فصلنامه بسپارش
سال دوازدهم شماره 3 (پیاپی 44، پاییز 1401)

On the other hand, according to the application fields of motion sensors and their frequent use, the need for hydrogel with desirable mechanical properties such as remarkable toughness, self-healing property after damage and dynamic stability is felt. Therefore, in this article, the recent advances for the preparation of hydrogel with high electrical conductivity, sensitivity to considerable strain, and desirable mechanical properties suitable for motion sensor design are reviewed. In the recent decade, flexible electronics have gained considerable attention due to their widespread use in various fields. In the meantime, there has been a growing demand for wearable strain sensors, which are applicable in human motion monitoring, robotics, touch panels, and so on. In this respect, integrating polymers with electrical conductive agents are the most common strategy to develop flexible electronics. Among polymers, the intrinsic electrical properties, appropriate mechanical properties, and biocompatibility of hydrogels made them a suitable candidates to serve as a strain sensor. However, it is essential to increase hydrogels electrical properties by using ions and electrical conductors to attain high strain sensitivity.On the other hand, the frequent use of hydrogels for human motion monitoring needs suitable mechanical properties such as sufficient toughness, dynamic durability, and high stretchability. To endow hydrogels with these features, some strategies such as nanocomposite hydrogel, double network, and inducing abundant reversible bonds within the hydrogels have been employed. Therefore, in this article, the latest achievements regarding the development of hydrogel-based strain sensors for human motion monitoring and the recent approaches leading to considerable electrical properties, high strain sensitivity, and suitable mechanical performance are reviewed.

The skin, as the first defense barrier against the entry of pathogens into the body, helps to heal the wounds through four stages including homeostasis, inflammation, proliferation, and regeneration. Today, various wound dressings have been introduced to help the body's immune system to improve the speed and quality of wound healing. Conventional wound dressings include polyurethane foams and elastomers, hydrocolloids, hydrogels, semipermeable films, alginate wound dressings, and electrospun polymer nanofibers. Wound dressings based on polymer nanofibers have received a lot of attention for reasons such as similarity to the extracellular matrix (ECM), the desired cell adhesion, high surface-to-volume ratio, gas exchange capability, nutrient supply, and fluid evaporation control. So far, the use of electrospun polyurethanes for the preparation of wound dressings has been reported in various studies. However, the results of studies on a wide range of wound dressings have shown that almost no polymer alone can heal different wounds, effectively. For this reason, many efforts have been made recently to develop polyurethane wound dressings to heal various types of wounds. In this regard, natural polymers have been used due to properties such as biological activity, biocompatibility, and biodegradability along with polyurethanes with desirable physical and mechanical properties. In this article, after introducing the the mechanism of wound healing and describing the characteristics of an ideal wound dressing, the polyurethane/natural polymer blends nanofibers for use as electrospun wound dressings will be discussed.

In-situ forming systems are liquid or viscous injectable materials that after being injected into the body, due to mixing with reactive substances or in response to new conditions (temperature, pH, presence of special molecules or ions, visible or ultraviolet light radiation), they formed a semi-solid material or gel. In the recent years, due to the unique characteristics of in situ forming systems, preparation and investigation of these systems for wound healing have gained increasing attentions. In addition to easy and non-invasive injection of in situ forming systems, these materials can completely fill irregular wound defects and adhere to the wound edge tissues. Also these materials can simultaneously act as a controlled drug delivery system, cell carrier/tissue scaffold, hemostatic agent and tissue-adhesive. Until now, several physical, chemical and enzymatically cross-linking methods have been used to prepare in situ forming systems/hydrogels. In this review, various emerging and innovative approaches being developed and utilized for the preparation of in situ forming systems/hydrogels for wound dressing are reviewed. Also challenges and future prospects of these systems are discussed.

Recently, the use of controlled-radical polymerization methods for the preparation of various polymer materials has received much attention due to the advantages of these methods and the elimination of the disadvantages of radical polymerization. There are many methods for controlled-living radical polymerization, but in general the three main methods for controlled-living radical polymerization are nitric oxide-mediated radical polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT). Among these methods, RAFT polymerization has attracted more attention due to its advantages over other methods used in the preparation of polymeric materials, including polymer nanocomposites. Nanocomposites are compounds obtained from a mixture of two or more different materials that are in the form of separate phases and at least one of their components has nanometer dimensions of less than 100 nm. The combination of high surface area in nanoparticles and different functional groups in the polymer can create unique properties in the nanocomposites. Due to these properties, polymer nanocomposites are widely used in various industries, including polymer catalysts, sensors, chemical adsorbents as well as drug delivery nanocarriers. In this article, the preparation of polymer nanocomposites based on various nanoparticles such as carbon, SiO2, Fe3O4, Au and MoS2 nanoparticles through RAFT polymerization and the effectiveness of these nanomaterials in drug delivery have been reviewed.

Nowadays, the use of prepregs has accelerated the composite manufacturing and has facilitated their processing. To prepare the epoxy prepregs, it is necessary to cure the resin slightly in order to maintain the overall shape of the prepreg and to hold the fibers together. Since epoxy resins require heat for curing and heat is release during the curing reaction, it is always difficult to control the degree of cure in the precuring stage. The progress of precuring reaction determines the mechanical properties and processability of the prepregs. One of the methods to control the degree of cure of epoxy resin for use in prepregs is to use two different curing systems with different conditions for each stage called dual curing system. In this article, while introducing the types of dual curing systems used for epoxy resin such as epoxy-acrylate, epoxy-phenol, epoxy-thiol, epoxy-siloxane, epoxy-sulfonium salt and epoxy-amine, the application of each system is reviewed. Due to the diversity of dual curing systems, different systems can be used to control the prepregs properties such as viscosity, curing percentage, shelf life and also improve the properties of the final composite. Studies show that, in order to increase the shelf life of prepregs using the click reaction with an optical initiator to perform the reaction of the first stage of curing and the thermal click reaction for the second stage of curing are most effective.

Epoxy resins usually have a brittle structure due to the cross-linked structure and poor resistance to crack growth. Therefore, increasing the toughness of epoxy resins in the presence of polymer nanoparticles is one of the fields of interest for researchers. Studying the degradation of epoxy nanocomposites and modeling the degradation kinetics have become widely used as an essential tool for engineers to predict the thermal stability of materials before using in industry, which leads to reduction in costs and an increase in product quality. Surface modification of carbon nanotubes and dispersion of nanoparticles are two important factors in the thermal stability of epoxy nanocomposites in the presence of carbon nanotubes. Hybrid epoxy nanocomposite in the presence of multi-walled carbon nanotubes and clay nanoparticles showed that the simultaneous presence of these nanoparticles can act as a preventive agent against thermal degradation and increase the activation energy of the degradation reaction. In this article, the effect of carbon nanotubes on morphology, rheological and mechanical properties, thermal gravimetric analysis, thermal stability of epoxy resin, and modeling of degradation kinetics of epoxy nanocomposites in the presence of carbon nanotubes are reviewed.

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