Morphology and Properties of Microcapsules with Different Core Releases

The morphology, mechanical properties, and permeability of hydrogen-bonded layer-by-layer (LbL) microcapsule shells assembled on cubic CdCO₃ cores have been studied in comparison with traditional shells assembled on spherical SiO₂ cores. We observed that the morphology of LbL shells is dramatically affected by the different release processes with highly porous and softened LbL shells as a result of the intense CO₂ gas formation and ion release during the removal of cubic CdCO₃ cores. A substantial increase in porosity is reflected in a dramatic change in the mesh size of LbL shells, from 2 nm for spherical capsules to above 35 nm for cubic capsules. Shells also possess enhanced permeability with a many fold increase in diffusion coefficient for dextran molecules and enhanced softening with the elastic modulus dropping by almost an order of magnitude for cubic capsules. These dramatic changes in shell morphology, porosity, permeability, and stiffness, observed in this study for the first time, are all important for the intelligent projection of controlled loading and unloading behavior of microcontainers with different shapes and composition, a component usually overlooked in current studies

Immobilization of Recombinant <i>E. coli</i> Cells in a Bacterial Cellulose–Silk Composite Matrix To Preserve Biological Function

Strategies for the encapsulation of cells for the design of cell-based sensors require efficient immobilization procedures while preserving biological activity of the reporter cells. Here, we introduce an immobilization technique that relies upon the symbiotic relationship between two bacterial strains: cellulose-producing <i>Gluconacetobacter xylinus</i> cells; and recombinant <i>Escherichia coli</i> cells harboring recombinase-based dual-color synthetic riboswitch (RS), as a model for cell-based sensor. Following sequential coculturing of recombinant cells in the cellulose matrix, final immobilization of <i>E. coli</i> cells was completed after reconstituted silk fibroin (SF) protein was added to a “living membrane” generating the composite bacterial cellulose-silk fibroin (BC-SF) scaffold. By controlling incubation parameters for both types of cells, as well as the conformations in SF secondary structure, a variety of robust composite scaffolds were prepared ranging from opaque to transparent. The properties of the scaffolds were compared in terms of porosity, water capacity, distribution of recombinant cells within the scaffolds matrix, onset of cells activation, and ability to protect recombinant function of cells against UV irradiation. The closer-fitted microstructure of transparent BC-SF scaffolds resulted in leakage-free encapsulation of recombinant cells with preserved RS function because of a combination of several parameters that closely matched properties of a biofilm environment. Along with proper elasticity, fine porosity, capacity to retain the water, and ability of SF to absorb UV light, the composite hydrogel material provided necessary conditions to form confined cell colonies that modified cell metabolism and enhanced cell resilience to the stresses induced by encapsulation

Silk Macromolecules with Amino Acid–Poly(Ethylene Glycol) Grafts for Controlling Layer-by-Layer Encapsulation and Aggregation of Recombinant Bacterial Cells

This study introduces double-brush designs of functionalized silk polyelectrolytes based upon regenerated silk fibroin (SF), which is modified with poly-l-lysine (SF-PLL), poly-l-glutamic acid (SF-PGA), and poly(ethylene glycol) (PEG) side chains with different grafting architecture and variable amino acid-PEG graft composition for cell encapsulation. The molecular weight of poly amino acids (length of side chains), molecular weight and degree of PEG grafting (<i>D</i>) were varied in order to assess the formation of cytocompatible and robust layer-by-layer (LbL) shells on two types of bacterial cells (Gram-negative and Gram-positive bacteria). We observed that shells assembled with charged polycationic amino acids adversely effected the properties of microbial cells while promoting the formation of large cell aggregates. In contrast, hydrogen-bonded shells with high PEG grafting density were the most cytocompatible, while promoting formation of stable colloidal suspensions of individual cell encapsulates. The stability to degradation of silk shells (under standard cell incubation procedure) was related to the intrinsic properties of thermodynamic bonding forces, with shells based on electrostatic interactions having stronger resistance to deterioration compared to pure hydrogen-bonded silk shells. By optimizing the charge density of silk polyelectrolytes brushes, as well as the length and the degree of PEG side grafts, robust and cytocompatible cell coatings were engineered that can control aggregation of cells for biosensor devices and other potential biomedical applications