Bacterial Networks on Hydrophobic Micropillars

Nanotopology-Enabled On-Site Pathogen Detection for Managing Atopic Dermatitis

Atopic dermatitis (AD), a prevalent skin condition often complicated by microbial infection, poses a significant challenge in identifying the responsible pathogen for its effective management. However, a reliable, safe tool for pinpointing the source of these infections remains elusive. In this study, a novel on-site pathogen detection that combines chemically functionalized nanotopology with genetic analysis is proposed to capture and analyze pathogens closely associated with severe atopic dermatitis. The chemically functionalized nanotopology features a 3D hierarchical nanopillar array (HNA) with a functional polymer coating, tailored to isolate target pathogens from infected skin. This innovative nanotopology demonstrates superior pathogenic capture efficiency, favorable entrapment patterns, and non-cytotoxicity. An HNA-assembled stick is utilized to directly retrieve bacteria from infected skin samples, followed by extraction-free quantitative loop-mediated isothermal amplification (direct qLAMP) for validation. To mimic human skin conditions, porcine skin is employed to successfully capture Staphylococcus aureus, a common bacterium exacerbating AD cases. The on-site detection method exhibits an impressive detection limit of 103 cells mL-1. The HNA-assembled stick represents a promising tool for on-site detection of bacteria associated with atopic dermatitis. This innovative approach enables to deepen the understanding of AD pathogenesis and open avenues for more effective management strategies for chronic skin conditions.

Gut-on-a-chip models for dissecting the gut microbiology and physiology

Microfluidic technologies have been extensively investigated in recent years for developing organ-on-a-chip-devices as robust in vitro models aiming to recapitulate organ 3D topography and its physicochemical cues. Among these attempts, an important research front has focused on simulating the physiology of the gut, an organ with a distinct cellular composition featuring a plethora of microbial and human cells that mutually mediate critical body functions. This research has led to innovative approaches to model fluid flow, mechanical forces, and oxygen gradients, which are all important developmental cues of the gut physiological system. A myriad of studies has demonstrated that gut-on-a-chip models reinforce a prolonged coculture of microbiota and human cells with genotypic and phenotypic responses that closely mimic the in vivo data. Accordingly, the excellent organ mimicry offered by gut-on-a-chips has fueled numerous investigations on the clinical and industrial applications of these devices in recent years. In this review, we outline various gut-on-a-chip designs, particularly focusing on different configurations used to coculture the microbiome and various human intestinal cells. We then elaborate on different approaches that have been adopted to model key physiochemical stimuli and explore how these models have been beneficial to understanding gut pathophysiology and testing therapeutic interventions.

Toward a better modulus at shallow indentations-Enhanced tip and sample characterization for quantitative atomic force microscopy

Approximations of the geometry of indenting probes, particularly when using shallow indentations on soft materials, can lead to the erroneous reporting of mechanical data in atomic force microscopy (AFM). Scanning electron microscopy (SEM) identified a marked change in geometry toward the tip apex where the conical probe assumes a near linear flat-punch geometry. Polydimethylsiloxane (PDMS) is a ubiquitous elastomer within the materials and biological sciences. Its elastic modulus is widely characterized but the data are dispersed and can display orders of magnitude disparity. Herein, we compare the moduli gathered from a range of analytical techniques and relate these to the molecular architecture identified with AFM. We present a simple method that considers sub-100 nm indentations of PDMS using the Hertz and Sneddon contact mechanics models, and how this could be used to improve the output of shallow indentations on similarly soft materials, such as polymers or cells.

A microfluidic approach for studying microcolonization of Escherichia coli O157:H7 on leaf trichome-mimicking surfaces under fluid shear stress

Escherichia coli O157:H7 have previously been associated with disease outbreaks associated with leafy green vegetables. However, the physical mechanisms that determine the spatial organization of bacteria onto leafy greens are still not clear. Microfluidics with embedded trichome-mimicking microposts were employed to investigate the role of shear flow and configuration of trichomes on E. coli O157:H7 microcolonization. We characterized the three-dimensional microcolonization of green fluorescent protein (GFP)-tagged E. coli O157:H7 using multiphoton fluorescence microscopy and compared their differences under static (no flow; incubated for 36 h at 37°C) and fluid shear conditions (750 nl/min for 36 h at 37°C). For micropatterned trichome arrays, we demonstrated that natural wax-mixed polydimethylsiloxane retains similar topographies and contact angles to the surface of trichome-bearing leafy greens. Our results showed that E. coli O157:H7 under fluid shear stress aligned their colonization parallel to the direction of flow. In a static condition, their colonization had no preferential alignment, with statistically similar angular distributions in all directions. In addition, depending on dimensions of the trichome arrays and flow conditions, different bacterial microcolonization patterns grew radially from initial attachment; they formed into filamentous structures and developed into bridges by surface hydrophobicity and flow-induced shear with a nutrient-rich medium. Collectively, these results demonstrate how the consequences of bacterial colonization in response to shear flow can affect pathogenic bacterial contamination of leafy greens and biofilm architectures.

Slippery Liquid-Like Solid Surfaces with Promising Antibiofilm Performance under Both Static and Flow Conditions

Biofilms are central to some of the most urgent global challenges across diverse fields of application, from medicine to industries to the environment, and exert considerable economic and social impact. A fundamental assumption in anti-biofilms has been that the coating on a substrate surface is solid. The invention of slippery liquid-infused porous surfaces─a continuously wet lubricating coating retained on a solid surface by capillary forces─has led to this being challenged. However, in situations where flow occurs, shear stress may deplete the lubricant and affect the anti-biofilm performance. Here, we report on the use of slippery omniphobic covalently attached liquid (SOCAL) surfaces, which provide a surface coating with short (ca. 4 nm) non-cross-linked polydimethylsiloxane (PDMS) chains retaining liquid-surface properties, as an antibiofilm strategy stable under shear stress from flow. This surface reduced biofilm formation of the key biofilm-forming pathogens Staphylococcus epidermidis and Pseudomonas aeruginosa by three-four orders of magnitude compared to the widely used medical implant material PDMS after 7 days under static and dynamic culture conditions. Throughout the entire dynamic culture period of P. aeruginosa, SOCAL significantly outperformed a typical antibiofilm slippery surface [i.e., swollen PDMS in silicone oil (S-PDMS)]. We have revealed that significant oil loss occurred after 2-7 day flow for S-PDMS, which correlated to increased contact angle hysteresis (CAH), indicating a degradation of the slippery surface properties, and biofilm formation, while SOCAL has stable CAH and sustainable antibiofilm performance after 7 day flow. The significance of this correlation is to provide a useful easy-to-measure physical parameter as an indicator for long-term antibiofilm performance. This biofilm-resistant liquid-like solid surface offers a new antibiofilm strategy for applications in medical devices and other areas where biofilm development is problematic.

Water vapor induced self-assembly of islands/honeycomb structure by secondary phase separation in polystyrene solution with bimodal molecular weight distribution

The formation of complex structures in thin films is of interest in many fields. Segregation of polymer chains of different molecular weights is a well-known process. However, here, polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. It was proven that at certain conditions, the phase separation occurred between two fractions of bimodal polystyrene/methyl ethyl ketone solution. The films were prepared by spin-coating, and the segregation between polystyrene phases was investigated by force spectroscopy. Next, water vapour induced secondary phase separation was investigated. The introduction of moist airflow induced the self-assembly of the lower molecular weight into islands and the heavier fraction into a honeycomb. As a result, an easy, fast, and effective method of obtaining island/honeycomb morphologies was demonstrated. The possible mechanisms of the formation of such structures were discussed.

Controlling Geometry and Flow Through Bacterial Bridges on Patterned Lubricant-Infused Surfaces (pLIS)

Spatial control of bacteria and biofilms on surfaces is necessary to understand the biofilm formation and the social interactions between bacterial communities, which could provide useful hints to study the biofilm-involved diseases. Here patterned lubricant-infused surfaces (pLIS) are utilized to fabricate connective structures named "bacterial bridges" between bacterial colonies of Pseudomonas aeruginosa by a simple dewetting method. It is demonstrated that the bacteria attached to hydrophilic areas and bacteria precipitated on lubricant infused borders both contribute to the formation of bacterial bridges. The geometry and distribution of bridges can be controlled using predesigned superhydrophobic-hydrophilic patterns. It is demonstrated that bacterial bridges connecting bacteria colonies act as bio-microfluidic channels and can transport liquids, nutrients, and antibacterial substances between neighboring bacteria clusters. Thus, bacterial bridges can be used to study formation, spreading, and development of bacterial colonies, and communication within and between isolated biofilms.

Guiding Bacterial Activity for Biofabrication of Complex Materials via Controlled Wetting of Superhydrophobic Surfaces

Superhydrophobic surfaces are promising for preventing fouling and the formation of biofilms, with important implications in the food chain, maritime transport, and health sciences, among others. In this work, we exploit the interplay between wetting principles of superhydrophobic surfaces and microbial fouling for advanced three-dimensional (3D) biofabrication of biofilms. We utilize hydrostatic and capillary pressures to finely control the air-water interface and the aerotaxis-driven biofabrication on superhydrophobic surfaces. Superhydrophobic 3D molds are produced by a simple surface modification that partially embeds hydrophobic particles in silicone rubber. Thereafter, the molds allow the templating of the air-water interface of the culture medium, where the aerobic nanocellulose-producing bacteria (Komagataeibacter medellinensis) are incubated. The biofabricated replicas are hollow and seamless nanofibrous objects with a controlled morphology. Gradients of thickness, topographical feature size, and fiber orientation on the biofilm are obtained by controlling wetting, incubation time, and nutrient availability. Furthermore, we demonstrate that capillary length limitations are overcome by using pressurized closed molds, whereby a persistent air plastron allows the formation of 3D microstructures, regardless of their morphological complexity. We also demonstrate that interfacial biofabrication is maintained for at least 12 days without observable fouling of the mold surface. In summary, we achieve controlled biofouling of the air-water interface as imposed by the experimental framework under controlled wetting. The latter is central to both microorganism-based biofabrication and fouling, which are major factors connecting nanoscience, synthetic biology, and microbiology.

Synergetic Combination of Interfacial Engineering and Shape-Changing Modulation for Biomimetic Soft Robotic Devices

Robotics is a frontal interdisciplinary subject across the fields of mechanical engineering, chemical and materials engineering, artificial intelligence, and nanotechnology. Robotic devices with a variety of frameworks, functionalities, and actuation modes have been developed and employed in the manufacture of advanced materials and devices with improved efficiency and automation. In recent years, soft robots have attracted a significant amount of interest among scientific researchers and technological engineers because they can offer the desired safety, adaptability, sensibility, and dexterity that conventional robotics cannot deliver. To date, emulating living creatures in nature has been a promising approach to design soft robots. For living creatures, both body deformation and their surface characteristic are essential for them to function in dynamic ecological environments. Body deformation offers athletic ability while surface characteristics provide extraordinary adaptable interactions with the environment. In this article, we discuss the recent progress of emulating the body deformation of living creatures such as shrinking/expanding, bending, and twisting and programmable deformations based on the manipulation of shape-changing behaviors of liquid-crystal polymeric materials (LCPs) and the interfacial technologies to build up various microstructures similar to the interface of living creatures. We further review the pioneering work that integrates interfacial engineering and the shape-changing modulation of LCPs to develop biomimetic soft robotic devices. We also provide an outlook for opportunities and challenges in the design and fabrication of advanced biomimetic soft robots based on the synergetic combination of interfacial engineering and shape-changing modulation.

UV Light Assisted Coating Method of Polyphenol Caffeic Acid and Mediated Immobilization of Metallic Silver Particles for Antibacterial Implant Surface Modification

Titanium implants are extensively used in biomedical applications due to their excellent biocompatibility, corrosion resistance, and superb mechanical stability. In this work, we present the use of polycaffeic acid (PCA) to immobilize metallic silver on the surface of titanium materials to prevent implant bacterial infection. Caffeic acid is a plant-derived phenolic compound, rich in catechol moieties and it can form functional coatings using alkaline buffers and with UV irradiation. This combination can trigger oxidative polymerization and deposition on the surface of metallic substrates. Using PCA can also give advantages in bone implants in decreasing inflammation by decelerating macrophage and osteoclast activity. Here, chemical and physical properties were investigated using FE-SEM, EDS, XPS, AFM, and contact angle. The in vitro biocompatibility and antibacterial studies show that PCA with metallic silver can inhibit bacterial growth, and proliferation of MC-3T3 cells was observed. Therefore, our results suggest that the introduced approach can be considered as a potential method for functional implant coating application in the orthopedic field.

Biofilm Bridges Forming Structural Networks on Patterned Lubricant-Infused Surfaces

Despite many decades of research, biofilm architecture and spreading mechanisms are still not clear because of the heterogenous 3D structure within biofilms. Here, patterned "slippery" lubricant-infused porous surfaces are utilized to study biofilm structure of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, and Staphylococcus aureus. It is found that bacteria are able to spread over bacteria-repellent lubricant-infused regions by using a mechanism, termed "biofilm bridges". Here, it is demonstrated that bacteria use bridges to form interconnected networks between distant biofilm colonies. Detailed structure of bridges shows a spatial distribution of bacteria with an accumulation of respiratory active bacteria and biomass in the bridges. The core-shell structure of bridges formed by two-species mixed population is illustrated. It is demonstrated that eDNA and nutrients have a strong effect on biofilm bridges formation. Thus, it is believed that biofilm bridging is important to reveal the structure and communication within biofilms.

Polymeric Nanowires for Diagnostic Applications

Polymer nanowire-related research has shown considerable progress over the last decade. The wide variety of materials and the multitude of well-established chemical modifications have made polymer nanowires interesting as a functional part of a diagnostic biosensing device. This review provides an overview of relevant publications addressing the needs for a nanowire-based sensor for biomolecules. Working our way towards the detection methods itself, we review different nanowire fabrication methods and materials. Especially for an electrical signal read-out, the nanowire should persist in a single-wire configuration with well-defined positioning. Thus, the possibility of the alignment of nanowires is discussed. While some fabrication methods immanently yield an aligned single wire, other methods result in disordered structures and have to be manipulated into the desired configuration.

Probiotics Biofilm-Integrated Electrospun Nanofiber Membranes: A New Starter Culture for Fermented Milk Production

Electrospun nanofiber membranes are widely investigated in the past few decades as candidates for tissue engineering, which can mimic natural extracellular matrix (ECM) and improve cell adhesion, proliferation, and expression on nanofiber membranes. However, the formation of bacterial biofilms on nanofiber membranes and application of the biofilm-integrated nanofiber membranes remain largely unknown. Here, electrospun cellulose acetate nanofiber membranes are first utilized as scaffold materials for Lactobacillus plantarum ( L. plantarum) biofilm formation. Nanofiber membranes proved to be an excellent scaffold for bacteria biofilm with high stability, where biofilms were interlocked with nanofibers forming a cohesive structure. In comparison with planktonic bacteria, L. plantarum biofilms on nanofiber membranes show excellent gastrointestinal resistance. Instead of decreasing, the number of viable cells increased after 3 h digestion in vitro. The L. plantarum biofilm-integrated nanofiber membranes were used as reusable starter cultures for fermented milk production showing excellent fermentative ability and higher survival of L. plantarum during shelf life. The viable cells in fermented milk remained at 11 log CFU/g throughout the reusable batches, which is far above the required value of 7 log CFU/g in commercial products. In addition, the produced fermented milk possesses shorter fermentation time and higher survival of probiotics during shelf life. The results suggest electrospun nanofiber membranes are ideal scaffold materials for bacteria biofilms immobilization in biotechnology and fermentation engineering, which broaden the potential use of electrospun nanofiber membranes in microbiology and strengthen the application of biofilms in fermentation engineering.

Fabrication of Low-Cost Flexible Superhydrophobic Antibacterial Surface with Dual-Scale Roughness

In this work, we report a large-area fabrication of a flexible superhydrophobic bactericidal surface decorated with copper hydroxide nanowires. This involves a simple two-step method which involves growth followed by transfer of the nanowires onto the polydimethylsiloxane (PDMS) surface by mechanical peeling. Additional roughness in PDMS is obtained through incomplete wetting of the nanoscale gaps which leads to dual-scale roughness and superhydrophobicity with a contact angle of 169° and hysteresis of less than 2°. The simplicity of the process makes it low-cost and easily scalable. The process allows fabrication of nonplanar 3D surfaces. The surface shows blood repellence and antibacterial activity against Escherichia coli with more than 5 log reductions in bacterial colony. The surface also shows hemocompatible behavior, making it suitable for healthcare applications. The fabricated surface is found to be extremely robust against stretching, twisting, sandpaper abrasion, solid weight impact, and tape peel test. The surface is found to withstand human weight multiple times without losing its hydrophobicity, making it suitable for several practical scenarios in healthcare and household applications.

Mechanical Contact Characteristics of PC3 Human Prostate Cancer Cells on Complex-Shaped Silicon Micropillars

In this study we investigated the contact characteristics of human prostate cancer cells (PC3) on silicon micropillar arrays with complex shapes by using high-resolution confocal fluorescence microscopy techniques. These arrays consist of micropillars that are of various cross-sectional geometries which produce different deformation profiles in adherent cells. Fluorescence micrographs reveal that some DAPI (4',6-diamidino-2-phenylindole)-stained nuclei from cells attached to the pillars develop nanometer scale slits and contain low concentrations of DNA. The lengths of these slits, and their frequency of occurrence, were characterized for various cross-sectional geometries. These DNA-depleted features are only observed in locations below the pillar's top surfaces. Results produced in this study indicate that surface topography can induce unique nanometer scale features in the PC3 cell.

Unraveling Antimicrobial Susceptibility of Bacterial Networks on Micropillar Architectures Using Intrinsic Phase-Shift Spectroscopy

With global antimicrobial resistance becoming increasingly detrimental to society, improving current clinical antimicrobial susceptibility testing (AST) is crucial to allow physicians to initiate appropriate antibiotic treatment as early as possible, reducing not only mortality rates but also the emergence of resistant pathogens. In this work, we tackle the main bottlenecks in clinical AST by designing biofunctionalized silicon micropillar arrays to provide both a preferable solid-liquid interface for bacteria networking and a simultaneous transducing element that monitors the response of bacteria when exposed to chosen antibiotics in real time. We harness the intrinsic ability of the micropillar architectures to relay optical phase-shift reflectometric interference spectroscopic measurements (referred to as PRISM) and employ it as a platform for culture-free, label-free phenotypic AST. The responses of E. coli to various concentrations of five clinically relevant antibiotics are optically tracked by PRISM, allowing for the minimum inhibitory concentration (MIC) values to be determined and compared to both standard broth microdilution testing and clinic-based automated AST system readouts. Capture of bacteria within these microtopologies, followed by incubation of the cells with the appropriate antibiotic solution, yields rapid determinations of antibiotic susceptibility. This platform not only provides accurate MIC determinations in a rapid manner (total assay time of 2-3 h versus 8 h with automated AST systems) but can also be employed as an advantageous method to differentiate bacteriostatic and bactericidal antibiotics.

Manipulating mammalian cell morphologies using chemical-mechanical polished integrated circuit chips

Tungsten chemical-mechanical polished integrated circuits were used to study the alignment and immobilization of mammalian (Vero) cells. These devices consist of blanket silicon oxide thin films embedded with micro- and nano-meter scale tungsten metal line structures on the surface. The final surfaces are extremely flat and smooth across the entire substrate, with a roughness in the order of nanometers. Vero cells were deposited on the surface and allowed to adhere. Microscopy examinations revealed that cells have a strong preference to adhere to tungsten over silicon oxide surfaces with up to 99% of cells adhering to the tungsten portion of the surface. Cells self-aligned and elongated into long threads to maximize contact with isolated tungsten lines as thin as 180 nm. The orientation of the Vero cells showed sensitivity to the tungsten line geometric parameters, such as line width and spacing. Up to 93% of cells on 10 μm wide comb structures were aligned within ± 20° of the metal line axis. In contrast, only ~22% of cells incubated on 0.18 μm comb patterned tungsten lines were oriented within the same angular interval. This phenomenon is explained using a simple model describing cellular geometry as a function of pattern width and spacing, which showed that cells will rearrange their morphology to maximize their contact to the embedded tungsten. Finally, it was discovered that the materials could be reused after cleaning the surfaces, while maintaining cell alignment capability.