Olga Shchepelina

Hydrogen-bonded LbL shells for living cell surface engineering

We report on the design of cytocompatible synthetic shells from highly permeable, hydrogen-bonded multilayers for cell surface engineering with preservation of long-term cell functioning. In contrast to traditional polyelectrolyte layer-by-layer (LbL) systems, shells suggested here are based on hydrogen bonding allowing gentle cell encapsulation using non-toxic, non-ionic and biocompatible components such as poly(N-vinylpyrrolidone) (PVPON) and tannic acid (TA) which were earlier exploited on abiotic surfaces but never assembled on cell surfaces. Here, we demonstrate that these LbL shells with higher diffusion facilitate outstanding cell survivability reaching 79% in contrast to only 20% viability level achieved with ionically paired coatings. We suggest that the drastic increase in cell viability and preservation of cell functioning after coating with synthetic shell stems from the minimal exposure of the cells to toxic polycations and high shell permeability.

Silk-on-silk layer-by-layer microcapsules.

A IO N Silks are made of proteins produced naturally by silkworms and spiders and are known as biocompatible, biodegradable, and extraordinarily robust biomaterials frequently utilized in biomaterial composites. [ 1 , 2 ] The versatility of silk proteins, along with their favorable characteristics and potential for processing in aqueous solution under ambient conditions, make silk-based materials excellent candidates for biomedical applications such as drug delivery systems and scaffolds for tissue engineering. [ 3 ]

pH-Responsive Layer-by-Layer Nanoshells for Direct Regulation of Cell Activity

Saccharomyces cerevisiae yeast cells encapsulated with pH-responsive synthetic nanoshells from lightly cross-linked polymethacrylic acid showed a high viability rate of around 90%, an indication of high biocompatibility of synthetic pH-responsive shells. We demonstrated that increasing pH above the isoelectric point of the polymer shell leads to a delay in growth rate; however, it does not affect the expression of enhanced green fluorescent protein. We suggest that progressive ionization and charge accumulation within the synthetic shells evoke a structural change in the outer shells which affect the membrane transport. This change facilitates the ability to manipulate growth kinetics and functionality of the cells with the surrounding environment. We observed that hollow layer-by layer nanoshells showed a remarkable degree of reversible swelling/deswelling over a narrow pH range (pH 5.0-6.0), but their assembly directly on the cell surface resulted in the suppression of large dimensional changes. We suggest that the variation in surface charges caused by deprotonation/protonation of carboxylic groups in the nanoshells controlled cell growth and cell function, which can be utilized for external chemical control of cell-based biosensors.

Anisotropic Micro‐ and Nano‐Capsules

In this work, we introduce anisotropically shaped, ultrathin micro- and nano-capsules fabricated by layer-by-layer approach. The original cubic and tetrahedral shapes of the template particles were replicated to produce hollow capsules with well-defined edges. Introducing tannic acid as a component of LbL shells resulted in enhanced chemical stability of these hollow polymer structures under a wide pH range due to high pK(a) value. Computational studies demonstrated increased mechanical stability of the anisotropic capsules under osmotic pressure variation due to sharp edges and vertices acting as a reinforcing frame in contrast to spherical microcapsules that undergo random buckling.

Robust and Responsive Silk Ionomer Microcapsules

We demonstrate the assembly of extremely robust and pH-responsive thin shell LbL microcapsules from silk fibroin counterparts modified with poly(lysine) and poly(glutamic) acid, which are based on biocompatible silk ionomer materials in contrast with usually exploited synthetic polyelectrolytes. The microcapsules are extremely stable in an unusually wide pH range from 1.5 to 12.0 and show a remarkable degree of reversible swelling/deswelling response in dimensions, as exposed to extreme acidic and basic conditions. These changes are accompanied by reversible variations in shell permeability that can be utilized for pH-controlled loading and unloading of large macromolecules. Finally, we confirmed that these shells can be utilized to encapsulate yeast cells with a viability rate much higher than that for traditional synthetic polyelectrolytes.

Direct probing of micromechanical properties of hydrogen-bonded layer-by-layer microcapsule shells with different chemical compositions.

The mechanical properties of hydrogen-bonded layer-by-layer (LbL) microcapsule shells constructed from tannic acid (TA) and poly(vinylpyrrolidone) (PVPON) components have been studied in both the dry and swollen states. In the dry state, the value of the elastic modulus was measured to be within 0.6-0.7 GPa, which is lower than the typical elastic modulus for electrostatically assembled LbL shells. Threefold swelling of the LbL shells in water results in a significant reduction of the elastic modulus to values well below 1 MPa, which is typical value seen for highly compliant gel materials. The increase of the molecular weight of the PVPON component from 55 to 1300 kDa promotes chain entanglements and causes a stiffening of the LbL shells with a more than 2-fold increase in elastic modulus value. Moreover, adding a polyethylenimine prime layer to the LbL shell affects the growth of hydrogen-bonded multilayers which consequently results in dramatically stiffer, thicker, and rougher LbL shells with the elastic modulus increasing by more than an order of magnitude, up to 4.3 MPa. An alternation of the elastic properties of very compliant hydrogen-bonded shells by variation of molecular weight is a characteristic feature of weakly bonded LbL shells. Such an ability to alter the elastic modulus in a wide range is critically important for the design of highly compliant microcapsules with tunable mechanical stability, loading ability, and permeability.

Replication of anisotropic dispersed particulates and complex continuous templates

Anisotropic nano-, micro- and mesoscale natural and synthetic structures possess a unique combination of physical properties due to a complex balance of steric factors and intermolecular interactions at multiple length scales. Utilizing such structures as templates for conformal replication allows reproduction of their unique shapes and properties into different synthetic materials. This review is devoted to the recent progress made on anisotropic microstructures suitable as sacrificial templates as well as techniques currently used for their precise replication into various materials. We present an overview of synthetic strategies used for the replication of both dispersed particulates and continuous templates with a number of recent examples of anisotropic organic and inorganic replicas presented. Strategies for generating adequate robust replicas and their expected assembling behavior are also briefly discussed.

Inkjet-assisted layer-by-layer printing of encapsulated arrays.

We present the facile fabrication of hydrogen-bonded layer-by-layer (LbL) microscopic dot arrays with encapsulated dye compounds. We demonstrate patterned encapsulation of Rhodamine dye as a model compound within poly(vinylpyrrolidone)/poly(methacrylic acid) (PVPON/PMAA) LbL dots constructed without an intermediate washing step. The inkjet printing technique improves encapsulation efficiency, reduces processing time, facilitates complex patterning, and controls lateral and vertical dimensions with diameters ranging from 130 to 35 μm (mostly controlled by the droplet size and the substrate hydrophobicity) and thickness of several hundred nanometers. The microscopic dots composed of hydrogen-bonded PVPON/PMAA components are also found to be stable in acidic solution after fabrication. This facile, fast, and sophisticated inkjet encapsulation method can be applied to other systems for fast fabrication of large-scale, high-resolution complex arrays of dye-encapsulated LbL dots.

Cell Surface Engineering with Edible Protein Nanoshells

Natural protein (silk fibroin) nanoshells are assembled on the surface of Saccharomyces cerevisiae yeast cells without compromising their viability. The nanoshells facilitate initial protection of the cells and allow them to function in encapsulated state for some time period, afterwards being completely biodegraded and consumed by the cells. In contrast to a traditional methanol treatment, the gentle ionic treatment suggested here stabilizes the shell silk fibroin structure but does not compromise the viability of the cells, as indicated by the fast response of the encapsulated cells, with an immediate activation by the inducer molecules. Extremely high viability rates (up to 97%) and preserved activity of encapsulated cells are facilitated by cytocompatibility of the natural proteins and the formation of highly porous shells in contrast to traditional polyelectrolyte-based materials. Moreover, in a high contrast to traditional synthetic shells, the silk proteins are biodegradable and can be consumed by cells at a later stage of growth, thus releasing the cells from their temporary protective capsules. These on-demand encapsulated cells can be considered a valuable platform for biocompatible and biodegradable cell encapsulation, controlled cell protection in a synthetic environment, transfer to a device environment, and cell implantation followed by biodegradation and consumption of protective protein shells.

Template-assisted assembly of the functionalized cubic and spherical microparticles.

The patterned template-assisted assembly of the cubic microparticles driven by the competing capillary, Columbic, and van der Waals forces had been studied in comparison with the traditional spherical colloidal microparticles. We observed that the spherical and cubic microparticles assembled with different probability in the channels of the hydrophobic-hydrophilic patterned substrates due to differences in a balance of adhesive and capillary forces. In contrast to highly selective assembly of spherical microparticles, selective deposition of cubic microcrystals with channels is impeded by strong adhesive forces facilitated by large specific interfacial areas between cube facets and substrate. The modification of the patterned substrate by functionalized coatings with oppositely charged topmost layers significantly increases the probability (to 86%) of the cubic microparticles to assemble into chemically modified channels. The introduction of ultrathin LbL shells on cubic microparticles and functionalization of patterned substrates are critical for the directed colloidal assembly of anisotropic microparticles into ordered aggregates.