Boron Nitride Nanotube Reinforced Polymers

Chitosan Reinforced with Boron Nitride Nanotubes

Another biopolymer that is commonly used in tissue engineering is the polysaccharide chitosan as it is non-toxic, has good biocompatibility, enzymatic degradation and antimicrobial activity against viruses, bacteria and fungi. It is produced by deacetylation of chitin, and its main applications are in wound patches for healing skin traumas [21-23]. Drawbacks that limit its applications in scaffold engineering are its low mechanical strength (like gelatin) but also its high swelling ratio and most importantly uncontrolled degradation. In order to address these issues the reinforcement with boron nitride nanotubes (BNNTs) has been examined.

BNNTs are biocompatible and have a high elastic modulus ~1.22 TPa [24], which allows them to increase the low strength of chitosan networks. Despite their high modulus, they have a high ductility and therefore their addition does not affect the ductility of the host polymer they reinforce [25]. Since BNNTs are not biodegradable cytoxicity measurements have been performed and it was shown that they did not affect cell death [26].

In fabricating BNNT-polymer composites it is necessary to functionalize the BNNTs in order to increase their hydrophyllicity and hence dispersion within the aqueous solution during the fabrication process. Use of surfactants is not preferred for biomedical applications as they can increase toxicity and therefore chemical modification with -OH is commonly performed. The following subsections summarize the work by [27].

Fig. 4.3 Scanning electron microscopy images of (a) pure chitosan scaffold surface; (b) chitosan reinforced with BNNT-OH (Reproduced with permission from Ref. [27])