دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و چهارم شماره 4 (پیاپی 174، مهر و آبان 1400)

Designing scaffolds with physical, mechanical, and biological properties like those of the extracellular matrix (ECM) of the target tissue, is the most critical challenge in tissue engineering. Ideally, proper cell proliferation can simultaneously occur with the degradation of the scaffold to finally restore and create the desired tissue within the scaffold. The use of biodegradable polymers or a combination of these polymers and ceramics, metals or carbon leads to the fabrication of scaffolds with the required properties. Thus far, different natural and synthetic polymers have been proposed for this purpose, of which aliphatic biodegradable and biocompatible polyesters as a result of their predictable and adjustable properties have been known as one of the best polymeric matrices in designing scaffolds used in tissue engineering. Due to the unique properties of these polymers, the number of research works performed on them for application in tissue engineering is increasing and therefore it is necessary to review the goals and challenges ahead. Accordingly, the present work has attempted to re-examine studies performed on widely used biodegradable aliphatic polyesters including poly(lactic acid)(PLA), poly(glycolic acid)(PGA), poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), and the family of microbial polyesters of the polyhydroxyalkanoates (PHA), especially poly(hydroxybutyrate) (PHB) as well as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer. This article specially focuses on the synthetic techniques and structural, physical, mechanical, and biological properties of these polymers to overcome the challenging task of designing ECM-like scaffolds by evaluating the various physical and chemical modification methods reported in recent research papers. The present study also reviews and discusses the application of these polyesters in soft and hard tissue engineering, such as bone, cartilage, ligament, tendon, muscle, spleen, cornea, and skin.

A thin film nanofiltration membrane was modified by poly(vinyl alcohol) (PVA) and chitosan-functionalized activated carbon nanoparticles. The effect of a surface layer formed on the structure and separation properties of prepared membranes was investigated.

Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), water content, porosity and mean pore size measurements, Na2SO4 and NaCl rejection, water flux as well as membrane flux recovery ratio for the study of antifouling ability were used for characterization of the membranes.

The FTIR results confirmed the formation of hydroxyl and amine groups on the surface of modified membranes. The SEM images also showed the formation of a uniform layer on the modified membranes. As shown in the SEM images, adding functionalized activated carbon nanoparticles into PVA leads to a heterogeneous and dense structure on the surface of modified membranes. Modification of pristine membrane by PVA and modified activated carbon nanoparticles up to 0.25% wt initially increased the water content, and subsequently with increase in nanoparticles ratio from 0.25 to 1.0% (wt), the water content decreased. The obtained results showed a larger mean pore size for all modified membranes compared to pristine membrane. Moreover, all modified membranes showed a higher flux in comparison with virgin membrane. In addition, salt rejection revealed that the surface modification of nanofiltration membrane has a positive effect in preventing smaller rejection amount despite the increase in the amount of flux. Sodium sulfate salt rejection was also measured more than sodium chloride salt rejection. Flux recovery ratio was also measured more than 92% for the modified membranes whereas it was more than 66% for pristine membrane that confirms the antifouling ability for the modified membranes.

Lignin-based adsorbents are one of the common materials for removal of heavy metal ions in wastewater treatment and the adsorption of metals extracted in mines. Therefore, it seems that industrial lignin and its carboxymethylated derivative are able to adsorb zinc and copper cations from aqueous solutions under different operating conditions.

Firs, industrial lignin was carboxymethylated by reacting with sodium chloroacetate. After carboxymethylation of lignin, the characterization tests including FTIR spectroscopy, 1H NMR spectroscopy, acid-base titration, pHpzc (pH point of zero charge) and zeta potential tests were performed. Concentration of ions in aqueous solutions was determined by atomic adsorption technique.

The results of structural characterization tests showed that the reaction of lignin with sodium chloroacetate removed the aromatic hydroxyl groups of lignin, while the concentration of carboxyl groups increased. Thus, it was found that lignin was carboxymethylated successfully. The results of zinc (II) and copper (II) ions adsorption showed that the maximum adsorption of copper ion in comparison with zinc ion occurs in the presence of the modified industrial lignin adsorbent at a pH close to 4. The kinetic study results showed that the adsorption of both ions follows a pseudo second-order model. In the isotherm studies, the Sips model showed the best performance for both the industrial and modified lignin samples. Maximum adsorption capacities for the zinc and copper ions by carboxymethylated lignin were observed to be 0.25 and 0.37 mmol/g, respectively, showing a significant improvement in comparison with unmodified kraft lignin. However, selectivity of the copper ion decreased in contrast. This improvement could be mainly attributed to the significant increase in active sites on carboxymethylated lignin.

Nowadays, lightening of polymer composites for specific applications and engineering purposes, especially electromagnetic wave absorber materials, has attracted research studies. In this work, polypropylene nanocomposite and hybrid foams incorporated with carbon nanotubes and glass fibers were produced through solid-state microcellular foaming using supercritical carbon dioxide.

First, the microstructure of nanocomposites, hybrids, and produced foams were examined by scanning electron microscopy. The electrical properties and electromagnetic interference shielding performance of the solid and foamed nanocomposites were investigated using a four-point probe method and a vector analyzer, respectively. The effect of glass fiber and CNT incorporation on tensile, compressive, and impact mechanical properties was also investigated.

Nanotubes were finely dispersed in the polypropylene matrix through melt compounding. By incorporation of CNTs, the average cell size reduced (from 49 to 22.5 μm), and cell density increased. Also, the SEM micrographs of the hybrid foams revealed that, in general, cell size increased by incorporating fiber due to nearby heterogeneous nucleation, and the size of cells that were not adjacent to the fiber decreased. As a result, a bimodal microstructure with two different cell sizes was obtained. With the incorporation of CNTs, electrical conductivity increased from ~10-16 to ~10-4 and ~10-5 for unfoamed and foamed PP/CNT3 samples, respectively, and EMI shielding effectiveness increased to 11 dB and 9.5 dB for unfoamed and foamed PP/CNT3 samples, respectively. The mechanical test results showed that the addition of nanoparticles help to improve mechanical properties, including tensile, compression and impact. In solid samples, the addition of glass fiber improves the modulus and tensile strength, but due to poor interaction with polypropylene, it reduces the tensile properties of the foams. The results of both compression and impact resistance tests of foams showed that these properties are enhanced with the addition of fibers and nanoparticles.

Nanofiltration (NF) is a very important technique in separation and purification of aqueous and non-aqueous mixtures in several applications, such as the retention of dyes from water, which is the largest application in this field. Nonetheless, it is still a key issue to enhance the rejection performance and improve the flux, the key factors for the performance of the final membrane. Accordingly, MIL-53(Al) nanoparticles were utilized in this research work because of their small pore sizes, significant hydrophilicity and outstanding water stability.

In this study, the synthesis of the MIL-53(Al) nanoparticles was conducted. Then, the preparation of polyethersulfone (PES)-MIL-53(Al) mixed matrix membranes was done through the VIPS-NIPS method, which is the vapor-induced phase inversion (VIPS) method coupled with non-solvent-induced phase inversion (NIPS) technique, in which the co-solvent of 1,4-dioxane was employed. Finally, the prepared nanoparticles and membranes were characterized using several techniques including attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffractometry (XRD), field-emission scanning electron microscopy (FE-SEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), and contact angle analyses.

Different membrane compositions with various MIL-53(Al) contents were prepared so that a membrane with superior performance in dye rejection application and high flux can be achieved. The performance of the fabricated membranes was investigated for rejection of various dyes in aqueous solutions including Reactive Red (RR), Direct Yellow (DY), Methyl Green (MG), and Crystal Violet (CV), based on which a great separation performance (dye rejections of 99.8, 99.5, 99.2, 98.8 and 97.1 for RR, MG, DY, CV and MB, respectively) and an excellent water flux (4.8 L/m2.h.bar) were provided by the membrane containing 0.06 wt% MIL-53(Al)..

The porosity and pore size of polystyrene (PS) porous films prepared by immersion precipitation can be adjusted by varying the composition of the ingredients. The effect of composition variations on the characteristics of porous films can be elucidated by thermodynamic parameters.

A PS/chloroform solution with additives (polystyrene-block-poly(acrylic acid), polyethylene glycol (PEG), and glycerol) and/or non-solvent (2-propanol) was prepared. Then, the solution was cast and immersed in a 2-propanol/chloroform coagulation bath. The resultant porous film was imaged by scanning electron microscopy (SEM) and investigated by image analysis. The phase diagram of system was plotted through experimental measurements (cloud point) and theoretical method. The thermodynamic properties of the solution and coagulation bath were evaluated using non-solvent osmotic pressure difference (ΔΠNS) and solvent osmotic pressure difference (ΔΠNS) between the solution and coagulation bath. Moreover, the approaching ratio of solution (ARSolution) and bath (ARBath) to the binodal curve was also obtained.

The porosity and pore size of the films increased with decreasing the polymer concentration and adding the additives to the casting solution. By decreasing polymer concentration from 17% wt to 12% wt, the film structure changed from dense to porous (35% porosity and average pore diameter 2.8 μm). Addition of small amounts of PEG400 and glycerol to the solution (20% by weight relative to PS) significantly increased the porosity of the films from 35% to 54% and 66%, respectively. The porosity and pore size decreased first and then increased with adding non-solvent to the solution. Adding solvent to the bath helps increase porosity. Addition of non-solvent to the solution and addition of solvent to the bath were accompanied by decreasing solvent quality (ARSolution increase) and decreasing precipitation power of coagulant (ARBath increase) for the polymer, respectively. The increase in porosity and pore size was mainly associated with increasing ΔΠNS and decreasing ΔΠS.