Endothelialisation and cell retention on gelation-chitosan coated electrospun polyurethane, poly (lactide-co-glycolide) and collagen-coated pericardium

Arterial bypass and heart valve replacements are two of the most common surgical treatments in cardiovascular surgery today. Currently, artificial materials are used as substitute for these cardiac tissues. However, these foreign materials do not have the ability to grow, repair or remodel and are thrombogenic, leading to stenosis. With the aid of tissue engineering, it is possible to develop functional identical copies of healthy heart valves and arteries, which are biocompatible. Although much effort has been made into this area, there are still inconsistencies with respect to
endothelialisation and cell retention on synthetic biological grafts. These variations may be attributed to differences in factors such as cell seeding density, incubation periods and effects of shear stress. In this study, we have compared the endothelialisation and cell retention between gelain chitosan-coated electrospun polyurethane (PU), poly (lactide co-glycolide) (PGA/PLA) and collagen-coated pericardium. Endothelial cells adhered to all of the materials as early as 1–day post seeding. After 7-day of seeding, the coverage on PU was almost 45% and that on PGA/PLA was about 25% and the least was on collagen-coated pericardium of approximately 15%. It was observed that the PU showed superior cell coverage and cell retention in comparison to the PGA/PLA and collagen-coated pericardium.

Covalent/crystallite cross-linked co-network hydrogels : an efficient and simple strategy for mechanically strong and tough hydrogels

Covalent/crystallite cross-linked co-network hydrogels have been prepared using epoxy and PVA through a cyclic freezing-thawing process. The PVA/epoxy hydrogels show enhanced mechanical strength and toughness. PVA/epoxy hydrogels with 4 wt% epoxy loading display maximum tensile strength and toughness of 1.1 MPa and 2838 kJ/m3 respectively. The fracture toughness of PVA/epoxy hydrogels ranges from 160 to 450 J/m2. Radius of gyration and fractal information of the hydrogels were obtained by fitting the SAXS data to the Guinier and power law models. The enhanced mechanical properties are attributed to the increase in covalent bonding and decrease in crystallite distribution with an increase in epoxy content. However a larger hysteresis is shown for PVA/epoxy hydrogels due to irreversible destruction of covalent bonds between epoxy and PVA.

Synthesis of ethyl oleate employing synthetic hydrogel-immobilized lipase of Bacillus coagulans MTCC-6375

Ten polymeric hydrogels were chemically synthesized by varying the concentrations of copolymer (DMA) and cross-linker (MBAm) molecules. An alkaline lipase of Bacillus coagulans MTCC-6375 was immobilized onto a poly (MAc-co-DMA-cl-MBAm)-hydrogel support at pH 8.5 and temperature 55ºC in 16 h. The bound lipase possessed 7.6 U.g⁻¹ (matrix) lipase activity with a specific activity of 18 U.mg⁻¹ protein. Hydrogel bound-lipase catalyzed esterification of oleic acid and ethanol to synthesize ethyl oleate in n-nonane. Various kinetic parameters were optimized to produce ethyl oleate using immobilized lipase. The optimal parameters were bound enzyme/substrate (E/S) ratio 0.62 mg/mM, ethanol/oleic acid 100 mM:75 mM or 100 mM:100 mM, incubation time 18 h and reaction temperature 55ºC that resulted in approximately 53% conversion of reactants into ethyl oleate in n-nonane. However, addition of a molecular sieve to the reaction mixture promoted the conversion to 58% in 18 h in n-nonane, which was equivalent to 55 mM of ethyl oleate produced.

Polymer-in-ionic-liquid electrolytes

In order to achieve high conductivity in a polymer electrolyte, polymer-in-ionic-liquid electrolytes have been explored. It is found in this study that poly[vinylpyrrolidone-co-(vinyl acetate)] (P(VP-c-VA)) in 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) amide (EtMeIm+Tf2N−) and poly(N,N-dimethyl acrylamide) (PDMAA) in trimethyl butyl ammonium bis(trifluoromethane sulfonyl) amide (N1114+Tf2N−) produce ion-conducting liquids and gels. The P(VP-c-VA)/ EtMeIm+Tf2N− mixture has a conductivity around 10−3 S · cm−1 at 22 °C, for copolymer concentrations up to 30 wt.-%. Thermal analysis shows that the Tg of the P(VP-c-VA)/ EtMeIm+Tf2N− system is well described by the Fox equation as a function of polymer content. Poly(methyl methacrylate) (PMMA)/ EtMeIm+Tf2N− gel electrolytes were prepared by in-situ polymerisation of the monomer in the ionic liquid. In the presence of 0.5–2.0 wt.-% of a crosslinking agent, these PMMA-based electrolytes displayed elastomeric properties and high conductivity (ca. 10−3 S · cm−1) at room temperature.

Formulation optimization for high drug loading colonic drug delivery carrier

High drug loading (DL) carrier is an effective way to cure the cancerous cells. High drug loading is also one of the key issues in the drug delivery research, especially the colonic drug delivery system by oral administration. The times of drug intake could be remarkably reduced if high drug loading carriers are administered. At the same time, the related formulation materials could be effectively utilized. One major obstacle with the preparation of this system is the difficulty to encapsulate the hydrophilic drug into hydrophobic encapsulation polymer. A design of high drug loading delivery system with biodegradable, biocompatible materials and optimization of the fabrication process is a potential solution to solve the problem. So in this research, 5-Fluorouracil (5-FU) loaded Poly (lactide-co-glycolide) (PLGA) nanoparticles were prepared by double emulsion and solvent evaporation method. Several fabrication parameters including theoretical drug loading, volume ratio of outer water phase to the first emulsion, pH value of outer aqueous phase and emulsifier PVA concentration were optimized to get a high drug loading nanoparticles. The result shows that with the increase of theoretical drug loading, the actual drug loading increased gradually. When adjusted the pH value of outer aqueous phase to the isoelectric point (8.02) of 5-Fluorouracil, the drug loading exhibited a higher one compared to other pH value solution. Relative higher volume ratio of outer water phase to the first emulsion was also beneficial for the enhancement of drug loading. But the nanoparticles size increased simultaneously due to the lower shearing force. When increased the PVA concentration, the drug loading showed an increase first and following a drop.

Shear-enhanced solution precipitation : a simple process to produce short polymeric nanofibers

The growing interest in polymeric nanofibers has been increasing the push for the development of simple and efficient nanofiber-preparation techniques. We herein describe how a conventional solution process is readapted to suit the needs for fast and efficient production of short polymeric nanofibers. Poly(ethylene-co-acrylic acid) (PEAA), a semi-crystalline polymer, was used as model. When a PEAA solution was injected into an alcoholic non-solvent while simultaneously applying high shear to the non-solvent system, PEAA nanofibers were obtained with average diameter as thin as 113 nm and length as short as 4.5 _m. The fiber diameter and length were also adjustable by varying the operating parameters. This one-step technique advances the currently available nanofabrication tools by adjusting a widely accepted concept to the nano-scale. It may constitute a viable method for large-scale production of short polymeric nanofibers.

Enzymatic synthesis of isopropyl myristate using immobilized lipase from Bacillus cereus MTCC 8372

A purified alkaline thermo-tolerant bacterial lipase from Bacillus cereus MTCC 8372 was immobilized on a Poly (MAc- co -DMA- cl -MBAm) hydrogel. The hydrogel showed approximately 94% binding capacity for lipase. The immobilized lipase (2.36 IU) was used to achieve esterification of myristic acid and isopropanol in n -heptane at 65 °C under continuous shaking. The myristic acid and isopropanol when used at a concentration of 100 mM each in n -heptane resulted in formation of isopropyl myristate (66.0 ± 0.3 mM) in 15 h. The reaction temperature below or higher than 65°C markedly reduced the formation of isopropyl myristate. Addition of a molecular sieve (3 Å × 1.5 mm) to the reaction mixture drastically reduced the ester formation. The hydrogel bound lipase when repetitively used to perform esterification under optimized conditions resulted in 38.0 ± 0.2 mM isopropyl myristate after the 3 ^rd cycle of esterification.

Synthesis of ethyl laurate by hydrogel immobilized lipase of Bacillus coagulans MTCC-6375

An alkaline thermo-tolerant lipase from Bacillus coagulans MTCC-6375 was purified and efficiently immobilized onto a synthetic hydrophobic poly (MAc-co-DMA-cl-MBAm)-hydrogel at pH 8.5 and temperature 55°C in 16 h. The hydrogel bound matrix possessed 7.6 IU g -1 matrix lipase activity with a specific activity of 18 IU mg -1 protein. Immobilized lipase was used to catalyze the esterification of lauric acid and ethanol to produce ethyl laurate in n-nonane. The reaction conditions that were optimized to produce ethyl laurate in n-nonane included enzyme/substrate (E/S) ratio, substrate concentration, reaction time and reaction temperature. The optimized parameters were E/S ratio of 0.5 mg mM -1, ethanol:lauric acid in ratio of 100 mM:100 mM and reaction time of 15 h at 65°C under continuous shaking (200 rpm). Optimized conditions resulted in 66% conversion of reactants into ethyl laurate in n-nonane in the presence of 300 mg molecular sieve mL -1 reaction mixture.

Chitosan-modified PLGA nanoparticles with versatile surface for improved drug delivery

Shortage of functional groups on surface of poly(lactide-co-glycolide) (PLGA)-based drug delivery carriers always hampers its wide applications such as passive targeting and conjugation with targeting molecules. In this research, PLGA nanoparticles were modified with chitosan through physical adsorption and chemical binding methods. The surface charges were regulated by altering pH value in chitosan solutions. After the introduction of chitosan, zeta potential of the PLGA nanoparticle surface changed from negative charge to positive one, making the drug carriers more affinity to cancer cells. Functional groups were compared between PLGA nanoparticles and chitosan-modified PLGA nanoparticles. Amine groups were exhibited on PLGA nanoparticle surface after the chitosan modification as confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The modified nanoparticles showed an initial burst release followed by a moderate and sustained release profile. Higher percentage of drugs from cumulative release can be achieved in the same prolonged time range. Therefore, PLGA nanoparticles modified by chitosan showed versatility of surface and a possible improvement in the efficacy of current PLGA-based drug delivery system.