Iranian polymer journal
Volume:18 Issue: 4, 2009

In this paper some of the latest studies and research works conducted on siliconebaseddrug delivery systems (DDS) are reviewed and some of more specific and important novel drug delivery devices are discussed in detail. An overview on rapidly growing developments on silicone-based drug delivery systems is provided by presenting the necessary fundamental knowledge on silicone polymers and a literature survey including an introductory account on some of the drugs that are diffused through silicone polymers. The results based on vast investigations over a period of a decade indicate that intravaginal and transdermal routes of administration of the drugs using silicone-based DDS are more developed. It is also found that silicone polymers are suitable candidates for the release of hormonal steroids for controlling the estrous cycle. Finally, some commercially available silicone-based DDS are described.

In this study, nerve guidance material was designed and fabricated from crystalline poly(L-lactic acid) (PLLA) with microtubules orientation structure by using thermalinduced phase separation (TIPS) technique and dioxane as solvent. Factors such as polymer concentration and temperature-gradient of the system which affect solvent crystallization, microtubules orientation structure, and tubs diameters of the scaffold have been studied. Thus, the tubular morphology, diameter and orientation of the microtubules could be controlled by adjusting the concentration of the polymer solution and temperature-gradient of the system. In vitro P19 mouse embryonic carcinoma cellline was used as a suitable model system to analyze neuronal differentiation. Tubularmorphology and differentiation of P19 cells were characterized using scanning electronmicroscopy (SEM). Results showed that these conditions provide tubular morphologywith varying tubs diameters. By evaluating P19 cell differentiation into neuron cells thatwas confirmed by immunofluorescence staining technique it was shown that most ofthe cells attached and differentiated on the surface of the scaffold, through which axonspenetrated randomly.

Composite microspheres were prepared by suspension polymerization of karaya gum and chitosan in oil-water emulsion using glutaraldehyde as a cross-linker. The composite microspheres morphology was investigated by scanning electron microscopy. It was found that the products were composed of a large quantity of microparticles with average diameters of 250-350 μm and a few microspheres with diameters of several micrometers. The composite microspheres are spherical particles with asperous surfaces. The thermal behaviour of composite microspheres was studied using both methods of thermogravimetric analysis and differential thermal analysis, further confirming the cross-linking reaction. The results suggest that the composite microspheres show good heat resistance after cross-linking reaction. In order to obtain an insight into the karaya gum/chitosan interactions, the composite microspheres were characterized by Fourier transform infrared spectroscopy (FTIR) to confirm the formation of Schiff’s. At the same time, the infrared spectrum indicates the presence of special functional groups on the surface of the microspheres, which involve ion-carboxyl, aldehyde, amino, and hydroxyl groups. The swelling kinetics of the composite microspheres at different pH values has been investigated. The composite microspheres swell at lower pH (<6) as well as higher pH range (pH>9), and the deswelling occurs in the pH range from 6 to 9.

Three groups of rectangular beams, comprising of sixteen specimens with variousamounts of torsional steel reinforcement were tested under pure torsion.Evaluating the effects of various steel torsional reinforcement ratios on the torsionalbehaviour of the strengthened beams was the objective of this investigation. Carbon fibre reinforced polymer (CFRP) sheet wrappings consisted of different configurations including anchored U-wrapping and full and strip wrappings. The total steel ratios, including longitudinal and transverse reinforcements considered in this study were 1.56%, 2.13%, and 3.03%, respectively. This study indicates that the CFRP contributionsto the torsional strength of the strengthened beams, having identical volumetricratio of CFRP reinforcement are quite dependent on the total amount of torsionalreinforcements. The above mentioned CFRP contributions will increase as the steel torsional reinforcement is increased. Experimental results show that increasing the steelreinforcement by 37% and 94%, increases the CFRP contribution to torsional strengthby up to 54% and 91% for strengthened beams with one CFRP ply; and by up to 60%and 111% for strengthened beams with two CFRP plies, respectively. In this experimentalwork, the effect of the number of CFRP plies is also investigated. It is found that theincrease in CFRP contribution to torsional strength concerning the beams strengthenedby one ply and two plies of CFRP sheets is close for various steel reinforcement ratios,when compared to increasing the total amount of steel reinforcement.

The non-isothermal crystallization kinetics of pure polypropylene (PP) and AB3 hyper-branched polymer (HBP)/PP blends (with 5% HBP content) were investigated with various cooling rates by differential scanning calorimetry (DSC) method. The Avrami analysis modified by Mandelkern and a method combined with Avrami and Ozawa equations were employed to describe the non-isothermal crystallization kinetics of the samples. The conclusion showed that at the same cooling rate, hyper-branched polymer could accelerate crystallization effectively. Furthermore, in the blends, the crystallization rate decreased when the higher molecular weight of HBP was added. An increase in the Avrami exponent showed that the addition of HBP influenced the mechanism of nucleation and the growth of PP crystallites. The possible reason and explanation could be attributed to the fractal structure of hyper-branched polymer which has an influence on the diffusion mode of crystallizable segments towards the growing nuclei. The polarized micrographs showed that the number of effective nuclei increased obviously in the HBP/PP blends where, HBP acts as a heterogeneous nucleation agent during the crystallization of the blends. In addition, the activation energy of crystallization was also obtained according to the Kissinger method and the results showed that the crystallization activation energy decreased remarkably in HBP/PP blends.

Aseries of novel interpenetrating polymer network (IPN) hydrogels based on soy protein (SP) and poly(acrylic acid) (PAA) were prepared with glutaraldehyde and N,N''-methylenebisacrylamide (BIS) as the cross-linking agents. The structure and properties of the IPN hydrogels were characterized by FTIR, SEM, and DSC. The effects of pH and SP and BIS contents on the behaviour and release mechanism of the model drug bovine serum albumin (BSA) were also investigated in detail. The FTIR data indicated that the absorption of BSA into the IPN hydrogels is purely physical process. The SEM showed that changing the content of SP or BIS can influence the pore size and pore wall thickness of the hydrogels. The DSC data signify that all the hydrogels had good compatibility and miscibility, as well. It was also found that the release profiles of BSA strongly are dependent on the value of pH. The release percentage of BSA decreased with increasing the contents of SP or BIS. The BSA release profile followed Fickian diffusion pattern at pH below the pKa of PAA and the non- Fickian diffusion at pH above the pKa of PAA. The results showed that the IPN hydrogels are suitable candidates for colon drug delivery.