Influence of laser writing of polyimides on the alignment of liquid crystals

The effect of direct laser writing in polyimides on the alignment of org. liq. crystals was investigated. Laser writing was performed below the ablation threshold, which resulted in local melting of the polyimide. A surface relief structure was obtained as a result of the fast heating and cooling cycle during laser writing. No alignment of org. liq. crystals in the vicinity of the surface relief structure was obsd. as a direct result of the laser writing process. However, it appeared to be possible to wipe out the alignment originating from the rubbing process. This property proved to be useful to generate complex patterns in twisted nematic liq. crystal cells with locally uniaxial alignment. The contrast between the nonpatterned and patterned areas ranged between 40 and 50, which illustrates that the earlier described phenomena are potentially useful in, for instance, personalized security features. [on SciFinder (R)

Multi-directional liquid crystal alignment techniques

Presently photo-alignment is a well established technol. for monolithic liq. crystal orientation as well as the formation of multiple liq. crystal domains controlling directionality and pretilt. The paper will discuss some methodologies to enhance photo-alignment of liq. crystals with features such as multi-directional alignment and periodic alignment. Multi-directional alignment is achieved with traditional photosensitive alignment materials such as polymeric cinnamic acid esters or coumarin contg. polymers. These are partly aligned by local exposure with UV light. This dets. the directionality of lateral liq. crystal alignment. The unexposed area, still contg. the unreacted vinyl groups, is exposed to thiol surfactant in the presence of a thermal initiator. The alkyl tails of the thiol provide a homeotropic alignment to the liq. crystal. Micrometer sized periodic structures are achieved by holog. exposure of photo-alignment films with two interfering laser beams. Besides striped alignment profile, also complex squared alignment profiles are obtained by two orthogonal holog. exposures. [on SciFinder (R)

Multi-directional liquid crystal alignment techniques

Presently photo-alignment is a well established technol. for monolithic liq. crystal orientation as well as the formation of multiple liq. crystal domains controlling directionality and pretilt. The paper will discuss some methodologies to enhance photo-alignment of liq. crystals with features such as multi-directional alignment and periodic alignment. Multi-directional alignment is achieved with traditional photosensitive alignment materials such as polymeric cinnamic acid esters or coumarin contg. polymers. These are partly aligned by local exposure with UV light. This dets. the directionality of lateral liq. crystal alignment. The unexposed area, still contg. the unreacted vinyl groups, is exposed to thiol surfactant in the presence of a thermal initiator. The alkyl tails of the thiol provide a homeotropic alignment to the liq. crystal. Micrometer sized periodic structures are achieved by holog. exposure of photo-alignment films with two interfering laser beams. Besides striped alignment profile, also complex squared alignment profiles are obtained by two orthogonal holog. exposures. [on SciFinder (R)

A versatile salt-based method to immobilize glycosaminoglycans and create growth factor gradients

Contains fulltext : 204547.pdf (publisher's version ) (Open Access

A Validated Model of GAG Deposition, Cell Distribution, and Growth of Tissue Engineered Cartilage Cultured in a Rotating Bioreactor

In this work a new phenomenological model of growth of cartilage tissue cultured in a rotating bioreactor is developed. It represents an advancement of a previously derived model of deposition of glycosaminoglycan (GAG) in engineered cartilage by (i) introduction of physiological mechanisms of proteoglycan accumulation in the extracellular matrix (ECM) as well as by correlating (ii) local cell densities and (iii) tissue growth to the ECM composition. In particular, previously established predictions and correlations of local oxygen concentrations and GAG synthesis rates are extended to distinguish cell secreted proteoglycan monomers free to diffuse in cell surroundings and outside from the engineered construct, from large aggrecan molecules, which are constrained within the ECM and practically immovable. The model includes kinetics of aggregation, that is, transformation of mobile GAG species into immobile aggregates as well as maintenance of the normal ECM composition after the physiological GAG concentration is reached by incorporation of a product inhibition term. The model also includes mechanisms of the temporal evolution of cell density distributions and tissue growth under in vitro conditions. After a short initial proliferation phase the total cell number in the construct remains constant, but the local cell distribution is leveled out by GAG accumulation and repulsion due to negative molecular charges. Furthermore, strong repulsive forces result in expansion of the local tissue elements observed macroscopically as tissue growth (i.e., construct enlargement). The model is validated by comparison with experimental data of (i) GAG distribution and leakage, (ii) spatial-temporal distributions of cells, and (iii) tissue growth reported in previous works. Validation of the model predictive capability-against a selection of measured data that were not used to construct the model-suggests that the model successfully describes the interplay of several simultaneous processes carried out during in vitro cartilage tissue regeneration and indicates that this approach could also be attractive for application in other tissue engineering systems. Biotechnol. Bioeng. 2010;105: 842-853