222 resultados para Break strength
Resumo:
This study reports the physicochemical and drug diffusion properties of rifampicin containing poly(epsilon-caprolactone) (PCL)/polyethylene glycol (PEG) networks, designed as bioactive biomaterials. Uniquely, the effects of the states of both rifampicin and PEG and the interplay between these components on these properties are described. PCL matrices containing rifampicin (1-5%, w/w) and PEG 200 (0-15%, w/w) were prepared by casting from an organic solvent (dichloromethane). The films were subsequently characterized in terms of their thermal/thermorheological, surface and tensile properties, biodegradation and drug diffusion/release properties. Incorporation of PEG and/or rifampicin significantly affected the tensile and surface properties of PCL, lowering the ultimate tensile strength, % elongation at break, Young modulus and storage and loss moduli. Both in the absence and presence of PEG, solubilisation of rifampicin within the crystalline domains of PCL was observed. PEG was present as a dispersed liquid phase. The release of rifampicin (3% loading) was unaffected by the presence of PEG. Similarly the release of rifampicin (5%) was unaffected by low concentrations of PEG (5-10%) however, at higher loadings, the release rate of rifampicin was enhanced by the presence of PEG. Rifampicin release (10% loading) was enhanced by the presence of PEG in a concentration dependent fashion. These observations were accredited to enhanced porosity of the matrix. In all cases, diffusion-controlled release of rifampicin occurred which was unaffected by polymer degradation. This study has uniquely illustrated the effect of hydrophilic pore formers on the physicochemical properties of PCL. Interestingly, enhanced diffusion controlled release was only observed from biomaterials containing high loadings of PEG and rifampicin (5, 10%), concentrations that were shown to affect the mechanical properties of the biomaterials. Care should therefore be shown when adopting this strategy to enhance release of bioactive agents from biomaterials. (C) 2011 Elsevier B.V. All rights reserved.
Resumo:
This study reports the effects of: the molecular weight ratio of poly(epsilon -caprolactone) (PCL) in blends containing polymer of high (50 000 g mol(-1)) and low (4000 g mol(-1)) molecular weight; the concentration (0, 1, and 5 wt-%) of poly(vinyl pyrrolidone/iodine) (PVP/I); and storage at 30 degreesC and 75% relative humidity; on the thermomechanical properties of films prepared by solvent evaporation from solutions containing both PCL and PVP/I. The tensile properties were found to be statistically dependent on the molecular weight ratio of PCL but not on the concentration of PVP/I. The reductions in tensile strength and elongation at break associated with increasing amounts of low molecular weight PCL were attributed to a reduction in the concentration of chain entanglements. No changes were observed in viscoelastic properties or the glass transition temperature. Following storage there were no changes in the tensile strength, glass transition temperature, or viscoelastic properties of the films; however, significant reductions in elongation at break were observed. It is suggested that this is due to hydrolytic chain scission of amorphous PCL. Inclusion of 5 wt-% PVP/I increased this process in films containing 100:0 and 80:20 high/low molecular weight PCL (but not 60.40), but the extent of this was small. This study highlighted significant aging properties of PCL in a moist atmosphere. Consequently, it is recommended that suitable packaging materials should be employed to control the exposure of PCL films to water during storage.
Resumo:
The photo-pump strengths of both the ((3 (d) over bar(4))(0)(3d(6))(0))(0)-(((3 (d) over bar(3))(3/2)(3d(6))(0))(3/2)(5 (f) over bar)(5/2))(1) and the ((3 (d) over bar(4))(0)(3d(6))0)0-(((3 (d) over bar(4))(0)(3d(5))(5/2))(5/2)(5f)(7/2))(1) transitions in Ni-like Sm34+ have been measured to be 2.0 x 10(-4) and 2.4 x 10(-4) photons/mode respectively. The implications of the measurement are briefly discussed in a comparison of the merits of automatically line matched photo-pump scheme to those of the collisional excitation Ni-like Sm+34 scheme.
