Patterned surfaces for biological applications: A new platform using two dimensional structures as biomaterials

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Effect of Atmospheric Pressure Plasma Jet Treatments on Magnesium Phosphate Cements: Performance, Characterization, and Applications

Atmospheric pressure plasma treatments are nowadays gaining importance to improve the performance of biomaterials in the orthopedic field. Among those, magnesium phosphate-based cements (MPCs) have recently shown attractive features as bone repair materials. The effect of plasma treatments on such cements, which has not been investigated so far, could represent an innovative strategy to modify MPCs' physicochemical properties and to tune their interaction with cells. MPCs were prepared and treated for 5, 7.5, and 10 min with a cold atmospheric pressure plasma jet. The reactive nitrogen and oxygen species formed during the treatment were characterized. The surfaces of MPCs were studied in terms of the phase composition, morphology, and topography. After a preliminary test in simulated body fluid, the proliferation, adhesion, and osteogenic differentiation of human mesenchymal cells on MPCs were assessed. Plasma treatments induce modifications in the relative amounts of struvite, newberyite, and farringtonite on the surfaces on MPCs in a time-dependent fashion. Nonetheless, all investigated scaffolds show a good biocompatibility and cell adhesion, also supporting osteogenic differentiation of mesenchymal cells.

Progress in Nanostructured Mechano-Bactericidal Polymeric Surfaces for Biomedical Applications

Bacterial infections and antibiotic resistance remain significant contributors to morbidity and mortality worldwide. Despite recent advances in biomedical research, a substantial number of medical devices and implants continue to be plagued by bacterial colonisation, resulting in severe consequences, including fatalities. The development of nanostructured surfaces with mechano-bactericidal properties has emerged as a promising solution to this problem. These surfaces employ a mechanical rupturing mechanism to lyse bacterial cells, effectively halting subsequent biofilm formation on various materials and, ultimately, thwarting bacterial infections. This review delves into the prevailing research progress within the realm of nanostructured mechano-bactericidal polymeric surfaces. It also investigates the diverse fabrication methods for developing nanostructured polymeric surfaces with mechano-bactericidal properties. We then discuss the significant challenges associated with each approach and identify research gaps that warrant exploration in future studies, emphasizing the potential for polymeric implants to leverage their distinct physical, chemical, and mechanical properties over traditional materials like metals.

Addressing a future pandemic: how can non-biological complex drugs prepare us for antimicrobial resistance threats?

Loss of effective antibiotics through antimicrobial resistance (AMR) is one of the greatest threats to human health. By 2050, the annual death rate resulting from AMR infections is predicted to have climbed from 1.27 million per annum in 2019, up to 10 million per annum. It is therefore imperative to preserve the effectiveness of both existing and future antibiotics, such that they continue to save lives. One way to conserve the use of existing antibiotics and build further contingency against resistant strains is to develop alternatives. Non-biological complex drugs (NBCDs) are an emerging class of therapeutics that show multi-mechanistic antimicrobial activity and hold great promise as next generation antimicrobial agents. We critically outline the focal advancements for each key material class, including antimicrobial polymer materials, carbon nanomaterials, and inorganic nanomaterials, and highlight the potential for the development of antimicrobial resistance against each class. Finally, we outline remaining challenges for their clinical translation, including the need for specific regulatory pathways to be established in order to allow for more efficient clinical approval and adoption of these new technologies.

Myriophyllum spicatum Leaves: Aerophily for Gas Collection and Transportation in Water

The unique living environment of aquatic plants makes them produce many fantastic properties different from land ones. For instance, the leaves of Myriophyllum spicatum show excellent hydrophobicity and aerophily characteristics. In this paper, the abundant morphological structure, composition, and aerophily properties of Myriophyllum spicatum leaves are revealed. The contact angle of the leaf surface can reach 122° in air, exhibiting wonderful gas collection ability under water. The results showed that the aerophily of the leaves is attributed to the multistage micro-nanostructure and waxy layer on the surface. The gas transportation toward the tips of leaves is based on the void gradient formed by the nanoscale morphology at different growth stages and the buoyancy as well. These features provide bionic experience for gas collection, bubble transportation, and liquid resistance reduction in water environments.

Effects of Biomimetic Micropatterned Surfaces on the Adhesion and Morphology of Cervical Cancer Cells

It has been demonstrated that micropatterned surfaces have an important influence on modulating cellular behavior. In recent years, with the rapid development of microfabrication techniques and in-depth study of nature, an increasing number of patterned structures imitating natural organisms have been successfully fabricated and widely evaluated. However, there are only a few reports about biomimetic patterned microstructures in biologically related fields. In our work, micropatterned polydimethylsiloxane (PDMS) was fabricated by mimicking the surface microstructures of natural Trifolium and Parthenocissus tricuspidata leaves using the template duplication method. The interactions between the two types of biomimetic micro-PDMS surfaces and two kinds of human cervical cancer cells (HeLa and SiHa) were investigated. HeLa and SiHa cells cultured on the two micropatterned PDMS samples exhibited more stretchable morphology, higher diffusion, and a much lower nuclear/cytoplasmic ratio than those cultured on flat PDMS surfaces, indicating a higher adhesion area of the cells. Both of the micro-PDMS substrates were found to induce significantly different morphological changes between HeLa and SiHa cells. This suggests that the micropatterned structure affects cell adhesion and morphology correlated with their surface geometric structure and roughness. The results reveal that biomimetic micropatterned surfaces from natural leaves significantly regulate the morphology and adhesion behavior of cervical cancer cells and are believed to be the new platforms for investigating the interaction between cells and substrates.

Viscoelasticity, Like Forces, Plays a Role in Mechanotransduction

Viscoelasticity and its alteration in time and space has turned out to act as a key element in fundamental biological processes in living systems, such as morphogenesis and motility. Based on experimental and theoretical findings it can be proposed that viscoelasticity of cells, spheroids and tissues seems to be a collective characteristic that demands macromolecular, intracellular component and intercellular interactions. A major challenge is to couple the alterations in the macroscopic structural or material characteristics of cells, spheroids and tissues, such as cell and tissue phase transitions, to the microscopic interferences of their elements. Therefore, the biophysical technologies need to be improved, advanced and connected to classical biological assays. In this review, the viscoelastic nature of cytoskeletal, extracellular and cellular networks is presented and discussed. Viscoelasticity is conceptualized as a major contributor to cell migration and invasion and it is discussed whether it can serve as a biomarker for the cells’ migratory capacity in several biological contexts. It can be hypothesized that the statistical mechanics of intra- and extracellular networks may be applied in the future as a powerful tool to explore quantitatively the biomechanical foundation of viscoelasticity over a broad range of time and length scales. Finally, the importance of the cellular viscoelasticity is illustrated in identifying and characterizing multiple disorders, such as cancer, tissue injuries, acute or chronic inflammations or fibrotic diseases.

Micro/Nanopatterned Superhydrophobic Surfaces Fabrication for Biomolecules and Biomaterials Manipulation and Analysis

Superhydrophobic surfaces display an extraordinary repulsion to water and water-based solutions. This effect emerges from the interplay of intrinsic hydrophobicity of the surface and its morphology. These surfaces have been established for a long time and have been studied for decades. The increasing interest in recent years has been focused towards applications in many different fields and, in particular, biomedical applications. In this paper, we review the progress achieved in the last years in the fabrication of regularly patterned superhydrophobic surfaces in many different materials and their exploitation for the manipulation and characterization of biomaterial, with particular emphasis on the issues affecting the yields of the fabrication processes and the quality of the manufactured devices.

Biopatterning: The Art of Patterning Biomolecules on Surfaces

Patterning biomolecules on surfaces provides numerous opportunities for miniaturizing biological assays; biosensing; studying proteins, cells, and tissue sections; and engineering surfaces that include biological components. In this Feature Article, we summarize the themes presented in our recent Langmuir Lecture on patterning biomolecules on surfaces, miniaturizing surface assays, and interacting with biointerfaces using three key technologies: microcontact printing, microfluidic networks, and microfluidic probes.

Bioinspired wettable-nonwettable micropatterns for emerging applications

Superhydrophilic and superhydrophobic surfaces are prevalent in nature and have received tremendous attention due to their importance in both fundamental research and practical applications. With the high interdisciplinary research and great development of microfabrication techniques, artificial wettable-nonwettable micropatterns inspired by the water-collection behavior of desert beetles have been successfully fabricated. A combination of the two extreme states of superhydrophilicity and superhydrophobicity on the same surface precisely, wettable-nonwettable micropatterns possess unique functionalities, such as controllable superwetting, anisotropic wetting, oriented adhesion, and other properties. In this review, we briefly describe the methods for fabricating wettable-nonwettable patterns, including self-assembly, electrodeposition, inkjet printing, and photolithography. We also highlight some of the emerging applications such as water collection, controllable bioadhesion, cell arrays, microreactors, printing techniques, and biosensors combined with various detection methods. Finally, the current challenges and prospects of this renascent and rapidly developing field are proposed and discussed.

Micropatterned Poly(ethylene glycol) Islands Disrupt Endothelial Cell-Substrate Interactions Differently from Microporous Membranes

Porous membranes are ubiquitous in cell co-culture and tissue-on-a-chip studies. These materials are predominantly chosen for their semi-permeable and size exclusion properties to restrict or permit transmigration and cell-cell communication. However, previous studies have shown pore size, spacing and orientation affect cell behavior including extracellular matrix production and migration. The mechanism behind this behavior is not fully understood. In this study, we fabricated micropatterned non-fouling polyethylene glycol (PEG) islands to mimic pore openings in order to decouple the effect of surface discontinuity from potential grip on the vertical contact area provided by pore wall edges. Similar to previous findings on porous membranes, we found that the PEG islands hindered fibronectin fibrillogenesis with cells on patterned substrates producing shorter fibrils. Additionally, cell migration speed over micropatterned PEG islands was greater than unpatterned controls, suggesting that disruption of cell-substrate interactions by PEG islands promoted a more dynamic and migratory behavior, similarly to enhanced cell migration on microporous membranes. Preferred cellular directionality during migration was nearly indistinguishable between substrates with identically patterned PEG islands and previously reported behavior over micropores of the same geometry, further confirming disruption of cell-substrate interactions as a common mechanism behind the cellular responses on these substrates. Interestingly, compared to respective controls, there were differences in cell spreading and a lower increase in migration speed over PEG islands compared prior results on micropores with identical feature size and spacing. This suggests that membrane pores not only disrupt cell-substrate interactions, but also provide additional physical factors that affect cellular response.

Micropatterned biofunctional lubricant-infused surfaces promote selective localized cell adhesion and patterning

Micropatterned biofunctional surfaces provide a wide range of applications in bioengineering. A key characteristic which is sought in these types of bio-interfaces is prevention of non-specific adhesion for enhanced biofunctionality and targeted binding. Lubricant-infused omniphobic coatings have exhibited superior performance in attenuating non-specific adhesion; however, these coatings completely block the surfaces and do not support targeted adhesion or patterning. In this work, we introduce a novel lubricant-infused surface with biofunctional micropatterned domains integrated within an omniphobic layer. This new class of micropatterned lubricant-infused surfaces simultaneously promotes localized and directed binding of desired targets, as well as repellency of undesired species, especially in human whole blood. Furthermore, this modification method is easily translatable to microfluidic devices offering a wider range of applications and improved performance for immunoassays in whole blood and inhibition of clot formation in microfluidic channels. The biofunctional micropatterned lubricant-infused surfaces were created through a bench-top straight forward process by integrating microcontact printing, chemical vapor deposition (CVD) of self-assembled monolayers (SAMs) of fluorosilanes, and further infusion of the SAMs with a bio-compatible fluorocarbon-based lubricant layer. The developed surfaces, patterned with anti-CD34 antibodies, yield enhanced adhesion and controlled localized binding of target biomolecules (e.g. antibodies) and CD34 positive cells (e.g. HUVECs) inside microfluidic devices, outperforming conventional blocking methods (e.g. bovine serum albumin (BSA) or poly(ethylene glycol) (PEG)) in buffer and human whole blood. These surfaces offer a straightforward and effective way to enhance blocking capabilities while preserving the biofunctionality of a micropatterned system in complex biological environments such as whole blood. We anticipate that these micropatterned biofunctional interfaces will find a wide range of applications in microfluidic devices and biosensors for enhanced and localized targeted binding while preventing non-specific adhesion.

Photolithographic Masking Method to Chemically Pattern Silk Film Surfaces

A method has been developed for selectively patterning silk surfaces using a photolithographic process to mask off sections of silk films, which allows selective and precise patterning of features down to 40 μm. This process is highly versatile, utilizes only low-cost equipment and can be used to rapidly prototype flat silk substrates with spatially controlled chemical patterns. Here we demonstrate the usefulness of this technique to deposit fluorescent dyes, labeled proteins and conducting polymers or to modify the surface charge of the silk protein in desired regions on a silk film surface.

Function-driven engineering of 1D carbon nanotubes and 0D carbon dots: mechanism, properties and applications

Metal-free carbonaceous nanomaterials have witnessed a renaissance of interest due to the surge in the realm of nanotechnology. Among myriads of carbon-based nanostructures with versatile dimensionality, one-dimensional (1D) carbon nanotubes (CNTs) and zero-dimensional (0D) carbon dots (CDs) have grown into a research frontier in the past few decades. With extraordinary mechanical, thermal, electrical and optical properties, CNTs are utilized in transparent displays, quantum wires, field emission transistors, aerospace materials, etc. Although CNTs possess diverse characteristics, their most attractive property is their unique photoluminescence. On the other hand, another growing family of carbonaceous nanomaterials, which is CDs, has drawn much research attention due to its cost-effectiveness, low toxicity, environmental friendliness, fluorescence, luminescence and simplicity to be synthesized and functionalized with surface passivation. Benefiting from these unprecedented properties, CDs have been widely employed in biosensing, bioimaging, nanomedicine, and catalysis. Herein, we have systematically presented the fascinating properties, preparation methods and multitudinous applications of CNTs and CDs (including graphene quantum dots). We will discuss how CNTs and CDs have emerged as auspicious nanomaterials for potential applications, especially in electronics, sensors, bioimaging, wearable devices, batteries, supercapacitors, catalysis and light-emitting diodes (LEDs). Last but not least, this review is concluded with a summary, outlook and invigorating perspectives for future research horizons in this emerging platform of carbonaceous nanomaterials.

Evaporation-Induced Biomolecule Detection on Versatile Superhydrophilic Patterned Surfaces: Glucose and DNA Assay

We introduce a droplet-based biomolecular detection platform using robust, versatile, and low-cost superhydrophilic patterned superhydrophobic surfaces. Benefitting from confinement and evaporation-induced shrinkage of droplets on wetted patterns, we show enrichment-based biomolecular detection using very low sample volumes. First, we developed a glucose assay using fluorescent polydopamine (PDA) based on enhancement of PDA emission by hydrogen peroxide (H₂O₂) produced in enzyme-mediated glucose oxidation reaction. Incubation in evaporating droplets resulted in brighter fluorescence compared to that in bulk solutions. Droplet assay was highly sensitive toward increasing glucose concentration while that in milliliter-volume solutions resulted in no fluorescence enhancement at similar time scales. This is due to droplet evaporation that increased the reaction rate by causing enrichment of PDA and glucose/glucose oxidase as well as increased concentration of H₂O₂ generated in shrinking droplet. Second, we chemically functionalized wetted patterns with single-stranded DNA and developed fluorescence-based DNA detection to demonstrate the adaptability of the patterned surfaces for a different class of assay. We achieved detection of glucose and DNA with concentration down to 130 μM and 200 fM, respectively. Patterned superhydrophobic surfaces with their simple production, sensitive response, and versatility present potential for bioanalysis from low sample volumes.

Bio-mimicking nano and micro-structured surface fabrication for antibacterial properties in medical implants

Orthopaedic and dental implants have become a staple of the medical industry and with an ageing population and growing culture for active lifestyles, this trend is forecast to continue. In accordance with the increased demand for implants, failure rates, particularly those caused by bacterial infection, need to be reduced. The past two decades have led to developments in antibiotics and antibacterial coatings to reduce revision surgery and death rates caused by infection. The limited effectiveness of these approaches has spurred research into nano-textured surfaces, designed to mimic the bactericidal properties of some animal, plant and insect species, and their topographical features. This review discusses the surface structures of cicada, dragonfly and butterfly wings, shark skin, gecko feet, taro and lotus leaves, emphasising the relationship between nano-structures and high surface contact angles on self-cleaning and bactericidal properties. Comparison of these surfaces shows large variations in structure dimension and configuration, indicating that there is no one particular surface structure that exhibits bactericidal behaviour against all types of microorganisms. Recent bio-mimicking fabrication methods are explored, finding hydrothermal synthesis to be the most commonly used technique, due to its environmentally friendly nature and relative simplicity compared to other methods. In addition, current proposed bactericidal mechanisms between bacteria cells and nano-textured surfaces are presented and discussed. These models could be improved by including additional parameters such as biological cell membrane properties, adhesion forces, bacteria dynamics and nano-structure mechanical properties. This paper lastly reviews the mechanical stability and cytotoxicity of micro and nano-structures and materials. While the future of nano-biomaterials is promising, long-term effects of micro and nano-structures in the body must be established before nano-textures can be used on orthopaedic implant surfaces as way of inhibiting bacterial adhesion.

Polymer Pen Lithography with Lipids for Large-Area Gradient Patterns

Gradient patterns comprising bioactive compounds over comparably (in regard to a cell size) large areas are key for many applications in the biomedical sector, in particular, for cell screening assays, guidance, and migration experiments. Polymer pen lithography (PPL) as an inherent highly parallel and large area technique has a great potential to serve in the fabrication of such patterns. We present strategies for the printing of functional phospholipid patterns via PPL that provide tunable feature size and feature density gradients over surface areas of several square millimeters. By controlling the printing parameters, two transfer modes can be achieved. Each of these modes leads to different feature morphologies. By increasing the force applied to the elastomeric pens, which increases the tip-surface contact area and boosts the ink delivery rate, a switch between a dip-pen nanolithography (DPN) and a microcontact printing (μCP) transfer mode can be induced. A careful inking procedure ensuring a homogeneous and not-too-high ink-load on the PPL stamp ensures a membrane-spreading dominated transfer mode, which, used in combination with smooth and hydrophilic substrates, generates features with constant height, independently of the applied force of the pens. Ultimately, this allows us to obtain a gradient of feature sizes over a mm² substrate, all having the same height on the order of that of a biological cellular membrane. These strategies allow the construction of membrane structures by direct transfer of the lipid mixture to the substrate, without requiring previous substrate functionalization, in contrast to other molecular inks, where structure is directly determined by the printing process itself. The patterns are demonstrated to be viable for subsequent protein binding, therefore adding to a flexible feature library when gradients of protein presentation are desired.