Stimuli-responsive and antibacterial cellulose-chitosan hydrogels containing polydiacetylene nanosheets Edwin Shigwenya Madivoli 1,2 , Justine Veronique Schwarte 2 , Patrick Gachoki Kareru 1 , Anthony Ngure Gachanja 1 , Katharina M. Fromm 2 1 Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya, 2 University of Fribourg, Fribourg Switzerland Herein, we report a stimuli-responsive hydrogel with inhibitory activity against Escherichiacoli prepared by chemical crosslinking of carboxymethyl chitosan (CMCs) and hydroxyethyl cellulose (HEC). The hydrogels were prepared by esterification of chitosan (Cs) with monochloroacetic acid to produce CMCs which were then chemically crosslinked to HEC using citric acid as the crosslinking agent. To impart a stimuli responsiveness property to the hydrogels, polydiacetylene-zinc oxide (PDA-ZnO) nanosheets were synthesized in situ during the crosslinking reaction followed by photopolymerization of the resultant composite. To achieve this, ZnO was anchored on carboxylic groups in 10,12-pentacosadiynoic acid (PCDA) layers to restrict the movement of the alkyl portion of PCDA during crosslinking CMCs and HEC hydrogels. This was followed by irradiating the composite with UV radiation to photopolymerize the PCDA to PDA within the hydrogel matrix so as to impart thermal and pH responsiveness to the hydrogel. From the results obtained, the prepared hydrogel had a pH-dependent swelling capacity as it absorbed more water in acidic media as compared to basic media. The incorporation of PDA-ZnO resulted in a thermochromic composite responsive to pH evidenced by a visible colour transition from pale purple to pale pink. Upon swelling, PDA ZnO-CMCs-HEC hydrogels had significant inhibitory activity against E. coli attributed to the slow release of the ZnO nanoparticles as compared to CMCs-HEC hydrogels. In conclusion, the developed hydrogel was found to have stimuli-responsive properties and inhibitory activity against E. coli attributed to zinc nanoparticles. References 1. Barbucci, R., Magnani, A. & Consumi, M. Swelling Behavior of Carboxymethylcellulose Hydrogels in Relation to Cross- Linking, pH, and Charge Density. Macromolecules 33, 7475–7480 (2000). 2. Bashir, S. et al. Fundamental concepts of hydrogels: Synthesis, properties, and their applications. Polymers (Basel). 12, 1–60 (2020). 3. Astrini, N., Anah, L. & Haryono, A. Crosslinking Parameter on the Preparation of Cellulose Based Hydrogel with Divynilsulfone. Procedia Chem. 4, 275–281 (2012). 4. Raucci, M. G. et al. Effect of citric acid crosslinking cellulose-based hydrogels on osteogenic differentiation. J. Biomed. Mater. Res. - Part A 103, 2045–2056 (2015). 5. Socrates, G. Infrared and Raman characteristic group frequencies, third edition . John Wiley & Sons, LTD (2001). doi:10.1002/jrs.1238. 6. Madivoli, E. S., Kareru, P. G., Gichuki, J. & Elbagoury, M. M. Cellulose nanofibrils and silver nanoparticles enhances the mechanical and antimicrobial properties of polyvinyl alcohol nanocomposite film. Sci. Rep. 12, 1–13 (2022). 7. Abreu, F. D. & Campana-Filho, S. P. Preparation and characterization of carboxymethylchitosan. Polimeros 15, 79–83. 8. Jang, S. et al. Polydiacetylene-Based Hydrogel Beads as Colorimetric Sensors for the Detection of Biogenic Amines in Spoiled Food. SSRN Electron. J. (2022) doi:10.2139/SSRN.3992991. 9. Hérault, N. et al. Silver-Containing Titanium Dioxide Nanocapsules for Combating Multidrug-Resistant Bacteria. Int. J. Nanomedicine 15, 1267–1281 (2020).
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