Papers by Author: Jin Rui Xu

Abstract: In this work ion conductivity and FC application were studied for the new type composite material based on SDC (samarium doped ceria) and Li2SO4. Significant conductivity enhancement was achieved, e.g. 10-2 – 0.4 Scm-1 for the SDC-Li2SO4 compared to 10-4 -10-2 Scm-1 for the SDC between 400 and 650°C. Some ion conductivity mechanisms were proposed correspondingly. Using the SDC-Li2SO4 composite materials as the electrolytes, we achieved high performances, 200-540 mWcm-2, for intermediate temperature (450-650°C) solid oxide FC (ITSOFC) applications. Sulfates, typically Li2SO4, have an excellent chemical stability in sulfur containing atmosphere. The sulfate-ceria (SDC-Li2SO4) composite materials can thus meet the demands to develop the sulfur tolerant and H2S FC technologies, which was also demonstrated successfully with significant importance for both fundamental and applied research.

Abstract: With the outstanding biocompatibility of hydroxyapatite (HA) and biodegradation of poly(D,L)lactide(PDLLA), and the expected good bio-mechanical compatibility, nano-HA / PDLLA (n-HA/PDLLA)composite has been paid great interests in hard tissue repair. One of the key factors affecting the potential of the composite is the degradation of the composite. That is what the mechanism of degradation in the composite is and if the degradation of the materials would induce the crack of the composite or a porous structure facile for tissue ingrowth would be formed. In this study, an n-HA/ PDLLA composite containing about 40% n-HA (wt%) was prepared and the degradation of the composite in bony tissue of rabbits and tissue response were studied by implanting composite rods and control HA rods into the femora of 16 New Zealand rabbits. After definite intervals, the histological analysis was completed by light microscopy and the degradation behavior was observed by scanning electron microscopy. The results suggested that a nano-HA/PDLLA composite was obtained and the materials showed good biocompatibility and osteoconductivity. The substantial degradation of the composite occurred at 8 weeks in vivo. After a longer period of implantation, the further degradation of the composite led to the formation of interconnected microporous and macroporous structure in the materials that might facilitate the tissue ingrowth in the composite.

Abstract: A nano-grade hydroxyapatite/collagen composite was prepared by an in situ synthesis technique from calcium nitrate, diammoniun hydrogen phosphate, and a cowhide collagen sol at low temperature. XRD and TEM analyses of the composite indicated that crystals formed in the collagen fibril matrix were nanohydroxyapatite with low crystallinity. Biocompatibility of the composite was evaluated by in vitro cytotoxicity test and in vivo genotoxicity and sensitization test. No mutagenic activity of the composite was observed in mouse micronucleus tests. No evidence of dermal sensitization of the composite was found in guinea pig maximization tests. The results from a filter diffusion test indicated that the composite did not induce a cytotoxic behavior. All these results suggest that the composite has excellent biocompatibility.

Abstract: The purpose of this study was to evaluate the behavior of nano-hydroxyapatite/ poly(D,L)lactide (n-HA/PDLLA) composite in vivo. The composite rods containing about 40wt% n-HA and control HA rods with a diameter of 2mm and a length of 6mm were implanted into the femora of 16 New Zealand rabbits. Composite wafers with a diameter of 5mm and a thickness of 1mm were implanted into the dorsal subcutis of 18 Wistar Albino rats. After definite intervals, the histological analysis was completed by light microscopy and the degradation behavior was observed by scanning electron microscopy. The histological analysis showed no obvious difference between n-HA /PDLLA composite and pure HA that had good biocompatibility and osteoconductivity. SEM analysis of the surface and cross section of the samples showed that the degradation of the composite started from surface, then into the inner gradually and formed multiple pores at surface. The pore size and porosity gradually increased along with time and a porous network may be formed.

Abstract: The osteoinductivity of calcium phosphate ceramics has been studied extensively, but the mechanism is still unclear and few reports about the molecular mechanism in the osteoinductive process. In this study the osteoblast related gene expressions induced by biomaterials were investigated by isolating the RNA from the tissue grown in porous hydroxyapatite/tricalcium phosphate (HA/TCP) ceramics implanted in rat femur muscle on day 7, 15, 30, 60, 90,120, and analyzed by RT-PCR technique. RNA extracted from muscle without implant was used as control at the same time. The results showed that osteopontin and osteocalcin genes, the important osteoblastic markers, expressed in early stage, on day 7 after implantation, and were detected at any period. Collagen type I gene expressed on day 60, 90 and 120. It revealed that osteoblast differentiation occurred very early before collagen type I expression after implanting HA/TCP ceramics in vivo.