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

Part 1: Material Science & Engineering
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

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- Polymer
- Silicone
- Medical fibers & biotextiles
- Hydrogels

- Applications of “Smart Polymers” as biomaterials

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- Bioresorbable and bioerodible materials

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Part 1: Material Science & Engineering

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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

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Chap.2. Classes of materials used in medicine- Polymer

Chapter 2

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Classes of materials
used in medicine

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Chap.2. Classes of materials used in medicine- Polymer

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Classes of biomaterials
-Polymers
-Metals
-Ceramics
-Natural materials
1. What is polymer?
-Long-chain, consists of many repeating units
(monomeric
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 (M about 500- 6,000)
. Great n: high polymer (104-106)
Mer and chain structure of (a) polytetraflouroethylene;
(b) polyvinylchloride; (c) polypropylene

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Chap.2. Classes of materials used in medicine- Polymer

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Polyethylene: (a) mer and chain structure; (b) Zigzac backbone structure of molecule
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Chap.2. Classes of materials used in medicine- Polymer

- The main backbone chain (polymeric

polymeric chain)
chain can be made up of different atoms such as
silicone rubber-SR or same atoms such as polyethylene-PE

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

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- 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, nonwater absorbing or 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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Chap.2. Classes of materials used in medicine- Polymer
3. Molecular weight (size)
Average molecular weight
Mn: Number average molecular weight
Mw: Weight average molecular weight
Ni: number of mole of species I

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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

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-Molecular weight distribution shows the homogenity of the properties

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Chap.2. Classes of materials used in medicine- Polymer

3. Synthesis (Polymerization)
3.1. Addition polymerization (chain reaction)

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- Simple addition of monomer molecules to each other

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- 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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Chap.2. Classes of materials used in medicine- Polymer

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Example for polymerization

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Example for polymerization

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Chap.2. Classes of materials used in medicine- Polymer

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Chap.2. Classes of materials used in medicine- Polymer

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Example for polymerization

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Chap.2. Classes of materials used in medicine- Polymer

4. Molecule structure

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4.1. Polymer structure

(a): Linear
(b)

(a)

(b): Branched
(c): Crosslinked
(d): Netwok (threedimensional)

(c)

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(d)

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Chap.2. Classes of materials used in medicine- Polymer
4.2. Molecule structure of copolymer

(a): Random
(a)

(b): Alternating
(c): Block

(d): Graft

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(b)

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(d)

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Chap.2. Classes of materials used in medicine- Polymer

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4.4. Polymer chain arrangement

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Chap.2. Classes of materials used in medicine- Polymer
5. Configuration (Tacticity or Stereoisomerism)
(For linear and branched polymer)
- Tacticity refers to the arrangement of substituent groups around extended polymer chain
- Atactic configuration: substituent groups at random on other side of extended chain
backbone; can not crystalize (amorphous polymer)
- Syndiotactic:
Syndiotactic substituents alternating from side to side of the backbone, may crystallize

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

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Relationship Structure- Characteristics

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Chap.2. Classes of materials used in medicine- Polymer

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7. Important polymeric implant materials

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Chap.2. Classes of materials used in medicine- Polymer

7.1. Polyamide (Nylons)

-Polymerize by step-reaction & ring-scission

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-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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Chap.2. Classes of materials used in medicine- Polymer
Basic chemical structure of PA

from diamine + diacidsNylon ; Nylon type 66 or 610

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Nylon type 6

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Aromatic polyamides, named Aramide

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Chap.2. Classes of materials used in medicine- Polymer

7.2. Polyethylene
- Can crystallize

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- 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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Chap.2. Classes of materials used in medicine- Polymer

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Chap.2. Classes of materials used in medicine- Polymer
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

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7.4.PVC

-Tubing (blood transfusion, feeding, dialysis) and blood storage bags
-Plasticizer problem
7.5 PDMS or SR.

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

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7.6. PEG: drug delivery, modify polymer surface to form non-fouling surface
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Chap.2. Classes of materials used in medicine- Polymer

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