Antibacterial polylactic acid fabricated via Pickering emulsion approach with polyethyleneimine and polydopamine modified cellulose nanocrystals as emulsion stabilizers.

Antibacterial biodegradable plastics are highly demanded for food package and disposable medical plastic consumables. Incorporating antibacterial nanoagents into polymer matrices is an effective method to endow polymers with antibacterial activity. However, synthesis of sustainable antibacterial nanoagents with high antibacterial activity via facile approach and well dispersion of them in polymer matrices are still challenging. In this study, polyethyleneimine (PEI) was grafted on surface of cellulose nanocrystals (CNCs) via the oxidation self-polymerization of dopamine (DA) and the Michael addition/Schiff base reaction between DA and PEI. The resulted PEI and polydopamine modified CNCs (PPCs) showed substantially enhanced antibacterial activity and reduced cytotoxicity for NIH3T3 than PEI due to increased local concentration and anchoring of PEI. The minimum concentration of PPCs to achieve antibacterial rate of 99.99 % against S. aureus and E. coli were about 50 and 20 µg/mL, respectively. PPCs displayed outstanding emulsifying ability, and PPC coated polylactic acid (PLA) microspheres were obtained by drying PPC stabilized PLA Pickering emulsion, leading to a well dispersion of PPCs in PLA. PPC/PLA film prepared by hot-pressing displayed great antibacterial performance and enhanced mechanical properties. Therefore, this study proposed a facile approach to fabricate biocompatible antibacterial nanoagents and plastics.

Water-dispersible and stable polydopamine coated cellulose nanocrystal-MXene composites for high transparent, adhesive and conductive hydrogels.

High conductive and transparent hydrogels with adhesion function are ideal candidates for soft electronic devices. However, it remains a challenge to design appropriate conductive nanofillers to endow hydrogels with all these characteristics. The 2D MXene sheets are promising conductive nanofillers for hydrogels due to excellent electricity and water-dispersibility. However, MXene is quite susceptible to oxidation. In this study, polydopamine (PDA) was employed to protect the MXene from oxidation and meanwhile endow hydrogels with adhesion. However, PDA coated MXene (PDA@MXene) were easily flocculated from dispersion. 1D cellulose nanocrystals (CNCs) were employed as steric stabilizers to prevent the agglomeration of MXene during the self-polymerization of dopamine. The obtained PDA coated CNC-MXene (PCM) sheets display outstanding water-dispersible and anti-oxidation stability and are promising conductive nanofillers for hydrogels. During the fabrication of polyacrylamide hydrogels, the PCM sheets were partially degraded into PCM nanoflakes with smaller size, leading to transparent PCM-PAM hydrogels. The PCM-PAM hydrogels can self-adhere to skin, and possess high transmittance of 75 % at 660 nm, superior electric conductivity of 4.7 S/m with MXene content as low as 0.1 % and excellent sensitivity. This study will facilitate the development of MXene based stable, water-dispersible conductive nanofillers and multi-functional hydrogels.