# Polymers and Polymer Nanocomposites for Cancer Therapy +
## 3 Biopolymers and Biopolymer Nanocomposites  
By definition, a biopolymer is any polymer that can be degraded by enzymes or through decomposition from the actions of bacteria or fungi. Biopolymers are commonly used in biomedical and healthcare applications. Their nanocomposites are gaining attention for use as antimicrobials, drug carriers, and sensors and in disease diagnosis, tissue engineering, wound healing, and cancer therapy. Biopolymer nanocomposites are very good at holding, protecting, and releasing bioactive drugs such as pharmaceutics, nutraceuticalals, enzymes, and probiotics. A review emphasized the source of biopolymers and their various uses, including cancer drug carriers [33]. Biopolymers can be classified as the following:  
1. [label=()]
2. agro-polymers based on the biomass of agro-resources as raw materials (e.g., starch and cellulose);
3. polymers based on microbial production (e.g., polyhydroxyalkanoates),
4. polymers that are synthesized by using biomass-based monomers (e.g., PLA) [34]. They are especially desired due to their biocompatibility and biodegradability. For special purposes, insoluble biopolymers such as collagen, elastin, chitosan (CS), keratin, and silk can be converted into soluble derivatives through chemical and enzymatic hydrolysis. CS as a drug carrier and curcumin (CUR) as a cancer drug are widely (and mainly) used for chemotherapy. CS applications in medicine and pharmacy are due to its biocompatibility, high charge density, nontoxicity, and mucoadhesion [35]. Polysaccharides have been recognized and applied as promising candidates in biomedical and biotechnological applications, such as diagnosis, bioactive therapy, controlled drug delivery, gene therapy, theranostics, cell encapsulation, tissue engineering, and medical devices, as a benefit of their biocompatibility, biodegradability, inherently low immunogenicity, and unique bioactive properties [36]. CS is a unique cationic polysaccharide derived from chitin, which is extracted from the shells of crabs and other crustaceans. The main advantage of using this polysaccharide for biomedical applications is that its properties can be tailored according to the end use application. CS also has colloidal stability, a tunable membrane, and the ability to encapsulate or integrate a broad range of drugs. CS-based matrices have been effectively used for the controlled delivery of many biomolecules, ranging from small drug molecules to biopolymers [37]. DOX HCl was loaded onto a nanocar made of CS-poly(methacrylic acid) shell and nFe\({}_{3}\)O\({}_{4}\) through electrostatic interactions and strong H bonds. The results obtained suggest that this nanocarir can provide a promising anticancer drug delivery system to effectively reduce the side effects of the drug in healthy tissues [38]. To improve the residence time of the chemotherapeutic agent, the sustained-release properties of a biodegradable nanocarir drug system were used. The advantages were the characteristics of the 5-fluorouracilacil (5-FU)-loaded CS nanoparticles. The sustained release of 5-FU-CS could solve the short half-life problem of 5-FU in hospital use and reduce the side effects caused by frequent drug administration [39]. The combination of CS and graphene can lead to a promising carrier for the loading and controlled release of therapeutic agents [40]. Silver nanoparticles (nAsg) have attracted a great deal of attention in biomedical research, especially in cancer theranostics. Biocompatible polymers such as PEG, pol(vinyl pyrolidone) (PVP), and CS were used for the reduction of Ag salt. In addition to the cancer activity and toxicity of biopolymer nAsg being assessed through synthesis in different conditions and with different properties, they were assessed against breast adenocarcinoma, human lung adenocarcinoma, and mouse embryonic fibroblast cell lines. An effective suppression of the proliferation of cancer cell growth was found [41].