Dynamic behavior of water in hydro-swollen crosslinked polymer gel as studied by PGSE 1H NMR and pulse 1H NMR

Effect of Mammalian Tissue Source on the Molecular and Macroscopic Characteristics of UV-Cured Type I Collagen Hydrogel Networks

The tissue source of type I collagen is critical to ensure scalability and regulation-friendly clinical translation of new medical device prototypes. However, the selection of a commercial source of collagen that fulfils both aforementioned requirements and is compliant with new manufacturing routes is challenging. This study investigates the effect that type I collagen extracted from three different mammalian tissues has on the molecular and macroscopic characteristics of a new UV-cured collagen hydrogel. Pepsin-solubilised bovine atelocollagen (BA) and pepsin-solubilised porcine atelocollagen (PA) were selected as commercially available raw materials associated with varying safety risks and compared with in-house acid-extracted type I collagen from rat tails (CRT). All raw materials displayed the typical dichroic and electrophoretic characteristics of type I collagen, while significantly decreased lysine content was measured on samples of PA. Following covalent functionalisation with 4-vinylbenzyl chloride (4VBC), BA and CRT products generated comparable UV-cured hydrogels with significantly increased averaged gel content (G ≥ 97 wt.%), while the porcine variants revealed the highest swelling ratio (SR = 2224 ± 242 wt.%) and an order of magnitude reduction in compression modulus (Ec = 6 ± 2 kPa). Collectively, these results support the use of bovine tissues as a chemically viable source of type I collagen for the realisation of UV-cured hydrogels with competitive mechanical properties and covalent network architectures.

Imaging Self-Healing Hydrogels and Chemotherapeutics Using CEST MRI at 3 T

Imaging hydrogel-based local drug delivery to the brain after tumor resection has implications for refining treatments, especially for brain tumors with poor prognosis and high recurrence rate. Here, we developed a series of self-healing chitosan-dextran (CD)-based hydrogels for drug delivery to the brain. These hydrogels are injectable, self-healing, mechanically compatible, and detectable by chemical exchange saturation transfer magnetic resonance imaging (CEST MRI). CD hydrogels have an inherent CEST contrast at 1.1 ppm, which decreases as the stiffness increases. We further examined the rheological properties and CEST contrast of various chemotherapeutic-loaded CD hydrogels, including gemcitabine (Gem), doxorubicin, and procarbazine. Among these formulations, Gem presented the best compatibility with the rheological (G': 215.3 ± 4.5 Pa) and CEST properties of CD hydrogels. More importantly, the Gem-loaded CD hydrogel generated another CEST readout at 2.2 ppm (11.6 ± 0.1%) for monitoring Gem. This enabled independent and simultaneous imaging of the drug and hydrogel integrity using a clinically relevant 3 T MRI scanner. In addition, the Gem-loaded CD hydrogel exhibited a longitudinal antitumor efficacy of Gem over a week in vitro. Furthermore, the CD hydrogel could be visualized by CEST after brain injection with a contrast of 7.38 ± 2.31%. These natural labels on both the chemotherapeutics and hydrogels demonstrate unique image-guided local drug delivery for brain applications.

Kinetic Insights into Marangoni Effect-Assisted Preparation of Ultrathin Hydrogel Films

In a previous work ( ACS Appl. Mater. Interfaces 2017, 9, 34349-34355), a facile approach was reported to prepare thin hydrogel films based on the Marangoni effect. After dripping onto a water surface, a drop of ethanol solution of poly(stearyl acrylate- co-acrylic acid) [P(SA- co-AAc)] spread quickly to form a thin film. The solvent exchange from ethanol to water led to the gelation of polymer solution which turned into a hydrogel film. Here, we investigate the scenario and seek for the governing kinetics of the Marangoni effect-assisted preparation of hydrogel films. By incorporating aggregation-induced emission fluorogens into the P(SA- co-AAc) solution, so that fluorescence appears at the gel state, we found that the spreading usually completed before the full gelation of the entire film. The spreading and formation of the gel films were influenced by the molar fraction of SA, f, and the polymer concentration of ethanol solution, C_P. The spreading was blocked when C_P was too high, whereas the film was fragmented into small pieces when C_P was too low. At an intermediate C_P, uniform hydrogel films were obtained. Steady spreading at a constant speed was observed during the processes which yielded uniform hydrogel films. Both C_P and f influenced the spreading process by tuning the surface tension of the ethanol solution and the viscoelasticity of the gelated film, as suggested by our theoretical model. This work provided kinetic insights into the Marangoni phenomena of viscous polymer solutions. The strategy and principle should be applicable to other systems on preparing thin supramolecular gel films with versatile functions.

Site-Specific Pre-Swelling-Directed Morphing Structures of Patterned Hydrogels

Morphing materials have promising applications in various fields, yet how to program the self-shaping process for specific configurations remains a challenge. Herein we show a versatile approach to control the buckling of individual domains and thus the outcome configurations of planar-patterned hydrogels. By photolithography, high-swelling disc gels were positioned in a non-swelling gel sheet; the swelling mismatch resulted in out-of-plain buckling of the disc gels. To locally control the buckling direction, masks with holes were used to guide site-specific swelling of the high-swelling gel under the holes, which built a transient through-thickness gradient and thus directed the buckling during the subsequent unmasked swelling process. Therefore, various configurations of an identical patterned hydrogel can be programmed by the pre-swelling step with different masks to encode the buckling directions of separate domains.

Surface sliding friction of negatively charged polyelectrolyte gels

The friction between two polyelectrolyte gels carrying the same or opposite sign of charges has been investigated using a rheometer. It is found that the friction was strongly dependent on the interfacial interaction between two gel surfaces. In the repulsive interaction case, especially, the friction was extremely low. The friction behavior is attempted to be described in terms of the hydrodynamic lubrication of the solvent layer between two like-charged gel surfaces, which is formed due to the electrostatic repulsion of the two gel surfaces. From the theoretical analysis (hydrodynamic mechanism), the friction behaviors were explained qualitatively, all of the experimental results, nevertheless, could not be understood well. The viscoelastic feature of the gel and the non-Newtonian behavior of water at the friction interface are considered to be important to elucidate the gel friction.

High-resolution diffusion-ordered spectroscopy to probe the microenvironment of JandaJel and Merrifield resins

The success of organic reactions performed on a gel-phase resin is highly dependent on the accessibility of solvents, catalysts, and reagents to the interior of the resin. A variety of techniques including EPR, fluorescence, and Hildebrand solubility parameters (delta) have been used to probe reaction capabilities and in particular the microenvironment of a gel-phase resin. To provide a more detailed picture of the matrix in question, researchers have turned to NMR for the determination of the diffusion coefficients of solvents and small molecules in swollen beads to provide a means to compare the microenvironment of swollen beads. Since Merrifield and JandaJel resins display different swelling properties and have significantly different kinetic behavior, we undertook a comparative study of the diffusion coefficients of solvents and small molecules in both resins by high-resolution (1)H DOSY NMR. Our results show the following: (1) diffusion values for all studied solvents and small molecules are 20-30% higher in JandaJel compared to Merrifield resins, (2) in the absence of interactions between the resin and a given molecule, the diffusion values mirror the swelling properties of the resin, and (3) in the presence of strong intermolecular interactions between the gel and the considered molecule, the diffusion behavior in the gel is primarily influenced by the strength of the interactions and secondarily by the swelling properties of the resin. These results clearly show that the microenvironment of JandaJels is more "solution-like" than that of Merrifield resins, presumably due to the higher swelling capacity.