The development of robust and thin CO 2 separation membranes that allow fast and selective permeation of CO 2 will be crucial for rebalancing the global carbon cycle. Hydrogels are attractive membrane materials because of their tunable chemical properties and exceptionally high diffusion coefficients for solutes. However, their fragility prevents the fabrication of thin defect-free membranes suitable for gas separation. Here, we report the assembly of defect-free hydrogel nanomembranes for CO 2 separation. Such membranes can be prepared by coating an aqueous suspension of colloidal hydrogel microparticles (microgels) onto a flat, rough, or micropatterned porous support as long as the pores are hydrophilic and the pore size is smaller than the diameter of the microgels. The deformability of the microgel particles enables the autonomous assembly of defect-free 30−50 nm-thick membrane layers from deformed ∼15 nm-thick discoidal particles. Microscopic analysis established that the penetration of water into the pores driven by capillary force assists the assembly of a defect-free dense hydrogel layer on the pores. Although the dried films did not show significant CO 2 permeance even in the presence of amine groups, the permeance dramatically increased when the membranes are adequately hydrated to form a hydrogel. This result indicated the importance of free water in the membranes to achieve fast diffusion of bicarbonate ions. The hydrogel nanomembranes consisting of amine-containing microgel particles show selective CO 2 permeation (850 GPU, α CO2/N2 = 25) against post-combustion gases. Acid-containing microgel membranes doped with amines show highly selective CO 2 permeation against post-combustion gases (1010 GPU, α CO2/N2 = 216) and direct air capture (1270 GPU, α CO2/N2 = 2380). The membrane formation mechanism reported in this paper will provide insights into the self-assembly of soft matters. Furthermore, the versatile strategy of fabricating hydrogel nanomembranes by the autonomous assembly of deformable microgels will enable the large-scale manufacturing of high-performance separation membranes, allowing low-cost carbon capture from postcombustion gases and atmospheric air.

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Electrostatic interaction between synthetic polymer nanoparticles (NPs) and proteins is of considerable importance in the design of NPs that capture, neutralize, and deliver target molecules in a biological milieu. Ionizable functional groups, such as carboxylic acids and amines, are often introduced to NPs to tune the affinity with target bio-macromolecules through electrostatic attraction and repulsion. However, acids/bases are not always ionized at a physiological pH because acidities of the functional groups depend on the microenvironment around the acids/bases that are imprinted during the polymerization process. Here, we show that electrostatic interaction between acid-/base-containing NPs and target proteins strongly depends on the pH of the solution during the NP polymerization process. To prepare NPs that capture target proteins by electrostatic interactions at physiological pH, NPs must be polymerized within a pH range where the acid/base monomer is ionized. Acid-/base-containing NPs that exhibit completely different interactions with the proteins can be prepared by changing the polymerization pH without changing monomer compositions. Our results indicate that polymerization pH should be carefully tuned to design acid-/base-containing NPs that show desired affinity to all proteins in a biological milieu and to proteins of interest.

Synthetic polymer nanoparticles (NPs) that recognize and neutralize target biomacromolecules are of considerable interest as "plastic antibodies", synthetic mimics of antibodies. However, monomer sequences in the synthetic NPs are heterogeneous. The heterogeneity limits the target specificity and safety of the NPs. Herein, we report the synthesis of NPs with uniform monomer sequences for recognition and neutralization of target peptides. A multifunctional oligomer with a precise monomer sequence that recognizes the target peptide was prepared via cycles of reversible additionfragmentation chain transfer (RAFT) polymerization and flash chromatography. The oligomer or blend of oligomers was used as a chain transfer agent and introduced into poly(N-isopropyl acrylamide) hydrogel NPs by radical polymerization. Evaluation of the interaction with the peptides revealed that multiple oligomers in NPs cooperatively recognized the sequence of the target peptide and neutralized its toxicity. Effect of sequence, combination, density and molecular weight distribution of precision oligomers on the affinity to the peptides was also investigated.

Synthetic polymer nanoparticles (NPs) that recognize and neutralize target biomacromolecules are of considerable interest as "plastic antibodies", synthetic mimics of antibodies. However, monomer sequences in the synthetic NPs are heterogeneous. The heterogeneity limits the target specificity and safety of the NPs. Herein, we report the synthesis of NPs with uniform monomer sequences for recognition and neutralization of target peptides. A multifunctional oligomer with a precise monomer sequence that recognizes the target peptide was prepared via cycles of reversible additionfragmentation chain transfer (RAFT) polymerization and flash chromatography. The oligomer or blend of oligomers was used as a chain transfer agent and introduced into poly(N-isopropyl acrylamide) hydrogel NPs by radical polymerization. Evaluation of the interaction with the peptides revealed that multiple oligomers in NPs cooperatively recognized the sequence of the target peptide and neutralized its toxicity. Effect of sequence, combination, density and molecular weight distribution of precision oligomers on the affinity to the peptides was also investigated.

Improving polyhydroxyalkanoate (PHA, a biodegradable plastic) production under photoautotrophic cultivation is challenging for sustainable bioproduction. In this study, we demonstrated the use of engineered nanogel particles to enhance PHA accumulation in the marine photosynthetic bacterium Rhodovulum sulfidophilum under photoautotrophic culture. We screened the effect of 13 engineered nanogel particles on the cell growth and PHA accumulation of R. sulfidophilum. The addition of anionic nanogel particles significantly enhanced PHA accumulation in R. sulfidophilum up to 157-fold compared to that without nanogel particles. By performing 13 C tracer experiments and gas chromatography−mass spectrometry analysis, we confirmed that HCO 3 − was assimilated throughout the central carbon metabolism and that the accumulated PHA was indeed incorporated from HCO 3 − . Our results indicate successful PHA production with the supplementation of engineered nanogel particles under photoautotrophic cultivation in R. sulfidophilum. Furthermore, the strategy of using engineered nanoparticles demonstrated in this study may be applicable to other microbial cell factories to produce other commodity metabolites.