Question

1. Define 5-character features of hydrogel that could affect either their performance to be used in stenting systems, their delivery to the tissue, and their ability to enable controlled drug delivery.
2. Define a specific hydrogel matrix and drug target for a metallic stent system. Provide the relevant rationale for the selections.

Answer 1

a) A hydrogel is a three - dimensional (3D) network of hydrophilic polymers that can swell in water and hold a large amount of water while maintaining the structure due to chemical or physical cross linking of individual polymer chains.

Main features are;

• Softness
• Flexibility
• Biocompatibility
• High water content
• Both solid and liquid like property

Advantages of hydrogels :

• administration via various routes
• Increase efficacy and therapeutic index of drug .
• Controlled release
• Reduce the exposure of sensitive tissue to toxic drugs
• Localised action

Disadvantages of hydrogels

• Production cost in high
• Short half life

Delivery to the tissue :

Hydogels are expected to have sustained release and adhere to the tissue for continuous drug delivery. The onset of its pharmacological action is often delayed and duration of its therapeutic effect is sustained.which means that the release of drug ingredients from a controlled drug release delivery system proceeds at a rate profile that is not only predictable kinetically but also reproducible from one unit to another.

b) polymer matrix is the main component of hydrogel. Hydrogel - forming natural polymers include proteins such as collagen and gelatin and polysaccharides such as starch , alginate and agarose.Synthetic polymers that form hydrogels are traditionally prepared using chemical polymerization method.

Advantages :

• Convenient to patient
• Avoid first pass effect
• Improved patient compliance
• Termination of drug is easy
• Used for drug with narrow therapeutic window
• Substitute for administration

Drug eluting stents are metal stents that have been coated with a pharmacologic agent that is known to suppress restenosis.

Most coronary angioplasty procedures or percutaneous coronary interventions involve implanting a stent , a small metal scaffold like device.

The stent is mounted on a baloon and guided to a blockage in the coronary artery.The baloon is inflated , compressing the obstructive plaques and opening of the blockage. The baloon then deflated and withdrawn but the stent is left behind to support the artery.

After receiving a drug eluting stent in addition to aspirin the patient must taken a second antiplatelet drug such as clopidogrel. The dual antiplatelet therapy meets to be continued for a year.

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