Biocompatibility polymer stability

Polyvinyl alcohol (PVA), which is a water soluble polyhidroxy polymer, is one of the widely used synthetic polymers for a variety of medical applications [197] because of easy preparation, excellent chemical resistance, and physical properties. [198] But it has poor stability in water because of its highly hydrophilic character. Therefore, to overcome this problem PVA should be insolubilized by copolymerization [43], grafting [199], crosslinking [200], and blending [201], These processes may lead a decrease in the hydrophilic character of PVA. Because of this reason these processes should be carried out in the presence of hydrophilic polymers. Polyfyinyl pyrrolidone), PVP, is one of the hydrophilic, biocompatible polymer and it is used in many biomedical applications [202] and separation processes to increase the hydrophilic character of the blended polymeric materials [203,204], An important factor in the development of new materials based on polymeric blends is the miscibility between the polymers in the mixture, because the degree of miscibility is directly related to the final properties of polymeric blends [205],... 

Protein drugs have been formulated with excipients intended to stabilize the protein in the milieu of the pharmaceutical product. It has long been known that a variety of low molecular weight compounds have the effect of preserving the activity of proteins and enzymes in solution. These include simple salts, buffer salts and polyhydroxylated compounds such as glycerol, mannitol, sucrose and polyethylene glycols. Certain biocompatible polymers have also been applied for this purpose such as polysaccharides and synthetic polymers such as polyvinyl pyrrolidone and even nonionic surfactants. 

Applications. Polymers with small alkyl substituents, particularly (13), are ideal candidates for elastomer formulation because of quite low temperature flexibility, hydrolytic and chemical stability, and high temperature stability. The ability to readily incorporate other substituents (in addition to methyl), particularly vinyl groups, should provide for conventional cure sites. In light of the biocompatibility of polysiloxanes and P—O- and P—N-substituted polyphosphazenes, poly(alkyl/arylphosphazenes) are also likely to be biocompatible polymers. Therefore, biomedical applications can also be envisaged for (3). A third potential application is in the area of solid-state batteries. The first steps toward ionic conductivity have been observed with polymers (13) and (15) using lithium and silver salts (78). 

As with normal hydrocarbon-based surfactants, polymeric micelles have a core-shell structure in aqueous systems (Jones and Leroux, 1999). The shell is responsible for micelle stabilization and interactions with plasma proteins and cell membranes. It usually consists of chains of hydrophilic nonbiodegradable, biocompatible polymers such as PEO. The biodistribution of the carrier is mainly dictated by the nature of the hydrophilic shell (Yokoyama, 1998). PEO forms a dense brush around the micelle core preventing interaction between the micelle and proteins, for example, opsonins, which promote rapid circulatory clearance by the mononuclear phagocyte system (MPS) (Papisov, 1995). Other polymers such as pdty(sopropylacrylamide) (PNIPA) (Cammas etal., 1997 Chung etal., 1999) and poly(alkylacrylicacid) (Chen etal., 1995 Kwon and Kataoka, 1995 Kohorietal., 1998) can impart additional temperature or pH-sensitivity to the micelles, and may eventually be used to confer bioadhesive properties (Inoue et al., 1998). 

A scientific breakthrough in order to design USCAs on demand can be seen in the third generation (Myomap, Quantison, BiSphere and Sonavist). Compared to the more or less free bubbles of the first and second generations, the novel type of USCAs consist of encapsulated microbubbles with a shell formed by a biopolymer (like human albumin) and/or a biocompatible synthetic polymer (like copolymers of poly-lactide and polyglycolide or derivatives of polycyanoacrylate). In addition to the prolongation of the lifetime in the blood stream, these polymer-stabilized microbubbles can be manufactured to fulfill certain needs, and to interact with diagnostic ultrasound in a defined and optimal manner. 

The drive towards microencapsulation systems based on the use of synthetic hydrophilic methacrylate based polymers is fueled by their proven biocompatibility, (56) hydrolytic stability, (57) ease of synthesis (66, 67) and enormous structural diversity made possible through copolymerization. In contrast, interest in polysaccharide gel formers such as alginate is founded upon the relative ease of capsule formation under physiological conditions. It would seem inevitable that attempts be made to combine the host biocompatibility and stability of methacrylate based polymers with the ease of capsule formation... 

F. Nakamura, M. Fujitani, Y. Machida, and T. Nagai, Physicochemical stability of halopredone acetate ground mixtures with biocompatible polymers [in Japanese], Yakuzaigaku 53, 161-168(1993). 

The synthetic biocompatible polymer, Jeffamine D2000, which was shown earlier to have interfacial properties [24], was added to the monomer phase to ensure cationic stabilization of the weak spots during the polymerization process. In this case, high solid contents were obtained when adding only small amounts of Jeffamine (0.5 to 2.5 wt.% with respect to the monomer phase), and very small and monodisperse latexes in the size range ca. 100 to 200 nm without any coagulate could easily be synthesized. It is interesting to note that when the Jeffamine con-... 

A review is presented of the use of degradable polymers for use in controlled drug delivery. Emphasis is given to the preparation, applications, biocompatibility, and stability of microspheres from hydrolytically degradable polymers. 320 refs. 

Polymers that, to date, have been investigated for their electrical conducting properties include polypyrrole, polyaniline, polythiophene, and polymer nanotube composites. The advantages of conducting polymers include good conductivity, biocompatibility, good stability, low impedance ability to entrap molecules, efficient charge transfer, and ability to entrap biomolecules. 

---