Mutanofactin promotes adhesion and biofilm formation of cariogenic Streptococcus mutans.

Cariogenic Streptococcus mutans is known as a predominant etiological agent of dental caries due to its exceptional capacity to form biofilms. From strains of S. mutans isolated from dental plaque, we discovered, in the present study, a polyketide/nonribosomal peptide biosynthetic gene cluster, muf, which directly correlates with a strong biofilm-forming capability. We then identified the muf-associated bioactive product, mutanofactin-697, which contains a new molecular scaffold, along with its biosynthetic logic. Further mode-of-action studies revealed that mutanofactin-697 binds to S. mutans cells and also extracellular DNA, increases bacterial hydrophobicity, and promotes bacterial adhesion and subsequent biofilm formation. Our findings provided an example of a microbial secondary metabolite promoting biofilm formation via a physicochemical approach, highlighting the importance of secondary metabolism in mediating critical processes related to the development of dental caries.

High orientation consistency and adjustable convex width of laser-induced periodic surface structures using picosecond laser pulse trains.

High orientation consistency and adjustable convex width of the low-spatial-frequency laser-induced periodic surface structures (LSFLs), crucial to the functional surface characteristics, have remained elusive. This paper proposes a new method to fabricate LSFLs with high orientation consistency on the rough surface of titanium by combining laser polishing and laser induction with LSFLs with a tunable convex width via laser melting as the post-treatment. Picosecond pulses trained with a 50-ns interval are applied to regulate the thermal incubation effect and achieve laser polishing and laser nanoscale melting. The melting time of titanium for laser polishing and laser nanoscale melting is determined to be on a microsecond time scale and around 100 ns, respectively. Experimental studies show that the surface texture of titanium lowers the orientation consistency of LSFLs and that its divergence angle is 30°. Picosecond pulses with a sub-pulse number of three are applied to achieve surface polishing and the formation of the rudiment of the LSFLs, followed by the picosecond laser induction. As a result, the divergence angle of LSFLs decreases from 30° to 12°. On this basis, aiming at the problem of the narrow adjustability of the convexity ratio of LSFLs, a nanoscale melting processing method based on picosecond pulse trains with a sub-pulse number of four is proposed, and LSFLs with the tunable convexity ratios from 0.3 to 0.87 are obtained.

Mechanism and morphology control of underwater femtosecond laser microgrooving of silicon carbide ceramics.

Silicon carbide (SiC) ceramics have been widely used for microelectronics, aerospace, and other industrial fields due to their excellent chemical stability and thermal tolerance. However, hard machinability and low machining precision of SiC ceramics are the key limitations for their further applications. To address this issue, a novel method of underwater femtosecond laser machining was introduced in this study to obtain high precision and smooth surface of the microgrooves of SiC ceramics. The removal profiles were characterized in terms of width, depth, and surface morphology, which exhibited high dependence on the femtosecond laser processing parameters. The instability during the underwater processing affected by laser-induced gas bubbles and material deposition, however, limits the high surface accuracy of microgrooves and processing efficiency. The process condition transformation from a bubble-disturbed circumstance to a disturbance-free model was carefully investigated through a high speed camera for the femtosecond laser processing of SiC ceramics in water. The experiment results indicated that degree of disturbed effect was heavily dependent on size, distribution, and motion of laser-induced gas bubble. Furthermore, some typical evolution mechanisms of gas bubble and their influence on the removal profiles of microgrooves were discussed in detail. Bubble evolution has been proven to be mainly responsible for the behavior of laser propagation (focus model, total reflection, etc.), which notably affects microstructural characteristic of the microgrooves.

Rutile TiO2 Flocculent Ripples with High Antireflectivity and Superhydrophobicity on the Surface of Titanium under 10 ns Laser Irradiation without Focusing.

We report on the formation of rutile TiO2 flocculent laser-induced periodic surface structures (LIPSSs) with high antireflectivity and superhydrophobicity on the surface of titanium under 10 ns 1064 nm laser irradiation without focusing. The center part of the Gaussian laser beam is used to deposit flocculent structure and the edge part used to produce LIPSSs. The melt and modification thresholds of titanium were determined first, and then, the melt and modification spot-overlap numbers, several responsible for the formation of flocculent structure and LIPSSs, were introduced. It is found that both the melt and modification spot-overlap numbers increase with an increase in laser fluence and spot-overlap number, contributing to the production of flocculent LIPSSs. LIPSSs are obtained with the modification spot-overlap number above 300, and the amount of flocculent structures increases with an increase in the peak laser fluence and spot-overlap number. Then, considering that the fine adjustment of the melt and modification spot-overlop numbers in one-time line scanning is quite difficult, the composite structure, of which both LIPSSs and flocculent structures are distinct, was optimized using laser line scanning twice. On this basis, a characterization test shows the sample full of the flocculent LIPSSs represents best antireflectivity with the value around 10% in the waveband between 260 and 2600 nm (advance 5 times in infrared wavelengths compared to the initial titanium surface), and shows the no-stick hydrophobicity with the contact angle of 160° and roll-off angle of 25° because of the pure rutile phase of TiO2.

Effects of Surface Wettability on the Dewetting Performance of Hydrophobic Surfaces.

We studied the impact dynamics of a droplet on two types of surfaces, i.e., nanostructured/hierarchical (NS/HS) surfaces, with different extents of hydrophobicity. It was found that the contact time is related to wetting hysteresis. It can be concluded that wetting hysteresis plays a significant role in the contact process of bouncing drops based on the work done against resistance produced by contact angle hysteresis (CAH). For similar surface roughness, the work done by CAH dominates, and a lower CAH creates a smaller contact time. Compared with NS surfaces, the energy stored during the Cassie-Baxter/Wenzel state transition because of the more pronounced air pocket formation provides the upward kinetic energy, resulting in rapid detachment of a droplet from HS surfaces. Thus, HS-3 has a smaller contact/elongation time (∼8/2 ms) because of the enhanced air pocket formation and more favorable wettability (larger contact angle (CA) and smaller contact angle hysteresis (CAH)) than other surfaces. In addition, the results show that surface morphology affects the contact time of bouncing drops mainly by influencing the elongation stage. For different Weber numbers (We), the upward energy storage dominates and results in different varying trends of contact time with We for NS-3 and HS-3. For further study, the morphology evolution of bouncing drops with We was also investigated in detail. The results show that a satellite droplet is launched in a certain We range because of high adhesion resulting from the Cassie-Baxter/Wenzel state transition. These findings provide guidelines for the preparation of surfaces for both self-cleaning and anti-icing purposes.

Designable Ultratransparent and Superhydrophobic Surface of Embedded Artificial Compound Eye with Extremely Low Adhesion.

Real-world implementation of artificial compound eye (ACE) has been limited by its poor transparency and high requirement for the stable Cassie state. In general, the improvement of surface dewetting performance sacrifices the transparency of ACE. Herein, ACE was obtained by an integrated manufacturing technology that combined photolithography, microprinting, and chemical growth. Through skillful manipulation of the fabrication process, dewetting hairs were fabricated on the top of micropillars and around the microlens. The combination of nanohairs and micropillars resulted in outstanding superhydrophobicity (∼170°), pristine lotus effect with low sliding angle (∼1°), and contact angle hysteresis (∼2°). Moreover, the surface showed almost no adhesion under a preload of 4 mN, exhibiting excellent stable Cassie state and antiadhesion performance. Furthermore, dynamic impact showed that the impacting droplet was quickly detached from the surface (contact time ∼14.1 ms) without sticking for We = 60. The designed transparency resulted in high performance of optical unit (∼99%, bare glass for comparison). Moreover, ACE exhibited better focusing and imaging capability under larger aperture diameter than microlens without nanohairs. We envision that this research presents a significant advancement in imparting superhydrophobicity and transparency to a so-far inapplicable family of optical devices for many practical outdoor applications.

Broad-Band Ultra-Low-Reflectivity Multiscale Micro-Nano Structures by the Combination of Femtosecond Laser Ablation and In Situ Deposition.

Functional surfaces with broad-band ultralow optical reflection have many potential applications in areas like national defense and energy conversion. For efficient, high-quality manufacturing of material surfaces with antireflection features, a novel machining method for multiscale micro-nano structures is proposed. This method can enable the collaborative manufacturing of both microstructures via laser ablation and micro-nano structures with high porosity via in situ deposition, and it can simplify the fabrication process of multiscale micro-nano structures. As a result, substantially improved antireflection properties of the treated material surface can be realized by optimizing light trapping of the microstructures and enhancing the effective medium effect for the micro-nano structures with high porosity. In ultraviolet-visible-near-infrared regions, average reflectances, as low as 2.21 and 3.33%, are achieved for Si and Cu surfaces, respectively. Furthermore, the antireflection effect of the treated surface can also be extended to the mid-infrared wavelength range, where the average reflectances for the Si and Cu surfaces decrease to 5.28 and 5.18%, respectively. This novel collaborative manufacturing method is both simple and adaptable for different materials, which opens new doors for the preparation of broad-band ultra-low-reflectivity materials.

Fabrication of Artificial Compound Eye with Controllable Field of View and Improved Imaging.

Many arthropods have compound eyes, which are made up of numerous separate visual units (microlenses) or ommatidia. These natural compound eyes have exceptional optical properties such as wide field of view (FOV), low aberration, and fast motion tracking capability. In this paper, a large-scale artificial compound eye (ACE) is fabricated efficiently using a combination of inkjet printing and air-assisted deformation processes. Both size and geometry of the microlens are controlled via superposed drops on the substrate. The simulation results show that the light intensity of the ACE follows a systematic distribution for tilted incident light, which represents a significant improvement, compared to planar distributed microlenses. We then manufacture ACEs with different heights and diameters, and their FOVs are compared with the theoretically predicted results. The measured FOV was 50°-140°. The acceptance angles for the different ACEs are determined, and their relationship with the ratio of height to radius (H/r) of the microlens is investigated in more detail. Furthermore, the imaging properties of the microlenses with different angles of incidences are studied, which suggest a FOV up to 140° and an acceptance angle of about 50°. The microlens captures images even at an angle of incidence of about 60°. The corresponding distortion in both the x and y directions is also investigated. Our findings provide guidelines for the development and fabrication of ACEs with large FOVs and acceptance angles, which may find applications in military, robotics, medical imaging, and astronomy.

Artificial Compound Eyes Prepared by a Combination of Air-Assisted Deformation, Modified Laser Swelling, and Controlled Crystal Growth.

This study presents the manufacturing process of bioinspired compound (BIC) eyes. The hierarchical eyes were accomplished by a combination of (i) modified laser swelling, (ii) air-assisted deformation, and (iii) controlled crystal growth. The results show that the addition of nanostructures on the surface effectively improved the water repellent performance with a contact angle (CA) of ∼160° and generally decreased the reflection by ∼25% in the wavelength range of 400-800 nm than the planar surface. Apart from these properties, the BIC eyes showed good optical performance. The convex structure has a circular shape and aspherical profile; this provides optical uniformity and constant resolution (full width at half-maximum = 1.9 µm) in all the directions. Furthermore, the BIC eyes reduced the imaging distortion by 1.5/3.4 and 2.3/3.1 times along the x and y axes, respectively, under 10° and 20° incident lights than a single lens. In the light acceptance range, the image displays almost no distortion.

Pseudo-topotactic conversion of carbon nanotubes to T-carbon nanowires under picosecond laser irradiation in methanol.

Pseudo-topotactic conversion of carbon nanotubes into one-dimensional carbon nanowires is a challenging but feasible path to obtain desired diameters and morphologies. Here, a previously predicted but experimentally unobserved carbon allotrope, T-carbon, has been produced from pseudo-topotactic conversion of a multi-walled carbon nanotube suspension in methanol by picosecond pulsed-laser irradiation. The as-grown T-carbon nanowires have the same diameter distribution as pristine carbon nanotubes, and have been characterized by high-resolution transmission electron microscopy, fast Fourier transform, electron energy loss, ultraviolet-visible, and photoluminescence spectroscopies to possess a diamond-like lattice, where each carbon is replaced by a carbon tetrahedron, and a lattice constant of 7.80 Å. The change in entropy from carbon nanotubes to T-carbon reveals the phase transformation to be first order in nature. The computed electronic band structures and projected density of states are in good agreement with the optical absorption and photoluminescence spectra of the T-carbon nanowires.T-carbon is a previously predicted but so far unobserved allotrope of carbon, with a crystal structure similar to diamond, but with each atomic lattice position replaced by a carbon tetrahedron. Here, the authors produce T-carbon nanowires via laser-irradiating a suspension of carbon nanotubes in methanol.