Natural fiber exoskeletons of insects and arthropods. In shells and exoskeletons, the chitin fibers contribute to their hierarchical structure. In nature, pure chitin (100% acetylation) does not exist. It instead exists as a copolymer with chitin's deacetylated derivative, chitosan. When the acetylized composition of the copolymer is over 50% acetylated it is chitin. This copolymer of chitin and chitosan is a random or block copolymer. Chitosan is a deacetylated derivative of chitin. When the acetylized composition of the copolymer is below 50% it is chitosan. Chitosan is a semicrystalline “polymer of β-(1-4)-2-amino-2-deoxy-D-glucose”. One difference between chitin and chitosan is that chitosan is
Polymer-drug conjugates tested in drug conjugates. Due to successful clinical proof-of-concept, second-generation conjugates are now being developed. Experimental chemotherapy and novel polymer-based combinations are currently under investigation. Instead of passive targeting developed so far, new approaches will provide receptor-mediated delivery. This will enable selective delivery of anticancer conjugates. A natural polymer dextrin and pendant chain polyacetals, have shown ability of pH-dependent degradation after incorporation into cell compartments. Also diethylstilboestrol (DES) conjugates can undergo pH-dependent degradation. Polymer-Directed Enzyme Prodrug Therapy (PDEPT) is an example of two-step anticancer treatment. Polymer-drug conjugates Polymer-drug conjugates are nano-medicine products under development for cancer diagnosis and treatment. There