Switchable Hydrophobic Pockets in DNA Protocells Enhance Chemical Conversion

Synthetic cell models help us understand living cells and the origin of life. Key aspects of living cells are crowded interiors where secondary structures, such as the cytoskeleton and membraneless organelles/condensates, can form. These can form dynamically and serve structural or functional purposes, such as protection from heat shock or as crucibles for various biochemical reactions. Inspired by these phenomena, we introduce a crowded all-DNA protocell and encapsulate a temperature-switchable DNA-b-polymer block copolymer, in which the synthetic polymer phase-segregates at elevated temperatures. We find that thermoreversible phase segregation of the synthetic polymer occurs via bicontinuous phase separation, resulting in artificial organelle structures that can reorient into larger domains depending on the viscoelastic properties of the protocell interior. Fluorescent sensors confirm the formation of hydrophobic compartments, which enhance the reactivity of bimolecular reactions. This study leverages the strengths of biological and synthetic polymers to construct advanced biohybrid artificial cells that provide insights into phase segregation under crowded conditions and the formation of organelles and microreactors in response to environmental stress.

Bioresponsive Polymers for Nanomedicine-Expectations and Reality!

Bioresponsive polymers in nanomedicine have been widely perceived to selectively activate the therapeutic function of nanomedicine at diseased or pathological sites, while sparing their healthy counterparts. This idea can be described as an advanced version of Paul Ehrlich’s magic bullet concept. From that perspective, the inherent anomalies or malfunction of the pathological sites are generally targeted to allow the selective activation or sensory function of nanomedicine. Nonetheless, while the primary goals and expectations in developing bioresponsive polymers are to elicit exclusive selectivity of therapeutic action at diseased sites, this remains difficult to achieve in practice. Numerous research efforts have been undertaken, and are ongoing, to tackle this fine-tuning. This review provides a brief introduction to key stimuli with biological relevance commonly featured in the design of bioresponsive polymers, which serves as a platform for critical discussion, and identifies the gap between expectations and current reality.

Effect of Thermal Stimulus on Kinetic Rehydration of Thermoresponsive Poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate) Thin Films Probed by In Situ Neutron Reflectivity

The kinetic rehydration of thin di-block copolymer poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate) (PO₂-b-PO₃₀₀) films containing two thermoresponsive components is probed by in situ neutron reflectivity (NR) with different thermal stimuli in the D₂O vapor atmosphere. The transition temperatures (TTs) of PO₂ and PO₃₀₀ blocks are 25 and 60 °C, respectively. After the one-step stimulus (rapid decrease in temperature from 60 to 20 °C), the film directly switches from a collapsed to a fully swollen state. The rehydration process is divided into four steps: (a) D₂O condensation, (b) D₂O absorption, (c) D₂O evaporation, and (d) film reswelling. However, the film presents a different rehydration behavior when the thermal stimulus is separated into two smaller steps (first decrease from 60 to 40 °C and then to 20 °C). The film first switches from a collapsed to a semiswollen state caused by the rehydrated PO₃₀₀ blocks after the first step of thermal stimulus (60 to 40 °C) and then to a swollen state induced by the rehydrated PO₂ blocks after the second step (40 to 20 °C). Thus, the kinetic responses are distinct from that after the one-step thermal stimulus. Both the time and extent of condensation as well as evaporation processes are significantly reduced in these two smaller steps. However, the final states of the rehydrated PO₂-b-PO₃₀₀ films are basically identical irrespective of the applied thermal stimulus. Thus, the final state of thermoresponsive di-block copolymer films is not affected by the external thermal stimuli, which is beneficial for the design and preparation of sensors or switches based on thermoresponsive polymer films.

Thermoresponsive Polymers Based on Tertiary Amine Moieties

Thermoresponsive polymers exhibiting unique reversible phase transition properties in aqueous solution in response to temperature stimuli have been extensively investigated. In the past two decades, thermoresponsive polymers based on tertiary amine moieties have achieved considerable progress and become an important family of thermoresponsive polymers, including tertiary amine functionalized poly((meth)acrylamide)s, poly((meth)acrylate)s, poly(styrene)s, poly(vinyl alcohol)s, and poly(ethylene oxide)s, which exhibit lower critical solution temperature and/or upper critical solution temperature in water or aliphatic alcohols. Their phase transition behavior can be modulated by the solution pH and CO₂ due to the protonation of tertiary amine moieties in acidic condition and deprotonation in alkaline condition and the charged ammonium bicarbonate formed by the tertiary amine moieties and CO₂ . The aim of this review is to summarize the recent progress in the thermoresponsive polymers based on tertiary amine moieties.

Adamantane Functionalized Poly(2-oxazoline)s with Broadly Tunable LCST-Behavior by Molecular Recognition

Smart or adaptive materials often utilize stimuli-responsive polymers, which undergo a phase transition in response to a given stimulus. So far, various stimuli have been used to enable the modulation of drug release profiles, cell-interactive behavior, and optical and mechanical properties. In this respect, molecular recognition is a powerful tool to fine-tune the stimuli-responsive behavior due to its high specificity. Within this contribution, a poly(2-oxazoline) copolymer bearing adamantane side chains was synthesized via triazabicyclodecene-catalyzed amidation of the ester side chains of a poly(2-ethyl-2-oxazoline-stat-2-methoxycarbonylpropyl-2-oxazoline) statistical copolymer. Subsequent complexation of the pendant adamantane groups with sub-stoichiometric amounts (0-1 equivalents) of hydroxypropyl β-cyclodextrin or β-cyclodextrin enabled accurate tuning of its lower critical solution temperature (LCST) over an exceptionally wide temperature range, spanning from 30 °C to 56 °C. Furthermore, the sharp thermal transitions display minimal hysteresis, suggesting a reversible phase transition of the complexed polymer chains (i.e., the β-cyclodextrin host collapses together with the polymers) and a minimal influence by the temperature on the supramolecular association. Analysis of the association constant of the polymer with hydroxypropyl β-cyclodextrin via 1H NMR spectroscopy suggests that the selection of the macrocyclic host and rational polymer design can have a profound influence on the observed thermal transitions.

Wearable Bracelet Monitoring the Solar Ultraviolet Radiation for Skin Health Based on Hybrid IPN Hydrogels

The risk of extensive exposure of the human epidermis to solar ultraviolet radiation is significantly increased nowadays. It not only induces skin aging and solar erythema but also increases the possibility of skin cancer. Therefore, a simply prepared, highly sensitive, and optically readable device for monitoring the solar ultraviolet radiation is highly desired for the skin health management. Because of the photoinitiated polymerization triggered by graphene-carbon nitride (g-C₃N₄) under ultraviolet radiation, g-C₃N₄ is homogeneously distributed in the hybrid hydrogels containing N-isopropylacrymide (NIPAM), poly(ethylene glycol) methyl ether methacrylate (OEGMA₃₀₀), and sodium alginate (SA). By further immersing the hybrid hydrogels into calcium chloride solution, hybrid alginate-Ca²⁺/P(NIPAM-co-OEGMA₃₀₀)/g-C₃N₄ interpenetrating polymeric network (IPN) hydrogels are obtained. Due to the homogeneous distribution of g-C₃N₄ and the existence of thermoresponsive polymers, the hybrid IPN hydrogels present good adsorption capability and high degradation efficiency for methylene blue (MB) especially at high temperature under ultraviolet radiation. Based on this unique property, the bracelet monitoring skin health is prepared by simply immersing the hybrid IPN hydrogels into the MB solution and then wrapping it with PET foil. Because the immersion time for the top, middle, and bottom parts of the hybrid IPN hydrogels is gradually increased, their colors vary from light to dark blue. A longer time is required for the discoloration of the darker part under solar ultraviolet radiation. Thus, the bracelet can be used to conveniently monitor the dose of solar ultraviolet radiation by simply checking the discoloration in the bracelet under sunshine. Due to the facile preparation and low cost of the bracelet, it is a promising candidate for wearable devices for skin health management.

Impact of Thermal History on the Kinetic Response of Thermoresponsive Poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol)methyl ether methacrylate) Thin Films Investigated by In Situ Neutron Reflectivity

The impact of thermal history on the kinetic response of thin thermoresponsive diblock copolymer poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate), abbreviated as PMEO₂MA-b-POEGMA₃₀₀, films is investigated by in situ neutron reflectivity. The PMEO₂MA and POEGMA₃₀₀ blocks are both thermoresponsive polymers with a lower critical solution temperature. Their transition temperatures (TTs) are around 25 °C (TT₁, PMEO₂MA) and 60 °C (TT₂, POEGMA₃₀₀). Thus, by applying different temperature protocols (20 to 60 or 20 to 40 to 60 °C), the PMEO₂MA-b-POEGMA₃₀₀ thin films experience different thermal histories: the first protocol directly switches from a swollen to a collapsed state, whereas the second one switches first from a swollen to a semicollapsed and finally to a collapsed state. Although the applied thermal histories differ, the response and final state of the collapsed films are very close to each other. After the thermal stimulus, both films present a complicated response composed of an initial shrinkage, followed by a rearrangement. Interestingly, a subsequent reswelling of the collapsed film is only observed in the case of having applied a thermal stimulus of 20 to 40 °C. The normalized film thickness and the D₂O amount of each layer in the PMEO₂MA-b-POEGMA₃₀₀ films are consistent at the end of the two different thermal stimuli. Hence, it can be concluded that the thermal history does not influence the final state of the PMEO₂MA-b-POEGMA₃₀₀ films upon heating. Based on this property, these thin films are especially suitable for the temperature switches on the nanoscale, which may experience different thermal histories.

Drug–polymer conjugates with dynamic cloud point temperatures based on poly(2-oxazoline) copolymers

A shift in cloud point temperatures of poly(2-oxazoline)/ACE inhibitor polymer drug conjugates occurs on release of the drug.