Engineered polymers for advanced drug delivery

Abstract

Engineered polymers have been utilized for developing advanced drug delivery systems. The development of such polymers has caused advances in polymer chemistry, which, in turn, has resulted in smart polymers that can respond to changes in environmental condition such as temperature, pH, and biomolecules. The responses vary widely from swelling/deswelling to degradation. Drug-polymer conjugates and drug-containing nano/micro-particles have been used for drug targeting. Engineered polymers and polymeric systems have also been used in new areas, such as molecular imaging as well as in nanotechnology. This review examines the engineered polymers that have been used as traditional drug delivery systems and as more recent applications in nanotechnology.

Figure 1

Different types of controlled release systems. (A) Drug delivery based on simple diffusion and partition. (B) Sustained release to prolong the therapeutic period. (C) Pulsatile release to tightly maintain homeostasis. (D) Release profile and drug conversion of the polymer-drug conjugate as a prodrug. (E) Temporally controlled (or sequential) release profile of multiple drugs. (F) On-site release to maximize therapeutic efficiency and to minimize side effect.

Figure 2

Targeting strategies for cancer therapy. (1) Passive targeting can be achieved by enhanced permeation and retention (EPR) effect mediated by leaky vascular structures. Accumulation of macromolecular drugs or nanoparticles increases local drug concentration by degradation of drug carriers at the extracellular space or inside cells after endocytosis. (2) Active targeting mediated by targeting ligands specifically localizes drug carriers at desired cells or tissues. Due to the ligands, primary action mechanism is drug release inside cells after endocytosis. (3) Smart polymer systems loading therapeutic drugs also can be localized by EPR effect. Depending on disease, disintegration or degradation of drug carrier to release drugs can occur. (4) Combination of targeting ligands and smart polymer systems provides more effective release of encapsulated drugs. By environmental signals, drugs can be liberated at the extracellular space or inside target cells according to predetermined program.