Under
the right conditions, some biological systems can maintain
high viability after being frozen and thawed, but many others (e.g.,
organs and many mammalian cells) cannot. To increase the rates of
post-thaw viability and widen the library of living cells and tissues
that can be stored frozen, an improved understanding of the mode of
action of polymeric cryoprotectants is required. Here, we present
a polymeric cryoprotectant, poly(methyl glycidyl sulfoxide) (PMGS),
that achieved higher post-thaw viability for fibroblast cells than
its small-molecule analogue dimethyl sulfoxide. By limiting the amount
of water that freezes and facilitating cellular dehydration after
ice nucleation, PMGS mitigates the mechanical and osmotic stresses
that the freezing of water imparts on cells and facilitates higher-temperature
vitrification of the remaining unfrozen volume. The development of
PMGS advances a fundamental physical understanding of polymer-mediated
cryopreservation, which enables new material design for long-term
preservation of complex cellular networks and tissue.
We report a partial elucidation of the relationship between polymer polarity and ionic conductivity in polymer electrolyte mixtures comprising a homologous series of nine poly(vinyl ether)s (PVEs) and lithium bis(trifluoromethylsulfonyl)imide. Recent simulation studies have suggested that low dielectric polymer hosts with glass transition temperatures far below ambient conditions are expected to have ionic conductivity limited by salt solubility and dissociation. In contrast, high dielectric hosts are expected to have the potential for high ion solubility but slow segmental dynamics due to strong polymer−polymer and polymer−ion interactions. We report results for PVEs in the low polarity regime with dielectric constants of about 1.3 to 9.0. Ionic conductivity measured for the PVE and salt mixtures ranged from about 10 −10 to 10 −3 S/cm. In agreement with the predictions from computer simulations, the ionic conductivity increased with dielectric constant and plateaued as the dielectric approached 9.0, comparable to the dielectric constant of the widely used poly(ethylene oxide).
Metal–organic
frameworks (MOFs) are a class of customizable
porous material, which have shown good performance in separation processes,
because of their large surface area and molecular recognition property.
Although the effects of chemical structure of MOFs on their separation
performance were extensively studied, the exploration of their surface
properties was still limited. This work demonstrated a MOF nanosheet
with large amount of coordinatively unsaturated metal sites, Cu(BDC)
(copper(II) benzenedicarboxylate), where the unsaturated Cu sites
were utilized to selectively adsorb organic molecules with Lewis basicity.
This work also investigated the direct growth of Cu(BDC) on the cellulose
substrate, where the MOF nanosheets were immobilized on the cellulose
substrate, enabling the composite material for practical applications.
The heterogeneous nucleation and growth of MOF nanosheets on the cellulose
were achieved by tuning the basicity of solution and reaction temperature.
We believe this direct growth approach can be applied to other MOF
composite materials for separation and purification purposes, as well
as other applications involving molecular recognition properties of
MOFs, such as sensing, catalysis, and enzyme immobilization.
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