Biodegradable cationic polymers

T.R Yang, W. Chin, J. Chemg, M. Shau, Synthesis of novel biodegradable cationic polymer N,N-diethylethylenediamine pol5mrethane as a gene carrier. Biomacromolecules 5 (September-October 2004) 1926-1932. 

In another example, biodegradable cationic polymers based on poly(j3-amino esters) (PbAE) were used for the development of site-specific drug and gene delivery systems. Under acidic conditions PbAE underwent rapid dissolution, releasing its content. For example, it has been observed that... 

Another cationic polymer, poly- -(4-aminobutyl)-L-glycolic) acid (PLAGA) has been shown to condense DNA efficiently and also to be less cytotoxic than PLL. PLAGA is biodegradable, not toxic to the cells, and enhances transfection in cultured cells (202). 

Water-soluble biodegradable polycarboxylates with an acetal or ketal weak link were inventions of Monsanto scientists in the course of their search for biodegradable deteigent polymers. However, the polymers were prevented by economics from reaching commercial status. The polymers are based on the anionic or cationic polymerization of glyoxylic esters at low temperature (molecular weight is inversely proportional to the polymerization temperature) and subsequent hydrolysis to the salt form of the polyacid, which is a hemiacetal (R = H) or ketal (R = CH3) if methylglyoxylic acid is used, and stable under basic conditions. 

Polysaccharide Containing Polymers. Chitosan (Table 7.3-1) is composed of 2-amino-2-deoxy p-D-glucan and is prepared from naturally occurring chitin via alkaline deacetylation. Unlike other cationic polymers chitosan is nontoxic and biodegradable, making it an ideal candidate for therapeutic applications. Although the density of positive charges of chitosan is lower than for other cationic polymers. 

Natural cationic polymers are generally non-toxic, derived from renewable resources, biocompatible, biodegradable and possess low immunogenicity. Most natural cationic polymers contain reactive sites, which can be easily modified to improve physicochemical properties. 

Various biodegradable polycarbonate(s) (PC) polymers have been fabricated via the organocatalytic ring-opening polymerisation of functional cyclic carbonate monomers, which were quarternised to create cationic polymers with various pendent structures such as alkyl, aromatic and imidazolinium (Figure 8.4). These polymers have shown excellent antimicrobial properties and haemolytic characteristics when assayed using rat red blood cells [98]. 

Cationic polymers were probably superior mucoadhesives due to the ability to develop molecular attraction forces by electrostatic interactions with the negative charges of the mucus the polyca-tionic chitosan was investigated as an ophthalmic vehicle. The polymer is biodegradable, biocompatible, and non-toxic. It possesses antimicrobial and wound-healing properties. Moreover, chitosan exhibits a pseudoplastic and viscoelastic behavior. ... 

A major drawback of nanopartides formulated using cationic polymers that has limited thdr progress toward use in dinical trials is toxidty. Although the molecular basis of toxidty is undear, the polycationic nature of the polymers appears to be the main origin of toxidty. Thus, recent efforts to devdop polymers with reduced toxidty have focused on low-MW polymers, biodegradable polymers, and polymers with reduced cationic charge density. 

Natural cationic polymers are derived from renewable sources and possess inherent positive charges. They are biodegradable and often possess low immunogenicity and low toxicity. Numerous natural cationic polymers have functional groups like carboxylic acid groups that can be further modified to carry therapeutic molecules. 

This group of cationic polymers includes all those natural polymers that require further modification in order to acquire a cationic character. Therefore, they differ from the biopolymers with inherent cationic properties and those cationic polymers that are produced artificially using polymerization methods. Such polymers often retain their biodegradability, while the introduction of positive charges leads to increased cytotoxicity and therefore decreased biocompatibility. 

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