Biopolymer modification approaches

Finally, the efficacy of bulk- and surface-modification approaches on 3D scaffolds of commonly used biopolymers remains a fruitful area of research. Therefore, the modification approaches discussed in this review should be transformed to CS nanoparticles and 3D microporous scaffolds. The development of CS nanohybrids is another emerging area that relies on nanoparticles of different sizes, shapes, and materials used to tune CS properties. Nanoparticles can be used to improve CS properties. Since CS is an implantable biomaterial, better control over CS shape memory properties is important for the development of minimally invasive surgeries. 

The realization of the reasons for poor biocompatibility of general alkoxides with biopolymers led to the development of approaches to minimize or eliminate the problem of the detrimental effect of alcohols. This can be done in two ways modification of the sol-gel processing or the silica precursor. This is considered in some detail below. 

The chemical modification of CS biopolymers via reductive amination, to yield alkylated CS derivatives, and further quaternisation result in very efficient antibacterial materials the degree of activity is correlated to the length of the alkyl chain and bacterial strain. The most active CS derivatives are more selective at killing bacteria than the quaternary ammonium disinfectants, cetylpyridinium chloride and benzalkonium chloride, and AMP. Vanillin can be used as a crosslinker of CS nsing this approach, functionalised antimicrobial polymers based on CS, vanillin. Tween 60 and so on may be easily prepared. Imino-CS biopolymer films, prepared by the acid condensation of the amino groups of CS with various aldehydes, can be used as functional biodynamic materials. 

FIGURE 4.1 Schematic approach used in the modification of biopolymers (a) blends, (b) chemical linkages, (c) cross-linking, (d) grafting, and (e) biocomposite formation (i, biopolymer matrix ii, biopolymer fillers iii, surface modified inorganic materials). (See insert for color representation of the figure.)... 

The advent of azide/alkyne click chemistry, reintroduced by Sharpless and Meldal earlier this century, has prompted an avalanche of publications in the fields of biochemistry, material science and biopolymers. As of 2008, more than 1000 publications on this subject are listed on the Sharpless website. I have noticed that gradually other [3+2] and [4+2] cycloaddition reactions are included, indicating that cycloaddition chemistry is useful for construction and modification of biopolymers. Especially, the [3+2] Huisgen chemistry is useful because in addition to azides many other 1,3-dipolar species react with dipolarophiles at room temperature and the yields often approach quantitative. There is also renewed interest in [4+2] Diels-Alder chemistry. 

Recently it was suggested that the modification of biopolymers with hydro-phobic residues enhance their binding to cell membranes and may promote them to penetrate into cells [50]. This approach was successfully applied for protein [51] and oligonucleotide [52] introduction into intact mammalian cells. 

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