses its property.

e. g. Polyethylene, Polypropylene, Polyvinyl chloride, Polystyrene,

Polyamides, Polyesters, and Polyurethanes. High temperature

thermoplastics include polyether ether ketones, liquid crystalline polymers,

Polysulfones, and polyphenylene sulfides.

Commodity plastics account for about 80% of plastics used for medical

devices in applications like lab ware, tubing, containers and molded

connectors.

Thermoplastics can be further categorized into amorphous and

semicrystalline polymers. Amorphous thermoplastics are long chain

molecules that have no order. Semicrystalline (or crystalline) polymers have

short range order and can align together to form ordered, crystalline

structures within amorphous regions. The extent of alignment and the

amount of crystallinity are determined by the polymers chemical structure,

which determines how well the polymer chains can align with each other.

Semicrystalline thermoplastics are typically opaque compared to amorphous

thermoplastics. Semicrystalline polymers have better chemical resistance

than amorphous thermoplastics because they have a lower amount of

amorphous regions that are permeable to chemicals and solvents.

Thermosets are formed when two or more components chemically react

with each other under ambient conditions or when induced by radiation or

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heat to form a highly cross linked network. The formation of thermosets is

an irreversible process. Thermosets are typically hard and rigid.

Elastomers are loosely cross linked polymers. They have the characteristics

of rubber in terms of flexibility and elasticity e.g. natural rubber, styrene

butadiene block copolymers, polyisoprene, polybutadiene, ethylene

propylene rubber, silicone elastomers, fluoroelastomers, polyurethane

elastomers, and nitrile rubbers.‖4

Poly (ethylene terephthalate) – PET or PETE

It is clear, tough and has good gas and moisture barrier properties making it

ideal for carbonated beverages, food containers and life saving fluid bottles

etc.

Poly (vinyl chloride) – PVC or V

In 1912 German chemist Fritz Klatte at Greisheim Electron unknowingly

made the first PVC in an attempt to create uses for large quantities of

acetylene gas fuel lamps. He had reacted acetylene with hydrochloric acid.

Not knowing what to do with the new material, it was stored for some time

and polymerization took place. It has excellent transparency, chemical

resistant, long term stability, and stable electrical properties. Vinyl products

can be broadly divided into rigid and flexible materials. The application

varies from water pipes and fittings to windows, laminates, blood bags,

medical tubing etc.

Polypropylene – PP

It has excellent chemical resistance and thus commonly used in packaging.

It has high melting point making it ideal for hot fill liquids. Like other

plastics PP has excellent resistance to water, salt and acid solutions that are

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destructive to metals. Typical applications include ketchups bottles,

medicine bottles and automobile battery casings.

Polystyrene –PS

PS is used to make a wide variety of containers, including those known as

‗‗Styrofoam‘‘ plates, dishes, cups, biomedical devices etc.

Other Plastics: Beside these various specialized plastic products can also

be seen in the market such as polycarbonate, polymethylmethacrylate,

Nylon, polyester, Glass fiber reinforced plastics, ABS copolymers, Teflon,

blends and multilayered combinations.

―A medical device that is adequately designed for its intended use should be

safe for that use. The device should not release any harmful substances into

the patient that can lead to adverse effects. Some manufacturers believe that

biocompatibility is sufficiently indicated if their devices are made of

medical grade material or materials approved by FDA as direct or indirect

additives. The term medical grade does not have an accepted legal or

regulatory definition and can be misleading without biocompatibility

testing. There is no universally accepted definition for biomaterial and

biocompatibility, yet the manufacturer who ultimately markets a device

were required by FDA to demonstrate biocompatibility of the product as

part of the assurance of its safety and effectiveness. The manufacturer is

responsible for understanding biocompatibility tests and selecting methods

that best demonstrate the following:

The lack of adverse biological response from the biomaterial

The absence of adverse effects on patients

The diversity of the materials used, types of medical devices, intended uses,

exposures, and potential harms present an enormous challenge to design and

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conduct well-defined biocompatibility testing programs. The experience

gained in one application area is not necessarily transferable to another

application. The same applies to different or sometimes slightly different

(variable) materials. Biocompatibility describes the state of a biomaterial

within a physiological environment without the material adversely affecting

the tissue or the tissue adversely affecting the material. Biocompatibility is a

chemical and physical interaction between the material and the tissue and

the biological response to these reactions. Biocompatibility assays are used

to predict and prevent adverse reactions and establish the absence of any

harmful effects of the material. Such assays help to determine the potential

risk that the material may pose to the patient. The proper use of

biocompatibility tests can reject potentially harmful materials while

permitting safe materials to be used for manufacturing the device.‖ 5

These factors include the type of device, intended use, liability, degree of

patient contact, nature of the components, and potential of the device to

cause harm. There are no universal tests to satisfy all situations, and there is

no single test that can predict biological performance of the material or

device and reliably predict the safety of the device. The types and intended

uses of medical devices determine the types and number of tests required to

establish biocompatibility. Biological tests should be performed under

conditions that simulate the actual use of the product or material as closely

as possible and should demonstrate the biocompatibility of a material or

device for a specific intended use. These tests were more extensive for a

new material than for those materials that have an established history of

long and safe uses. All materials used in the manufacture of a medical

device should be considered for an evaluation of their suitability for

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intended use. Consideration should always be given to the possibility of the

release of toxic substances from the base materials, as well as any

contaminants that might remain after the manufacturing process or

sterilization.

―Biocompatibility is generally demonstrated by tests utilizing toxicological

principles that provide information on the potential toxicity of materials in

the clinical application. Biocompatibility should not be defined by a single

test. It is highly unlikely that a single parameter were able to ensure

biocompatibility; therefore it is necessary to test as many biocompatibility

parameters as appropriate. It is also important to test as many samples as

possible, therefore suitable positive and negative controls should produce a

standard response index for repeated tests.‖ 5

―Biocompatibility testing should be designed to assess the potential adverse

effects under actual use conditions or specific conditions close to the actual

use conditions. The physical and biological data obtained from

biocompatibility tests should be correlated to the device and its use.

Accuracy, reproducibility, and interpretability of tests depend on the method

and equipment used and the investigator‘s skill and experience.‖ 5

―Toxicity may come from leachable components of the material due to

differences in formulation and manufacturing procedures. Products are

frequently composed of components; however simple examples are a

disposable syringe (needle, barrel, plunger, lubricant, and stopper etc.).

Changing a component can significantly alter the biocompatibility of a

product, and certain components, by the nature of both their composition

and exposure to patients, are more likely to present biocompatibility

problems. An example is the common disposable plastic syringe, of which

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billions are used each year. For the syringe, the most likely problem

component is the stopper—the flexible piece at the end of the plunger. The

stopper is most commonly made of natural rubber, and has direct contact

with fluids entering the body (and frequently a fluid path).

Plastics used in medical device applications must meet stringent

performance requirements through production, packaging, shipping, end

use, and disposal. Many devices and device kits are sterilized before they

are shipped for use. During manufacturing and during end use they also

come in contact with various chemicals, solvents, bodily fluids, skin,

organs, and tissues. The materials used in medical devices must be resistant

to the sterilization methods, chemicals, and fluids that they encounter, be

compatible with bodily fluids, skin and tissues and still maintain their

safety, effectiveness, and functionality. Requirements for plastics use in

medical device include the following:

Material characterization

Sterilization resistance

Chemical and lipid resistance

Extractables and leachables characterization

Biocompatibility and haemocompatibility

Shelf life and stability

Many devices need to be packaged and sterilized either before distribution

or before use. Examples of such device are exam and surgical gloves, clean

room garments, specimen cups, wound care products, sutures, needles,

syringes, catheters, drain bags, IV bags, fluid delivery systems, dialysis

equipments, implants, surgical instruments, dental instruments, surgery

supplies, and combination products.

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All materials used in such medical devices including the plastics used in

them must be capable of being sterilized without loss of performance.

Sterilization can be defined as the removal or destruction of all living

organisms including resistant forms such as bacterial and fungal spores.

Pyrogens are substances that can cause a fever. A product may be sterile but

it still may contain pyrogens.

Cleanliness does not mean sterile.

The main sterilization methods used in medical devices are:

Autoclaving (steam, dry heat)

Ethylene oxide (EtO)

Radiation (gamma radiation, electron beam radiation)

Gamma radiation can negatively affect plastics in the following ways:

Formation of radicals leading to chain scission and degradation

Formation of radicals leading to cross linking

Color change

Chain scission leads to degradation and reduces toughness, elongation, and

impact strength. The high energy gamma radiation forms radicals along the

polymer chain. These radicals subsequently degrade the polymer to lower

molecular weight chains leading to reduce physical properties. However

many stabilizers like phenols, HALS (hindered amine light stabilizers),

phosphates etc have been used to absorb the energy or quench and capture

the free radicals formed, thus preventing degradation. Color correction tints

like ultramarine blue are used to compensate for the color change and

maintain a clear, transparent plastic after radiation. Those polymers that

require stabilization are given bellow:

16

Transparent polymers like polyvinyl chloride, acrylics, polycarbonates, and

polyurethanes have a tinting agent and some polymers also require free

radical scavengers or quenchers to prevent degradation.

Plastics used in medical devices can come into contact with various solvents

and chemicals either during the manufacturing process or during end use.

The medical devices must maintain their integrity, performance, and

aesthetics when exposed to such solvents and chemicals. Chemical can react

with the additives causing them to leachout of the part or form unwanted

byproducts. Chemicals used in a manufacturing environment include the

following:

Acids

Bases

Solvents (methylethyl ketone, tetrahydrofuran, methylene chloride,

ethylene oxide, alcohols, ethyl acetate)

Processing aids-greases, oils, mold release like silicones etc.

Solvents like MEK and THF are used in the joining of plastics. Ethylene

oxide and ethylene glycols are used in the sterilization of plastics. Many

plastics are exposed to mold release agents like silicon sprays during

production.‖ 4

―The following are some of the sources of possible toxic substances in

medical device materials. Each source is then discussed separately.

Residual monomers

Residual solvents

Degradation products

By-products from irradiation

Sterilization residuals

17

Formulation additives

Inadvertent contaminants

Bacterial endotoxins

Residual monomers

Polymerization results in a distribution of molecular weights. Although

monomers are usually toxic, the toxicity of the polymeric unit generally

decreases as the molecular weight increases. Residual monomers result

from incomplete polymerization; their concentration can be controlled by

carefully regulating polymerization conditions.

Residual solvents

Solvents are often an integral part of manufacturing and may remain behind

in fluid materials such as adhesives, adhesive removers, barrier pastes, gels,

or lubricants. Some acrylate adhesive systems are now water-based, which

eliminates the concern for residual solvents. When the solvent is an integral

component of the final product, as with adhesive removers and certain

barrier pastes, its presence and potential transdermal absorption must be

addressed in labeling.‖5

Degradation products

Materials may undergo degradation during manufacture, sterilization, or

storage, or after application to or implantation in the body. During

manufacture, heat may thermally degrade a material; polyvinyl chloride is

especially susceptible to heat and may release hydrochloric acid, resulting in

an autocatalytic unzipping process. During sterilization,

polytetrafluorethylene is susceptible to irradiation breakdown, resulting in

the release of hydrofluoric acid. Stored materials exposed to light and

oxygen may suffer ultraviolet degradation or oxidation. Implanted

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materials, particularly metals, may corrode or be biologically degraded. 6

Stabilizers added to the polymer can protect against degradation. Materials

should be tested for degradation and biocompatibility only after both

manufacture and a suitable ageing period.

By-products from irradiation

Gamma irradiation is becoming an increasingly common method of

sterilization; 2-3 Mrad is the usual sterilization dose. It is also used to

facilitate cross-linking in certain formulations. As a result, many materials

undergo degradation. Polyglycolic acid, used in suture production, is

virtually destroyed by irradiation. Most medical polymers decrease in

molecular weight as a result of chain scission. Polypropylene and other

polymers may undergo chain scission, cross-linking, and oxidation. Any

material that is irradiation sterilized should be tested for biocompatibility

afterward, although most medical polymers remain useful.

Sterilization residuals

―Chemical sterilization with ethylene oxide has a long history of use; the

main advantages are that the procedure is carried out at low temperatures

and the sterilization facility need not deal with radioactive sources. Ethylene

oxide, which is itself toxic, also degrades into toxic ethylene chlorohydrin

and ethylene glycol. Even after extensive degassing, some materials do not

release these toxic molecules. All materials that are to be ethylene oxide

sterilized must be tested for toxic residuals. The principle concerns with the

biocompatibility of polymers are additives, residual monomers, and

contaminants that are leachable in the body. The result of the additives and

contaminants being in plastic is that a range of toxic materials may be

leached from many plastics. Identified toxic materials in polymers i.e.

19

Aluminium, Acrylonitrile (monomer), Arsenic, Benzene, Benzoic peroxide,

Bisphenol A, Cadmium, Carbon tetrachloride, Dibutyl tin, Epoxy curing

agents, Ethylene dichloride, Ethylene oxide, Formaldehyde, Ketones and

hydrocarbons, Lead, Mercaptobenzothiazole, Methyl chloride, Methylene

chloride, Methylene dianiline, Nickel, PAHs on carbon black, Pyrene,

Tricresyl phosphate, Triphenyl phosphate.‖ 5

1.3 Plastics and their Additives

The finished plastic material is made by the chemical chain called as

monomer and several other chemicals added to give its desired shape, color

and several other properties which are known as additives. There are about

2000 additives utilized in various types of plastic and can be divided in

following common major classes:

Antiblocking agents, Antimicrobial agents, Antioxidants, Antistatic agents,

Coloring agents, Fillers, Impact modifiers, Mold release agents, Plasticizers,

Preservatives, Slip agents, Stabilizers (light and heat) etc.

1.3.1 Antioxidants

Antioxidants are additives that retard or inhibit the oxidative degradation of

the plastic material within the intended processing and usage limits of the

materials. ―Degradation is initiated by the action of highly reactive free

radicals caused by heat, radiation, mechanical shear, or metallic impurities.

The initiation of free radicals may occur during polymerization, processing,

or fabrication. Once the first step of initiation occurs, propagation follows.

The function of an antioxidant is to prevent the propagation steps of

oxidation. It must be effective at low concentration, non toxic, conveniently

and safely handled, and low in cost. Beside this, it must not impart

20

undesirable characteristics to the system in which it is used. Antioxidants

are classified as primary or secondary antioxidants depending on the

method by which they prevent oxidation.‖ 7

The most widely used antioxidants in plastics are phenolics. Phenolics are

mainly used in polyolefins, styrenics, and engineering resins. Phenolics are

generally stain resistant and include simple phenolics (BHT), various

polyphenolics, and bisphenolics. A phenolic antioxidant may then be used

for long term protection. Primary antioxidants are generally radical

scavengers or H- donors i.e. hindered phenols such as BHT, Irganox1010,

or Irganox 1076, cyanox 2246 and 425 and bisphenol A. Long term

protection for the polymer, secondary antioxidants is typically

hydroperoxide decomposers i.e. trivalent phosphorus compounds such as

tris-nonylphenyl phosphate (TNPP) is the most commonly used

organophosphite followed by tris (2, 4-di-tert-butylphenyl) phosphate

(Irgafos 168). Organophosphite are used in polyolefins, styrenics, and

engineering resins. Phosphite can improve colour and engineering resins

stability, but can be corrosive if hydrolysed. Thioesters act as secondary

antioxidants and also provide high heat stability to a variety of polymers

(polyolefins and styrenics). Secondary antioxidants are typically used in

synergistic combination with primary antioxidants. Lactone stabilizers are a

new class of materials that are reputed to stop the autoxidation process

before it starts.

21

CC

OH

BHT

C

C

HO CH2 CH2 C

O

H2

C C4

Irgnox 1010

O

O O

P

Irgafos 168

22

1.3.2 Plasticizers

According to the ASTM D-883 definition, a plasticizer is a material

incorporated into a plastic to increase its workability, flexibility, or

dispensability. The addition of a plasticizer may lower the melt viscosity,

elastic modulus, and Tg. It should be relatively non volatile, non mobile,

inert, inexpensive, nontoxic, and compatible with the system to be

plasticized. The plasticizers are chemically and thermally stable organic

solvents or low melting solids which when mixed with a polymer modifies

its flow as well as the mechanical and electrical properties. Waldo Semon

patented the use of tricresyl phosphate as a plasticizer for PVC in 1933.

This was later replaced by the less toxic di-2-ethylhexyl phthalate (DEHP),

which is now the most widely used plasticizer. The worldwide production

of plasticizer is approximately 3.2 million tons annually. Volume wise,

about 90% of the plasticizers are used with PVC and PVC containing

systems. Plasticizers can be broadly classified into four types according to

their chemical constitution; phthalates, aliphatic esters, phosphates and

miscellaneous. The USEPA regulates many phthalates and adipates by

methods 606, 506-1, and 8061. There is a balance between compatibility

and migration. Generally, the larger the ester grouping the less the migration

up to a point where compatibility becomes a problem and where

compatibility now becomes the limiting factor. The development of

plasticizers has been plagued with toxicity problems. Thus, the use of highly

toxic polychlorinated biphenyls (PCBs) has been discontinued. Phthalic acid

esters, such as DEHP, may be extracted from blood stored in plasticized

PVC blood bags and tubing. These problems have been solved by using

oligomeric polyester as non migrating plasticizers instead of DEHP, in

23

appropriate situation. Recently, some limited tests have indicated a

relationship of prenatal exposure to phthalates and reproductive

abnormalities of male babies.

O

OR1

OR2

O

Phthalates

O

O

O

O

CH3

CH3

DMP

O

O

O

O

CH2CH3

CH2CH3

DEP

O

O

O

O DOP

24

O

O

O

O

DEHP

O

O

O

O

CH2CH2CH2CH3

CH2CH2CH2CH3

DBP

1.3.3 Stabilizers

Stabilizers are used to prevent the degradation of a material due to high

processing temperatures or to extend their life stability under degrading

environmental conditions. The effectiveness of a stabilizer also depends on

the presence of oxygen i.e. some are effective in its presence while other are

less effective. The effectiveness of a stabilizer is very much dependent upon

the grade of resin (degree of polymerization) in which they are

compounded. Some stabilizers are highly effective in one grade of PVC but

only moderate in another. A judicious choice of stabilizers is therefore very

important in the formulation of plastic. The presence of other additives such

as plasticizers and fillers also sometimes strongly influence the efficiency of

a stabilizer for e.g. Phosphates and chlorinated extenders often reduce the

efficiency of a stabilizer. The major classes of stabilizers are mixed metal

salt blends, organotin compounds, alkyl/aryl organophosphate, epoxy

compounds, polyfunctional alcohols etc.

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Light Stabilizers

―Light stabilizers are used to protect plastics, especially polyolefin‘s,

polystyrenes, from discoloration, embrittlement, and degradation by UV

light. The major classes of light stabilizers are:

UV absorbers excited state quenchers, and free radical terminators.

UV absorbing materials

―UV absorbing materials are the substances which give characteristic

absorption peak in UV region. The commonly used UV absorbing materials

are derivatives of benzophenones, benzotriazoles, phenyl esters,

diphenylacrylates, which are added during the synthesis of plastic to protect

them from degradation from sunlight and fluorescent light.‖ 7

“Benzophenones UV absorbers have been used for many years in

polyolefin‘s, PVC, and other resins. Some important benzophenones are, 2-

hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2,

4- dihydroxy-4-n-dodecycloxybenzophenone.‖ 7

O

benzophenone

26

O

OC8H17

OH

2-hydroxy-4-n-octoxybenzophenone

“Benzotriazoles UV absorbers are highly effective in high temperature

resins such as acrylics and polycarbonate. Some important benzotriazole are

2-(2-hydroxy-5-methylphenyl) benzotriazole, 2, 2-(2-hydroxy-5-tert-

octylphenyl) benzotriazole, 2-(32-tert-butyl-2-hydroxy-5 methylphenyl) -5

chlorobenzotriazole, 2-(32, 52-di-tert-butyl-22 hydroxyphenyl)-52

chlorobenzotriazole etc.‖ 7

CH3

N

N

N

HO

2-(2-hydroxy-5-methylphenyl) benzotriazole(Tinuvin PED)

“Benzoates and salicylates such as 3, 5-di-t-butyl-4-hydroxy benzoic acid

n- hexadecyl ester function by rearranging to 2-hydroxybenzophenone

analogs when to UV light to perform as UV absorbers.

Phenyl esters like 3, 5-di-t-butyl-4-hydroxybenzoic acid N-hexadecyl ester.

O

OCH3

OH

2-hydroxy-4-methoxybenzophenone

27

Diphenylacrylates like Ethyl-2-cyano-3, 3-diphenyl acrylate, 2-ethylhexyl-

2-cyano-3, 3-diphenyl acrylate.

Nickel compounds are used as excited state quenchers and hindered amine

light stabilizers (HALS) are used as free radical terminators.‖ 7

1.4 Cytotoxicity

The cell or tissue culture including cytotoxicity methods is a fair predictor

of biocompatibility when used together with other appropriate tests. 8, 9

Several highly specialized cell culture methods are available to monitor the

biocompatibility of the raw materials used in manufacturing the device or

auditing the manufacturing process. Cell or tissue culture testing offers

several advantages, including the following:

It is simple, rather inexpensive, and easy to perform.

It allows testing of a biomaterial on human tissue.

It is sensitive to toxic material. It is easy to manipulate and allow

more than one end-point investigation.

It can be used to construct a dose-response curve.

It can give quick and quantitative results and allows direct access or

direct observation or measurement.

The objective of cell cytotoxicity testing is to screen the biocompatibility of

the polymeric and elastomeric portions of medical devices using

mammalian cell cultures. Cytotoxicity is a useful method for screening

material. It can also serve as a quality control mechanism for batch testing

programs, and is a basic part of all device biocompatibility evaluation.10-12

It

is one of the oldest assays designed specifically to screen plastics for

toxicity.13

Given the extreme sensitivity of this test, materials found to be

cytotoxic must be assessed along with the results of in vivo and other

28

studies to evaluate the risk to human health. Unlike the other studies utilized

in biocompatibility testing, cytotoxicity is not a pass or fail test. Failure in

cytotoxicity is generally grounds for performing a confirmatory test such as

an implantation or intracutaneous reactivity.14

The great majority of toxic

compounds are chemically stable and produce their characteristic effects by

interference with biochemical or physiological homeostatic mechanisms.

Cytotoxicity assays measure loss of some cellular or intercellular structure

and/or functions, including cell death. They are generally simple to perform,

are reproducible, and have a clearly defined endpoint. A variety of cell lines

have been used, including corneal epithelial cells, lung fibroblasts, Chinese

hamster ovary (CHO) cells, canine renal cells, HeLa (human tumor cell

line) cells, and microorganisms. Most cells in culture are fibroblasts.

Primary cells that are taken directly from an animal often are difficult to

establish in culture and become fibroblasts, losing the normal functions of

growing differentiated cells. Numerous conditions have to be optimized for

obtaining good growth of differentiated cells. Most cultured cells have a

fibroblastic appearance, although they may not be true fibroblasts. For

example, cells grown under non optimum conditions can temporarily take

an appearance of fibroblasts. The fibroblasts in culture can take over

cultures because they grow readily on plastic surfaces. The recent success in

growing differentiated cells was partially due to techniques that have been

developed to remove and limit the growth of fibroblasts to allow other cells

to grow. The possible cytotoxicity end points are15-18

as follows:

Microscopic examination of cell morphology, membrane integrity, and

fragility, Cell population and density, Cell adhesiveness, Cytopathic effect,

Total protein content, Rate of growth, Rate of protein synthesis, Total DNA

29

content, Rate of DNA synthesis, Colony-forming efficiency, Trypan blue

uptake and other dye uptake, Biochemical assays of enzymes.

Much of the initial work on the range of cytotoxicity assays that have been

developed (and their end point measurement methods) was done with the

goal.19-25

Early cell culture methods merely estimated the numbers of living

or dead cells, but now morphological analysis by electron microscopy

reveals a spectrum of microcellular changes, and cell function tests measure

biochemical parameters, indicating the nature of cell stress. Although many

modifications have been made, cell culture tests are of four main types: gel

diffusion, direct contact, extracts dilution, and cell function tests.

As discussed above, several tissue culture methods are available for testing

biomaterials. These are divided into two major groups: one tests the toxicity

of a soluble extract of the material, and the other tests the toxicity by the

direct contact of cells with the material or components of the device.

The text extracts is incorporated into the culture medium, which is usually

double strength minimum essential medium supplemented with serum and

other essential nutrients at the maintenance level. The toxic effect on the

monolayer, such as cell lysis and microscopic observation of cell

morphology changes, is usually checked after 24 and 48 hr. Cell lysis can be

scored by direct microscopic observation or with the use of radiolabels or

tryphan blue dye uptake. The inhibition of cell growth is a more informative

test requiring more time and skill. Distilled water extract is incorporated

into the tissue culture medium and inoculated with the cells in the tissue

culture tubes. After 72 hr, the extent of cell growth is determined by total

protein assay, such as the Lowery photometric method, on the removed cells

from the individual tubes. Most cells in culture are fibroblasts. Primary

30

cells that are taken directly from an animal often are difficult to establish in

culture and become fibroblasts, losing the normal functions of growing

differentiated cells. Numerous conditions have to be optimized for obtaining

good growth of differentiated cells.

1.5 Testing medical disposables using the Limulus Amoebocyte

Lysate (LAL) test

The discovery of the horseshoe crab's most significant biological role in

recent medicine was made by Frederick Bang in the early 1950's. Bang

discovered that the horseshoe crab's blood cells, called amoebocytes,

contain a clotting agent that attaches to dangerous endotoxins produced by

gram negative bacteria. The test was accepted by the United States Food

and Drug Administration (FDA) in 1983 as a standard test for endotoxins.

In 1987, the FDA established guidelines for LAL testing of pharmaceuticals

and medical devices.

During the early days of the pharmaceutical industry it was noticed that

some solutions when injected into the bloodstream induced fevers.

Investigations found that almost all of these fevers were associated with a

group of contaminants termed pyrogens. These were classified as either

exogenous or endogenous pyrogens. Exogenous pyrogens are fever causing

materials found in the environment, of these endotoxins are the most

researched and are lipopolysacchrides (LPS), found in the outer membrane

of the cell wall of Gram -ve microorganisms, they are heat stable and can

cause severe patient reactions when present in parenterals or medical

devices. Endotoxin toxicity is not dependent upon a living cell, heat

sterilization or other chemical/physical processes are ineffective control

measures as killing the cells actually releases 'free' endotoxin from the cell

31

wall. As all mammals can be affected by endotoxins (although sensitivity

levels vary) one of the first tests used to determine if endotoxins were

present, was the Rabbit Pyrogen Test (RPT). A rabbit was inoculated with

the test substance and then monitored it to see if a fever was induced. This

test however does not give a quantitative result, is time consuming and is

not suitable for products that may in themselves adversely affect the animal.

The most commonly used approach now is a Limulus Amoebocyte Lysate

or LAL test. The LAL test focuses in particluar on 2-keto-3-deoxyoctonoic

acid and it is this which is used as an indicator in the majority of endotoxin

assays. LAL is a reagent derived from the blood cells of the horseshoe crab,

unlike a mammal the crab does not have a developed immune system,

however the LAL component in its blood will bind to and inactivate

endotoxins, in the crab the resulting clot also forms a protective barrier

against bacterial infection. At its simplest the LAL test consists of adding

LAL reagent to the sample in a test tube, incubating at 37°C for 1 hour. The

tube is then gently inverted if a gel or clot has formed then a positive result

is recorded.

The Gel-clot is the simplest and most widely used, it is also fully described

by most pharmacopeias. The method can be qualitative or semi-quantitative

when comparing a sample against a dilution series of an endotoxin standard.

Can be used to provide a pass/fail for a certain limit and is best used with

low sample numbers. The method may be performed manually with little or

no requirement for instrumentation. Because the potency of an endotoxin to

cause pyrogenic reaction will vary according to the nature of the toxin, the

FDA developed Endotoxin Units (EU) for result comparisons.

32

1.6 Regulations for Medical Devices and Application to Plastics

Suppliers in India

―The Central Drugs Standards Control Organization (CDSCO) under the

Ministry of Health and Family Welfare regulates the licensing, import,

manufacture, and sale of medical devices into the Country. Approval can be

facilitated by evidence of approval from the US FDA, the EU MDD (CE-

Certificate) and approvals from Australia, Canada, Japan, and other

countries. ISO Certification for specific manufacturing practices (ISO

13485) is also accepted. Device master files must contain details of good

manufacturing practices including components and materials used in the

device. It must also include the manufacturing and quality assurance

processes, risk assessment, design verification, sterilization, stability,

biocompatibility, and toxicological data associated with the materials, and

production of the finished device.‖4

Various fillers and additives can be added to plastics to tailor their

properties for specific applications and performance requirements. Fillers

and additives can provide flexibility, stiffness, hardness, conducting

properties, colors, impact, toughness, thermal properties, moisture

transmission and gas barrier properties, and surface properties. In addition,

various degrees of chemical resistance, radiation resistance, and

biocompatibility can be achieved.

33

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