Novel photopolymerizable biodegradable triblock polymers for tissue engineering scaffolds: synthesis and characterization

For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3.     

Effect of exposure dose on the replication fidelity and profile of very high aspect ratio microchannels in SU-8

We are interested in using SU-8 dense gratings with very high aspect ratio microchannels as the master mold for fabrication of child molds needed for replication. For such applications, the sidewall taper angle and mask replication fidelity of SU-8 are very important. Increasing the exposure time was experimentally observed to decrease the width of the microchannel and the sidewall angle of SU-8 bars. A new diffraction-refraction-reflection model was also developed. The calculated microchannel width and sidewall angle at high exposure dose agreed well with the experimentally observed values indicating that reflection at the silicon substrate was significant. The larger than calculated actual microchannel width for low exposure dose was shown to be due to leaching of unreacted SU-8 in the developer. Dense gratings of high aspect ratio SU-8 bars separated by high aspect ratio (19.1) microchannels were also demonstrated.     

Effects of silicone acrylate on morphology, kinetics, and surface composition of photopolymerized acrylate mixtures

Films (ca. 150 microm thick) of twelve acrylate mixtures, which contained various proportions of hydrocarbon acrylates [mainly oligo(ethylene glycol) diacrylate, (OEGDA)] and small amounts of a silicone hexaacrylate (in proportion of 5% or less), were cured on a nickel substrate, and X-ray photoelectron spectroscopy analysis of the nickel-side surface compositions showed that for formulations with and without the silicone hexaacrylate, this surface was enriched with OEGDA and saturated (up to 50%) with the silicone hexaacrylate, respectively. The silicone hexaacrylate phase-separated and formed micelles which migrated to the resin-nickel interface. Silicone hexaacrylate, inherently less reactive, also significantly slowed the photopolymerization of the mixtures. The sequential homopolymerization of OEGDA and silicone hexaacrylate in a formulation was elicited using real-time Fourier transform infrared spectroscopy. The design-of-experiment approach was used to quantify the influence of the components on gelation time and the nickel-side surface composition as well as provide the statistical models to predict these two properties for new compositions.     

The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution

O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.     

Bottom-contact poly(3,3'-didodecylquaterthiophene) thin-film transistors with gold source-drain electrodes modified by alkanethiol monolayers

A series of alkanethiol monolayers (CH 3(CH 2) n-1 SH, n = 4, 6, 8, 10, 12, 14, 16) were used to modify gold source-drain electrode surfaces for bottom-contact poly(3,3'-didodecylquaterthiophene) (PQT-12) thin-film transistors (TFTs). The device mobilities of TFTs were significantly increased from approximately 0.015 cm (2) V (-1) s (-1) for bare electrode TFTs to a maximum of approximately 0.1 cm (2) V (-1) s (-1) for the n = 8 monolayer devices. The mobilities of devices with alkanethiol-modified Au electrodes varied parabolically with alkyl length with values of 0.06, 0.1, and 0.04 cm (2) V (-1) s (-1) at n = 4, 8, and 16, respectively. Atomic force microscopy investigations reveal that alkanethiol electrode surface modifications promote polycrystalline PQT-12 morphologies at electrode/PQT-12 contacts, which probably increase the density of states of the PQT-12 semiconductor at the interfaces. The contact resistance of TFTs is strongly modulated by the surface modification and strongly varies with the alkanethiol chain length. The surface modifications of electrodes appear to significantly improve the charge injection, with consequent substantial improvement in device performance.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

Adhesion contact dynamics of fibroblasts on biomacromolecular surfaces

Biomacromolecules like gelatin and chitosan have emerged as highly versatile biomimetic coatings for applications in tissue engineering. The elucidation of the interfacial kinetics of cell adhesion on biomacromolecular surfaces will pave the way for the rational design of chitosan/gelatin-based systems for cell regeneration. Biomacromolecular ultra-thin films, chemically immobilized on fused silica are ideal experimental models for determining the effect of surface properties on the biophysical cascades following cell seeding. In this study, confocal reflectance interference contrast microscopy (C-RICM), in conjunction with phase contrast microscopy and fluorescence confocal microscopy, was applied to detect the adhesion contact dynamics of 3T3 fibroblasts on chitosan and gelatin ultrathin films. X-ray photoelectron spectroscopy (XPS) confirmed the immobilization of chitosan or gelatin on the silanized glass surface. Both the initial cell deformation rate and the change of two-dimensional spread area of the 3T3 fibroblasts are higher on gelatin-modified surfaces than on chitosan surfaces. The steady-state adhesion energy of 3T3 fibroblasts on gelatin film is three times higher than that on chitosan film. Immuno-staining of actin further demonstrates the different organization of cytoskeleton, likely induced by the change in cell signaling mechanism on the two biomacromolecular surfaces. The better attachment of 3T3 fibroblast to gelatin is postulated to be caused by the presence of adhesive domains on gelatin.     

Models for capacitated lot-sizing problem with backlogging,setup carryover and crossover

Setup operations are significant in some production environments. It is mandatory that their production plans consider some features, as setup state conservation across periods through setup carryover and crossover. The modelling of setup crossover allows more flexible decisions and is essential for problems with long setup times. This paper proposes two models for the capacitated lot-sizing problem with backlogging and setup carryover and crossover. The first is in line with other models from the literature, whereas the second considers a disaggregated setup variable, which tracks the starting and completion times of the setup operation. This innovative approach permits a more compact formulation. Computational results show that the proposed models have outperformed other state-of-the-art formulation.