Bora Mavis

Synthesis, characterization and osteoblastic activity of polycaprolactone nanofibers coated with biomimetic calcium phosphate

Immersion of electrospun polycaprolactone (PCL) nanofiber mats in calcium phosphate solutions similar to simulated body fluid resulted in deposition of biomimetic calcium phosphate layer on the nanofibers and thus a highly bioactive novel scaffold has been developed for bone tissue engineering. Coatings with adequate integrity, favorable chemistry and morphology were achieved in less than 6h of immersion. In the coating solutions, use of lower concentrations of phosphate sources with respect to the literature values (i.e., 3.62 vs. 10 mM) was substantiated by a thermodynamic modeling approach. Recipe concentration combinations that were away from the calculated dicalcium phosphate phase stability region resulted in micron-sized calcium phosphates with native nanostructures. While the nano/microstructure formed by the deposited calcium phosphate layer is controlled by increasing the solution pH to above 6.5 and increasing the duration of immersion experimentally, the nanostructure imposed by the dimensions of the fibers was controlled by the polymer concentration (12% w/v), applied voltage (25 kV) and capillary tip to collector distance (35 cm). The deposited coating increased quantitatively by extending the soak up to 6h. On the other hand, the porosity values attained in the scaffolds were around 87% and the biomimetic coatings did not alter the nanofiber mat porosities negatively since the deposition continued along the fibers after the first 2h. Upon confirming the non-toxic nature of the electrospun PCL nanofiber mats, the effects of different nano/microstructures formed were evaluated by the osteoblastic activity. The levels of both alkaline phosphatase activity and osteocalcin were found to be higher in the coated PCL nanofibers than in the uncoated PCL nanofibers, indicating that biomimetic calcium phosphate on PCL nanofibers supports osteoblastic differentiation.

Cellular Behavior on Epidermal Growth Factor (EGF)-Immobilized PCL/Gelatin Nanofibrous Scaffolds

Nano-scaled poly(ε-caprolactone) (PCL) and PCL/gelatin fibrous scaffolds with immobilized epidermal growth factor (EGF) were prepared for the purpose of wound-healing treatments. The tissue scaffolds were fabricated by electrospinning and the parameters that affect the electrospinning process were optimized. While the fiber diameters were 488 ± 114 nm and 663 ± 107 nm for PCL and PCL/gelatin scaffolds, respectively, the porosities were calculated as 79% for PCL and 68% for PCL/gelatin scaffolds. Electrospun PCL and PCL/gelatin scaffolds were first modified with 1,6-diaminohexane to introduce amino groups on their surfaces, then EGF was chemically conjugated to the surface of nanofibers. The results obtained from Attenuated Total Reflectance Fourier Transform Infrared (ATR–FT-IR) spectroscopy and quantitative measurements showed that EGF was successfully immobilized on nanofibrous scaffolds. L929 mouse fibroblastic cells were cultivated on both neat and EGF-immobilized PCL and PCL/gelatin scaffolds in order to investigate the effect of EGF on cell spreading and proliferation. According to the results, especially EGF-immobilized PCL/gelatin scaffolds exerted early cell spreading and superior and rapid proliferation compared to EGF-immobilized PCL scaffolds and neat PCL, PCL/gelatin scaffolds. Consequently, EGF-immobilized PCL/gelatin scaffolds could potentially be employed as novel scaffolds for skin tissueengineering applications.

Homogeneous Precipitation of Layer Double Hydroxides

Structure of nickel precipitate from decomposition of urea was found to be α-Ni(OH)2. FTIR analysis revealed the intercalation of cyanate (OCN ), which is an intermediate product of urea decomposition. This observation implied that the assumption of single step decomposition of urea to carbon dioxide and ammonia was over simplified. For quantitative analysis on the effects of critical system parameters like initial pH and metal ion concentration, a detailed analysis of the possible reactions in urea system was carried out. Numerical solutions to reaction pathways predicted significant accumulation of the intermediate cyanate in the time-temperature range investigated. Further elaboration was possible by considering the effects of hydrolysis products of Ni 2+ and Ni-amine, Ni-cyanate, and Ni-carbonate complexes in the numerical simulations. Chemical analysis of the precipitate showed a decrease in nitrogen content with increasing reaction times. This was consistent with the predicted decrease in concentration of Ni-cyanate complexes with time. At extended digestion times, formation of Ni-amine complexes limits the complete recovery of the Ni 2+ . From the two phases of Ni(OH)2, α-phase, with its larger interlayer spacing, offers enhanced electrochemical properties but it transform into thermodynamically stable β-phase. Stabilizing αphase with Co 2+ substitution which oxidizes irreversibly to Co 3+ with electrochemical cycling along with forming layer double hydroxides (LDH’s: [M 2+ 1-xM 3+ x(OH)2] x+ [A nx/n] x·mH2O) were studied. Various compositions of LDH’s containing Ni 2+ /Co 2+ and Al 3+ ions were produced by urea and tested with chronopotentiometry to assess their potential utility as rechargeable electrode materials. Introduction Homogeneous precipitation in aqueous solutions has been widely used to prepare various metaloxide precursor powders [1-5]. Urea decomposition in the presence of transition metal ion, Ni 2+ yields α-Ni(OH)2 as the precipitate [6]. Same system was also investigated in detail by Soler Illia et al. [7]. Results from their work indicated that the second step of urea decomposition becomes important in cases where the interaction between cyanate (OCN ; product of first step) and the transition metal ion is strong. It is known that Ni 2+ ions can form tetrahedral complexes with cyanate [8,9]. FTIR results from our group and others confirmed these findings [10,11]. A thorough analysis of the literature on urea decomposition in aqueous solutions indicated that second step (cyanate hydrolysis) could be represented with five reactions (Fig. 1B). Depending on the pH range and the metal ion employed, a few will dominate. A comprehensive numerical solution to the hydrolysis process was possible through the use of a reaction kinetics program, KINSIM [12]. Furthermore, effects of hydrolysis products of Ni 2+ and possible Ni-amine, Ni-cyanate, and Nicarbonate complexes were also incorporated using equilibrium constant and by assuming a fast reverse reaction rate constant. This led to finding the forward rate by, kforward = kreverse × Kequilibrium. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 41-44 doi:10.4028/www.scientific.net/KEM.264-268.41

Microemulsion Synthesis Strategies for ZrW2O8 Precursors

A zirconium tungstate (ZrW2O8) precursor was synthesized by a novel sol-gel method with zirconium oxychloride and tungstic acid as the zirconium and tungsten sources, respectively. Heat treatment at 600oC for 10 hours was adequate to crystallize the precursor. Use of excess zirconium source and the concentration of hydrochloric acid were found to affect the phase purity and crystallization temperature of ZrW2O8. Sizes of particles obtained were in submicron range in the absence of a microemulsion system. On the other hand, using water/oleylamine/hexane reverse micelle microemulsion technique monodispersed particles with sizes between 10 to 100nm were obtained. Nanoparticles were then successfully dispersed in a solvent with a carrier polymer to produce ZrW2O8 nanofibers with electrospinning technique.