Enhanced Mechanical Durability of Polymeric Nanowires via Carbyne-Enriched Plasma Coatings for Bactericidal Action

Abstract

Carbon-based materials have emerged as promising biomaterials due to their biocompatibility and inherent antibacterial properties. Carbyne, a unique allotrope of carbon, characterized by sp-hybridized carbons forming alternating single and triple bonds, exhibits exceptional toughness. Herein, we explore the potential of carbyne-enriched plasma coatings for antibacterial applications in conjunction with micro- and nano-textured polymeric surfaces. We investigate and characterize carbyne-enriched plasma coatings onto superhydrophilic or superhydrophobic poly (methyl methacrylate) (PMMA) plasma micro-nanotextured surfaces. Our analysis evaluates the wetting properties and durability of these surfaces, particularly in liquid immersion conditions. The integration of carbyne-enriched plasma coatings serves a dual purpose: it enhances the chemical bactericidal action and protects surface micro-nanostructures from deformation due to capillary forces thanks to the material’s innate toughness. The results show that the micro-nanotextured and carbyne-enriched coated PMMA surfaces exhibit a significant bactericidal activity as expressed by a bactericidal index of approximately 50%, owing to the combined effect of both the surface topography and the plasma-deposited carbyne coating.

1. Introduction

In recent years, carbon-based materials have gained significant attention as emerging biomaterials, since, despite their biocompatibility, they have been associated with antibacterial activity [1]. They have been studied in various biomedical applications regarding their incorporation as surface coatings, for example, on surgical implants, with or without the inclusion of a bactericidal agent (e.g., silver) [1,2] and on clinical contact lenses [3]. Their mechanism of bactericidal action has lately been identified as electrochemical, since it is related to a decrease in the surface zeta potential of bacteria cells in contact, which further alters their membrane’s permeability, this way compromising their viability [4].

One of the natural allotropic modifications of carbon is carbyne. Also known as linear acetylenic carbon (LAC), carbyne represents a distinctive allotrope of carbon, characterized by sp-hybridized carbons connected with alternating single and triple bonds [(-C≡C-)_n] forming a repeating unit. Noteworthy for its exceptional toughness, carbyne exhibits a Young’s modulus of 32.7 TPa, exceeding that of diamond by a factor of 30 (diamond has a Young’s modulus of about 1 TPa) [5], while materials such as diamond-like carbon (DLC) films, predominantly composed of sp²-hybridized carbon, exhibit a Young’s modulus of 200 GPa, two orders of magnitude lower than that of carbyne coatings [6]. The unique properties of carbyne render it an ideal candidate for various cutting-edge applications, particularly in nanoelectronics, MEMs (Micro-Electro-Mechanical Systems), and biosensors [7].

Carbyne is a material with registered antibacterial applications in fields like reconstructive surgery, as a coating in elements of cardio valves, fiber blood vessels, and threads, etc. [8,9]. Carbyne-like coatings bear an advantage compared to other carbon materials, such as diamond, thanks to their unique molecular structure. Specifically, carbyne chains can be terminated with compounds, like cyano (-CN), and hydrocarbon (-CH, -CH₃) groups [10,11] for enhanced antibacterial activity [1], unlike diamond-like carbon coatings, which should be specifically modified by bactericidal agents with possible long-term toxicity impacts [12], such as silver, copper, and iron, to achieve a comparable antibacterial effect [13]. Carbyne coatings, even when combined with such bactericidal agents, do not allow their extended accumulation, and they significantly lower their distribution and toxic effect in the bloodstream and the surrounding tissues (heart, brain, kidney) [14] due to their remarkable hardness that delays their wear off and therefore, the agent’s release [2].

Alternatively to the electrochemical bactericidal action of compounds like cyano and hydrocarbon groups, it has been shown that specifically tailoring the surface structuring can lead to bactericidal action. A plethora of groups have developed specially tailored texturing on surfaces that exhibit bactericidal action [15,16]. For example, Epstein et al. researched the effect of nanostructures on the growth of biofilm [17], while Ivanova et al. tested black silicon as a bactericidal surface, achieving bactericidal action under specific conditions [18]. Our group has previously tested and achieved bactericidal action on hierarchical micro- and nano-textured PMMA surfaces, prepared using oxygen plasma [19,20,21].

A problem that occurs with micro- and nano-textured surfaces, especially polymeric ones, is that the micro-nanostructures are usually fragile, especially in applications related to liquids (note that biomedical applications and microfluidic systems require functional surfaces immersed in some kind of liquid). Our group has explored the mechanical stability of high aspect ratio Si pillars [22]. The results suggest that mechanical stability is mostly at risk due to the adhesive forces between the structures instead of the capillary forces during the drying of wetted structures. On the other hand, according to Chandra et al. [23] on polymeric surfaces, the capillary forces induced due to liquid evaporation from inside the texturing are more crucial, due to the lower surface energy, compared to Si.

It is evident that the use of textured polymeric surfaces for bactericidal applications is promising but not achievable for repeated use at the current state. In this study, we try to combine the chemical bactericidal action and toughness of plasma-deposited carbyne coatings with the mechanical action of micro- and nano-textured surfaces to enhance the mechanical robustness of micro- and nano-textured surfaces. Our focus lies in characterizing carbyne-enriched coatings, extending to those on super hydrophilic or superhydrophobic polymeric (PMMA) surfaces, fabricated via plasma treatment. This analysis aims to evaluate both the wetting properties and durability of these surfaces, particularly in the context of liquid immersion. The final step is the use of such surfaces for bactericidal action, where the addition of the carbyne-enriched plasma coating has a dual purpose; firstly, of adding a chemical bactericidal action, and secondly of strengthening the surface structures against the capillary forces, due to the innate toughness of the material.

2. Materials and Methods

2.1. Materials

Poly (methyl methacrylate) (PMMA) sheets with a thickness of 1.5 mm, obtained from IRPEN (Barcelona, Spain), were employed as the substrate material due to their excellent mechanical and chemical stability. PMMA was cut into square samples measuring 1.5 × 1.5 cm² for morphology characterization, wetting durability characterization, and antibacterial testing.

2.2. Carbyne-Enriched Plasma-Deposited Films

The carbyne-enriched coating was developed with the assistance of the company Swissimpianti Sagl, Balerna, Switzerland. Ion-assisted plasma deposition is employed to grow the carbyne-enriched coating on the polymeric surfaces. This method involves the use of argon and carbon plasma beams to stimulate and deposit carbon material onto the surface. The carbon plasma is released by heating a graphite cathode at 3000 °C using electron bombardment. In addition, the ion beam bends the carbon chains, which stabilizes the growing chain ensemble. The formed carbon chains are directed to impinge the substrate using an electrode system [24]. Two different conditions were used, resulting in two different layer thicknesses 40 nm and 100 nm, with the deposition parameters shown in

Table 1. Carbyne deposition parameters.

	40 nm Thickness	100 nm Thickness
Ion Plasma Voltage/Current (V/mA)	2000/115	750/70
Carbon Plasma Pulses (#)	3000	7000
Carbon Plasma Voltage/Frequency (V/Hz)	300/3	300/3
Pressure (Pa)	0.128	0.128
Duration (min)	5	5

Note: The symbol ‘#’ denotes the number of pulses.

.

2.3. PMMA Texturing

PMMA surfaces were textured using oxygen plasma etching, a process extensively documented by our group and applied in various applications, e.g., [25]. For the oxygen treatment, a reactive ion etcher (Nextral Alcatel NE330, Colombes, France) was used and the corresponding treatment conditions were as follows: power of 400 W, gas pressure of 40 mTorr, and a flow rate of 100 sccm.

2.4. Hydrophobic Coating

For the superhydrophobic surfaces, a thin layer of a Teflon-like film was deposited on top of the carbyne-enriched coated, textured surfaces using C₄F₈ plasma deposition. A deposition time of 1 min results in a film of 40 nm thickness (measured on a flat Si wafer through ellipsometry). For the deposition process, the system that was used was a custom-built inductively coupled plasma (ICP) reactor, which is housed within the laboratories of the Plasma group at INN Demokritos, and the deposition parameters were as follows: power of 500 W, bias voltage of 0 V, gas pressure of 40 mTorr, and a flow rate of 25 sccm.

2.5. Morphology Characterizaiton, Elemental Analysis, and Wetting Characterization

The texturing of the surfaces was studied by scanning electron microscopy (SEM) using the JEOL (Tokyo, Japan) JSM-7401F FEG, at 2kV beam voltage. EDX analysis was conducted using a ThermoFisher Scientific (Waltham, MA, USA) Apreo 2 field emission gun scanning electron microscope (FE-SEM) equipped with an ULTIM-MAX Silicon Drift Detector (65 mm² area) from Oxford Instruments (Abingdon, Oxfordshire, England), operating at an accelerating voltage of 5 kV. To normalize the measurements, the counts recorded in each energy window were divided by the total counts of the entire spectrum.

Raman spectra were acquired in a confocal Raman microscope with an excitation laser wavelength of 532 nm [Aplha300R, WITec (Ulm, Germany), 75 mW nominal output] at room temperature.

The surfaces’ wettability was measured by means of their water static contact angle with the Kruss Scientific (Hamburg, Germany) DSA 25 system. Advancing and receding contact angles were measured as well, and an approximation of the surface hysteresis was calculated. The contact angle of 5 μL deionized water drops was determined using specialized software after depositing the drop onto the surface. To assess contact angle hysteresis, drops increasing/decreasing in volume from 5 to 25 μL and backwards were utilized, with contact angle measurements taken as the water volume varied.

2.6. Durability Tests

The test involved immersing the as-prepared samples in deionized water. Surfaces treated for 10 min with two different carbyne-enriched coating thicknesses (40 and 100 nm) were subjected to water immersion and then left to dry under normal environmental conditions.

In addition, the superhydrophobic version of such surfaces was also tested using liquids of lower surface tension. In this case, a mixture of isopropanol/water 18% v/v was used corresponding to a surface tension value of 35 mN/m. This value was chosen since it has been reported in our previously published work as the critical point where the plasma-treated surfaces just fail to meet the criteria of superhydrophobicity [25].

2.7. Bacteria Culture and Viability Testing

Testing of the antibacterial activity of the carbyne-enriched coating was performed on four different kinds of poly (methyl methacrylate) (PMMA) surfaces. In specific, (i) plain surfaces, used as reference (flat), (ii) carbyne-enriched coated surfaces (flat + carbyne), (iii) micro-nanotextured surfaces (rough), and (iv) micro-nanotextured and coated with carbyne-enriched surfaces (rough + carbyne).

The Gram-negative bacteria, Escherichia coli (Top10 strain, INVITROGEN, Waltham, MA, USA) was used for the antibacterial assay. Bacteria were grown in Luria–Bertani (LB) broth overnight in a shaking incubator (LabTech, Hopkinton, MA, USA) at 37 °C and 180 rpm under aerobic conditions. The next day, bacteria cells were harvested after two sequential centrifugations (5000× g rpm, 3 min, RT) and resuspended in Dulbecco′s Phosphate-Buffered Saline (DPBS), pH ≃ 7.4 (biowest, Nuaillé, France), at the initial concentration, and in various dilutions (1:7, 1:8, and 1:9). The optical density at 600 nm (OD600) of bacteria was later measured, and the dilution closer to OD600 = 0.23 was kept, from which serial dilutions in DPBS were performed to yield a final concentration of ≃10⁴ CFU/mL for the assay.

For the viability testing, the PMMA surfaces of 1.5 × 1.5 cm² were submerged in 12-well plates (CELLSTAR, Greiner Bio-one, Kremsmünster, Austria). Bacteria of 6.6 (±0.3) × 10⁴ CFU/mL initial concentration, at a volume of 1.6 mL, were inoculated on each surface and left to incubate at 37 °C under mild agitation (50 rpm) for 4 h. After the incubation, bacteria were collected from each surface and 100 μL of their 1:20 dilution in DPBS were uniformly spread on LB agar plates. Two transfers of 100 μL aliquots to agar plates were performed from each surface (two plates for every surface). Duplicates of each different kind of surface were used, therefore resulting in four plates for every different kind, satisfying statistical purposes. The plates were incubated at 37 °C for 16 h. The experiment was performed in triplicate. The antibacterial activity of each surface was evaluated by determining bacteria viability using the standard plate count method.

3. Results and Discussion

3.1. Film Characterization

Raman spectroscopy was used to investigate the bond structure of the deposited films (Figure 1a). A wider Raman spectrum is also shown in Supporting Information (Figure S5). A flat peak between 900 and 1000 cm⁻¹ can be observed, corresponding to the second-order phonon band from the silicon substrate [26]. More importantly, the characterization showed clear bands in the region of 2000 to 2300 cm⁻¹, which are specifically associated with -C≡C- bonds and have been used for the precise identification of the carbyne phase [27,28]. Nevertheless, defined D (1350 cm⁻¹) and G (1587 cm⁻¹) bands can also be observed, suggesting the presence of sp²-bonded carbon. Although these spectra indicate a small percentage of sp¹-bonded carbyne species with respect to sp²- and sp³-bonded carbon components on the samples (characterized several days after the film deposition), this suggests a substantial initial concentration of carbyne in the freshly deposited film, as it has been indicated in previous work [29,30]. This has been attributed to the inherent metastability of sp-bonded carbon species (carbyne) and thus its rapid exponential decay with a time constant of 22 h under high vacuum and 0.58 h in dry air [30]. These results are also in agreement with ex situ XPS spectroscopy characterization performed on similar carbyne-enriched films [31].

The carbyne-enriched coating was deposited on PMMA surfaces. Figure 1b presents the EDX spectra of rough PMMA surfaces (treated in oxygen plasma for 20 min) before and after carbyne coating. Before coating, the surface composition shows approximately 90% carbon and 10% oxygen, reflecting an increase in carbon [32,33] attributed to contamination from environmental carbon species and surface modification induced by oxygen plasma treatment. After carbyne coating deposition, the EDX spectrum exhibits a single dominant carbon peak, corresponding to nearly 100% carbon, with the oxygen signal no longer detectable. This significant reduction in oxygen confirms that the surface is fully covered by the carbyne-enriched film, demonstrating the successful deposition process. In Figure 1, c images of the contact angle measurements are presented, along with a graph depicting the contact angle measurements at key stages of the procedure. The untreated (flat) PMMA plate exhibits a contact angle of approximately 65°. After the deposition of the carbyne-enriched film, the contact angle slightly increases to about 75°. Remarkably, the contact angle remains constant even after 4 months of storage in normal environmental conditions.

Following an oxygen plasma activation of the surface (conditions detailed in Section 2.3 above, with a duration of 30 s), the contact angle reduces significantly to 18°. This low contact angle persists for at least a few hours after the process, but after 3 weeks, it gradually returns to the initial value.

3.2. Topography Characterization of Carbyne-Enriched Coated Micro-Nanotextured Surfaces

During the oxygen plasma etching of PMMA surfaces, as ions sputter the substrate, they also affect the electrode and chamber walls, causing particles from these components to be deposited on the substrate. These particles serve as micro-masks, reducing the etching rate of the substrate in the areas where they are deposited. This process leads to the formation of polymeric nanowires, which, with the increase in process time, increase in height. Upon reaching a critical value, they tend to bundle with neighboring nanowires, resulting in bundled nanowires. As the process time further increases, these wires can reach 4–5 μm in height or even higher.

We fabricated PMMA surfaces with texturing of different heights, one reaching 1.5–2 μm after 10 min of treatment, and one reaching more than 5 μm after a 20 min treatment. SEM images of the topography can be seen in Figure 2a,b.

3.3. Wetting Characterization

In Figure 1d, the contact angle measurements on the rough PMMA surfaces with the carbyne-enriched coating are presented. The freshly prepared surfaces exhibit excellent superhydrophilicity both before and after the deposition of the carbyne-enriched coating. This is a result of the hydrophilization of the PMMA surface (during nanotexturing in the oxygen plasma) and its induced high roughness, leading to superhydrophilicity according to the Wenzel model. It is evident that even coating of the hydrophilized PMMA surface with the carbyne-enriched film is not sufficient to avert the superhydrophilic nature of the surface, probably due to impartial coverage of the rough PMMA surface with carbyne, allowing sufficient hydrophilic groups to be exposed on the surface to interact with water. However, over time, there is an observed increase in the contact angle from 0° to 140°, as a result of the well-known hydrophobic recovery (aging) of the plasma-nanotextured PMMA surfaces [34]. It is noteworthy that this transition takes 4 months for the 20 min-treated surface, as opposed to just 3 months for the 10 min-treated one (the more enhanced is the surface roughness, i.e., for the 20 min-etched surface, the slower the hydrophobic recovery). However, the delay in hydrophobic recovery from 1 month, typical for plasma-nanotextured PMMA surfaces [34], to 4 months, as demonstrated here, can be attributed to carbyne-enriched deposition. This increase in contact angle towards superhydrophobicity has a detrimental effect on our envisioned applications, such as bactericidal action, where hydrophilic surfaces are essential to induce good spreading of bacterial solutions on the surface of interest, and therefore carbyne-coated PMMA surfaces seem to extend the lifetime of plasma-nanotextured PMMA substrates as antibacterial surfaces. Nevertheless, if further extension of their lifetime for, e.g., antibacterial use is desirable, an additional activation step is required.

To address this issue, we employed an additional activation step through oxygen plasma treatment of the carbyne-coated PMMA surface. As shown in Figure 1d, this process effectively reduces the contact angle back to zero and maintains the superhydrophilic nature of the surfaces for at least a few hours after the plasma treatment. This treatment is easily employable before the use of such surfaces in various applications.

3.4. Surface Mechanical Durability

The mechanical durability of the rough PMMA surfaces coated with the carbyne-enriched film was examined through a series of liquid immersion tests to evaluate the potential usage of such surfaces for reusable bactericidal action.

The first test involved immersing the as-prepared samples in water. Surfaces treated for 10 min with two different carbyne-enriched coating thicknesses (40 and 100 nm) were subjected to water immersion and then left to dry under normal environmental conditions. As the water within the surface texture evaporates due to surface tension, it pulls the nanowires together, resulting in their destruction. In Figure 3, SEM images showcase PMMA surfaces textured with oxygen plasma for 10 min: Figure 3a without a carbyne-enriched coating and Figure 3d,g with 40 and 100 nm carbyne-enriched coatings, respectively. Figure 3b,e,h depict the surfaces after water immersion. The results reveal the complete destruction of nanostructures on the PMMA surfaces without the carbyne-enriched coating (Figure 3b). Conversely, the 40 nm carbyne-enriched coating appears to provide some protection, with Figure 3e showing the surface retaining the texturing morphology relatively unaltered. Notably, the 100 nm coating seems to offer complete protection, as the topography remains unchanged after water immersion (Figure 3h).

After evaluating the mechanical durability of superhydrophilic surfaces, the durability of superhydrophobic surfaces coated with carbyne was also tested. The key factor that imparts extreme water repellency to these surfaces is the addition of a thin 40–50 nm Teflon-like coating obtained through C₄F₈ plasma deposition. Indeed, water surface contact angles were measured extremely high at 165 ± 3°, while contact angle hysteresis was extremely low <5°. To induce wetting on such surfaces, a mixture of isopropanol/water 18% v/v was used. The corresponding SEM images after wetting (Figure 3c,f) reveal that in the case of the carbyne-coated surface, the micro- and nanostructures can withstand the durability test of wetting using the low surface tension liquid and remain intact (Figure 3f). On the contrary, the structures of the superhydrophobic surface without a carbyne-enriched coating aggregate and coalesce after wetting (Figure 3c), reducing the roughness and height.

3.5. Bacteria Culture and Viability Test

The antibacterial activity of each surface was evaluated by determining bacteria viability using the standard plate count method. Specifically, the number of colonies on the plates is counted, from which the bacterial concentration in colony-forming units per mL (CFU/mL) is calculated, taking into account the dilution factor and the volume plated, according to Equation (1):

(CFU/mL) = (N × TDF)/V

(1)

where N is the number of colonies counted, TDF is the total dilution factor (in case of serial dilutions), and V is the volume transferred (0.1 mL).

The bactericidal index, I, was used to determine the killing effect of each PMMA surface, and was calculated by Equation (2):

$$\mathrm{I}=(\overline{C}-{\overline{C}}_{\mathit{flat}})/{\overline{C}}_{\mathit{flat}}\times 100\%$$

(2)

where $\overline{C}$_flat is the average bacterial concentration on the flat PMMA surfaces, used as a reference, and $\overline{C}$ is the average bacterial concentration on the surface of interest.

The antibacterial activity of flat and carbyne-enriched coated PMMA, rough PMMA, as well as rough and carbyne-enriched coated PMMA surfaces, with reference to flat (plain) PMMA surfaces, against E. coli after calculation of the viable bacteria concentration is presented in Figure 4. On the flat PMMA surfaces, viable bacteria concentration was 8.9 (±0.6) × 10⁴ CFU/mL, lowering to 6.0 (±0.3) × 10⁴ CFU/mL on the flat and carbyne-enriched coated surfaces, and similarly, to 5.7 (±0.3) × 10⁴ CFU/mL on the rough surfaces, further being reduced to 4.7 (±0.2) × 10⁴ CFU/mL on the rough and carbyne-enriched coated surfaces. In more detail, the antibacterial effect of each surface can be better represented by the bactericidal indices shown in

Table 2. Bactericidal index, I, of carbyne-enriched coated (flat + carbyne), micro-nanotextured (rough), and micro-nanotextured and carbyne-enriched coated (rough + carbyne) PMMA surfaces against E. coli after 4 h dwelling time. The highest bactericidal activity is noted from the textured and carbyne-enriched coated PMMA surfaces.

PMMA Surface	I (%)	δΙ (%)
Flat + Carbyne	32	5
Rough	36	6
Rough + Carbyne	46	5

. The flat PMMA surfaces bearing the carbyne-enriched coating demonstrated an approximately 33% bactericidal index, which is comparable with the one recorded on the rough surfaces, reaching 36%. The carbyne-enriched coating alone registers a killing effect, verifying the existing studies that claim a moderate antibacterial activity of the coating [2]. As mentioned before [4], this is attributed to the electrochemical modification of bacterial membranes which affects their survival. In more detail, it has been demonstrated [4] that the physical contact of bacterial membranes with carbon-based materials, such as the carbyne-enriched coatings studied here, leads to a decrease in the membrane’s zeta potential; thus, resulting in an increase in membrane permeability, however this is not accompanied by the mechanical destruction of bacterial cells. The coating’s antibacterial effect appears similar in magnitude to the one caused by the micro-nanotopography of the rough surfaces. Previous studies from our group [19] have already demonstrated the antibacterial activity of the micro-nanotextured PMMA surfaces, which is attributed to the mechanical rupture of the bacterial membrane by the induced topography, in addition to the bacteria lysis induced by reactive oxygen species [16]. Indeed, adhesion of bacteria cells on the roughened PMMA surfaces is expected to cause drastic stretching of the bacterial membrane, especially in the suspended part between the contact points of the membrane with the surface nanowires, which in turn could lead to irreversible membrane rupture and bacteria death. In addition, even for flat PMMA substrates, the presence of reactive oxygen species (ROS) has been demonstrated [16] in correlation with the presence of free bacterial DNA, adding ROS-mediated oxidative damage contribution to bacterial death.

By further combining this topography with the carbyne-enriched coating, the killing effect of the rough and carbyne-enriched coated surfaces is increased to approximately 50% (46%). It is deduced that carbyne’s inherent stiffness [35], when used to coat the plasma-generated topography, additionally enhances the rigidity of the texturing, thereby rendering more effective the mechanical killing of the bacteria. Moreover, the supplementary electrochemical antibacterial activity of carbyne is assumed, given its mechanism of action, which increases the bacterial membrane’s passive permeability. An approximately 10% enhancement of the bactericidal effect is noted with the incorporation of the carbyne-enriched coating to the rough surface. Herein, E. coli was tested, as a representative Gram-negative bacterium, since Gram-negative bacteria are known to be more resistant to antibacterial agents, due to their distinctive membrane structure [36]. Reports in the literature [4] have studied the antibacterial activity of carbon-based nanomaterials such as carbyne, for both Gram-positive and Gram-negative bacteria. The bactericidal index I determined in this work for E. coli on carbyne-enriched coatings (~32%) is almost half of that for the Gram-positive bacteria (S. aureus and E. faecalis) previously studied, as a result of the reduced resistance of Gram-positive bacteria compared to Gram-negative ones. However, the determined bactericidal index, I, for E. coli on carbyne-enriched plasma-textured surfaces (~46%) is much higher than that of other Gram-negative bacteria reported in the literature (e.g., P. aeruginosa, I~0%). This is clearly an advantage of the prepared films combining plasma-nanotextured PMMA wires with carbyne-enriched coatings.

4. Conclusions

In conclusion, the enhanced durability of carbyne-enriched plasma-coated, textured polymeric surfaces was assessed and demonstrated for water-related applications. First, the carbyne-enriched coating was characterized as demonstrating a high carbon content and the presence of -C≡C- bonds. Additionally, aging of the carbyne-enriched plasma-textured surface, leading to an increase in its water contact angle, was observed. However, the surface hydrophilicity was restored (through oxygen plasma activation) for at least a few hours.

Subsequently, textured polymeric surfaces through oxygen plasma etching were tested, previously shown to exhibit antibacterial properties. With the introduction of the carbyne-enriched plasma coating, increased efficiency and mechanical durability of the surface was demonstrated. Indeed, the results demonstrated that the carbyne-enriched coating reinforces the nanotopography against damage during water immersion. In addition, the superhydrophobic, carbyne-coated polymeric surfaces survive on the wetting of lower surface tension liquids. Finally, the carbyne-enriched coating itself noted a mild antibacterial activity against the Gram-negative bacteria, E. coli. The micro-nanotextured and carbyne-enriched coated PMMA surfaces exhibited a significant bactericidal effect of approximately 50%, owing to the combined action of both the surface topography and the chemistry of the coating. Similar results are expected for other Gram-negative bacteria, while variations might appear with Gram-positive bacteria.