Fundamentals of BIOMATERIALS By Professor Dr Fadhil Attiya

Fundamentals of BIOMATERIALS By Professor Dr. Fadhil Attiya Chyad University of Technology Department of Materials Engnieering

What is Biomaterial? n A biomaterial can be defined as any material used to make devices to replace a part or a function of the body in a safe, reliable, economic, and physiologically acceptable manner. n A biological material is a material such as bone, skin, or artery produced by a biological system. n The success of a biomaterial is highly dependent on three major factors: (1) the properties and biocompatibility of the implant, (2) the health condition of the recipient (3) the competency of the surgeon who implants and monitors its progress. n n n 2

Biocompatibility Requirements • Acute systemic toxicity • Cytotoxicity • Hemolysis • Intravenous toxicity • Mutagenicity • Oral toxicity • Pyrogenicity • Sensitization 3

The Requirements for an Implant • Acceptance of the plate to the tissue surface, i. e. , biocompatibility • Pharmacological acceptability (nontoxic, nonallergenic, nonimmunogenic, noncarcinogenic, etc. ) • Chemically inert and stable (no time-dependent degradation) • Adequate mechanical strength • Adequate fatigue life • Sound engineering design • Proper weight and density • Relatively inexpensive, reproducible, and easy to fabricate and process for large-scale production 4

Application & Classification 5

Examples of Biomaterials application n Artificial hip joint Needed because natural joint wear out. n Replacement hip joint are implanted in more than 90 000 humans each year in US. n Fabricated from titanium, ceramics, composite, UHMWPE. n After 10 -15 years, the implant may loose, require another operation. n 6

Examples of Biomaterials application n Prosthetic Heart valve n Fabricated from carbon, metal, elastomers, fabrics, natural valves and tissue chemically pretreated. 7

Examples of Biomaterials application n Intraocular lenses (IOL) n n n Used to replace a natural lense when it become cloudy due to cataract formation. Fabricated of poly (methyl methacrylate), silicone elastomer, soft acrylic polymers or hydrogels. Complication: IOL stimulate outgrowth cells from the posterior lens capsule → cloud the vision. 8

Bioceramics • The class of ceramics used for repair and replacement of diseased and damaged parts of the musculoskeletal system are referred to as bioceramics. • The field of bioceramics is relatively new (1970 s), but many bioceramics are not new materials. 9

Advantages & Disadvantages Advantages: — Biocompatible — Wear resistant — Lightweight (certain compositions) Disadvantages: — Low tensile strength — Difficult to fabricate — Low toughness — Not resiliant 10

Ceramic Implants and the Structure of Bone • The ceramic should be compatible with the physiological environment • Its mechanical properties should match those of the tissue being replaced • Most concern in the use of bioceramics: • Cancellous (spongy bone) • Cortical (compact bone) 11

Bioinert Ceramics Bioinert ceramics: — maintain their physical and mechanical properties while in the host. — resist corrosion and wear, and have all the properties for bioceramics. 12

Bioactive Ceramics — A bioactive material is one that elicits a specifi c biological response at the interface of the material, which results in the formation of a bond between tissues and the material. Some types of bioactive ceramics: — Bioactive glasses — Bioactive glass-ceramics — Hydroxyapatite (HA) 13

Ceramic Implants and the Structure of Bone • The ceramic should be compatible with the physiological environment • Its mechanical properties should match those of the tissue being replaced • Most concern in the use of bioceramics: • Cancellous (spongy bone) • Cortical (compact bone) 14

Bioactive Glasses — The first and most thoroughly studied bioactive glass is known as Bioglass. R 45 S 5 and was developed at the University of Florida. — Bioglass. R 45 S 5 is a multicomponent oxide glass with the following composition (in wt%): 45% Si. O 2, 24. 5% Na 2 O, 24. 4% Ca. O, and 6% P 2 O 5 Fabrication of BGs: — BGs can be made using the processes developed for other silicate glasses. The constituent oxides, or compounds that can be decomposed to oxides, are mixed in the right proportions and melted at high temperatures to produce a homogeneous melt. On cooling a glass is produced. — It is necessary to use high-purity starting materials and often the melting is performed in Pt or Pt alloy crucibles to minimize contamination 15

Advantages and disadvantages of BGs Advantages: — a relatively rapid surface reaction — the reaction rates and mechanisms have been determined — the bonding process (Si. O 2–hydroxycarboapatite layer) — close to that of cortical bone. Disadvantages: — mechanically weak — tensile bending strengths are typically 40– 60 MPa — the fracture toughness is low 16

Bioactive Glass-Ceramics • Glass-ceramics are produced by ceramming a glass: converting it to a largely crystalline form by heat treatment • Typical bioactive glass-ceramics: • Cerabone. R A-W is a glass-ceramic containing oxyfluoroapatite (A) and wollastonite (W). • Ceravital. R is primarily now used in middle ear operations. • Bioverit IR is a class of bioactive machinable glass. 17

Hydroxyapatite (HA) Key Properties of HA — The ability to integrate in bone structures and support bone ingrowth, without breaking down or dissolving (i. e it is bioactive). — Hydroxyapatite is a thermally unstable compound, decomposing at temperature from about 800 -1200 o. C depending on its stoichiometry. — Generally speaking dense hydroxyapatite does not have the mechanical strength to enable it to succeed in long term load bearing applications 18

Hydroxyapatite (HA) — Two forms for biomedical applications: either dense or porous — Bioceramic Coatings: Coatings of hydroxyapatite are often applied to metallic implants (most commonly titanium/titanium alloys and stainless steels) to alter the surface properties. — Bone Fillers： Hydroxyapatite may be employed in forms such as powders, porous blocks or beads to fill bone defects or voids. 19

Bioceramics in Composite — main reason forming composites is to improve the mechanical properties, most often toughness, above that of the stand-alone ceramic. — The first bioceramic composite was a stainless-steel fiber/bioactive glass composite made of Bioglass 45 S 5 and AISI 316 L stainless steel. Other current bioceramic composites of interest: — Ti-fiber-reinforced bioactive glass — Zr. O 2 -reinforced A-W glass — TCP-reinforced PE — HA-reinforced PE 20

Porous Bioceramics Applications of Porous Bioceramics 21

Porous Bioceramics 22

Applications of Bioceramic 23

Polymeric Biomaterials Advantages of polymeric biomaterials are ease of manufacturability to produce various shapes (latex, film, sheet, fibers, etc. ), ease of secondary processability, reasonablecost, and availability with desired mechanical and physical properties. Applications of polymeric biomaterials: — medical disposable supply — prosthetic materials — dental materials — implants — dressings — extracorporeal devices — encapsulants — polymeric drug delivery systems — tissue engineered products 24

Medical Applications of Biodegradable Polymers • • • Wound management Sutures Staples Clips Adhesives Surgical meshes Orthopedic devices Pins Rods Screws Tacks Ligaments • • • Dental applications Guided tissue regeneration. Membrane Void filler following tooth extraction Cardiovascular applications Stents Intestinal applications Anastomosis rings Drug delivery system Tissue engineering controlled drug release tissue engineering Required properties: — non-toxic — capable of maintaining good mechanical integrity until degraded — capable of controlled rates of degradation 25

Metallic Biomaterials 26

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