Công nghệ vật liệu trong y sinh học biom aterials chapter 2 classes of materials used in medicine

3 Advanced Program Biomedical Engineering – HUST, VietnamChapter 2 Classes of materials used in medicine Chap.2.. Classes of materials used in medicine- Polymer 4 Advanced Program Biomed

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1 Advanced Program Biomedical Engineering – HUST, Vietnam

Chap 1 Properties of materials

- The structure of solids

- Mechanical properties of materials

- Surface properties of materials

- Role of water in biomaterials Chap 2 Classes of materials used in medicine

- Polymer

- Silicone

- Medical fibers & biotextiles

- Hydrogels

- Applications of “Smart Polymers” as biomaterials

- Bioresorbable and bioerodible materials

Part 1: Material Science & Engineering

Chap 2.(cont.)

- Natural materials

- Metals

- Ceramics, glasses, and glass-ceramics

- Composite

- Nonfouling (Anti-fouling) surfaces

- Surface modification of materials used in medicine

- Textured and porous materials

- Surface-immobilized Biomolecules

cuu duong than cong com

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Chapter 2

Classes of materials used in medicine

Chap.2 Classes of materials used in medicine- Polymer

Classes of biomaterials

-Polymers

-Metals

-Ceramics

-Natural materials

1 What is polymer?

-Long-chain, consists of many repeating units

(monomeric units units)

-Small molecule (repeating units) link together by

primary covalent bonding

-Monomer Monomer: initial substance to form polymer

(ethylene, methyl methacrylate, amide…)

- n (number of repeating units, degree of

polymerization

polymerization): over 1,000 to form strong solids

Small n: oligomer oligomer (M about 500- 6,000)

Great n: high polymer high polymer (104-106)

Mer and chain structure of (a) polytetraflouroethylene;

(b) polyvinylchloride; (c) polypropylene

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Polyethylene: (a) mer and chain structure; (b) Zigzac backbone structure of molecule

- The main backbone chain (polymeric chain) can be made up of different atoms such as polymeric chain

silicone rubber-SR or same atoms such as polyethylene-PE

-Homopolymer Homopolymer: polymer containing one type of repeating units (PMMA, SR, PVC, PE)

-Copolymer Copolymer: two or more type of repeating units (styrene-butadiene rubber, polylactide

polyglycolic acid

- Very different from molecule structure

- Can be synthetic (PE,PP, PMMA) or natural (cellulose, natural rubber, collagen, DNA…)

- Wide range of characteristics (biodegradable or not, hydrophilic or hydrophobic, non-water absorbing or non-water swelling, saturated or not saturated)

- Properties depend on chemical structure, geological structure, polymerization degree (molecular weight

- Classification: thermoplastics, thermosetting, elastomer

2 Nomenclature of polymer

- Usually: adding prefix poly to name of monomer (ethylene- polyethylene; methyl

methacrylate- polymethyl-methacrylate)

- Name of monomers (phenol and formaldehyde- phenolformadehyde

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3 Molecular weight (size)

Average molecular weight

Mn: Number average molecular weight Mw: Weight average molecular weight

Ni: number of mole of species I Mi: molecular weight of species I

Molecular weight distribution

PI: Mw/Mn: Polydispersity index (indicates the breadth of molecular weight

distribution

-Average molecular weight is very important for mechanical properties, adsorption and processing

-Molecular weight distribution shows the homogenity of the properties

3 Synthesis (Polymerization)

3.1 Addition polymerization (chain reaction)

- Simple addition of monomer molecules to each other

- Without the lost of any atoms (no side products)

- Monomers should contain un-saturated bonding such as double bonds, triple bonds, dien (ethylene, acetylene, butadiene…)

- Initiators (can be free radicals, cations, anions or stereospecific catalyst) :usually needed to open double bonds to cause activate site

- Polymerization mechanism: initiation (form activated site for reaction), propagation (additional reaction for rapid chain growth) and termination

- Can result in homo-polymer or copolymer

- Examples: PE, PP, PMMA, PVC

3.2 Condensation polymerization (stepwise growth)

- Two different monomers react to from a covalent bond

- Usually produces small molecules condensed out as side products (water, salt, HCl…)

- Examples: polyester, polyamide, polysiloxane, poly(ethylene terephtalate)

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Example for polymerization

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4 Molecule structure

4.1 Polymer structure

(a): Linear (b): Branched (c): Crosslinked (d): Netwok (three-dimensional)

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4.2 Molecule structure of copolymer

(a): Random (b): Alternating (c): Block (d): Graft (a)

(b)

(c)

(d)

4.4 Polymer chain arrangement

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5 Configuration (Tacticity or Stereoisomerism)

(For linear and branched polymer)

- Tacticity refers to the arrangement of substituent groups around extended polymer chain

-Atactic Atactic configuration: substituent groups at random on other side of extended chain

backbone; can not crystalize (amorphous polymer)

-SyndiotacticSyndiotactic: substituents alternating from side to side of the backbone, may crystallize

-Isotactic Isotactic: substituents located on the same side of the zigzac plane of chain backbone,

may crystallize

Relationship Structure- Characteristics

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7 Important polymeric implant materials

7.1 Polyamide (Nylons)

-Polymerize by step-reaction & ring-scission

-Have interchain hydrogen bonding and high degree of crystallinity, lead to excellent fiber-forming ability, used for surgical sutures

- Basic chemical structure repeating units: different, lead to very different polyamides

- Nylons are hydroscopic & lose their strength in vivo when implanted (water molecules serve as plasticizers

- Proteolytic enzymes also attack amides groups

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Basic chemical structure of PA

from diamine + diacidsNylon ; Nylon type 66 or 610

Nylon type 6

Aromatic polyamides, named Aramide

7.2 Polyethylene

- Can crystallize

- Can polymerized at high pressure with radical catalyst (low density PE), or at low pressure with Ziegler catalyst (high-density PE- not contain branches)

- Crystallinity: very vary

- can be used in solid or porous form

- HDPE: used as tubing for drains and catheters

- Ultra-molecular weight PE (UHMWPE): extensively used in orthopedic implant fabrications (joint implants)

- Biocompatibility: poor

7.2 Polypropylene

-Usually crystallize (except atactic)

- Have exceptional high flexural fatigue life, used to make intergrally molded hinges for finger joint prostheses

-Have excellent environmental stress-cracking resistance, used for sutures and hernia repair

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7.3 Polyacrylates

-Have excellent physical and coloring properties, easy to fabricate

-Extensively used for detal cement (polyacrylic acid), hard contact lenses, bone cement

* Polymethyl metacrylate (PMMA)

-Hydrophobic, amorphous, transparent, glassy at room temperature, tough, stable, excellent light transmittance

-Used as major ingredient for bone cement, good for intraocular and hard contact lenses

•Poly HEMA: soft contact lenses

7.4.PVC

-Tubing (blood transfusion, feeding, dialysis) and blood storage bags

-Plasticizer problem

7.5 PDMS or SR

-For finger joint, hart valves, breath implant, for chin, ear, nose reconstruction

-Oxygenator membranes

7.6 PEG: drug delivery, modify polymer surface to form non-fouling surface

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