PH-sensitive polymer

Chitosan would not seem suitable as a pH-sensitive polymer because it is soluble at acidic pH values, and becomes insoluble approximately at pH 6.5. Nevertheless, an enteric coating can protect chitosan from the acidity of the stomach. When the preparation reaches the intestine, the en-... 

Figure 3 Acetaminophen release from temperature- or pH-sensitive polymer NiPAAM/ BMA/DEAEMA at pH 2 and 7 and 37°C.

Serres, A., M. Baudys, and S.W. Kim, Temperature and pH-sensitive polymers for human calcitonin delivery. Pharmaceutical Research, 1996.13(2) 196-201. 

Numerous cases exist in the pharmaceutical field in which pH control of drug delivery may be beneficial. For example, the ability to store a drug molecule in the dry state in a polymer, to be released when the polymer reaches a region in the gastrointestinal tract that is characterized by a certain pH range (acidic in stomach, alkaline in the small intestine) has prompted a number of researchers to study pH-sensitive polymer gels as potential drug carriers for oral delivery [1-4]. 

The principle upon which this approach is based is an enzyme-substrate reaction that produces a change in pH and a hydrolytically labile, pH-sensitive polymer containing dispersed therapeutic agent that can vary the erosion rate and concomitant drug release in response to that pH change. Figure 1 shows two types of drug... 

The device shown in Figure 1(a) consists of a pH-sensitive polymer surrounded by a hydrogel containing immobilized enzyme. As the enzyme substrate diffuses from the external environment into the hydrogel and is converted to either an acidic or basic product, the pH within the hydrogel either increases or decreases and the polymer then responds to that pH change by altering its erosion rate. 

In spite of these formidable challenges, the attractiveness of oral route has fueled the exploration of an incredibly diverse set of strategies to deliver proteins and peptides and the subject has been exhaustively reviewed. The various approaches include permeation enhancers, enzyme inhibitors, mucoadhesives, multifunctional matrices that simultaneously incorporate the above strategies, enteric coatings that offer protection from the acidic environment of the stomach, encapsulation (liposomes, microspheres, and nanoparticles), pH-sensitive polymers, microemulsions, carriers (delivery agents), and protein modification either to simply enhance permeability or to exploit specific transporters. While proof-of-concept has been demonstrated with most of these delivery systems in animal... 

Fig. 2. Release rates of encapsulated HPTS at 37°C for liposomes prepared with the pH-sensitive polymer poly(NIPAM-co-MAA) (Mn = 11,000 M /M =2.1) at pH 5.0 (filled circled, 5.8 (filledsquared), and 7.4 (filled trlangled). The extent of content release was calculated from HPTS fluorescence intensity (X. =413 nm, A, =512 nm) relative to measurement after vesicle disruption with 10% (v/ /) Triton X-100...

Cheung CY, Murthy N, Stayton PS, Hoffman AS. A pH-sensitive polymer that enhances cationic lipid-mediated gene transfer. Bioconjung Chem 2001, 12, 906-910. 

Al-Anazi, H. A., Sharma, M.M., 2002. Use of pH sensitive polymer for conformance control. Paper SPE 73782 presented at SPE International Symposium Formation Damage Control, Lafayette, Louisiana, 20-21 February. 

Choi, S.K., Ermel, Y.M., Bryant, S.L., Huh, C., Sharma, M.M., 2006. Transport of a pH-sensitive polymer in porous media for novel mobility control applications. Paper SPE 99656 presented at the SPE/DOE Symposium on Improved Oil Recovery, Tulsa, 22-26 April. 

The methionine and lysine monohydrochloride cores are produced by a melt-binder extrusion spheronization process. Particle diameters are ranging from 1.5 to 2.5 mm. The coating is composed of hydrophobic substances and a pH-sensitive polymer which is able to dissolve or swell in the acidic abomasal medium. The cores are coated in a fluid-bed coater using a solvent-free process (Fig. 3). 

Chen G, Imanishi Y, Ito Y (1997) Micropattem immobilization of a pH-sensitive polymer. Macromolecules 30 7001-7003... 

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