Engineered Microcapsules Fabricated from Reconstituted Spider Silk

Abstract

In applications such as flavor encapsulation, drug delivery, and biomedical devices, microencapsulation is developing into an increasingly effective method for the protection and delivery of active ingredients. Herein, we show that spider-silk proteins are well-suited for producing responsive microcapsules with high mechanical stability. Emulsion interfaces are harnessed to induce the controlled self-assembly of these proteins into predominantly b-sheet configurations, resulting in a mechanically stable thin polymer shell. Capsules transferred into a continuous phase can readily encapsulate large molecules, while allowing small molecules to permeate freely. The capsules demonstrate good chemical stability, which is attributed to the b-sheet-rich structure of the self-assembled spider-silk proteins. These microcapsules represent a new class of biomimetic materials, exhibiting functionalities that can be further modified and controlled on the molecular level.

Statistical Mechanics of Thin Spherical Shells

“…[75], artificial microscopic shells have also been constructed from polyelectrolytes [22], proteins [87], and polymers [88]. Such microcapsules can be made extremely thin, with the thickness of several nanometers, where thermal fluctuations can become relevant.…”

“…Such microcapsules can be made extremely thin, with the thickness of several nanometers, where thermal fluctuations can become relevant. For example, microcapsules with h ≈ 6 nm thickness were fabricated from reconstituted spider silk [87] with R 0 ≈ 30 μm and E 0 ≈ 1 GPa, where we find…”

The elaborate structure of spider silk

“…Such amphiphilic composition is reminiscent of surfactants or biological membranes and, in the case of spider silks, is thought to be crucial for phase separation during the spinning process (see below). [33][34][35] Additionally, the unusual amphiphilic pattern might be responsible for formation of micelles postulated as intermediate structures during thread assembly (see below). 36 Quaternary structure and protein stability.…”

Assembly mechanism of recombinant spider silk proteins

“…S1 and Materials and Methods]. Under distinct solvent conditions these engineered silk proteins controllably assemble into different morphologies, such as nanofibrils (6), hydrogels (7), films (9,10), and microcapsules (11). Further, conditions for a liquidliquid phase separation have been identified, leading to large colloidal assemblies that likely reflect a prerequisite for silk fiber formation (12).…”