Polymer blends for controlled release coatings

The use of polymer blends as coating materials for controlled drug delivery systems can offer major advantages, including: (i) facilitated adjustment of desired drug release patterns, mechanical properties and drug release mechanisms, (ii) improved film formation and storage stability, and (iii) the possibility to develop novel strategies for site specific drug delivery within the gastro intestinal tract (e.g., colon targeting). However, these systems are more complex than coatings based on only one polymer and care has to be taken when using this type of formulations. For instance, the blended polymers can be incompatible, aqueous polymer dispersions might flocculate and plasticizers potentially redistribute from one polymer into the other during curing and/or long term storage. This article gives an overview on the current state of the art of the use of polymer blends as coating materials for controlled drug delivery, explaining the major advantages and potential pitfalls. Special emphasis is laid on the underlying drug release mechanisms and practical examples for various types of applications are given. Due to the higher complexity of the systems, a thorough understanding of the most important mass transport phenomena involved in the control of drug release can be very helpful to render the optimization of this type of advanced delivery systems more efficient.