Microencapsulation within crosslinked polyethyleneimine membranes

Preparation and Characterization of κ‐Carrageenan Immobilized Urease

Urease was encapsulated within kappa-carrageenan beads. Various parameters, such as amount of kappa-carrageenan and enzyme activity, were optimized for the immobilization of urease. Immobilized urease was thoroughly characterized for pH, temperature, and storage stabilities and these properties were compared with the free enzyme. The free urease activity quickly decreased and the half time of the activity decay was about 3 days at 4 degrees C. The immobilized urease remained very active over a long period of time and this enzyme lost about 70.43% of its orginal activity over the period of 26 days for storage at 4 degrees C. The Michaelis constant (Km) and maximum reaction velocity (Vmax) were calculated from Lineweaver-Burk plots for both free and immobilized enzyme systems. Vmax = 227.3 U/mg protein, Km = 65.6 mM for free urease and Vmax = 153.9 U/mg protein, Km = 96.42 mM for immobilized urease showed a moderate decrease of enzyme specific activity and change of substrate affinity.

Interfacial Polymerization within a Simplified Microfluidic Device: Capturing Capsules

A simple approach to a microfluidic device is described. The device is composed of flexible tubing and a needle inserted orthogonal to the long axis of the tubing. This design is well suited to creating oil-water interfaces allowing the formation of laminar flows and monodisperse emulsions. The system is characterized by mapping the phases observed as a function of organic phase flow and Reynolds number. In addition, the device allows interfacial polymerization reactions to capture low coefficient of variation capsules. The shell structure and surface are examined by scanning electron microscopy.

Hemolysate-filled polyethyleneimine and polyurea microcapsules as potential red blood cell substitutes: effect of aqueous monomer type on properties of the prepared microcapsules

In this paper, we describe the synthesis and characterization of rabbit hemolysate-filled polyethyleneimine (PEI)- or polyurea (PU)-type artificial red blood cells (ARBCs) with different membrane compositions. These microcapsules were prepared by making use of the interfacial polymerization (IP) reaction between the water-soluble amine monomers (triethylamine (TEA), ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGATA), diethylenetriamine (DETA), tetramethyl diaminomethane (TMDAM), piperazine hexahydrate (PPHH), l-lysine monohydrochloride (LLMH) or PEI) and 2,4-toluylene diisocyanate (TDI) as an oil-soluble shell monomer. The resultant microcapsules were spherical and with mean diameters of 8.71-63.33 microm. Microcapsules having sulfonic acid groups on their surfaces were prepared by using a combination of the functional amines (DETA, LLMH or PEI) and 4,4'-diaminostilbene-2,2'-disulfonic acid (DASSA). Oxygen-binding abilities of the ARBCs were measured by a Clark-type oxygen electrode. The obtained results revealed that the highest oxygen-binding abilities were obtained with the PU-ARBCs prepared with DETA alone or in combination with EGATA. Unfortunately, these microcapsules exhibited large diameters and wider size distribution curves (span values (S) = 1.3, 1.7, geometric standard deviation sigma(g) = 1.85, 2.18, respectively). However, the novel ARBCs (sulfonated PU-PEI graft copolymer membrane microcapsules (SPU/PEI-ARBCs)) prepared had good oxygen affinity, the smallest mean diameter (d = 8.71 microm) and the best distribution (S = 0.9, sigma(g) = 1.48) and a flow behavior identical to rabbit RBCs. Therefore, these unique microcapsules can be recommended for scale-up considerations as a promising blood substitute.

Effect of media composition on long-term in vitro stability of barium alginate and polyacrylic acid multilayer microcapsules

For a number of applications stability of microcapsules is a critical factor. Since the maintenance of polyelectrolyte complexes depends considerably on the ion composition we tested the physical properties of barium alginate capsules and searched for conditions to improve stability by a multilayer coating with polyethylenimine (PEI) and polyacrylic acid (PAA). Mechanical stability and diameters were determined in barium alginate capsules and compared with multilayer capsules. Multilayer coating resulted in smaller capsules than barium complexing alone. The difference was more pronounced when CaCl2 was used instead of NaCl during coating. Barium alginate capsules and application of CaCl2 during coating led to continuous pressure profiles, whereas NaCl resulted in bursting at a defined pressure, indicating the additional contribution to mechanical stability by the outer layers. After 7 d culture, mechanical stability of coated capsules decreased in RPMI and NaCl but was most pronounced in sodium citrate. The capsule diameter increased in sodium citrate, less pronounced in NaCl and was significantly different to RPMI and double distilled water. During long-term culture in RPMI, the diameter increased and mechanical stability decreased significantly. Multilayer coating improved mechanical stability which was impeded most in sodium citrate, to a lesser extent by NaCl and RPMI even after long-term exposure.

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.