Loading Capacity versus Enzyme Activity in Anisotropic and Spherical Calcium Carbonate Microparticles Senem Donatan, †,# Alexey Yashchenok,* ,†,∥,# Nazimuddin Khan, ‡,# Bogdan Parakhonskiy,* ,§,∥,⊥,# Melissa Cocquyt, ⊥ Bat-El Pinchasik, †,∇ Dmitry Khalenkow, ⊥ Helmuth Mö hwald, † Manfred Konrad, ‡ and Andre Skirtach †,⊥ † Department of Interfaces, Max Planck Institute of Colloids and Interfaces, Golm/Potsdam D-14476, Germany ‡ Enzyme Biochemistry Group, Max Planck Institute for Biophysical Chemistry, Gö ttingen D-37077, Germany § A.V. Shubnikov Institute of Crystallography RAS, 119333 Moscow, Russia ∥ Remote Controlled Theranostic Systems Lab, Institute of Nanostructres and Biosystems, Saratov State University, 410012 Saratov, Russia ⊥ Department of Molecular Biotechnology, NB-Photonics Group, Ghent University, Ghent 9000, Belgium ∇ Department of Physics at Interfaces, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany * S Supporting Information ABSTRACT: A new method of fabrication of calcium carbonate microparticles of ellipsoidal, rhomboidal, and spherical geometries is reported by adjusting the relative concentration ratios of the initial salt solutions and/or the ethylene glycol content in the reaction medium. Morphology, porosity, crystallinity, and loading capacity of synthesized CaCO 3 templates were characterized in detail. Particles harboring dextran or the enzyme guanylate kinase were obtained through encapsulation of these macromolecules using the layer-by-layer assembly technique to deposit positively and negatively charged polymers on these differently shaped CaCO 3 templates and were characterized by confocal laser scanning fluorescence microscopy, fluorometric techniques, and enzyme activity measurements. The enzymatic activity, an important application of such porous particles and containers, has been analyzed in comparison with the loading capacity and geometry. Our results reveal that the particles’ shape influences morphology of particles and that, as a result, affects the activity of the encapsulated enzymes, in addition to the earlier reported influence on cellular uptake. These particles are promising candidates for efficient drug delivery due to their relatively high loading capacity, biocompatibility, and easy fabrication and handling. KEYWORDS: vaterite, enzyme, calcium carbonate, polyelectrolyte, enzyme-catalyzed reaction ■ INTRODUCTION A promising strategy to enhance the cellular targeting efficacy in drug delivery systems is mimicking the biological behavior, 1 which is often related to shape-specific, anisotropic, and noncovalent interactions between biological molecules. 2 In addition, the delivery of biomolecules can be enhanced by choosing a delivery vehicle of a desired geometry. Therefore, development of nonspherical carriers with elongated, filamen- tous morphologies, 3 or anisotropic delivery systems 4−8 is regarded as an essential advance due, in part, to more effective cellular targeting 9,10 and uptake. 11 Alteration of biological responses was reported for particles with similar compositions, but with different geometries 12−14 entering the biodistribution pathways. 15−17 Not only were capsules produced by various anisotropic shapes but they were also shown to change shape in the case of hydrogel-based containers. 13,18,19 Inhalation is viewed as a particularly important area of medical application of anisotropic particles because of their favorable hydrodynamic properties. The shape has also been identified to play a major role in the uptake of drug carriers into cells. 20 Capsules with cubical, 21,22 semispherical, 22 and elliptical 23 shapes showed a relatively high penetration rate in cells in comparison with spherical capsules produced from the same material. For example, red blood cells elongate upon passing through small vessels or capillaries. But in the case of particles or even capsules, extensive compressibility is not possible. This prompts development of different anisotropic carriers. To date, anisotropic particles and carriers have been assembled by different methods, 24−28 whereas fabrication of anisotropic calcium carbonate particles through controlling the ratio of salts also has been reported. 23,29 Such different anisotropic shapes of drug delivery carriers were shown to facilitate cell uptake, 37,25 i.e., the uptake of capsules by cells depended on the aspect ratio of particles and capsules. Received: March 23, 2016 Accepted: May 11, 2016 Published: May 11, 2016 Research Article www.acsami.org © 2016 American Chemical Society 14284 DOI: 10.1021/acsami.6b03492 ACS Appl. Mater. Interfaces 2016, 8, 14284−14292