Bicontinuous Nanoporous Frameworks: Caged Longevity for Enzymes

Abstract

The preparation of bicontinuous nanoporous covalent frameworks, which are promising for caging active enzymes, is demonstrated. The frameworks have three‐ dimensionally continuous, hydrophilic pores with widths varying between 5 and 30 nm. Enzymes were infiltrated into the bicontinuous pore by applying a pressured enzyme solution. The new materials and methods allowed the amount of caged proteins to be controlled precisely. The resulting enzyme‐loaded framework films could be recycled many times with nearly no loss of catalytic activity. Entropic trapping of proteins by a bicontinuous pore with the right size distribution is an unprecedented strategy toward facile in vitro utilization of biocatalysts.

Facile Synthesis of Robust and Pore-Size-Tunable Nanoporous Covalent Framework Membrane by Simultaneous Gelation and Phase Separation of Covalent Network/Poly(methyl methacrylate) Mixture

“…This is in contrast to the previous result that hydrophobic solvent did not pass through the hydrophilic NCF derived from PEG/UN blends. 39 Noticeably, the solvent flux through the NCF-PM40 was inversely proportional to the solvent viscosity. This is in consistence with the Hagen− Poiseuille equation, 47 suggesting that the NCF pore structure maintains without significant swelling and dissolution of the skeleton under common organic solvents.…”

“…The ability of PMMA to be rapidly extracted out of the PMMA/UN blend is highly advantageous when compared with PEG or PSF, which required at least 1 week to be extracted from their blends. 39,40 The shorter extraction time of PMMA than PEG from their blend with UN may be accounted for by the lower affinity of the PMMA to the UN pore surface than of the PEG to the PEG-grafted pore surface. In addition, there may exist some degree of entanglement between the free (extractable) PEG chains and the grafted (residual) PEG chains at the interface, which also prevent rapid diffusion of PEG chains from the pores.…”

“…PMMA/UN blends were prepared similarly to the previous report instead of using poly-(ethylene glycol) as a polymer for blending. 39 Samples of the UN monomer solution were typically kept for 60 h at 25 °C, and then each sample was mixed with a different specific amount of PMMA to yield a weight fraction of the polymer between 0.1−0.7. (Weight fraction represents the mass ratio of a polymer relative to a total mass from the polymer and UN monomers.)…”

“…Further study showed that a mixture of the UN sol with poly(ethylene glycol) (PEG) could phase-separate and produce a bicontinuous nanostructure upon solvent evaporation. 39 Selective extraction of the PEG from the phase-separated blend using water yielded threedimensionally continuous mesoporous channels (with pore size of 5−30 nm). The resulting porous UN, referred as nanoporous covalent framework (NCF), has several advantages including the rigidity of the nanoscale framework, threedimensionally continuous pore structure, and solutionprocessability of the covalent network.…”

“…The preparation of the NCF using PEG (NCF-PEG) as a pore-generating agent (porogen), however, had limitations such as the long extraction time for removing the PEG and the difficulty in functionalizing the nanopore due to residual PEG chains grafted on the surface. 39 The pore size and distribution were not easily controlled by blending composition. Replacing the PEG with polysulfone (PSF) as a porogen 40 provided an NCF with no polymer graft on the pore surface, but rapid vitrification of PSF during solvent evaporation resulted in low porosity and poor controllability of pore size even after tedious extraction of the porogen (PSF).…”