Mechanical Engineering homework help

/in /by

Mechanical Engineering homework help.

Classes of Materials Used in Medicine

 
Classes of Materials Used in Medicine

  • Introduction
  • Polymers
  • Hydrogels
  • Metals
  • Ceramics
  • Silicon biomaterials
  • Natural materials
  • Composite materials

Polymers

  • Polymers are a special kind of macromolecule
  • The word polymer comes from the Greek words

“poly,” meaning “many”, and “meres,” meaning
“parts” or “repeating units”

  • A Polymer consists of a large chain of repeating molecules (monomers) that are attached in an end to end fashion

Description of Polymers

  • Imagine a string of beads
    • Each bead is identical (for example, red sphere)
    • Represents the “mer”
    • The string can contain 100’s of beads
    • Represents the “poly” characteristic
    • The string in between the beads represents the chemical bond between monomers

Length of Polymers

  • Polymer chains are HUGE!
  • Polymers typically consist of between

20,000 and 40,000 individual monomers
– If each bead on the string of beads were one inch apart, one polymer molecule could be as long as 10 football fields!!!

  • This chain length is what gives the polymer most of its desirable characteristics

How big are Polymers ?
Check out the chain of beads on the right. Imagine each bead is an ethylene unit;

Ethylene                Polyethylene

Then because there are only 200  ethylene units in this chain (ie it is a 200 – mer),its molecular weight is only 5,600 (= 28 x 200).
Question; if a chain has a molecular B. 15,000 weight of 420,000, how many ethylene  C. 150,000 units does it contain ?                    D. I don’t know and I don’t care!
Even more  molecular weight !
Commercially produced polyethylene’s often have molecular weights in the hundreds of thousands.
To give you a feel for this, imagine that each ethylene unit has a length of 1 inch instead of a couple of angstroms,

                                [-CH2-CH2-]    = 1 inch

then the length of a fully stretched out chain of molecular weight 420,000 would be almost one quarter of a mile !
These are very big molecules indeed.

Description of Polymers

  • Polymer chains are flexible, and usually

“clump” together into a smaller shape

  • This enables the individual chains to interact and become entangled
  • This helps to give a polymer its strength and flexibility

Types of Polymers

  • There are two main types of polymers
  • Natural
  • (cotton, silk, wood, leather…)
  • Synthetic
  • (plastics, nylon, latex…)

 
Polymers
ØPolymers are broadly classified into:
ØSynthetic
ØNatural
ØSynthetic polymers are obtained via polymerization of petroleum-based raw materials through engineered industrial processes using catalysts and heat
Synthetic Polymers
 
 
 
 
 
 
 

Ø  Polyethylene
Ø  Polypropylene
Ø  Polytetrafluoroethylene
(Teflon®)
Ø  Polyvinylchloride
Ø  Polyvinylidenechloride
Ø  Polystyrene
Ø  Polyvinylacetate
Ø  Polymethylmethacrylate
(Plexiglas®)
Ø  Polyacrylonitrile		 Ø  Polybutadiene
Ø  Polyisoprene
Ø  Polycarbonate
Ø  Polyester
Ø  Polyamide (nylons)
Ø  Polyurethane
Ø  Polyimide
Ø  Polyureas
Ø  Polysiloxanes
Ø  Polysilanes
Ø

Polyethers

Natural Polymers

ØNatural polymeric materials have been used throughout history for clothing, decoration, shelter, tools, weapons, and writing materials ØExamples of natural polymers:
ØStarch
ØCellulose (wood)
ØProtein
ØHair
ØSilk
ØDNA and RNA
ØHorn
ØRubber

Natural polymers

  • The wide variety of natural polymers relevant tothe field of biomaterials includes plant materials such as cellulose, sodium alginate, and natural rubber, animal materials such as tissue-based heart valves and sutures, collagen, glycosaminoglycans (GAGs), heparin, and hyaluronic acid, and other natural materials such as deoxyribonucleic acid (DNA), the genetic material of all living creatures.

Natural vs. Synthetic Polymers
Silk
 
Different types of Polymers –
Natural Rubber

  • Polymer cross-linked with sulfur (vulcanization)

 
 
The task of the biomedical engineer is to select a biomaterial with properties that most closely match those required for a particular application.
Because polymers are long-chain molecules, their properties tend to be more complex than those of their short-chain precursors.
Thus, in order to choose a polymer type for a particular application, the unusual properties of polymers must be understood
Molecular Weight (I)

  • Molecular weight, Mi: Mass of a mole of chains.

Lower M                                        higher M

M
M		 n  
w 		x i M i
w i M i

M n  total wt of polymer
total # of molecules
Mw is more sensitive to higher molecular weights
Adapted from Fig. 14.4, Callister 7e.
TABLE : Mechanical Properties of Biomedical Polymers
Fig.  (A) Polymerization of methyl methacrylate (addition polymerization). (B) Synthesis of poly(ethylene terephthalate) (condensation polymerization).
 
Term paper (1-2 pages)
 
Choose any one of following topic and explain type of materials used, applications and their properties

  • Biomaterials and medical applications
  • Applications of hydrogels in medicine
  • Dental biomaterials
  • Implantable Biomaterials Ø Prosthetic vascular grafts
  • Knee and hip joint replacement materials
  • Modern biomaterials and medical applications
  • Polymer based biomaterials
  • Polymer Scoffolds

 

Mechanical Engineering homework help