Parametric study on conductive patterns by low-temperature sintering of micron silver ink.

The fabrication of dense conductive patterns was achieved by low-temperature sintering of 1-3 µm micron silver flakes. A small amount of 20-50 nm nanosilver particles were added in the gaps of the micron silver flakes. The effects of sintering temperature, holding time and heating rate on the morphological evolution and formation mechanism of the sintered silver pattern were investigated in detail. Interestingly, rapid sintering (RS) can be achieved by removing the heating process from 70 °C up to the sintering temperature. The electrical resistivity of the sintered silver patterns was 10.8 × 10-6 Ω cm at 140 °C for 30 min under a pressure of 10 MPa. Moreover, the electrical resistivity of the sintered silver pattern for RS for 20 min does not change significantly after 6000 bending cycles. This work provides a new method to fabricate conductive patterns using micron silver flakes with the purpose of promoting the application of silver inks.

Halloysite@Polyaniline Nanoparticles Loaded with the Praseodymium (III) Cation for Improving Active Corrosion Protection of Waterborne Epoxy Coating.

The corrosion resistance of the waterborne epoxy coating is poor during long-term service, which greatly limits its widespread application. In this paper, the halloysite nanotubes (HNTs) were modified by polyaniline (PANI) and then used as nanocontainers to encapsulate the green corrosion inhibitor praseodymium (III) cations (Pr3+), obtaining HNTs@PANI@Pr3+ nanoparticles. A scanning electron microscope, transmission electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis were applied to characterize the formation of PANI and the absorption of Pr3+ cations. The corrosion-inhibiting ability of the HNTs@PANI@Pr3+ nanoparticles for iron sheets and the anticorrosion properties of the nanocomposite coatings were evaluated by the electrochemical impedance spectroscopy technique. The results indicated that the coating containing HNTs@PANI@Pr3+ nanoparticles exhibited excellent anticorrosion performance. After immersion in 3.5 wt % NaCl solution for 50 days, its Zf=0.01 Hz value was still as high as 9.4 × 108 Ω cm2. The icorr value was 3 orders of magnitude lower than that of the pure WEP coating. The excellent anticorrosion property of the HNTs@PANI@Pr3+ coating could be attributed to the synergy of three beneficial factors, including evenly distributed nanoparticles, PANI, and Pr3+ cations. This research will provide theoretical and technical support for the development of waterborne coatings with high corrosion resistance.

Prolonged release from PLGA/HAp scaffolds containing drug-loaded PLGA/gelatin composite microspheres.

Porous scaffolds that can prolong the release of bioactive factors are urgently required in bone tissue engineering. In this study, PLGA/gelatin composite microspheres (PGMs) were carefully designed and prepared by entrapping poly(L: -lactide-co-glycolide) (PLGA) microspheres (PMs) in gelatin matrix. By mixing PGMs with PLGA solution directly, drug-loaded PLGA/carbonated hydroxyapatite (HAp)/PGMs composite scaffolds were successfully fabricated. In vitro release of fluorescein isothiocyanate-dextran (FD70S) as a model drug from the scaffolds as well as PMs and PGMs was studied by immersing samples in phosphate buffered saline (pH = 7.4) at 37°C for 32 days. Compared with PMs, PGMs and PLGA/HAp/PGMs scaffolds exhibited slow and steady release behavior with constant release rate and insignificantly original burst release. The swelling of PGMs, diffusion of drugs, and degradation of polymer dominated the release behaviors synergistically. The PLGA/HAp/PGMs scaffold offers a novel option for sequential or simultaneous release of several drugs in terms of bone regeneration.

Preparation of PLGA scaffolds with graded pores by using a gelatin-microsphere template as porogen.

Porous scaffolds with graded pores are crucial to osteochondral regeneration. In this study, a technique combining solution casting with gelatin-microsphere template leaching has been developed to produce poly(L-lactide-co-glycolide) (PLGA) scaffolds with graded pores. The traditional emulsification and solvent extraction method was improved by using the gradient ethanol/water solutions to extract water to prepare gelatin microspheres with a smooth surface without the use of any surfactant. Gelatin microspheres with different diameters were in sequence put into a custom-made cylindrical Teflon mold and bonded together to obtain gelatin-microsphere templates. By using the gelatin-microsphere templates as porogen, PLGA scaffolds with graded pore size across the cylindrical axis were prepared. The porosity of the scaffold was as high as 95%. The pore size effect on osteoblasts was studied. The results showed that the graded scaffolds possessed good biocompatibility for osteoblast growth. During the 14 days culture, the cell proliferation of all the three pore layers displayed the trend of increasing. The proliferation rate of the large pore layer was lower than the other two layers. However, the difference of alkaline phosphatase activity on the three pore layers was not statistically significant. We assumed that it was probably because of the hydrophobicity and the short culture time. It was demonstrated that gradient ethanol/water solutions provided a simple way to prepared gelatin microspheres. The graded scaffolds would provide potential application for osteochondral regeneration.

Controllable dual-release of dexamethasone and bovine serum albumin from PLGA/ß-tricalcium phosphate composite scaffolds.

Localized dual-drug delivery from biodegradable scaffolds is an important strategy in tissue engineering. In this study, porous poly(L-lactide-co-glycolide) (PLGA)/ß-tricalcium phosphate scaffolds containing both dexamethasone (Dex) and bovine serum albumin (BSA) were prepared by incorporating Dex-loaded and BSA-loaded microspheres into the scaffolds. PLGA microspheres containing Dex or BSA were prepared by spray-drying and double emulsion/solvent evaporation, respectively. In vitro release studies indicated that microspheres prepared from PLGA in 3:1 molar ratio of L-lactide/glycolide and 89.5 kDa relative molecular mass showed prolonged release profiles compared with those prepared from PLGA in 1:1 L-lactide/glycolide molar ratio and 30.5 kDa relative molecular mass. Additionally, introduction of poly(ethylene glycol) in the PLGA chain could improve the encapsulation efficiency and reduce the release rate. Based on the above results, controllable dual-release of Dex and BSA with relatively higher or lower release rate was achieved by incorporating Dex-loaded and BSA-loaded microspheres with different release profiles into the PLGA/ß-tricalcium phosphate scaffolds.

Effect of cyclic loading on in vitro degradation of poly(L-lactide-co-glycolide) scaffolds.

The in vitro degradation performance of porous scaffolds is very important in tissue engineering, especially the scaffold implanted in the environment imitating the repaired tissue. In this paper, the effect of cyclic loading on in vitro degradation of porous poly(L-lactide-co-glycolide) (PLGA) scaffolds was studied by incubating the samples in phosphate-buffered saline at 37 degrees C and pH 7.4 under dynamic conditions (cyclic loading) and static conditions (shaking water bath) for 12 weeks. The results showed earlier morphological variations and faster reduction in mass, dimensions and relative molecular mass of the scaffolds under dynamic conditions. Mechanical properties (the compressive modulus and the compressive strength) of the PLGA scaffolds under both conditions tended to increase in the first 3 weeks, but showed a decrease tendency afterward. The scaffolds under dynamic conditions were too brittle to be further characterized after degradation for 6 weeks, while those under static conditions endured degradation until week 8. The degradation mechanism of the PLGA scaffolds under cyclic loading was clearly explained and a three-stage degradation model based on the degradation behaviors of the scaffolds under two conditions was presented.