فصلنامه بسپارش
سال هفتم شماره 2 (پیاپی 23، تابستان 1396)

Unique properties of gold nanoparticles, such as the surface plasmon resonance (SPR), easy synthesis and modification, control on size and shape, chemically inertness and biocompatibility have attracted much attentionin recent years. The plasmonic properties of gold nanostructures for different applications can be controlled by changing their size and the shape. Introducing gold nanoparticles into polymer systems or their surface modification will improve their solution stability and make them susceptible to respond to external stimuli due to the existing functionalities. Smart gold-polymer nanocomposite with defined properties can be obtained by employing responsive polymers to light, temperature and pH stimuli. Controlling SPR properties of gold nanoparticles make them appropriate for different purposes like photothermal treatment of cancer cells, photodynamic therapy, plasmonic vesicles for drug delivery system, surface enhanced Raman scattering (SERS) and tumor computed tomography imaging. Coating of magnetic nanoparticles with gold promotes their colloidal stability, optical and conductive properties and also enhances their surface chemical reactions and biocompatibility for in vivo applications. In addition, the remote control of plasmonic properties will become feasible by an external electromagnetic field.

Taking a drug/medicine by conventional methods (digestive and indigestive) by patients leads to the release of high dosage of drug in their body. The concentration of drug decreases after a few hours and the patients need to take the next dose again, and such cycle continues. By development of nanoscience and its technology, some new controlled drug delivery systems have been proposed instead. These new systems are expected to improve patient's convenience and compliance, because they are made of biocompatible and biodegradable polymers in controlling drug delivery in the body. Biodegradable polymers can be classified as synthetic and natural polymers with their own specific features. To control the delivery of the drugs, a blend of polymers can be used. In this paper, the effect of blended synthetic biodegradable polymers on controlled drug delivery by electrospun nanofiber is reviewed.

Prepreg is a pre-engineered laminating material manufactured by impregnating a fiber-reinforcement with a resin. Wetting of fibers by the resin is one of the key parameters in prepreg manufacturing process, because of its contribution on the mechanical properties of the prepreg. It is worth mentioning that there are two main mechanisms for increasing the wetting of the fibers by the resin; the first one is through the formation of chemical bonds between the resin and fibers, and the second one is increasing the ability of resin to penetrate through the fibers and make mechanical entanglement between the resin and fibers. Various methods exist to achieve both these mechanisms, such as, surface modification of fibers, changing the resin formulation, increasing the contact time between resin and fibers, and reducing the viscosity of the resin. In this paper, advantages and disadvantages of the above-mentioned methods are evaluated. In general, it can be said that increasing the wetting of fibers by the resin alone cannot be considered as a target in prepreg manufacturing process, because in orderto improve the wetting of the fibers by the resin, there should be changes made in other conditions of the produced prepreg such as mechanical properties, final price, production time, etc..Therefore, finding the optimal values for the parameters like wetting of the fibers by the resin is essential.

Polyurethane adhesives have wide applications in various industries. These adhesives are made of two major components, including isocyanate and polyol. In their synthesis, in accordance with their usage, other materials such as chain extenders, solvents, catalysts and additives are used. Despite all their advantages such as appropriate flexibility, high abrasion resistance, excellent mechanical properties and good adhesion to various surfaces, the adhesion strength of polyurethane adhesives highly depend on process parameters such as ratio of components, molecular weight of polyols, type of isocyanates and polyols, their surface quality and the process temperature. In this study, polyurethane adhesives and the effects of three variablessuch as, reactive component ratio, molecular weight of polyols and surface quality on polyurethane adhesive strength and properties are evaluated. Two variables of crystallization and the ratio of NCO/OH affect the hardness values of polyurethane adhesives, so that by increasing crystallinity and NCO/OH ratiothe stiffnessshows an ascending trend. By increasing of chain extender content (decreasing polyol content)the adhesive young's modulus is significantly increased. This is while the elongation-at-break shows a gradual decline. Also, higher polyol molecular weight increases the storage modulus of polyurethane adhesive. Different ways of surface treatment shows different results of surface roughness. In this fashion, the wettability of resin/substrate is also affected. It is worth mentioning thatapolyurethane-stainless steel system without proper preliminary cleaning process exhibits poor adhesion and polyurethane-SBS rubber system without surface modification has low adhesion strength.

Composite structures should be acceptable in terms of their appearance and resistance to environmental factors and chemicals and their desirable physical properties. To achieve these requirements, “gel coat” is used as surface layer in composites. Composite structures are vulnerable when exposed to moisture environment. Mechanical properties of composite structures are strongly affected by water and moisture absorption, especially in composites made of hydrolysable resins such as polyesters. This causes osmotic swelling and loss of mechanical properties. The adsorbed water in presence of liquids caused by chemical reactions, create soft and gel-like surface that reduces the protective effect of “gelcoat”. On the other hand, resin leaching is another disadvantage of composite structures which could cause fiber leaching in the long term and increase corrosion resistance. Therefore, suitable choice of “gel coat” can increase the surface chemical resistance, reduce moisture absorption and increase the lifetime of composite structures. Also, recent progress in the field of nanoscience makes them appropriate choices for improving properties of the composites. In this paper, we investigated the importance of “gel coat” and the effective factors such as thickness and type of resin in the manufacture of composite structures in various industries and finally the effects of nanofillers on mechanical properties and water absorption.

Current research suggests that carbon nanotubes (CNTs) as biomaterials have immense potential for applications in regenerative medicine. The focus of regenerative medicine is on developing methods that can be applied to create functional tissues, to repair or replace tissues/organs lost due to trauma or diseases. In this respect, the structural and mechanical properties of CNTs make them applicable for use as composites for tissue engineering. CNTs can act as delivery vehicles for drugs and gene therapy and thus are suitable for therapeutics in regenerative medicine. The external carbon sheath of the CNTs can be functionalized for usein targeting, drug delivery, and as imaging agents. Further intrinsic physical properties of carbon nanotubes can be harnessed for therapeutics and imaging applications. The use of carbon nanotubes has been proved as contrasting agent in imaging. This work focuses on the latest developments in applications of carbon nanotubes for regenerative medicine. Carbon nonotubes have been under investigation in the past decade for an array of applications due to their unique and versatile properties. In the field of regenerative medicine, they have shown great promise to improve the properties of tissue engineering scaffolds and perform drug delivery and imaging of engineering tissues. The work is a review of the latest advances.

Coordination polymers (CPs), also known as metal-organic frameworks (MOFs), can be synthesized using organic bridging ligands and metal ions (or metal clusters). Structures with various architectures including one-, two- or three-dimensional polymeric networks can be formed depending on the bridging ligands, their donor atoms and coordination geometry of metal ions. In the structure of these inorganic-organic hybrid materials, there are different interactions such as coordination bonds, hydrogen bonds, π…π and CH…π interactions. These compounds are of industrial interests owing to their potential applications in the field of gas adsorption and storage, magnetism, drug delivery, heterogeneous catalysis and chemical sensors. Many published reports have made contributions to the preparation of porous coordination polymers with helical conformation using transition metals and chiral/achiral bridging ligands. Helical structural motifs have gained considerable importance because of their similarities in biological systems and useful applications. This paper presents an overview on selected examples of CPs with single-, double- and multi-stranded helical chains and discusses various factors that influence their constructions such as non-covalent interactions, ligand structure and counter ions. The connectivity between chirality of the building blocks and helicity of chains is also explained. Furthermore, the properties of helical CPs and some of their possible applications are explained in this article.

Polyhedral oligomeric silsesquioxane (POSS) - polymer composite materials have been extensively studied in recent years, as they possess nanoscopic structures and functional properties that are not typically seen in conventional hybrid materials. POSS nanoparticles are 1–3 nm in size, monodisperse and rigid. Incorporation of POSS nanoparticles into both thermoplastic and thermoset polymeric matrices by chemical cross-linking or physical blending methods provides excellent reinforcement. In this review, first, we introduce the various structures of polyhedral oligomeric silsesquioxane and then highlight studies on POSS- polymer nanocomposites with an emphasis on enhancements in mechanical, thermal stability and glass transition. The properties of POSS-containing polymer nanocomposites vigorously depend on the amount of POSS and the state of the POSS dispersion (which depends on the surface functional group of POSS). Incorporation of POSS through chemical cross-linking into polymer can influence its structureand improve mechanical properties by reinforcement.The incorporation of POSS nanoparticles into polymer through physical blending relies on favorable surface interactions between POSS and polymer. POSS having surface functional groups that have favorable surface interactions can disperse uniformly in the polymeric matrix. Uniform dispersion of POSS in polymeric matrices helps to improve physical properties of the nanocomposites. Because of the excellent properties, POSS containing polymer nanocomposites are found in diverse area such as tissue engineering and biomedicines.

Today biosensors are synthesized in analytical chemistry, which are used for clinical diagnostics, environmental analysis, product monitoring, detection and drug screening.Synthetic biomimetic receptors like molecular imprinting polymer (MIPs) have shown to be a potential alternative to biomolecules as recognition element for biosensing. MIPs are capable of recognizing and binding target molecules with similar specificity and selectivity. One of the main challenges in MIP sensor development is the miniaturization of MIP structures and their interfacing with transducers or with microchips. So, photostructuring is suggested as one of the most suitable methods for patterning MIPs at the micro and nano scale on the transducer surface. In this study, photopolymerization, photopatterning of MIPs and their biosensing applications are described from 1972 up to 2012. Also, some lithoghraphy methods are recommended for MIP photostructures. MIP fifilms patterning by the use of optical methods is fairly compared to other structuring approaches such as soft lithography or mechanical microspotting, which is a new method with ability to synthesize nanostructure with high quality, precision and resolution. The contact and proximity printing, projection photolithography, microstereo-lithography, and near-fifield assisted optical lithography were all successfully combined with MIPs, resulting in specifificity and selectivity high-resolution patterns.

Hydrogels are cross-linked three-dimensional networks that are capable of absorbing large amounts of water without being dissolved. Hydrogels can be prepared by crosslinking of either natural or synthetic polymers. Recently, interests in preparation and biomedical applications of the hydrogels prepare dusing natural polymers have grown intensively due to their excellent biocompatibility, biodegradability, biofunctionality and other desirable properties. Until now, several chemical and physical crosslinking methods have been studied to achieve hydrogels from natural polymers. Among chemical crosslinking methods, ionizing irradiation presents several advantages as it may occur without the need to add chemical initiators/crosslinking agent with subsequent separation of side reaction products, and the final products can be sterilized simultaneously during hydrogel formation. Usually, ionizing irradiation of a few natural polymers causes the chain scission reaction with consequent formation of lower molecular weight fragments. In recent years, several researchers have focused on the development of new methods to prepare hydrogels from natural polymers by ionizing irradiation. Some of these methods are irradiation at paste-like state, irradiation of polymers bearing carboxylic acid groups at acidic media, irradiation in presence of alkyne gas and chemical grafting with vinyl compounds.