Biomaterials for Soft Tissue Replacement 1

8/16/2019 Biomaterials for Soft Tissue Replacement 1

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BIOMATERIALS Biomedical Engineering

Sem-III

Prof. Arunkumar Ram

Module 9: Biomaterials for

Soft Tissue Replacement


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INTRODUCTION

On what factors does success of biomaterials

depends?

1.

Materials used2. Design considerations

2

Prof. Arunkumar Ram Dept. of Biomedical Engg.

B i o m a t e r i a l s

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INTRODUCTION

The success of soft

tissue implant has

been primarily

because of

development of

synthetic polymers.

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INTRODUCTION

Why success of soft tissue is on polymers?

• Polymers can be tailor made to match the

properties of soft tissues.

• Made into various physical forms

• Liquids for space fillings

• Fibers for sutures materials

• Films for catheter balloons

• Knitted fabrics for blood vessels

• Solid forms for weight bearing applications

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INTRODUCTION


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INTRODUCTION


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INTRODUCTION


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INTRODUCTION

Minimal requirement for a soft tissue implant

• They should achieve a close approximation of

physical properties especially flexibility and texture.

• They should not deteriorate or change properties

after implantation with time.

• They should not cause adverse tissue reaction.

• They should be non carcinogenic, nontoxic, non

allergenic, non immunogenic.

• They should be sterilizable.

• They should be low cost8



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SUTURES, SURGICAL T APES AND

A DHESIVES

Two kinds of sutures

• Absorbable

• Non Absorbable

• Also classified on the basis of their origin

• Natural Sutures (catgut, silk and cotton)

• Synthetic Sutures (nylon, polyethylene, polypropylene

• Also classified on their physical form

• Monofilament

• Multifilament

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A DHESIVES

The absorbable suture catgut made up of collagen derived

from sheep intestinal submucosa.

Treated with chromic salt (chromium salt) to increase its

strength and is cross linked.

This treatment extends the life of catgut suture by 3-7

days upto 20-40 days

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A DHESIVES

It is very interesting to know….

Stress concentration at a surgical knot

decreases the suture strength of catgut by half,

no matter what kind of knotting technique you

use.

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A DHESIVES

Most effective knotting technique is the square knot

technique with three ties to prevent loosening.

But one of the studies reveal that whether you make loose

knot or tight knot, there is no measureable difference in

the wound healing

But recommended to have loose suturing, it lessens pains

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A DHESIVES

Catgut and other absorbable sutures (PGA, PLA) invokes

tissue reactions although the effect diminishes as they are

being absorbed.

Silk and cotton show more reaction as compared to synthetic

sutures like polyester, nylon, polyacronitrile.

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A DHESIVES

Risk of Infection

If suture is contaminated, risk of infection may increase

many folds.

Polypropylene, nylon, PGA sutures developed lesserdegrees of infection than sutures made from chromic

catgut and polyester.

The cause of infection is micro organism not biomaterial

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A DHESIVES

Surgical Tapes and Staples

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A DHESIVES

Surgical Tapes and Staples

Why are surgical tapes used?

1. Avoid pressure necrosis (death of body cells/tissues)

2. Scar tissue formations

3. Problem of stitch abscesses (collection of pus)

4. Problems of Weakened Tissues

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A DHESIVES

Problem with Surgical Tapes/Band aids

1. Misaligned Wound edges

2. Poor adhesion caused by moisture, dirt.

3. Wound drainage

4. Late separation of tapes etc…

Applications

Assembling scraps of donor skin for skin graft.

Correcting nerve tissues for neural growth, etc…

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A DHESIVES

STAPLES

Staples made up of metals (Ta, Stainless steel, TI-Ni Alloy)

can be used for closure of large surgical incision

In procedures like Cesrean section

Intestinal surgery

Surgery for bone fracture

Tissue response is similar to synthetic sutures.

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A DHESIVES

STAPLES

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A DHESIVES

STAPLES

Time for a Video

1_GIA Surgical Stapler.mp4

2_surgery simple interrupted suturing

wound.mp4

(WARNING: Light hearted people close

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http://localhost/var/www/apps/conversion/tmp/scratch_3/1_GIA%20Surgical%20Stapler.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/2_surgery%20simple%20interrupted%20suturing%20%20wound.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/2_surgery%20simple%20interrupted%20suturing%20%20wound.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/2_surgery%20simple%20interrupted%20suturing%20%20wound.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/2_surgery%20simple%20interrupted%20suturing%20%20wound.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/1_GIA%20Surgical%20Stapler.mp4


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A DHESIVES

Tissue Adhesives

Special environment of tissues and their

regenerative capacity makes tissue adhesives

difficult.

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A DHESIVES

Ideal Characteristics of Tissue Adhesives

Should be able to wet and bond tissue

Be capable of rapid polymerization without

producing much heat or toxic by products

Be Resorbable

Not to interfere with normal healing process

Have ease of applications during surgery Be Sterilizable

Have adequate shell life

Ease of large scale production22



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A DHESIVES

Alkyl-α-cyanoacrylate is best know tissue

adhesive

With addition of some plasticizers and

adhesive they are commercially available as

Eastman 910®, Crazy Glue®

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A DHESIVES

0

100

200

300400

500

600

700

1 3 7 10 14

Suture

Methyl-2-

cyanoacrylate

TIME (days)

Bond Strength

(grams)

Bond Strength of Wounds with different closure materials 24



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A DHESIVES

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Bond strength of adhesive treated wound is about

half that of sutured wounds after 10 days.

Because of lower strength and lesser

predictability of in vivo performance, this is

limited to use after trauma in fragile tissues or

after extensive surgery in soft tissue.


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PERCUTANEOUS AND SKIN IMPLANTS

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Percutaneous devices (Trans or through the

skin)

Artificial kidneys, hearts

Prolonged injection of drugs and nutrients.

Artifical skin (maintaining body temperature of

several burned patients)


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Percutaneous Devices

Problem of obtaining a functional and viable interface

between the tissue and implant (percutaneous) is due to

following factors

1. Initial attachment of the implant with the tissue may

occur but this may not continue for a long time

• Dermal tissue cells turn over continuously and dynamically

2. Down growth of epithelium around the implant mayoccur.

3. Opening large enough may give way for bacteria to

penetrate.


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Many variables are involved in development of

percutaneous devices

1. End-use factors

• Transmission of information (biopotentials, temperature,

pressure, blood flow rate)

• Energy (electrical stimulation, power for heart assistdevice)

• Matter (cannula for blood)

• Load (attachment of prosthesis)


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prcutaneous devices

2. Engineering factors

• Material selection: polymers, ceramics, metals, and composites

• Design Variation: button, tube, porous or smooth surface.

• Mechanical Stresses: soft or hard tissue interface, porous or smoothinterfaces


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prcutaneous devices

3. Biological factors

• Implant host: man, dog, hog, rabbit, sheep, etc

• Implant location: abdominal, dorsal, forearm, etc.

4. Human Factors

• Postsurgical care

• Implantation technique

• Esthetic look


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PD-Skin Interface

D

A

B

C

E

Epidermis

Dermis

Hypodermis

Fascia


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PD-Skin Interface

A. Interface between epidermis and PD should be completely

sealed against invasin by foreign organisms

B. Interface between dermis and PD should reinforce the

sealing of A, as well as resist mechanical stresses.

C. Interface between hypodermis and PD should reinforce the

function of B

D. Implant material should meet all requirement of an implant

for soft tissue replacement.

E. The line where epidermis, air and PD meet is called a three

phase line which is similar to A


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Artificial Skin

• An example of percutaneous implants.

• Material that can adhere to a large(burned) surface

and thus prevent the loss of fluids, electrolytes, and

other biomolecules until the wound is healed.

• Autografting and Homografting are the only

permanent skin implant solution available.


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Artificial Skin

• Several polymeric materials including reconstituted

collagen have also been tried as burns dressings.

• Among them are co-polymers of vinyl chloride and

acetate and methyl-2-cynoacrylate.

• Plastic tapes have sometimes been used to hold skin

grafts during microtoming (ultrathin sectioning)

and grafting procedures.


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Artificial Skin

• Several polymeric materials including reconstituted

collagen have also been tried as burns dressings.

• Among them are co-polymers of vinyl chloride and

acetate and methyl-2-cynoacrylate.

• Plastic tapes have sometimes been used to hold skin

grafts during microtoming (ultrathin sectioning)

and grafting procedures.


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M AXILLOFACIAL IMPLANTS

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Maxillofacial Implants

The art and science of anatomic, functional, or

cosmetic reconstruction by means of artificial

substitutes of those regions in the maxilla,

mandible, and face that are missing or defective

because of surgical intervention, trauma, etc.


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There are many polymeric materials available for

extraoral implants which requires

1. Color and texture should match with the patients

2. Mechanically and chemically stable

3. Easily fabricated

Polyvinyl chloride and acetate copolymers Polymethyl

methacrylate silicone and polyurethane rubbers, are

currently used.


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For maxillary, mandibular and facial bone defects,

metallic materials such as tantalum, titaniu and Co-Cr

alloys etc. are used.

For soft tissues like gum and chin, polymers such as

silicone rubber, PMMA etc. are used for augmentation.


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E AR AND E YE IMPLANTS

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Ear Implants

The use of implants can restore the

conductive loss from otosclerosis (a heredity defect that

involves a change in the bony tissue of the ear

Chronic otitis media (inflammation of middle ear, which

may cause partial or complete impairment of the ossicular

chain: malleus, incus and stapes)


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Ear Implants

Stapes Prosthesis


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Ear Implants

Incus Replacement Prosthesis


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Ear Implants

Whole ossicular chain Prosthesis


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Ear Implants

Polyethylene total ossicular replacement

This porous polyethylene total ossicular replacement

implant is used to obtain a firm fixation of the implant bytissue in growth.

Helps in sound conduction.


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Ear Implants

Materials used

Poly tetra fluoroethylene

Ploy ethylene

Silicone rubber

Stainless steel

Tantalum

Polytetrafluoroethylene-carbon composite (Proplast)

Porous polyethylene (Plastipore)

Pyrolite Carbon (Pyrolite)


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Ear Implants

Artificial Ear Implants capable of processing speech have

been developed and are undergoing clinical evaluation.

Implants have got electrode to stimulate the cochlearnerve cells.

Also speech processor-converts sound waves into electrical

signals.


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Ear Implants


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Ear Implants

3_How the VIBRANT SOUNDBRIDGE Middle Ear

Implant Works.mp4

http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/3_How%20the%20VIBRANT%20SOUNDBRIDGE%20Middle%20Ear%20Implant%20Works.mp4


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Eye Implants

• Eye implants used to restore the functionality of

cornea and lens when they are damaged or diseased.

• Cornea is usually transplanted from a suitable donor.


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Eye Implants

Usually made from “transparent” acrylics, especially

PMMA, which has a comparatively high refractive

index (1.5)

Intraoccular lenses implanted surgically to replace

the original eye lens


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Eye Implants

4_Eye Implants For The Blind.avi.mp4

5_Retinal Implants.mp4

http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/5_Retinal%20Implants.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4http://localhost/var/www/apps/conversion/tmp/scratch_3/4_Eye%20Implants%20For%20The%20Blind.avi.mp4


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BLOOD INTERFACING IMPLANTS

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Blood Interfacing Implants divided into two categories

Short Term Devices

Membranes for artificial organs (kidney and heart/lung

machine)

Tubes catheters for transport of blood

Long term Implants

Vascular implants

Implantable artificial organs

Pacemakers


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Requirement for Blood Interfacing Devices

Blood Compatibility

Blood Coagulation

Implant should not cause blood coagulation

Implants should not cause damage to proteins, enzymes,

and blood components (RBC, WBC and Platelets)

Implants should not cause hemolysis (red blood cell

rupture)


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Vascular Implants

Early Arterial replacements were solid wall tubes made of

glass, aluminum, gold, silver and PMMA.

These implants developed clots and became useless.

1950’s porous implants were introduced, but there was tissue

ingrowth. This minimizes clotting.

Proper fixation of the Implant.


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Vascular Implants

Crimping of Blood vessels done to prevent kinking when the

implants is flexed.

Crimping allows expansion of the graft in the longitudinaldirection which reduces strain on the prosthesis wall.

Arteries expand circumferentially and longitudinally to

accommodate the pulsatile flow of the blood.


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Vascular Implants

The type of material, geometry of implant influence the rate

and nature of tissue ingrowth.

No. of polymeric material used to fabricate implants Nylon

Polyester

PTFE

Polypropylene

Silicon Rubber

Recently a pyrolytic carbon coated arterial graft has been developed by

technique of ULTI deposition


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Heart Valve Implants

Four Valves in Human body

Left ventricular valves become incompetent more

frequently

More importantly Aortic Valve


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An artificial heart valve is a mechanism that mimics the

function of a human heart valve

It’s used for patients with a heart valvular disease or have a

damaged valve

Heart valves are used to provide the heart with a

unidirectional blood flow

They act as pumps


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1960’s –Flexible leaflets that mimicked the natural valves.

But the leaflets could not bear the fatigue for more than 3

Years.

Hemolysis, Regurgitation, incompetence were major problem


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Material Requirement for heart valves same as that of

vascular implants.

Additional requirement of blood flow and pressure regulation.

Formed elements of blood should not be damaged.

Blood pressure should not drop below clinically significant

value.


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Heart Valve Implants-Types

Mechanical- There are three types. The caged ball, tilting

disk, and bi-leaflet

Tissue(biological)- valves that are used from animals to

implant them back into humans


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All the types of mechanical heart valves are still in use today.

Usually made of titanium or carbon which makes them strong

and very durable

Three types of mechanical heart valves


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Using valves from other animals.

The porcine valve of a pig is the

most comparable valve to a human.

Xenotransplantation

Pericardial valves: Biological valve

tissue can be taken from a cow or

horses pericardial sac and be sewed

to a metal frame.


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All valves have sewing ring that is covered with various polymeric

fabrics.

This helps during initial fixation of the implant

Later the ingrown tissue will render the fixation viable in a

manner similar to the porous vascular implants.

The cage itself is usually made of metals and covered with fabrics

to reduce noise, or with pyrolytic carbon.

The disc is coated with pyrolytic carbon at the same time.


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The ball (or disc) is usually made of a hollow structure composed

of solid polymers

Polypropylene

Polyoxymethylene

Polychlorotrifluoroethylene

Metals (titanium, Co-Cr alloys) or pyrolytic carbon deposited on graphite

substrate.


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Heart Valve Implants-Advantages

Mechanical heart valves: The biggest advantage is the

durability. While the tissue heart valves are estimated to last

about 10-15 years, a mechanical heart valve can last 30 year

Tissue heart valves: There is minimal blood regurgitation,

minimal transvalvular pressure gradient, self repairing.

Does not require and anti-coagulant drug.


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Heart Valve Implants-Disadvantages

Mechanical heart valves – In order to decrease the risk of

blood clotting, the patient must take blood thinners. Some

patients can hear their mechanical heart valve open and

close.

Tissue heart valves – Wear, there is a small possibility that the

body will reject the valve, inability to implant them into infantsand children.

.


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Heart Valve Implants-Implanting

Both mechanical and tissue heart valves require open heart

surgery

It’s more common in tissue valves for a re-operation

Complete recovery from surgery could be a couple of weeks

to several months

Currently: 55% mechanical valves

45% tissue valves


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Artificial Heart

Useful for short term use in keeping the patients with

end stage heart disease alive until a transplant heart

becomes available.

Concern is the power supply

Externally powered supply

Can keep alive person for 112 days

But external connection restricted the movements.


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Artificial Heart


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Artificial Heart


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Pacemakers

A cardiac pacemaker use to assist the regular contraction rhythm

of heart muscles.

It should deliver the exact amount of electrical stimulation to the

heart at varying heart rates.

Consist of conducting electrodes attached to stimulator.


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Pacemakers

Electrodes are well insulated with rubber (usually silicone or

polyurethane) except for tip which is sutured or directly

embedded into the cardiac wall.

The tip is usually made up of non corrosive noble metal with

reasonable mechanical strength such as Pt-10%Ir Alloy.

The most significant problems are the fatigue of the electrodes

(they are coiled like spring to prevent this) and formation of

collagenous scar tissue at the tip, which increases threshold

electrical resistance at the point of tissue contact.


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Pacemakers

Battery and electronic components are sealed by a titanium case

while the electrodes outlet are sealed by polypropylene cuff.

Changed after 2-5 years due to limitation of the power source.

Nuclear powered pacemaker is also commercially available.

Lithium powered batteries now available


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Pacemakers


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Artificial Kidney Dialysis Membrane

Primary function of kidney to remove metabolic waste product.

Achieved by passing blood through glomerulus under a pressure

about 75 mm Hg.


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The main filtrate is urea (70 times the urea content of normal

blood)

Sodium

Chloride

Bicarbonated

Potassium

Glucose

Creatinine and uronic acid


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Artificial kidney uses a synthetic semipermeable membrane to

perform the filtering action in a way similar to that of a natural

kidney

The membrane is the key component of the artificial kidney

machine.

In addition it also consists of a bath of saline fluid into which the

waste products diffuse out from the blood to a vein.


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Three types of kidney dialyzers are available


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Flat Plate Dialyzer

First developed and have two or four layers.

Blood passes through the spaces between the membrane layers while the

dialysate passes through the spaces between the membrane and restraining

boards.


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Coil Membrane

Consist of two cellophane tubes (9 cm in circumference and 108 cm long) are

flattened and coiled with an open mesh spacer material of nylon.


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Hollow Fiber Membrane

Made up of hollow fibers

Each fibers have dimension of 255 and 285 um inside and outside diameter and

13.5 cm long.

Each unit contains about 11,000 hollow fibers.

The blood flows through the fibers while dialysate is passed outside of the

fibers


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The fibers can also be made from (soda-lime) glass which is made

porous by phase separation techniques.

Can be cleaned and sterilized.

Majority membranes are made up of cellophanes, which is derived

from cellulose.

Cupraphane

Visking

Biomaterials for Soft Tissue Replacement 1

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