The emergence of new infectious agents has become a significant concern – now more than ever as the world faces health and economic consequences brought by a global pandemic. The development and use of antimicrobial materials are only expected to rise as we employ more stringent measures in controlling our environment and in preventing future outbreaks.
Driven by the rising awareness regarding safety and health maintenance, the global antimicrobial coatings industry anticipates a sharp increase of demand, as reported by Global Market Insights.
The antibacterial materials and coatings market was valued at more than $3 billion in 2017. It is expected to register a compound annual growth rate of around 12.5% over 2018-2024, reaching $7 billion by the end of 2024.
Infectious agents are usually spread through airborne droplets produced from sneezing or coughing. These body fluids can settle on surfaces, and person-to-person transmission is possible if an individual touches these respiratory droplets.
In a study conducted by Neely and Maley, pathogens like Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus were found to survive for a day on materials used in hospitals.
Some microbes even lived for more than 90 days. These microorganisms are endemic in intensive care units (ICU) and are associated with an increased likelihood of illness and death. Disinfectants, as with hydrogen peroxide, are not ideal due to their limited residual effect and environmental toxicity issues.
This current structure calls for a need to explore materials that can provide antimicrobial activity, thereby cutting down the occurrence of possible outbreaks.
The ideal antibacterial material
Antibacterial materials contain antimicrobial agents that are capable of inhibiting or killing microbes on their surface or within their surroundings. They can be antimicrobial polymers, antibacterial plastics, antimicrobial nanomaterials, or antimicrobial ceramics.
An ideal antimicrobial material depicts the following features:
- safe to use;
- cheap and easy to synthesize;
- covers a wide range of antimicrobial activity;
- highly stable for extended periods;
- water-insoluble (if used in water disinfection);
- not susceptible to decay;
- should not release toxic products.
Types of antimicrobial materials and coatings
1. Antimicrobial polymers
The versatile macromolecular properties of a polymer make it a favourable option against microbial contamination, particularly in the biomedical field. Also known as polymeric biocides, antimicrobial polymers can inhibit the growth of disease-causing microorganisms.
Materials that exhibit antimicrobial action without any refinements and have inherent self-sanitizing properties are called intrinsic antimicrobial materials. Natural polymers, polymers with guanidine groups, polymers containing quaternary nitrogen atoms, polymers containing halogens, and polymers mimicking natural peptides are some of the many polymeric materials with intrinsic antimicrobial activity.
Some natural polymers include chitosan, heparin, and e-polylysine. Chitosan-based materials are seen with promising potential due to their biodegradability, non-toxicity, biocompatibility, and antimicrobial activity.
Imparting antimicrobial activity to polymers is also possible through chemical modifications. Some modifications include covalent incorporation of lower molecular weight antimicrobials, coupling of antimicrobial peptides, and grafting of natural polymers into synthetic polymers.
Polymeric antimicrobial food packaging is making its round as companies switch to antibacterial packaging for a safer product and increased shelf life.
Other applications of antimicrobial polymers can be found in mold remediation, powder coatings, and the construction industry.
2. Antibacterial plastics
a) Antimicrobial plastics
An antimicrobial plastic is a synthetic polymer material containing antimicrobial additives, which make it effective against microbial growth. It exhibits antibacterial properties by disrupting cell-to-cell communication through the formation of anti-adhesive surfaces, thereby killing bacteria.
Antimicrobial plastics in commercial use, such as high chairs, water filters, and food storage containers, are more durable than plastics without any antimicrobial active ingredients. The additives blended into thermoplastic and thermoset polymers work to minimize the presence of microorganisms that causes the plastic to degrade quicker, further extending the functional lifetime of a plastic. Some compatible plastic materials include polypropylene (PP), polycarbonate (PC), polystyrene (PS) and polyethylene (PE/LDPE).
b) Antimicrobial bioplastics
Albumin, soya, and whey protein serve as favourable raw materials for the manufacture of bioplastics. Albumin-based plastics hinders the growth of E. coli and bacillus subtilis on their surface, while immunoglobulins and glycomacropeptides found in whey protein bind the toxin and prevent microbial infection.
There are also test methods available to determine whether albumin or whey plastics can be used in healthcare systems, such as in medical products packaging and infection testing for medical applications.
3. Antimicrobial ceramics
An antimicrobial ceramic is a non-metallic solid material incorporated with an additive within its glaze that makes it resistant to bacterial growth. In a study conducted by Drelich et al., it was shown that a copper-infused ceramic could serve as a promising antibacterial product for water disinfection.
Copper and copper compounds have claimed to kill a variety of microorganisms, including bacteria (gram positive and negative), fungi, viruses (enveloped and non-enveloped), yeast, and spores.
It is able to kill 99.9% of harmful bacteria within two hours and to keep killing over 99% of bacteria regardless of repeated exposure to the copper surface, according to the Copper Development Association (CDA). Populations of both Klebsiella pneumoniae and Staphylococcus aureus in contaminated water, when exposed to the porous copper-infused antimicrobial ceramic stone, were reduced by >99.9% in 3 hours.
Antibacterial ceramic applications can be found in sinks, bathtubs, toilets, showers, and kitchen appliances.
4. Antimicrobial nanomaterials
a) Organic and inorganic nanoparticles
Organic nanoparticles can eliminate microbes by releasing antimicrobial agents or contact-killing cationic surfaces. In an experiment conducted by Jones et al., Poly-epsilon- caprolactone (PCL) was blended with poly(N-Vinylpyrrolidone)-iodine, imparting antibacterial properties to the biomaterials as a result, without any change in mechanical or rheological properties. PCL degradation also promoted anti-adherence of Escherichia coli.
Inorganic nanoparticles are more stable at higher temperatures than their organic counterparts, allowing them to withstand harsh processing conditions. As a result, inorganic nanoparticles are often used as antimicrobial materials.
b) Metal oxide nanoparticles
Metal oxide nanoparticles cause cell membrane damage by electrostatic interaction. Proton leakage induces reactive oxygen species generation which damages organic biomolecules such as lipids, carbohydrates, nucleic acids, and proteins, thereby causing microbial death.
Aluminium oxide showed growth inhibition of Escherichia coli. Antimony trioxide is also toxic to Staphylococcus aureus and Bacillus subtilis microbes. Other metal oxide nanoparticles such as cobalt oxide, iron oxide, magnesium oxide, zinc oxide, titanium dioxide, and silver nanoparticles also showed promising results of antimicrobial activity.
Silver nanoparticles have excellent antibacterial properties compared to other metals. The strong bond of silver ions with thiolate groups of proteins and cellular enzymes makes them an ideal additive in healthcare fabrics such as face masks, private curtains, bandages, wound dressings, bed sheets, and other textiles related to healthcare. In 2015, the use of silver in antimicrobial powder coatings accounted for 50% of the industry’s total revenue. It also expected to generate $2 billion by 2024.
It’s only a matter of time till antibacterial materials, particularly in the surface coatings market, gain more traction as a primary raw material should governments implement stricter norms in enforcing self-sanitation measures.
Moreover, its application in many industries like construction, food packaging, textiles, mold remediation, furniture, kitchenware, and automotive will further strengthen its hold in the global market.
 Siedenbiedel F, Tiller JC. Antimicrobial Polymers in Solution and on Surfaces: Overview and Functional Principles. Polymers. 2012; 4(1):46-71.
 Drelich, A. J., Miller, J., Donofrio, R., & Drelich, J. W. (2017). Novel Durable Antimicrobial Ceramic with Embedded Copper Sub-Microparticles for a Steady-State Release of Copper Ions. Materials (Basel, Switzerland), 10(7), 775. https://doi.org/10.3390/ma10070775
 Silva, Sara & Almeida, António & Vale, Nuno. (2019). Combination of Cell-Penetrating Peptides with Nanoparticles for Therapeutic Application: A Review. Biomolecules. 9. 10.3390/biom9010022.