Submitted by

Ashish Dua

INTRODUCTION

Biomedical textiles are textile products and constructions for medical and biological applications.

These are used in contact with tissue, blood, cells and other living substances.

Main attributes

Bio stability(It is the ability of a material to perform with an appropriate host,

responsible for a specific application)

Biocompatibility(It is ability of the device to perform its intended function, with the desired

degree of incorporation in the host)

MEDICAL TEXTILES AND BIOMEDICAL TEXTILES

Medical textiles

These are textile products and constructions for medical applications

Applications are:

Protective and healthcare textiles

Dressings, bandages

Hygiene products

Biomedical textiles

These are fibrous structures used in specific biological environments, their

performance depends on biocompatibility with cells and biological tissue or

fluids.

Applications are:

Implantable materials and devices

Tissue engineering

Neural repairs

The design of a biomedical textile is driven by its end function.

The main factors included are:

Function:The textile needs to fulfil the purpose for which it was designed.

Biocompatibility:This refers to the reaction of the textile with blood and tissue in the body.

Cost:This depends on the raw materials, manufacturing process and product

end-use.

Product approval:Each country has its own regulations and standards for medical textiles.

BIOCOMPATIBLE POLYMERS

Protein fibres of biological origin obtained from bovine skin

Properties : Excellent biocompatibility

Low immunogenicity

Uses: Artificial tissues

Wound dressing

Sutures

Soft contact lens

Protein fibres of biological origin and derived from small intestine of sheep or oxen

Properties: Hard to handle

Uses: Sutures

Polylactic acid (PLA)

Cornstarch sugar is fermented into lactic acid, which is then polymerised

Properties: Slow degrading polymer

Good tensile strength

Uses: Orthopaedic applications

Polyglycolic acid (PGA)

Properties: High tensile modulus

Greater hydrolytic susceptibility

Excellent mechanical properties

Uses: Resorbable sutures

Salts of alginic acid occurring in seaweed.

Properties: Generates a moist healing environment

Uses: Wound healing

Natural biopolymer, contains amino sugars obtained from shells of crabs,

wings of insects, fungi. Alkali treatment of chitin yields chitosan and result

can then be spun into filament having strength similar to viscose structure of

chitin and chitosan.

Properties: Biocompatible

Bacteriostatic

Fungistatic

Uses: Artificial skin

High performance fibres, obtained by pyrolysing PAN

Properties: Low strength

High elongation

Uses: Medical and surgerical applications

CLASSIFICATION OF BIOMEDICAL TEXTILES

Depending upon the fibres used:

These materials are absorbed by the body after 2-3 months of implantation.

For example: Polyamide, Polyurethane

These materials are absorbed slowly by the body after implantation and take

more than 6 months to degrade.

For example: Polyester, Carbon, PTFE

DEPENDING ON AREA OF APPLICATION:o Implantable materials

Sutures

Artificial ligaments

Artificial tendons

Artificial skin

Hernia net

o Scaffolds (Tissue engineering)

Artificial kidney

Artificial liver

Mechanical lung

o Neural repair

IMPLANTABLE TEXTILE MATERIALS

The artificial material replaces the body tissue when healing is notpossible or no replacement tissue is available. Bio hybrid organsconsists of an artificial material which combined with cells.

REQUIREMENTS OF AN IMPLANT

Porosity, this determines the rate at which tissue will grow and encapsulate the implant.

Small circular fibres are better encapsulated by human tissue than larger fibres with irregular cross sections.

Non-toxicity, fibre polymer or fabrication techniques must be non-toxic and fibres should be free of contaminants.

Biodegradability and bio-stability depending on the application. A suitable artificial surface for body cells to adhere to and grow on.

S. No. PRODUCT

APPLICATION

FIBRE TYPE YARN OR FABRIC

TYPE

1. Sutures

Biodegradable

Non-biodegradable

Collagen, Polyglycolide, Polylactide

Monofilament,

braided

Polyamide, Polyester, Teflon, Polypropylene,

Polyethylene

Monofilament,

braided

2. Soft tissue implants

Artificial ligaments

Artificial tendons

Artificial skin

Artificial cornea

Polyethyene, Silk

Braided

Polyamide, Polyester, Teflon Woven, Braided

Low density polyethylene Nonwoven

Polymethyl methacrylate, silicon, collagen Nonwoven

3. Orthopaedic implants

Artificial joint/bonesSilicon, Polyethylene, Carbon Knitted, Woven

4. Cardiovascular implants

Vascular grafts

Heart valvesPolyester, Teflon Knitted, Woven

Polyester Knitted, Woven

SUTURES

Sutures are threads, that are monofilament or multifilament which are

used to sew the open wounds after a surgery. The type of suture used

depends upon physical, biological and chemical culture of the tissue

where it is to be put into.

Characteristics for suture materials

Tensile strength

Non toxic

Strength retention

Knot security Wound before suture

Easy handling properties

Infection potential

They must lack the wick effects

Wound after suture

PROPERTIES OF SUTURES

Handling:

Three properties of a suture affect its handling:

Memory (they tend to stay in one position)

Elasticity (measure of how a suture returns to its original length after

stretching)

Knot strength (force needed for a knot to slip)

Tensile strength:

It is a measure of force necessary to break a suture, the weakest part of a

suture is the knot, consideration of strength is important in areas under

tension.

Natural or synthetic:

Sutures can be made from natural materials- e.g., catgut, silk, or linen.

Natural sutures tend to cause an inflammatory tissue reaction but these are

still useful in some fields as, silk in plastic surgery.

Sutures made from synthetic materials are – Polyester, Polypropylene

Monofilament or multifilament –

Monofilament sutures are single stranded; multifilament sutures are

several strands braided together.

Braided sutures have better handling property but cause tissue drag and the

spaces between filaments can harbour bacteria.

Monofilaments do not have these problems but tend to have significant

memory and can be difficult to handle.

Absorbable or non-absorbable--

Absorbable sutures are constructed from the materials which are broken

down in tissue after a given period of time usually from ten days to four

weeks. They are therefore applied in many inner tissues of the body.

Non Absorbable sutures are made from materials which are not

metabolized by the body, and used either on skin wound closure, where the

sutures can be removed after a few weeks, or in some inner tissues in which

absorbable sutures are in adequate.

o Tissue –

Ultimately, the type of suture depends on where it is to be used. In the skin,

non- absorbable sutures can be used, provided they are removed. Ideally, the

suture should be a monofilament. In the face, sutures should be removed as

quickly as possible to minimise scarring.

Production Process

Produce Filament

Braiding

Stretching & Coating

Needle Attachment

Classification of implantable materials:

Soft Tissue Implants

Hard Tissue Implants

Soft Tissue Implants

Strength and flexibility of textile material make it particularly suitable for

biomedical implants.

Soft tissue compatible biological polymers are collagen, silk protein,

cellulose, chitin and chitosan.

Soft tissue artificial materials include silicone rubber, polyurethane, hydro

gels and carbon fibre.

These includes:

Artificial tendon and artificial ligament

Artificial skin

Hernia net

Artificial cornea

ARTIFICIAL TENDONS AND LIGAMENTS

Ligaments connect bone to bone

Tendons connect muscle to bone

Woven and knitted structures are used asartificial ligaments.

Braided fabrics with a stress strainbehaviour similar to natural tendons orligaments are the most suitablestructures.

Braided composite textile structuresmade from carbon and polyester areparticularly suitable for knee ligamentreplacement.

Bioabsorbable polymers are alsopreferable for manufacturing of ligamentsand tendons.

Major requirements of artificial tendons and

ligaments

Biological

Bio compatibility

Long term stability

Supporting tissue proliferation

Bio mechanical

Physiological progressive stress strain behaviour

Low creeping

High shear strength

Porosity

Flexibility

Skin Dressing

In order to conform to irregular surface, elastic

and flexible materials are used for skin dressing,

which are able to promote skin regeneration.

For flexibility and absorbability of the body

fluid, skin dressing is obtained from woven and

non woven fabrics as well as also from micro

porous layer.

Collagen and chitin are the most commonly

using skin dressing materials, besides which

there is no material which can meet the

requirements of a skin substitute exactly.

The necessary properties for a skin substitute are as follows:

Tissue compatibility

Inner surface structure that permit growth of fibro vascular

tissue

Prevention of wound contraction

Flexibility

Pliability to permit conformation to irregular wound surface

Elasticity to permit motion of underlying body tissues

Resistance to linear and shear stresses

Low cost and indefinite self life.

Two essential requirements for skin dressing:

i) It should prevent the dehydration of the wound and also able to resist the

bacterial entry.

ii) It should be permeable enough to allow the passage of discharge

through pores and cuts.

Hernia net

Meshes are used in hernia repair and abdominal wall replacement, where

mechanical strength and fixation are important.

The composite meshes made up of polyester, polypropylene and carbon fibres.

Required properties of the mesh are:

Strength

Flexibility

Appropriate pore size and pore size

distribution

Good dimensional stability

Easy to mould

Artificial cornea

Soft contact lenses are made of transparent hydro

gel with high oxygen permeability.

Hard contact lenses are made of polymethyl

methacrylate and cellulose acetate butyrate.

Flexible contact lenses are made from silicone

rubber. A specialised polymer Poly 2-hydroxyethyl

methacrylate is commercial used to make contact

lenses.

Lenses should have following properties :

High surface energy

Flexibility

Optical properties

Should be easily wettable by tears

Permeability of the lens to oxygen

HARD TISSUE IMPLANTS

Hard tissue compatible materials must possess excellent mechanical

properties.

Properties of the polymer for hard tissue implants are

Good processability

Chemical stability

Bio compatibility

These includes:

Orthopaedic implants

Cardiovasclar implants

ORTHOPAEDIC IMPLANTS

The applications include artificial bone, bone cement and artificial

joints. Orthopaedic implants are used to replace bones and joints,

and fixation plates are used to stabilize fractured bones. Textile

structural composites like carbon composites have replaced by metal

implants. A non woven man made from graphite and Teflon is used

around the implants to promote tissue growth.

CARDIOVASCLAR IMPLANTS

Categories

Vascular grafts

Heart valves

Vascular Grafts

Vascular graft is an artificial vein or artery

used to replace segments that are blocked or

weakened. Straight or branched grafts are

possible by using either the weft or warp

knitting technology. Knitted vascular grafts

have a porous structure, which allow the graft

to be encapsulated with new tissue.

Disadvantage it can cause blood leakage

through the interstices directly after the

implantation

To reduce this risk, knitted grafts with internal

and external velour surfaces are used

Woven Dacron vascular graft

Knitted Dacron vascular graft

Knitted Dacron bifurcation graft

Requirements of good vascular graft are:

Non-fraying

Flexibility

Durability

Biocompatibility

Stability to sterilization

Resistance to bacteria/viruses

Blood compatibility

Porous structure

Heart valvesThe heart valves assist cardiothoracicsurgeon in treating valvular diseases.

The heart valves are of two types:

• Mechanical valve

• Tissue valve

Mechanical valve are used for youngerpatients and require periodical check-ups andafter a periodical period, the patient need tobe operated a second time. Mechanicalvalves are made up of titanium, aroundwhich is a knitted fabric to be stitched to theoriginal tissue called as sewing ring. Thesewing ring of the caged-disc type ofprostheses uses a silicon rubber insert undera knitted composite PTFE and polypropylenefibre cloth.

Tissue valve are used for slightly agedpatients and do not require any periodiccheckups.

Scaffolds

Tissue engineering support structures or „scaffolds‟ which are artificialdevices, designed to act as templates for attached cells and newly formedtissues. The scaffolds' three-dimensional, porous structures encourage cellattachment, proliferation and migration through an interconnectednetwork of pores. New tissue forms gradually and can be implanted intothe body.

Design factors:

Allow cell attachment and migration

Deliver and retain cells and biochemical factors

Enable diffusion of vital cell nutrients and expressed products

Exert certain mechanical and biological influences to modify the behaviour of the cell phase

Scaffolds used in tissue engineering must also fulfill the following requirements:

Be biocompatible

Resist biodegradation

High porosity

Adequate pore size to facilitate cell seeding and diffusion

Rate of biodegradation should coincide with rate of tissue formation

EXTRACORPOREAL DEVICES

S.No. PRODUCT APPLICATION FIBRE TYPE FUNCTION

1. Artificial liver Hollow viscose Remove waste product

from patient‟s blood

2. Artificial kidney Hollow viscose Separate and dispose

body‟s Plasma proteins

3. Mechanical lung Hollow propylene, Hollow

silicone, silicon membrane

Remove carbon dioxide

from blood and supply

the oxygen

Artificial liver

The liver has multiple functions essential to maintain life including

carbohydrate metabolism, synthesis of proteins, amino acid

metabolism, urea synthesis, lipid metabolism, drug biotransformation

and waste removal. The artificial liver utilizes the functions of separating,

disposing & supply of fresh plasma in hollow viscose fibres or membranes

similar to those used for artificial kidney to perform their function. In the

case of extracorporeal devices, cells are grown to confluence in devices

resembling dialysis cartridges, and then inserted into a „circuit‟ outside the

patient‟s body, where blood from the patient flows through the cartridge,

contacting the cells, and then back into the patient.

Artificial kidney

The kidneys serve as filtering devices of

the blood. The nephrons, the working units

of the kidney, filter waste materials out of

the blood and produce urine to secrete

toxins from body. The kidneys also

maintain normal concentrations of body

fluids, which play a key role in

homeostasis.

The material used in dialysis membranes

are regenerated cellulose, cellulose

triacetate, acrylonitrile copolymer,

poly(methyl methacrylate), ethylene-

vinyl alcohol copolymer, polusulfone

and polyamide which can be grouped as

cellulose and synthetic polymer systems.

The function of the artificial kidney is achieved by circulating

the blood through a membrane, which may be either a flat

sheet or a bundle of hollow regenerated cellulose fibres in the

form of cellophane. In an external artificial kidney, a

haemodialyser, is used which can perform many of the

functions of a kidney. Since the dialyser is a foreign substance

to the human body, when the blood is circulated through the

dialyser, the leucocyte count in the blood decreases over the

first 20 minutes of dialysis, but recovers to its original value

after 1 hour. It is made up from a bundle of hollow fibres

through which the blood circulates. The objective is to

improve the surface of hollow fibres so that the leucocyte

decrease does not occur. Hemodialysis includes removal of

metabolic substances, adjustment of electrolytes and pH and

removal of excess water by ultrafiltration and dialysis, which

is usually a membrane separation process.

Mechanical lung

Oxygenate body‟s blood and remove cellular by products most of whichconsisted of CO2.The microporous membranes of the mechanical lungpossess high permeability to gases but low permeability to liquids andfunctions in the same manner as the natural lung allowing oxygen tocome into contact with the patient‟s blood.

Silicone or polypropylene fibres are used for fabricating mechanical lung soas to allow the permeation of gases. The mechanical lung should ideally functionfor at least 1 to 3 weeks. But the present mechanical lung can function only for aweek. This is because, ability to remove carbon dioxide falls off. The lung is aform of gas exchanger to supply oxygen to the blood and remove carbon dioxide.Microporous membranes that provide high permeability for gas flow and lowpermeability for liquid flow which is similar to the natural lung where oxygenand blood come into contact. In these devices, oxygen flows around hollow fibresat extremely low pressure. Blood flows inside of the fibres. The oxygenpermeates the micropores of the fibres and comes in contact with the blood. Thepressure gradient between the blood and oxygen is kept near zero to preventmixing of oxygen and blood. Red blood cells capture oxygen by diffusionprocess.

PP hollow fibre exhibits good compatibility with blood and excellent gaspermeability. Its use allows a design of a compact artificial lung that is easy andsafe to operate. However, its long term use causes a leak of blood plasmacomponents.

Neural Repair

Nerve guidance channel

These are used to bridge the damaged nerve endings and facilitate the

passage of molecules secreted by the nerve and bar fibrous tissue from

infiltrating the area thus preventing repair. An innovation is the use of

electrically conducting polymers such as polypyrole to promote nerve

regeneration by allowing a locally applied electrical stimulus. It is a

blossoming field of textile research, since the nerve guidance channel may

be a single continuous hollow tube, or it may be a hollow tube comprised of

fibres.

Technology: Extruded Tube In vitro: cells growing into the tube In vivo: neural implant

FUTURE DEVELOPMENTS

o Auxetic fibers:

Bandage made of polymers such as Teflon , polypropylene and nylon are used

in fabrics that are projected for use in wounds that swell. As the wound swells,

the auxetic bandage does as well. The inner “voids” of the bandage would

release the healing agent during the healing process and once it begins to heal,

the bandage will contract and the healing agent will stop being released. Thus,

the auxetic fibres provide a means of controlled drug delivery.

o Shape-memory:

These materials store a permanent shape to memory as well as maintain their

temporary shape, so that when they are in the compressed temporary form, they

can be inserted into the body through a small incision and then upon reaching

body temperature would change to the permanent shape. These materials can

also be biodegradable, so that repeat surgery for removal of the implant would

not be required.

Electronics :

The use of electronic devices in textile implants is envisaged, for example,

as monitors in artificial arteries, stents and heart valves constructed from

textiles. When the implant begins to not function properly, they would act as

warning devices and trigger electrical pulses or the release of drugs to

overcome the problem, at least temporarily.

Controlled drug delivery :

Drugs present as additives in resorbable fabrics would gradually be released

on breakdown of the fabrics. Another intriguing innovation is the

development of soluble glass fibres for the controlled release of drugs in a

wide range of concentrations and delivery periods.

REFERENCES

1. Supriya Pal, Asian Textile journal, June 2009, Pg 47

2. O.L. Shanmugasundaram, Asian Dyer, April 2008, Pg 54

3. J. Hayavadana & Anil Kumar, Asian Textile Journal, September 2006, Pg 81

4. Indra Doraiswamy & K P Chellamani, Asian Textile Journal, December 2008, Pg 49

5. S. Viju, The Indian Textile Journal, June 2008, Pg 75

6. M K Panthaki, The Indian Textile Journal, Feburary 2008, Pg 63

7. S. Viju, Asian Textile journal, May 2008, Pg 37

8. Dr S K Basu, The Indian Textile Journal, December 2008, Pg 91

9. O.L. Shanmugasundaram, Asian Dyer, October 2007, Pg 56

10. M L Gulrajani, ATT, Jan- March 2008, Pg 29

11. Dr J Srinivasan & S Kathirvelu, The Indian Textile Journal, October 2006, Pg 45

12. O.L. Shanmugasundaram, The Indian Textile Journal, September 2008, Pg 99

13. A. K. Moghe & B. S. Gupta, TJTI, Vol. 99 No. 5, Pg 467

14. Henen Jedda, Saber Ben Abdessalem TJTI, Vol. 99 No. 3, Pg273

15. www.expresstextile.com

16. http://www.csiro.au/science/TissueEngineering.html#

17. US Patent 6146651

18. Biomedical Textiles, Maria Cieslewski, November 13, 2006, ELE 382