1. Biomedical & Functional Materials
Marking Scheme will be based on:
Portfolio
Quizzes, tests
Assignment Sessions
Projects & Practical work
Books
Biomaterials Principles and Applications, Joon B. Park, Joseph D. Bronzino
Biomaterials Science: An Introduction to Materials in Medicine, Buddy D. Ratner
Biomaterials, Sujata V. Bhat

2. An Introduction to the course
Functional Materials
Material which is not primarily used for its mechanical properties but for other properties such as physical or chemical.
Biomedical Materials
is a nonviable material used in a medical device, intended to interact with biological systems (Williams, 1987)
Biomaterials are rarely used on their own but are more commonly integrated into devices or implants. Thus, the subject cannot be explored without also considering biomedical devices and the biological response to them.

3. Some Important Definitions
Biomaterials:
Any substance, other than a drug, or a combination of substances, synthetic or natural in origin which can be used for any period of time, as a whole or part of a system which treats, augments or replaces any tissue, organ or function of the body.
A biomaterial is a nonviable material used in a medical device, intended to interact with biological systems (Williams, 1987)
If the word “nonviable” is removed, the definition becomes even more general and can address new tissue engineering and hybrid artificial organ applications where living cells are used.
Consensus:
A nonviable material used in a medical device, intended to interact with biological systems.

4. Some Important Definitions
Medical Device:
An instrument, apparatus, implement, machine, contrivance, in vitro reagent, or other similar or related article which intended for use in the diagnosis , cure, mitigation or treatment of disease or other conditions
It does not depend on being metabolized or being part of a chemical action within or on the body
Implant
Any medical device made from one or more biomaterials that is intentionally placed within the body, either totally or partially buried beneath an surface
it is usually intended to remain there for a significant period of time
epithelial surface 4

5. CHARACTERISTICS OF BIOMATERIALS AS A FIELD
It’s Multidisciplinary
Some disciplines that intersect in the development, study and application of biomaterials include: bioengineer, chemist, chemical engineer, electrical engineer, mechanical engineer, materials scientist, biologist, microbiologist, physician, veterinarian, ethicist, nurse, lawyer, regulatory specialist and venture capitalist.
It Uses Many Diverse Materials
Many different synthetic and modified natural materials are used in biomaterials and some understanding of the differing properties of these materials is important.
A hip joint might be fabricated from metals and polymers (and sometimes ceramics) and will be interfaced to the body via a polymeric bone cement – 3 different types of materials
The End product is the Development of Devices

6. Functional Materials Definition: Examples:
Material which is not primarily used for its mechanical properties but for other properties such as physical or chemical.
Examples:
Superconductors
An element, intermetallic, compound that will conduct electricity without any resistance below a certain temperature
Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields
Dielectric Material
electrically insulating material
contains polar molecules that reorient in external electric field
Used as insulating material between the plates of a capacitator 6

7. Functional Materials - Examples
Ferromagnetic Materials
The ability to become highly magnetic and have the ability to retain a permanent magnetic moment
Future Applications:
The Mercedes-Benz SilverFlow makes use of metallic particles and a special liquid that can be arranged via magnetic fields in different forms, thus creating a different vehicle depending on the user's requirements
Any damage can be self repaired and a variety of color/configuration/size are possible 7

8. Assignment #1 Q1) Explain & Compare the following:
Piezoelectric Materials
Feroelectric Materials
Pyroelectric Materials
Q2) Explain the working principles of the ‘Invisibility Cloak’ and the research so far made in this field
Due Date: 25th Jan 2010

9. Biomedical Materials Biomedical Materials
is a nonviable material used in a medical device, intended to interact with biological systems (Williams, 1987)
By contrast, a biological material is a material such as skin or artery, produced by a biological system.
Artificial materials that simply are in contact with the skin, such as hearing aids and wearable artificial limbs, are not included in our definition of biomaterials since the skin acts as abarrier with the external world.

10. A Little History on Biomaterials
Romans, Chinese, and Aztecs used gold in dentistry over 2000 years ago, Cu not good.
Copper ion poisoning
Aseptic surgery 1860 (Lister)
Bone plates 1900, joints 1930
Turn of the century, synthetic plastics came into use
WWII, shards of PMMA [poly(methyl methacrylate), aka Lucite or Plexiglass] unintentionally got lodged into eyes of aviators, led to its use in lenses
Parachute cloth used for vascular prosthesis
1960- Polyethylene and stainless steel being used for hip implants 10

11. First Generation Implants
“ad hoc” implants
specified by physicians using common and borrowed materials
most successes were accidental rather than by design
Examples
gold fillings, wooden teeth, PMMA dental prosthesis
steel, gold, ivory, etc., bone plates
eyes and other body parts
dacron and parachute cloth vascular implants 11

12. Dental Applications - Gold
Because of its bio-compatibility, malleability and resistance to corrosion, gold has been used in dental work for nearly three thousand years. The Etruscans in the seventh century BC used gold wire to hold in place substitute teeth, usually from a cow or calf, when their own were knocked out. The first printed book on dentistry published in 1530 recommends gold leaf for filling cavities. 12

13. Intraocular Lens 3 basic materials - PMMA, acrylic, silicone
An intraocular lens (IOL) is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as a form of refractive surgery to change the eye's optical power.
Advances in technology have brought about the use of silicone and acrylic, both of which are soft foldable inert materials. This allows the lens to be folded and inserted into the eye through a smaller incision
Acrylic is not always an ideal choice due to its added expense
For a gruesome yet painless eye procedure: 13

14. Material for Intraocular Lens
Silicones are polymers that include silicon together with carbon, hydrogen, oxygen and sometimes other chemical elements
silicones are mixed inorganic-organic polymers with the chemical formula [R2SiO]n, where R is an organic group such as methyl, ethyl, or phenyl
consist of an inorganic silicon-oxygen backbone (…-Si-O-Si-O-Si-O-…) with organic side groups attached to the silicon atoms
They are largely inert, man-made compounds with a wide variety of forms and uses:
Typically heat-resistant, nonstick, and rubber-like, they are commonly used in cookware, medical applications, sealants, adhesives, lubricants, insulation
Poly(methyl methacrylate) (PMMA) is a transparent thermoplastic. It is sold under many trade names, including Policril, Plexiglass, Gavrieli.
Acrylic, or acrylic fiber refers to polymers or copolymers containing polyacrylonitrile. 14

15. Vascular Implants
Parachute cloth and Dacron 15

16. Second generation implants
engineered implants using common and borrowed materials developed through collaborations of physicians and engineers
built on first generation experiences
used advances in materials science
Examples — Second generation implants
Ultra high molecular wt
titanium alloy dental and orthopaedic implants
cobalt-chromium-molybdinum orthopaedic implants
UHMW polyethylene bearing surfaces for total joint replacements
heart valves and pacemakers 16

17. Artificial Hip Joints

18. Third generation implants
bioengineered implants using bioengineered materials
few examples on the market
some modified and new polymeric devices
many under development
Example - Third generation implants
tissue engineered implants designed to re grow rather than replace
artificial skin
cartilage cell procedure
uses your own cartilage cells (chondrocytes) to repair the articular cartilage damage in your knee. When implanted into a cartilage injury, your own cells can form new cartilage
some resorbable bone repair cements
calcium-phosphate bone cements
genetically engineered “biological” components 18

20. Substitute Heart Valves

21. SEM displaying the cross section of a composite disk, which had been seeded with cultured bone marrow stromal cells.

22. Synthetic polymer scaffolds
... in the shape of a nose (left) is "seeded" with cells called chondrocytes that replace the polymer with cartilage over time (right) to make a suitable implant. 22

23. Evolution of Biomaterials
Structural
Soft Tissue Replacements
Functional Tissue Engineering Constructs

25. Assignment #2
Q) Define and differentiate between the following terminologies: Biocompatibility Host reaction Bioinert Bioactive 25

26. Metallic Biomaterials
Metals make attractive biomaterials because of they possess the following properties:
excellent electrical
mechanical properties
closely packed atomic arrangement resulting in high specific gravity and good strength
high melting points
Applications in the human body:
as total hip and knee joints, for fracture healing aids as bone plates and screws, spinal fixation devices, and dental implants
in devices such as vascular stents, catheter guide wires, orthodontic archwires, and cochlear implants 26

27. Metallic Implants Two primary purposes
As prosthesis – to replace a portion of the body such as:
joints, long bones & skull plates
Fixation Devices – to stabilize broken bones while the normal healing proceeds
Bone plates, intramedullary nails, screws and sutures
Problems:
Biocompatibility: The ability of a material to perform with an appropriate host response in a specific situation
Corrosion
Design of metallic implants
Design limitations the of anatomy
Physics properties of the tissue and reactions of the tissue to the implant and of the implant to the tissues (Host Response) 27

28. Different Metallic Biomaterials
Stainless Steel
SS 316
SS 316L
CoCr Alloys
the castable CoCrMo alloy
The CoNiCrMo alloy which is usually wrought by (hot) forging
Ti alloys
Pure Ti
Ti6Al4V
TiNi Alloys
Nitinol
Shape Memory effect
Platinum group metals (PGM)
Pt, Pd, Rh, Ir, Ru, and Os
extremely corrosion resistant
poor mechanical properties
pacemaker tips
conductivity. 28

29. Development of SS for use in human body
The first metal alloy developed specifically for human use was the “vanadium steel” which was used to manufacture bone fracture plates and screws.
Vanadium steel is no longer used in implants since its corrosion resistance is inadequate in vivo
The first stainless steel utilized for implant fabrication was the 18-8 (type 302 in modern classification), which is stronger and more resistant to corrosion than the vanadium steel.
Later 18-8sMo stainless steel was introduced which contains a small percentage of molybdenum to improve the corrosion resistance in chloride solution (salt water). This alloy became known as type 316 stainless steel
In the 1950s the carbon content of 316 stainless steel was reduced from 0.08 to a maximum amount of 0.03% (weight percent), and hence became known as type 316L stainless steel 29

30. Advantage of SS 316 & 316L over other grades of Steel
Biocompatible
These austenitic stainless steels cannot be hardened by HT but can be hardened by cold working
possesses better corrosion resistance than any other steels
The inclusion of molybdenum enhances resistance to pitting corrosion in salt water

31. The 316L Stainless Steel
(ASTM) recommends type 316L rather than 316 for implant fabrication.
The only difference in composition between the 316L and 316 SS is the maximum content of carbon, i.e., 0.03% and 0.08%, respectively.
So what makes 316L special?????

32. Mechanical Properties & Corrosion Resistance of 316L32

33. Assignment #3
Q) Why is Stainless Steel chosen instead of other grades of Steel for use as a biomaterial? And among Stainless Steel why is 316 L considered to be the most suitable biomaterial? Justify your answers with all possible reasons. Q) Read Chapter #3 of Biomaterials by Sujata Bhat and read chapter 1 of Biomaterials principles and Applications by Joon B. Park Q) What is sensitization of Steel. How can it be restricted?

34. Mechanical Properties & Corrosion Resistance of 316L
Even the 316L stainless steels may corrode inside the body under certain circumstances in a highly stressed and oxygen depleted region, such as the contacts under the screws of the bone fracture plate. Thus, these stainless steels are suitable for use only in Temporary implant devices such as fracture plates, screws, and hip nails.
Surface modification methods are widely used in order to improve corrosion resistance, wear resistance, and fatigue strength of 316L stainless steel
anodization, passivation
glow-discharge nitrogen implantation 34

35. Deficiency Factors Responsible for failure of SS implants
Deficiency of Mo
Use of sensitized steel
Inadvertent use of mixed metals and incompatible components
Topography and metallurgical finish
Improper implant and implant material selection

36. Assignment #2
Q) Define and differentiate between the following terminologies: Biocompatibility Host reaction Bioinert Bioactive 36

37. Metallic Biomaterials
Metals make attractive biomaterials because of they possess the following properties:
excellent electrical
mechanical properties
closely packed atomic arrangement resulting in high specific gravity and good strength
high melting points
Applications in the human body:
as total hip and knee joints, for fracture healing aids as bone plates and screws, spinal fixation devices, and dental implants
in devices such as vascular stents, catheter guide wires, orthodontic archwires, and cochlear implants 37

38. Metallic Implants Two primary purposes
As prosthesis – to replace a portion of the body such as:
joints, long bones & skull plates
Fixation Devices – to stabilize broken bones while the normal healing proceeds
Bone plates, intramedullary nails, screws and sutures
Problems:
Biocompatibility: The ability of a material to perform with an appropriate host response in a specific situation
Corrosion
Design of metallic implants
Design limitations the of anatomy
Physics properties of the tissue and reactions of the tissue to the implant and of the implant to the tissues (Host Response) 38

39. Different Metallic Biomaterials
Stainless Steel
SS 316
SS 316L
CoCr Alloys
the castable CoCrMo alloy
The CoNiCrMo alloy which is usually wrought by (hot) forging
Ti alloys
Pure Ti
Ti6Al4V
TiNi Alloys
Nitinol
Shape Memory effect
Platinum group metals (PGM)
Pt, Pd, Rh, Ir, Ru, and Os
extremely corrosion resistant
poor mechanical properties
pacemaker tips
conductivity. 39

40. Development of SS for use in human body
The first metal alloy developed specifically for human use was the “vanadium steel” which was used to manufacture bone fracture plates and screws.
Vanadium steel is no longer used in implants since its corrosion resistance is inadequate in vivo
The first stainless steel utilized for implant fabrication was the 18-8 (type 302 in modern classification), which is stronger and more resistant to corrosion than the vanadium steel.
Later 18-8sMo stainless steel was introduced which contains a small percentage of molybdenum to improve the corrosion resistance in chloride solution (salt water). This alloy became known as type 316 stainless steel
In the 1950s the carbon content of 316 stainless steel was reduced from 0.08 to a maximum amount of 0.03% (weight percent), and hence became known as type 316L stainless steel 40

41. Advantage of SS 316 & 316L over other grades of Steel
Biocompatible
These austenitic stainless steels cannot be hardened by HT but can be hardened by cold working
possesses better corrosion resistance than any other steels
The inclusion of molybdenum enhances resistance to pitting corrosion in salt water

42. The 316L Stainless Steel
(ASTM) recommends type 316L rather than 316 for implant fabrication.
The only difference in composition between the 316L and 316 SS is the maximum content of carbon, i.e., 0.03% and 0.08%, respectively.
So what makes 316L special?????

43. Mechanical Properties & Corrosion Resistance of 316L43

44. Assignment #3
Q) Why is Stainless Steel chosen instead of other grades of Steel for use as a biomaterial? And among Stainless Steel why is 316 L considered to be the most suitable biomaterial? Justify your answers with all possible reasons. Q) Read Chapter #3 of Biomaterials by Sujata Bhat and read chapter 1 of Biomaterials principles and Applications by Joon B. Park Q) What is sensitization of Steel. How can it be restricted?

45. Mechanical Properties & Corrosion Resistance of 316L
Even the 316L stainless steels may corrode inside the body under certain circumstances in a highly stressed and oxygen depleted region, such as the contacts under the screws of the bone fracture plate. Thus, these stainless steels are suitable for use only in Temporary implant devices such as fracture plates, screws, and hip nails.
Surface modification methods are widely used in order to improve corrosion resistance, wear resistance, and fatigue strength of 316L stainless steel
anodization, passivation
glow-discharge nitrogen implantation
The
engineer must consequently be careful when
selecting materials of this type. 45

46. Deficiency Factors Responsible for failure of SS implants
Deficiency of Mo
Use of sensitized steel
Inadvertent use of mixed metals and incompatible components
Topography and metallurgical finish
Improper implant and implant material selection

47. Co –Cr Alloys Co between Fe and Ni Forms solid solution with Cr
Molybedum added to produce fine grains which results in higher strength
The chromium enhances corrosion resistance as well as solid solution strengthening of the alloy.
Metallic Co –used in beginning of the century but was not very ductile or corrosion resistant
1930s – vitallium – 30% Cr, 7% W 0.5% C in Co
Mostly for metallic dental castings
To replace the more expensive gold alloys
Larger partial denture castings
Cast vitallium: dentistry and now recently in artificial joints
Wrought vitallium: stems of heavily loaded joints suchh as femoral hip stems

48. Cannot be considered even solely as tertiary or quaternary systems – contain C, Mo, Ni, W, Fe
E varies from 185 to 250 GN/m2 – roughly equal to SS 316 and twice that of Ti
The ASTM lists four types of CoCr alloys which are recommended for surgical implant applications:
(1) cast CoCrMo alloy (F75), (2) wrought CoCrWNi alloy (F90), (3) wrought CoNiCrMo alloy (F562), and (4) wrought CoNiCrMoWFe alloy (F563).

50. Cast Alloy
the alloy is cast by a lost wax (or investment casting)method which involves making a wax pattern of the desired component
A wax model of the implant is made and a ceramic shell is built around it
the wax is then melted out in a oven (100~150°C),
the mold is heated to a high temperature burning out any traces of wax or gas-forming materials,
molten alloy is poured with gravitational or centrifugal force
the mold is broken after cooled
The mold temperature is about 800~1000°C and the alloy is at 1350~1400°C.
coarse ones formed at higher temperatures will decrease the strength. However, a high processing temperature willresult in larger carbide precipitates with greater distances between them, resulting in a less brittle material. Again there is a complementary (trade-off) relationship between strength and toughness.

51. Porous coated Co-Cr implants
Forged Alloy
More uniform microstructure
Usually hot forged
The superior fatigue and ultimate tensile strength of the wrought CoNiCrMo alloy make it suitable for the applications which require long service life without fracture or stress fatigue. Such is the case for the stems of the hip joint prostheses.
Expensive – sophisticated press and tooling
Porous coated Co-Cr implants
Bone in growth applications
Sintered beads – gravity sintering
Plasma flame sprayed metal powders
Diffusion bonded

54. Acetabular cup

55. Titanium based Alloys
It was found that titanium was tolerated in cat femurs, as was stainless steel and Vitallium® (CoCrMo alloy)
Advantages
Lightness (4.5 g/cm3) and good mechanical properties
Young’s modulus is half that SS and Co-Cr
Implies greater flexibility
Disadvantages
High cost and reactivity

56. Ti Alloys
One of the most widely used titanium alloys for biomedical applications:Ti6Al4V
The Ti6Al4V alloy has approximately the same fatigue strength (550 MPa) as that of CoCr alloy
Titanium alloys can be strengthened and mechanical properties varied by controlled composition and thermomechanical processing techniques.
Ti exists in two allotropic forms: α- & β –phase
The presence of Vanadium tends to form the α-β phase at room temperature.
Exact composition and thermal history determines its properties

57. Nitinol
Alloy of Ni-Ti
Can be designed to change its shape or dimensions in response to an increase in temperature – small enough to be tolerated by the adjacent tissues in which it is embedded.
FCC ---- Martensite
It has good strain recoverability, notch sensitivity and has excellent fatigue, biocompatibility and corrosion resistance

58. Applications Shape memory Stents
a stent is a man-made 'tube' inserted into a natural passage/conduit in the body to prevent, or counteract, a disease-induced, localized flow constriction.