BIOMATERIALS AND ARTIFICIAL BIOMATERIALS AND ARTIFICIAL ORGANORGAN

BM1303BM1303

S.SudhaS.SudhaLecturer Lecturer

Dept of Biomedical EnggDept of Biomedical Engg

UNIT IUNIT I

INTRODUCTION TO BIOMATERIALSINTRODUCTION TO BIOMATERIALS

During the last two decades, significant advances During the last two decades, significant advances have been made in thedevelopment of have been made in thedevelopment of biocompatible and biodegradable materials for biocompatible and biodegradable materials for medicalapplications.medicalapplications.

In the biomedical field, the goal is to develop and In the biomedical field, the goal is to develop and characterize artificial materialsor, in other words, characterize artificial materialsor, in other words, “spare parts” for use in the human body to “spare parts” for use in the human body to MEASURE,RESTORE and IMPROVE physical MEASURE,RESTORE and IMPROVE physical functions and enhance survival and qualityof life.functions and enhance survival and qualityof life.

What’s a biomaterial?What’s a biomaterial?

1980 - 1980 - Passive Passive and and inert inert point of viewpoint of view Any substance or drugs, of synthetic or natural origin, which 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 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 bodyincreases or replaces any tissue,organ or function of the body

1990 – 1990 – Active Active point of viewpoint of view Non-living material used in a medical device and designed to interact Non-living material used in a medical device and designed to interact

with biological systemswith biological systems

Classification of biomaterials

First generation: INERTDo not trigger any reaction in the host: neither rejected nor recognition “do not bring any good result”

Second generation: BIOACTIVEEnsure a more stable performance in a long time or for the period you want

Third generation: BIODEGRADABLEIt 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 response

Mechanical Properties of Metals

How do metals respond to external loads? Stress and Strain Tension Compression Shear TorsionElastic deformationPlastic 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 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)

Typical mechanical properties of metals

The yield strength and tensile strength vary with priorthermal and mechanical treatment, impurity levels,etc. This variability is related to the behavior ofdislocations in the material. But elasticmoduli are relatively insensitive to these effects.The yield and tensile strengths and modulus ofelasticity decrease with increasing temperature,ductility increases with temperature.

Mechanics of MaterialsMechanics 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 MaterialsMechanics 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.

Viscoelasticity

Definition: time-dependent materialbehavior where the stress response of thatmaterial depends on both the strain appliedand the strain rate at which it was applied! Examples biological materials polymer plastics metals at high temperatures

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

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

Wound healingWound healing

All wounds heal following a a specific All wounds heal following a a specific sequence of phases which may overlapsequence of phases which may overlap

The process of wound healing depends on the The process of wound healing depends on the type of tissue which has been damaged and the type of tissue which has been damaged and the nature of tissue disruption nature of tissue disruption

The phases are:The phases are: Inflammatory phaseInflammatory phase Proliferative phaseProliferative phase Remodelling or maturation phaseRemodelling or maturation phase

The ways in which wounds healThe ways in which wounds heal

Three basic classifications exist:Three basic classifications exist: Healing by primary intentionHealing by primary intentionTwo opposed surfaces of a clean, incised wound Two opposed surfaces of a clean, incised wound (no significant degree of tissue loss) are held together. (no significant degree of tissue loss) are held together. Healing takes place from the internal layers outwardsHealing takes place from the internal layers outwards Healing by secondary IntentionHealing by secondary IntentionIf there is significant tissue loss in the formation of theIf there is significant tissue loss in the formation of thewound, healing will begin by the production ofwound, healing will begin by the production ofgranulation tissue wound base and walls.granulation tissue wound base and walls. Delayed primary healingDelayed primary healing

If there is high infection risk – patient is given antibiotics If there is high infection risk – patient is given antibiotics and closure is delayed for a few days e.g. bitesand closure is delayed for a few days e.g. bites

Wound assessmentWound assessment

WOUND ASSESSMENT

Lab tests: TcPO2 Size, depth

& location

Wound bed:• necrosis• granulation

Surrounding skin: colour, moisture,

Wound edge

Odour or exudate

Signs of infection

The healing processThe healing process

Day 0 – 5Day 0 – 5 The healing response starts at the moment of injury – The healing response starts at the moment of injury –

the clotting cascade is initiatedthe clotting cascade is initiated This is a protective tissue response to stem blood lossThis is a protective tissue response to stem blood loss The inflammatory phase is characterised by heat, The inflammatory phase is characterised by heat,

swelling, redness, pain and loss of function at the swelling, redness, pain and loss of function at the wound sitewound site

Early (haemostasis)Early (haemostasis) Late (phagocytosis)Late (phagocytosis) This phase is short lived in the absence of infection or This phase is short lived in the absence of infection or

contaminationcontamination

GranulationGranulation

Day 3 – 14Day 3 – 14 Characterised by the formation of granulation Characterised by the formation of granulation

tissue in the woundtissue in the wound Granulation tissue consists of a combination of Granulation tissue consists of a combination of

cellular elements including: cellular elements including: Fibroblasts, inflammatory cells, new capillaries Fibroblasts, inflammatory cells, new capillaries

embedded in a loose extra-cellular collagen matrix, embedded in a loose extra-cellular collagen matrix, fibronectin and hyularonic acidfibronectin and hyularonic acid

Moist wound healingMoist wound healing

Basic concept is that the presence of exudate will Basic concept is that the presence of exudate will provide an environment that stimulates healingprovide an environment that stimulates healing

Exudate contains:Exudate contains: Lysosomal enzymes, WBC’s, Lymphokines, growth factors……..Lysosomal enzymes, WBC’s, Lymphokines, growth factors……..

There are clinical studies which have shown that There are clinical studies which have shown that wounds maintained in a moist environment have wounds maintained in a moist environment have lower infection rates and heal more quicklylower infection rates and heal more quickly

Factors affecting healingFactors affecting healing

Immune statusImmune status Blood glucose levels Blood glucose levels (impaired white cell function)(impaired white cell function) HydrationHydration (slows metabolism) (slows metabolism) Nutrition Nutrition Blood albumin levels Blood albumin levels (‘building blocks’ for repair, colloid osmotic (‘building blocks’ for repair, colloid osmotic

pressure - oedema)pressure - oedema) Oxygen and vascular supplyOxygen and vascular supply Pain Pain (causes vasoconstriction)(causes vasoconstriction) Corticosteroids Corticosteroids (depress immune function)(depress immune function)

Host Reactions to BiomaterialsHost Reactions to Biomaterials Effect of the Implant on the HostEffect of the Implant on the Host LocalLocal

Blood material interactionsBlood material interactions Protein adsorptionProtein adsorption CoagulationCoagulation FibrinolysisFibrinolysis Platelet adhesion, activation, releasePlatelet adhesion, activation, release Complement activationComplement activation Leukocyte adhesion, activationLeukocyte adhesion, activation HemolysisHemolysis

ToxicityToxicity

Modification of normal healingModification of normal healing EncapsulationEncapsulation Foreign body reactionForeign body reaction Pannus formationPannus formation

InfectionInfection TumorgenesisTumorgenesis

Systemic and remoteSystemic and remote EmbolizationEmbolization HypersensitivityHypersensitivity Elevation of implant elements in the bloodElevation of implant elements in the blood Lymphatic particle transportLymphatic particle transport

Effect of the Host on the ImplantEffect of the Host on the Implant

Physical – mechanical effectsPhysical – mechanical effects Abrasive wearAbrasive wear FatigueFatigue Stress corrosion, crackingStress corrosion, cracking CorrosionCorrosion Degeneration and dissolutionDegeneration and dissolution

Biological effectsBiological effects Absorption of substances from tissuesAbsorption of substances from tissues Enzymatic degradationEnzymatic degradation CalcificationCalcification

Temporal Variation of Inflammatory Temporal Variation of Inflammatory ResponseResponse

Activated by injury to Activated by injury to vascularized connective vascularized connective tissuetissue

Series of reactionsSeries of reactions Various cellsVarious cells Controlled by Controlled by

endogenous and endogenous and autocoid mediatorsautocoid mediators

UNIT IIUNIT II

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

molds.

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

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

used 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.

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 bioceramicInteraction 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

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

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

UNIT IIIUNIT III

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 polymerizationLoss of H20, HCl or other molecule Polymer properties are more complex than for simpler materialsTypes of polymersBiological polymers DNA, cellulose, starch, proteins, rubber, etc Often reconstituted to form usable polymer Mainly collected from animalsSynthetic polymers Fabricated from petroleum products (generally) May be also a modified biological polymer Most plastics and similar materials

ClassificationClassification

examplesexamples examplesexamples examplesexamples

Thermoplastics Thermosets Elastomers or Rubbers

Polymers

Classes of Polymers (I)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 can’t easily be reshaped

or recycled

Classes of Polymers (II)Classes of Polymers (II)

Elastomers and rubbersElastomers and rubbers Large amounts of elastic deformationLarge amounts of elastic deformation Some (light) cross-linkingSome (light) cross-linking

Typically, about 1 in 100 molecules are cross-Typically, about 1 in 100 molecules are cross-linked on averagelinked on average

Average number of cross-links around 1 in 30 Average number of cross-links around 1 in 30 yields a more rigid and brittle material (closer yields a more rigid and brittle material (closer to a thermoset)to a thermoset)

Crosslinks allows material to return to Crosslinks allows material to return to original shape without plastic deformationoriginal shape without plastic deformation

elastomer

thermoset

Definitions 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 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 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 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

PTFE (Polytetrafluoroethylene)PVC(Polyvinylchloride)

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

Elastomers - EntropyElastomers - Entropy

If you stretch it far enough the chains will line up straight enough to crystallize

Elastomer vs. Thermoplastic Elastomer vs. Thermoplastic ElastomersElastomers

• 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)

ThermosetsThermosets DisadvantageDisadvantage

Thermosets are difficult to re-formThermosets are difficult to re-form Advantages in engineering design applications Advantages in engineering design applications

1.1. High thermal stability and insulating propertiesHigh thermal stability and insulating properties2.2. High rigidity and dimensional stabilityHigh rigidity and dimensional stability3.3. Resistance to creep and deformation under loadResistance to creep and deformation under load4.4. Light-weightLight-weight

Crosslinking of thermosets Crosslinking of thermosets 10-50% of the ‘mers’ in a chain are crosslinked10-50% of the ‘mers’ in a chain are crosslinked Heat treatment, vulcanization processes link existing Heat treatment, vulcanization processes link existing

chainschains Two part chemistries (resin and curing agent) are mixed Two part chemistries (resin and curing agent) are mixed

and react at room temp or elevated temperatures – and react at room temp or elevated temperatures – multi-functional end groupsmulti-functional end groups

Polymers as BiomaterialsPolymers as Biomaterials HydrogelsHydrogels

swellable materials, usually acrylic copolymers, e.g. poly(2-swellable materials, usually acrylic copolymers, e.g. poly(2-hydroxyethyl methacrylate):hydroxyethyl methacrylate): PHEMAPHEMA

More in lecture 10More in lecture 10 Piezoelectric materialsPiezoelectric materials

materials that generate transient electrical charges on their materials that generate transient electrical charges on their surfaces upon mechanical deformation, e.g. polyvinylidene surfaces upon mechanical deformation, e.g. polyvinylidene fluoride, collagenfluoride, collagen

Resorbable materialsResorbable materials Resorbed with time, e.g. polyglycolic and polylactic acidResorbed with time, e.g. polyglycolic and polylactic acid More in lecture 11More in lecture 11

Fluorinated PolymersFluorinated Polymers

PTFE PTFE Plain or expanded (Gore-Tex)Plain or expanded (Gore-Tex) Vascular grafts, sutures, middle ear prosthesesVascular grafts, sutures, middle ear prostheses

Fluorocarbons Fluorocarbons High affinity for oxygenHigh affinity for oxygen Blood substitutesBlood substitutes

Vinylidene Fluoride (PVDF)Vinylidene Fluoride (PVDF) PiezoelectricPiezoelectric Actuators, nerve guidanceActuators, nerve guidance

PTFE unsuccessful in joint replacements

Polymethyl methacrylate Polymethyl methacrylate PMMAPMMA A hydrophobic linear chain polymer that is transparent, A hydrophobic linear chain polymer that is transparent,

amorphous and glassy at room temperature (also known as amorphous and glassy at room temperature (also known as plexiglass or lucite)plexiglass or lucite)

Good light transmittance, toughness, and stabilityGood light transmittance, toughness, and stability A good material for intraocular lenses and hard contact lensesA good material for intraocular lenses and hard contact lenses Also used as a bone cementAlso used as a bone cement

PolyethylenePolyethylene PEPE High density form (HDPE) High density form (HDPE)

Used for tubing in catheters and drainsUsed for tubing in catheters and drains High molecular weight form (UHMWPE) High molecular weight form (UHMWPE)

Contact surface in artificial hips, kneesContact surface in artificial hips, knees Good toughness, resistance to fat and oils, and low Good toughness, resistance to fat and oils, and low

costcost

Polyethylene GlycolPolyethylene Glycol

PEGPEG Short chain neutral hydrophilic polymerShort chain neutral hydrophilic polymer Shown to repel cells due to surface energyShown to repel cells due to surface energy

Used for coatings – non-thrombogenicUsed for coatings – non-thrombogenic Wound healing: polymerization on the woundWound healing: polymerization on the wound

Microencapsulation and drug deliveryMicroencapsulation and drug delivery

Biological PolymersBiological Polymers Many cellular and extracellular materials are Many cellular and extracellular materials are

polymerspolymers Polysaccharides (made from monosaccharides)Polysaccharides (made from monosaccharides)

CelluloseCellulose AlginateAlginate

Proteins (made from amino acids)Proteins (made from amino acids) CollagenCollagen Actin Actin FibrinFibrin

Nucleic Acids (made from nucleotides)Nucleic Acids (made from nucleotides) DNA DNA RNARNA

More in lecture 12More in lecture 12

SiliconesSilicones Silicone polymers Silicone polymers

e.g. Polydimethylsinoxane (PDMS)e.g. Polydimethylsinoxane (PDMS) No carbon backbone – silicone and oxygen insteadNo carbon backbone – silicone and oxygen instead Elastomers (with crosslinks)Elastomers (with crosslinks)

Silicones as biomaterialsSilicones as biomaterials Very low TVery low Tgg Excellent flexibility and stability Excellent flexibility and stability Used in catheters, pacemaker leads, Used in catheters, pacemaker leads,

vascular grafts, and breast and vascular grafts, and breast and facial implantsfacial implants

High oxygen permeability - membrane High oxygen permeability - membrane oxygenatorsoxygenators

Common clinical applications and types of polyCommon clinical applications and types of polymers

used in medicine

Polymers In Specific ApplicationsPolymers In Specific Applications

65

applicationapplication properties and design requirementsproperties and design requirements polymers usedpolymers used

dentaldental •stability and corrosion resistance, stability and corrosion resistance, plasticityplasticity•strength and fatigue resistance, strength and fatigue resistance, coating activitycoating activity•good adhesion/integration with tissuegood adhesion/integration with tissue•low allergenicitylow allergenicity

PMMA-based resins PMMA-based resins for fillings/prosthesisfor fillings/prosthesispolyamidespolyamidespoly(Zn acrylates)poly(Zn acrylates)

ophthalmicophthalmic •gel or film forming ability, gel or film forming ability, hydrophilicityhydrophilicity•oxygen permeabilityoxygen permeability

polyacrylamide gelspolyacrylamide gelsPHEMA and PHEMA and copolymerscopolymers

orthopedicorthopedic •strength and resistance to mechanical strength and resistance to mechanical restraints and fatiguerestraints and fatigue•good integration with bones and good integration with bones and musclesmuscles

PE, PMMA PE, PMMA PL, PG, PLGPL, PG, PLG

cardiovascularcardiovascular •fatigue resistance, lubricity, fatigue resistance, lubricity, sterilizabilitysterilizability•lack of thrombus, emboli formationlack of thrombus, emboli formation•lack of chronic inflammatory lack of chronic inflammatory responseresponse

silicones, Teflon, silicones, Teflon, poly(urethanes), poly(urethanes), PEOPEO

drug deliverydrug delivery •appropriate drug release profile appropriate drug release profile •compatibility with drug, compatibility with drug, biodegradabilitybiodegradability

PLG, EVA, PLG, EVA, silicones, HEMA, silicones, HEMA, PCPP-SAPCPP-SA

suturessutures •good tensile strength, strength good tensile strength, strength retentionretention•flexibility, knot retention, low tissue flexibility, knot retention, low tissue dragdrag

silk, catgut, PLG, silk, catgut, PLG, PTMC-GPTMC-GPP, nylon,PB-TEPP, nylon,PB-TE

UNIT IVUNIT IV

Soft Tissue ImplantsSoft Tissue Implants Attempts have been made to replace or augment most Attempts have been made to replace or augment most

of the soft tissues in the body of the soft tissues in the body Connective tissues: skin, ligament, tendon, cartilage Connective tissues: skin, ligament, tendon, cartilage Vascular tissue: blood vessels, heart valves Vascular tissue: blood vessels, heart valves Organs: heart, pancreas, kidney Organs: heart, pancreas, kidney Other: eye, ear, breastOther: eye, ear, breast

Most soft tissue implants are constructed from Most soft tissue implants are constructed from synthetic polymers synthetic polymers Possible to choose and control the physical and mechanical Possible to choose and control the physical and mechanical

properties properties Flexibility in manufacturingFlexibility in manufacturing

"Soft tissue implants" can also be designed for soft "Soft tissue implants" can also be designed for soft tissue repair tissue repair

Sutures Sutures

Used to repair incisions and lacerationsUsed to repair incisions and lacerationsImportant characteristics for sutures::Important characteristics for sutures:: Tensile strength Tensile strength Flexibility Flexibility Non-irritating Non-irritating

Tissue AdhesivesTissue Adhesives

Used for repair of fragile, non-suturable Used for repair of fragile, non-suturable tissues tissues Examples: Liver, kidney, lungExamples: Liver, kidney, lung

The bond strength for adhesive closed tissues The bond strength for adhesive closed tissues is not as strong after 14 days as for suture is not as strong after 14 days as for suture closed tissuesclosed tissues

Percutaneous ImplantsPercutaneous Implants Refers to implants that cross the skin barrier Refers to implants that cross the skin barrier

In contact with both the outside environment and the In contact with both the outside environment and the biological environmentbiological environment

Used for connection of the vascular system to external Used for connection of the vascular system to external "organs" "organs" Dialysis Dialysis Artifical heart Artifical heart Cardiac bypassCardiac bypass

Also used for long term delivery of medication or nutrition Also used for long term delivery of medication or nutrition (IV)(IV)

Main Problems: Main Problems: Attachment of skin (dermis) to implant difficult to maintain Attachment of skin (dermis) to implant difficult to maintain

through ingrowth due to rapid turnover of cells through ingrowth due to rapid turnover of cells Implant can be extruded or invaginated due to growth of Implant can be extruded or invaginated due to growth of

skin around the implant skin around the implant Openings can also allow for the entrance of bacteria, which Openings can also allow for the entrance of bacteria, which

may lead to infectionmay lead to infection

Artifical Skin Artifical Skin

Is actually a percutaneous implant -- contacts both Is actually a percutaneous implant -- contacts both external and biological environmentsexternal and biological environments

No current materials available for permanent skin No current materials available for permanent skin replacement replacement

Design ideas: Design ideas: Graft should be flexible enough to conform to wound bed Graft should be flexible enough to conform to wound bed

and move with body and move with body Should not be so fluid-permeable as to allow the Should not be so fluid-permeable as to allow the

underlying tissue to become dehydrated but should not underlying tissue to become dehydrated but should not retain so much moisture that edema (fluid accumulation) retain so much moisture that edema (fluid accumulation) develops under the graft develops under the graft

Artificial Skin - PossibilitiesArtificial Skin - Possibilities

Polymeric or collagen-based membrane Polymeric or collagen-based membrane Some are too brittle and toxic for use in burn victims Some are too brittle and toxic for use in burn victims Flexibility, moisture flux rate, and porosity can be controlled Flexibility, moisture flux rate, and porosity can be controlled

Fabrics and sponges designed to promote tissue ingrowth Fabrics and sponges designed to promote tissue ingrowth Have not been successfulHave not been successful

Immersion of patients in fluid bath or silicone fluid to prevent Immersion of patients in fluid bath or silicone fluid to prevent early fluid loss, minimize breakdown of remaining skin, and early fluid loss, minimize breakdown of remaining skin, and reduce painreduce pain

Culturing cells Culturing cells in vitroin vitro and using these to create a living skin and using these to create a living skin graft graft Does not require removal of significant portions of skin Does not require removal of significant portions of skin

Soft Tissue AugmentationSoft Tissue Augmentation

Generally used for reconstructive or cosmetic Generally used for reconstructive or cosmetic enhancement enhancement

Functions include one or more of the following Functions include one or more of the following Space filler Space filler Mechanical support Mechanical support Fluid carrier or storerFluid carrier or storer

Common applications for soft tissue augmentation Common applications for soft tissue augmentation are: are: Maxillofacial implants Maxillofacial implants Eye and ear implants Eye and ear implants Fluid transfer implants Fluid transfer implants Breast implants Breast implants

Maxillofacial implantsMaxillofacial implants Designed to replace or enhance hard or soft tissue in the jaw and faceDesigned to replace or enhance hard or soft tissue in the jaw and face Intraoral prosthetics (implanted) are used to reconstruct areas that are Intraoral prosthetics (implanted) are used to reconstruct areas that are

missing or defective due to surgical intervention, trauma, or missing or defective due to surgical intervention, trauma, or congenital conditioncongenital condition

Must meet all biocompatibility requirementsMust meet all biocompatibility requirements Metals such as tantalum, titanium, and Co-Cr alloys can be used to Metals such as tantalum, titanium, and Co-Cr alloys can be used to

replace bony defectsreplace bony defects Polymers are generally used for soft tissue augmentation Polymers are generally used for soft tissue augmentation

Gums, chin, cheeks, lips, etc.Gums, chin, cheeks, lips, etc. Injectable silicone had been examined for use in correcting facial Injectable silicone had been examined for use in correcting facial

deformities; however, it has been found to cause severe tissue deformities; however, it has been found to cause severe tissue reactions in some patients and can migratereactions in some patients and can migrate

Extraoral prosthetics (external attachment) should: Extraoral prosthetics (external attachment) should: Match the patients skin in color and texture Match the patients skin in color and texture Be chemically and mechanically stable Be chemically and mechanically stable Not creep, change colors, or irritate skin Not creep, change colors, or irritate skin Be easily fabricated Be easily fabricated Have been fabricated out of numerous polymers Have been fabricated out of numerous polymers

Fluid Transfer Implants Fluid Transfer Implants May be designed as permanent implants to treat chronic May be designed as permanent implants to treat chronic

problems problems Hydrocephalus Hydrocephalus

Build up of cerebrospinal fluid in the brain Build up of cerebrospinal fluid in the brain Can result in brain damage if pressure becomes too high Can result in brain damage if pressure becomes too high Treated by draining the fluid to the vascular system or Treated by draining the fluid to the vascular system or

abdominal cavity abdominal cavity Uses a permanent shunt from the ventricles of the brain, Uses a permanent shunt from the ventricles of the brain,

under the skin, to the receiving tissue under the skin, to the receiving tissue Tubing is made of silicone rubber made radiopaque to allow Tubing is made of silicone rubber made radiopaque to allow

for observation with x-raysfor observation with x-rays Ear Infections Ear Infections

"Tubes" in the ears are drainage tubes designed to remove "Tubes" in the ears are drainage tubes designed to remove fluid from the middle ear fluid from the middle ear

Constructed from teflon or other inert materials Constructed from teflon or other inert materials Not permanent implants (removed after several years) Not permanent implants (removed after several years)

Orthopaedic Soft TissueOrthopaedic Soft Tissue Replacement of cartilage, ligaments, and tendonsReplacement of cartilage, ligaments, and tendons Difficult to obtain fixation with bone Difficult to obtain fixation with bone

Screws or pins involve stress concentrations and the possibility of Screws or pins involve stress concentrations and the possibility of corrosion corrosion

Strength of anchorage depends on thickness of cortical bone at Strength of anchorage depends on thickness of cortical bone at attachment siteattachment site

In many cases autographs are used - may be patellar tendon In many cases autographs are used - may be patellar tendon for ACL reconstructionfor ACL reconstruction

Allographs - cryo-preserved, fresh-frozen, or freeze dried Allographs - cryo-preserved, fresh-frozen, or freeze dried specimens taken from cadavers specimens taken from cadavers Often attached to treated bony insertion sites which can be used as Often attached to treated bony insertion sites which can be used as

bone grafts (See Figure 6) bone grafts (See Figure 6) Preservation and cold sterilization procedures may adversely affect Preservation and cold sterilization procedures may adversely affect

properties of implantsproperties of implants Available from tissue banks Available from tissue banks

Artificial Orthopaedic Soft TissuesArtificial Orthopaedic Soft Tissues Ligament Augmentation Devices (LAD's) Ligament Augmentation Devices (LAD's)

Artificial materials used to take some of the stress normally applied to Artificial materials used to take some of the stress normally applied to a ligament while healing occurs a ligament while healing occurs

May or may not be resorbable May or may not be resorbable Gore-Tex: non-resorbable Gore-Tex: non-resorbable PDS: resorbable plastic PDS: resorbable plastic

Contradictory results exist in the literature as to the effectiveness of Contradictory results exist in the literature as to the effectiveness of LAD'sLAD's

Ligament scaffolds Ligament scaffolds Made of polyester or other polymers Made of polyester or other polymers Used to induce tissue ingrowth Used to induce tissue ingrowth May be implanted alone or with a section of tissue (fat pat, fascia lata, May be implanted alone or with a section of tissue (fat pat, fascia lata,

piece of tendon) to increase rate of ingrowthpiece of tendon) to increase rate of ingrowth Region of fixation for artifical ligaments or reconstructions Region of fixation for artifical ligaments or reconstructions

with LAD's for the ACL deviates from normal more than for with LAD's for the ACL deviates from normal more than for reconstructions with patellar tendon alone reconstructions with patellar tendon alone Fibrous tissue instead of normal transition from ligament to bone Fibrous tissue instead of normal transition from ligament to bone

Total Hip ReplacementTotal Hip Replacement A prosthetic hip that is implanted in a similar A prosthetic hip that is implanted in a similar

fashion as is done in people.  It replaces the painful fashion as is done in people.  It replaces the painful arthritic joint.  arthritic joint. 

The modular prosthetic hip replacement system The modular prosthetic hip replacement system used today has three components – the femoral used today has three components – the femoral stem, the femoral head, and the acetabulum.  Each stem, the femoral head, and the acetabulum.  Each component has multiple sizes which allow for a component has multiple sizes which allow for a custom fit.  custom fit. 

The components are made of cobalt chrome The components are made of cobalt chrome stainless steel and ultra high molecular weight stainless steel and ultra high molecular weight polyethylene. polyethylene. CementlessCementless and and cemented prosthesiscemented prosthesis systems are available. systems are available.

Common Causes of Hip Pain and Common Causes of Hip Pain and Loss of Hip MobilityLoss of Hip Mobility

OsteoarthritisOsteoarthritis Usually occurs after age Usually occurs after age

50 and often in an 50 and often in an individual with a family individual with a family history of arthritis. In this history of arthritis. In this form of the disease, the form of the disease, the articular cartilage articular cartilage cushioning the bones of cushioning the bones of the hip wears away. The the hip wears away. The bones then rub against bones then rub against each other, causing hip each other, causing hip pain and stiffness.pain and stiffness.

OperationOperationRemoving the Femoral HeadRemoving the Femoral Head

Once the hip joint is Once the hip joint is entered, the femoral entered, the femoral head is dislocated from head is dislocated from the acetabulum.the acetabulum.

Then the femoral head Then the femoral head is removed by cutting is removed by cutting through the femoral through the femoral neck with a power neck with a power saw. saw.

Reaming the AcetabulumReaming the Acetabulum After the femoral head is After the femoral head is

removed, the cartilage is removed, the cartilage is removed from the removed from the acetabulum using a acetabulum using a power drill and a special power drill and a special reamer. reamer.

The reamer forms the The reamer forms the bone in a hemispherical bone in a hemispherical shape to exactly fit the shape to exactly fit the metal shell of the metal shell of the acetabular component. acetabular component.

Inserting the Acetabular ComponentInserting the Acetabular Component

A trial component, which is A trial component, which is an exact duplicate of your an exact duplicate of your hip prosthesis, is used to hip prosthesis, is used to ensure that the joint will be ensure that the joint will be the right size and fit for the the right size and fit for the client. client.

Once the right size and shape Once the right size and shape is determined for the is determined for the acetabulum, the acetabular acetabulum, the acetabular component is inserted into component is inserted into place. place.

Preparing the Femoral CanalPreparing the Femoral Canal

To begin replacing the To begin replacing the femoral head, special rasps femoral head, special rasps are used to shape and scrape are used to shape and scrape out femur to the exact shape out femur to the exact shape of the metal stem of the of the metal stem of the femoral component. femoral component.

Once again, a trial Once again, a trial component is used to ensure component is used to ensure the correct size and shape. the correct size and shape. The surgeon will also test The surgeon will also test the movement of the hip the movement of the hip joint.joint.

Inserting Femoral StemInserting Femoral Stem Once the size and Once the size and

shape of the canal shape of the canal exactly fit the exactly fit the femoral component, femoral component, the stem is inserted the stem is inserted into the femoral into the femoral canal. canal.

Attaching the Femoral HeadAttaching the Femoral Head The metal ball that The metal ball that

replaces the femoral replaces the femoral head is attached to head is attached to the femoral stem. the femoral stem.

The Completed Hip ReplacementThe Completed Hip Replacement• Client now has a new Client now has a new

weight bearing surface to weight bearing surface to replace the affected hip. replace the affected hip.

• Before the incision is Before the incision is closed, an x-ray is made to closed, an x-ray is made to ensure new prosthesis is in ensure new prosthesis is in the correct position. the correct position.

Treatment by KinesiologistTreatment by Kinesiologist-Early Postoperative Exercises--Early Postoperative Exercises-

Regular exercises to restore your normal hip motion Regular exercises to restore your normal hip motion and strength and a gradual return to everyday and strength and a gradual return to everyday activties.activties.

Exercise 20 to 30 minutes a day divided into 3 Exercise 20 to 30 minutes a day divided into 3 sections.sections.

Increase circulation to the legs and feet to prevent Increase circulation to the legs and feet to prevent blood clotsblood clots

Strengthen musclesStrengthen muscles Improve hip movementImprove hip movement

UNIT VUNIT V

Artificial heart valveArtificial heart valve

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

Types of heart valve prostheses Types of heart valve prostheses There are two main types of artificial heart valves: the There are two main types of artificial heart valves: the

mechanicalmechanical and the and the biological valvesbiological valves.. Mechanical heart valves Mechanical heart valves

Percutaneous implantation Percutaneous implantation Stent framed Stent framed Not framed Not framed

Sternotomy/Thoracotomy implantation Sternotomy/Thoracotomy implantation Ball and cage Ball and cage Tilting disk Tilting disk Bi-leaflet Bi-leaflet Tri-leaflet Tri-leaflet

Biological heart valves Biological heart valves Allograft/isograft Allograft/isograft Xenograft Xenograft

Types of mechanical heart valves Types of mechanical heart valves

Design challenges of heart valve Design challenges of heart valve prostheses prostheses

A replaceable model of Cardiac A replaceable model of Cardiac Biological Valve Prosthesis.Biological Valve Prosthesis.

Thrombogenesis / Thrombogenesis / haemocompatibility haemocompatibility

Mechanisms: Mechanisms: Forward and backward flow Forward and backward flow

shear shear Static leakage shear Static leakage shear Presence of foreign material (i.e. Presence of foreign material (i.e.

intrinsic coagulation cascade) intrinsic coagulation cascade) Cellular maceration Cellular maceration

Valve-tissue interaction Valve-tissue interaction Wear Wear Blockage Blockage Getting stuck Getting stuck Dynamic responsiveness Dynamic responsiveness

Failure safety Failure safety Valve orifice to anatomical orifice Valve orifice to anatomical orifice

ratio ratio Trans-valvular pressure gradient Trans-valvular pressure gradient Minimal leakages Minimal leakages Replaceable Models of Biological Replaceable Models of Biological

Valves Valves

Artificial limbArtificial limb

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

Lower Limb ProsthesisLower Limb Prosthesis Components of the Components of the

ProsthesisProsthesis Socket- Forms the Socket- Forms the

connection between the connection between the residual limb and the residual limb and the prosthesis.prosthesis.

Sleeve- Provides suction Sleeve- Provides suction suspension for prosthesis. suspension for prosthesis.

Shank (pylon)- Transfers Shank (pylon)- Transfers weight from socket to the weight from socket to the foot-ankle.foot-ankle.

Foot-ankle- Absorbs shock Foot-ankle- Absorbs shock and impact and provides and impact and provides stability.stability.

Dental implantDental implant

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

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).

Surgical Procedure

STEP 1: INITIAL SURGERY

STEP 2: OSSEOINTEGRATION PERIOD STEP 3: ABUTMENT CONNECTION STEP 4: FINAL PROSTHETIC RESTORATION

Success Rateslower 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 themodification of existing designs.

John Brunski

Com

paris

on o

f Im

plan

t Sys

tem

sAstra Tech.

ITI

Bicon

Perfectly elastic large displacement non-linear contact finite element analysis for different

insertion depths.

Perfectly Elastic Finite Element Results

050000

100000150000200000250000300000350000400000450000500000

0.47 0.49 0.51 0.53 0.55 0.57 0.59Vertical Position

Con

tact

Pre

ssur

e (P

) psi

Interference depth: 0.002 in

Interference depth: 0.004 in

Interference depth: 0.006 in

Contact pressure increases linearly with insertion depth.

Elastic-plastic large displacement non-linear contact finite element analysis for different

insertion depths

Stress(MPA)

% Strain

Bilinear Isotropic Hardening Model

Contact Pressure Distribution for Different Insertion Depths

Elastic-Plastic Finite Element Results

0

50000

100000

150000

200000

250000

300000

0.45 0.47 0.49 0.51 0.53 0.55 0.57 0.59Vertical Position

Con

tact

Pre

ssur

e (P

) psi

Interference depth: 0.004 inInterference depth: 0.006 in

Interference depth: 0.008 inInterference depth: 0.010 in

Contact pressure increases non-linearly with largerinsertion 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 interfaces