PH-responsive systems

Changes in pH cause phase changes in certain random copolymers of acrylic acid and methacrylamidopropyl trimethylammonium chloride, which make them ideal candidates for pH-responsive systems. At different pH values, the positively and negatively charged groups interact... 

The micellization of a polypeptide eontaining DHBC has been also studied under variable solution pH and temperature [30]. A sehizophrenic solution behavior was observed for a PNIPAM-PGA block copolymer. At room temperature and low pH values micelles having polypeptide cores were formed, while at elevated temperatures and increased pH values micelles with PNIPAM cores were observed. It has to be noted that the formation of PGA eoie micelles was accompanied by a coil-to-helix transition of the polypeptide sequence. The above transition had as a result a different micellization kinetic profile for the system in eomparison with other conventional pH responsive systems. 

The experiment was then reproduced with (PSS/PAH) capsules templated on fully decomposable CdCOj cores, in order to eliminate a possible effect of the M F material [29]. The results were reproducible and encapsulation was successful using true capsules, showing that the (PSS/PAH) pair is a usable pH-responsive system. 

Surface charge reversal One more mechanism of drug release from the pH-responsive system is surface charge reversal, which involves a change in the surface charge to facilitate the release of drugs. For example, a few researchers have developed mesoporous silica NPs, which were surface-functionalized with different densities of positively charged trimethylammonium (TA]... 

Figure 2.9 shows a schematic representation of the uptake and release mechanisms employed in this pH-responsive system. By tuning the pH and electrolyte content of the system, a 98% release of loaded material could be achieved. 

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