Biofouling-resistant tubular fluidic devices with magneto-responsive dynamic walls.

Biofouling of tubular fluidic devices limits the stability, accuracy, and long-term uses of lab-on-a-chip systems. Healthcare-associated infection by biofilm formations on body-indwelling and extracorporeal tubular medical devices is also a major cause of mortality and morbidity in patients. Although diverse antifouling techniques have been developed to prevent bacterial contamination of fluidic devices based on antimicrobial materials or nanoscale architectures, they still have limitations in biocompatibility, long-term activity, and durability. In this study, a new conceptual tubular fluidic device model that can effectively suppress bacterial contamination based on dynamic surface motions without using bactericidal materials or nanostructures is proposed. The fluidic device is composed of a magneto-responsive multilayered composite. The composite tube can generate dynamic surface deformation with controlled geometries along its inner wall in response to a remote magnetic field. The magnetic field-derived surface wave induces the generation of vortices near the inner wall surface of the tube, enabling sweeping of bacterial cells from the surface. As a result, the dynamic composite tube could effectively prevent biofilm formation for an extended time of 14 days without surface modification with chemical substances or nanostructures.

Hybrid Architectures of Heterogeneous Carbon Nanotube Composite Microstructures Enable Multiaxial Strain Perception with High Sensitivity and Ultrabroad Sensing Range.

Low-dimensional nanomaterials are widely adopted as active sensing elements for electronic skins. When the nanomaterials are integrated with microscale architectures, the performance of the electronic skin is significantly altered. Here, it is shown that a high-performance flexible and stretchable electronic skin can be produced by incorporating a piezoresistive carbon nanotube composite into a hierarchical topography of micropillar-wrinkle hybrid architectures that mimic wrinkles and folds in human skin. Owing to the unique hierarchical topography of the hybrid architectures, the hybrid electronic skin exhibits versatile and superior sensing performance, which includes multiaxial force detection (normal, bending, and tensile stresses), remarkable sensitivity (20.9 kPa-1 , 17.7 mm-1 , and gauge factor of 707 each for normal, bending, and tensile stresses), ultrabroad sensing range (normal stress = 0-270 kPa, bending radius of curvature = 1-6.5 mm, and tensile strain = 0-50%), sensing tunability, fast response time (24 ms), and high durability (>10 000 cycles). Measurements of spatial distributions of diverse mechanical stimuli are also demonstrated with the multipixel electronic skin. The stress-strain behavior of the hybrid structure is investigated by finite element analysis to elucidate the underlying principle of the superior sensing performance of the electronic skin.

Reusable mechano-bactericidal surface with echinoid-shaped hierarchical micro/nano-structure.

Biofilms formed owing to the attachment of bacteria to surfaces have caused various problems in industries such as marine transportation/logistics and medicine. In response, many studies have been conducted on bactericidal surfaces, and nanostructured surfaces mimicking cicada and dragonfly wings are emerging as candidates for mechano-bactericidal surfaces. In specific circumstances involving mechano-bactericidal activity, certain nanostructured surfaces could exhibit their bactericidal effects by directly deforming the membranes of bacteria that adhere to these nanostructures. Additionally, in most cases, debris of bacterial cells may accumulate on these nanostructured surfaces. Such accumulation poses a significant challenge: it diminishes the mechano-bactericidal effectiveness of the surface, as it hinders the direct interaction between the nanostructures and any new bacteria that attach subsequently. In specific circumstances involving mechano-bactericidal activity, certain nanostructured surfaces could exhibit their bactericidal effects by directly deforming the membranes of bacteria that adhere to these nanostructures. Additionally, in most cases, debris of bacterial cells may accumulate on these nanostructured surfaces. Such accumulation poses a significant challenge: it diminishes the mechano-bactericidal effectiveness of the surface, as it hinders the direct interaction between the nanostructures and any new bacteria that attach subsequently.In other words, there is a need for strategies to remove the accumulated bacterial debris in order to sustain the mechano-bactericidal effect of the nanostructured surface. In this study, hierarchical micro/nano-structured surface (echinoid-shaped nanotextures were formed on Al micro-particle's surfaces) was fabricated using a simple pressure-less sintering method, and effective bactericidal efficiency was shown against E. coli (97 ± 3.81%) and S. aureus (80 ± 9.34%). In addition, thermal cleaning at 500 °C effectively eliminated accumulated dead bacterial debris while maintaining the intact Al2O3 nanostructure, resulting in significant mechano-bactericidal activity (E. coli: 89 ± 6.86%, S. aureus: 75 ± 8.31%). As a result, thermal cleaning maintains the intact nanostructure and allows the continuance of the mechano-bactericidal effect. This effect was consistently maintained even after five repetitive use (E. coli: 80 ± 16.26%, S. aureus: 76 ± 12.67%).

Dragging 3D printing technique controls pore sizes of tissue engineered blood vessels to induce spontaneous cellular assembly.

To date, several off-the-shelf products such as artificial blood vessel grafts have been reported and clinically tested for small diameter vessel (SDV) replacement. However, conventional artificial blood vessel grafts lack endothelium and, thus, are not ideal for SDV transplantation as they can cause thrombosis. In addition, a successful artificial blood vessel graft for SDV must have sufficient mechanical properties to withstand various external stresses. Here, we developed a spontaneous cellular assembly SDV (S-SDV) that develops without additional intervention. By improving the dragging 3D printing technique, SDV constructs with free-form, multilayers and controllable pore size can be fabricated at once. Then, The S-SDV filled in the natural polymer bioink containing human umbilical vein endothelial cells (HUVECs) and human aorta smooth muscle cells (HAoSMCs). The endothelium can be induced by migration and self-assembly of endothelial cells through pores of the SDV construct. The antiplatelet adhesion of the formed endothelium on the luminal surface was also confirmed. In addition, this S-SDV had sufficient mechanical properties (burst pressure, suture retention, leakage test) for transplantation. We believe that the S-SDV could address the challenges of conventional SDVs: notably, endothelial formation and mechanical properties. In particular, the S-SDV can be designed simply as a free-form structure with a desired pore size. Since endothelial formation through the pore is easy even in free-form constructs, it is expected to be useful for endothelial formation in vascular structures with branch or curve shapes, and in other tubular tissues such as the esophagus.

Flexible and transparent nanohole-patterned films with antibacterial properties against Staphylococcus aureus.

In this paper, we explore the development of a multi-functional surface designed to tackle the challenges posed by Staphylococcus aureus (S. aureus), a common opportunistic pathogen. Infections caused by S. aureus during surgical procedures highlight the need for effective strategies to inhibit its adhesion, growth, and colonization, particularly on the surfaces of invasive medical devices. Until now, most existing research has focused on nanopillar structures (positive topographies). Uniform nanopillar arrays have been shown to control bacterial behavior based on the spacing between nanopillars. However, nanopillar structures are susceptible to external friction, impact, and force, making it challenging to maintain their antibacterial properties. Therefore, in this study, we investigate the antibacterial behavior of nanohole structures, which offer relatively superior mechanical robustness compared to nanopillars. Moreover, for applications in medical devices such as laparoscopes, there is a pressing need for surfaces that are not only transparent and flexible (or curved) but are also equipped with antibacterial properties. Our study introduces a scalable multi-functional surface that synergistically combines antibacterial and anti-fog properties. This is achieved by fabricating thin films with variously sized holes (ranging from 0.3 µm to 4 µm) using polyurethane acrylate (PUA). We assessed the activity of S. aureus on these surfaces and found that a 1 µm-diameter-hole pattern significantly reduced the presence of live S. aureus, without any detection of dead S. aureus. This bacteriostatic effect is attributed to the restricted proliferation due to the confined area provided by the hole pattern. However, the persistence of some live S. aureus on the surface necessitates further measures to minimize bacterial adhesion and enhance antibacterial effectiveness. To address this challenge, we coated the zwitterionic polymer 2-methacryloyloxyethyl phosphorylcholine (MPC) onto the nanohole pattern surface to reduce S. aureus adhesion. Moreover, in long-term experiments on surfaces, the MPC-coated effectively inhibited the colonization of S. aureus (18 h; 82%, 7 days; 83%, and 14 days; 68% antibacterial rate). By integrating PUA, MPC, and nanohole architectures into a single, flexible platform, we achieved a multi-functional surface catering to transparency, anti-fogging, and anti-biofouling requirements. This innovative approach marks a significant advancement in surface engineering, offering a versatile solution applicable in various fields, particularly in preventing S. aureus contamination in invasive medical devices like laparoscopes. The resultant surface, characterized by its transparency, flexibility, and antibacterial functionality, stands out as a promising candidate for mitigating S. aureus-related risks in medical applications.

A new mold structure to replicate patterns over 1 microm in depth for substrate conformal imprint lithography.

This paper shows an improved mold replication process that uses polyurethane acrylate (PUA) and polyethylene terephthalate (PET) for the fabrication of an ultraviolet (UV) imprinting mold used in substrate conformal imprint lithography (SCIL). With the conventional replication process, which uses hard polydimethylsiloxane (h-PDMS) as a pattern layer, it is difficult to detach the mold from a silicon master for metal oxide semiconductor field effect transistor (MOSFET) that has patterns with over 1-micron depth. However, the method proposed in this paper allows us to easily replicate patterns that have more than 1-micron depth. The key idea of this method is to use PET film as a bonding layer to attach the PUA layer to the polydimethylsiloxane (PDMS) cushion layer to overcome the weak the adhesion force between the PUA and PDMS layer. We demonstrate how to make the modified replica mold and present imprinting results obtained using this replica mold in the SCIL process.

PEGDMA-Based Pillar-Shape Nanostructured Antibacterial Films Having Mechanical Robustness.

Antibacterial surfaces are one of the most important surfaces in the medical and marine industries. Many researchers are studying antibacterial surfaces to kill bacteria or prevent adhesions. Various materials and structures are applied to the surface to inhibit the adhesion of bacteria or kill the adhered bacteria. Nowadays, a dual strategy is preferred rather than a single strategy. In this study, nanopillar structures were fabricated using polyethylene glycol dimethacrylate (PEGDMA), which has an antifouling effect. Afterward, the fabricated nanostructured PEGDMA was assessed to confirm the intrinsic antibacterial effect and mechanically induced antibacterial functions. The adhesion of Gram-negative and Gram-positive bacteria can be effectively reduced by the PEG hydration layer formation, steric repulsion, and flexible chain, and the nanostructure can damage the bacterial membrane. In addition, we performed antibacterial experiments on a nanopillar-structured surface made of PEGDMA. Furthermore, we revealed that the mechanical robustness of the nanopillared surface was superior to that of the nanocone-structured surface using computational analysis. Nanopillar structures fabricated using PEGDMA are promising candidates for antifouling and antibacterial surfaces and can be applied in various industries.

Fabrication of Nanostructured Polycaprolactone (PCL) Film Using a Thermal Imprinting Technique and Assessment of Antibacterial Function for Its Application.

In the use of the medical devices, it is essential to prevent the attachment of bacteria to the device surface or to kill the attached bacteria. To kill bacteria, many researchers have used antibiotics or studied nanostructure-based antibacterial surfaces, which rely on mechanical antibacterial methods. Several polymers are widely used for device fabrication, one of which is polycaprolactone (PCL). PCL is biocompatible, biodegradable, easy to fabricate using 3D printing, relatively inexpensive and its quality is easily controlled; therefore, there are various approaches to its use in bio-applications. In addition, it is an FDA-approved material, so it is often used as an implantable material in the human body. However, PCL has no inherent antibacterial function, so it is necessary to develop antibacterial functions in scaffold or film-based PCL medical devices. In this study, process parameters for nanopillar fabrication were established through a simple thermal imprinting method with PCL. Finally, a PCL film with a flexible and transparent nanopillar structure was produced, and the mechano-bactericidal potential was demonstrated using only one PCL material. PCL with nanopillars showed bactericidal ability against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) bacteria cultured on its surface that resulted in membrane damage and death due to contact with nanopillars. Additionally, bacteriostatic results were shown to inhibit bacterial growth and activity of Staphylococcus aureus (S. aureus) on PCL nanostructured columns. The fabricated nanopillar structure has confirmed that mechanically induced antibacterial function and can be applied to implantable medical devices.

Bifunctional Amphiphilic Nanospikes with Antifogging and Antibiofouling Properties.

Over the past few decades, extensive research efforts have been devoted to developing surfaces with unique functionalities, such as controlled wettability, antibiofouling, antifogging, and anti-icing behavior, for applications in a wide range of fields, including biomedical devices, optical instruments, microfluidics, and energy conservation and harvesting. However, many of the previously reported approaches have limitations with regard to eco-friendliness, multifunctionality, long-term stability and efficacy, and cost effectiveness. Herein, we propose a scalable bifunctional surface that simultaneously exhibits excellent antifogging and antibiofouling properties based on the synergistic integration of an eco-friendly and bio-friendly polyethylene glycol (PEG) hydrogel, oleamide (OA), and nanoscale architectures in a single flexible platform. We demonstrate that the PEG-OA-nanostructure hybrid exhibits excellent antifogging performance owing to its enhanced water absorption and spreading properties. We further show that the triple hybrid exhibits notable biofilm resistance without the use of toxic biocides or chemicals by integrating the "fouling-resistant" mechanism of the PEG hydrogel, the "fouling-release" mechanism of OA, and the "foulant-killing" mechanism of the nanostructures.

Undulatory topographical waves for flow-induced foulant sweeping.

Diverse bioinspired antifouling strategies have demonstrated effective fouling-resistant properties with good biocompatibility, sustainability, and long-term activity. However, previous studies on bioinspired antifouling materials have mainly focused on material aspects or static architectures of nature without serious consideration of kinetic topographies or dynamic motion. Here, we propose a magnetically responsive multilayered composite that can generate coordinated, undulatory topographical waves with controlled length and time scales as a new class of dynamic antifouling materials. The undulatory surface waves of the dynamic composite induce local and global vortices near the material surface and thereby sweep away foulants from the surface, fundamentally inhibiting their initial attachment. As a result, the dynamic composite material with undulating topographical waves provides an effective means for efficient suppression of biofilm formation without surface modification with chemical moieties or nanoscale architectures.

Hydrogel Nanospike Patch as a Flexible Anti-Pathogenic Scaffold for Regulating Stem Cell Behavior.

Vertically aligned nanomaterials, such as nanowires and nanoneedles, hold strong potential as efficient platforms onto which living cells or tissues can be interfaced for use in advanced biomedical applications. However, their rigid mechanical properties and complex fabrication processes hinder their integration onto flexible, tissue-adaptable, and large-area patch-type scaffolds, limiting their practical applications. In this study, we present a highly flexible patch that possesses a spiky hydrogel nanostructure array as a transplantable platform for enhancing the growth and differentiation of stem cells and efficiently suppressing biofilm formation. In vitro studies show that the hydrogel nanospike patch imposes a strong physical stimulus to the membranes of stem cells and enhances their osteogenic, chondrogenic, and adipogenic differentiation and the secretion of crucial soluble factors without altering cell viability. At the same time, the array exhibits effective bactericidal properties against Gram-positive and Gram-negative bacteria. In vivo studies further demonstrate that the flexible hydrogel patch with its spiky vertical nanostructures significantly promotes the regeneration of damaged cranial bone tissues while suppressing pathogenic bacterial infections in mouse models.

Graphene-Layered Eggshell Membrane as a Flexible and Functional Scaffold for Enhanced Proliferation and Differentiation of Stem Cells.

The eggshell membrane (ESM) is usually regarded as an agricultural byproduct waste, even though it has unique properties as a biomaterial. In particular, the ESM has a flexible and highly pure microfibrous network structure that can be used as an artificial extracellular matrix (ECM) platform for engraftment or as a tissue-engineered scaffold. In this study, flexible and functional scaffolds were constructed using an ESM and graphene, and their applicability for stem cell and tissue engineering was analyzed. The graphene-layered ESM (GEM) scaffolds show enhanced characteristics, such as ECM-like hierarchical micro- and nanostructures and better mechanical and hydrophilic properties than those of a raw ESM. The GEM scaffolds can control the adhesion properties of stem cells, enhancing the proliferation and osteogenic properties of the cells compared with the effects of a raw ESM. Additionally, the GEM scaffolds can improve the secretion of growth factors from stem cells, possibly through enhanced cell-substrate interactions, thereby promoting the proliferation and differentiation of these cells.

Lipid-Hydrogel-Nanostructure Hybrids as Robust Biofilm-Resistant Polymeric Materials.

Despite extensive efforts toward developing antibiofilm materials, efficient prevention of biofilm formation remains challenging. Approaches based on a single strategy using either bactericidal material, antifouling coatings, or nanopatterning have shown limited performance in the prevention of biofilm formation. This study presents a hybrid strategy based on a lipid-hydrogel-nanotopography hybrid for the development of a highly efficient and durable biofilm-resistant material. The hybrid material consists of nanostructured antifouling, biocompatible polyethylene glycol-based polymer grafted with an antifouling zwitterionic polymer of 2-methacryloyloxyethyl phosphorylcholine. Based on the unique composite nanostructures, the lipid-hydrogel-nanostructure hybrid exhibits superior dual functionalities of antifouling and bactericidal activities against Gram-negative and Gram-positive bacteria, compared with those of surfaces with simple nanostructures or antifouling coatings. Additionally, it preserves the robust antibiofilm activity even when the material is damaged under external mechanical stimuli thanks to the polymeric composite nanostructure.

Partially Cured Photopolymer with Gradient Bingham Plastic Behaviors as a Versatile Deformable Material.

We present rheological and mechanical behaviors of a partially cured photopolymer. When an ultraviolet (UV)-curable resin is exposed to UV light in atmospheric conditions, a partially cured layer is formed on the top of the resin owing to inhibitory effects of oxygen. Interestingly, such a partially cured resin behaves like a Bingham plastic with a yield stress, being a rigid solid at low shear stress and a viscous liquid at high stress. Unlike typical Bingham plastic materials, however, deformation rate saturation is observed with an increase in applied stress, which is attributed to the gradient in the degree of photopolymerization of the resin (termed "gradient Bingham plastic"). This gradient Bingham plastic can be utilized for the robust fabrication of diverse 3D, multiscale structures.

Flexible and Shape-Reconfigurable Hydrogel Interlocking Adhesives for High Adhesion in Wet Environments Based on Anisotropic Swelling of Hydrogel Microstructures.

This study presents wet-responsive, shape-reconfigurable, and flexible hydrogel adhesives that exhibit strong adhesion under wet environments based on reversible interlocking between reconfigurable microhook arrays. The experimental investigation on the swelling behavior and structural characterization of the hydrogel microstructures reveal that the microhook arrays undergo anisotropic swelling and shape transformation upon contact with water. The adhesion between the interlocked microhook arrays is greatly enhanced under wet conditions because of the hydration-triggered shape reconfiguration of the hydrogel microstructures. Furthermore, wet adhesion monotonically increases with water-exposure time. A maximum adhesion force of 79.9 N cm-2 in the shear direction is obtained with the hydrogel microhook array after 20 h of swelling, which is 732.3% greater than that under dry conditions (i.e., 9.6 N cm-2). A simple theoretical model is developed to describe the measured adhesion forces. The results are in good agreement with the experimental data.