Capsules formation

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Teppema, J.S., Robinson, J.E. and Ruitenberg, E.J. (1973) Ultrastructural aspects of capsule formation in Trichinella spiralis infection in the rat. Parasitology 66, 291-296. 

Recently, we proposed an alternative process for encapsulating biomacromolecules within PE microcapsules. This approach involves using nanoporous particles as sacrificial templates for both enzyme immobilization and PE multilayer capsule formation (Figure 7.2, route (I)) [66,67]. Unlike previous LbL encapsulation strategies, this approach is not limited to species that undergo crystallization, and is not dependent upon adjustments in electrostatic interactions within PE microcapsules to alter shell permeability characteristics. The salient feature of this method is that it is applicable to a wide range of materials for encapsulation. 

Two methods of capsule formation were employed static beaker tests and atomizer screenings. In the beaker tests, which comprised the first phase of the screening (Step 2 of Fig. 1), a small volume of inner polymer solution was extruded from a Pasteur pipette as a droplet (nominally 2-3 mm) into a receiv-... 

Polymer Attributes to Be Considered in Capsule Formation via Polyelectrolyte Complexation... 

Polymer Composition (Inner/Outer/Co ating) Membrane Method of Type Capsule Formation Observations... 

A comparison of Tables 1 and 5 reveals the novelty of our multicomponent approach to capsule formation and permeability control. Of the existing chemistries in Table 5 only capsules 3,4, and 5 conform to our recipe (technol-... 

The liposomes did not interfere with alginate capsule formation and were retained within the finished capsules. When myoglobin (used as a model protein) was not entrapped within liposomes but was simply enclosed as "free" protein within the coated alginate beads, 60% of it diffused out of the capsule over the first two days. In contrast, delayed release was achieved with microencapsulated liposomes containing myoglobin. Very little myoglobin appeared outside the capsules until 10 days after the start of the release experiment. It required a further 12 days to reach a level of 60% and not until 50 days after the start of the experiment was 100% release achieved. (Figure 5)... 

The immediate cause of the ropy or slimy condition is the bacterial formation of gums or mucins by bacteria. Gums are the more common cause. These are probably galactans produced by fermentation of lactose. Some of the active peptonizing bacteria produce sliminess by formation of mucins, which are combinations of proteins with a carbohydrate radical. Development of sliminess is closely associated with capsule formation (Hammer 1930). 

The instructions for gelatin mass preparation direct that gelatin powder be blended with water, a plasticizer, and colorant until a uniform consistency is achieved, then heated until molten. The recommended blend time is 20 min at a temperature of 60°C + 5°. The temperature of the molten gelatin just prior to formation into a ribbon is critical too high a temperature causes the gelatin to deteriorate, and a low temperature affects flow rate. Both conditions are to be avoided for their deleterious effect on capsule formation. For these reasons,... 

Our belief is that vascularizing compounds can increase vessel growth within the encapsulation tissue surrounding a foreign body and probably improve sensor function modestly. Nonetheless, they have not been found to overcome the relentless process of collagen deposition and capsule formation caused by the foreign body reaction, which eventually blocks sensor function. In addition, they could have several major side effects. 

Goreish HH, Lewis AL, Rose S, Lloyd AW. The effect of phosphorylcholine-coated materials on the inflammatory response and fibrous capsule formation in vitro and in vivo observations. Journal of Biomedical Materials Research A 2004, 68, 1-9. 

The influence of NO in thrombogenesis, bacterial infection, angiogenesis, and the immune response suggest that its active release into the tissue surrounding a sensor may minimize the FBR. Sensor coatings that release NO could reduce the occurrence and severity of bacterial infection, minimize inflammation and collagen capsule formation, and promote the formation of new blood vessels, all of which would create a more favorable implant environment. Since NO is reactive (i.e., has a short half-life), the effects of NO would remain localized to the area from which it is released. 

One of the major problems related to the capsule formation is capsule agglomeration. It involves the irreversible or largely irreversible sticking together of microcapsules that can occur during the encapsulation process and/or during the isolation step. 

Fig. 8 Hollow capsule fabrication by the polyelectrolyte LbL self-assembly. The core is alternately coated with polycation and polyanion, followed by core dissolution and capsule formation...

Scheme 3.13 Dimeric capsule formation in a triureidocalix[6]arene.

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