Abstract
Antibacterial membranes have attracted researchers’ interest in recent years as a possible approach for dealing with biofouling on the membrane surface. This research aims to see if blending AZ63 Mg alloy into a polyethersulphone (PES) membrane can improve antifouling and separation properties. The composite membranes’ pure water flux continued to increase from pristine PES to PES/AZ63 2.00 wt%. The results showed that PES/AZ63 2.00 wt% membrane supplied the highest permeate flux of E. coli. The steady-state fluxes of AZ63 composite membranes were 113.24, 104.38 and 44.79 L/m2h for PES/AZ63 2.00 wt%, 1.00 wt%, and 0.50 wt%, respectively. The enhanced biological activity of AZ63 was studied based on antioxidant activity, DNA cleavage, antimicrobial, anti-biofilm, bacterial viability inhibition and photodynamic antimicrobial therapy studies. The maximum DPPH scavenging activity was determined as 81.25% with AZ63. AZ63 indicated good chemical nuclease activity and also showed moderate antimicrobial activity against studied strains. The highest biofilm inhibition of AZ63 was 83.25% and 71.63% towards P. aeruginosa and S. aureus, respectively. The cell viability inhibition activity of AZ63 was found as 96.34% against E. coli. The photodynamic antimicrobial therapy results displayed that AZ63 demonstrated 100% bacterial inhibition when using E. coli.
HIGHLIGHTS
AZ63 Mg alloy was blended to polyethersulphone (PES) membrane.
Biologic activity of AZ63 was studied based on antioxidant activity, DNA cleavage, antimicrobial, anti-biofilm, bacterial viability inhibition and photodynamic antimicrobial therapy studies.
INTRODUCTION
Due to a changing climate, an increasing population and economy, and changing lifestyles, water scarcity is becoming an increasing concern (Debaere & Kapral 2021). Water crises have become accepted as one of the world's greatest future concerns. Therefore, water recycling and reuse have become one of the most essential ways of avoiding scarcity (Ahmad et al. 2022). Membrane technologies are increasingly being used in tertiary processes for water recycling and reuse. However, while the treatment of water or wastewater, biofilm formation by gram-negative and gram-positive bacteria cause serious membrane biofouling, which decreases water flux and membrane lifetime (Kim et al. 2022). Antibacterial membranes have attracted researchers' interest in recent years as a possible approach for dealing with this problem(Jiang et al. 2022). Antibacterial materials are very important in membranes, and many different materials have been used in literature such as titanium, graphene, silver, etc. (Anis et al. 2022; Peng et al. 2022; Vatanpour et al. 2022). Magnesium (Mg) is often regarded as the best green material of the twenty-first century (Xu et al. 2019). Its low density, in particular, makes them popular for addressing major environmental pollution and energy problems (Yao et al. 2022). Excellent mechanical strength and stiffness, outstanding damping ability, huge hydrogen storage capabilities, and high theoretical specific capacity for batteries are only a few of the other physical and chemical features of magnesium alloys (Yang et al. 2021). Mg alloys are being used in a growing number of automotive components, including frames, seats, and steering wheels (Bu et al. 2020). They're also interesting candidates for many other uses, such as computer components, aerospace components, and defense equipment (Gottfried 2020; Han et al. 2020; Song et al. 2020). Furthermore, among the bio metal materials, Mg alloy has gotten a lot of interest because of its exceptional biocompatibility and degradability (Tong et al. 2022). In recent studies, it has been also understood that Mg has a good antibacterial ability due to the alkalinity that increases with the degradation (Chen et al. 2018; Yan et al. 2018; Ma et al. 2020). Consequently, in this study, highly efficient antibacterial membranes were prepared using an AZ63 magnesium alloy, and its biological activity was studied based on antioxidant, DNA cleavage, antimicrobial, photodynamic antimicrobial therapy, anti-biofilm and bacterial viability inhibition studies.
MATERIALS AND METHODS
Materials
Polyethersulfone (PES Ultrason E6020P, MW: 58,000 g/mol) was supplied from BASF Company (Germany). N-methyl-2-pyrrolidone (NMP) was supplied from Sigma-Aldrich. The two-stage Millipore Direct-Q3UV purification system was utilized to get the distilled water used in all studies. The AZ63 Mg alloy powder (particle size < 45 μm) used in this study was obtained from a local provider in Istanbul.
Preparation of AZ63 Mg alloy blended PES membranes
Pristine and AZ63 alloy blended PES membranes were prepared using the phase inversion method. Full description of the membrane synthesis procedures may be found elsewhere (Dizge et al. 2017). Table 1 lists the casting solution's composition. Before experiments, all membranes were pressured under 5 bar with deionized water.
The manufactured membranes' casting solution composition (wt%)
Membrane sample . | PES . | NMP . | AZ63 Mg alloy . |
---|---|---|---|
Pristine PES | 14 | 86.0 | 0.00 |
PES/AZ63-0.5 | 14 | 85.5 | 0.50 |
PES/AZ63-1.0 | 14 | 85.0 | 1.00 |
PES/AZ63-2.0 | 14 | 84.0 | 2.00 |
Membrane sample . | PES . | NMP . | AZ63 Mg alloy . |
---|---|---|---|
Pristine PES | 14 | 86.0 | 0.00 |
PES/AZ63-0.5 | 14 | 85.5 | 0.50 |
PES/AZ63-1.0 | 14 | 85.0 | 1.00 |
PES/AZ63-2.0 | 14 | 84.0 | 2.00 |
Characterization of pristine and composite membranes
The surface morphology of the manufactured pristine PES and AZ63 blended PES membranes was characterized by scanning electron microscopy (SEM, Gemini Zeiss Supra 55). After drying at room temperature, the membranes were coated with a gold layer. The SEM images were taken using a 20.0 kV acceleration voltage. The filtration performances of the manufactured membranes were evaluated using a dead-end flat sheet membrane module (Sterlitech, HP4750) with a filtration area of 14.6 cm2 and an operating pressure of 1 bar.
DPPH scavenging activity
DNA cleavage activity
To examine the effect of AZ63 on DNA, E. coli pBR322 plasmid DNA was utilized. After homogeneously mixing three different concentrations of AZ63 Mg alloy, an amount equal to plasmid DNA was put on top and incubated for 60 min at 37 °C. The plasmid DNA used as a control was not treated with AZ63 Mg alloy. The negative control and mixes were placed onto the agarose gel at the end of the period. The electrophoresis parameters were 90 min, 80 volts, and 120 ampere. Finally, a transilluminator was used to visualize DNA molecules (Yıldız et al. 2017; Jawoor et al. 2018).
Antimicrobial activity
The antibacterial activity of the synthesized AZ63 Mg alloy was studied using the microdilution technique. In this study, a total of 8 microorganisms were used including two yeast strains, three Gr−ve and three Gr + ve. Details about microorganism have been given elsewhere Farajzadeh et al. (2022). Two-fold serial dilutions of AZ63 were performed. Then, strains prepared in the range of 0.5 McFarland Scale were added to the wells in the same amount in a specific order. Finally, the plates were incubated at 37 °C for one day. The plates were examined at the end of the incubation time, and the miniumum inhibitory concentration (MIC) was determined as the lowest concentration that inhibited microbial growth.
Biofilm inhibition activity
Bacterial cell viability activity and antibacterial photodynamic activity
Utilization of PES membrane blended with AZ63 for E. coli removal and its antifouling performance
RESULTS AND DISCUSSION
Characterization of AZ63 Mg alloy particles
Characterization of AZ63 Mg alloy particles blended PES membranes
AZ63 blended PES membranes (a) pristine PES membrane, (b) PES/0.5%AZ63, (c) PES/1.0%AZ63, (d) PES/2.0%AZ63.
AZ63 blended PES membranes (a) pristine PES membrane, (b) PES/0.5%AZ63, (c) PES/1.0%AZ63, (d) PES/2.0%AZ63.
Flux performance of AZ63 Mg alloy blended membranes
Variation of (a) permeability coefficient (Jp) of deionized water versus transmembrane pressure and (b) E. coli flux of pristine and AZ63 PES membranes.
Variation of (a) permeability coefficient (Jp) of deionized water versus transmembrane pressure and (b) E. coli flux of pristine and AZ63 PES membranes.
DPPH scavenging activity
DNA cleavage ability
DNA cleavage activity of AZ63. Lane 1, pBR 322 DNA; Lane 2, pBR 322 DNA + 100 mg/L AZ63; Lane 3, pBR 322 DNA + 200 mg/L of and AZ63.
DNA cleavage activity of AZ63. Lane 1, pBR 322 DNA; Lane 2, pBR 322 DNA + 100 mg/L AZ63; Lane 3, pBR 322 DNA + 200 mg/L of and AZ63.
Antimicrobial activity
In the presented study, the antimicrobial activity of AZ63 on various microorganisms was investigated using the microdilution method. MIC values of the results are given in Table 2. The studied strains were found to have varying susceptibility to AZ63. MIC values of Gram-positive bacteria were 256 mg/L, 256 mg/L, and 512 mg/L for E. hirae, E. fecalis, and S. aureus, respectively. MIC values of fungal strains were 512 mg/L and 512 mg/L for C. parapisilosis and C. tropicalis respectively. MIC values were determined as 1,024 mg/L against Gram-negative bacteria E. coli, P. aeruginosa, and L. pneumophila. When we compared the susceptibility of the studied strains to AZ63, the order was as follows from most susceptible to least susceptible; Gr +ve> fungi >Gr –ve. Most researchers are reported that bacteria-killing of magnesium and its alloys are attributed to high pH levels (alkalinity) caused by their degradation (Lin et al. 2019). Antimicrobial activities of magnesium alloys have been reported in various studies. (Lin et al. 2019) reported that they studied the antibacterial activity of ZK60. They noticed that microbial growth reduction was observed when using ZK60. In another study, Lock et al. (2014) indicated that magnesium alloys reduced E. coli viability and decreased microbial growth over a 3-day incubation period in a synthetic urine solution when compared with now used trading polyurethane stent. Sun et al. (2020) reported that the contact-killing antibacterial ability against adherent E. coli and S. aureus of Mg alloys were evaluated via the bacteria counting process, in which the adherent bacteria were detached from the sample and recultured on agar plates. They found that the antibacterial activity of the Mg alloys was 63.50% against E. coli and 48.13% against S. aureus. Mandal et al. (2021) informed that Fe-Mn-Cu alloy showed significant bactericidal activity when compared to the base alloy against E. coli. Based on our results, AZ63 showed varying degrees of antimicrobial activity against all strains tested, which is consistent with published results. It can be concluded that AZ63 can find use as a surface material in various fields in the prevention of infections caused by microorganisms.
The test microorganisms' minimum inhibitory concentration (MIC)
Microorganisms . | AZ63 . |
---|---|
E. coli | 1,024 |
P. aeruginosa | 1,024 |
L. pneumophila subsp. pneumophila | 1,024 |
E. hirae | 256 |
E. fecalis | 256 |
S. aureus | 512 |
C. parapisilosis | 512 |
C. tropicalis | 512 |
Microorganisms . | AZ63 . |
---|---|
E. coli | 1,024 |
P. aeruginosa | 1,024 |
L. pneumophila subsp. pneumophila | 1,024 |
E. hirae | 256 |
E. fecalis | 256 |
S. aureus | 512 |
C. parapisilosis | 512 |
C. tropicalis | 512 |
*mg/L.
Biofilm inhibition activity
Bacterial cell viability activity and antibacterial photodynamic activity
Utilization of PES membrane blended with AZ63 for E. coli removal
Utilization of polyethersulfone(PES) membrane blended with synthesized AZ63 for E. coli removal. (a) Inlet E. coli suspension (b) permeate of PES membrane, (c) permeate of PES membrane blended with 0.5 wt% AZ63, (d) permeate of PES membrane blended with 1 wt% AZ63, and (e) permeate of PES membrane blended with 2 wt% AZ63.
Utilization of polyethersulfone(PES) membrane blended with synthesized AZ63 for E. coli removal. (a) Inlet E. coli suspension (b) permeate of PES membrane, (c) permeate of PES membrane blended with 0.5 wt% AZ63, (d) permeate of PES membrane blended with 1 wt% AZ63, and (e) permeate of PES membrane blended with 2 wt% AZ63.
CONCLUSION
As a result, the biological activities of AZ63 were also investigated in the presented study and remarkable results were obtained. AZ63 showed 81.25% DPPH radical scavenging activity and exhibited excellent chemical nuclease activity. The investigated Mg alloy, AZ63, displayed good antibiofilm characteristics when incubated with P. aeruginosa and S. aureus. It was observed to have average antimicrobial activity on the strains studied. It was also observed that AZ63 displayed excellent cell viability effect on E. coli and antimicrobial photodynamic therapy activity of AZ63 was tested by using LED irradiation and 100% bacterial growth inhibition was observed. Moreover, the antimicrobial efficiency of the PES membrane blended with AZ63 was investigated and it was found that 100% E. coli removal efficiencies were achieved with PES membrane blended with 1 and 2 wt% AZ63. When all the biological activity results of AZ63 are evaluated together, we can say that this biocompatible material can find application in various fields after further studies.
ETHICAL APPROVAL
This article does not contain any studies with human participants or animals performed by any of the authors.
FUNDING
No funding was received to assist with the preparation of this manuscript.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.