Direct Probing of Micromechanical Properties of Hydrogen-Bonded Layer-by-Layer Microcapsule Shells with Different Chemical Compositions

Abstract

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.

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

“…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 . Overall, the stiffness of hollow LbL microcapsules depended on the degree of cross‐linking time, molecular weight, template dissolution, and pH . For instance, the elastic modulus of hydrogen‐bonded shells based on single poly (methacrylic acid)‐co‐NH 2 component or tannic acid/poly‐vinylpyrrolidone (TA/PVPON) varied in the range of 0.7 to 5 MPa with different cross‐linking time and templates.…”

Theranostic Multilayer Capsules for Ultrasound Imaging and Guided Drug Delivery

“…As demonstrated previously, by decreasing the molecular weight of PVPON from 1300 to 360 kDa and to 55 kDa, the Young’s modulus of the (TA/PVPON) shell in the wet state could be decreased from 4.3 to 1.6 and to 0.89 MPa, respectively. 45 Thus, the nanoparticle-free hydrogen-bonded (TA/PVPON) system affords improved biocompatibility and controllable US-triggered drug release via regulation of the capsule shell composition and thickness.…”

One-Step Fabrication of pH-Responsive Membranes and Microcapsules through Interfacial H-Bond Polymer Complexation

“…This could be due to the huge thickness difference between thin multilayers and our thick membrane. Other techniques in the literature including osmotic buckling 27 , or AFM measurements 28 , report Young modulus of the order of 1 to 100 MPa. In our experiment, if interfacial shear modulus is divided by the membrane thickness (540 nm), a bulk modulus G ′ = 13.1 MPa is obtained, which is on the same order of magnitude as what is found in the literature.

Figure 4( a ) Frequency sweeps (at strain amplitude = 0.1%) performed on a PMAA-PPO membrane, at several pH from 3 to 5.5.

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