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Unformatted text preview: Biomaterials: Properties, Types and applications Part II- Ceramics MECH 634- SPRING SEMESTER 2010 Prepared by: Nasser-Eddin M., Ph.D 1 OUTLINES OUTLINES Biomaterials: Properties, Types, and Applications 4.1 Ceramics properties and application 4.2 Case study 2 Ceramic Ceramic Biomaterials (Bioceramics) The The class of ceramics used for repair and replacement of diseased and damaged parts of the musculoskeletal system are referred to as bioceramics. bioceramics OBJECTIVES OBJECTIVES To To examine chemical/physical properties of ceramics To To introduce the use of ceramics as biomaterials To To explore concepts and mechanisms of bioactivity 3 Ceramics Ceramics (keramikos- pottery in Greek) keramikosCeramics Ceramics are polycrystalline compounds Usually Usually inorganic Highly Highly inert Hard Hard and brittle High High compressive strength Generally Generally good electric and thermal insulators Good Good aesthetic appearance Applications: Applications: orthopaedic orthopaedic implants dental dental applications compromise noncompromise of non-load bearing for bioactivity 4 Types Types of Bioceramics 5 Mechanical Mechanical Properties 6 Nature’s Nature’s Ceramic Composites Natural Natural hard tissues are “ceramic”“ceramic”polymer composites: • Bones, Teeth Tissue Tissue = organic polymer fibers + mineral + living cells Mineral Mineral component (Ceramic) • Bone: hydroxyapatite (HA) – Ca5(PO4)3OH Mineralization Mineralization under biological conditions: • Many elemental substitutions • Protein directed crystallization • Unique characteristics – crystal morphology and solubility Synthetic Synthetic calcium phosphates are used as biomaterials – “bioactive” Synthetic HA Bone HA 7 Bioactivity Bioactivity vs. Biocompatibility Biocompatibility Biocompatibility : Objective Objective is to minimize inflammatory responses and toxic effects Bioactivity Bioactivity - Evolving concept: The The characteristic that allows the material to form a bond with living tissue (Hench, 1971) The The ability of a material to stimulate healing and trick the tissue system into responding as if it were a natural tissue (Hench (Hench 2002). Advantages: Advantages: Bone tissue – implant interface, enhanced healing response, extends implant life Biodegradability: Biodegradability: Breakdown Breakdown of implant due to chemical or cellular actions If If timed to rate of tissue healing transforms implant to scaffold for tissue regeneration Negates Negates issues of stress shielding, implant loosening, long term stability 8 Inert Inert Ceramics: Alumina History History: since since early seventies more than 2.5 million femoral heads implanted worldwide. alumina-onalumina-on-alumina implants have been FDA monitored over 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) 380 High hardness: Low Low friction Low Low wear Corrosion Corrosion resistance Friction: surface finish of <0.02 um Wear: no wear particles generated – biocompatible 9 Inert Inert Ceramics: Aluminum Oxides (Alumina – Al2O3) Applications Applications orthopaedics: orthopaedics: • femoral head • bone screws and plates • porous coatings for femoral stems • porous spacers (specifically in revision revision surgery) • knee prosthesis dental: dental: crowns and bridges 10 10 Alumina Alumina Bioinertness Results Results in biocompatibility – low immune response Disadvantage: Disadvantage: • Minimal bone ingrowth • Non-adherent fibrous membrane Non• Interfacial failure and loss of implant can occur 11 Bioactive Bioactive Ceramics: Glass Ceramics Glass: Glass: an an inorganic melt cooled to solid form without crystallization an an amorphous solid Possesses Possesses short range atomic order Brittle! Brittle! Glass Glass-ceramic is a polycrystalline solid prepared by controlled crystallization crystallization of glass 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 bone- • • 12 12 Composition Composition includes SiO2, CaO and Na2O Bioactivity Bioactivity depends on the relative amounts of SiO2, CaO and Na2O Cannot Cannot be used for load bearing applications Ideal Ideal as bone cement filler and coating due to its biological activity 13 Calcium Calcium (Ortho) Phosphate Structure Structure resembles bone mineral; thus used for bone replacement 7 different forms of PO4 based calcium phosphates exist - depend different on Ca/P ratio, presence of water, pH, impurities and temperature 14 14 Calcium Calcium Phosphate • Powders • Scaffolds • Coatings for implants – metals, heart valves to inhibit clotting • Self-Setting bone cement 15 15 Calcium Calcium Phosphates Uses Uses repair repair material for bone damaged trauma or disease void void filling after resection of bone tumors repair repair and fusion of vertebrae repair repair of herniated disks repair repair of maxillofacial and dental defects ocular ocular implants drugdrug-delivery coatings coatings for metal implants, heart valves to inhibit clotting 16 Why Why Use Bioceramics? General Options Toxic/ Imunogenic/ Disease transmission? Mechanical Properties? Bioactive? Degradable? Autograft Allograft Metals Ceramics Polymers Composites Excellent Moderate Low 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 17 Pros Pros and Cons Ceramics and glasses Advantages • Very biocompatible (particularly with bone) • Inert • Low wear rates • Resistant to microbial attack • Strong in compression • Difficult to machine Disadvantages • Brittleness • Potential to fail catastrophically 18 18 Ceramics Ceramics and glasses-Application 1-déjà vu! glasses1- In this artificial hip joint, the polymer bearing surface and some of the metallic components have been replaced by ceramics to improve the durability of the joint replacement. This design features a ceramic femoral head and acetabular cup. (Photograph of the LINEAGE 1 ceramic– ceramic acetabular cup system is courtesy of Wright Medical Technology, Inc.) 19 Due to the high melting point of most ceramics, which prevents them from being cast or extruded, ceramic components are typically made from powdered stock. the porosity must be nearly totally removed or the residual porosity acts as microcracks within the material and weakens it. In other applications such as bone graft substitutes it is desirable to have large pores pores like those in trabecular or cancellous bone so that cells can infiltrate the material and grow new vital tissue. In this case, pores are typically created by using second phases, such as polymer beads, that maintain pore space during the early processing steps and are then burned out during the final sintering stage. If there is an insufficient amount of the patient’s own bone or donor bone available to fill a bone defect, synthetic bone graft substitutes made of calcium phosphate or calcium sulfate may be used. (Photograph of OSTEOSET1surgical grade calcium sulfate resorbable beads is courtesy of Wright Medical Technology, Inc.) 20 Homework II 21 Case Study for Ceramics DENTAL DENTAL IMPLANTS AND USE OF CERAMICS 22 Dental Prosthesis-StrautmanDental Prosthesis-Strautman-Germany 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 35 35 36 36 ...
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This note was uploaded on 02/07/2011 for the course MECH 633 taught by Professor Mohammadnasserdine during the Spring '10 term at American University of Beirut.

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