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Title: BIOMATERIALS AND ARTIFICIAL ORGAN BM1303 S'Sudha Lecturer Dept of Biomedical Engg


1
BIOMATERIALS AND ARTIFICIAL ORGAN
BM1303S.SudhaLecturer Dept of Biomedical
Engg
2
UNIT I
3
INTRODUCTION TO BIOMATERIALS
  • During the last two decades, significant advances
    have been made in thedevelopment of biocompatible
    and biodegradable materials for
    medicalapplications.
  • In the biomedical field, the goal is to develop
    and characterize artificial materialsor, in other
    words, spare parts for use in the human body to
    MEASURE,RESTORE and IMPROVE physical functions
    and enhance survival and qualityof life.

4
Whats a biomaterial?
  • 1980 - Passive and inert point of view
  • Any substance or drugs, of synthetic or
    natural origin, which can be used for any period
    alone or as part of a system and that increases
    or replaces any tissue,organ or function of the
    body
  • 1990 Active point of view
  • Non-living material used in a medical device
    and designed to interact with biological systems

5
Classification of biomaterials
  • First generation INERT
  • Do not trigger any reaction in the host neither
    rejected nor recognition do not bring any good
    result
  • Second generation BIOACTIVE
  • Ensure a more stable performance in a long time
    or for the period you want
  • Third generation BIODEGRADABLE
  • It can be chemically degraded or decomposed by
    natural effectors (weather, soil bacteria,
    plants, animals)

6
What is a biocompatible material?
  • Synthetic or natural material used in intimate
    contact with living tissue (it canbe implanted,
    partially implanted or totally external).
  • Biocompatible materials are intended to
    interface with biological system toEVALUATE,
    TREAT, AUGMENT or REPLACE any tissue, organ or
    function ofthe body.
  • A biocompatible device must be fabricated from
    materials that will not elicit an adverse
    biological response

7
Mechanical Properties of Metals
  • How do metals respond to
    external loads?
  • Stress and Strain
  • Tension
  • Compression
  • Shear
  • Torsion
  • Elastic deformation
  • Plastic Deformation
  • Yield Strength
  • Tensile Strength
  • Ductility
  • Toughness
  • Hardness

8
Stress-Strain Behavior
  • Elastic deformation
  • Reversible when the stress
  • is removed, the material
  • returns to the dimension it
  • had before the loading.
  • Usually strains are small
  • (except for the case ofplastics).
  • Plastic deformation
  • Irreversible when the stress
  • is removed, the material
  • does not return to its
  • previous dimension.

9
Stress-Strain Behavior Plastic deformation
  • Plastic deformation
  • stress and strain are not proportional the
    deformation is not reversible deformation occurs
    by breaking and rearrangement of atomic bonds (in
    crystalline materials primarily by motion of
    dislocations)

10
Typical mechanical properties of metals
  • The yield strength and tensile strength vary
    with prior
  • thermal and mechanical treatment, impurity
    levels,
  • etc. This variability is related to the behavior
    of
  • dislocations in the material. But elastic
  • moduli are relatively insensitive to these
    effects.
  • The yield and tensile strengths and modulus of
  • elasticity decrease with increasing temperature,
  • ductility increases with temperature.

11
Mechanics of Materials
  • The point up to which the stress and strain are
    linearly related is called the proportional
    limit.
  • The largest stress in the stress strain curve is
    called the ultimate stress.
  • The stress at the point of rupture is called the
    fracture or rupture stress.
  • The region of the stress-strain curve in which
    the material returns to the undeformed state when
    applied forces are removed is called the elastic
    region.
  • The region in which the material deforms
    permanently is called the plastic region.
  • The point demarcating the elastic from the
    plastic region is called the yield point. The
    stress at yield point is called the yield stress.

12
Mechanics of Materials
  • The permanent strain when stresses are zero is
    called the plastic strain.
  • The off-set yield stress is a stress that would
    produce a plastic strain corresponding to the
    specified off-set strain.
  • A material that can undergo large plastic
    deformation before fracture is called a ductile
    material.
  • A material that exhibits little or no plastic
    deformation at failure is called a brittle
    material.
  • Hardness is the resistance to indentation.
  • The raising of the yield point with increasing
    strain is called strain hardening.
  • The sudden decrease in the area of cross-section
    after ultimate stress is called necking.

13
Viscoelasticity
  • Definition time-dependent material
  • behavior where the stress response of that
  • material depends on both the strain applied
  • and the strain rate at which it was applied!
  • Examples
  • biological materials
  • polymer plastics
  • metals at high temperatures

14
Elastic versus viscoelastic behaviors
  • For a constant applied strain
  • An elastic material has a unique material
    response
  • A viscoelastic material has infinite material
    responses depending on the strain-rate

15
Viscoelastic Hysteresis
  • Viscoelastic solid
  • some energy is dissipated with dashpots (as
    heat)some energy is stored in springs. Area in
    the hysteresis loop is a function of loading rate
  • For viscoelastic material, energy is dissipated
    regardless of whether strains(or stresses) are
    small or large
  • Under repetitive loading, a viscoelastic
    material will heat up

16
Wound healing
  • All wounds heal following a a specific sequence
    of phases which may overlap
  • The process of wound healing depends on the type
    of tissue which has been damaged and the nature
    of tissue disruption
  • The phases are
  • Inflammatory phase
  • Proliferative phase
  • Remodelling or maturation phase

17
The ways in which wounds heal
  • Three basic classifications exist
  • Healing by primary intention
  • Two opposed surfaces of a clean, incised wound
  • (no significant degree of tissue loss) are held
    together.
  • Healing takes place from the internal layers
    outwards
  • Healing by secondary Intention
  • If there is significant tissue loss in the
    formation of the
  • wound, healing will begin by the production of
  • granulation tissue wound base and walls.
  • Delayed primary healing
  • If there is high infection risk patient is
    given antibiotics
  • and closure is delayed for a few days e.g.
    bites

18
Wound assessment
Lab tests TcPO2
Signs of infection
Size, depth location
Odour or exudate
WOUND ASSESSMENT
  • Wound bed
  • necrosis
  • granulation

Wound edge
Surrounding skin colour, moisture,
19
The healing process
  • Day 0 5
  • The healing response starts at the moment of
    injury the clotting cascade is initiated
  • This is a protective tissue response to stem
    blood loss
  • The inflammatory phase is characterised by heat,
    swelling, redness, pain and loss of function at
    the wound site
  • Early (haemostasis)
  • Late (phagocytosis)
  • This phase is short lived in the absence of
    infection or contamination

20
Granulation
  • Day 3 14
  • Characterised by the formation of granulation
    tissue in the wound
  • Granulation tissue consists of a combination of
    cellular elements including
  • Fibroblasts, inflammatory cells, new capillaries
    embedded in a loose extra-cellular collagen
    matrix, fibronectin and hyularonic acid

21
Moist wound healing
  • Basic concept is that the presence of exudate
    will provide an environment that stimulates
    healing
  • Exudate contains
  • Lysosomal enzymes, WBCs, Lymphokines, growth
    factors..
  • There are clinical studies which have shown that
    wounds maintained in a moist environment have
    lower infection rates and heal more quickly

22
Factors affecting healing
  • Immune status
  • Blood glucose levels (impaired white cell
    function)
  • Hydration (slows metabolism)
  • Nutrition
  • Blood albumin levels (building blocks for
    repair, colloid osmotic pressure - oedema)
  • Oxygen and vascular supply
  • Pain (causes vasoconstriction)
  • Corticosteroids (depress immune function)

23
Host Reactions to Biomaterials
  • Effect of the Implant on the Host
  • Local
  • Blood material interactions
  • Protein adsorption
  • Coagulation
  • Fibrinolysis
  • Platelet adhesion, activation, release
  • Complement activation
  • Leukocyte adhesion, activation
  • Hemolysis
  • Toxicity

24
  • Modification of normal healing
  • Encapsulation
  • Foreign body reaction
  • Pannus formation
  • Infection
  • Tumorgenesis
  • Systemic and remote
  • Embolization
  • Hypersensitivity
  • Elevation of implant elements in the blood
  • Lymphatic particle transport

25
Effect of the Host on the Implant
  • Physical mechanical effects
  • Abrasive wear
  • Fatigue
  • Stress corrosion, cracking
  • Corrosion
  • Degeneration and dissolution
  • Biological effects
  • Absorption of substances from tissues
  • Enzymatic degradation
  • Calcification

26
Temporal Variation of Inflammatory Response
27
  • Activated by injury to vascularized connective
    tissue
  • Series of reactions
  • Various cells
  • Controlled by endogenous and autocoid mediators

28
UNIT II
29
Types of Metallic Implants
  • Stainless steel
  • Cobalt Based Alloys
  • Titanium Alloys

30
Stainless Steels
  • Fe 60-65 wt, Cr 17-19 wt , Ni 12-14 wt
  • Carbon content reduced to 0.03 wt for better
    The most common stainless steel 316Lresistance
    to in vivo corrosion.
  • Why reduce carbon Reduce carbide (Cr23C6)
    formation at grain boundary. Carbide impairs
    formation of surface oxide
  • Why add chromium corrosion resistance by
    formation of surface oxide.
  • Why add nickel improve strength by increasing
    face centered cubic phase (austenite)

31
Stainless Steels
  • Good stainless steel
  • Austenitic (face centered cubic)
  • No ferrite (body centered cubic)
  • No carbide
  • No sulfide inclusions
  • Grain size less then 100mm
  • Uniform grain size

32
Cobalt Based Alloys
  • Common types for surgical applications
  • ASTM F75
  • ASTM F799
  • ASTM F790
  • ASTM F 562

33
Cobalt Alloys ASTM F75
  • Co-Cr-Mo
  • Surface oxide thus corrosion resistant
  • Wax models from molds of implants
  • Wax model coated with ceramic and wax melted away
  • Alloy melted at 1400 C and cast into ceramic
    molds.

34
Cobalt Alloys ASTM F75
  • Three caveats
  • Carbide formation corrosion. Solution
    annealing at 1225 C for one hour.
  • Large grain size reduced mechanical strength
  • Casting defects stress concentration,
    propensity to fatigue failure

35
Cobalt Alloys ASTM F799, ASTM F90
  • Cobalt Alloys ASTM F799
  • Modified form of F75 hot forged after casting
  • Mechanical deformation induces a shear induced
    transformation of FCC structure to HCP.
  • Fatigue, yield and ultimate properties are twice
    of F75.
  • Cobalt Alloys ASTM F90
  • W and Ni are added to improve machinability and
    fabrication
  • Mechanical properties similar to F75
  • Mechanical properties double F75 if cold worked

36
Titanium Based Alloys
  • Lighter
  • Good mechanical properties
  • Good corrosion resistance due to TiO2solid oxide
    layer
  • Ti-6 wt Al-4 wt V (ASTM F136) is widely used
  • Contains impurities such as N, O, Fe, H, C
  • Impurities increase strength reduce ductility

37
Titanium Alloys ASTM F136
  • HCP structure transforms to BCP for temperatures
    greater than 882 C.
  • Addition of Al stabilizes HCP phase by increasing
    transformation temperature
  • V has the inverse effect.

38
ceramic
  • Any of various hard, brittle, heat-resistant and
    corrosion-resistant materials made by shaping and
    then firing a nonmetallic mineral,such as clay,
    at a high temperature
  • Clinical success requires
  • Achievement of a stable interface with
    connective tissue
  • Functional match of the mechanical behavior
    of the implant with the tissue to be replaced
  • Critical Issues
  • Integrity of bioceramic
  • Interaction with the tissue

39
Hydroxyapatites (HA)
  • Chemically similar to mineral component of bones
  • It will support bone ingrowth and
    osseointegration
  • when used in orthopaedic, dental and
    maxillofacial applications
  • Chemical formula Ca5(PO4)3OH
  • Hexagonal Bravais lattice
  • The chemical nature of hydroxyapatite lends
    itself to substitution common substitutions
    involve carbonate, fluoride and chloride
    substitutions for hydroxyl groups

40
Uses for HA
  • Facial augmentation with hydroxyapatite has been
    used for the following
  • corrections Cheek, Chin, Jaw, Nose, Browbone.
  • Skeletal repair biomaterials
  • Ocular prosthesis
  • Hydroxyapatite from coral
  • The eye muscles can be attacheddirectly to this
    implant, allowing it to move within the
    orbit-just like the natural eye.

41
Calcium Phosphate Bioceramics
  • There are several calcium phosphate ceramics that
    are consideredbiocompatible most are resorbable
    and will dissolve when exposed tophysiological
    environments.
  • Hydroxyapatite is thermodynamically stable at
    physiological pH values actively takes part in
    bone bonding, forming strong chemical bonds with
    surrounding bone
  • Mechanical properties unsuitable for load-bearing
    applications such as orthopaedics
  • Used as a coating on materials such as titanium
    and titanium alloys,where it can contribute its
    'bioactive' properties, while the metallic
    component bears the load
  • Coatings applied by plasma spraying

42
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43
UNIT III
44
Polymeric Biomaterials
  • What is a polymer?
  • Long chain molecules that consist of a number of
    repeating units (mers)
  • Fabricated from monomers which change somehow in
    polymerization
  • Loss of H20, HCl or other molecule
  • Polymer properties are more complex than for
    simpler materials
  • Types of polymers
  • Biological polymers
  • DNA, cellulose, starch, proteins, rubber, etc
  • Often reconstituted to form usable polymer
  • Mainly collected from animals
  • Synthetic polymers
  • Fabricated from petroleum products (generally)
  • May be also a modified biological polymer
  • Most plastics and similar materials

45
Classification
  • examples examples examples

46
Classes of Polymers (I)
  • Thermoplastic polymers
  • Long chains with very limited or no cross-linking
  • They behave in a plastic, ductile manner (above
    Tg)
  • Melt when heated and are thus easily remolded and
    recycled
  • Thermoset polymers
  • Highly cross-linked, 3D network structures
  • Generally brittle (at most temperatures)
  • Decompose when heated and cant easily be
    reshaped or recycled

47
Classes of Polymers (II)
  • Elastomers and rubbers
  • Large amounts of elastic deformation
  • Some (light) cross-linking
  • Typically, about 1 in 100 molecules are
    cross-linked on average
  • Average number of cross-links around 1 in 30
    yields a more rigid and brittle material (closer
    to a thermoset)
  • Crosslinks allows material to return to original
    shape without plastic deformation

elastomer
thermoset
48
Definitions
  • Oligomer- molecules with nlt10 (less than ten
    monomers)
  • Degree of polymerization, P number of monomer
    residues per chain
  • Functionality number of bonding sites per
    monomer.A monomer must possess at least two
    bonding sites
  • Homopolymer
  • A-A-A-A-A-A-A-A
  • Copolymer
  • Random A-B-A-A-A-B-B-A-B-B-B-A-B-B
  • Alternating A-B-A-B-A-B-A-B-A-B
  • Block A-A-A-A-A-B-B-B-B-B-B
  • Graft As with Bs on branches
  • Linear polymer- no branches
  • Branched polymer - multiple branches
  • Crosslinked polymer- links between branches

49
Polymer Basics
  • Polymerization process
  • Initiation I ? 2R (the active center which acts
    as a chain carrier is created)
  • Propagation RM1 M ? RM2 (growth of
    macromolecular chain)
  • Termination kinetic chain is brought to halt

50
  • Synthesis Reactions
  • Addition polymerization
  • Condensation polymerization
  • Source Askeland Phule p 677

51
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52
PE (Polyethylene) PP (Polypropylene)
  • Used in high density form astubing for drains and
    catheters
  • Ultra high molecular weight form used as acetabul
    component in artificial hips and other
    prosthetic joints
  • Has good toughness and wear resistance
  • Resistant to lipid absorption
  • High rigidity
  • Good chemical resistance
  • Good tensile strength
  • Excellent stress cracking resistance
  • Used for sutures and hernia repair

53
PTFE (Polytetrafluoroethylene)PVC(Polyvinylchlori
de)
  • Aka Teflon
  • Very hydrophobic
  • Good lubricity
  • Low wear resistance
  • Used for catheters and vascular grafts (Gore-Tex)
  • Made flexible and soft bythe addition of
    plasticizers
  • Not suitable for long term use because
    plasticizers can be extracted by thebody
  • Used as tubing for blood transfusions, feeding
    anddialysis, and blood storagebags

54
Elastomers - Entropy
If you stretch it far enough the chains will line
up straight enough to crystallize
55
Elastomer vs. Thermoplastic Elastomers
  • Some amorphous polymer exhibit elastomeric
    behavior, yet have no chemical crosslinks
  • Usually block copolymers possessing both rubbery
    regions and stiff regions in the chain
  • Physical interactions between stiff chain regions
    act a physical crosslinks
  • Rubbery regions allow large
    deformations
  • Thermoplastic in nature can be
    melted since there are no chemical
    crosslinks

Styrene butadiene styrene (SBS)
56
Thermosets
  • Disadvantage
  • Thermosets are difficult to re-form
  • Advantages in engineering design applications
  • High thermal stability and insulating properties
  • High rigidity and dimensional stability
  • Resistance to creep and deformation under load
  • Light-weight
  • Crosslinking of thermosets
  • 10-50 of the mers in a chain are crosslinked
  • Heat treatment, vulcanization processes link
    existing chains
  • Two part chemistries (resin and curing agent) are
    mixed and react at room temp or elevated
    temperatures multi-functional end groups

57
Polymers as Biomaterials
  • Hydrogels
  • swellable materials, usually acrylic copolymers,
    e.g. poly(2-hydroxyethyl methacrylate) PHEMA
  • More in lecture 10
  • Piezoelectric materials
  • materials that generate transient electrical
    charges on their surfaces upon mechanical
    deformation, e.g. polyvinylidene fluoride,
    collagen
  • Resorbable materials
  • Resorbed with time, e.g. polyglycolic and
    polylactic acid
  • More in lecture 11

58
Fluorinated Polymers
  • PTFE
  • Plain or expanded (Gore-Tex)
  • Vascular grafts, sutures, middle ear prostheses
  • Fluorocarbons
  • High affinity for oxygen
  • Blood substitutes
  • Vinylidene Fluoride (PVDF)
  • Piezoelectric
  • Actuators, nerve guidance

PTFE unsuccessful in joint replacements
59
Polymethyl methacrylate
  • PMMA
  • A hydrophobic linear chain polymer that is
    transparent, amorphous and glassy at room
    temperature (also known as plexiglass or lucite)
  • Good light transmittance, toughness, and
    stability
  • A good material for intraocular lenses and hard
    contact lenses
  • Also used as a bone cement

60
Polyethylene
  • PE
  • High density form (HDPE)
  • Used for tubing in catheters and drains
  • High molecular weight form (UHMWPE)
  • Contact surface in artificial hips, knees
  • Good toughness, resistance to fat and oils, and
    low cost

61
Polyethylene Glycol
  • PEG
  • Short chain neutral hydrophilic polymer
  • Shown to repel cells due to surface energy
  • Used for coatings non-thrombogenic
  • Wound healing polymerization on the wound
  • Microencapsulation and drug delivery

62
Biological Polymers
  • Many cellular and extracellular materials are
    polymers
  • Polysaccharides (made from monosaccharides)
  • Cellulose
  • Alginate
  • Proteins (made from amino acids)
  • Collagen
  • Actin
  • Fibrin
  • Nucleic Acids (made from nucleotides)
  • DNA
  • RNA
  • More in lecture 12

63
Silicones
  • Silicone polymers
  • e.g. Polydimethylsinoxane (PDMS)
  • No carbon backbone silicone and oxygen instead
  • Elastomers (with crosslinks)
  • Silicones as biomaterials
  • Very low Tg
  • Excellent flexibility and stability
  • Used in catheters, pacemaker leads,
  • vascular grafts, and breast and
  • facial implants
  • High oxygen permeability - membrane
  • oxygenators

64
Common clinical applications and types of
polyCommon clinical applications and types of
polymersused in medicine
65
Polymers In Specific Applications
65
66
UNIT IV
67
Soft Tissue Implants
  • Attempts have been made to replace or augment
    most of the soft tissues in the body
  • Connective tissues skin, ligament, tendon,
    cartilage
  • Vascular tissue blood vessels, heart valves
  • Organs heart, pancreas, kidney
  • Other eye, ear, breast
  • Most soft tissue implants are constructed from
    synthetic polymers
  • Possible to choose and control the physical and
    mechanical properties
  • Flexibility in manufacturing
  • "Soft tissue implants" can also be designed for
    soft tissue repair

68
Sutures
  • Used to repair incisions and lacerations
  • Important characteristics for sutures
  • Tensile strength
  • Flexibility
  • Non-irritating

69
Tissue Adhesives
  • Used for repair of fragile, non-suturable tissues
  • Examples Liver, kidney, lung
  • The bond strength for adhesive closed tissues is
    not as strong after 14 days as for suture closed
    tissues

70
Percutaneous Implants
  • Refers to implants that cross the skin barrier
  • In contact with both the outside environment and
    the biological environment
  • Used for connection of the vascular system to
    external "organs"
  • Dialysis
  • Artifical heart
  • Cardiac bypass
  • Also used for long term delivery of medication or
    nutrition (IV)
  • Main Problems
  • Attachment of skin (dermis) to implant difficult
    to maintain through ingrowth due to rapid
    turnover of cells
  • Implant can be extruded or invaginated due to
    growth of skin around the implant
  • Openings can also allow for the entrance of
    bacteria, which may lead to infection

71
Artifical Skin
  • Is actually a percutaneous implant -- contacts
    both external and biological environments
  • No current materials available for permanent skin
    replacement
  • Design ideas
  • Graft should be flexible enough to conform to
    wound bed and move with body
  • Should not be so fluid-permeable as to allow the
    underlying tissue to become dehydrated but should
    not retain so much moisture that edema (fluid
    accumulation) develops under the graft

72
Artificial Skin - Possibilities
  • Polymeric or collagen-based membrane
  • Some are too brittle and toxic for use in burn
    victims
  • Flexibility, moisture flux rate, and porosity can
    be controlled
  • Fabrics and sponges designed to promote tissue
    ingrowth
  • Have not been successful
  • Immersion of patients in fluid bath or silicone
    fluid to prevent early fluid loss, minimize
    breakdown of remaining skin, and reduce pain
  • Culturing cells in vitro and using these to
    create a living skin graft
  • Does not require removal of significant portions
    of skin

73
Soft Tissue Augmentation
  • Generally used for reconstructive or cosmetic
    enhancement
  • Functions include one or more of the following
  • Space filler
  • Mechanical support
  • Fluid carrier or storer
  • Common applications for soft tissue augmentation
    are
  • Maxillofacial implants
  • Eye and ear implants
  • Fluid transfer implants
  • Breast implants

74
Maxillofacial implants
  • Designed to replace or enhance hard or soft
    tissue in the jaw and face
  • Intraoral prosthetics (implanted) are used to
    reconstruct areas that are missing or defective
    due to surgical intervention, trauma, or
    congenital condition
  • Must meet all biocompatibility requirements
  • Metals such as tantalum, titanium, and Co-Cr
    alloys can be used to replace bony defects
  • Polymers are generally used for soft tissue
    augmentation
  • Gums, chin, cheeks, lips, etc.
  • Injectable silicone had been examined for use in
    correcting facial deformities however, it has
    been found to cause severe tissue reactions in
    some patients and can migrate
  • Extraoral prosthetics (external attachment)
    should
  • Match the patients skin in color and texture
  • Be chemically and mechanically stable
  • Not creep, change colors, or irritate skin
  • Be easily fabricated
  • Have been fabricated out of numerous polymers

75
Fluid Transfer Implants
  • May be designed as permanent implants to treat
    chronic problems
  • Hydrocephalus
  • Build up of cerebrospinal fluid in the brain
  • Can result in brain damage if pressure becomes
    too high
  • Treated by draining the fluid to the vascular
    system or abdominal cavity
  • Uses a permanent shunt from the ventricles of the
    brain, under the skin, to the receiving tissue
  • Tubing is made of silicone rubber made radiopaque
    to allow for observation with x-rays
  • Ear Infections
  • "Tubes" in the ears are drainage tubes designed
    to remove fluid from the middle ear
  • Constructed from teflon or other inert materials
  • Not permanent implants (removed after several
    years)

76
Orthopaedic Soft Tissue
  • Replacement of cartilage, ligaments, and tendons
  • Difficult to obtain fixation with bone
  • Screws or pins involve stress concentrations and
    the possibility of corrosion
  • Strength of anchorage depends on thickness of
    cortical bone at attachment site
  • In many cases autographs are used - may be
    patellar tendon for ACL reconstruction
  • Allographs - cryo-preserved, fresh-frozen, or
    freeze dried specimens taken from cadavers
  • Often attached to treated bony insertion sites
    which can be used as bone grafts (See Figure 6)
  • Preservation and cold sterilization procedures
    may adversely affect properties of implants
  • Available from tissue banks

77
Artificial Orthopaedic Soft Tissues
  • Ligament Augmentation Devices (LAD's)
  • Artificial materials used to take some of the
    stress normally applied to a ligament while
    healing occurs
  • May or may not be resorbable
  • Gore-Tex non-resorbable
  • PDS resorbable plastic
  • Contradictory results exist in the literature as
    to the effectiveness of LAD's
  • Ligament scaffolds
  • Made of polyester or other polymers
  • Used to induce tissue ingrowth
  • May be implanted alone or with a section of
    tissue (fat pat, fascia lata, piece of tendon) to
    increase rate of ingrowth
  • Region of fixation for artifical ligaments or
    reconstructions with LAD's for the ACL deviates
    from normal more than for reconstructions with
    patellar tendon alone
  • Fibrous tissue instead of normal transition from
    ligament to bone

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Total Hip Replacement
  • A prosthetic hip that is implanted in a similar
    fashion as is done in people.  It replaces the
    painful arthritic joint. 
  • The modular prosthetic hip replacement system
    used today has three components the femoral
    stem, the femoral head, and the acetabulum.  Each
    component has multiple sizes which allow for a
    custom fit. 
  • The components are made of cobalt chrome
    stainless steel and ultra high molecular weight
    polyethylene. Cementless and cemented prosthesis
    systems are available.

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Common Causes of Hip Pain and Loss of Hip Mobility
  • Osteoarthritis
  • Usually occurs after age 50 and often in an
    individual with a family history of arthritis. In
    this form of the disease, the articular cartilage
    cushioning the bones of the hip wears away. The
    bones then rub against each other, causing hip
    pain and stiffness.

80
OperationRemoving the Femoral Head
  • Once the hip joint is entered, the femoral head
    is dislocated from the acetabulum.
  • Then the femoral head is removed by cutting
    through the femoral neck with a power saw.

81
Reaming the Acetabulum
  • After the femoral head is removed, the cartilage
    is removed from the acetabulum using a power
    drill and a special reamer.
  • The reamer forms the bone in a hemispherical
    shape to exactly fit the metal shell of the
    acetabular component.

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Inserting the Acetabular Component
  • A trial component, which is an exact duplicate of
    your hip prosthesis, is used to ensure that the
    joint will be the right size and fit for the
    client.
  • Once the right size and shape is determined for
    the acetabulum, the acetabular component is
    inserted into place.

83
Preparing the Femoral Canal
  • To begin replacing the femoral head, special
    rasps are used to shape and scrape out femur to
    the exact shape of the metal stem of the femoral
    component.
  • Once again, a trial component is used to ensure
    the correct size and shape. The surgeon will also
    test the movement of the hip joint.

84
Inserting Femoral Stem
  • Once the size and shape of the canal exactly fit
    the femoral component, the stem is inserted into
    the femoral canal.

85
Attaching the Femoral Head
  • The metal ball that replaces the femoral head is
    attached to the femoral stem.

86
The Completed Hip Replacement
  • Client now has a new weight bearing surface to
    replace the affected hip.
  • Before the incision is closed, an x-ray is made
    to ensure new prosthesis is in the correct
    position.

87
Treatment by Kinesiologist-Early Postoperative
Exercises-
  • Regular exercises to restore your normal hip
    motion and strength and a gradual return to
    everyday activties.
  • Exercise 20 to 30 minutes a day divided into 3
    sections.
  • Increase circulation to the legs and feet to
    prevent blood clots
  • Strengthen muscles
  • Improve hip movement

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UNIT V
89
Artificial heart valve
  • An artificial heart valve is a device implanted
    in the heart of a patient with heart valvular
    disease. When one of the four heart valves
    malfunctions, the medical choice may be to
    replace the natural valve with an artificial
    valve. This requires open-heart surgery.

90
Types of heart valve prostheses
  • There are two main types of artificial heart
    valves the mechanical and the biological valves.
  • Mechanical heart valves
  • Percutaneous implantation
  • Stent framed
  • Not framed
  • Sternotomy/Thoracotomy implantation
  • Ball and cage
  • Tilting disk
  • Bi-leaflet
  • Tri-leaflet
  • Biological heart valves
  • Allograft/isograft
  • Xenograft

91
Types of mechanical heart valves
92
Design challenges of heart valve prostheses
  • A replaceable model of Cardiac Biological Valve
    Prosthesis.
  • Thrombogenesis / haemocompatibility
  • Mechanisms
  • Forward and backward flow shear
  • Static leakage shear
  • Presence of foreign material (i.e. intrinsic
    coagulation cascade)
  • Cellular maceration
  • Valve-tissue interaction
  • Wear
  • Blockage
  • Getting stuck
  • Dynamic responsiveness
  • Failure safety
  • Valve orifice to anatomical orifice ratio
  • Trans-valvular pressure gradient
  • Minimal leakages
  • Replaceable Models of Biological Valves

93
Artificial limb
  • An artificial limb is a type of prosthesis that
    replaces a missing extremity, such as arms or
    legs. The type of artificial limb used is
    determined largely by the extent of an amputation
    or loss and location of the missing extremity.
    Artificial limbs may be needed for a variety of
    reasons, including disease, accidents, and
    congenital defects.

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Lower Limb Prosthesis
  • Components of the Prosthesis
  • Socket- Forms the connection between the residual
    limb and the prosthesis.
  • Sleeve- Provides suction suspension for
    prosthesis.
  • Shank (pylon)- Transfers weight from socket to
    the foot-ankle.
  • Foot-ankle- Absorbs shock and impact and provides
    stability.

95
Dental implant
  • A dental implant is an artificial tooth root
    replacement and is used in prosthetic dentistry
    to support restorations that resemble a tooth or
    group of teeth. There are several types of dental
    implants. The major classifications are divided
    into osseointegrated implant and the
    fibrointegrated implant. Earlier implants, such
    as the subperiosteal implant and the blade
    implant were usually fibrointegrated

96
WHAT IS A DENTAL IMPLANT?
  • Dental implant is an artificial titanium
    fixture (similar to those used in orthopedics)
  • which is placed surgically into the jaw bone to
  • substitute for a missing tooth and its root(s).

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Surgical Procedure
STEP 1 INITIAL SURGERY STEP 2 OSSEOINTEGRATION
PERIOD STEP 3 ABUTMENT CONNECTION STEP 4
FINAL PROSTHETIC RESTORATION
Success Rates
lower jaw, front 90 95 lower jaw, back 85
90 upper jaw, front 85 95 upper jaw, back
65 85
98
First Implant Design by Branemark
 
All the implant designs are obtained by
the modification of existing designs.
John Brunski
99
Astra Tech.
Comparison of Implant Systems
ITI
Bicon
100
Perfectly elastic large displacement non-linear
contact finite element analysis for different
insertion depths.
  • Contact pressure increases linearly with
    insertion depth.

101
Elastic-plastic large displacement non-linear
contact finite element analysis for different
insertion depths
Bilinear Isotropic Hardening Model
Stress (MPA)
Strain
102
Contact Pressure Distribution for Different
Insertion Depths
  • Contact pressure increases non-linearly with
    larger
  • insertion depths.

103
FUTURE WORK
  • Comparison of different implant designs in
  • terms of stress distribution in the bone due to
  • occlusal loads.
  • Modeling non-homogenous bone material
  • properties by incorporating with CT scan data.
  • Comparison of different implant-abutment
  • interfaces
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