No abstract

We report on the modification of polytetrafluoroethylene (PTFE) by exposure to the ultraviolet (UV) light of a Xe(2)*-excimer lamp at a wavelength of 172 nm in an ammonia atmosphere. Typical treatment times were up to 30 min. Subsequently, the samples were grafted with the amino acid alanine from an aqueous solution. The samples were characterized by means of optical transmission spectroscopy, laser-induced fluorescence and contact-angle measurements. We studied the adhesion of rat aortic smooth muscle cells (SMC) and mouse fibroblasts (3T3 cells) to the modified polymer samples using an in vitro technique, where the population density and spread of adhering cells is determined 24 h after seeding by image analysis. For both cell types the exposure of PTFE to UV-light in an ammonia atmosphere resulted in a significant increase in the number of adhering cells and in the size of their spreading area. The grafting with alanine enhanced this effect. Additional experiments with human endothelial cells (HEC) also demonstrated improved adhesion to modified PTFE. Thus, PTFE modified by our method appears to be a promising material for fabrication of artificial vascular prostheses and implants or for cultivation of skin substitutes.

No abstract

High molecular weight partially hydrolyzed polyacrylamides (HPAM), have been shown to effectively increase oil recovery of medium viscous and heavy oil.Using a rheometer, these polymers show shear thinning behavior. However, determining the apparent viscosity from coreflood tests for different frontal velocities, an increase in the apparent viscosity is observed. This apparent increase is attributed to the visco-elastic properties of the polymers.In this paper, a set of laboratory experiments has been performed for cores similar to the rock in the 8 th Torton Horizon (8 TH) of the Matzen Field in Austria. The results show that for the conditions in the near-wellbore region of the reservoir, an increase in apparent viscosity is expected. In addition, the relationship of velocity versus apparent viscosity for pre-sheared polymers was investigated. Dependent on the amount of pre-shearing, the apparent viscosity was significantly decreased. For different polymer concentrations, the apparent viscosity versus velocity of the pre-sheared polymers was almost identical.A polymer injection pilot performed in the 8 TH in the Matzen Field in Austria confirmed that shearing of the polymer solution in the near-wellbore occurs for injection below the fracturing pressure. Above the fracturing pressure, the flow velocities are significantly decreased owing to the large surface area of the fracture. Hence, polymer injection should be performed above the fracturing pressure to improve sweep efficiency.

We studied the adhesion and proliferation of human umbilical-vein endothelial cells (HUVEC) and human aortic smooth-muscle cells (HASMC) on modified polymer samples. The polymers under investigation were either PTFE (polytetrafluoroethylene) or PET [poly(ethylene terephthalate)], which are among the most frequently employed biomaterials in reconstructive medicine. The polymer surfaces were modified by exposure to the UV light of an excited-xenon-dimer (Xe2*) Excimer lamp (Heraeus-Noblelight, Hanau, Germany) at a wavelength of 172 nm in an NH3 atmosphere. On modified PTFE, this resulted in a significant increase in the number of adhering HUVEC or HASMC 1 day after seeding and in the formation of a confluent cell layer after 3-4 days. On PET, HUVEC adhesion and proliferation rates were already high on untreated samples and could not be significantly increased by the UV-light treatment, but the cells were distributed more homogenously on the treated samples. Cell proliferation was in all cases comparable with, or even better than, that obtained on standard polystyrene (PS) Petri dishes used in cell cultivation. As on PS Petri dishes, the proliferation of HASMC on modified PTFE was faster than that of HUVEC under similar culture conditions.