RESUMEN
The aim of this study was to evaluate two biodegradable polymeric systems as scaffolds for bone tissue engineering. Rat bone marrow cells were seeded and cultured for 1 week on two biodegradable porous polymeric systems, one composed of poly(ethylene glycol)-terephthalate/poly(butylene terephthalate) (PEGT/PBT) and the other composed of cornstarch blended with poly(epsilon-caprolactone) (SPCL). Porous hydroxyapatite granules were used as controls. The ability of cells to proliferate and form extracellular matrix on these scaffolds was assessed by a DNA quantification assay and by scanning electron microscopy examination; their osteogenic differentiation was screened by the expression of alkaline phosphatase. In addition, the in vivo osteogenic potential of the engineered constructs was evaluated through ectopic implantation in a nude mouse model. Results revealed that cells were able to proliferate, differentiate, and form extracellular matrix on all materials tested. Moreover, all constructs induced abundant formation of bone and bone marrow after 4 weeks of implantation. The extent of osteogenesis (approximately 30% of void volume) was similar in all types of implants. However, the amount of bone marrow and the degree of bone contact were higher on HA scaffolds, indicating that the polymers still need to be modulated for higher osteoconductive capacity. Nevertheless, the findings suggest that both PEGT/PBT and SPCL systems are excellent candidates to be used as scaffolds for a cell therapy approach in the treatment of bone defects.
Asunto(s)
Células de la Médula Ósea/metabolismo , Sustitutos de Huesos , Tereftalatos Polietilenos/análogos & derivados , Polímeros , Ingeniería de Tejidos , Fosfatasa Alcalina/metabolismo , Animales , Células de la Médula Ósea/citología , ADN/metabolismo , Microscopía Electrónica de Rastreo , Ácidos Ftálicos , Poliésteres , Polietilenglicoles , Ratas , Almidón , Factores de TiempoRESUMEN
Screening was performed on nine carriers to find an improved formulation for Agrobacterium radiobacter K84 cells. The survival data showed that it is possible to preserve A. radiobacter cells on dry solid supports for a long time provided that the storage temperature is 4 degrees C and that the inoculation volume for 4 x 10(9) CFU g-1 is not less than 0.15 ml g of carrier-1. On the other hand, a substantial carrier water content was necessary for room temperature storage. Many materials proved to be suitable as microbial carriers; in some cases, vermiculite allowed long storage times comparable to those reported for peat or carboxymethyl cellulose, which are already employed in some commercial A. radiobacter K84 products. Furthermore, vermiculite assured full and immediate biological activity in the prevention of crown gall, showing that it is suitable for a new formulation of strain K84. A hypothesis to explain the different survival abilities in wet and dry conditions is presented.
Asunto(s)
Preservación Biológica , Rhizobium/crecimiento & desarrollo , Técnicas Bacteriológicas , Medios de Cultivo , Desecación , Análisis de Regresión , TemperaturaRESUMEN
Nitrogen, as KNO3 or NH4NO3, can inhibit the photoinduction of protoperithecia in Neurospora crassa when present in the medium at a high concentration but does not inhibit the photoinduction of carotenoids. The point at which the presence of high nitrogen levels is no longer inhibitory is 5 h after illumination.
RESUMEN
The treatment of undifferentiated mycelia with heavy suspensions of their own conidia triggers protoperithecial development. This effect was also observed with white collar (wc) mutants and suggests that the wc genes are not structural genes necessary for morphogenesis of protoperithecia but that they are probably involved in regulation.
Asunto(s)
Mutación , Neurospora crassa/crecimiento & desarrollo , Neurospora/crecimiento & desarrollo , Genotipo , Calor , Neurospora crassa/genética , Neurospora crassa/efectos de la radiación , Especificidad de la Especie , Rayos UltravioletaRESUMEN
White collar (wc) mutants of Neurospora crassa are thought to be regulatory mutants blocked in the photoinduction of carotenogenesis. Eight new wc mutants have been isolated after UV mutagenesis; their morphology and linear growth rate are not altered, although blue light-induced carotenogenesis is completely blocked. All of the wc mutations fall into two complementation groups corresponding to the already-known wc-1 and wc-2 loci. It is shown that the wc mutations impair another blue light effect, the photoinduction of protoperithecia formation, as well as the low constitutive production of protoperithecia in the dark. These effects are not due to the lack of carotenoids since the albino mutants show a normal sexual development. The pleiotropic effects of the mutations in the wc genes indicate that they play a key role in the mechanisms of regulation of the blue light-induced responses of N. crassa.