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

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.

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.

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

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

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 http://www.superconductors.org/INdex.htm 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

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

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

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.

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

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

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

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: http://www.youtube.com/watch?v=kN-KqYcjEqk 13

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

Vascular Implants Parachute cloth and Dacron 15

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

Artificial Hip Joints http://www.totaljoints.info/Hip.jpg

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

Substitute Heart Valves

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

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

Evolution of Biomaterials Structural Soft Tissue Replacements Functional Tissue Engineering Constructs

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

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

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

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

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

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

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?????

Mechanical Properties & Corrosion Resistance of 316L 32

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?

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

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

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

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

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

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

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

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

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?????

Mechanical Properties & Corrosion Resistance of 316L 43

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?

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

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

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

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).

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.

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

Acetabular cup

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

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

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

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.