Properties and Skin Compatibility of Films Based on Poly(Lactic Acid) (PLA) Bionanocomposites Incorporating Chitin Nanofibrils (CN)

Abstract

Nanobiocomposites suitable for preparing skin compatible films by flat die extrusion were prepared by using plasticized poly(lactic acid) (PLA), poly(butylene succinate-co-adipate) (PBSA), and Chitin nanofibrils as functional filler. Chitin nanofibrils (CNs) were dispersed in the blends thanks to the preparation of pre-nanocomposites containing poly(ethylene glycol). Thanks to the use of a melt strength enhancer (Plastistrength) and calcium carbonate, the processability and thermal properties of bionanocomposites films containing CNs could be tuned in a wide range. Moreover, the resultant films were flexible and highly resistant. The addition of CNs in the presence of starch proved not advantageous because of an extensive chain scission resulting in low values of melt viscosity. The films containing CNs or CNs and calcium carbonate resulted biocompatible and enabled the production of cells defensins, acting as indirect anti-microbial. Nevertheless, tests made with Staphylococcus aureus and Enterobacter spp. (Gram positive and negative respectively) by the qualitative agar diffusion test did not show any direct anti-microbial activity of the films. The results are explained considering the morphology of the film and the different mechanisms of direct and indirect anti-microbial action generated by the nanobiocomposite based films.

Keywords: anti-microbial; chitin nanofibrils; poly(butylene succinate); poly(lactic acid); skin compatibility; starch.

Figure 1

SEM image of a diluted 1:1000 sample of chitin suspension.

Figure 2

DSC first heating thermograms of F1, F2, F3 and F4 mixtures.

Figure 3

DSC second heating thermograms of F1, F2, F3 and F4 mixtures.

Figure 4

SEM micrograph related to: (a) F2; (b,c) F4; (d–f) F7. The micrographs (a–e) were obtained by the signal of secondary electrons (SEI modality). Micrograph (f) was obtained by signal due to backscattered electrons (CBS modality).

Figure 5

Relative gene expression of (a)TNF-α, (b)TGF-β, (c) IL-6, (d) IL-8, (e) IL-1α, (f) IL-1β and (g) HBD-2 in HaCat cells treated with F4 and F7 for 6 and 24 h. Data are mean ± SD and are expressed as percentage of increment relative to untreated cells (ctrl).

Figure 5

Relative gene expression of (a)TNF-α, (b)TGF-β, (c) IL-6, (d) IL-8, (e) IL-1α, (f) IL-1β and (g) HBD-2 in HaCat cells treated with F4 and F7 for 6 and 24 h. Data are mean ± SD and are expressed as percentage of increment relative to untreated cells (ctrl).

Figure 6

Plates of Agar diffusion test against (a,c) S. aureus and (b,d) Enterobacter spp., with no inhibition halos observed (inhibition zone ≤ 10 mm) for any sample tested: F4, F13 or F14.

Figure 7

(a) MVR variation due to PS addition; (b) MVR trends as a function of time for F1, F2, F3 and F4 formulations; (c) Torque trends as a function of time for F1, F2, F3 and F4 formulations.

Figure 8

(a) First part of the stress-strain curves for the formulations without calcium carbonate; (b) Figure 2. F4 and F7.