Repetitive on-demand drug release from polymeric matrices containing a macroscopic spherical iron core

A system for multiple on-demand drug release has been prepared that can be activated with an alternating magnetic field as external trigger. The core/shell samples have been developed based on a macroscopic spherical iron core coated with a thermoresponsive polymer, poly(styrenestat-butyl methacrylate), containing ibuprofen as a model drug. During exposure of the samples to the magnetic field (ON state), the release rate of ibuprofen is significantly increased, up to 35 times the release rate without the magnetic field (OFF state). Using one sample or two samples in line with the magnetic field does not influence the ON/OFF ratio of the system, showing the possibility of using multiple samples to increase and tune the drug dose. Increasing the concentration of ibuprofen in the polymer layer is shown to increase the release rate in both the ON and OFF states. Increasing the size of the iron core and, consequently, decreasing the polymer thickness, was found to only increase the release rate during exposure resulting in higher ON/OFF ratios. The developed on demand drug delivery systems represents a promising development towards on demand drug delivery implants

Repetitive on-demand drug release by magnetic heating of iron oxide containing polymeric implants

Drug release from a polymeric matrix has been externally triggered using an alternating magnetic field in order to develop an on-demand drug delivery implant. Superparamagnetic iron oxide nanoparticles have been distributed in a poly(methyl methacrylate) core, coated with a thermoresponsive layer of poly(butyl methacrylate-stat-methyl methacrylate) containing ibuprofen as a model drug. The release rate of ibuprofen reversibly increased, up to 25-fold, upon exposure to the magnetic field and was found to increase with higher iron oxide loading. Finally, magnetically triggered on-demand drug release was demonstrated under physiologically relevant conditions, namely 37 degrees C in PBS buffer with high ibuprofen content in the implant and only 15 minutes triggering time

Temperature-induced morphology control in the polymer- foaming process

Supercritical carbon dioxide (scCO2) is a promising foaming agent for the production of polymeric foams, representing an environmentally friendly alternative for the foaming agents currently used. During the expansion phase of the scCO2-foaming process, temperature plays an essential role. This study focuses on relating the effects of temperature and pressure profiles on the foaming process and the resulting foam morphology. Therefore, several experiments have been performed in a high pressure reaction calorimeter (RC1e) that can be set to three different modes: isothermal, adiabatic, and isoperibolic. It has been observed that the foaming could be divided into four stages: nucleation, slow cell growth, fast cell growth, and shrinkage. The degree of shrinking that occurs is for a great deal dependent on the exposure to higher temperatures at the end of the foaming process. Since shrinkage does not occur in the adiabatic mode, this mode gives the best control on the foam morphology

Influence of the CO 2

Ultrasound-induced polymer scission is a nonrandom process which alters the molecular weight distribution of polymers. However, transient cavitation, and consequently polymer scission, is not possible in concentrated polymer solutions due to the high liquid viscosity. The addition of an antisolvent can be used to circumvent this problem because the antisolvent decreases the gyration radius of polymer chains, which induces a reduction in liquid viscosity. To determine the influence of carbon dioxide (CO2) as an antisolvent on the ultrasound-induced scission rate, ultrasonic scission experiments of poly(methyl methacrylate) have been performed in bulk methyl methacrylate (MMA) as well as in CO2-expanded MMA. Modeling the experimental time-dependent molecular weight distributions (MWD) has revealed the scission kinetics at different polymer concentrations and CO2 fractions. At low polymer concentrations, the scission rate is decreased upon an increased CO2 content. This is a result of the higher vapor pressure of CO2, which cushions the cavitation. However, at higher polymer concentrations, this effect is counteracted by the viscosity reduction induced by CO2. As a consequence, the scission rate in CO2-expanded MMA is higher as compared to bulk MMA for solutions with a high polymer concentration. The results show that ultrasound-induced scission in pressurized CO2 can alter and control the MWD of polymers even in concentrated polymer solutions, whereas ultrasound-induced scission in bulk solutions is limited to relatively low polymer concentrations

Silica-grafted diethylzinc and a silsesquioxane-based zinc alkyl complex as catalysts for the alternating oxirane-carbon dioxide copolymerization

A novel zinc silsesquioxane complex ([(c-C5H9)(7)Si7O11(OSiMePh2)](2)Zn4Me4 (1)) has been used as a model compound for silica-grafted zinc catalysts in the copolymerization of cyclohexene oxide and CO2. Complex 1 exists as a dimer in the solid state and is moderately active in the copolymerization, and polycyclohexene carbonates have been obtained with a carbonate content of 79-98%. Polymerizations with ZnEt2-treated silica particles resulted in polymer particles with (M) over bar (n) and (M) over bar (w) values and carbonate contents comparable to those of the polymers obtained with 1. It was further demonstrated that CO2 consumption can be followed online by monitoring the decrease of system pressure during the reaction. CO2 consumption has been interpreted in relation to both polycarbonate and cyclic carbonate formation. These measurements represent the intrinsic kinetics of this reaction, which appear to be directly related to CO2 pressure

CCDC 670959: Experimental Crystal Structure Determination

Related Article: R.Duchateau, W.J.van Meerendonk, S.Huijser, B.B.P.Staal, M.A.van Schilt, G.Gerritsen, A.Meetsma, C.E.Koning, M.F.Kemmere, J.T.F.Keurentjes|2007|Organometallics|26|4204|doi:10.1021/om700367x,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.