Abstract:
Infectious viruses and bacteria threaten human health globally by causing acute and chronic infectious diseases. Accordingly, developing antibacterial and antiviral materials with a broad range of biocidal activities is a priority. The demand for such materials is increasing in modern societies due to the emergence of drug-resistant microbial species and lethal viruses with long-term viability on surfaces. The ongoing worldwide COVID pandemic has increased the necessity for materials with active antibacterial and antiviral properties. This research thesis has focused on developing sustainable and environmentally friendly antibacterial and antiviral materials, systems and methodologies.
The thesis starts with a comprehensive review of the novel approaches for developing sustainable and environmentally friendly antibacterial and antiviral platforms. The initial experimental work described in the thesis was focused on exploring high surface area biopolymer electrospun nanofiber mats as a carrier for a highly antibacterial natural essential oil. Cellulose acetate (CA) nanofiber mats encapsulated with lemon myrtle essential oil (LMEO) were produced, and the electrospinning process was optimized. Electrospun CA nanofibers had a white colour, low water activity and proper thermal stability. The efficacy of the resulting fiber mats as a prospective active antibacterial material was evaluated. The fiber morphological, thermal, and optical properties and vapour phase release profile were investigated. The LMEO-loaded CA electrospun nanofibers eliminated Escherichia coli and Staphylococcus aureus by 100%, even at the lowest loading concentration of LMEO of 2 wt%. Encapsulation of natural bioactive compound LMEO into CA biopolymer by means of electrospinning resulted in stable, highly antibacterial and stable nanofibers, with excellent application potential as active packaging or wound dressing materials.
The work then progresses into investigating the capacitance-related biocidal activities of laser-induced graphene (LIG) after being charged at a constant low-voltage potential (1-2 V). Different CO2 laser parameters were employed to produce laser-induced graphene electrodes (LIG) on a polyimide substrate with different electric double layer capacitance (EDLC) values. The electrochemical, morphological and structural properties of the LIG electrodes were studied. The charged electrodes showed potent antibacterial and antiviral performance against gram-negative (E. coli) and gram-positive (S. aureus) bacteria, as well as non-enveloped (PhiX174) and enveloped (HSV-1) viruses. A direct relation between the capacitance of the electrodes and their antibacterial properties was observed. The charged LIG electrodes
sustained their antibacterial effect even after being stored for a week. The antiviral effect of positively charged electrodes was higher than negatively charged ones, and it increased with the increase of applied charging potential magnitude. The LIG electrodes showed great potential as novel sustainable, environmentally friendly rechargeable active surfaces, which have great potential application in air filtration, respiratory masks and various biomedical and public surfaces.
The concept of capacitance-based biocidal active surfaces was then extended to a simple and commercially available conductive and high surface area carbon cloth substrate. A simple, low-voltage, low-cost and flexible carbon cloth supercapacitor (CCSC) has been developed with highly efficient antibacterial and antiviral surface properties. This novel active supercapacitor platform is rechargeable and reusable, with an environmentally friendly mechanism of inactivation of bacteria and viruses. CCSC can be charged at a low constant potential of 1 to 2 V. The stored electrical charge in CCSC destabilizes viruses' electrokinetic properties, disrupts their infectivity upon virus contact with the surface and disinfects bacteria through membrane electroporation. The optimized CCSC showed excellent electrochemical properties, stability, flexibility and retention of its full capacitance under high bending angles. The positively charged CCSCs side yielded 6 log CFU reduction of E. coli bacterial inocula and 5 log reduction in PFU of HSV-1 herpes virus (an enveloped double-stranded DNA virus). This study showed that supercapacitors have great potential as rechargeable, sustainable and environmentally friendly active materials for different applications, including wound dressings, personal protective equipment (e.g., masks) and air filtration systems.