Notes of Lesson on BIOMATERIALS

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Notes of Lesson on BIOMATERIALS Powered By Docstoc


   Dept of Biomedical Engg

   During the last two decades, significant advances
    have been made in thedevelopment of
    biocompatible and biodegradable materials for
   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
    functions and enhance survival and qualityof life.
                What‟s 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
     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)
    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
      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
                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.
      Stress-Strain Behavior: Plastic
   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)
    Typical mechanical properties of

   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.
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.
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.

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!
 biological materials

 polymer plastics

 metals at high temperatures
Elastic versus viscoelastic behaviors

For a constant applied
 An elastic material has
  a unique material
 A viscoelastic material
  has infinite material
  responses depending on
  the strain-rate
             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
   Under repetitive loading, a
   viscoelastic material will heat up
                  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
         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
             Wound assessment
                  Lab tests:
Signs of
infection         TcPO2                  Size, depth
                                         & location

Odour or        WOUND ASSESSMENT

                                   Wound bed:
                                   • necrosis

Wound edge                         • granulation
               Surrounding skin:
               colour, moisture,
               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

   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
                 Moist wound healing

   Basic concept is that the presence of exudate will
    provide an environment that stimulates healing
   Exudate contains:
           Lysosomal enzymes, WBC‟s, 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
          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)
     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
      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
        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
Temporal Variation of Inflammatory
   Activated by injury to
    vascularized connective
   Series of reactions
   Various cells
   Controlled by
    endogenous and
    autocoid mediators
      Types of Metallic Implants

   Stainless steel
   Cobalt Based Alloys
   Titanium Alloys
               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)
             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
          Cobalt Based Alloys

 Common types for surgical applications:
 – ASTM F75

 – ASTM F799

 – ASTM F790

 – ASTM F 562
         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
       Cobalt Alloys: ASTM F75

 Three caveats:
 – Carbide formation ® corrosion. Solution:
  annealing at 1225 °C for one hour.
 – Large grain size ® reduced mechanical

 – Casting defects ® stress concentration,

  propensity to fatigue failure
        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
           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
   Contains impurities such as N, O, Fe, H, C
   Impurities increase strength reduce ductility
    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.
  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
             Hydroxyapatites (HA)

   Chemically similar to mineral component of bones
   It will support bone ingrowth and osseointegration
   when used in orthopaedic, dental and maxillofacial
   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
                   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.
       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
                 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

Thermoplastics   Thermosets   Elastomers or

 examples        examples      examples
         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
• Thermoset polymers:
  – Highly cross-linked, 3D network structures
  – Generally brittle (at most temperatures)
  – Decompose when heated and can’t easily be reshaped
    or recycled
             Classes of Polymers (II)
   Elastomers and rubbers                                elastomer

       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 thermoset
             yields a more rigid and brittle material (closer to
             a thermoset)
       Crosslinks allows material to return to
        original shape without plastic deformation
   Oligomer- molecules with n<10 (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
   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 A‟s with B‟s on branches
   Linear polymer- no branches
   Branched polymer - multiple branches
   Crosslinked polymer- links between branches
                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
   Synthesis Reactions:
   Addition polymerization
   Condensation polymerization
   Source: Askeland & Phule p 677
PE (Polyethylene) PP (Polypropylene)

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

   Aka Teflon                  Made flexible and soft
   Very hydrophobic             bythe addition of
   Good lubricity               plasticizers
   Low wear resistance         Not suitable for long
                                 term use because
   Used for catheters and       plasticizers can be
    vascular grafts (Gore-       extracted by thebody
                                Used as tubing for
                                 blood transfusions,
                                 feeding anddialysis, and
                                 blood storagebags
    Elastomers - Entropy

If you stretch it far enough the chains will
line up straight enough to crystallize
      Elastomer vs. Thermoplastic
• 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”                  Styrene butadiene styrene (SBS)

   – Rubbery regions allow large
   – Thermoplastic in nature; can be
     melted since there are no chemical
   Disadvantage
        Thermosets are difficult to re-form
   Advantages in engineering design applications
    1.   High thermal stability and insulating properties
    2.   High rigidity and dimensional stability
    3.   Resistance to creep and deformation under load
    4.   Light-weight
   Crosslinking of thermosets
        10-50% of the „mers‟ in a chain are crosslinked
        Heat treatment, vulcanization processes link existing
        Two part chemistries (resin and curing agent) are mixed
         and react at room temp or elevated temperatures –
         multi-functional end groups
           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
         Fluorinated Polymers
   PTFE
       Plain or expanded (Gore-Tex)
       Vascular grafts, sutures, middle ear prostheses
   Fluorocarbons
       High affinity for oxygen
       Blood substitutes
                                               PTFE unsuccessful in
   Vinylidene Fluoride (PVDF)                 joint replacements

       Piezoelectric
       Actuators, nerve guidance
           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
   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
            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
                 Biological Polymers
   Many cellular and extracellular materials are
       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
   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
Common clinical applications and types of polyCommon clinical
             applications and types of polymers
                      used in medicine
              Polymers In Specific Applications
application      properties and design requirements polymers used

dental           •stability and corrosion resistance,     PMMA-based resins
                 plasticity                               for fillings/prosthesis
                 •strength and fatigue resistance,        polyamides
                 coating activity                         poly(Zn acrylates)
                 •good adhesion/integration with tissue

                 •low allergenicity

ophthalmic       •gel or film forming ability,            polyacrylamide gels
                 hydrophilicity                           PHEMA and
                 •oxygen permeability                     copolymers
orthopedic       •strength and resistance to mechanical PE, PMMA
                 restraints and fatigue                 PL, PG, PLG
                 •good integration with bones and

cardiovascular   •fatigue resistance, lubricity,          silicones, Teflon,
                 sterilizability                          poly(urethanes),
                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
       Flexibility in manufacturing
   "Soft tissue implants" can also be designed for soft
    tissue repair

 Used to repair incisions and lacerations
Important characteristics for sutures::
 Tensile strength

 Flexibility

 Non-irritating
                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
             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
      Dialysis
      Artifical heart

      Cardiac bypass

   Also used for long term delivery of medication or nutrition
   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
                       Artifical Skin

   Is actually a percutaneous implant -- contacts both
    external and biological environments
   No current materials available for permanent skin
   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
           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
       Does not require removal of significant portions of skin
            Soft Tissue Augmentation

   Generally used for reconstructive or cosmetic
   Functions include one or more of the following
       Space filler
       Mechanical support
       Fluid carrier or storer
   Common applications for soft tissue augmentation
       Maxillofacial implants
       Eye and ear implants
       Fluid transfer implants
       Breast implants
               Maxillofacial implants
   Designed to replace or enhance hard or soft tissue in the jaw and
   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
             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)
              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
       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
    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
   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
          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.
     Common Causes of Hip Pain and
         Loss of Hip Mobility
   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.
            Removing 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
        Reaming the Acetabulum
   After the femoral head is
    removed, the cartilage is
    removed from the
    acetabulum using a
    power drill and a special
   The reamer forms the
    bone in a hemispherical
    shape to exactly fit the
    metal shell of the
    acetabular component.
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
   Once the right size and shape
    is determined for the
    acetabulum, the acetabular
    component is inserted into
    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
         Inserting Femoral Stem
   Once the size and
    shape of the canal
    exactly fit the
    femoral component,
    the stem is inserted
    into the femoral
     Attaching the Femoral Head
   The metal ball that
    replaces the femoral
    head is attached to
    the femoral stem.
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.
        Treatment by Kinesiologist
              -Early Postoperative Exercises-
   Regular exercises to restore your normal hip motion
    and strength and a gradual return to everyday
   Exercise 20 to 30 minutes a day divided into 3
   Increase circulation to the legs and feet to prevent
    blood clots
   Strengthen muscles
   Improve hip movement
            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.
    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
Types of mechanical heart valves
         Design challenges of heart valve
   A replaceable model of Cardiac                    Failure safety
    Biological Valve Prosthesis.                      Valve orifice to anatomical orifice
   Thrombogenesis /                                   ratio
    haemocompatibility                                Trans-valvular pressure gradient
        Mechanisms:                                  Minimal leakages
             Forward and backward flow
              shear                                   Replaceable Models of Biological
             Static leakage shear                     Valves
             Presence of foreign material (i.e.
              intrinsic coagulation cascade)
             Cellular maceration
   Valve-tissue interaction
   Wear
   Blockage
   Getting stuck
   Dynamic responsiveness
                 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.
           Lower Limb Prosthesis
   Components of the
   Socket- Forms the
    connection between the
    residual limb and the
   Sleeve- Provides suction
    suspension for prosthesis.
   Shank (pylon)- Transfers
    weight from socket to the
   Foot-ankle- Absorbs shock
    and impact and provides
                 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
 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).
             Surgical Procedure


              Success Rates
          lower jaw, front – 90 – 95%
          lower jaw, back – 85 – 90%
          upper jaw, front – 85 – 95%
          upper jaw, back – 65 – 85%
 First Implant Design by Branemark

All the implant designs are obtained by the
     modification of existing designs.

                           John Brunski
        Comparison of Implant Systems


                               Astra Tech.
      Perfectly elastic large displacement non-linear
       contact finite element analysis for different
                      insertion depths.
                                                Perfectly Elastic Finite Element Results
                                    450000                                   Interference depth: 0.002 in

         Contact Pressure (P) psi
                                    400000                                   Interference depth: 0.004 in
                                    350000                                   Interference depth: 0.006 in
                                         0.47    0.49     0.51      0.53        0.55       0.57         0.59
                                                                 Vertical Position

 Contact pressure increases linearly with insertion depth.
     Elastic-plastic large displacement non-linear
     contact finite element analysis for different
                    insertion depths
              Bilinear Isotropic Hardening Model

                                              % Strain
 Contact Pressure Distribution for Different
              Insertion Depths
                                          Elastic-Plastic Finite Element Results
                                                                     Interference depth: 0.004 in

   Contact Pressure (P) psi
                              250000                                 Interference depth: 0.006 in
                                                                     Interference depth: 0.008 in
                              200000                                 Interference depth: 0.010 in




                                   0.45   0.47   0.49    0.51     0.53     0.55       0.57          0.59
                                                         Vertical Position

 Contact pressure increases non-linearly with larger
insertion depths.
              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

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