GBM, a grade IV glioma classified by World Health
Organization, is considered highly malignant, vascular and invasive subtype.
Hypoxia and neovascularization are signature histopathologic features of GBM,
which is most lethal during first year after initial diagnosis despite surgical
resection and other standard therapies. Temozolomide chemotherapy andradiotherapy against GBM tumor cells have led to a significant improvement intumor growth and patient survival in newly diagnosed and recurrent GBM. The
survival advantage conferred by temozolomide chemotherapy is associated with
methylation of the promoter region of the gene encoding O6-methylguanine
DNAmethyltransferase (MGMT). Both tumor protein p53 (TP53) and MGMT are
involved in DNA repair after chemotherapy or radiotherapy, which may contribute
to drug resistance. In addition, tumor cells acquiring several mutations during
tumor progression could contribute to therapy resistance in GBM.
Increased productivity is one of the most important
objectives in continuous production of ethanol. It is generally accepted that a
high concentration of yeast favors an increased ethanol yield of the
fermentation process . Several techniques that promote the accumulation ofbiomass in fermenters have been used in continuous fermentation processes,
including cell immobilization in polymeric matrices and cell recycle by
centrifugation or filtration through membranes. Good performances have been
reported for processes using immobilized cells; however, procedures and
materials involved in this technique are inaccessible to a large number of
small industrial units . Centrifugation and filtration equipments are extremely
expensive and prone to mechanical problems; the use of these equipments is
limited due to high investment and maintenance costs. Since yeast separation by
conventional methods is an expensive operation in alcoholic fermentation
plants, alternative separation techniques using cheaper equipment such as
hydrocyclones and settlers have been investigated aiming to reduce the costs
involved in ethanol production.
Although solid particles can settle under the action of a
centrifugal force, gravitational sedimentation is understood as the settling of
particles within a fluid under the force of gravity. The factors that controlthe settling velocity are the solids concentration in the slurry, the densities
of solid and liquid, the size and shape of the particles and the viscosity of
the medium. However, the most important factors are the particle size and
particle density.
