Original text is in : http://www.devicelink.com/mpb/archive/97/11/003.html
* I just summarized until last violet table( where it appears:"5. Lowman AM, and Peppas NA, "Complexation Graft Copolymers as Oral Drug Delivery Systems," Polym Preprints, 38(2):566–567, 1997.")Polymers in Controlled Drug Delivery
Lisa Brannon- Peppas
Polymers are large molecules made of a lot of monomers ( small molecules) covalently bonded. These great molecules are used in controlled drug delivery, that is to say, polymer is combined with active agent, and the latter is released from the material in a predesegned way. This procedure has the goal of reaching better therapies, because it avoides probable both under and overdosis. In fact there is controlled drug delivery systems of long term administration, which allows blood drug level be constant(contrarily of traditional tablets or injections), between the desired maximum(above it there is toxicity) and minimum( under this drug doensn’t have effect).
Biomaterials used for delivery systems should be inert, biocompatible, mechanically strong, comfortable for the patient, safe from accidental releases, between others characteristics. Examples of these biomaterials are: polyvinyl alcohol, polyvinilpirrolidone and polysiloxanes. Each one has different properties like hydrophilicity , that is necessary to get soluble and finally release drug, insulating ability, which is useful in creams for repel water, suspension capabilities, etc.
On the other hand, it’s necessary degrade polymers after they release drug. Luckily, there are polymers designed to degrade inside body into biologically compatible molecules , which then are metabolized and removed. It’s necessary consider some important factors that affect biodegradation of polymers, that is to say, they may produce potentially non desirable molecules e.g. : configuration structure, molecular weight ditribution, sterilization process, mechanism of hydrolysis,etc.
There are different mechanisms of releasing, and they may happen together or only one of these is presented in a releasing system. They are : diffusion, degradation and swelling followed by diffusion.
There are two important releasing systems : matrix drug delivery system, where releasing rate decreases with time and reservoir device system, where drug delivery rate can remain constant.
An important polymer kind, are intelligent polymers, due to they release active agent only when they are placed in a suitable biological environment. These appropiate environments may occurs with a definite pH, temperature, ionic strength, etc.
There are significant application of polymers on diabetes disease and most of they are based on the reaction of blood glucose with glucose oxidase, which produces insulin releasing. In some cases glucose/glucose oxidase reaction reduces pH, and this can produce swelling of polymer, releasing insuline, in other cases, polymer-insulin matrix is sorrounded by a glucose oxidase layer, which reacts and produce insulin releasing in a definite pH. A current delivery system, made of “molecular gates” ,deliveres insulin in response to glucose at low pH.
Moreover, noninvasive glucose monitoring system has been designed. This system brings minute quantities of blood glucose to skin, where it’s possible measure blood glucose levels.
