Shape Memory Polymers


Brandon Wilson, Nick Makansi
NOTE- We were given permission to do a Metal Alloy instead of a Polymer, because of the nature of shape memory polymers.

Overview

Shape Memory Polymers (SMP) are polymers that have the ability to retain and return to a predefined shape. This property makes this these polymers extremly valuable to medical implants, as well as fabric marketing. SMPs are molded into the form remembered by the polymer by many repetitions of heating, deformation, then cooling.

The concept of Shape Memory Polymers was first discovered in Europe in the early 1900s but was furthered in the Naval Ordinance Lab with the creation of Nitinol (Nickel Titanuium) in the 1960s. Nitinol is approximately a 50:50 ratio of Nickel to Titanium. Nitinol is a material called a Shape Memory Alloy because the bond between Nickel and Titanium creates an alloy. When a scientist in the Naval Ordinance Lab
wrapped Nitinol around his finger and then touched the Nitinol wire with the end of a cigarette; the wire began to unravel. The heat of the cigarrette triggered the Nitinol to revert back to its original shape; SMPs react to an ouiside stimulus, such as temperature change.

Two properties allow Nitinol to remember it's shape: Thermal Memory (Shape Memory or Thermal Shape Recovery) and Superelasticity (Mechanical Memory or Elastic Shape Recovery). Thermal shape recovery occurs when an SMP remembers its original shape by a change in temperature. Elastic shape recovery occurs when a mechanical force is applied to an SMP then released; when the force is released the polymer returns to its original shape. Thermal memory and Mechanical memory are linked through the atomic structure.




General

Technical and Common Name: Shape Memory Polymers
Polymer Type: Synthetic
Biodegradability: SMP's can be engineered to be biodegradable or not to suit the purpose for which the material is made. Some medical SMPs are biodegradable because it is beneficial for them to break down in the body. Other SMPs, such as stints used in heart surgery, are not biodegradable.

General Properties

Physical

  • More flexible than non shape memory materials
  • Preforms shape memory proccess when initiated with an outside stimulus (temperature change, application/release of mechanical force, aplication of a magnetic field, and change in pH.

Chemical

  • Atomic structure is altered in two phases:
    1. Austenite- high temperature phase
    2. Martensite- Low temperature phase


  • ||

    Nitinol Properties

Physical

    • Abrasive material before machining process because of the titanium oxide surface
    • Metal alloy of Nickel and Titanium (NiTi)
    • Density = 6.45 to 6.5 g/cm3
    • Heating at 500 C degrees is neccessary to set a shape for Nitinol
  • Chemical

    • The Titanium oxide layer protects Nitinol from corrosion (reasearchers have indicated Nitinol is more resistant from corrosion than stainless steel.
    • Biocompatable with the human body (Biocompatablity-the ability of a material to perform with an appropriate host response in a specific application)
Nitinol (NiTi) Structure
Nitinol (NiTi) Structure


Electron "Sea" Model
Electron "Sea" Model

Properties of Metals:


1. High electrical conductivity
2. High thermal conductivity
3. Ductility, malleability, pliability
4. Luster


Metallic Bonding:

When metals bond they form crystals. Electrons may travel throughout that crystal without being attatched to any ion.
Electrons in a metallic bond are said to be delocalized, meaning they are distributed throughout the crystal.

Electron-Sea Model:

Metals are pictured as a "sea" of cations and electrons.

Medical Uses: Surgery,implants, etc

Because of SMPs unique ability to remember and change shape, this makes it very valuable to medical procedures and surgeries. For instance, Nitinol is very valuable to make stints for heart surgery to clear away clogs in valves and vessels. While this had to be done by inflating a balloon before, it is now able to be done by modern-technology SMPs. The shape-memory ability of SMPs allow them to be placed into the body with small incisions. For example, a degradable shape memory suture was created.

http://www.youtube.com/watch?v=rZpZhSdgdSI</span>
- Video of a lecture given at UC Berkeley by a "Nitinol Metallurgist" about the background and medical uses of Nitinol
http://www.memry.com/nitinolfaq/nitinolfaq.html#whatisnitinol AND http://www.nitinol.info/
-Two companies that specialize in Nitinol products




Citations

"Nitionol Devices & Components." NDC 13 may 2008 <http://www.nitinol.info/flash/index.php>.
-Company that works with Nitionol devices and products of nitinol
"Dr. Allen Pelton." UC Berkeley Youtube Channel 20 AUG 2008 13 may 2008 <http://www.youtube.com/watch?v=rZpZhSdgdSI>.</span>
-lecture from Dr. Allen Pelton on the background and uses of Nitinol

Lendlein, Andreas . "Biodegradable, Elastic Shape-Memory Polymers for Potential Biomedical Applications." Science Magazine 25 APR 2002 13 may 2008 <http://www.sciencemag.org/cgi/content/abstract/296/5573/1673>.</span>
- Article describing the medical benefits of Shape-Memory Polymers.

"Nitionol FAQ." Memry Corperation 13 may 2008 <http://www.memry.com/nitinolfaq/nitinolfaq.html#whatisnitinol>.</span>
-general background information on nitinol
"Shape Memory Polymers." Wikipedia 13 may 2008 <http://en.wikipedia.org/wiki/Shape_Memory_Polymers>.</span>
- wikipedia article on Shape Memory Polymers