In nature, individual cells are compartmentalized by
a membrane that protects the cellular elements from the
surrounding environment while simultaneously equipped with an
antioxidant defense system to alleviate the oxidative stress resulting
from light, oxygen, moisture, and temperature. However, this
mechanism has not been realized in cellular mimics to effectively
encapsulate and retain highly reactive antioxidants. Here, we report
cell-inspired hydrogel microcapsules with an interstitial oil layer
prepared by utilizing triple emulsion drops as templates to achieve
enhanced retention of antioxidants. We employ ionic gelation for
the hydrogel shell to prevent exposure of the encapsulated
antioxidants to free radicals typically generated during photopolymerization.
The interstitial oil layer in the microcapsule serves
as an stimulus-responsive diffusion barrier, enabling efficient encapsulation and retention of antioxidants by providing an adequate
pH microenvironment until osmotic pressure is applied to release the cargo on-demand. Moreover, addition of a lipophilic reducing
agent in the oil layer induces a complementary reaction with the antioxidant, similar to the nonenzymatic antioxidant defense system
in cells, leading to enhanced retention of the antioxidant activity. Furthermore, we show the complete recovery and even further
enhancement in antioxidant activity by lowering the storage temperature, which decreases the oxidation rate while retaining the
complementary reaction with the lipophilic reducing agent.
KEYWORDS: droplet microfluidics, cell-inspired microcapsule, encapsulation
more »
« less
Controllable Fabrication of Inhomogeneous Microcapsules for Triggered Release by Osmotic Pressure
Inhomogeneous microcapsules that can encapsulate various cargo for controlled release triggered by osmotic shock are designed and reported. The microcapsules are fabricated using a microfluidic approach and the inhomogeneity of shell thickness in the microcapsules can be controlled by tuning the flow rate ratio of the middle phase to the inner phase. This study demonstrates the swelling of these inhomogeneous microcapsules begins at the thinnest part of shell and eventually leads to rupture at the weak spot with a low osmotic pressure. Systematic studies indicate the rupture fraction of these microcapsules increases with increasing inhomogeneity, while the rupture osmotic pressure decreases linearly with increasing inhomogeneity. The inhomogeneous microcapsules are demonstrated to be impermeable to small probe molecules, which enables long‐term storage. Thus, these microcapsules can be used for long‐term storage of enzymes, which can be controllably released through osmotic shock without impairing their biological activity. The study provides a new approach to design effective carriers to encapsulate biomolecules and release them on‐demand upon applying osmotic shock.
more » « less- NSF-PAR ID:
- 10459201
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 15
- Issue:
- 42
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Dynamic microcapsules are reported that exhibit shell membranes with fast and reversible changes in permeability in response to external stimuli. A hydrophobic anhydride monomer is employed in the thiol–ene polymerization as a disguised precursor for the acid‐containing shells; this enables the direct encapsulation of aqueous cargo in the liquid core using microfluidic fabrication of water‐in‐oil‐in‐water double emulsion drops. The poly(anhydride) shells hydrolyze in their aqueous environment without further chemical treatment, yielding cross‐linked poly(acid) microcapsules that exhibit trigger‐responsive and reversible property changes. The microcapsule shell can actively be switched numerous times between impermeable and permeable due to the exceptional mechanical properties of the thiol–ene network that prevent rupture or failure of the membrane, allowing it to withstand the mechanical stresses imposed on the capsule during the dynamic property changes. The permeability and molecular weight cutoff of the microcapsules can dynamically be controlled with triggers such as pH and ionic environment. The reversibly triggered changes in permeability of the shell exhibit a response time of seconds, enabling actively adjustable release profiles, as well as on‐demand capture, trapping, and release of cargo molecules with molecular selectivity and fast on‐off rates.
-
more » « less
Abstract A hydrogel microcapsule with an intermediate thin oil layer is presented to achieve smart release of a broad range of cargoes triggered via diverse stimuli. A microfluidic technique is used to produce triple emulsion droplets with a thin oil layer that separates the innermost aqueous phase from the hydrogel prepolymer phase, which transforms into a hydrogel shell via photopolymerization. The intermediate oil layer within the hydrogel microcapsule acts as an effective diffusion barrier, allowing encapsulation of various small cargoes within a porous hydrogel shell until a stimulus is applied to destabilize the oil layer. It is demonstrated that diverse stimuli including chemical dissolution, mechanical stress, and osmotic pressure can be utilized to release the encapsulated cargo on‐demand. In addition, osmotic pressure and the hydrogel shell thickness can be independently tuned to control the onset time of release as well as the release behavior of multi‐cargo encapsulated hydrogel microcapsule. The release can be either simultaneous or selective.
-
Microcapsules allow for the controlled containment, transport, and release of cargoes ranging from pharmaceuticals to fragrances. Given the interest from a variety of industries in microcapsules and other core–shell structures, a multitude of fabrication strategies exist. Here, we report on a method relying on a mixture of temperature-responsive microgel particles, poly( N -isopropylacrylamide) (pNIPAM), and a polymer which undergo fluid–fluid phase separation. At room temperature this mixture separates into colloid-rich (liquid) and colloid-poor (gas) fluids. By heating the sample above a critical temperature where the microgel particles shrink dramatically and develop a more deeply attractive interparticle potential, the droplets of the colloid-rich phase become gel-like. As the temperature is lowered back to room temperature, these droplets of gelled colloidal particles reliquefy and phase separation within the droplet occurs. This phase separation leads to colloid-poor droplets within the colloid-rich droplets surrounded by a continuous colloid-poor phase. The gas/liquid/gas all-aqueous double emulsion lasts only a few minutes before a majority of the inner droplets escape. However, the colloid-rich shell of the core–shell droplets can solidify with the addition of salt. That this method creates core–shell structures with a shell composed of stimuli-sensitive microgel colloidal particles using only aqueous components makes it attractive for encapsulating biological materials and making capsules that respond to changes in, for example, temperature, salt concentration, or pH.more » « less
-
more » « less
Abstract Encapsulated anticorrosion agents provide a suitable alternative to dispersion of metal‐based compounds in protective polymeric coatings on metal substrates. Stimuli‐responsive microcapsules enhance protection abilities by autonomously responding to corrosion‐induced environmental changes, rather than relying on damage‐induced mechanical stimuli. This work reports pH‐responsive microcapsules with triggered release over a wide range of acidic pH values (pH < 6) and robust enough to be incorporated in commercial solvent‐based epoxy coatings. The pH responsiveness is achieved by integrating acid labile ketals that undergo rapid hydrolysis within the cross‐linked polyamide shell and readily release acetylenic diol or jojoba oil as the anticorrosive agent. The microcapsules are stable up to a temperature of 150 °C and provide long‐term room temperature stability up to 3 months. Degradation and release kinetics of the microcapsules are quantified at various pH levels (1 ≤ pH ≤ 9) using1H NMR and gas chromatography, respectively. Microcapsules exhibit complete release in under 5 min at pH 1 and ≈2 hours at pH 5, respectively. Coating performance is evaluated by electrochemical corrosion tests conducted in 5 wt% salt solutions with varying pH and concentration of the microcapsules in the coating. Inhibition efficiencies up to 70% are achieved in acidic saltwater solutions.
