Permeability and Micromechanical Properties of Silk Ionomer Microcapsules

Abstract

We studied the pH-responsive behavior of layer-by-layer (LbL) microcapsules fabricated from silk fibroin chemically modified with different poly amino acid side chains: cationic (silk-poly L-lysine, SF-PL) or anionic (silk-poly-L-glutamic acid, SF-PG). We observed that stable ultrathin shell microcapsules can be assembled with a dramatic increase in swelling, thickness, and microroughness at extremely acidic (pH < 2.5) and basic (pH > 11.0) conditions without noticeable disintegration. These changes are accompanied by dramatic changes in shell permeability with a 2 orders of magnitude increase in the diffusion coefficient. Moreover, the silk ionomer shells undergo remarkable softening with a drop in Young's modulus by more than 1 order of magnitude due to the swelling, stretching, and increase in material porosity. The ability to control permeability and mechanical properties over a wide range for the silk-based microcapsules, with distinguishing stability under harsh environmental conditions, provides an important system for controlled loading and release and applications in bioengineering.

Robust Microcapsules with Controlled Permeability from Silk Fibroin Reinforced with Graphene Oxide

“…Furthermore, the effect of cross‐linking was investigated by comparing the deformation of (SF‐PL/GO) 3.5 capsules with and without cross‐linking at different dextran concentrations (Figure f). The deformation limit of capsules without cross‐linking is slightly higher than that of cross‐linked capsules, consistent with previously reported studies in which cross‐linking contributed to the enhanced mechanical properties . However, this deformation percentage of non cross‐linked silk‐graphene oxide composite shells is low compared to the cross‐linked pure silk ionomers based capsules, indicating that graphen oxide sheets work as a major reinforcing factor of the strong mechanical properties of (SF‐PL/GO) n shells.…”

“…Furthermore, the calculated elastic modulus value in the swollen state was within 1.5 – 1.6 MPa for purely silk microcapsules with 4 and 5 bilayers. These values are comparable but lower than that previously reported for silk ionomer capsules (around 8.5 MPa) from surface force spectroscopy This difference can be related to the fact that AFM measures localized compressive modulus in contrast to microscopic bending stability tested with osmotic measurements in this study. On the other hand, these values are close to the elastic modulus of approximately 1 MPa reported for polyelectrolyte multilayer films with natural components such as chitosan/hyaluronan, poly‐L‐lysine/hyaluronan and poly (allyamine hydrochloride)/poly‐L‐gluctamic acid from AFM nanoindentation .…”

Bimorph Silk Microsheets with Programmable Actuating Behavior: Experimental Analysis and Computer Simulations

“…Upon immersion of the composite planar silk microsheets into a 0.06 M NaOH solution, the silk ionomers layer underwent significant swelling, due to the reduction of the ionic bonding in the LbL thin film at extreme basic conditions, 44 while the silk β-sheet layers remained a constant volume, due to the physical cross-linked β-sheet. The structure and shape of the silk-on-silk microtubes were revealed using confocal microscopy by staining with FITC, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 indicating closed tubes with multilayer shells (Figure 3b).…”

Pharmacological aspects of release from microcapsules — from polymeric multilayers to lipid membranes

“…Figure 1 depicts all these stimuli, which in fact provide complementary measures not only for simply inducing release, but also for achieving desired release profiles [32][33][34].…”