Kuo Chen

Hydrogels, with their distinctive three-dimensional networks of hydrophilic polymers, drive innovations across various biomedical applications. The ability of hydrogels to absorb and retain significant volumes of water, coupled with their structural integrity and responsiveness to environmental stimuli, renders them ideal for drug delivery, tissue engineering, and wound healing. This review delves into the classification of hydrogels based on cross-linking methods, providing insights into their synthesis, properties, and applications. We further discuss the recent advancements in hydrogel-based drug delivery systems, including oral, injectable, topical, and ocular approaches, highlighting their significance in enhancing therapeutic outcomes. Additionally, we address the challenges faced in the clinical translation of hydrogels and propose future directions for leveraging their potential in personalized medicine and regenerative healthcare solutions.

One of the major challenges in the technology of sequencing DNA using single-molecule electrophoresis through a nanopore is to control the translocation of the macromolecule across the pore in order to allow sufficient time for accurate sequence reading at limited recording bandwidths. If the translocation speed is too fast, the signatures of the bases passing through the sensing region of the nanopore overlap in time, presenting difficulties in accurately identifying the bases in a sequential manner. Even though several strategies, such as enzyme ratcheting, have been implemented to reduce the translocation speed, the challenge to achieve a substantial reduction in the translocation speed continues to be of paramount significance. Toward achieving this goal, we have fabricated a nonenzymatic hybrid device that can reduce the translocation speed of long DNAs by more than 2 orders of magnitude, in comparison with the current status of the art. This device is made of a tetra-PEG hydrogel that is chemically anchored to the donor side of a solid-state nanopore. The idea behind this device is based on the recent discovery of the topologically frustrated dynamical state of confined polymers, whereby the front hydrogel matter of the hybrid device provides multiple entropic traps for a single DNA molecule holding it back against the electrophoretic driving force that pulls the DNA through the solid-state nanopore portion of the device. As a demonstration of slowing DNA translocation by a factor of about 500, we find the average translocation time realized in the present hybrid device for 3 kbp DNA as 23.4 ms, whereas the corresponding time for the bare solid-state nanopore under otherwise identical conditions is 0.047 ms. Our measurements on 1 kbp DNA and λ-DNA show that such a slowing down of DNA translocation with our hybrid device is general. An additional feature of our hybrid device is its incorporation of all features of the conventional gel electrophoresis to separate different DNA sizes in a clump of DNAs and to streamline them in an orderly and slow manner into the nanopore. Our results suggest the high potential of our hydrogel-nanopore hybrid device in further advancing the single-molecule electrophoresis technology to accurately sequence very large biological polymers.

The degradation of ultrahigh molecular weight poly(ethylene oxide) (UHMWPEO) was investigated in three volatile organic solvents, methanol, chloroform, and tetrahydrofuran. Particularly, degradation rate was determined by means of Ubbelohde viscometry and degradation products were characterized by using electron spin resonance spectroscopy (ESR) and Fourier transform infrared spectroscopy (FTIR). The highest degradation rate was observed for UHMWPEO in tetrahydrofuran, with the lowest one in methanol. The ESR results showed that PEO‐C• and •OH radicals were produced during the degradation process. Among these selected solvents, tetrahydrofuran was found to generate free radicals through an autoxidation mechanism. This would accelerate the degradation of UHMWPEO, resulting in the observed highest degradation rate in the UHMWPEO/tetrahydrofuran solution. Esters were also detected in the degradation products of these UHMWPEO solutions, while formates and formate ions were generated in the solutions of UHMWPEO/tetrahydrofuran and UHMWPEO/cloroform except for PEO/methanol. Furthermore, the degradation mechanism of UHMWPEO was deduced. This work enabled an in‐depth understanding on the thermo‐oxidative degradation mechanism of UHMWPEO in representative organic solvents, which would be instructive for developing optimal solution‐based processing technique of UHMWPEO.

Using fluorescence microscopy and single-particle tracking, we have directly observed the dynamics of λ-DNA trapped inside poly(acrylamide-co-acrylate) hydrogels under an externally applied electric field. Congruent with the recent discovery of the nondiffusive topologically frustrated dynamical state (TFDS) that emerges at intermediate confinements between the traditional entropic barrier and reptation regimes, we observe the immobility of λ-DNA in the absence of an electric field. The electrophoretic mobility of the molecule is triggered upon application of an electric field with strength above a threshold value E_c. The existence of the threshold value to elicit mobility is attributed to a large entropic barrier, arising from many entropic traps acting simultaneously on a single molecule. Using the measured E_c which depends on the extent of confinement, we have determined the net entropic barrier of up to 130 k_BT, which is responsible for the long-lived metastable TFDS. The net entropic barrier from multiple entropic traps is nonmonotonic with the extent of confinement and tends to vanish at the boundaries of the TFDS with the single-entropic barrier regime at lower confinements and the reptation regime at higher confinements. We present an estimate of the mesh size of the hydrogel that switches off the nondiffusive TFDS and releases chin diffusion in the heavily entangled state.