PubMed Health⌕ Search

Biomedical subjects

R J Neufeld

Publications and source records attributed to R J Neufeld.

At least 19 recordsLinked to original sources
PubMed1999

Microencapsulation of lipophilic drugs in chitosan-coated alginate microspheres.

Chitosan-coated alginate microspheres containing a lipophilic marker dissolved in an edible oil, were prepared by emulsification/internal gelation and the potential use as an oral controlled release system investigated. Microsphere formation involved dispersing a lipophilic marker dissolved in soybean oil into an alginate solution containing insoluble calcium carbonate microcrystals. The dispersion was then emulsified in silicone oil to form an O/W/O multiple phase emulsion. Addition of an oil soluble acid released calcium from carbonate complex for gelation of the alginate. Chitosan was then applied as a membrane coat to increase the mechanical strength and stabilize the microspheres in simulated intestinal media. Parameters studied included encapsulation yield, alginate concentration, chitosan molecular weight and membrane formation time. Mean diameters ranging from 500 to 800 micron and encapsulation yields ranging from 60 to 80% were obtained. Minimal marker release was observed under simulated gastric conditions, and rapid release was triggered by transfer into simulated intestinal fluid. Higher overall levels of release were obtained with uncoated microspheres, possibly due to binding of marker to the chitosan membrane coat. However the slower rate of release from coated microspheres was felt better suited as a delivery vehicle for oil soluble drugs.

Alginates↗
PubMed1999

Electrophoretic extraction and analysis of DNA from chitosan or poly-L-lysine-coated alginate beads.

Alginate beads containing entrapped DNA were produced using both external and internal calcium sources, and coated with chitosan or poly-L-lysine membranes. The beads were assayed with DNase nuclease to determine formulation conditions offering the highest level of DNA protection from nucleic acid hydrolysis, simulating gastrointestinal exposure. A method was developed to extract and assay intracapsular DNA through a modified agarose electrophoresis system. Both external and internally gelled beads were permeable to DNase (Mw = 31 kDa), indicated by the absence of DNA after nuclease exposure. At low levels of DNase exposure, coated high guluronic content alginate beads offered a higher level of DNA protection compared with coated beads with low guluronic alginate. No apparent correlation was found with chitosan membrane molecular weight and degree of deacetylation; however, increasing poly-L-lysine molecular weight appeared to increase DNase exclusion from beads. At elevated levels of DNase exposure, DNA hydrolysis was evident within all coated beads with the exception of those coated with the highest molecular weight poly-L-lysine (Mw = 197.1 kDa), which provided almost total nuclease protection. Optimal combination then for DNA protection from nucleases is a high guluronic alginate core, coated with high molecular weight poly-L-lysine.

Journal Article↗
PubMed1998

DNA protection from extracapsular nucleases, within chitosan- or poly-L-lysine-coated alginate beads.

DNA was immobilized within alginate matrix using an external or an internal calcium source, and then membrane coated with chitosan or poly-L-lysine. Membrane thickness increased with decreasing polymer molecular weight and increasing degree of deacetylation (chitosan). Beads were exposed to a 31,000 molecular weight nuclease to determine the levels of DNA protection offered by different membrane and matrix combinations. Almost total hydrolysis of DNA was observed in alginate beads following nuclease exposure. Less than 1% of total double-stranded DNA remained unhydrolyzed within chitosan- or poly-L-lysine-coated beads, corresponding with an increase in DNA residuals (i.e. double- and single-stranded DNA, polynucleotides, bases). Chitosan membranes did not offer sufficient DNA protection from DNase diffusion since all of the double-stranded DNA was hydrolyzed after 40 min of exposure. Both chitosan and poly-L-lysine membranes reduced the permeability of alginate beads, shown by enhanced retention of DNA residuals after DNase exposure. The highest level of DNA protection within freshly prepared beads was obtained with high molecular weight (197,100) poly-L-lysine membranes coated on beads formed using an external calcium source, where over 80% of the double-stranded DNA remained after 40 min of DNase exposure. Lyophilization and rehydration of DNA beads also reduced permeability to nucleases, resulted in DS-DNA recoveries of 60% for chitosan-coated, 90% for poly-L-lysine-coated, and 95% for uncoated alginate beads.

Alginates↗
PubMed1998

External versus internal source of calcium during the gelation of alginate beads for DNA encapsulation.

Alginate gels produced by an external or internal gelation technique were studied so as to determine the optimal bead matrix within which DNA can be immobilized for in vivo application. Alginates were characterized for guluronic/mannuronic acid (G/M) content and average molecular weight using 1H-NMR and LALLS analysis, respectively. Nonhomogeneous calcium, alginate, and DNA distributions were found within gels made by the external gelation method because of the external calcium source used. In contrast, the internal gelation method produces more uniform gels. Sodium was determined to exchange for calcium ions at a ratio of 2:1 and the levels of calcium complexation with alginate appears related to bead strength and integrity. The encapsulation yield of double-stranded DNA was over 97% and 80%, respectively, for beads formed using external and internal calcium gelation methods, regardless of the composition of alginate. Homogeneous gels formed by internal gelation absorbed half as much DNAse as compared with heterogeneous gels formed by external gelation. Testing of bead weight changes during formation, storage, and simulated gastrointestinal (GI) conditions (pH 1.2 and 7.0) showed that high alginate concentration, high G content, and homogeneous gels (internal gelation) result in the lowest bead shrinkage and alginate leakage. These characteristics appear best suited for stabilizing DNA during GI transit.

Alginates↗
PubMed1995

Blood urea clearance with microencapsulated urease.

The response of a kidney patient to treatment using a microencapsulated urease artificial kidney (MUAK) system was modelled. The model was used to simulate the patient's response and reactor performance for an initial blood urea concentration of 10 mM and a MUAK void volume of 0.5. The performance of the reactor was strongly dependent on the enzyme activity. An optimal activity of 10 mM sec-1 was achieved in the analysis. After operation for 4 h at a flow rate of 200 ml min-1, the reduction in blood urea concentration for reactor dimensions of 2 x 10 cm, 2 x 20 cm, 4 x 10 cm and 4 x 20 cm were 38%, 52%, 60% and 62%, respectively. The effect of flow rate on the performance of urea removal was studied using the reactor dimensions of 4 x 10 cm (optimal design). The results for flow rates of 100, 200, 300 and 400 ml min-1 predicted blood urea reductions of 38, 60, 70 and 76%, respectively. Although, the conversion of urea in the reactor decreased from 100% to 96% for the respective flows of 100 to 400 ml min-1, the high turnover of reactor volume at a higher flow rate was responsible for the improved reduction of the patient's blood urea level. The model has the ability to predict the performance of the MUAK and the patient's blood urea level simultaneously, at various operating conditions.

Humans↗
PubMed1995

Microencapsulation of DNA within alginate microspheres and crosslinked chitosan membranes for in vivo application.

Calf thymus DNA was microencapsulated within crosslinked chitosan membranes, or immobilized within chitosan-coated alginate microspheres. Microcapsules were prepared by interfacial polymerization of chitosan, and alginate microspheres formed by emulsification/internal gelation. Diameters ranged from 20 to 500 microns, depending on the formulation conditions. Encapsulated DNA was quantified in situ by direct spectrophotometry (260 nm) and ethidium bromide fluorimetry, and compared to DNA measurements on the fractions following disruption and dissolution of the microspheres. Approximately 84% of the DNA was released upon core dissolution and membrane disruption, with 12% membrane bound. The yield of encapsulation was 96%. Leakage of DNA from intact microspheres/capsules was not observed. DNA microcapsules and microspheres were recovered intact from rat feces following gavage and gastrointestinal transit. Higher recoveries (60%) and reduced shrinkage during transit were obtained with the alginate microspheres. DNA was recovered and purified from the microcapsules and microspheres by chromatography and differential precipitation with ethanol. This is the first report of microcapsules or microspheres containing biologically active material (DNA) being passed through the gastrointestinal tract, with the potential for substantial recovery.

Animals↗
PubMed1995

Performance features for urea hydrolysis in a CSTR with microencapsulated urease.

The factors which influence the steady state performance of a CSTR operation with microencapsulated urease for the regeneration of a dialysated solution have been studied at various enzyme activities. The theoretical model considered the effect of microcapsule diameter, pH-dependent kinetics, and product inhibition and substrate depletion, in relation to urea conversion and the capsule effectiveness factor. The limiting effects of pH, product inhibition and substrate depletion were also studied individually and in combination under eight case studies. The base case which included these three limiting factors in the reaction process, predicted the lowest urea conversion values at the enzyme activities considered. However, the effectiveness factor for each case at a fixed microcapsule diameter depended on the enzyme activity. This behaviour was studied for two different microcapsule diameters, 5 microns and 500 microns. At enzyme activities lower than 1 mM/s, a model considering Michaelis-Menten kinetics alone, predicted the highest effectiveness factors. On the other hand, beyond 1 mM/s enzyme activity, the lowest effectiveness factors were predicted, although higher conversions than that of the base case were achieved. This might be due to the rapid depletion of substrate at high activities when Michaelis-Menten kinetics were considered, leads to residual substrate concentrations (Sr) lower than the Michaelis-Menten constant Km,o; a condition for a dramatic drop in the intraparticle reaction rate. The limiting factors in the base case held Sr at a relatively higher value than Km,o.

Dialysis Solutions↗
PubMed1994

Immobilization of cells for application in the food industry.

Immobilization of cells offers advantages to the food process industries, including enhanced fermentation productivity and cell stability and reduced downstream processing costs due to facilitated cell recovery and recycle. This article summarizes the varied immobilization methodologies, including adsorption, entrapment, covalent binding, and microencapsulation. Examples of interest to the food industry are provided, together with a review of the physiological effects of immobilization. Topics in process engineering include immobilized cell bioreactor configurations and the scale-up potential of the various immobilization techniques.

Fermentation↗
PubMed1992

Production of alginate beads by emulsification/internal gelation. I. Methodology.

Small diameter alginate beads (microspheres) were formed via internal gelation of alginate solution emulsified within vegetable oil. Gelation was initiated by addition of an oil-soluble acid thereby reducing the pH of the alginate solution and releasing soluble Ca2+ from the citrate complex. Smooth, spherical, micron-sized beads were formed. The mean diameter ranged from 200 to 1000 microns, controlled by the reactor impeller design and rotational speed. The technique has potential for large-scale and continuous applications in immobilization.

Alginates↗
PubMed1992

Lactococcus lactis release from calcium alginate beads.

Cell release during milk fermentation by Lactococcus lactis immobilized in calcium alginate beads was examined. Numbers of free cells in the milk gradually increased from 1 x 10(6) to 3 x 10(7) CFU/ml upon successive reutilization of the beads. Rinsing the beads between fermentations did not influence the numbers of free cells in the milk. Cell release was not affected by initial cell density within the beads or by alginate concentration, although higher acidification rates were achieved with increased cell loading. Coating alginate beads with poly-L-lysine (PLL) did not significantly reduce the release of cells during five consecutive fermentations. A double coating of PLL and alginate reduced cell release by a factor of approximately 50. However, acidification of milk with beads having the PLL-alginate coating was slower than that with uncoated beads. Immersing the beads in ethanol to kill cells on the periphery reduced cell release, but acidification activity was maintained. Dipping the beads in aluminum nitrate or a hot CaCl2 solution was not as effective as dipping them in ethanol. Ethanol treatment or heating of the beads appears to be a promising method for maintaining acidification activity while minimizing viable cell release due to loosely entrapped cells near the surface of the alginate beads.

Alginates↗
PubMed1991

Evaluation of a new turbidimeter design incorporating a microprocessor-controlled variable pathlength cuvette.

A microprocessor-controlled, variable pathlength turbidimeter was designed, constructed, and its operation verified and accuracy determined using formazin as a turbidity standard. The turbidimeter was also characterized with the fermentation broths of Saccharomyces cerevisiae and Escherichia coli. The range of turbidities quantified using the instrument spanned from 70 to 1,000 Nephlometric Turbidity Units, with a measurement accuracy between 2% and 11% of the instrument's full-scale reading. The precision of the instrument was determined to be 0.077%. The turbidimeter was used to continuously monitor the biomass concentration of an Escherichia coli fermentation and provided instantaneous concentration estimates which corresponded with gravimetrically determined biomass concentrations to within 12%.

Equipment Design↗
PubMed1991

Activity and distribution of urease following microencapsulation within polyamide membranes.

Urease was microencapsulated by forming a semipermeable polyamide membrane around aqueous microdroplets (266 microns mean diameter) containing the soluble enzyme. The yield of the interfacial polymerization technique, determined spectrophotometrically, was 83% of the original enzyme on a mass basis, resulting in a final intracapsular urease concentration of 62.3 mg ml-1 or 0.1 mM. Similar absorption spectra of broken and intact microcapsules suggested that spectrophotometry may be applied in performing direct studies on the intact microcapsules. The high activity yield of urease microcapsules relative to the mass of entrapped enzyme (92.5%) indicated minimal effects of mass transfer limitation. The mass of active urease incorporated into the nylon membrane represented 6% of the encapsulated enzyme activity. The soluble intracapsular enzyme fraction (94%) was released into solution upon rupture of the membrane. A complete mass and activity balance of the encapsulated enzyme was achieved.

Capsules↗
PubMed1988

The mannoprotein of Saccharomyces cerevisiae is an effective bioemulsifier.

The mannoprotein which is a major component of the cell wall of Saccharomyces cerevisiae is an effective bioemulsifier. Mannoprotein emulsifier was extracted in a high yield from whole cells of fresh bakers' yeast by two methods, by autoclaving in neutral citrate buffer and by digestion with Zymolase (Miles Laboratories; Toronto, Ontario, Canada), a beta-1,3-glucanase. Heat-extracted emulsifier was purified by ultrafiltration and contained approximately 44% carbohydrate (mannose) and 17% protein. Treatment of the emulsifier with protease eliminated emulsification. Kerosene-in-water emulsions were stabilized over a broad range of conditions, from pH 2 to 11, with up to 5% sodium chloride or up to 50% ethanol in the aqueous phase. In the presence of a low concentration of various solutes, emulsions were stable to three cycles of freezing and thawing. An emulsifying agent was extracted from each species or strain of yeast tested, including 13 species of genera other than Saccharomyces. Spent yeast from the manufacture of beer and wine was demonstrated to be a possible source for the large-scale production of this bioemulsifier.

Emulsions↗
PubMed1984

Uptake of Metal Ions by Rhizopus arrhizus Biomass.

Rhizopus arrhizus biomass was found to absorb a variety of different metal cations and anions but did not absorb alkali metal ions. The amount of uptake of the cations was directly related to ionic radii of La, Mn, Cu, Zn, Cd, Ba, Hg, Pb, UO(2), and Ag. The uptake of all the cations is consistent with absorption of the metals by sites in the biomass containing phosphate, carboxylate, and other functional groups. The uptake of the molybdate and vanadate anions was strongly pH dependent, and it is proposed that the uptake mechanism involves electrostatic attraction to positively charged functional groups.

Journal Article↗
PubMed1980

Cell surface measurements in hydrocarbon and carbohydrate fermentations.

Acinetobacter calcoaceticus was grown in 11-liter batch fermentations with hexadecane or sodium citrate as the sole source of carbon. Surface and interfacial tension measurements of the microbial broth indicated that surface-active compounds were being produced only during growth on the hydrocarbon substrate. Contact angle measurements of an aqueous drop on a smooth lawn of cells in a hexadecane bath indicated a highly hydrophobic surface of the cells in the initial stages of the hydrocarbon fermentation (120 degrees contact angle). At this stage, the entire cell population was bound to the hydrocarbon-aqueous interface. The contact angle dropped rapidly to approximately 45 degrees after 14 h into the fermentation. This coincided with a shift of the cell population to the aqueous phase. Thus, the cells demonstrated more hydrophilic characteristics in the later stages of the fermentation. Contact angles on cells grown on sodium citrate ranged from 18 to 24 degrees throughout the fermentation. The cells appear to be highly hydrophilic during growth on a soluble substrate. From the contact angle and aqueous-hydrocarbon interfacial tension, the surface free energy of the cells was calculated along with the cell-aqueous and cell-hydrocarbon interfacial tension. The results of these measurements were useful in quantitatively evaluating the hydrophobic nature of the cell surface during growth on hydrocarbons and comparing it with the hydrophilic nature of the cell surface during growth on a soluble substrate.

Journal Article↗
PubMedDate not supplied

Kinetics and activity distribution of urease coencapsulated with hemoglobin within polyamide membranes.

A 91.5% mass yield of urease and hemoglobin (Hb), co-encapsulated within polyamide membranes, was determined spectrophotometrically. The specific activity yield of microencapsulation was 84%, twofold higher than values previously reported, as a result of optimization of encapsulation conditions. The kinetic parameters and pH activity profiles of intracapsular urease were determined to be similar to those corresponding to the free enzyme. Similar activities were also observed for intact and microcapsule homogenate, indicating minimal mass transfer and diffusional limitation. The active configuration of the enzyme appears to remain intact upon microencapsulation. The application of a kinetic model for encapsulated urease further indicated that the kinetics were reaction-controlled with minimal mass transfer restrictions.

Capsules↗