Microencapsulation limitations

Polyamide, collodion (cellulose nitrate), ethylcellulose, cellulose acetate butyrate or silicone polymers have been used for preparation of permanent microcapsules. This method offers a double specificity due to the presence of both the enzyme and a semipermeable membrane. Moreover, it allows simultaneous immobilization of many enzymes in a single step and the surface area for contacting the substrate and the catalyst is large. The need of high protein concentration and the restriction to low molecular weight substrates are the main limitations of enzyme microencapsulation. 

Abstract. Microencapsulation is widely use in industry but remains relatively unknown from the public. The reason is that microcapsules are not an end-product, but generally a technique to overcome process limitations. Microencapsulation allows immobilization, protection, release and functionalisation of active ingredients. Despite the high diversity of methods, this paper proposes a classification and description of the main technologies to produce microcapsules. 

Evangelou, V. P. 1995b. Pyrite Oxidation and its Control. Acid Mine Drainage, Surface Chemistry, Molecular Oxidation Mechanisms, Microbial Role, Kinetics, Control, Ameliorates, Limitations, Microencapsulation. CRC/Lewis Press, Boca Raton, FL. 

Transplantation of islets of Langerhans as a means of treating insulin-dependent diabetes mellitus has become an important field of interest [217-219]. However, tissue rejection and relapse of the initial autoimmune process have limited the success of this treatment. Immunoisolation of islets in semipermeable microcapsules has been proposed to prevent their immune destruction [220, 221]. Nevertheless, a pericapsular cellular reaction eventually develops around micro-encapsulated islets, inducing graft failure [222]. Since empty microcapsules elicit a similar reaction [223], the reaction is not related to the presence of islets within the capsule but is, at least partially, caused by the capsule itself. Consequently, microcapsule biocompatibility appears to constitute a major impediment to the successful microencapsulated islet transplantation. 

As mentioned in Section 17.3.1, retention of quadrivalent actinide oxides within the phosphate matrix is not a major issue because these oxides are insoluble in water, and all that is needed is their microencapsulation by the phosphate components of the matrix. This was demonstrated in a number of studies on UO2 and PUO2 and their surrogate Ce02. If the actinides are found in a trace amount in the waste, their chemical form is not so important because the phosphate matrix immobilizes them very efiectively. For example, the wastewater in the case study given in Section 16.3.2.2 contained 32 pCi/ml of and 0.6 pCi/ml of The ANS 16.1 tests conducted on the waste forms with 18.6pCi/g loading of combined U in the waste form showed that the leaching index was 14.52. XCLP tests also showed that levels in the leachate were below the detection limit of 0.2 pCi/ml. This implies that microencapsulation of trace-level U is very efiective in the Ceramicrete matrix. 

Encapsulated delivery systems are developed with a specific purpose for each target application. To date, most research has been directed at stabilizing extracted bioactives and delivering the required levels in food. Their ultimate delivery to a target site depends on the core, the material and the methods used for encapsulation as well as the food vehicle used for delivery. Although there have been many technological advances there are still limitations to the use of microencapsulated ingredients in some applications. 

Despite the extensive use of PLGA polymers in the microencapsulation arena, it has been found through decades of research that the PLGA microparticle systems are not universally suited for different applications. One of the limitations in the prevalent PLGA systems is that bulk hydrolysis of the polymer induces acidification of microenvironment of the microparticles, which can be detrimental to various payloads such as proteins and nucleic acids. In addition, their drug release kinetics are not readily tunable and, thus, are inappropriate for specific applications.f ... 

Rapid expansion of supercritical solutions (RESS) processing is used to prepare microspheres. Microencapsulation takes place when a pressurized supercritical solvent containing the shell material and the active ingredient is released through a small nozzle the abrupt pressure drop causes the desolvation of the shell material and the formation of a coating layer around the active ingredient (74). A prerequisite for this technology is that the compounds effectively dissolve in the SCF, which limits its application. 

The search for chlorine bleach alternatives as well as development of technologies for stabilizing peroxide bleaches will continue. Microencapsulation technology for formulating LADDs containing chlorine bleaches has shown limited success [150,151,155,159],... 

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