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The emerging fields of tissue engineering and biomaterials have begun to provide potential treatment options for liver failure. The goal of the present study is to investigate the ability of a poly L-lactic acid (PLLA) nanofiber scaffold to support and enhance hepatic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs). A scaffold composed of poly L-lactic acid and collagen was fabricated by the electrospinning technique. After characterizing isolated hMSCs, they were seeded onto PLLA nanofiber scaffolds and induced to differentiate into a hepatocyte lineage. The mRNA levels and protein expression of several important hepatic genes were determined using RT-PCR, immunocytochemistry and ELISA. Flow cytometry revealed that the isolated bone marrow-derived stem cells were positive for hMSC-specific markers CD73, CD44, CD105 and CD166 and negative for hematopoietic markers CD34 and CD45. The differentiation of these stem cells into adipocytes and osteoblasts demonstrated their multipotency. Scanning electron microscopy showed adherence of cells in the nanofiber scaffold during differentiation towards hepatocytes. Our results showed that expression levels of liver-specific markers such as albumin, α-fetoprotein, and cytokeratins 8 and 18 were higher in differentiated cells on the nanofibers than when cultured on plates. Importantly, liver functioning serum proteins, albumin and α-1 antitrypsin were secreted into the culture medium at higher levels by the differentiated cells on the nanofibers than on the plates, demonstrating that our nanofibrous scaffolds promoted and enhanced hepatic differentiation under our culture conditions. Our results show that the engineered PLLA nanofibrous scaffold is a conducive matrix for the differentiation of MSCs into functional hepatocyte-like cells. This represents the first step for the use of this nanofibrous scaffold for culture and differentiation of stem cells that may be employed for tissue engineering and cell-based therapy applications.
Pseudomonas fluorescens BM07 was characterized as a producer of cold-induced biopolymer by decreasing the temperature down to as low as 10°C. It was previously shown that the synthesis of BM07 biopolymer was inhibited at 30°C. The present study was conducted to investigate the biosorption of mercury (Hg²⁺) ions on the BM07 cells grown on Ml minimal medium at two temperatures (10°C and 30°C). The effects of various factors including pH, contact time, initial concentration of metal and cell biomass on the biosorption yield were also studied. Study of the effect of pH on mercury removal indicated that the metal biosorption increased with increasing pH from 3.0 to 7.0. The optimum adsorption pH value was found to be 7.0. Our results showed that, at optimum pH, BM07 cells were able to uptake the mercury up to 102 and 60 mg Hg²⁺/g dry biomass for 10°C and 30°C grown cells respectively. The removal capacity of cells increased when the cell biomass concentrations increased. The maximum removal efficiency was obtained when cells concentration was 0.83 mg dry biomass/ml for both conditions. The initial metal ion concentration significantly influenced the equilibrium metal uptake and adsorption yield. The equilibrium data were analyzed using Langmuir adsorption model. The qmax was 62.9 and 82.25 mg Hg²⁺/g dry biomass for cells grown at 30°C and 10°C respectively. The results suggest that, the existence of residual cold-induced biopolymer on the external surface of cells may play an important role in biosorption efficiency, as P. fluorescens BM07 cells which were grown at 10°C under similar conditions showed higher efficiency to biosorbe mercury than non-polymer producing cells grown at 30°C.
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