Search

Gels are giant single molecules that consist of a very large number (∼Avogadro’s number) of cross-linked nanometer-size polymer chains. Unlike most low-molecular-weight compounds, the extensively c...

Partially deuterated poly(ethylene glycol) (PEG) networks were fabricated by cross-linking a protonated four-arm PEG prepolymer (4hPEG) with a deuterated linear PEG (2dPEG) via a cross-end-coupling...

Dynamically crosslinked gels are appealing materials for applications that require time-dependent mechanical responses. DNA duplexes are ideal crosslinkers for building such gels because of their excellent sequence addressability and flexible tunability in bond energy. However, the mechanical responses of most DNA gels are complicated and unpredictable despite the high potential of DNA. Here, we demonstrate a DNA gel with a highly homogeneous gel network and well-predictable mechanical behaviors by using a pair of star-polymer-DNA precursors with presimulated DNA sequences showing the two-state transition. The melting curve analysis of the DNA gels reveals the good correspondence between the thermodynamic potentials of the DNA crosslinkers and the presimulated values by DNA calculators. Stress-relaxation tests and dissociation kinetics measurements show that the macroscopic relaxation time of the DNA gels is approximately equal to the lifetime of the DNA crosslinkers over four orders of magnitude from 0.1-2,000 sec. Furthermore, a series of durability tests find the DNA gels are hysteresis-less and self-healable after the applications of repeated temperature and mechanical stimuli. These results demonstrate the great potential of star-polymer-DNA precursors for building gels with predictable and tunable viscoelastic properties, suitable for applications such as stress-response extracellular matrices, injectable solids, and soft robotics.

Tetra-arm poly(ethylene glycol) (TetraPEG) gels are tough materials whose toughness originates from their uniform network structure. They can be formed by combining the termini of tetra-arm polymers via chemical reactions with high conversion efficiency, such as the Michael addition, condensations using an active ester group, and alkyne-azide cycloadditions. Herein, we report the synthesis of a tetra-PEG gel using a tetra-arm polymer with N-phenylmaleimide moieties at the polymer ends (tetra-N-aryl MA PEG) as a scaffold. Tetra-N-aryl MA PEG can be obtained via a simple maleimidation using the modification agent p-maleimidophenyl isocyanate (PMPI), which directly transforms the hydroxy groups at the polymer ends into reactive N-aryl maleimide groups in a one-pot reaction. The thus-obtained tetra-N-aryl MA PEG was fully characterized using high-performance liquid chromatography (HPLC), matrix-assisted laser desorption ionization time of flight mass spectrometry, and proton nuclear magnetic resonance spectroscopy. HPLC analysis not only demonstrated the high purity of tetra-N-aryl MA PEG and the full conversion of the hydroxy groups, but also provided an effective characterization method for N-aryl maleimide-based PEG using a simple protocol, which enables us quantitative analysis of functionalized polymers with different N-aryl maleimide numbers. Furthermore, we fabricated a TetraPEG gel via Michael addition of the obtained tetra-N-aryl MA and thiol-terminated TetraPEGs. Thus, this report presents the application of tetra-N-aryl MA PEG as an effective precursor to obtain a uniform network structure and a method for its characterization; these results should provide support for the development of functional molecules, soft materials, and further functional materials based on the uniform-network-structure concept.

The dynamics of thermoresponsive and biocompatible gels was investigated using dynamic light scattering. The gels were copolymerized by two types of ethylene glycol methacrylates having short and long hydrophilic side chains consisting of ethylene oxide units. Their dynamics was decomposed to fast and slow modes. The critical temperature was determined from the fast mode (cooperative diffusion) and was controlled lineally by the copolymerization ratio of the two monomers, which is one of the advantages in the gel system. The formation mechanism of hydrophobic domains in the gels was investigated from the slow mode. The hydrophobic domains grew in the gels by rising temperature, and they were copolymerization ratio dependent. The domain formation was suppressed as the copolymerization ratio of the longer side chain was increased. The results of this study should lead to new design strategy for the bioapplications, including drug delivery systems that require a retention of their smart functions.

The dynamics of thermoresponsive conetwork gels consisting of poly(ethylene glycol) (PEG) and poly(ethyl glycidyl ether-co-methyl glycidyl ether) (PEMGE) (PEG-PEMGE gel) was systematically investigated as a function of temperature and the mole fraction of the thermoresponsive modules (PEMGE) r using dynamic light scattering (DLS). The PEG-PEMGE gels were prepared by end-linking of four-armed hydrophilic modules (Tetra-PEG) and four-armed lower critical solution temperature (LCST)-type modules (Tetra-PEMGE) in water by the molar ratio of (1 − r): r, where r was varied from 0.1, to, 0.2, 0.3, and 0.4. The dynamics of the conetwork gels was discussed with the ensemble-average of the field correlation function, g E ( 1 ) ( τ ) , which was classified to three temperature regions: at low temperatures below LCST of PEMGE (≈23 °C) (region I), the dynamics was insensitive to r. On the other hand, strong r-dependence was observed for temperatures ≥ LCST (regions II and III). By approaching the LCST (region II), the slow dynamics component in g E ( 1 ) ( τ ) became more pronounced due to formation of hydrophobic domains. Additionally, the power-law exponent of the slow mode decreased in region II (near the LCST). In region III, the slow dynamics disappeared as a result of the further growth and immobilization of the hydrophobic domains.