Photon correlation spectroscopy and pulsed-field-gradient nuclear magnetic resonance have been utilized in order to investigate the characteristic features of the recently established (both experimentally and theoretically) diffusive "polydispersity" relaxation process for concentration fluctuations in homogeneous diblock copolymer melts and solutions. This is accomplished using semidilute solutions of a symmetric mixture of two diblock copolymers with similar molecular weights and almost mirror compositions in a common good solvent. Mixing of the two asymmetric diblocks leads to a system with almost symmetric composition and with narrow molecular weight distribution, but with large effective composition polydispersity. Above the order to disorder transition (ODT), the theoretical expressions for the amplitude and the relaxation rate of the polydispersity mode can quantitatively describe the observed diffusive relaxation. Similarly to the situation in homopolymer blends, the thermodynamic forces can significantly retard the diffusion coefficient and lead to an increase in the dynamic intensity with increasing copolymer concentration. The intervention of the ODT alters this concentration dependence at copolymer concentrations #J near but below #JODT.

Two cylinder-forming polystyrene-block-polybutadiene block copolymers of type A-B with antisymmetric composition (polymer PI with A : B = 3 : 1 (w/w) and polymer P2 with A : B = 1 : 3 (w/w)) and their binary mixture were studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) in order to determine the microphase structure. The cylindrical microstructure is confirmed for both copolymers, whereas, in the mixture, both techniques have unambiguously shown that a regular lamellar structure is obtained at the polymer-polymer composition P1 : P2 = 1 : 1 (ratio of the numbers of chains). Qualitatively, the same results are obtained for corresponding systems simulated by the cooperative motion algorithm (CMA). Direct observations of the structure as well as the cooperative structure factors determined in the strong segregation limit for the simulated systems indicated lamellar structures in the blend of composition P1 :P2 = 1 : 1, in contrast to the microfibrillar morphology of the copolymers. The simulation additionally indicated a polymer-polymer microseparation. The experimental and simulation results are compared with theoretical predictions based on the self consistent field theory.

The kinetics of the microphase separation transition in a diblock copolymer of polystyrene/ polyisoprene was studied with time-resolved small-angle X-ray scattering. Using synchrotron radiation it was possible to determine the structure factor in time intervals of 10 s. The relaxation of the structure factor after temperature jumps within the disordered regime was found to be wave vector dependent in accordance with Cahn-Hilliard theory. For quenches from the disordered into the ordered state an additional, slow process was found which consists mainly of a decrease in the width of the first-order reflection. It is interpreted as the perfectioning of the lamellar order. Whereas the corresponding relaxation time had been found to decrease strongly with supercooling for shallow quenches, it is found to increase again for deeper quenches.

Mesenchymal stem cells (MSCs) are widely used in cell therapy due to their convenience, multiline differentiation potential, reproducible protocols, and biological properties. The potential of MSCs to impregnate magnetic microcapsules and their possible influence on cell function and ability to response to magnetic field have been explored. Interestingly, the cells suspended in media show much higher ability in internalization of microcapsules, then MSCs adhere into the surface. There is no significant effect of microcapsules on cell toxicity compared with other cell line-capsule internalization reported in literature. Due to internalization of magnetic capsules by the cells, such cell engineering platform is responsive to external magnetic field, which allows to manipulate MSC migration. Magnetically sorted MSCs are capable to differentiation as confirmed by their conversion to adipogenic and osteogenic cells using standard protocols. There is a minor effect of capsule internalization on cell adhesion, though MSCs are still able to form spheroid made by dozen of thousand MSCs. This work demonstrates the potential of use of microcapsule impregnated MSCs to carry internalized micron-sized vesicles and being navigated with external magnetic signaling.