Liquid-core microcapsules: A mechanism for the recovery and purification of selected molecules in different environments

Liquid-core microcapsules can be described as miniature sized particles ( 1.2 l/hr of microspheres and > 2 l/hr of liquid-core microcapsules, and this can be easily and naturally elevated to higher volumes by increasing the number of nozzles on the encapsulator. Firstly the microcapsules were used as an innovative technique (known as capsular perstraction) to recover the commonly found pharmaceutically active compounds; sulfamethoxazole, metoprolol, furosemide, carbamazepine, clofibric acid, warfarin and diclofenac from water. The approach of preparing capsules with different solvents within their cores and combining them in water, contaminated with pharmaceuticals, enabled a rapid recovery of the drugs from this sphere. In addition the uptake of warfarin was examined to assess the conditions affecting mass transfer of the molecules into the capsules. It was subsequently determined that the stagnant organic layer was the main limiting factor. This part of the study emphasized how the characteristics (size and membrane thickness) of capsules can affect the removal rate of compounds into the liquid-core and also how the rate of extraction can be simply controlled by varying these parameters during the capsule manufacturing process. In a second application, the capsular extraction technology was further developed by adopting it as an aide for the recovery and purification of the antibiotic geldanamycin from Bennett’s medium. From this work it was shown how a small quantity of capsules was capable of rapidly extracting the molecule from the culture medium. Again the limitations to mass transfer were accessed, and it was discovered that the main rate limiting step was the external resistance outside of the capsules, which can be governed by controlling the outer turbulence. In a further development the capsules showed their potential to be used as a mechanism for concentrating, purifying and enabling crystallization of the extractant, using a very simplistic and straightforward procedure, which was not destructive to the microcapsules, hence enabling their continuous re-use. Finally the capsules were applied to a real-time situation, in order to examine the feasibility of using the simple, non-toxic and sterile technology as a novel in-situ product recovery technique, to improve the production and recovery yield of geldanamycin in cultures containing the bacterium Streptomyces hygroscopicus. Implementation of this approach resulted in the rapid removal of the metabolite from an environment which was causing its break-down and seriously affecting recovery yields. Extraction enabled the molecule to be transferred into a stable and secure domain, where it was protected from external influences. This removal improved overall net production by 30% compared to fermentations containing no capsules. Most importantly however, the capsule-facilitated recovery process acted as a methodology, which enabled high recoveries (> 53%) of the fermented geldanamycin to be obtained as highly purified crystals (> 97%) using a facile, inexpensive and reproducible process, which should be easily implemented at a lab-scale or industrial-level