Polyurethanes for controlled drug delivery

Polyurethanes (PUs) are found everywhere the chair we sit on, the comfortable bed we sleep on, every nook and comer of our house, the car we drive, the refrigerator and air conditioner that comfort us, and many other day-to-day objects. PUs can also be used for dmg delivery and may be fabricated as bioinert, biodegradable, stimulus-responsive, shape-memory, conjugated, self-assembled, rigid, flexible, and porous systems. 

4 and 2,6 toluene dllsocyante (TDI) Lysine diisocyanate methyl ester 

Practically, for better control, PUs are synthesized using three different components Dls (ahphatic or aromatic), polyols (mostly diols or triols), and chain extenders (diols or diamines). 

Aromatic Dls are more reactive than aliphatic ones. PUs made from aliphatic Dls are more resistant to ultraviolet irradiation, while aromatic Dl-based PUs can undergo photodegradation [14], The structures of the Dls, polyols, and chain extenders play key roles in the final polymer properties [15]. 

Polyester-based PUs are more sensitive to hydrolytic cleavage than polyether-based PUs. However, the introduction of bulky alkyl side groups into a hydroxyl-terminated polyester (e.g., poly(2,4-diethyl-l,5-pentamethyleneadipate) yields PUs that are more hydrolytically stable with regard to hydrolysis [16]. Polyethylene oxide-based PUs exhibit water sensitivity due to their hydrophihcity and the water-absorbing capacity 

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Biodegradable polyurethanes have been proposed and studied before (9-72). The difference in our study is the inclusion of a phosphoester linkage instead of the commonly used polyester component. This seems to provide more flexibility as the side chain of the phosphate or phosphonate can be varied. For controlled drug delivery applications, drugs can be linked to this site to form a pendant delivery system. Moreover, for certain medical applications, fast degradation rate is obtainable by the introduction of these hydrolyzable phosphoester bonds. With the LDI based polyurethanes, drugs or other compounds of interest can also be coupled to the ester side chain of the lysine portion. 

Case-Study Characterization of a New Biodegradable Polyurethane PU (TEG-HMDI) as Matrix-Forming Excipient for Controlled Drug Delivery... 

Ethylene vinyl acetate has also found major applications in drug delivery. These copolymers used in drug release normally contain 30-50 wt% of vinyl acetate. They have been commercialized by the Alza Corporation for the delivery of pilocarpine over a one-week period (Ocusert) and the delivery of progesterone for over one year in the form of an intrauterine device (Progestasert). Ethylene vinyl acetate has also been evaluated for the release of macromolecules such as proteins. The release of proteins form these polymers is by a porous diffusion and the pore structure can be used to control the rate of release (3). Similar nonbiodegradable polymers such as the polyurethanes, polyethylenes, polytetrafluoroethylene and poly(methyl methacrylate) have also been used to deliver a variety of different pharmaceutical agents usually as implants or removal devices. 

As we shall see in Chapter 15, polyurethane is a polymer of choice for a wide variety of biomedical applications. Polyurethane is used extensively in the construction of devices such as vascular prostheses, membranes, catheters, plastic surgery, heart valves, and artificial organs. Polyurethanes are also used in drug delivery systems such as the sustained and controlled delivery of pharmaceutical agents, for example, caffeine and prostaglandin. ... 

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