Programming Self-Assembly and Stimuli-Triggered Response of Hydrophilic Telechelic Polymers with Sequence-Encoded Hydrophobic Initiators

Fabrication of Hierarchical Assemblies through Temperature-Triggered Liquid Crystallization Driven Self-Assembly

Functional hierarchy is prevalent in biological systems owing to natural evolution. Efforts to replicate these structures in artificial materials have gained traction in materials science. Although artificial hierarchical structures are fabricated at different scales based on site-specific interactions using ABC-type block copolymers (BCPs), the fabrication of such hierarchical structures using AB-type BCPs via a simple and efficient method remains challenging. Herein, a class of amphiphilic BCPs (PDenm-b-PACholn) is reported comprising dendronized oligoethylene glycol (Den) and cholesterol (AChol) as hydrophilic and hydrophobic moieties, respectively. By employing the collapse of PDenm blocks at a specific temperature, the fabrication of bundled fibers and multilayer vesicles is achieved with an obvious hierarchy. Different from common reversible aggregation-disaggregation processes of thermal-responsive polymers, the ordering of the core-forming block with liquid crystalline (LC) properties provides robustly physical cross-linking, coupled with epitaxial growth and the lateral fusion of LC blocks, guiding the formation of stable hierarchical micellar structures. It is highlighted that the combination of temperature-sensitive properties and LC ordering alignment offers a novel approach for constructing hierarchical structures using AB-type BCPs via an efficient one-step assembly method.

Breathable Lignin Nanoparticles as Reversible Gas Swellable Nanoreactors

The design of stimuli-responsive lignin nanoparticles (LNPs) for advanced applications has hitherto been limited to the preparation of lignin-grafted polymers in which usually the lignin content is low (<25 wt.%) and its role is debatable. Here, the preparation of O₂ -responsive LNPs exceeding 75 wt.% in lignin content is shown. Softwood Kraft lignin (SKL) is coprecipitated with a modified SKL fluorinated oleic acid ester (SKL-OlF) to form colloidal stable hybrid LNPs (hy-LNPs). The hy-LNPs with a SKL-OlF content ranging from 10 to 50 wt.% demonstrated a reversible swelling behavior upon O₂ /N₂ bubbling, increasing their size - ≈35% by volume - and changing their morphology from spherical to core-shell. Exposition of hy-LNPs to O₂ bubbling promotes a polarity change on lignin-fluorinated oleic chains, and consequently their migration from the inner part to the surface of the particle, which not only increases the particle size but also endows hy-LNPs with enhanced stability under harsh conditions (pH < 2.5) by the hydration barrier effect. Furthermore, it is also demonstrated that these new stimuli-responsive particles as gas tunable nanoreactors for the synthesis of gold nanoparticles. Combining a straightforward preparation with their enhanced stability and responsiveness to O₂ gas these new LNPs pave the way for the next generation of smart lignin-based nanomaterials.

Stimuli-Induced Architectural Transition as a Tool for Controlling the Enzymatic Degradability of Polymeric Micelles

Enzyme-responsive polymeric micelles hold great potential as drug delivery systems due to the overexpression of disease-associated enzymes. To achieve selective and efficient delivery of their therapeutic cargo, micelles need to be highly stable and yet disassemble when encountering their activating enzyme at the target site. However, increased micellar stability is accompanied by a drastic decrease in enzymatic degradability. The need to balance between stability and enzymatic degradation has severely limited the therapeutic applicability of enzyme-responsive nanocarriers. Here, we report a general modular approach for designing stable enzyme-responsive micelles whose enzymatic degradation can be enhanced on demand. The control over their response to the activating enzyme is achieved by stimuli-induced splitting of triblock amphiphiles into two identical diblock amphiphiles, which have the same hydrophilic-lipophilic balance as the parent amphiphile. This architectural transition drastically affects the micelle-unimer equilibrium and therefore increases the sensitivity of the micelles toward enzymatic degradation. As a proof of concept, we designed UV- and reduction-activated splitting mechanisms, demonstrating the ability to use architectural transition as a tool for tuning amphiphile-protein interactions, providing a general solution toward overcoming the stability-degradability barrier for enzyme-responsive nanocarriers.

Catalyst-Free Synthesis of Lignin Vitrimers with Tunable Mechanical Properties: Circular Polymers and Recoverable Adhesives

Biobased circular materials are alternatives to fossil-based engineering plastics, but simple and material-efficient synthetic routes are needed for industrial scalability. Here, a series of lignin-based vitrimers built on dynamic acetal covalent networks with a gel content exceeding 95% were successfully prepared in a one-pot, thermally activated, and catalyst-free "click" addition of softwood kraft lignin (SKL) to poly(ethylene glycol) divinyl ether (PDV). The variation of the content of lignin from 28 to 50 wt % was used to demonstrate that the mechanical properties of the vitrimers can be widely tuned in a facile way. The lowest lignin content (28 wt %) showed a tensile strength of 3.3 MPa with 35% elongation at break, while the corresponding values were 50.9 MPa and 1.0% for the vitrimer containing 50 wt % of lignin. These lignin-based vitrimers also exhibited excellent performance as recoverable adhesives for different substrates such as aluminum and wood, with a lap shear test strength of 6.0 and 2.6 MPa, respectively. In addition, recyclability of the vitrimer adhesives showed preservation of the adhesion performance exceeding 90%, indicating a promising potential for their use in sustainable circular materials.

Dual Biochemically Breakable Drug Carriers from Programmed Telechelic Homopolymers

Well-defined hydrophilic telechelic dibromo poly(triethylene glycol monomethyl ether acrylate)s were prepared by single-electron transfer living radical polymerization employing a hydrophobic difunctional initiator containing acetal and disulfide linkages. Although the resulting homopolymers have low hydrophobic contents (<8.5 wt % of the entire structure), they are able to self-assemble in water into nanoscale micellelike particles via chain folding. Acetal and disulfide linkages were demonstrated to be "keystone" units for their dual stimuli-responsive behavior under biochemically relevant conditions. Their site-selective middle-chain cleavage under both acidic pH and reductive conditions splits the homopolymer into two equal-sized fragments and results in the breakdown of the nanoassemblies. The drug loading/delivery potential of these nanoparticles was investigated using curcumine combining in vitro drug release, cytotoxicity, and cellular uptake studies with human cancer cell lines (HT-29 and HeLa). Importantly, this strategy may be extended to prepare innovative nanoplatforms based on hydrophilic homopolymers or random copolymers for intelligent drug delivery.