CLASSIFICATION OF BIOMATERIALS

Metals

Semiconductor Materials

Ceramics

Polymers

Synthetic BIOMATERIALS

Orthopedic screws/fixation

Dental Implants

Dental Implants

Bone replacements

BiosensorsImplantable Microelectrodes

Skin/cartilageDrug Delivery Devices Ocular

implants

METALIC BIOMATERIALS

Crystal structures and strong metallic bonds - orthopedic applications

- the face and jaw surgery

- cardio-vascular surgery

material joint prosthesis and bone renewal

Dental implant

Artificial heart parts, heart valve

Metals used as Biomaterials

SteelCobalt-containing alloysTitanium and titanium containing alloysDental amalgam (XHg)GoldNickel- titanium alloys

Corrosion;

The undesired chemical reaction of metals with their surruondings that forms oxygen, hydroxide and other compounds then degradation

Corroding Metal X Biocompatible

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Ceramic Biomaterials (Bioceramics)

The class of ceramics used for repair and replacement of diseased and damaged parts of the musculoskeletal system are referred to as bioceramics.

OBJECTIVES To examine chemical/physical properties of ceramics To introduce the use of ceramics as biomaterials To explore concepts and mechanisms of bioactivity

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Ceramics

(keramikos- pottery in Greek)

Ceramics are refractory polycrystalline compounds Usually inorganic Highly inert Hard and brittle High compressive strength Generally good electric and thermal insulators Good aesthetic appearance

Applications: orthopaedic implants dental applications compromise of non-load bearing for bioactivity

BIOCERAMICS

Bioceramics;

Repair the parts of body that injured or lost their function, restructuring or special ceramics are designed to replace ;

- polycrystalline structure ceramic (alumina),

- bioactive glass,

- bioactive glass-ceramics,

- bioactive composites…

Using Areas of Bioceramics

Glasses,Diagnostic devices, Thermometers,Tissue culture vessels.

Filling materials, Gold-porcelain coating,Prosthetic parts

Health Sector

Dental

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Structure

Ceramic Structure: AmXn

A: A: metal, +vemetal, +ve

X: X: nonmetal, nonmetal, -ve-ve

CsCl NaCl

ZnS

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Nature’s Ceramic Composites

Natural hard tissues are “ceramic”-polymer composites:

» Bones, Teeth, Shells Tissue = organic polymer fibers +

mineral + living cells Mineral component (Ceramic)

» Bone: hydroxyapatite (HA) – Ca5(PO4)3OH

Mineralization under biological conditions:

» Many elemental substitutions

» Protein directed crystallization

» Unique characteristics – crystal morphology and solubility

Synthetic calcium phosphates are used as biomaterials – “bioactive”

Synthetic HA Bone HA

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Types of Ceramics

nearly bioinert

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Bioactivity vs. Biocompatibility

Biocompatibility : Objective is to minimize inflammatory responses and toxic effects

Bioactivity - Evolving concept: The characteristic that allows the material to form a bond with

living tissue (Hench, 1971) The ability of a material to stimulate healing and trick the

tissue system into responding as if it were a natural tissue (Hench 2002).

Advantages: Bone tissue – implant interface, enhanced healing response, extends implant life

Biodegradability: Breakdown of implant due to chemical or cellular actions If timed to rate of tissue healing transforms implant to scaffold

for tissue regeneration Negates issues of stress shielding, implant loosening, long

term stability

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Classification based on tissue attachment

B. Amsden CHEE 340 14

Mechanical Properties

BIOCERAMICS

Bioactive ceramic, that allows the chemical bond formation between tissue and implantBioinert ceramic, that doesn’t allow the chemical bond formation between tissue and implant

BIOINERT BIOACTIVE

MATERIAL TISSUE

TOXIC DEAD

Bioinert

NON-TOXIC

Bioactive

Soluble

Various thicknesses of fibrous tissue

binding of tissue-implant interface,

Tissue replaces

İmplant place

Classification of Bioceramics According to Tissue Responses

Ceramic implants are non-toxic

Implant Type Tissue response

Example

Nonporous, dense and inert ceramics

The formation of very fine fibrous tissue

Alumina, Zirconia

Porous inert ceramics

The tissue growth in pores

Hydroxyapatite

Resorbable ceramics

Absorption Tricalcium phosphate

Bioactive glasses

Bioceramics According to Structural Functions

Oxide ceramics, inert structure, polycrystalline ceramics consisting of metal ions in the plane formed by the dissolution of oxygen ions

Alumina (Al2O3) orthopedic applications

Zirconia (ZrO2) femoral prosthese

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Inert Ceramics: Alumina

History: since early seventies more than 2.5 million femoral heads implanted

worldwide. alumina-on-alumina implants have been FDA monitored over 3000 implants have been successfully implemented since 1987

Smaller the grain size and porosity, higher the strength E = 380 GPa (stress shielding may be a problem)

High hardness: Low friction Low wear Corrosion resistance Friction: surface finish of <0.02 umWear: no wear particles generated – biocompatible

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Inert Ceramics: Aluminum Oxides (Alumina – Al2O3)

Applications orthopaedics:

»femoral head»bone screws and plates»porous coatings for femoral stems»porous spacers (specifically in revision

surgery)»knee prosthesis

dental: crowns and bridges

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Alumina

Bioinertness Results in biocompatibility – low immune response

Disadvantage:»Minimal bone ingrowth»Non-adherent fibrous membrane » Interfacial failure and loss of implant can occur

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Inert Ceramics: Zirconia, ZrO2

zirconium; named from the Arabic, zargun = gold color

Fabrication:• Obtained from the mineral zircon• Addition of MgO, CaO, CeO, or Y2O3 stabilize

tetragonal crystal structure (e.g. 97 mol%ZrO2 and 3 mol%Y2O3)

• Usually hot-pressed or hot isostatically pressed

Applications:

• orthopaedics: femoral head, artificial knee, bone screws and plates, favored over UHMWPE due to superior wear resistance

• dental: crowns and bridges

Glass and glass-ceramics: Silica(SiO2) –based ceramics (Includes Lithium-Aluminum or Magnesium-Aluminum crystals )

Bioglass: Instead of some silica groups, calcium, phosphorus or sodium is present (SiO2, Na2O, CaO, P2O5)

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Bioactive Ceramics: Glass Ceramics

Glass: an inorganic melt cooled to solid form without crystallization an amorphous solid Possesses short range atomic order Brittle!

Glass-ceramic is a polycrystalline solid prepared by controlled crystallization of glass

Glass ceramics were the first biomaterials to display bioactivity (bone system):• Capable of direct chemical bonding with the host tissue• Stimulatory effects on bone-building cells

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Bioactive Ceramics: Glass Ceramics

Composition includes SiO2, CaO and Na2O

Bioactivity depends on the relative amounts of SiO2, CaO and Na2O

Cannot be used for load bearing applications

Ideal as bone cement filler and coating due to its biological activity

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Bioactive Ceramics: Glass ceramics

B

AC

D

SiO2

CaO Na2OA: Bonding within 30 days

B: Nonbonding, reactivity too low

C: Nonbonding, reactivity too high

D: Bonding

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Bioactive Ceramics: Glass Ceramics

Bioactive: capable of direct chemical bonding with the host biological tissue

Glass:

• an inorganic melt cooled to solid form without crystallization

• an amorphous solid

• possesses short range atomic order BRITTLE!

Glass-ceramic is a polycrystalline solid prepared by controlled crystallization of glass LESS BRITTLE

Calcium-phosphate ceramics ; their structure is the form of multiple oxides of calcium and phosphate atoms

Hydroxyapatite Ca5(PO4)3OH,

Tricalcium phosphate, Ca3(PO4)2

Oktacalcium phosphate CaH(PO4)3.2OH

In medicine and dentistry

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Biodegradable Ceramics: Calcium (Ortho) Phosphate

Structure resembles bone mineral; thus used for bone replacement Coating of metal implants to promote bone ingrowth Different forms exist depending on Ca/P ratio, presence of water,

impurities and temperature

7 different forms of PO4 based calcium phosphates exist - depend on Ca/P ratio, presence of water, pH, impurities and temperature

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Calcium Phosphate

• Powders

• Scaffolds

• Coatings for implants – metals, heart valves to inhibit clotting

• Self-Setting bone cement

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Calcium Phosphates

Uses repair material for bone damaged trauma or disease void filling after resection of bone tumors repair and fusion of vertebrae repair of herniated disks repair of maxillofacial and dental defects ocular implants drug-delivery coatings for metal implants, heart valves to inhibit clotting

Advantage of Bioceramics

The resistance to Microorganisms,Temparature, Solvents pH changesHigh pressures is the advantage in health and dental aplications

Bioceramics are used repair or renewal of a hard

connective tissue in the skeleton

The elderly, the bones are very brittle

slow-moving cracks, uncertainties to durability in different strokes and pressures

The most important reasons for limiting the use of bioceramics,

Interaction of bioceramics with tissues

All materials placed on live tissue, takes response from tissue

TISSUE - IMPLANT

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Why Use Bioceramics?

GeneralOptions

Toxic/ Imunogenic/ Disease transmission?

Mechanical Properties?

Bioactive? Degradable?

Autograft

Allograft

Metals

Ceramics

Polymers

Composites

Excellent

LowModerate

Advantages to Bioceramics:

• Biological compatibility and activity

•Less stress shielding

•No disease transmission

•Unlimited material supply

Disadvantage of Bioceramics:

• Brittleness – not for load bearing applications