Amino acid-based polymers

Uchegbu and coworkers have studied the complexation and delivery of DNA using a unique poly(amino acid)-based polymer vesicle. A polymer of either poly (L-lysine) or poly(L-omithine) was functionalized with methoxy-poly(ethylene glycol) (mPEG) and hydrophobic palmitic acid chains to synthesize an amphiphilic triblock of either mPEG-6-poly(L-lysine)-6-palmitoyl or mPEG-Z>-poly(L-omithine)-6-palmitoyl. Vesicles formed from these polymers were complexed with DNA and showed improved transfection in vitro over poly(amino acid) complexed with DNA or DNA alone [82]. 

Amino acid-based polymers have been investigated as a potential source of valuable biomaterials for several decades. However, with the notable exception of poly(y-substituted glutamates), most amino acid-derived polymers exhibit problems with immunogenicity and poor mechanical properties for most biomedical applications. In order to overcome these limitations, Bourke and Kohn " devised a combinatorial strategy using amino acid monomers polymerized through non-amide... 

Cationic amino acid-based polymers possess limited transfection efficacies due to their high toxieities. To solve this problem. Pun and colleagues prepared poly(L-lysine) (PLL) and poly(hydroxypropyl methacrylate) (PHPMA)... 

Amino acid-based polymers synthesized from naturally occurring amino acids, for example by amidation of the amino group of an amino acid... 

From 1970, amino acids-based homo- and copolymers were studied for biomedical applications the idea was quite intuitive, because proteins are made of amino acids. However, initial studies showed that most poly(amino acids) could not be employed for biomedical applications because of immunogenicity problems and poor mechanical properties. Only a small number of poly(y-substituted glutamates) possess adequate characteristics to be interesting. In order to improve mechanical and physiological features of these materials, amino acids can be used as monomeric building blocks in polymers that do not have a backbone with the conventional structure which can be found in peptides. These materials are the so called non-peptide amino acids-based polymers or amino-acid-derived polymers with modified backbone , and can be divided into four main categories (Bourke and Kohn, 2003) ... 

Amino acids are natural nutrients. Polymers derived from amino acids may have advantageous biocompatibility, as demonstrated by PLA. However, amino acid based polymers often do not have good material properties. They are often difficult to process into 3-D structure, and possess poor mechanical properties. Tyrosine-derived polymers have been developed in the Kohn group as biodegradable polymers, which have shown certain promising properties (56), and have been used for bone tissue engineering research (57). 

Fig. 10 (a-j) Weak polycations without steric stabilizer other amino acid-based polymers such as polyglutamic acid, polyomithine, polyhistidine, etc. 

By certain physical factors like thermal, ultraviolet irradiation, high pressure and other chemical parameters like organic solvents the helical pol5mers are easily denaturalized. A variety of helical polymers are synthesized, which include polyisocyanates, polyisocyanides, polychloral, polymethacrylates, polysilanes, polythiophenes, poly (p-phenylene)s, poly(l-methylpropargyl-ester)s, poly(phenylacetylene)s and poly (-unsaturated ketone) [18-24] (Fig. 1). Other polymers are whose optical activity is main chain or side chain chirality dependent e.g. amino-acid-based polymers are nontoxic, biocompatible and biodegradable. 

Chung, I.-D., Britt, R, Xie, D., Harth, E., Mays, J. Synthesis of amino acid-based polymers via atom transfer radical polymerization in aqueous media at ambient temperature. Chem. Commun. 8, 1046-1048 (2005)... 

AAms like NIPAAm and N-ethylmethylacrylamide (EMA) or AAms containing proline and hydroxyproline moiety, iV-acryloyl-L-proline (A-Pro-OH) and N-acryloyl-4-trans-L-proline (A-Hyp-OH), can be readily polymerized. The latter case afforded well-defined amino acid based polymers. A-B-A stereoblock polymers with atactic PNIPAAm as a hydrophilic block (either A or B) and a non-water-soluble block consisting of isotactic PNIPAAm can also be synthesized using RAFT polymerizations. The synthesis of polyam-... 

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