2 research outputs found
Interfacial Shear Strength and Adhesive Behavior of Silk Ionomer Surfaces
The interfacial shear
strength between different layers in multilayered
structures of layer-by-layer (LbL) microcapsules is a crucial mechanical
property to ensure their robustness. In this work, we investigated
the interfacial shear strength of modified silk fibroin ionomers utilized
in LbL shells, an ionic–cationic pair with complementary ionic
pairing, (SF)-poly-l-glutamic acid (Glu) and SF-poly-l-lysine (Lys), and a complementary pair with partially screened
Coulombic interactions due to the presence of polyÂ(ethylene glycol)
(PEG) segments and SF-Glu/SF-LysÂ[PEG] pair. Shearing and adhesive
behavior between these silk ionomer surfaces in the swollen state
were probed at different spatial scales and pressure ranges by using
functionalized atomic force microscopy (AFM) tips as well as functionalized
colloidal probes. The results show that both approaches were consistent
in analyzing the interfacial shear strength of LbL silk ionomers at
different spatial scales from a nanoscale to a fraction of a micron.
Surprisingly, the interfacial shear strength between SF-Glu and SF-LysÂ[PEG]
pair with partially screened ionic pairing was greater than the interfacial
shear strength of the SF-Glu and SF-Lys pair with a high density of
complementary ionic groups. The difference in interfacial shear strength
and adhesive strength is suggested to be predominantly facilitated
by the interlayer hydrogen bonding of complementary amino acids and
overlap of highly swollen PEG segments
Bimorph Silk Microsheets with Programmable Actuating Behavior: Experimental Analysis and Computer Simulations
Microscaled self-rolling
construct sheets from silk protein material have been fabricated,
containing a silk bimorph composed of silk ionomers as an active layer
and cross-linked silk β-sheet as the passive layer. The programmable
morphology was experimentally explored along with a computational
simulation to understand the mechanism of shape reconfiguration. The
neutron reflectivity shows that the active silk ionomers layer undergoes
remarkable swelling (eight times increase in thickness) after deprotonation
while the passive silk β-sheet retains constant volume under
the same conditions and supports the bimorph construct. This selective
swelling within the silk-on-silk bimorph microsheets generates strong
interfacial stress between
layers and out-of-plane forces, which trigger autonomous self-rolling
into various 3D constructs such as cylindrical and helical tubules.
The experimental observations and computational modeling confirmed
the role of interfacial stresses and allow programming the morphology
of the 3D constructs with particular design. We demonstrated that
the biaxial stress distribution over the 2D planar films depends upon
the lateral dimensions, thickness and the aspect ratio of the microsheets.
The results allow the fine-tuning of autonomous shape transformations
for the further design of complex micro-origami constructs and the
silk based rolling/unrolling structures provide a promising platform
for polymer-based biomimetic devices for implant applications