Antibacterial Surfaces with Nanoparticle Incorporation for Prevention of Hospital-Acquired Infections

246 Pages·2016·5.59 MB·English

Antibacterial Surfaces with
Nanoparticle Incorporation for
Prevention of Hospital-Acquired
Infections

This thesis is presented to UCL in partial fulfilment of the requirements for the
Degree of Doctor of Philosophy

Sandeep K. Sehmi

2016

Supervised by: Professor Alexander J. MacRobert, Professor Ivan
P. Parkin and Dr Elaine Allan
Declaration
I, Sandeep Sehmi, confirm that the work presented in this thesis is my own.
Where information has been derived from other sources, I confirm that
this has been indicated in the thesis.

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Abstract
This thesis describes the incorporation of nanoparticles into polymers as
antibacterial surfaces for preventing hospital-acquired infections (HAIs).
With a high prevalence of HAIs, the use of antibacterial materials can
contribute in reducing bacterial contamination associated with frequently
touched surfaces in hospitals (e.g. push plates, bed rails, or keyboards). The
combination of nanoparticles and light-activated antibacterial agents
demonstrate lethal bactericidal activity when encapsulated into medical
grade polymer sheets. Upon white light activation, these polymers exhibit
significant photobactericidal activity against a range of Gram-negative and
Gram-positive bacteria via the production of reactive oxygen species at the
polymer surface, through multi-site mechanistic pathways (Type I and/or
Type II). These samples are tested under various light intensities to mimic
clinical surroundings, but more significantly, some materials show highly
efficacious antibacterial activity in dark conditions.
All polymers are prepared using a simple ‘swell-encapsulation-shrink’
method, which impregnates the nanoparticles into the polymer substrate
and on the surface. These include copper and zinc oxide nanoparticles
synthesised with different capping agents. The antibacterial activity of a
commonly used biocide encapsulated into the polymer is also assessed.
The photosensitiser (crystal violet) is then coated onto the polymer surface
in the case of ZnO nanoparticles and activated by white light (~500 – 6600
lux).
The combination of crystal violet and zinc oxide nanoparticles is
investigated further by adapting the microbiological protocol to more
closely replicate a clinical environment and using a lower intensity of light
to carry out the antibacterial testing. In addition, the mechanisms
operating within the crystal violet and zinc oxide system are examined
using specific inhibitors and singlet oxygen quenchers to determine
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whether Type I, Type II, or both photochemical pathways are responsible
for the reduction of bacteria in the light and dark.
The samples were tested against a range of hospital pathogens, including
Escherichia coli, Staphylococcus aureus, methicillin-resistant Staphylococcus
aureus, Pseudomonas aeruginosa and Clostridium difficile endospores. The
novel and highly effective antimicrobial materials detailed in this thesis
demonstrate a very strong potential to be used in hospitals for reducing
the incidence of HAIs.

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Acknowledgements
Firstly, I would like to give special thanks to my primary and secondary
supervisors, Prof. Alexander MacRobert, Prof. Ivan Parkin and Dr. Elaine
Allan for their invaluable expertise, advice and support over the last three
years. Thank you for giving me the opportunity to do an inter-disciplinary
PhD that I have enjoyed so much and gained countless experience in a
range of subject fields. I would especially like to thank Elaine for teaching
me microbiology (from scratch!). I have appreciated every discussion and
meeting we have had as a group. You have all provided endless guidance
and encouragement and I’ve thoroughly enjoyed being part of this
research team.
I would like to thank students and mentors at the Division of Surgery and
Interventional Sciences research group and the Eastman Dental Institute
who have supported me along the way. Thank you to collaborators from
the Chemistry department at Imperial College. UCL Chemistry has been my
home for the last 7 years so it will definitely be missed the most! I would
like to thank every single person who has helped me and shared the
experience with me, in particular, my partner in crime, Sapna Ponja! I look
forward to celebrating this moment with you when you become Dr as well
. Its going to be so weird not seeing you everyday and I just want to
thank you for being a huge part of this crazy amazing experience.
I would like to thank my wonderful best friends and family for their love
and support along the way. Last but definitely not least, I would like to
thank my parents for being the most supportive and motivational people in
my life. All the success throughout my education has been possible
because of you and I would not be where I am today if it wasn’t for you.
You’re both extremely hardworking people which has inspired me to strive
for excellence and I hope to continue to make you proud in the future.
Love you both!
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Publications
Publications associated with this thesis:

1. SK Sehmi, S Noimark, J Weiner, E Allan, AJ MacRobert, IP Parkin.
Potent Antibacterial Activity of Copper Embedded into Silicone and
Polyurethane. ACS Applied Materials & Interfaces, 7 (41), 22807-
22813, 2015.

2. SK Sehmi, E Allan, AJ MacRobert and IP Parkin. The Bactericidal
Activity of Glutaraldehyde-Impregnated Polyurethane.
MicrobiologyOpen, 2016. doi: 10.1002/mbo3.378

3. SK Sehmi, S Noimark, JC Bear, WJ Peveler, M Bovis, E Allan, AJ
MacRobert and IP Parkin. Lethal Photosensitisation of
Staphylococcus aureus and Escherichia coli using Crystal Violet and
Zinc Oxide-Encapsulated Polyurethane. Journal of Materials
Chemistry B, 3 (31), 6490-6500, 2015.

4. SK Sehmi, S Noimark, SD Pike, JC Bear, WJ Peveler, CK Williams, E
Allan, IP Parkin and AJ MacRobert. Enhancing Antibacterial Activity
of Light-Activated Surfaces Containing Crystal Violet and ZnO
nanoparticles: Investigation of Nanoparticle Size, Capping Ligand
and Dopants. ACS Omega, 1 (3), 334-343, 2016.

5. SK Sehmi, K Alkhuder, S Noimark, SD Pike, CK Williams, MSP
Shaffer, IP Parkin, AJ MacRobert and E Allan. Antibacterial surfaces
for Hospitals with Activity against Hospital-Acquired Pathogens and
Clostridium Difficile Spores. (Manuscript in preparation)

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Table of Contents

1. Hospital-Acquired Infections 1
1.1 Introductory remarks . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Introduction to the Incidence of Hospital-Acquired Infections . . 1
1.3 Antimicrobial Resistance . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Common Pathogens in Hospitals . . . . . . . . . . . . . . . . . . 5
1.4.1 Methicillin-resistant Staphylococcus aureus . . . . . . 7
1.4.2 Escherichia coli . . . . . . . . . . . . . . . . . . . . . . 7
1.4.3 Pseudomonas aeruginosa . . . . . . . . . . . . . . . . 8
1.4.4 Clostridium difficile . . . . . . . . . . . . . . . . . . . . 9
1.5 Prevention Strategies . . . . . . . . . . . . . . . . . . . . . . . . 9
1.6 Alternative methods to basic cleaning . . . . . . . . . . . . . . . 13
1.6.1 Ozone . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6.2 Steam vapour . . . . . . . . . . . . . . . . . . . . . . 14
1.6.3 Hydrogen peroxide . . . . . . . . . . . . . . . . . . . . 1 4
1.6.4 Gas plasma . . . . . . . . . . . . . . . . . . . . . . . . 15
1.6.5 UV light . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.6.6 High-intensity narrow spectrum . . . . . . . . . . . . . 16
1.7 Antibacterial Surfaces . . . . . . . . . . . . . . . . . . . . . . . . 16
1.7.1 Biocide leaching . . . . . . . . . . . . . . . . . . . . . 17
1.7.2 Antimicrobial polymers . . . . . . . . . . . . . . . . . 18
1.7.3 Anti-adhesive coatings . . . . . . . . . . . . . . . . . 19
1.7.4 Silver-coated surfaces . . . . . . . . . . . . . . . . . . 19
1.7.5 Copper and copper alloy surfaces . . . . . . . . . . . 20
1.7.6 Light-activated antibacterial surfaces . . . . . . . . . 20
1.7.6.1 Titanium oxide-based antibacterial surfaces . 21
1.7.6.2 Dye-based antibacterial surfaces . . . . . . . . 22
1.7.7 Concerns over antibacterial surfaces . . . . . . . . . . 22

2. Photo-Activated Surfaces 38

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2.1 Introduction to Photodynamic Therapy . . . . . . . . . . . . . . 38
2.1.1 Photochemistry . . . . . . . . . . . . . . . . . . . . . 41
2.1.1.1 Non-radiative transitions . . . . . . . . . . . . 42
2.1.1.2 Radiative transitions . . . . . . . . . . . . . . . 42
2.1.2 Mechanism of action . . . . . . . . . . . . . . . . . . 42
2.2 Antibacterial Action of Nanoparticles . . . . . . . . . . . . . . . 47
2.2.1 Use of nanoparticles in a clinical environment . . . . 47
2.2.1.1 Antibacterial mechanism of nanoparticles . . 49
2.2.2 Copper nanoparticles . . . . . . . . . . . . . . . . . . 50
2.2.3 Magnesium oxide nanoparticles . . . . . . . . . . . . 51
2.2.4 Zinc oxide nanoparticles . . . . . . . . . . . . . . . . . 53
2.3 Dye and nanoparticle-incorporated polymers . . . . . . . . . . 54
2.3.1 Polymer types . . . . . . . . . . . . . . . . . . . . . . . 5 5
2.3.1.1 Polyvinyl chloride . . . . . . . . . . . . . . . . 55
2.3.1.2 Silicone . . . . . . . . . . . . . . . . . . . . . . 56
2.3.1.3 Polyurethane . . . . . . . . . . . . . . . . . . . 56
2.3.2 Overview of the research at the Materials Research
Centre, UCL . . . . . . . . . . . . . . . . . . . . . . . . 56
2.4 Research aims . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3. Copper-Encapsulated Silicone and Polyurethane; Antimicrobial
Polymers without White Light Activation 75
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2.1 Chemicals and Reagents . . . . . . . . . . . . . . . . . 77
3.2.2 Synthesis of Copper Nanoparticles . . . . . . . . . . . 78
3.2.3 Material Preparation . . . . . . . . . . . . . . . . . . 78
3.2.3.1 Polymer System Optimisation – Organic Solvent
Concentration . . . . . . . . . . . . . . . . . . 78
3.2.3.2 Polymer Samples Prepared for Antibacterial
Testing . . . . . . . . . . . . . . . . . . . . . . 79
3.2.4 Material Characterisation . . . . . . . . . . . . . . . . 79

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3.2.4.1 Characterisation of Copper Nanoparticles . . . 79
3.2.4.2 Characterisation of Modified Polymer Samples 80
3.2.5 Antibacterial Activity . . . . . . . . . . . . . . . . . . . 80
3.2.5.1 Microbiology Assay . . . . . . . . . . . . . . . 80
3.2.5.2 Statistical Significance . . . . . . . . . . . . . . 81
3.2.5.3 Further Antimicrobial Testing for Mechanistic
Evaluation . . . . . . . . . . . . . . . . . . . . . 8 2
3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 82
3.3.1 Material Characterisation . . . . . . . . . . . . . . . . 82
3.3.1.1 Characterisation of Copper Nanoparticles . . 82
3.3.1.2 Characterisation of Modified Polymer Samples 84
3.3.2 Antibacterial Activity . . . . . . . . . . . . . . . . . . . 88
3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5

4. Glutaraldehyde-Encapsulated Polyurethane; Antimicrobial Polymer
without White Light Activation 103
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
4.2.1 Chemicals and Reagents . . . . . . . . . . . . . . . . . 107
4.2.2 Material Preparation . . . . . . . . . . . . . . . . . . . 107
4.2.3 Material Characterisation . . . . . . . . . . . . . . . . 108
4.2.4 Antibacterial Activity . . . . . . . . . . . . . . . . . . . 109
4.2.4.1 Statistical Significance . . . . . . . . . . . . . . 109
4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 110
4.3.1 Material Preparation . . . . . . . . . . . . . . . . . . . 110
4.3.2 Material Characterisation . . . . . . . . . . . . . . . . 111
4.3.3 Antibacterial Activity . . . . . . . . . . . . . . . . . . . 114
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 19

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5. Crystal Violet and 18 nm ZnO Nanoparticles Encapsulated into
Polyurethane; White Light Activated Antimicrobial Polymers 125
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
5.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.2.1 ZnO Nanoparticles . . . . . . . . . . . . . . . . . . . . 129
5.2.1.1 Chemicals and Reagents . . . . . . . . . . . . . 129
5.2.1.2 Nanoparticle Synthesis . . . . . . . . . . . . . 129
5.2.1.3 Nanoparticle Characterisation . . . . . . . . . . 130
5.2.2 Polymer Samples . . . . . . . . . . . . . . . . . . . . . 130
5.2.2.1 Chemicals and Reagents . . . . . . . . . . . . . 130
5.2.2.2 Material Preparation . . . . . . . . . . . . . . . 131
5.2.2.3 Material Characterisation . . . . . . . . . . . . 132
5.2.3 Antibacterial Activity . . . . . . . . . . . . . . . . . . . 134
5.2.3.1 Microbiology Assay . . . . . . . . . . . . . . . . 1 34
5.2.3.2 Statistical Significance . . . . . . . . . . . . . . 135
5.2.3.3 Hydrogen Peroxide and Singlet Oxygen
Detection . . . . . . . . . . . . . . . . . . . . . 135
5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 136
5.3.1 ZnO Nanoparticle Synthesis and Characterisation . . . 136
5.3.2 Preparation and Characterisation of Polymer Samples 137
5.3.3 Antibacterial Activity . . . . . . . . . . . . . . . . . . . 144
5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

6. Crystal Violet and 3 nm ZnO Nanoparticles Encapsulated into
Polyurethane; Antimicrobial Polymers Activated by Low Intensity
White light Source 165
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
6.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
6.2.1 ZnO Nanoparticles . . . . . . . . . . . . . . . . . . . . . 169
6.2.1.1 Nanoparticle Synthesis . . . . . . . . . . . . . 169
6.2.1.2 Nanoparticle Characterisation . . . . . . . . . 170
6.2.2 Polymer Samples . . . . . . . . . . . . . . . . . . . . . 171

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