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That is, the polymer is unstable in a water based environment. This is the prevailing mechanism for the polymers degradation. This occurs in two stages. 1. Water penetrates the bulk of the device, attacking the chemical bonds in the amorphous phase and converting long polymer chains into shorter water-soluble fragments.
Vinyl polymers are subject of several structural variations, which greatly expands the range of polymers and their applications. With the exception of polyethylene, vinyl polymers can arise from head-to-tail linking of monomers, head-to-head combined with tail-to-tail, or a mixture of those two patterns. Additionally the substituted carbon center in such polymers is stereogenic (a "chiral center")
A few examples of hydrogel use include organ regeneration, [2] wound healing, [3] [4] [5] and drug delivery. [ 6 ] [ 7 ] Hydrogels are generally classified based on the following characteristics: material, crosslinking mechanism, physical structure, electric charge, and response to stimuli. [ 8 ]
The polymer is dissolved in an organic solvent (such as dichloromethane). Powdered drug and filler (typically an inert sugar) are added to the liquid solution and rapidly mixed to obtain a homogeneous mixture. The drug-filler-polymer mixture is then cast into a mold at −80 °C and freeze-dried until solid.
The biodegradable polymers used in biomedical applications typically consist of hydrolyzable esters and hydrazones. These molecules, upon external stimulation, go on to be cleaved and broken down. The cleaving activation process can be achieved through use of an acidic environment, increasing the temperature, or by use of enzymes. [ 82 ]
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Polymer-drug conjugates are drug molecules held in polymer molecules, which act as the delivery system for the drug. Polymer drugs have passed multidrug resistance (MDR) testing and hence may become a viable treatment for endocrine-related cancers. A cocktail of pendant drugs could be delivered by water-soluble polymer platforms.
An industrially important example is vinyl chloride, precursor to PVC, [3] a plastic commonly known as vinyl. Chessboard made from polyvinyl chloride. Vinyl is one of the alkenyl functional groups. On a carbon skeleton, sp 2-hybridized carbons or positions are often called vinylic. Allyls, acrylates and styrenics contain vinyl groups.