Iranian Polymer Journal
Year:2010 | Volume:19 | Issue:6 (120)|Papers Count:7

Synthetic polymeric systems are considered vitally important in tissue regeneration. The reasons lay behind their specific characteristics such as porosity, hydrophilicity, degradation time, and mechanical properties which are variable to a large extent. The segmented polyurethanes have been used as biomaterials in medical field because they possess unique properties. In this study, the perforated polyurethane (PPU) scaffold as cartilage substitution was prepared and evaluated through biological assays. During the in vitro stage, the behaviour of both primary chondrocyte cells and L929 cell line in presence of PPU were examined. To evaluate in vivo performance of the scaffolds, PPUs were implanted in the scapula cartilage of twelve mixed-bred female sheep and comparisons were made with the implanted autologous cartilages as control. The results of in vitro studies showed some round and aggregated chondrocyte cells grown after 2 weeks of cell culture along with a considerable growth and attachment of L929 cells. In vivo studies showed that there is no significant difference between the restored PPUs and the autologous cartilage control. Our studies support the potential use of PPU as a proper substitute or rather as an assistant in cartilage repair. Obviously, further studies are needed to qualify the constituted cartilages regarding proteoglycan and collagen productions.

Some specific structure-properties relationship of a polyampholyte carboxymethyl chitosan-g-poly (acrylic acid-co-trimethylallyl ammonium chloride) (CMCTS-g- (PAA-co-PTMAAC)) hydrogel and the properties of water in the hydrogel were investigated by DSC measurement. The freezing water and non-freezing water contents of the hydrogel were determined quantitatively by examining their relationship with the structure and constitutive parameters of the polyampholyte hydrogel. The experimental results showed that higher swelling ratio of the hydrogel could decrease the content of the non-freezing water. It was found that the shape of the exothermic or endothermic curves and the peak temperature were strongly influenced by the heating/cooling rate or heating/cooling cycling. A hysteresis loop was evident during the process of heating/cooling cycling and the temperature interval between Tmax+ and Tmax- was increased by higher heating/cooling rate. The cross-linking degree of the hydrogel, molar ratio of two monomers and the neutralization degree of the anionic acrylic acid also have a great influence on the water content at various states. The results showed that the amount of non-freezing water in the hydrogel increased gradually as the cross-linking degree increased, but it was reduced while the molar ratio of TMAAC increased. By increasing the neutralization degree of acrylic acid, the amount of the non-freezing water was also increased.

The study of moisture absorption capacity of nylon 6 and 66 tyre cords through the storage time period before use for the manufacture of tyres is critical. Hitherto, the problem has either been generally overlooked or side-lined by more tangible aspects of manufacturing process. For this purpose, the moisture exposure and absorption level of high tenacity nylon 6 and 66 tyre cords, dipped in resorcinol formaldehyde latex (RFL) solution are investigated in this study. After dipping in RFL, the nylon cords were subsequently exposed to a standard atmosphere (20 ±2°C and 65±2% relative humidity) for a period of 24 h. The changes in mechanical characteristics and adhesion strength were reflected in lower adhesion strength of the nylon cords due to moisture absorption and higher elongation-at-break. These changes were attributed to the plasticizer effect of moisture on the molecular chains of nylon 6 and 66 tyre cords while concurrently degrading the isocyanate groups of RFL. Drying treatment at 105°C on conditioned nylon cords neither could stop the decomposition of isocyanate groups nor compensated the tensile strength of the cords by removing their moisture. In addition, elongation-at-break of dried cords increased considerably. Besides, the comparison of mechanical properties and adhesion strength of nylon 6 and 66 tyre cords showed that nylon 6 cords are more sensitive to moisture than nylon 66 cords due to difference in their molecular structure.

Biodegradable polymers have been extensively investigated as nano-carrier delivery systems in anti-cancer therapy. The anti-cancer drugs generally suffer from low aqueous solubility, short in vivo half-life and haphazard side effects. In this work, biodegradable poly(d,l-lactide-co-glycolide) nanoparticles (PLGA) containing tamoxifen citrate as a model anti-cancer drug were prepared using an o/w emulsification- solvent evaporation method. Dynamic light scattering (DLS), scanning electron microscopy (SEM) and analytical HPLC procedures were used to characterize the nanoparticles in terms of particle size, morphology and drug content. The characteristics of the nanoparticles including size, drug loading, and the efficiency of encapsulation were optimized by means of a full factorial experimental design over the influence of four different independent variables. Analyses of variance (ANOVA) were used to evaluate the optimized conditions for the preparation of nanoparticles. Based on the results, the most significant variables were homogenization speed and concentration of PLGA in organic phase with known total volume. Also, the interactions between the percentage of PVA and the amount of PLGA and organic phase volume were the most important cross-factor parameters. The optimum formulation condition with 192 nm mean size and 33 w/w% loading capacity was established by using 3 mg.mL-1 PLGA/dichloromethane in 7 w/v% PVA solution and 40% oil/water solvent ratio for emulsification at 24000 rpm homogenization rate. The results of this work facilitate the development of nano-carriers for tamoxifen delivery through optimization studies to control nanoparticles with specific properties and establish correlations between optimum production conditions and the required nano-carrier desired characteristics.

Amphiphilic polysiloxanes as polyelectrolytes have good water solubility and are considered as important conducting polymers. They have potential applications in biomaterials and composites. A series of novel amphiphilic polysiloxanes with pendant multi-cationic side chains were synthesized by ring-opening polymerization of cyclosiloxane and graft reactions. Such amphiphilic polysiloxanes impart good self-emulsifying property. A coupling reagent such as N,N-(g-dimethylamino-propyl)-g- aminopropyl dimethoxysilane was used in the polymerization reaction and benzyl chloride was used as a cationic reagent in the graft reaction. FTIR, 1H NMR, and 13C NMR were used to characterize the structures of functional groups of the prepared amphiphilic polysiloxanes. The viscosities and quantitative amount of cationic groups of novel polysiloxanes were evaluated. The amphiphilic polysiloxanes modified with multi-quaternary ammonium groups exhibit excellent surface activity. With increased cationic degree the surface energy of polymer solutions is dropped to lower value. The wettability of the polyester materials improves when they are treated with the novel amphiphilic polysiloxanes.

Tissue engineering scaffolds produced by electrospinning feature a structural similarity with the natural extracellular matrices. In this study, for the first time, poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) and chitosan/poly(vinyl alcohol) (PVA) were simultaneously electrospun from two different syringes and mixed on a rotating drum to prepare homogeneous nanofibrous composite scaffold. The concentration of the spinning solutions and the ratios of PCL/HA-chitosan/PVA were varied and adjusted to acquire nanofibres with narrow diameter distribution. It was found that the PCL/HA spun fibres became thick and non-uniform in diameter by decreasing the solution concentration and voltage, and yet the effect of flow rate was negligible. Meanwhile, the diameters of chitosan/PVA fibres decreased and became more uniform by decreasing the solution concentration and tip-to-target distance. Furthermore, HA nanocrystals reinforce the scaffold and increase its mechanical strength, though by changing its mechanical behaviour make it more brittle. SEM morphology of the PCL/HA electrospun nanocomposite revealed that HA nanocrystals were kept suspended in solution during the electrospinning process, and laid inside the PCL nanofibres. This feature may provide a mechanism for controlled release of HA nanoparticles in cell culture studies. It was assumed that the nanofibrous composite scaffold of electrospun PCL/HA-chitosan/PVA can potentially be used for the osteogenic differentiation of stem cells.

In recent years, the application of high-density multi-layer circuit boards in electronic products has put forward more set of requirements, especially on the thermal stability of the insulation ink, as the key material in the manufacturing of printed circuit board (PCB). Both o-cresol formaldehyde epoxy (OCFEP) and cyanate ester (CE) resins show outstanding thermal stability for application in PCB. In this work, cyanate prepolymer (PCE) and a PCE/OCFEP composite system were prepared. The curing behaviour of cyanate prepolymer/o-cresol formaldehyde epoxy resin system was studied with non-isothermal differential scanning calorimetry (DSC). Combined with the application requirement, the curing process of the system was determined as: 130°C/1h+140°C/1h+180°C/1h. The DSC results also revealed that the apparent activation energy of curing reaction was 83.22, 66.32 and 78.48 kJ/mol when PCE content was 80, 60 and 40 wt%, respectively. This indicates that there was an optimal proportion of PCE and OCFEP in the system. The curing kinetics followed the first order reaction. Theoretical analysis on the curing proccess of the system with 60 wt% PCE showed that the thermal stability increased with increased post-processing temperature. This study could provide some guides and basic data for the development of insulation ink for high-density multi-layer printed circuit boards.