Chapter 1: Antimicrobial Materials—An Overview

Chapter 1: Antimicrobial Materials—An Overview
By Shaheen Mahira ; Anjali Jain ; Wahid Khan ; Abraham J. Domb
DOI: https://doi.org/10.1039/9781788012638-00001
Published: 31 Jul 2019
Special Collection: 2019 ebook collection
Series: Biomaterials Science Series
Page range: 1 – 37

Infectious disease management has become an increasing challenge in recent years. According to the Centers for Disease Control and Prevention and the World Health Organization, microbial infections are a top concern. Pathogenic microorganisms are of main concern in hospitals and other healthcare locations, as they affect the optimal functioning of medical devices, surgical devices, bone cements, etc. Combatting microbial infections has become a serious health concern and major challenging issue due to antimicrobial resistance or multidrug resistance and has become an important research field in science and medicine. Antibiotic resistance is a phenomenon where microorganisms acquire or innately possess resistance to antimicrobial agents. New materials offer a promising antimicrobial strategy as they can kill or inhibit microbial growth on their surface or within the surrounding environment with superior efficacy, low toxicity and minimized environmental problems. The present chapter focuses on classification of antimicrobial materials, surface modification and design requirements, their mode of action, antimicrobial evaluation tests and clinical status.

1.2 Antimicrobial Materials
1.2.1 Antimicrobial Polymers
1.2.1.1 Polymers with Intrinsic Antimicrobial Activity
1.2.1.1.1 Natural Polymers
1.2.1.1.1.1 Chitosan
Firstly, positively charged chitosan can interact with negatively charged microbial cell surfaces and will either prevent the transport of essential materials into cells or result in leakage of cellular contents. In the second mechanism, chitosan binds with cellular DNA (via protonated amine moieties) and results in microbial RNA synthesis inhibition.

Cross-linked, quaternized chitosan/polyvinylpyrrolidone electrospun mats were found to be attractive materials for wound dressings as they were more efficient in inhibiting Gram-positive and Gram-negative bacterial growth.
Novel composite scaffolds based on α-chitin/nanosilver and β-chitin/nanosilver  exhibited profound antibacterial activity towards Staphylococcus aureus and Escherichia coli.
1.2.1.1.1.2 Heparin
About 33% of uncoated stents were colonized by bacteria, while no biofilms were detected on heparin-coated stents.
1.2.1.1.1.3 ε-Polylysine
ε-Polylysine (ε-PL) is a hydrophilic linear polyamide composed of 25–30 residues of L-lysine with ε-amino and α-carboxyl group linkage.
1.2.1.1.2 Polymers Containing Quaternary Nitrogen Atoms
1.2.1.1.2.1 Polymers with Aromatic or Heterocyclic Groups
1.2.1.1.2.2 Polyacrylamides and Polyacrylates
1.2.1.1.2.3 Polysiloxanes
1.2.1.1.2.4 Polyionenes
1.2.1.1.2.5 Polyoxazolines
1.2.1.1.2.6 Hyperbranched and Dendritic Polymers

1.2.1.1.3 Polymers with Guanidine Groups
Polyguanidines and polybiguanides   Polyhexamethylene biguanide
1.2.1.1.4 Polymers Mimicking Natural Peptides
Antimicrobial peptides (AMPs)
List of antimicrobial peptides.

1.2.1.1.5 Polymers Containing Halogens
1.2.1.1.5.1 Polymers Containing Fluorine
Polymers containing fluorine are most attractive, due to their unique properties such as oil and water repellence due to lower polarizability and high electronegativity of fluorine atoms; higher chemical, thermal and weather resistance; lower dielectric constant and lower surface energy.
Quaterfluo®,
1.2.1.1.5.2 Polymers Containing Chlorine
antimicrobial properties improved upon increasing triclosan groups without any leaching of triclosan.
It acts by deactivation of fatty acid synthesis of bacteria by inhibiting enoylacyl carrier protein reductase.
1.2.1.1.5.3 N-Halamine Compounds
N-Halamines are formed by halogenation of amide, imide or amine groups by covalent bonding.
They are the most promising candidates as antimicrobials, due to their fast and total killing action against various microbes without any environmental concerns and long-term stability, and it is highly unlikely that microbes will establish resistance to them.

1.2.3 Antimicrobial Plastics

Al In medicine and for food safety, titanium-, copper- and zinc-based nanostructures also show promising antimicrobial effects.
Liu et al. prepared plastics with excellent antibacterial activity by adding Ag/TiO2 to resins.
Matet et al. synthesized plasticized chitosan-based polymers containing good antibacterial properties and mechanical strength with easy scale-up.
de Olyveira et al. developed a polyethylene composite containing silver microparticles.
 
1.2.4 Antimicrobial Ceramics
Hydroxyapatite doped with silver, copper oxide and zinc oxide can be used to improve antibacterial properties
1.3 Ideal Features of Antimicrobial Materials
An ideal antimicrobial polymer should have following characteristics:
highly stable over long periods of time;
easily and inexpensively synthesized;
should not decompose or emit toxic products;
should be water insoluble for disinfection of water;
should possess broad spectrum of antimicrobial activity;
should be non-toxic and non-irritating.
1.4 Factors Affecting Antimicrobial Activity
1.4.1 Effect of Molecular Weight
1.4.2 Effect of Counter Ions
1.4.3 Charge Density
1.4.4 Effect of Spacer Length and Alkyl Chain Length
1.4.5 pH Effect

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