Bioresponsive polymers

It should be also noted that the field of smart polymer surfaces is not limited to the macromolecular structures presented in the first part of this chapter. Although some classic stimuli-responsive polymers such as PNIPAM or poly(acrylic acid) have been studied for several years, new exciting options are reported every week in the polymer literature. For instance, the synthesis of chemo- and bioresponsive polymers is a topic in full expansion [9], Thus, new developments in the fields of bioassays and biosensors may be expected in the near future. For instance, more advanced surface concepts (e.g., multiresponsive behaviors, signal cascades) can be anticipated with reasonable certainty. 

We also reported the fer-polymerization strategy with the intent to combine DES (diethylstilboestrol), which is a diol, into the polymer backbone [23]. Hydrolytic degradation studies with these bioresponsive polymers showed an enhanced rate of hydrolysis of the polymer backbone at pH 5.5, in which 65% of DES was released over 96h, in comparison to pH 7.4, where only 4% of DES was released during the same time [23]. This DES containing ter-polyacetal has continued to be developed by Vicent etal. [32,71]. 

Yu H, Wagner E (2009) Bioresponsive polymers for nonviral gene delivery. Curr Opin Mol Ther 11 165-178... 

Polymers can be designed to be bioresponsive and to change their properties in various biological compartments, for example their conformation and charge. They may contain chemical bonds that are cleaved under temporal or spatial control, or they may associate/dissociate in a controlled fashion. Bioresponsiveness of the carrier is required in several steps of the transport (Fig. 1). 

The following sections discuss how polymers and polyplexes can be chemically designed to be bioresponsive in three key delivery functions (1) polyplex surface shielding, (2) interaction with lipid bilayers, and (3) polyplex stability. 

Meyer M, Dohmen C, Philipp A, Kiener D, Maiwald G, Scheu C, Ogris M, Wagner E (2009) Synthesis and biological evaluation of a bioresponsive and endosomolytic siRNA-polymer conjugate. Mol Pharmaceutics 6 752-762... 

Keywords Bioresponsive Cationic polymers Chemical programming DNA ... 

There are numerous examples of polymer surfaces that react with a change of their properties when brought into contact with certain species. These trigger species can be low molar mass molecules (chemoresponsive) or complex biomolecules like DNA or proteins (bioresponsive). Both types of responsive surfaces exist in several varieties depending on their mode of action and the parameter that they affect. 

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