Multicore-shell PNIPAm-co-PEGMa microcapsules for cell encapsulation

The overall goal of this study was to fabricate multifunctional core-shell microcapsules with biological cells encapsulated within the polymer shell. Biocompatible temperature responsive microcapsules comprised of silicone oil droplets (multicores) and yeast cells embedded in a polymer matrix (shell) were prepared using a novel microarray approach. The cross-linked polymer shell and silicone multicores were formed in situ via photopolymerization of either poly(N-isopropylacryamide)(PNIPAm) or PNIPAm, copolymerized with poly(ethylene glycol monomethyl ether monomethacrylate) (PEGMa) within the droplets of an oil-in-water-in-oil double emulsion. An optimized recipe yielded a multicore-shell morphology, which was characterized by optical and laser scanning confocal microscopy (LSCM) and theoretically confirmed by spreading coefficient calculations. Spreading coefficients were calculated from interfacial tension and contact angle measurements as well as from the determination of the Hamaker constants and the pair potential energies. The effects of the presence of PEGMa, its molecular weight (M(n) 300 and 1100 g/mol), and concentration (10, 20, and 30 wt %) were also investigated, and they were found not to significantly alter the morphology of the microcapsules. They were found, however, to significantly improve the viability of the yeast cells, which were encapsulated within PNIPAm-based microcapsules by direct incorporation into the monomer solutions, prior to polymerization. Under LSCM, the fluorescence staining for live and dead cells showed a 30% viability of yeast cells entrapped within the PNIPAm matrix after 45 min of photopolymerization, but an improvement to 60% viability in the presence of PEGMa. The thermoresponsive behavior of the microcapsules allows the silicone oil cores to be irreversibly ejected, and so the role of the silicone oil is 2-fold. It facilitates multifunctionality in the microcapsule by first being used as a template to obtain the desired core-shell morphology, and second it can act as an encapsulant for oil-soluble drugs. It was shown that the encapsulated oil droplets were expelled above the volume phase transition temperature of the polymer, while the collapsed microcapsule remained intact. When these microcapsules were reswollen with an aqueous solution, it was observed that the hollow compartments refilled. In principle, these hollow-core microcapsules could then be filled with water-soluble drugs that could be delivered in vivo in response to temperature.     

Effect of Fe-modified α-Al2O3 on the properties of Pd/α-Al2O3 catalysts in selective acetylene hydrogenation

The use of nanocrystalline Fe-modified α-Al₂O₃ prepared by sol–gel and solvothermal method as supports for Pd catalysts resulted in an improved catalyst performance in selective acetylene hydrogenation. Moreover, the amount of coke deposits was reduced due to lower acidity of the Fe-modified α-Al₂O₃ supports.     

Effects of Compositions and Processing Variables on Barrier and Mechanical Properties of Liquid Crystalline Polymer/Polyethylene Blend Films

Cast films of liquid crystalline polymer (LCP) and low density polyethylene (LDPE) blends have been produced and investigated. Effects of LCP content and processing parameters, i.e., processing temperature profile, screw speed, and post-die drawing, on morphology and O₂ barrier property are presented. Increasing processing temperature and LCP content tend to enhance aspect ratios (L/D) of the LCP dispersed phase and at the same time influencing LCP structure. These effects are clearly observed when LCP content is increased from 10 % to 30 % by wt. At high temperature profiles, LCP morphologies are presented in a more or less ‘ribbon’ or ‘tape’ like structure together with a common LCP fibrillar structure. Films of 10% and 30% LCP produced at two optimum temperature profiles show a noticeable proportion of LCP tape-like structure and interestingly high barrier properties of ∼1.6 and 5.5 times that of the neat LDPE films. High barrier characteristics of such LCP/PE blend films are indicated by low oxygen transmission rate values. Apart from processing temperature effect, increases of screw speed result in films having smaller aspect ratios for both LCP fibers and ribbons; films also exhibit poorer barrier and mechanical properties. However, post-die drawing clearly demonstrates a positive effect in improving aspect ratios of the LCP domains and the resulting films' moduli. Effects of post-die drawing on enhancing films' barrier properties become more pronounced at high LCP content. By comparing with the neat LDPE film (30 μm thick) having modulus of ∼180 MPa and OTR of ∼11000 cc/m².day, the developed LCP/PE films containing 30 wt% LCP show remarkably high modulus values of ∼1100 MPa with low OTR of ∼2000 cc/m².day.