2. BIOMATERIALS- CLASSIFICATION
When a synthetic material is placed within the human
body, tissue reacts towards the implant in a variety of
ways depending on the material type.
The mechanism of tissue interaction depends on the
tissue response to the implant surface.
Biomedical materials can be divided roughly in to
three main types governed by the tissue response.
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Biomaterial lecture 2
MSc: Amir N.Saud
3. BIOINERT BIOMATERIALS
The term bioinert refers to any material that once
placed in the human body has minimal interaction
with its surrounding tissue.
Examples of these are stainless steel, titanium,
alumina, partially stabilized zirconia, and ultra high
molecular weight polyethylene.
Generally a fibrous capsule might form around bioinert
implants hence its biofunctionality relies on tissue
integration through the implant.
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Biomaterial lecture 2
MSc: Amir N.Saud
4. BIOACTIVE BIOMATERIALS
Bioactive refers to a material, which upon being placed
within the human body interacts with the surrounding
bone and in some cases, even soft tissue.
This occurs through a time –dependent kinetic
modification of the surface, triggered by their
implantation within the living bone .
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Biomaterial lecture 2
MSc: Amir N.Saud
5. BIORESORBABLE BIOMATERIALS
Bioresorbable refers to a material that upon placement
within the human body starts to dissolve and slowly
replaced by advancing tissue (such as bone).
Common examples of bioresorbable materials are
tricalcium phosphate [Ca3(PO4)2] and polylactic-
polyglycolic acid copolymers.
Calcium oxide, calcium carbonate and gypsum are other
common materials that have been utilized during the
last three decades.
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Biomaterial lecture 2
MSc: Amir N.Saud
6. CLASSIFICATION OF BIOMATERIAL BASED ON THE APPLICATION IN
THE MEDICAL FIELD BIOMATERIAL
• Metals and alloys biomaterials
• Ceramics biomaterials
• Polymer biomaterials
• Composite biomaterials
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Biomaterial lecture 2
MSc: Amir N.Saud
7. METALLIC IMPLANT MATERIALS
Metals are used as biomaterial due to their excellent electrical and thermal
conductivity and mechanical properties. Since some electrons are independent
in metals, they can quickly transfer an electric charge and thermal energy. The
mobile free electrons as the binding force to hold the positive metal ions
together. This attraction is strong, as evidenced by the closely-packed atomic
arrangement resulting in high specific gravity and high melting points of most
metals
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Biomaterial lecture 2
MSc: Amir N.Saud
8. METALLIC IMPLANT MATERIALS
Metals have been used in various forms as implants. The first metal developed specifically for
human use was “Sherman Vanadium Steel,” which was used to manufacture bone fracture plates
and screws. Most metals used for manufacturing implants (e.g., Fe, Cr, Co, Ni, Ti, Ta, Mo, and W)
can be tolerated by the body in minute amounts. Sometimes those metallic elements,
in naturally occurring forms, are essential in cell functions (Fe), synthesis of a vitamin B12 (Co),
but cannot be tolerated in large amounts in the body. The biocompatibility of implant metals is of
considerable concern because they
can corrode in the hostile body environment. The consequences of corrosion include loss of
material, which will weaken the implant, and probably more important, that the corrosion
products escape into tissue, resulting in undesirable effects.
biomaterial
Biomaterial lecture 2
MSc: Amir N.Saud
9. METALLIC IMPLANT MATERIALS
Some metals are used as passive substitutes for hard tissue
replacement
such as:
1- Total hip;
2- Knee joints;
3- For fracture healing aids as bone plates and screws;
4- Spinal fixation devices;
5- Dental implants, because of their excellent mechanical
properties, and
corrosion resistance;
6- Vascular stents;
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Biomaterial lecture 2
MSc: Amir N.Saud
10. THE MOST COMMON METALLIC IMPLANT ALLOYS
*Stainless steel
Stainless steel was first used successfully as an important material in the surgical field. And its
type:
I- Type 302 stainless steel was introduced, which is stronger and more resistant to corrosion than
the vanadium steel;
II- Type 316 stainless steel was introduced, which contains a small percentage of molybdenum
(18-8sMo) to improve the corrosion resistance in chloride solution (salt water).
III- Type 316L stainless steel. The carbon content was reduced from 0.08 to a maximum amount
of 0.03% for better corrosion resistance to chloride solution.
*The ASTM (American Society of Testing and Materials) recommends type 316L rather than
316 for implant fabrication, Even type 316L stainless steels may corrode inside the
body under certain circumstances, such as in a highly stressed and oxygen-depleted region.
They are, however, suitable to use in temporary devices such as fracture plates, screws, and
hip nails.
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Biomaterial lecture 2
MSc: Amir N.Saud
11. These materials are usually referred to as cobalt-chromium alloys. There are
basically two types:
1- The CoCrMo alloy [ Cr (27-30%), Mo (5-7%), Ni (2.5%)] has been used for
many decades in dentistry, and in making artificial joints;
2- The CoNiCrMo alloy [Cr (19-21%), Ni (33-37%), and Mo (9-11%)] has
been used for making the stems of prostheses for heavily loaded joints, such as
knee and hip.
The ASTM lists four types of CoCr alloys, which are recommended for
surgical implant applications:
1) CoCrMo alloy [Cr (29-30%), Mo (5-7%), Ni (2.5%)];
2) CoCrWNi alloy [Cr (19-21%), W (14-16%), Ni (9-11%)];
3) CoNiCrMo alloy [Ni (33-37%), Cr (19-21%), Mo (9-11%)];
4) CoNiCrMoWFe alloy [Ni (15-25%), Cr (18-22%), Mo (3-4%), W (3-4%),
Fe (4-6%)].
biomaterial
Biomaterial lecture 2
MSc: Amir N.Saud
12. The two basic elements of Co-based alloys form a solid solution of up to 65 w/o Co and
the remainder is Cr. Molybdenum is added to produce finer grains, which results in
higher strength, The chromium enhances corrosion resistance.
One of the most promising wrought Co-based alloys is the CoNiCrMo alloy originally
called MP35N (Standard Pressed Steel Co.), which contains approximately 35 w/o Co
and Ni each. The alloy has a high degree of corrosion resistance to seawater (containing
chloride ions) under stress
The superior fatigue and ultimate tensile strength of the wrought CoNiCrMo alloy
make it very suitable for applications that require a long service life without fracture or
stress fatigue. Such is the case for the stems of the hip joint prostheses. This advantage
is more appreciated when the implant has to be replaced with another one since it is
quite difficult to remove the failed piece of implant embedded deep in the femoral
medullary canal
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Biomaterial lecture 2
MSc: Amir N.Saud
13. TITANIUM AND ITS ALLOYS
Titanium and its alloys are getting great attention in both medical
and dental fields because of:
(a) Excellent biocompatibility;
(b) Light weight;
(c) Excellent balance of mechanical properties;
(d) Excellent corrosion resistance.
Biomaterial lecture 2
MSc: Amir N.Saud
14. They are commonly used for implant devices replacing failed
hard tissue, for example,
(1) artificial hip joints,
(2) artificial knee joint,
(3) bone plate,
(4) dental implants,
(5) dental products, such as crowns, bridges and dentures,
(6) used to fix soft tissue, such as blood vessels
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Biomaterial lecture 2
MSc: Amir N.Saud
15. One titanium alloy (Ti6Al4V) is widely used to manufacture implants.
The main alloying elements of the alloy are Aluminum (5.5-6.5%) and
Vanadium (3.5-4.5%). The addition of alloying elements to titanium enables it
to have a wide range of properties:
1- Aluminum tends to stabilize the a-phase; it increases the
transformation temperature from a- to b-phase.
2- Vanadium stabilizes the b-phase by lowering the temperature
of transformation from a to b.
In the elemental form, titanium has a high melting point (1668oC) and
possesses a hexagonal closely packed structure (hcp) a up to a temperature of
882.5oC. Titanium transforms into a body centered cubic structure (bcc) b above
this temperature.
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Biomaterial lecture 2
MSc: Amir N.Saud
16. titanium-nickel alloys show unusual properties, that is,
after it is deformed the material can snap back to its
previous shape following heating of the material. This
phenomenon is called (shape memory effect) SME. The
equiatomic TiNi or NiTi alloy (Nitinol) exhibits an
exceptional SME near room temperature: if it is plastically
deformed below the transformation temperature it reverts
back to its original shape as the temperature is raised.
Biomaterial lecture 2
MSc: Amir N.Saud
17. DENTAL METALS
Dental amalgam is an alloy made of liquid mercury and
other solid materials particulate alloys made of silver, tin,
copper, etc. The rationale for using amalgam as a tooth
filling material is that since mercury is a liquid at room
temperature it can react with other metals such as silver
and tin and form a plastic mass that can be packed into the
cavity, and which hardens (sets) with time
The solid alloy is mixed with (liquid) mercury in a
mechanical vibrating mixer and the resulting material is
packed into the prepared cavity
.
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Biomaterial lecture 2
MSc: Amir N.Saud
18. The final composition of dental amalgams typically contains
45% to 55% mercury, 35% to 45% silver, and about 15% tin
after fully set in about one day.
Silver -- increases strength and expansion
Tin -- decrease lengthens the setting time.
Copper -- increases strength, reduces tarnish and corrosion,
and reduces creep
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Biomaterial lecture 2
MSc: Amir N.Saud
19. GENERAL CHARACTERISTICS OF
AMALGAM
--ease of manipulation
--acceptable marginal adaptation
--technique insensitivity
--self sealing
--biocompatible
--good wear resistance
--low cost
20. GOLD AND GOLD ALLOYS
Gold and gold alloys are useful metals in dentistry as a result
of their durability, stability, and corrosion resistance. Gold
fillings are introduced by two methods: casting and malleting.
Cast restorations are made by taking a wax impression of the
prepared cavity, making a mold from this impression in a
material such as gypsum silica, which tolerates high
temperature, and casting molten gold in the mold. The
patient is given a temporary filling for the intervening time.
Gold alloys are used for cast restorations, since they have
mechanical properties superior to those of pure gold.
Corrosion resistance is retained in these alloys provided they
contain 75 w/o or more of gold and other noble metals
.
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Biomaterial lecture 2
MSc: Amir N.Saud
21. Copper, alloyed with gold, significantly increases its strength. Platinum
also improves strength, but no more than about 4% can be added.
Silver compensates for the color of copper.
Gold alloys of different composition are available. Softer alloys
containing more than 83% gold are used for inlays, which are not
subjected to much stress. Harder alloys containing less gold are chosen
for crowns and cusps, which are more heavily stressed.
Malleted restorations are built up in the cavity from layers of pure gold
foil. The foils are degassed before use, and the layers are welded
together by pressure at room temperature. In this type of welding the
metal layers are joined by thermal diffusion of atoms from one layer to
another. Since intimate contact is required in this procedure, it is
particularly important to avoid contamination. The pure gold is
relatively soft, so this type of restoration is limited to areas not
subjected to much stress
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Biomaterial lecture 2
MSc: Amir N.Saud
22. OTHER METALS
Tantalum has been subjected to animal implant studies and
has been shown very biocompatible. Due to its poor
mechanical properties and its high density (16.6gm/cm3) it
is restricted to few applications such as wire sutures for
plastic surgeons and neurosurgeons, and a radioisotope for
bladder tumors.
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Biomaterial lecture 2
MSc: Amir N.Saud
23. NiCu and CoPd alloys are of interest in cancer treatment since their
magnetic properties enable them to be heated by an oscillating
magnetic field. In this form of cancer treatment, referred to as
hyperthermia, a “seed” (1 cm long, 1 mm diameter) is implanted in the
tumor, then subjected to induction heating to kill tumor cells without
harming adjacent tissue. This method is used for prostate cancer.
Induction heating is by a Helmholtz coil at radio frequency
(RF).
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Biomaterial lecture 2
MSc: Amir N.Saud
24. Surface modifications of metal alloys such as coatings by
plasma spray, physical or chemical vapor deposition, ion
implantation, and fluidized bed deposition have been used
in industry. Coating implants with tissue compatible
material such as hydroxyapatite, oxide ceramics, bio-glass,
and pyrolytic carbon are typical applications in implants.
Such efforts have been largely ineffective if the implants
are subjected to a large loading. The main problem is in the
eliminating of the coating or eventual wear of the coating.
The added cost of coating or ion implanting hinders the use
of such techniques unless the technique shows unequivocal
superiority compared to the non-treated implants.
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Biomaterial lecture 2
MSc: Amir N.Saud
