The first aspect of the magnetically responsive multilayer composite addressed in the dissertation is the interaction between the magnetic field and structural deformation. The composition of the multilayer structure and the mechanical properties were analyzed for deformation optimization. The surface undulation of the dynamic composition caused significant fluid velocity changes just above the deformed region.
The antifouling properties of the dynamic wavy composite were quantified by colony forming units (CFU) and surface coverage. Further improvement in antifouling properties was also achieved by the addition of nanostructure and chemical moieties to the top surface of the composite. FEA for the dynamic undulating wave under a controlled magnetic field. results showing the propagation of the dimple generated by the unidirectional translation of a magnet.
Phase diagram showing different regimes of colony forming unit (CFU) counting according to activation period (T) and dimple depth (H) of topographic waves. Tilted and (ii) schematic cross-sectional illustrations showing the concept and structure of the dynamic composite-based catheter with improved antifouling performance.
Introduction
Research background
- Antifouling strategy I: Passive prevention of biofilm formation
- Antifouling strategy II: Active elimination of pre-formed biofilm
- Newly proposed antifouling strategy: Active prevention of biofilm formation
The antifouling strategy I is the way to prevent biofilm formation by repelling or killing bacteria (Figure 3). In total, the antifouling strategy I, which is passive prevention of biofilm formation, mainly used nanostructured surface modification or antimicrobial materials for antifouling. In contrast to antifouling strategy I, strategy II is an active and dynamic approach, defined by the active elimination of preformed biofilm.
Among the various dynamic movements to inhibit biofouling, antifouling strategy II includes dynamic movements used to eliminate the biofilm already formed. To solve the problems related to fouling and overcome the limitations of existing anti-fouling strategies, the new anti-fouling strategy “active prevention of biofilm formation” is proposed here (Figure 8). In addition, the surface with the new antifouling strategy can maintain its antifouling property even under long-term exposure if periodic stimuli are provided because it is a.
Research purpose and objectives
Research concept and outline
Magnetic field-responsive bioinspired undulatory surface
Design and actuation of the multilayered dynamic undulatory composite
- Analysis of batoidea pectoral fin structure and undulatory fin gait
- Composition of the multilayered structure
- Magnetic field-driven dynamic undulation
Theoretical analysis of the magnetic field-driven structural deformation
- Theoretical equations
- Finite element analysis and comparison with experimental results
Summary
Experimental
- Fabrication of the responsive dynamic undulatory composite
- Control of the undulatory topographical waves of the dynamic composite
Undulation-induced ambient flow analysis
Particle image velocimetry analysis
- Ambient flow velocity induced by undulatory topographical waves
- Pathline analysis
Theoretical analysis: Fluidic behavior induced by structural deformation
- Theoretical equations
- Finite element analysis and comparison with experimental results
Modulation and optimization of antifouling-related fluidic behavior
Summary
Experimental
- Particle image velocimetry analysis
- Characterization of the flow over the undulatory surface
- Finite element analysis
Flow-induced proactive foulant-sweeping
Particle (E. coli) trajectory analysis under static/dynamic state
- Kinematic analysis (displacement and velocity)
- Dynamic modes and moment scaling spectrum analysis
The antifouling performance of the dynamic undulating composite was investigated by growing Escherichia coli (E. coli) cells on the surface. Real-time optical images of bacterial movements and swim tracks on the dynamic surface and static control surface were sequentially captured. Random swimming trajectories are observed on the static surface without any specific direction in the bacterial swimming patterns (Figure 30A).
To quantify bacterial movement on corrugated composite and static control surfaces, cell movements in the X and Y directions for each surface are plotted as a function of time. The displacements of the bacterial cells on the static surface are relatively small and within ± 100 μm in both the x and y directions during the tested period of 40 s (Figure 31A, i to ii). However, the Y displacements on the dynamic surface are immensely scattered compared to those on the static surface or the X displacements on the dynamic surface (Fig. 31A-iv).
Therefore, bacterial cells on the dynamic surface move at a high speed (~200 μm s-1) in the y-direction while cells on the static surface have a relatively low speed, both in the x- and y-directions (Figure 31B). Quantitative comparisons of the displacements of individual bacterial cells with respect to wave propagation vectors show that the directions of bacterial cell movement are highly consistent with the direction of wave propagation (Figure 32). We classified the different bacterial movements on static and dynamic surfaces by adopting the momentum scaling spectrum (MSS) theory.
Dispersive particle tracks can be measured using this theory by calculating the displacement moments of individual particles [67]. The plot of γv versus ν is called the MSS and the slope of the MSS (SMSS) is used as a criterion to distinguish the dynamical modes of the dispersive particles. The average value of SMSS and the diffusion coefficient Dv of bacterial cells on the static surface are 0.63 and 25.3 μm2 s-1, respectively.
This result confirms that undulating topographic waves induce apparent directional fluid flows and therefore enable the sweep of planktonic bacterial cells. coli trajectories on static and dynamic surfaces.
Quantification of antifouling properties using CFU and areal coverage of the biofilm . 42
For example, the area of bacterial coverage on the dynamic surface with H of 0.394 mm and T of 60 s is about 37.2% lower than that of the static surface. This is because, for a fixed H value, a smaller T leads to higher vorticity and larger shear stresses in the wall (Figure 28). According to previous studies, at high flow velocity, the hydrodynamic boundary layer that forms close to the surface decreases [62, 63].
In addition, planktonic bacterial cells that swim at a higher current speed have a lower chance of coming into contact with the surface. This implies that sufficient deformation of the bottom surface (but less than ~0.4 mm) is necessary to induce large vortices and larger shear stresses in the wall to prevent bacterial adhesion (Figure 28, A to B). As briefly described, nanostructures or chemical moieties could be added over the soft PUA skin layer of the wavy composite (Figure 38, i to iv).
Addition of nanostructure and chemical work to the skin layer (soft-PUA). i) Atomic force microscope image of nanoneedle array, (ii) Transmission electron microscope image of MPC-coated nanoneedles, (iii) MPC molecular structure, (iv) ATR-FTIR spectroscopy of soft PUA and. Previous studies have reported that nanostructures with sharp tips can induce bacterial cell lysis while physically tearing the cell membrane [ 6 , 68 ]. MPC is a well-known, effective antifouling material that uses its zwitterionic property to electrically repel bacteria (Figure 2).
By generating a nanoscale needle array or coating of the antifouling polymer MPC over the skin layer, the biofilm resistance of the dynamic assembly can be further improved for the same T and H values (Figure 41). Anti-biofilm tests for four different types of surfaces under various static and dynamic conditions. Interestingly, the dynamic surface with proper period and depth of waves (e.g., T = 3 s and H = 0.394 mm) exhibits excellent anti-biofilm performance that is superior to that of the static surface with nanoneedles or MPC grafting (Figure 42) , A to B).
This result confirms that the dynamic corrugated composite proposed in this study can serve as an effective antifouling material with high performance.
Application to medical tube: the undulatory inner wall
The quantitative CV assay further supports the claim that the dynamic waveform tube has remarkable biofilm resistance compared to the static tube (97.7% lower normalized OD compared to the static surface) (Figure 45B). In addition, the durability of the system was confirmed as the dynamic composite maintained its structure and undulating motion without failure for 6 days of the experiment.
Summary
Experimental
- Real-time analysis of bacterial trajectories
- Moment scaling spectrum analysis
- Anti-biofilm assay
The cultured bacteria concentration was measured using a spectrophotometer (GENESYS 20, Thermo Fisher Scientific, USA) at a wavelength of 600 nm (OD600) to obtain an optical density of 0.3. Then, the suspended culture medium was separated by centrifugation (5910R, Eppendorf, Germany) at 5000 rpm for 10 min, and replaced with fresh culture medium to provide sufficient nutrients to the bacteria. The obtained bacteria were grown at 37°C for 2 hours and the concentration was adjusted to OD600 of 0.1.
The dynamic composite specimens were then sterilized with 70% ethanol and 1 min UV exposure and immersed in the bacterial suspension followed by incubation for 18 h at 37 °C. During incubation, the surface of the composite specimens was rippled with controlled wave depths and periods using a permanent magnet installed on a linear actuator. To quantify the area coverage and colony forming unit (CFU) assay, specimens were prepared in multiple batches and incubated simultaneously.
After the incubation process, the samples were rinsed three times with phosphate buffered saline (PBS) and then placed in 24-well plates with a physical size of 1 × 1 cm2. The stained samples were kept in a dark environment at room temperature for 15 min and rinsed with PBS solution three times. The samples were monitored with a multi-photon confocal microscope (LSM 780 Configuration 16 NLO, Zeiss, Germany), and then the surface coverage of the stained bacteria was analyzed using Image J software (NIH, Bethesda, MD, USA).
For the CFU assay, the PBS-rinsed samples were transferred to a falcon tube with 1 ml of sterile PBS and vortexed for 5 min to remove all bacteria from the sample's surface. Serially diluted bacterial solution was plated on LB agar surface, incubated for 18 hours, and then the cultured bacteria were counted to quantify the CFUs.
Conclusion and perspectives
The final research objective was to improve the antifouling performance and propose a field of application. Kong, “In situ assembly of antifouling/bacterial silver nanoparticle and hydrogel composites by controlled particle release and matrix softening,” ACS Appl. Lee et al., “Tuneable multimodal drop-reflection dynamics and anti-icing performance of a magnetically responsive hair array,” ACS Nano, vol.
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Hoon Eui Jeong for the motivation, encouragement and guidance throughout the research and writing of the thesis.
