Surfaces, bioresponsive

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. 

Fig. 1 Bioresponsive polyplexes. (a) Systemic circulation of shielded polyplexes in blood stream and attachment to cell surface receptor (b) endocytosis into endosomes, deshielding by cleavage of PEG linkers and activation of membrane-destabilizing component by acidic pH or other means (c) endosomal escape into cytosol (d) siRNA transfer to form a cytosolic RNA-induced silencing complex complex (e) cytosolic migration and intranuclear import of pDNA (/) presentation of pDNA in accessible form to the transcription machinery...

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. 

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. 

Biomaterial wettability can influence the bioresponse of cultured cells [41,42]. Therefore, Li et al prepared vitronectin-coated dishes with different surface charges and wettabilities for hESC culture vitronectin (VN)-coated tissue culture polystyrene dishes (VN-TCPS), VN-coated polyethylene terephthalate films (VN-coated PET), VN-coated polystyrene films that were plasma-treated in advance (VN-coated PS-plasma), VN-coated PET films that were coated with poly-L-lysine in advance (VN-coated PET+PLL), and VN-coated PET films that were coated with polyacrylic... 

FIGURE 85.1 A cartoon representation of multifunctional bioresponsive dendrimer-based delivery system with a targeting moiety, an imaging agent, drug, nucleic acid, and surface capping moieties. 

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