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Title: Organic Phase Fabrication of Core-Shell Materials for the Encapsulation of Biomolecules
Keywords: Layer-by-Layer, core-shell materials, microencapsulation, biomolecules, capsules, self-assembly
Issue Date: 10-Aug-2010
Source: BAI JIANHAO (2010-08-10). Organic Phase Fabrication of Core-Shell Materials for the Encapsulation of Biomolecules. ScholarBank@NUS Repository.
Abstract: Encapsulation of biomolecules within microcapsules has seen tremendous progress in the biomedical field, such as in bioanalysis, bioreactor and drug delivery applications, and is a growing interest amongst researchers in the recent years. Core-shell materials, a sub-class of microcapsules, are commonly employed for the encapsulation of biomolecules due to the mechanical stability these microcapsules can provide. However, biomolecule encapsulation problems (e.g. low encapsulation efficiency, poor control on encapsulated biomolecules quantity or poor retention stability) are associated with using current aqueous phase encapsulation techniques. The use of an organic phase for fabrication of core-shell materials and encapsulation of biomolecules is rarely demonstrated. Therefore, this PhD work involves the novel organic phase fabrication of core-shell materials and encapsulation of biomolecule with high encapsulation efficiency and retention stability. Desired biomolecules are first pre-loaded into agarose microbeads fabricated via a water-in-oil emulsion technique. Following, these agarose microbeads are stabilized in anyhydrous 1-butanol by depositing amino-polystyrene microparticles along the periphery and surface of each microbead. Termed as `matrix-assisted colloidosomes (MACs)?, the surfaces of these microparticles stabilized agarose microbeads were next deposited with polymers (non-ionized polyallylamine (niPA) and poly(acrylic acid) (niPAA) ) dissolved in 1-butanol, via the Reverse-Phase LbL technique, for the fabrication of polymeric shells around each MAC core template. It was demonstrated that a high encapsulation efficiency of biomolecules could be obtained through the organic phase fabrication MAC RP-LbL core-shell materials; and with almost 100% retention stability after 7 days incubation in an aqueous dispersant. In addition, encapsulated glucose oxidase (GOx) and horseradish peroxidise (HRP) could retain their bioactivity in these MAC RP-LbL core-shell materials. Asides from microparticles, ADOGEN? 464 (a cationic surfactant) was also used to stabilize these agarose microbeads in 1-butanol. High retention stability of dextran (> 500,000 Da) was observed but poor retention stability of dextran (< 155,000 Da) was observed for agarose (core) RP-LbL (shell) microcapsules fabricated using ADOGEN? 464 and the RP-LbL technique. Remarkably, incubation of only niPA with agarose microbeads in 1-butanol (as solvent and dispersant respectively) results in a thick uniform polymeric layer forming in the peripheral matrix around each core microbead. This novel polymeric shell fabrication technique is driven by diffusion and is termed as the ?inwards deposition of concentric niPA layers? technique. Upon stabilization of these layers into shells, with a cross-linker, these core-shell materials could be stably dispersed in an aqueous phase and were demonstrated to be capable of encapsulating and retaining pre-loaded low MW FITC-dextran (4,000 Da). The retention efficiency was determined to be ~95% after a 5 days incubation period in an aqueous dispersant. Separate incubation of niPA or niPA conjugated with a dye (FITC or TRITC), inclusive of washing steps, results in the fabrication of shells consisting of distinct coloured striated layers. Permutation of the color sequence allows for encoding purposes. It was also demonstrated that the thickness could be tuned, through manipulation of niPA volume or incubation time, and would therefore allow for an agarose core-shell microcapsule encoding system with at least 2 levels of encoding. Lastly, encapsulated GOx and HRP were demonstrated to have retained their bioactivity in these unique encoded core-shell materials and further highlight the potential of utilizing the ?inwards deposition of concentric niPA layers? technique for potential multiplexing applications.
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