Surface Of Gel Beads Research Articles

Fluidized-bed and packed-bed characteristics of gel beads

Abstract A liquid-fluidized bed or packed bed with gel beads is attractive as an immobilized-cell bioreactor. The performance of such bioreactors is influenced by the physical behavior of these beads. Three different but related aspects involving the drag force between particles and liquid were studied for five types of gel beads, differing in diameter and density: (1) the terminal settling velocity of a single gel bead, (2) the pressure drop over a packed bed and (3) the voidage in a liquid-fluidized bed. Qualitatively, the same trends in these aspects were observed for gel beads as for conventional solids. Quantitatively, however, these aspects were incorrectly predicted by established models (with one exception). It was found that the drag force between gel bead and flowing liquid is smaller than that for conventional solids. As an explanation, two hypotheses are suggested. The first one attributes the drag reduction to small amounts of dissolved polymer. The second one attributes the smaller drag force to the surface nature of gel beads: gel beads contain over 95% of water and thus can be regarded as ‘rigid’ water droplets. Hence, the gel bead surface might show water-like properties. As an alternative to drag-coefficient relations for conventional solids, the drag coefficient of a single gel bead in a packed or fluidized bed could successfully be described by adapting an existing relation. The success of this description facilitates a more rational design of packed and fluidized beds of gel beads.

Nucleotide Isolation by Boronic Acid Functionalized Hydrogel Beads

Aminophenyl boronic acid (APBA) modified hydrogel beads were prepared as a new sorbent for nucleotide isolation. Spherical hydrogel beads, obtained by suspension copolymerization, were the base material for the sorbent. The carboxyl groups on the gel bead surface were activated with a water soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). APBA was then covalently attached to the activated structure via the amine groups. The maximum APBA attached to the gel was 34mg/g. The reversible adsorption-desorption behavior of β-nicotinamide adenine dinucleotide (β-NAD) was investigated by using 3.5 and 34mg/g of APBA on the hydrogel beads. The equilibrium -NAD adsorption capacities for these beads were determined as approximately 25 and 100mg/g, respectively. The -NAD absorption capacity of these APBA beads is significantly greater than similar supports.

Mathematical modelling of immobilized animal cell growth.

A two-dimensional mathematical model for animal cell growth was employed to study the suspension, as well as stationary, culture of micro-encapsulated and gel immobilized animal cells. For stationary microcapsules with low-viscosity intracapsular liquid, it was found that capsule radius, capsule loading and medium-change time have the most significant effects on the intracapsular cell density. The model was also adapted to simulate other scenarios of cell growth such as in gel beads and suspended microcapsules. The simulated time course of oxygen concentration and specific growth rate revealed a complicated interaction between material transport and cell growth kinetics. With the mass transfer coefficient for oxygen transfer (KLa') into the medium equal to 4.0 hr-1, for instance, it was found that the specific growth rate of the microencapsulated cells was controlled by the supply of glucose and oxygen. When the value of KLa' was reduced to 0.6 hr-1, however, oxygen supply appeared to be the sole factor affecting the specific growth rate. In the case of suspended gel beads, a simulation revealed a higher cell density towards the gel bead surface. The transport of nutrients and oxygen to the central region of the gel bead was apparently blocked by the surrounding cells.

Controlled mycelial growth for kojic acid production using Ca-alginate-immobilized fungal cells.

Conidia of Aspergillus oryzae were immobilized in Ca-alginate beads and then incubated in a nutrient medium to yield an immobilized biocatalyst producing kojic acid. The immobilized cell cultures produced kojic acid linearly during cultivation. Regardless of the size of the immobilized particles, there existed an optimal nitrogen concentration for the maximum production rate of kojic acid, at which smaller bead sizes resulted in a higher production rate. When the growth of mycelia were confined within the bead surface and segregated from each other by gel material, they produced kojic acid with maximal catalytic activity and exhibited the highest conversion yield of glucose. The extent of mycelial segregation was especially higher in cultures of smaller bead particles, and the depth of mycelial growth was 150 to 250 microns from the gel bead surface in all cultures of different nitrogen concentrations and bead sizes. Therefore, for the maximum expression of catalytic activities of immobilized mycelial cultures, it was found very critical to optimally control the mycelial distribution in gel beads by the culture conditions affecting mycelial growth.

Scanning Electron Microscopy of Ca-Alginate-Immobilized Aureobasidium Pullulans Grown Under Various Culture Conditions

The morphological development of a glucoamylase-producing strain of Aureobasidium pullulans immobilized Ca-alginate was investigated during semicontinuous fermentations a fluidized-bed reactor. A dense mycelium layer was developed by the fungus on the gel bead surface which gave the beads a pellet-like configuration. Varying culture conditions, such as bead, substrate and CaCl2 concentrations and aeration rate, had a consistent effect on both enzyme production and morphological development of the in situ grown cells. Optimization of the growth conditions appeared to be necessary to prevent fungal overgrowth and to enable the immobilized inoculum to continue a sustained level of glucoamylase production over a great number of transfers.

Raw‐starch Digestion by Chalara paradoxa Immobilized in Calcium Alginate Gels

AbstractThe spores of raw starch digesting fungus Chalara paradoxa were entrapped in calcium‐alginate beads and preincubated in growth medium. The fungus devoloped a mycelium layer below and on the gel bead surface so that nutrition and oxygen in this area had direct contact with mycelia. The fungus on the bead could produce amylase and could digest raw corn starch continuously for 40 d with corn steep liquor as a nitrogen source.

Application of solvent extraction to ethanol fermentation

The basic problems of applying solvent extraction to ethanol fermentation were investigated. The selection of solvents was based on the selectivity ratio, which was expressed as the ratio of the ethanol distribution coefficient to the water distribution coefficient. Solvents with high selectivity ratios of more than 50 were found mainly among the alcohols and esters. However, most of these solvents were toxic to ethanol-producing microorganisms. We tried to make a barrier to solvent molecules beneath the surface of gel beads immobilizing the cells as a protection against solvent toxicity. Porapack Q was found to be an effective barrier, and the ethanol production rate of immobilized cells protected with Porapack Q did not change event after the production of eight batches in medium saturated with sec-octanol, which was the most toxic solvent used in our experiments.

Analysis of dispersion mechanism in gel chromatography. II. Dispersion mechanism in gel chromatography of proteins.

The dispersion mechanism in gel chromatography of proteins was quantitatively studied on the basis of a dispersion model which gave consideration to the contribution of gel phase diffusion and longitudinal dispersion in a column. Particularly, the effect of gel phase diffusion was examined in detail by comparing the values determined by applying the moment analysis to the elution curve and those obtained for a single gel bead.When the distribution coefficient of solute was small and the particle size of gel was large, the elution curve was asymmetrical and had a prolonged tail of low concentration. The gel phase diffusion coefficient determined from the elution curve was much higher than that for a single gel bead owing to the effect of the tail. This suggested that only a small portion near the gel bead surface was accessible to most of the solute applied owing to the much lower diffusion velocity in gel than the superficial velocity. The column efficiency improved as compared with the theoretical result...