Rational Design of Flexible and Stretchable Electronics based on 3D Printing

Flexible and stretchable electronics have been considered as the key component for the next generation of flexible devices. There are many approaches to prepare the devices, such as dip coating, spin coating, Mayer bar coating, filtration and transfer, and printing, etc. The effectiveness of these methods has been proven, but some drawbacks cannot be ignored, such as lacking pattern control, labor consuming, requiring complex pretreatment, wasting conductive materials, etc. In this investigation, we propose to adopt 3D printing technology to design flexible and stretchable electronics. The objective is to rationally design flexible and stretchable sensors, simplify the preparation process, form the sample with the complex desirable patterns, and promote the performance of the samples. The dissertation comprises of three major parts: water-induced polymer swelling and its application in soft electronics, utilizing 3D printing to transfer conductive layer into elastomer for building soft electronics, and 3D printing of functional devices. In the first part, we developed the soft electronics with wrinkled structure via 3D printing and water-induced polymer swelling, which can avoid some disadvantages in conventional method, e.g., pre-stretching and organic solvent-induced polymer swelling, including mechanical loss, negative effect to human health, and unidirectionally response to external deformation. Water-induced polymer swelling was achieved by introducing soluble particles into silicone matrixes and soaking the polymer composites in aqueous solution. We have investigated the characteristics and mechanisms of water-induced polymer swelling. Then, the conductive materials were deposited on the swollen sample to form the desired wrinkled structures for stretchable sensors. Furthermore, a dopamine layer was adopted to enhance the adhesion of matrix and conductive layer. The improvement was a key enabler to achieve superior electrical properties of 3D printed stretchable sensors for long-term cyclic stretching. We have demonstrated a series of human motion detection by using these stretchable strain sensors. Another part is designing flexible electrodes with desirable complex pattern by transferring a conductive layer into soft substrates during a 3D printing process. Taking advantage of extrusion pressure and polymer adhesion, the thin conductive layers were embedded into the printed polymer patterns, which can achieve conductive flexible electronics with desirable complex patterns. High-quality transfer has been achieved through adjusting conductive layer thickness, nozzle-to-substrate distance, and printing parameters, etc. Moreover, various printing patterns were created, and their properties were exhibited. The stretchable sensors showed an outstanding stress-strain relationship and electrical response to external deformations. The third part is about 3D printing of functional devices. In the collaborated study, the drug particles were introduced into silicone matrix to prepare the drug-eluting devices. When water molecules transported into the silicone matrix, the loaded drug particles decomposed and released nitric oxide (NO) enabling antibacterial properties. It is noted that 3D printing is creatively employed to form the desirable patterns. We also observed a self-wiring effect in the printing process, i.e., the printed device is covered by a drug-free layer due to the diffusion of a low viscosity silicone component during printing, which can be utilized to prevent drug release bursts and to form a gradient drug-loaded device. The printed samples showed a sustainable NO release and good antibacterial property. Furthermore, the water-induced polymer swelling was possible to be used as actuator in humidity environment. There are some highlights deserving emphasis in the dissertation. Firstly, the water-induced polymer swelling is proposed to develop the flexible and stretchable electronics. The findings have a wide potential application. Additionally, a drug-eluting polymer device with a drug-loaded bulk and a drug-free coating is prepared via leveraging self-wiring effect in 3D printing. The structure can regulate the drug release rate. On the other hand, the additive manufacturing platform offers unique opportunities to produce drug-eluting silicone devices in a customized manner. Finally, 3D printing is employed to encapsulate the conductive layers to achieve the flexible electronics with patterned structure and high performances. The facile and effective approach provides a distinctive view in advancing the development of stretchable electronics

DOUBLE EMULSIONS RELEVANT TO FOOD SYSTEMS: FABRICATION, CHARACTERIZATION, AND APPLICATIONS

Systems of the W/O/W type continue to be of growing interest to food scientists and technologists for two main reasons. First, there is the possibility of preparing a reduced-fat emulsion product by the replacement of a conventional oil-in-water emulsion by the equivalent W/O/W emulsion having a lower actual oil content but a similar in-mouth perceived texture. Second, there is the capability to encapsulate and protect a sensitive hydrophilic bioactive compound. However, it is always a bottleneck to obtain robust formulations using economically viable ingredients and processing operations. To improve its performance for practical applications in food production, efforts have been made to overcome the difficulties. Herein, we examined the impact of crystallizing the oil phase on the ability of W/O/W emulsions to encapsulate and retain a model hydrophilic bioactive. The results showed that the texture and stability of the W/O/W emulsions prepared in this study were highly dependent on their composition. The concentrations of both hydrophilic and hydrophobic stabilizers had to be optimized to produce emulsions that contained relatively small droplets, (initially) had relatively low viscosities, and that were stable to coalescence and phase separation. Our results provide some useful insights into the formulation of double emulsions for the encapsulation of hydrophilic bioactive agents. In addition, two novel applications of double emulsion have been investigated to provide insight for food production market. One is to protect natural color (anthocyanin) from pH-induced color changes, the other one is to study the impact of fat crystallization on the resistance to osmotic stress, which could be a potential for temperature-triggered release

Chapter 34 - Biocompatibility of nanocellulose: Emerging biomedical applications

Nanocellulose already proved to be a highly relevant material for biomedical applications, ensued by its outstanding mechanical properties and, more importantly, its biocompatibility. Nevertheless, despite their previous intensive research, a notable number of emerging applications are still being developed. Interestingly, this drive is not solely based on the nanocellulose features, but also heavily dependent on sustainability. The three core nanocelluloses encompass cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). All these different types of nanocellulose display highly interesting biomedical properties per se, after modification and when used in composite formulations. Novel applications that use nanocellulose includewell-known areas, namely, wound dressings, implants, indwelling medical devices, scaffolds, and novel printed scaffolds. Their cytotoxicity and biocompatibility using recent methodologies are thoroughly analyzed to reinforce their near future applicability. By analyzing the pristine core nanocellulose, none display cytotoxicity. However, CNF has the highest potential to fail long-term biocompatibility since it tends to trigger inflammation. On the other hand, neverdried BNC displays a remarkable biocompatibility. Despite this, all nanocelluloses clearly represent a flag bearer of future superior biomaterials, being elite materials in the urgent replacement of our petrochemical dependence

Glosarium Kimia

386 p.; 24 cm

Polymer Blends and Compatibilization

The market is continuously looking for substitutes for expensive polymers or tailor made polymers for specific applications. Therefore, polymer blends are gaining more interest since they possess a great potential to fulfill these needs. Blending not only results in better final properties, but can also improve the processing behavior and reduce costs. In the field of polymer blends, there are numerous parameters that influence the morphology, e.g., viscosity ratio, blend composition, shear conditions, and blend ratio. There is still a great deal of potential to scientifically exploit the possibilities of blend technology, which is necessary to obtain a foundation based on science, engineering, technology, and applications in order to make it possible to tailor polymer blends as desired. However, combining two or more different polymers to receive favorable properties by blending often results in immiscible polymer blends. This immiscibility goes hand-in-hand with phase separation leading to weak mechanical properties. The high interfacial tension causing this can be reduced by compatibilization of polymer blends. There are different methods to achieve this, such as adding block and graft copolymers, reactive polymers to form block and graft copolymers, nanoparticles or organic molecules. Using suitable compatibilizers, not only is the interfacial adhesion between matrix and its blends reduced, but also the dispersion of the dispersed phase is improved, the adhesion between the phases is enhanced and the morphology is stabilized. This can lead to improved mechanical and morphological properties. Designing new polymer blends or improving the properties of immiscible polymer blends by compatibilization is very challenging, but an excellent way to exploit the full potential of polymers for applications and their varied needs. This Special Issue is a source of information on all recent aspects of polymer blend technology

Advances and Applications of Nano-antimicrobial Treatments

Nowadays, great concerns are associated with the resistance demonstrated by many microorganisms towards the conventional antibiotic therapies. The failure of traditional antimicrobials, and the increasing healthcare costs, have encouraged scientific research and the development of novel antimicrobial agents. Particularly, there is a great deal of interest in nanotechnologies and in antibacterial products obtained through the incorporation of antibacterial agents or the deposition of antibacterial coatings for prevention of biofilm-associated infections. The main focus of the forthcoming Special Issue is, therefore, to present the most recent efforts in scientific research in the development of advanced antimicrobial materials, with special attention to nature-inspired antimicrobial agents and antimicrobials nanomaterials and nanocoatings. For this purpose, we intend to collect original research articles and reviews on the synthesis and characterization of antimicrobial agents, as well as on the development of antimicrobial products for different applications

Functional Polymers as Innovative Tools in the Delivery of Antimicrobial Agents

This Special Issue explored different topics concerning recent progress in the synthesis and characterization of suitable innovative macromolecular systems, proposed as carriers of specific antimicrobial molecules, to be employed in the biomedical and pharmaceutical fields. Many infectious diseases are induced by omnipresent micro-organisms, including bacteria, viruses, protozoa, fungi, and algae, and, consequently, are very common, accounting for a significant share of the global disease burden. Unfortunately, antimicrobial resistance, adverse effects, and the high cost of antimicrobials are crucial health challenges worldwide. One of the common efforts in addressing this issue lies in improving the existing antimicrobial delivery systems. In this regard, nanoparticles as well as three-dimensional hydrophilic systems represent valuable tools able to ensure excellent performances. Biocompatible polymeric particles, entrapping these bioactive molecules, are capable of releasing them over a desired period of time, thereby decreasing the frequency of their administration. At the same time, these systems are able to protect antimicrobial drugs from degradation, enhancing their bioavailability. This Special Issue serves to highlight and capture the contemporary progress recorded in this field

Smart and Functional Polymers

This book is based on the Special Issue of the journal Molecules on “Smart and Functional Polymers”. The collected research and review articles focus on the synthesis and characterization of advanced functional polymers, polymers with specific structures and performances, current improvements in advanced polymer-based materials for various applications, and the opportunities and challenges in the future. The topics cover the emerging synthesis and characterization technology of smart polymers, core?shell structure polymers, stimuli-responsive polymers, anhydrous electrorheological materials fabricated from conducting polymers, reversible polymerization systems, and biomedical polymers for drug delivery and disease theranostics. In summary, this book provides a comprehensive overview of the latest synthesis approaches, representative structures and performances, and various applications of smart and functional polymers. It will serve as a useful reference for all researchers and readers interested in polymer sciences and technologies

Physical and chemical properties of sporopollenin exine particles

The chemical structure of sporopollenin was extensively reviewed, along with some considerations pertaining to its physical and biological properties. A comparative study is presented of extraction protocols to isolate exines from L. clavatum, in particular, but with extension to spores from other species, namely, Lycopodium spec., Ambrosia trifida, Aspergillus niger and Chlorella vulgaris. Physical aspects of the materials extracted were studied, including size (highlighting large and small types of commercial “Lycopodium”), wall thickness, mechanical resistance and density.Encapsulation of a wide variety of compounds in sporopollenin microcapsules was investigated using passive, vacuum, compression and centrifugation methods. Diverse products, with molecular weights ranging from less than 1kDa to 464kDa, were successfully encapsulated in exines, including both polar (e.g. dyes, proteins, carbohydrates and oligonucleotides) and non-polar products (e.g. oils and waxes). It was shown that a protein, alkaline phosphatase, does not lose its initial activity after it has been encapsulated in exines and subsequently released.Sporopollenin was found to grant oils protection against photooxidation triggered by UV light and the extinction coefficient of sporopollenin was determined (20,000-40,000m¯¹). Protective abilities offered by exines to oils against aerial oxidation, and refining effects of sporopollenin on rancid fats, were studied, completed by a preliminary investigation of sporopollenin’s redox characteristics. A flavour test on 20 volunteers showed that exines mask the taste of encapsulated cod liver oil up to a 1/1 (w/w) loading level.Sporopollenin was also used in solid-phase organic synthesis. It was established that the reaction of ammonia, primary aliphatic amines and aniline with sporopollenin formed an amide bond on a carboxylic group of the sporopollenin. A short diamine was attached to sporopollenin in order to construct a spacer arm by further reaction between the free amino end and succinic anhydride. Sporopollenin was derivatised with bromine and chlorine by addition to the unsaturated functional groups, substitution of the hydroxyl groups and chloromethylation of the aromatic rings. The attached halogen atoms were then successfully substituted by azide and thiols. The thiol availability to nucleophilic substitution and formation of disulphide bridges was assessed