We report on the encapsulation of enzyme (catalase) by the controlled polymer multilayer coating of
biocrystals, achieved by the sequential adsorption of oppositely charged polyelectrolytes onto enzyme
crystal templates. An extremely high enzyme loading in each polymer capsule is obtained, and the activity
of the encapsulated enzyme is preserved. The polymer-encapsulated enzyme is stable against protease
degradation: The polymer-coated enzyme retains 100% of its activity after incubation for 100 min with
protease, whereas uncoated, solubilized catalase loses more than 90% of its initial activity within 100 min
under the same conditions. This simple, general, and versatile approach can potentially be applied for the
encapsulation of various crystallized substances for catalysis and drug delivery applications.
Two uncharged microcrystalline substances, pyrene (PYR) and fluorescein diacetate (FDA), were rendered
water dispersible by treatment with various amphiphilic substances and subsequently encapsulated by
exposure to an alternating sequence of cationic and anionic polyelectrolytes. The amphiphilic compounds
employed to charge the microcrystals were ionic surfactants, phospholipids, and polyelectrolytes with an
amphiphilic nature. Polyelectrolyte layers were self-assembled onto the pre-charged microcrystalline
templates by means of electrostatic layer-by-layer deposition, thus forming a multilayered polymeric shell
around the crystalline cores. The semipermeable nature of the polymer multilayer shell was thereafter
exploited to remove the templated core by exposure to a mild organic solvent. The release behavior of
solubilized PYR and FDA from the crystalline core was examined by monitoring their fluorescence after
dissolution with ethanol. Complete removal of the core yielded hollow polymer capsules of micrometer
dimensions. The capsule porosity was found to be influenced by the amphiphile used to pre-charge the
microcrystal surface. The strategy presented is expected to be a general approach for the encapsulation
of hydrophobic, low molecular weight compounds such as drugs, as well as providing a novel and facile
pathway to the fabrication of polymer multilayered microcapsules with controlled release properties for
drug delivery.
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