Study On The Biomimetic Preparation Of Polydopamine-Titanium Hybrid Microcapsules And Their Applications For Enzyme Immobilization

Microcapsules, a unique hollow structure, have been widely exploited in a varietyof fields, including medicine, food, dyes and others. The organic capsules usuallyexhibit multifunctional and tunable properties, but poor mechanical strength. Incomparison, inorganic capsules have the superior mechanical strength, whereas therigidity and inertness often restrict their broad applicability. Hybrid microcapsulesintegrates the advantages of organic materials (multi-functional, etc.) and inorganicmaterials (high strength, etc.). Hybrid microcapsules can control the interactionbetween the organic component and inorganic component (hydrogen bonding,covalent bonding, coordinate bonding, etc.), create hierarchical structures andintegrate multiple functionalities.Inspired by the existence form and the formation process of natural organicmaterials and inorganic materials, we put forward to the strategy of preparing hybridmicrocapsules. In this study, different organic-inorganic hybrid microcapsules weredesigned by synergy of bioadhesion and biomineralization, and then used as enzymeimmobilization carriers. In this study, the adhesion layer was formed throughbioadhesion and Michael addition reaction on CaCO3(PSS) template surface, thentitania induced by the inducer which grafted onto the adhesion layer to formbiomineral layer. Finally, the hybrid microcapsules were acquired after the removal oftemplates. In this study, three kind of hybrid microcapsules are fabricated by changingthe type of inducer, the bioadhesion and Michael addition reaction in two steps or inone step. The wall of hybrid microcapsules consisted of two layers: organic layer(adhesion layer) and inorganic layer (biomineral layer). The adhesion layer wasformed through rapid oxidative self-polymerization of dopamine and Michael additionreaction of the inducer with catechol groups of dopamine; the biomineral layer wasformed through hydrolysis and condensation of titanium precursor.Firstly, in the process of fabrication hybrid microcapsules, the bioadhesion andMichael addition reaction were accomplished in two steps. Cysteamine was graftedonto the PDA layer to conferring the adhesion layer with mineralization-inducingcapability. The PDA-CYS-Ti microcapsules acquired much higher mechanicalstability than pure PDA microcapsules. Catalase (CAT) was physically encapsulated in the microcapsule lumen. The immobilization efficiency of CAT in thePDA-CYS-Ti microcapsules was93%, and the specific activity was16U/mg. Theimmobilized CAT exhibited good pH stability at pH7.0-9.0.Secondly, in the process of fabrication PDA-PEI-Ti hybrid microcapsules, thebioadhesion and Michael addition reaction were also accomplished in two steps.Polyethyleneimine, which was covalently attached to PDA layer by reaction betweencatechol group and amino group, conferred the adhesion layer withmineralization-inducing capability. The structures (thickness, etc.) of the hybridmicrocapsules could be tuned by varying the molecular weight and concentration ofPEI and other factors. CAT was encapsulated in the PDA-PEI-Ti microcapsules. Theimmobilization efficiency of CAT in the PDA-PEI-Ti microcapsules was94%, andthe specific activity was70U/mg. The immobilized CAT exhibited good pH stabilityat pH6.0-9.0.Thirdly, in the process of fabrication PDA/PEI-Ti microcapsules, the bioadhesionand Michael addition reaction were accomplished in one step. Dopamine andpolyethyleneimine were covalently linked before adhension on the surface of CaCO3template, simultaneously, conferred the adhesion layer with mineralization-inducingcapability. The structures (thickness, etc.) of the hybrid microcapsules could be tunedby varying the molecular weight of PEI and molar ratio of dopamine/PEI. Theimmobilization efficiency of CAT in the PDA/PEI-Ti microcapsules was86%, andthe specific activity was211U/mg. The immobilized CAT exhibited good pHstability at pH4.0-10.0.