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BIOMATERIALS
ENT 311/4
Lecture 9
Blood Contacting Implants or
Devices
Prepared by: Nur Farahiyah Binti Mohammad
Date: 26th August 2008
Email : [email protected]
Teaching Plan
COURSE CONTENT
and identify
blood contacting
implant.
Describe and
recommend primary
requirements for
biomaterials for blood
contacting implant.
Discuss the
development of
biomaterials for long
term implant
Identify common
problems for heart
valve prosthesis, total
artificial hearts and
pace makers
DELIVERY
MODE
LEVEL OF
COMPLEXITY
Lecture
Knowledge
Define
Supplement
Repetition
Application
Analysis
Evaluation
COURSE
OUTCOME
COVERED
Ability
to describe
the concept of
biocompatibility &
basic concepts of
materials used in
medical application
Ability
to select
biomaterials that
can be used for
different medical
applications and
explain the criteria
that will lead to a
successful implants
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1.0 Introduction
Blood contacting implants or devices
have a direct contact with the blood.
 Blood comes in contact with foreign
materials either for a short term or
long term.

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1.0 Introduction

Short term extracorporeal
devices (outside the body):
Dialyzers
 Blood oxygenator
 Tubes and catheters for
transport the blood

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1.0 Introduction

Long term blood contacting implant:
Heart valves prostheses
 Vascular grafts
 Cardiac pacemakers
 Implantable artificial organs

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2.0 Primary requirement

The primary requirement for biomaterials for
long-term implants are:








Blood compatibility (blood compatible)
Non-toxicity
Durability
Non-irritating to tissue
Resistant to platelet and thrombus deposition
Nondegradable in physiological enviroment
Do not absorb blood element
Do not release foreign substance
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3.0 Design consideration
The implant should mimic the function
of organ that it replace without
interfering with the surrounding
anatomical structures.
 Must be suitable size and weight
 Biomaterial chosen must be easily
available, inexpensive, easily
machinable and sterilizable.

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3.0 Design consideration

As an example: artificial heart valve is required to
open and close on an average once every second
(valves open and close 30 million times per year).
The biomaterial chosen must be such that the valve
is durable and will not fail under fatigue stress after
implantation in patient.
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Revision
“ Biocompatibility is the ability of a
material to perform with an appropriate
host response in a specific application”
(William, 1987).
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Revision

In vivo test for tissue compatibility
1. Sensitization
2. Irritation
3. Intracutaneous
reactivity
4. Systemic toxicity (acute toxicity)
5. Subcronic toxicity (subacute toxicity)
6. Genotoxicity
7. Implantation
8. Hemocompatibility (Blood compatibility)
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4.0 Blood compatibility

Blood compatibility can be defined as the
property of material or device that permits it
to function in contact with blood without
inducing adverse reactions.

Implant should not


Induce coagulation (blood clotting)
Damage blood cells
 Should not induce Hemolysis (the breaking
open of red blood cells and the release of
hemoglobin into the surrounding fluid)
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4.0 Blood compatibility
4.1 Blood Coagulation

Coagulation is a complex process by
which blood forms clots.
4.1.1 Mechanism:
 Intrinsic
 Initiated
by blood contact with either a
damaged portion of the blood vessel wall or
another thrombogenic (clot causing) surface.
 Takes 7-12 minutes to form a soft clot
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4.0 Blood compatibility

Extrinsic
 Result
of the presence of a foreign body or
tissue damage (other than blood vessel)
 Takes 5-12 seconds to form a soft clot
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4.0 Blood compatibility
4.1.2 Factor affect the blood compatibility
of a material
i.
Surface roughness


Rough surface have a greater surface
area and contact surface with blood
compared to smooth surfaces
Result in faster coagulation
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4.0 Blood compatibility
Surface Charge
ii.

The tunica intima (the innermost layer of artery or vein)
of a normal blood vessel has a negative surface charge
due to proteins at surface of the cell membrane.

Formed blood element (red cells, white cells, and
platelets) also have a negative charge.

Natural repulsive force between intima and cells
minimizes cell damage and coagulation
Low surface tension
iii.

Blood cells less likely to adhere to a surface with a low
surface tension
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4.0 Blood compatibility
iv.





Heparinized surfaces
Heparin is a polysaccharide with negative
charge.
Heparin is a naturally-occurring anticoagulant
produced by basophils and mast cells.
Heparin acts as an anticoagulant, preventing the
formation of clots and extension of existing clots
within the blood.
it allows the body's natural clot lysis
mechanisms to work normally to break down
clots that have already formed
Attempt made to attach heparin chemically to
the surface of the implant to prevent blood clot.
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4.0 Blood compatibility
4.2 HEMOLYSIS
 Motion at a blood-surface interface may
damage red and white blood cell resulting in
cell death.
 Damage of cell occurs with shear stresses on
the cells of less than 500dyn/cm2 .
 Chronic and accumulated damage of red
blood cells and leakage of the cellular
contents can result in:



Anemia
Kidney Failure
Toxemia
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Blood contacting implant
or devices
BLOOD IN CONTACT
Long term
Short term
Heart valve prostheses
Vascular grafts
Cardiac pacemakers
Blood oxygenator of
heart lung machine
Dialyzer of hemodialysis
machine
Tubes and catheters for
transport the blood
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5.0 Heart valve prostheses
HEART VALVES
 Heart valves are very important, as they
prevent the backflow of blood, which
ensures the proper direction of blood flow
through the circulatory system.
 Without these valves, the heart would have
to work much harder to push blood into
adjacent chambers. The heart is composed
of 4 valves: tricuspid, pulmonary, mitral,
and aortic.
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5.0 Heart valve prostheses
HEART VALVE PROBLEMS
 There are numerous complications and
diseases of the heart valves that prevent the
proper flow of blood.
 Heart valve diseases fall into two categories,

Stenosis


The stenotic heart valve prevents the valve from
opening fully, due to stiffened valve tissue. Hence, there
is more work required to push blood through the valve
Incompetence.

the incompetent valves cause inefficient blood
circulation by permitting backflow of blood in the heart
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Stenosis
Incompetence
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5.0 Heart valve prostheses
TREATMENT OPTIONS
 On a large scale, medication is the
best alternative, although in some
cases defective valves have to be
replaced with a prosthetic valve in
order for the patient to live a normal
life
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5.0 Heart valve prostheses
MAIN PROSTHETIC HEART VALVE

Heart valve prostheses can be classified
into two type:
1.
2.

Mechanical prostheses : made of non-biological
materials.
Biological heart valve: made of biological tissue
Heart valves are designed to fit the
peculiar requirements of blood flow
through the specific chambers of the heart,
with emphasis on producing more central
flow and reducing blood clots.
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5.0 Heart valve prostheses
1.
a)


MECHANICAL PROSTHESIS
Caged ball
This valve uses a small
ball that is held in place
by a welded metal cage.
The ball in cage design
was modeled after ball
valves used in industry
to limit the flow of fluids
to a single direction
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5.0 Heart valve prostheses
b.



Tilting disc
Have a polymer disc held in
place by two welded strut
The disc floats between the
two struts in such a way, as to
close when the blood begin to
travel backward and then
reopen when blood begin to
travel again.
The titling-disc valves open at
an angle of 60° and close shut
at rate of 70 times/minute
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5.0 Heart valve prostheses

Advantages:
Provide improved central flowwhile still
preventing backflow
 Reduce mechanical damage to blood cells
 Reduce blood clotting and infection


Problem:

Have a tendency for the outlet strut to
fracture as a result of fatigue from the
repeated ramming (smash into) of the
struts by the disc.
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5.0 Heart valve prostheses
Bileaflet valves
Consist of two semicircular
leaflets that pivot on hinges
Advantages:
c.



Provide the closest approximation
to centarl flow achieved in natural
heart valve.
Disadvantages:



They do not close completely,
which allows some backflow.
Since backflow is one of the
properties of defective valves, the
bileaflet valves are still not ideal
valves.
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5.0 Heart valve prostheses
d.



Trileaflet heart valve
Afford true central flow
characteristic with reduced
back flow
Good wear characteristic.
Significantly improve patient’s
quality of life.

This will be achieved due to reduced
consumption of anticoagulants by the
patients, reduced noise, low blood
hemolysis, and the elimination of the
need for repeated implantations
because of high reliability of the
mechanical design.
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5.0 Heart valve prostheses

BIOMATERIAL USED IN MECHANICAL HEART VALVE
Heart valve type
Component
Biomaterial
Caged ball
Ball/occluder
Cage
Silicone rubber (Silastic)
Cobalt-chromium alloy (Stellite 21®) or titanium
Silicone rubber inser under knitted composite
Teflon and polypropylene cloth
Suture ring
Tilting disc
Leaflet
Housing/strut
Suture ring
Polyacetal (Delrin®),pyrolytic carbon, ultra height
molecular polyethylene (UHMWPE)
Cobalt-chromium alloy (Haynes 25®) or titanium
Teflon® or Dacron®
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5.0 Heart valve prostheses
Heart valve type Component
Biomaterial
Bileaflet
Leafleat
Housing
Suture ring
Pyrolytic carbon
Pyrolytic carbon
Double velour Dacron® tricot knit polyester
Trileaflet
Leaflet
Ring
Pyrolytic carbon
Titanium alloy coated with high-density
turbostratic carbon
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5.0 Heart valve prostheses
Advantages of mechanical
heart valve
High durability- typically
last for the lifetime of the
patient
Disadvantages of
mechanical heart valve
1. The increased risk of
blood clotting
2. When blood clots of
any kind occur in the
heart, there is a high
probability of a heart
attack or stroke.
3. Patient need to take
anti-coagulant drug
4. Anti-coagulant caused
birth defects in the
first trimester of fetal
development
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5.0 Heart valve prostheses
2.
i.
ii.
BIOLOGICAL/ PROSTHETIC TISSUE HEART
VALVE
Human tissue valves
Animal tissue valve
Advantages:

Design of valve are closer to the design of
the natural valve.

Do not require long term anticoagulant

Do not cause damage to blood cells

Do not suffer from many of structural
problems experienced by the mechanical
heart valve
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Human Tissue valve
Homograft: valves that are transplanted
from another human being
Autograft: valves that are transplanted
from one position to another within the
same person.




Dysfunctional aortic valve (exit of the left
ventricle) is removed, patient’s pulmonic valve
is then transplanted to the aortic position.
A homograft pulmonic valve is usually used to
replace the patient’s pulmonic valve.
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Human Tissue valve
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Animal tissue valve
Refereed as heterograft or xenograft
valves.
 The two common prosthesis valve from
animal tissue are:

PORCINE VALVES
 BOVINE PERICARDIAL VALVE

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Animal tissue valve

PORCINE VALVES
 Valve
tissue from pig
 Valve tissue is sewn to a metal wire stent
made of cobalt-nickel alloy.
 The wire is bent to form three U-shaped
prongs.
 A Dacron cloth sewing skirt is attached to the
base of the wire stent, and then the stents
themselves are also covered with cloth.
 Porcine valves have good durability and usually
last for ten to fifteen years.
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Animal tissue valve

BOVINE PERICARDIAL VALVE
 Bovine
pericardial valves are similar to porcine
valves in design.
 The major difference is the location of the
small metal cylinder which joins the ends of
the wire stents together.
 In the case of pericardial valves, the metal
cylinder is located in the middle of one of the
stent post loops.
 Pericardial valves have excellent
hemodynamics and have durability equal to
that of standard porcine valves after 10 years.
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Porcine valve
Leafleat
Stent
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Pericardial valve
Leafleat
Suture ring
Stent
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Biological tissue valves
Heart valve type
Component
Biomaterial
Porcine
bioprosthesis
Leaflets
Porcine aortic valve fixed by stabilized
gluteraldehyde
Polypropylene stent covered with Dacron,
Elgiloy wire covered with porous knitted Teflon
cloth
Stent
Pericardial
bioprosthesis
Suture ring
Dacron, soft silicone rubber insert covered with
porous Teflon cloth
Leaflets
Stent
Bovine pericardial tissue fixed by stabilized
gluteraldehyde
Polypropylene stent covered with Dacron,
Elgiloy wire covered with porous knitted Teflon
cloth
Suture ring
PTFE fabric over silicone rubber filter
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Biological tissue valves
Advantages of biological
heart valve
1.
2.
3.
4.
Design of valve are closer
to the design of the natural
valve.
Do not require long term
anticoagulant
Do not cause damage to
blood cells
Do not suffer from many of
structural problems
experienced by the
mechanical heart valve
Disadvantages of
biological heart valve
1.
2.
Stiffening of the tissue due
to the build up calcium.
Calcification can cause a
restriction of blood flow
through the valve
(stenosis) or cause tears in
the valve leaflets.
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Common problem with
implanted heart valve
Mechanical valve
1.
2.
3.
4.
5.
6.
7.
8.
Thrombo-embolism
Structural failure
Red blood cell and platelet
destruction
Tissue overgrowth
Damage to endothelial
lining
Tearing of sutures
Paravalvular leakage
Infection
Biological tissue valve
1.
2.
3.
4.
Tissue calcification (build
up of calcium around the
tissue
Leaflet rupture
Paravalvular leakage
Infection
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Prosthetic heart valve
type
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Conclusion
The future for replacement heart
valves lies in tissue engineering.
 The most ideal replacement would be
formed from the patient's tissue, and
tailored to the right shape and
dimensions.
 This would improve the biocompatibily
factor, and increase the life expectancy
of the heart valve.

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6.0 VASCULAR GRAFT
BLOOD VESSELS
 Blood vessel are the channels through
which blood is distributed to body
tissue.
 Blood vessel are classified as either:
Arteries (carry blood away from the heart)
 Capillaries
 Veins (carry blood to the heart)

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6.0 VASCULAR GRAFT
BLOOD VESSELS PROBLEMS



Vascular graft is needed to replace diseased
blood vessel such as atherosclerosis blood
vessel and aortic aneurysm .
Atherosclerosis is a disease in which plaque
(plak) builds up on the insides of your
arteries.
Aneurysm is blood-filled dilation (balloonlike bulge) of a blood vessel caused by
disease or weakening of the vessel wall.
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Blood vessel problem
Aneurysm
Atherosclerosis
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6.0 VASCULAR GRAFT
TREATMENT OPTIONS
 The main treatment for atherosclerosis
is lifestyle changes. You also may need
medicines and medical procedures.
 For aortic aneurysms or aneurysms
that happen in the vessels that supply
blood to the arms, legs, and head (the
peripheral vessels), surgery involves
replacing the weakened section of the
vessel with an artificial tube.
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6.0 VASCULAR GRAFT
Type
Description
BIOLOGICAL GRAFT
Autograft
Graft transplanted from part of a patient’s body to
another.
Example: saphenous vein graft for pheripheral bypass
Allograft
Homograft. Transplanted vascular graft tissue derived
from the same species as recipient.
Xenograft
Heterograft. Surgical graft of vascular tissue derived
from animal. Example: moddified bovine heterograft
SYNTHETIC GRAFT
Dacron
PTFE
(polytetrafluoroethylene)
Other
Woven, knitted
Expanded, knitted
Nylon, polyurethane
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6.0 VASCULAR GRAFT

Polyurethane vascular graft
photographed in situ in carotid artery
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Synthetic graft - Dacron

Dacron grafts are manufactured in either a
woven or knitted form.
knitted
woven
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Synthetic graft - Dacron





Woven grafts have smaller pores and do not
leak as much blood.
To reduce the blood loss knitted grafts
should be pre-clotted prior to insertion.
They are less frequently used than woven
grafts.
Dacron grafts have recently been
manufactured coated with protein
(collagen/albumin) to reduced the blood loss
and antibiotics to prevent graft infection.
Dacron grafts are frequently used in aortic
and aorto-iliac surgery.
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Synthetic graft - PTFE
Polytetrafluoroethylene (PTFE) is a
knitted graft.
 Its smooth surface is less
thrombogenic than Dacron.
 Its smooth wall is prone to kinking as
it passes around joints necessitating it
to be externally supported.

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Synthetic graft-stent
graft




A stent graft is a tubular device, which is
composed of special fabric supported by a
rigid structure, usually metal.
The rigid structure is called a stent.
An average stent on its own has no
covering, and therefore is usually just a
metal mesh.
Although there are many types of stent,
these stents are used mainly for vascular
intervention.
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Synthetic graft-stent graft



The device is used primarily in endovascular
surgery. Stent grafts are used to support
weak points in arteries, commonly known as
an aneurysm.
Stent grafts are most commonly used in the
repair of an abdominal aortic aneurysm, in a
procedure called an EVAR (Endovascular
Aneurysm Repair ).
The theory behind the procedure is that
once in place inside the aorta, the stent
graft acts as a false lumen for blood travel
through, instead of into the aneurysm sack.
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Problem

The commonest complications
associated with the use of vascular
grafts are:
Graft occlusion (blockage)
 Graft infection (Graft infection is
thankfully rare (1-2%))
 True and false aneurysms at the site of
anastomosis
 Distal embolisation (blocking of a graft)
 Erosion in to adjacent structures

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Conclusion



Most of the vascular graft are stiffer
compared to the host artery.
Development with more compliant grafts
and in modifying the surface interaction of
the graft with blood may result in reducing
the problems with loss of patency.
Recent advance is to engineered vascular
graft from recipients own tissue. This will
provide better biocompatibility and
performance.
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