Modification of the hydrophilic/hydrophobic characteristic of zein film surfaces by contact with oxygen plasma treated PDMS and oleic acid content

A Review of Methods to Modify the PDMS Surface Wettability and Their Applications

Polydimethylsiloxane (PDMS) has attracted great attention in various fields due to its excellent properties, but its inherent hydrophobicity presents challenges in many applications that require controlled wettability. The purpose of this review is to provide a comprehensive overview of some key strategies for modifying the wettability of PDMS surfaces by providing the main traditional methods for this modification and the results of altering the contact angle and other characteristics associated with this property. Four main technologies are discussed, namely, oxygen plasma treatment, surfactant addition, UV-ozone treatment, and the incorporation of nanomaterials, as these traditional methods are commonly selected due to the greater availability of information, their lower complexity compared to the new techniques, and the lower cost associated with them. Oxygen plasma treatment is a widely used method for improving the hydrophilicity of PDMS surfaces by introducing polar functional groups through oxidation reactions. The addition of surfactants provides a versatile method for altering the wettability of PDMS, where the selection and concentration of the surfactant play an important role in achieving the desired surface properties. UV-ozone treatment is an effective method for increasing the surface energy of PDMS, inducing oxidation, and generating hydrophilic functional groups. Furthermore, the incorporation of nanomaterials into PDMS matrices represents a promising route for modifying wettability, providing adjustable surface properties through controlled dispersion and interfacial interactions. The synergistic effect of nanomaterials, such as nanoparticles and nanotubes, helps to improve wetting behaviour and surface energy. The present review discusses recent advances of each technique and highlights their underlying mechanisms, advantages, and limitations. Additionally, promising trends and future prospects for surface modification of PDMS are discussed, and the importance of tailoring wettability for applications ranging from microfluidics to biomedical devices is highlighted. Traditional methods are often chosen to modify the wettability of the PDMS surface because they have more information available in the literature, are less complex than new techniques, and are also less expensive.

pH Effect on the Structure, Rheology, and Electrospinning of Maize Zein

As a simple and convenient technology to fabricate micron-to-nanoscale fibers with controllable structure, electrostatic spinning has produced fiber films with many natural advantages, including a large specific surface area and high porosity. Maize zein, as a major storage protein in corn, showed high hydrophobicity and has been successfully applied as a promising carrier for encapsulation and controlled release in the pharmaceutical and food areas. Proteins exhibit different physical and chemical properties at different pH values, and it is worth investigating whether this change in physical and chemical properties affects the properties of electrospun fiber films. We studied the pH effects on zein solution rheology, fiber morphology, and film properties. Rotational rheometers were used to test the rheology of the solutions and establish a correlation between solution concentration and fiber morphology. The critical concentrations calculated by the cross-equation fitting model were 17.6%, 20.1%, 20.1%, 17.1%, and 19.5% (w/v) for pH 4, 5, 6, 7, and 8, respectively. The secondary structure of zein changed with the variation in solution pH. Furthermore, we analyzed the physical properties of the zein films. The contact angles of the fiber membranes prepared with different pH spinning solutions were all above 100, while zein films formed by solvent evaporation showed hydrophilic properties. The results indicated that the rheological properties of zein solutions and the surface properties of the film were affected by the pH value. This study showed that zein solutions can be stabilized to form electrospun fibers at a variety of pH levels and offered new opportunities to further enhance the encapsulation activity of zein films for bioactive materials.

Fabrication of a bionic compound eye on a curved surface by using a self-assembly technique

Microlens arrays on curved surfaces are regarded as critical elements of bionic compound eyes (BCEs), which exhibit the comparative advantages of a wide field of view and tracking fast-moving objects. However, the fabrication of a curved microlens array is still challenging. Along these lines, in this work, a straightforward, rapid, and low-cost technique for the fabrication of curved microlens arrays is reported by using the self-assembly technique. A reactive ion etching process treated the surface of the curved polydimethylsiloxane (PDMS) substrate to generate a hydrophobic-hydrophilic pattern. Then, the curved microlens array can be realized by dewetting a liquid glue onto the substrate using the dip-coating method and followed by crosslinking. The proposed BCE structure consists of 2400 microlenses (400 - µm diameter and 440 - µm center distance) arranged in a hexagonal configuration on a curved PDMS surface (34 - mm diameter and 40.4 - mm curvature radius). A field-of-view of 50° was demonstrated, which has potential applications in various fields including imaging sensors, medical diagnostics, machine vision systems, and photodetectors.

Applications of Polymers for Organ-on-Chip Technology in Urology

Organ-on-chips (OOCs) are microfluidic devices used for creating physiological organ biomimetic systems. OOC technology brings numerous advantages in the current landscape of preclinical models, capable of recapitulating the multicellular assemblage, tissue-tissue interaction, and replicating numerous human pathologies. Moreover, in cancer research, OOCs emulate the 3D hierarchical complexity of in vivo tumors and mimic the tumor microenvironment, being a practical cost-efficient solution for tumor-growth investigation and anticancer drug screening. OOCs are compact and easy-to-use microphysiological functional units that recapitulate the native function and the mechanical strain that the cells experience in the human bodies, allowing the development of a wide range of applications such as disease modeling or even the development of diagnostic devices. In this context, the current work aims to review the scientific literature in the field of microfluidic devices designed for urology applications in terms of OOC fabrication (principles of manufacture and materials used), development of kidney-on-chip models for drug-toxicity screening and kidney tumors modeling, bladder-on-chip models for urinary tract infections and bladder cancer modeling and prostate-on-chip models for prostate cancer modeling.

Low-Cost Multifunctional Vacuum Chamber for Manufacturing PDMS Based Composites

Polydimethylsiloxane (PDMS) is one of the best known elastomers and has been used in several areas of activity, due to its excellent characteristics and properties, such as biocompatibility, flexibility, optical transparency and chemical stability. Furthermore, PDMS modified with other materials promotes the desired changes to broaden its range of applications in various fields of science. However, the heating, mixing and degassing steps of the manufacturing process have not received much attention in recent years when it comes to blending with solid materials. For instance, PDMS has been extensively studied in combination with waxes, which are frequently in a solid state at room temperature and as a result the interaction and manufacturing process are extremely complex and can compromise the desired material. Thus, in this work it is proposed a multifunctional vacuum chamber (MVC) with the aim to improve and accelerate the manufacturing process of PDMS composites combined with additives, blends and different kinds of solid materials. The MVC developed in this work allows to control the mixing speed parameters, temperature control and internal pressure. In addition, it is a low cost equipment and can be used for other possible modifications with different materials and processes with the ability to control those parameters. As a result, samples fabricated by using the MVC can achieve a time improvement over 133% at the heating and mixing step and approximately 200% at the last degassing step. Regarding the complete manufacturing process, it is possible to achieve an improvement over 150%, when compared with the conventional manufacturing process. When compared to maximum tensile strength, specimens manufactured using the MVC have shown a 39% and 65% improvement in maximum strain. The samples have also shown a 9% improvement in transparency at room temperature and 12% at a temperature of about 75 °C. It should be noted that the proposed MVC can be used for other blends and manufacturing processes where it is desirable to control the temperature, agitation speed and pressure.

Non-animal proteins as cutting-edge ingredients to reformulate animal-free foodstuffs: Present status and future perspectives

Consumer interest in protein rich diets is increasing, with more attention being paid to the protein source. Despite the occurrence of animal proteins in the human diet, non-animal proteins are gaining popularity around the world due to their health benefits, environmental sustainability, and ethical merit. These sources of protein qualify for vegan, vegetarian, and flexitarian diets. Non-animal proteins are versatile, derived mainly from cereals, vegetables, pulses, algae (seaweed and microalgae), fungi, and bacteria. This review's intent is to analyze the current and future direction of research and innovation in non-animal proteins, and to elucidate the extent (limitations and opportunities) of their applications in food and beverage industries. Prior knowledge provided relevant information on protein features (processing, structure, and techno-functionality) with particular focus on those derived from soy and wheat. In the current food landscape, beyond conventionally used plant sources, other plant proteins are gaining traction as alternative ingredients to formulate animal-free foodstuffs (e.g., meat alternatives, beverages, baked products, snack foods, and others). Microbial proteins derived from fungi and algae are also food ingredients of interest due to their high protein quantity and quality, however there is no commercial food application for bacterial protein yet. In the future, key points to consider are the importance of strain/variety selection, advances in extraction technologies, toxicity assessment, and how this source can be used to create food products for personalized nutrition.

A Flexible Pressure Sensor Based on Magnetron Sputtered MoS2

Although two-dimensional (2D) layered molybdenum disulfide (MoS₂) has widespread electrical applications in catalysis, energy storage, and photodetection, there are few reports available regarding sputtered MoS₂ for piezoresistive sensors. In this research, we found that the resistance of magnetron sputtered MoS₂ on a flexible substrate changed significantly and regularly when pressure was applied. Scanning electron microscope (SEM) and atomic force microscope (AFM) images revealed an MoS₂ micro-grain-like structure comprising nano-scale particles with grooves between the particles. Chemical characterization data confirmed the successful growth of amorphous MoS₂ on a polydimethylsiloxane (PDMS) substrate. A micro-thickness film flexible sensor was designed and fabricated. In particular, the sensor with a 1.5 μm thick polydimethylsiloxane (PDMS) substrate exhibited the best resistance performance, displaying a maximum ΔR/R of 70.39 with a piezoresistive coefficient as high as 866.89 MPa⁻¹ while the pressure was 0.46 MPa. A proposed flexible pressure sensor based on an MoS₂ film was also successfully used as a wearable pressure sensor to measure plantar pressure and demonstrated good repeatability. The results showed that the thin film pressure sensor had good piezoresistive performance and high sensitivity.

Surface Modification Techniques for Endothelial Cell Seeding in PDMS Microfluidic Devices

Microfluidic lab-on-a-chip cell culture techniques have been gaining popularity by offering the possibility of reducing the amount of samples and reagents and greater control over cellular microenvironment. Polydimethylsiloxane (PDMS) is the commonly used polymer for microfluidic cell culture devices because of the cheap and easy fabrication techniques, non-toxicity, biocompatibility, high gas permeability, and optical transparency. However, the intrinsic hydrophobic nature of PDMS makes cell seeding challenging when applied on PDMS surface. The hydrophobicity of the PDMS surface also allows the non-specific absorption/adsorption of small molecules and biomolecules that might affect the cellular behaviour and functions. Hydrophilic modification of PDMS surface is indispensable for successful cell seeding. This review collates different techniques with their advantages and disadvantages that have been used to improve PDMS hydrophilicity to facilitate endothelial cells seeding in PDMS devices.

A systematic review and meta-analysis of fish oil encapsulation within different micro/nanocarriers

Fish oil is one of the most important sources of omega 3 polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid and docosahexaenoic acid which are the most important PUFAs with several health benefits. However, PUFAs are prone to oxidation and have a poor water solubility which limits the use of fish oils into food formulations. Encapsulation techniques can be applied to overcome these challenges. There is a large number of published micro/nanoencapsulation papers, where each of them contains a limited number of wall materials, feed formulation, encapsulation technique, and storage conditions. Therefore, without systematic evaluation of the data extracted from available studies, the design of functional foods containing fish oil would not be very successful. The objective of this systematic review is a meta-analysis of published researches on the nano/microencapsulation of fish oil. A comprehensive literature search was performed between 1 October and 31 December 2019 with encapsulation, fish oil, and oxidative stability keywords. Overall, 39 qualified articles were selected for the statistical analysis. Based on the technique used for encapsulation, the fish oil-loaded carriers were classified into four main groups: (a) spray-dried particles; (b) freeze-dried particles; (c) electrospun fibers and electrosprayed capsules; and (d) other carriers prepared by supercritical antisolvent, gelation, liposomes, spray-freeze drying, and transglutaminase catalyzed cross-linking. The three most frequent methods applied for fish oil encapsulation were spray drying (42.86%), freeze drying (21.43%), and electrohydrodynamic (19.04%) methods, respectively. Averagely, the best encapsulation efficiency was obtained for electrohydrodynamic processes. Also, the combination of polysaccharide-protein based wall materials provided the best performance in terms of fish oil encapsulation efficiency.

Photonics in nature and bioinspired designs: sustainable approaches for a colourful world

Biological systems possess nanoarchitectures that have evolved for specific purposes and whose ability to modulate the flow of light creates an extraordinary diversity of natural photonic structures. In particular, the striking beauty of the structural colouration observed in nature has inspired technological innovation in many fields. Intense research has been devoted to mimicking the unique vivid colours with newly designed photonic structures presenting stimuli-responsive properties, with remarkable applications in health care, safety and security. This review highlights bioinspired photonic approaches in this context, starting by presenting many appealing examples of structural colours in nature, followed by describing the versatility of fabrication methods and designed coloured structures. A particular focus is given to optical sensing for medical diagnosis, food control and environmental monitoring, which has experienced a significant growth, especially considering the advances in obtaining inexpensive miniaturized systems, more reliability, fast responses, and the use of label-free layouts. Additionally, naturally derived biomaterials and synthetic polymers are versatile and fit many different structural designs that are underlined. Progress in bioinspired photonic polymers and their integration in novel devices is discussed since recent developments have emerged to lift the expectations of smart, flexible, wearable and portable sensors. The discussion is expanded to give emphasis on additional functionalities offered to related biomedical applications and the use of structural colours in new sustainable strategies that could meet the needs of technological development.

Development of chia seed (Salvia hispanica) mucilage films plasticized with polyol mixtures: Mechanical and barrier properties

Food packaging is one of the main contributors to the high rates of environmental contamination; therefore, interest has emerged on the use of biopolymers as alternative materials to replace conventional food packaging. Chia seed (Salvia hispanica) is recognized by having a high content of a polysaccharide called mucilage. The aim of this study was to evaluate the feasibility using of chia seed mucilage (CSM) and a polyol mixture containing glycerol and sorbitol for the development of films. CSM films with higher sorbitol content showed superior tensile strength (3.23 N/mm²) and lower water vapor permeability (1.3*10^-9 g/m*s*Pa), but had poor flexibility compared to other treatments. Conversely, high glycerol content showed high elongation at break (67.55%) and solubility (22.75%), but poor water vapor permeability and tensile strength. Film formulations were optimized implementing a factorial design according to response surface methodology. Raman spectra analysis showed shifts from 854 to 872 cm^-1 and 1061 to 1076 cm^-1, β (CCO) modes, indicating an increase in hydrogen bonding, responsible for the high tensile strength and decreased water vapor permeability observed in this study. The optimum conditions of polyol concentration were 1.3 g of glycerol and 2.0 g of sorbitol per g of CSM. Based on these results, chia seed mucilage can successfully be used to develop biofilms with potential to be used in drug delivery and edible food coating applications.

Development of mucoadhesive vaginal films based on HPMC and zein as novel formulations to prevent sexual transmission of HIV

Although vaginal films were initially developed for a fast release of the drug, with the adequate formulation they can also be useful for sustained release. The latest strategies for the prevention of the sexual transmission of HIV have moved towards sustained-release dosage forms, so films may be an effective strategy that could also improve the patient's comfort. A hydrophilic polymer (hydroxypropylmethyl cellulose) and an amphiphilic polymer (zein) have been evaluated for the development of Tenofovir sustained-release vaginal films. The modification of the film's properties by the inclusion of polar (glycerol and polyethylene glycol 400 (PEG)) and amphiphilic (tributyl citrate and oleic acid) plasticisers was also evaluated. The films' physicochemical and mechanical properties were determined. The in vitro release of Tenofovir from the films and their bioadhesive capacity and behaviour in simulated vaginal fluid were also assessed. The combination of hydroxypropylmethyl cellulose and zein in films (ratio 1:5), with the inclusion of PEG (40% w/w) proved not only to have excellent mechanical properties, but was also able to release TFV in a sustained manner for 120 h and remain attached to biological tissues throughout this time. This film could be an interesting option for the prevention of sexual transmission of HIV.

Effect of glow discharge plasma on surface modification of chitosan film

Glow discharge plasma (GDP) was used to modify chitosan films to obtain desirable properties. The chitosan films were treated with GDP of 0-800 W for 1 min, respectively. The molecular structure of chitosan films changed under GDP treatment. Chitosan films showed an enhancement of crystallinity with the increasing power of GDP, and the GDP treatment provided them with higher thermal stability, manifested as the exothermic peaks shifted from 291.5 °C (0 W) to 294.1 °C (800 W). Scanning electron microscope (SEM) indicated that the surface of chitosan films got rougher with 0-600 W GDP treatment, accompanied by the increase of tensile strength (TS), and the TS did not increase with the 800 W GDP treatment. However, the water vapor permanent (WVP) became higher with GDP treatment. GDP treatment also exhibited influence on chromatic aberration of chitosan films. GDP is proved to be a promising green, pollution-free, rapid technology to modify chitosan films.

Supramolecular Loop Stitches of Discrete Block Molecules on Graphite: Tunable Hydrophobicity by Naphthalenediimide End-Capped Oligodimethylsiloxane

The noncovalent functionalization of surfaces has gained widespread interest in the scientific community, and it is progressively becoming an extremely productive research field offering brand new directions for both supramolecular and materials chemistry. As the end-groups often play a dominant role in the surface properties obtained, creating loops with end-groups only at the surface will lead to unexpected architectures and hence properties. Here we report the self-assembly of discrete block molecules-structures in-between block copolymers and liquid crystals-featuring oligodimethylsiloxanes (ODMS) end-capped with naphthalenediimides (NDIs) at the 1-phenyloctane/highly oriented pyrolytic graphite (1-PO/HOPG) interface. These structures produce unprecedented vertically nanophase-separated monolayers featuring NDI moieties that regularly arrange on the HOPG surface, while the highly dynamic ODMS segments form loops above them. Such arrangement is preserved upon drying and generates hydrophobic HOPG substrates in which the ODMS block length tunes the hydrophobicity. Thus, the exact structural fidelity of the discrete macromolecules allows for the correlation of nanoscopic organization with macroscopic properties of the self-assembled materials. We present a general strategy for tunable hydrophobic coatings on graphite based on molecularly combining crystalline aromatic moieties and immiscible oligodimethylsiloxanes.

Polymers and biopolymers at interfaces

This review updates recent progress in the understanding of the behaviour of polymers at surfaces and interfaces, highlighting examples in the areas of wetting, dewetting, crystallization, and 'smart' materials. Recent developments in analysis tools have yielded a large increase in the study of biological systems, and some of these will also be discussed, focussing on areas where surfaces are important. These areas include molecular binding events and protein adsorption as well as the mapping of the surfaces of cells. Important techniques commonly used for the analysis of surfaces and interfaces are discussed separately to aid the understanding of their application.

Graphene as Barrier to Prevent Volume Increment of Air Bubbles over Silicone Polymer in Aqueous Environment

The interaction of air bubbles with surfaces immersed in water is of fundamental importance in many fields of application ranging from energy to biology. However, many aspects of this topic such as the stability of surfaces in contact with bubbles remain unexplored. For this reason, in this work, we investigate the interaction of air bubbles with different kinds of dispersive surfaces immersed in water. The surfaces studied were polydimethylsiloxane (PDMS), graphite, and single layer graphene/PDMS composite. X-ray photoelectron spectroscopy (XPS) analysis allows determining the elemental surface composition, while Raman spectroscopy was used to assess the effectiveness of graphene monolayer transfer on PDMS. Atomic force microscopy (AFM) was used to study the surface modification of samples immersed in water. The surface wettability has been investigated by contact angle measurements, and the stability of the gas bubbles was determined by captive contact angle (CCA) measurements. CCA measurements show that the air bubble on graphite surface exhibits a stable behavior while, surprisingly, the volume of the air bubble on PDMS increases as a function of immersion time (bubble dynamic evolution). Indeed, the air bubble volume on the PDMS rises by increasing immersion time in water. The experimental results indicate that the dynamic evolution of air bubble in contact with PDMS is related to the rearrangement of surface polymer chains via the migration of the polar groups. On the contrary, when a graphene monolayer is present on PDMS, it acts as an absolute barrier suppressing the dynamic evolution of the bubble and preserving the optical transparency of PDMS.

Advances in Nanotechnology as They Pertain to Food and Agriculture: Benefits and Risks

Nanotechnology is an emerging and rapidly developing toolbox that has novel and unique applications to food science and agriculture. Fast and impressive developments in nanotechnology for food and agriculture have led to new experimental prototype technologies and products. Developing various types of nanodelivery systems, detection tools, nanoscale modifications of bulk or surface properties, fabrication of wide-range bionanosensors, and biodegradable nanoplatforms can potentially improve consumer health and safety, product shelf life and stability, bioavailability, environmental sustainability, efficiency of processing and packaging, and real-time monitoring. Some recently developed nanotechnology techniques and potential product applications of nanotechnology are summarized in this review. Exposure to nanomaterials may be harmful to the consumer and the environment and might increase the potential of risk. For this reason, evaluation of the potential risks resulting from the interaction of nanomaterials with biological systems, humans, and the environment is also reviewed.

Novel Asymmetric Wettable AgNPs/Chitosan Wound Dressing: In Vitro and In Vivo Evaluation

A novel silver nanoparticles (AgNPs)/chitosan composite dressing with asymmetric wettability surfaces was successfully prepared via a simple two-step method for biomedical applications as wound healing materials. First, AgNPs were assembled into the chitosan sponge which was prepared by lyophilization process. Then one side of the sponge was modified by a thin layer of stearic acid. The incorporation of AgNPs into chitosan dressing could enhance the antibacterial activity against drug-sensitive and drug-resistant pathogenic bacteria. The asymmetric surface modification endows the dressing with both highly hydrophobic property and inherent hydrophilic nature of chitosan. The hydrophobic surface of the dressing shows waterproof and antiadhesion for contaminant properties, whereas the hydrophilic surface preserves its water-absorbing capability and efficiently inhibits the growth of bacteria. Furthermore, the AgNPs/chitosan composite dressing displays improved moisture retention and blood clotting ability compared to the unmodified dressings. Cytocompatibility test evaluated in vitro and in a wound infection model illustrates the nontoxic nature of the composite dressing. More importantly, the in vivo wound healing model evaluation in mice reveals that the asymmetric AgNPs/chitosan dressing promotes the wound healing and accelerates the reepithelialization and collagen deposition. The silver accumulation in mice body treated by the composite dressing is far lower than that of the clinically used Acasin nanosilver dressing treated mice. This work indicates the huge potential of the novel AgNPs/chitosan wound dressing with asymmetrical wettability for clinical use.