Acetone dissolves the polymer, allowing the gas of the foaming agent to escape. The polymer collapses on itself and is more dense because the gas has been removed.

a. Branched LDPE does not have the required strength for this application.

b. The require strength could be obtained by lining up the molecules of the HDPE in a specific way. By using a thin liner of HDPE, it allows sufficient flexibility.

Plastic bad undergoes ecking when stretch, where the molecules slide past each other, in the direction of the pull. Since bonds are broken and formed, the process is irreversible, the length increases and thickness decreases. Since cellulose molecules in paper are more rigid, which does not allow the molecules to slide past each other, resulting in no necking. The bonds are not formed again after breakage.

a.
i) Non toxic so as to eliminate foreign body respond.
if) The time it takes for the polymer to degrade is proportional to the time required for therapy.
iii) Products from biodegradation are not cytotoxic.
iv) Material easily processed.

b. Hydrogel. It is water absorbing (uses water to transmit oxygen to the eyes), non-toxic, durable and comfortable to wear.

c. Soft: Hydrogel. Thinner lenses, oxygen permeable.
Hard: PMMA. Gas permeable (naturally porous to allow oxygen flow), have a higher clarity but may cause discomfort.