Antibacterial Composites of NFC and Inorganic Nanoparticles prepared by Polyelectrolytes Assembly

Transcription

1 Antibacterial Composites of NFC and Inorganic Nanoparticles prepared by Polyelectrolytes Assembly Natércia Martins, U Aveiro Patrizia Sadocco, SSCCP SUNPAP Workshop,

2 OUTLINE Introduction General aim of research Selected nanoparticles The materials Inorganic nanoparticles: Ag, TiO 2 and ZnO Electrostatic assembly of NPs onto NFC Antimicrobial activity of functionalized NFC composites Bacteriostatic and/or bactericidal action Distinct bacteria: S.aureus, K. pneumoniae Coated paper sheets Conclusions

3 Introduction

4 General aim of research To impart new properties to NFC and their paper coated derivatives, such as antibacterial and catalytic activity, as a result of functionalization with inorganic nanoparticles (Ag, TiO 2 and ZnO).

5 Ag, TiO 2 and ZnO NPs have been selected to functionalize NFC Ag NPs Strong inhibitory and bactericidal activities towards a broad spectrum of microorganisms Mechanisms of antibacterial action Slow Ag + ions release, followed by disruption of DNA replication Nanoparticles attach to the surface of the cell membrane disturbing its proper function. Some of the NPs penetrate inside the cell and interact with DNA causing cell death.

6 TiO 2 NPs Bactericidal agent when exposed to UV light (it is a well known photocatalyst) Low cost The mechanism of antibacterial action is based on the generation of reactive oxygen species via photocatalysis.

7 ZnO NPs Efficient photoactive antimicrobial agent under ambient lighting conditions Antibacterial action suggested to be related to: Generation of reactive oxygen species via photocatalysis Nanoparticles-cell interactions: attachment to the cell walls or accumulation in the cytoplasm of the cells Cationic release

8 The materials

9 Chemical-physical properties of NPs used in NFC functionalization Ag, TiO 2, SiO 2 water suspensions ZnO diethylene glycol suspension Materials supplied by Colorobbia Chemical-Physical properties ± Titanium Dioxide Silver Silicon Dioxide Zinc oxide Appearance - White liquid Dark brown liquid White liquid White liquid Crystalline Phase - Anatase Silver Amorphous wurtzite Concentration TiO 2 (%w/w) Density (g/cm 3 ) Particles Dimension (nm) (DLS Malvern Instruments) Polidispersity Index ph N.A Cationic Surfactant (%w/w)

10 PRODUCTION OF NFC-PE-Ag, NFC-PE-TiO 2 and NFC-PE-ZnO NANOCOMPOSITES

11 Electrostatic assembly of NPs (Ag, TiO 2 and ZnO) onto NFC Cationic Polyelectrolyte P+ P- Anionic Polyelectrolyte NFC NFC

12 Nature of the polyelectrolyte (PE) The assembly of NPs onto NFC was less effective when PAH (weak polyelectrolyte) was used instead of PDDA (strong polyelectrolyte) but maintaining the anionic polyelectrolyte (PSS). poly(diallyldimethylammonium chloride) PDDA Poly(allylamine hydrochloride) PAH poly(sodium 4-styrenesulfonate) PSS

13 Intensity K/M NFC-PE-Ag nanocomposites LbL assembly using polyelectrolytes SEM (PDDA/PSS/PDDA) nm UV-vis Wavelength (nm) Number of deposition cycles (n) (200) (110) (111) XRD n = 1 n = 2 n =3 n = 4 n = (004) (200) (220) Ag NPs content / º

14 K/M NFC-PE-TiO 2 nanocomposites LbL assembly using polyelectrolytes (PDDA/PSS/PDDA) SEM (6K x) (15K x) (40K x) EDX Ti 0.5 UV-vis nm Wavelength (nm)

15 (112) (102) (110) (103) Intensity _ (110) (101) (002) (100) K/M (110) (200) NFC-PE-ZnO nanocomposites LbL assembly using polyelectrolytes (PDDA/PSS/PDDA) SEM (4K x) (15K x) (40K x) XRD UV-vis nm / º Wavelength (nm)

16 Antimicrobial properties of NFC based composites

17 NFC (control) AgLbL30 (0,011%Ag) AgLbL29 (0,018%Ag) AgLbL28 (0,035%Ag) AgLbL27 (0,11%Ag) NFC (control) AgLbL30 (0,011%Ag) AgLbL29 (0,018%Ag) AgLbL28 (0,035%Ag) AgLbL27 (0,11%Ag) log CFU NFC-PE-Ag nanocomposite water suspension. - antibacterial activity increases by increasing Ag content in the nanocomposite - NFC/Ag nanocomposites 10,0 9,0 8,0 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0,0-1,0-2,0 Inoculum T0 S. aureus K. pneumoniae

18 log CFU NFC-PE-TiO 2 nanocomposite water suspension - antibacterial activity increases by increasing TiO 2 content in the nanocomposite - S. aureus 8,0 7,0 INOCULUM 6,0 5,0 4,0 3,0 2,0 1,0 0,0 NFC (control) NFC-PDDA TiLbL51 (1,6%) TiLbL50 (9,1%) TiLbL64 (18,5%) Results obtained at low nutrients concentration (12.5% NB)

19 NFC (control) NFC-PDDA NFC/SiO2/TiO2 (0,0166%) (7,84%) NFC (control) NFC-PDDA NFC/SiO2/TiO2 (0,0166%) (7,84%) NFC/SiO2/TiO2 (0,083%) (26,24%) log CFU Avoiding cellulose damage due to TiO 2 photocatalitic activity: NFC/SiO 2 /TiO 2 nanocomposite water suspension. - antibacterial activity S.aureus - 9,0 8,0 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0,0 NFC/SiO2/TiO2 NPs suspensions Inoculum T0 12,5% NB 100% NB Stronger bacteria Enhanced resistance of NFC to photodegradation observed after sterilisation treatment at 120 o C.

20 NFC (control) NFC-PE ZnLbL125 (2.0 %) ZnLbL127 (8.2 %) ZnLbL129 (28.0%) NFC (control) NFC-PE ZnLbL126 (2.0%) ZnLbL128 (9.3%) ZnLbL130 (30.6%) NFC (control) NFC-PE ZnLbL112 (32.2%) ZnLbL124 (2.0%) log CFU NFC-PE-ZnO nanocomposite water suspension - antibacterial activity increases by increasing ZnO content in the nanocomposite - S. aureus, 100% NB 10,0 8,0 6,0 4,0 2,0 0,0-2,0 PDDA 0.1% PDDA 0.7% PDDA/PSS/PDDA

21 NFC-PE-Ag coated paper

22 Paper coating experiments Size press machine Two NFC-PE-Ag starch-based coating formulations with a total solid content of 6% were used. The NFC-PE-Ag content of the formulations was 11% and 29 % with respect to starch. Antibacterial effect was detected on paper

23 Antibacterial activity toward S.aureus of paper coated by NFC-PE-Ag nanocomposite by starch based coating Samples Ag a) (µg/g) Initial inoculum (log CFU t 0 ) After contact (log CFU T 18h ) Bacteriostatic activity (log reduction) Bactericidal activity (log reduction) Untreated paper (control) _ Coated paper (control) 100 % starch 1 Layer Coated paper 11 % NFC-PE-Ag / Starch 2 Layers Coated paper 11 % NFC-PE-Ag / Starch 1 Layer Coated paper 29 % NFC-PE-Ag / Starch 2 Layers Coated paper 29 % NFC-PE-Ag / Starch _ < < < a) Ag content on paper sheet as determined by ICP Average coating load on paper = 1.6 g / m 2 for 1 layer; 2.8 g / m 2 for 2 layers.

24 Conclusions and perspectives Antimicrobial tests show that suspensions of NFC-PE-Ag, NFC-PE-TiO 2 and NFC-PE-ZnO nanocomposites exhibit bacteriostatic and bactericidal activity towards S.aureus and K. pneumoniae bacteria. NFC functionalized with inorganic nanoparticles can be used as additive in paper coating to limit microbial proliferation. Paper coated with NFC-PE-Ag can show antibacterial activity. Limitation: pale yellow colour even for paper samples with the lowest amount of Ag content TiO 2 photoactivity induce oxidation of cellulose, possible strategies are under investigation to avoid cellulose damages: SiO 2 based nanocomposites, silane modified TiO 2 to tune photoactivity. Preliminary results show that ZnO can be a potential alternative to TiO 2. Toxicological effects for ZnO NPs should be specially considered.

25 THANK YOU for your attention! The research leading to these results has received funding from the European Community s Seventh Framework Programme under grant agreement nº

26 TEAM Natércia Martins Tito Trindade Carmen Freire Armando Silvestre Carlos Pascoal Neto Patrizia Sadocco Jessica Causio Giovanni Baldi