Dynamics of hydration water in gelatin and hyaluronic acid hydrogels

Water state, thermal transition behavior and structure of hydrated gelatin films

The state of water, thermal transition behaviors, molecular interactions, crystalline structure, and mechanical performance of hydrated gelatin films were studied by differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), X-ray diffraction, and universal testing instruments. The DSC results showed that with increase of the water content, two types of water, including unfreezable bound water and freezable water, appeared in turn. Below a critical water content of 30%, the glass transition temperature (Tg) of the hydrated gelatin films decreased notably with an increase in water content, which leveled off at water content higher than this threshold. This observation suggests that only the unfreezable water exhibits a plasticizing effect. In addition, the melting temperature (Tm) of hydrated gelatin films decreased continuously with an increase in water content, whereas the melting enthalpy showed a non-monotonic dependence on hydration level. Structural analysis showed that at medium hydration levels up to 13.4% water content, the unfreezable water facilitated the formation of additional triple helices, confirmed by DSC results. Spectral data revealed that the -OH groups of unfreezable water molecules interacted with the -NH groups of the protein via hydrogen bonds. Moreover, the mechanical properties of the hydrated gelatin films were sensitive to their hydration level, and the tensile strength was dominated by the helix content of the protein films. These results show the feasibility of using hydration to regulate the microstructure and properties of biopolymers.

Hydration effects on thermal transitions and molecular mobility in Xanthan gum polysaccharides

In this work, the xanthan gum (XG) polysaccharide is studied over a wide range of temperatures and water fractions 0 ≤ hw ≤ 0.70 (on a wet basis) by employing differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The investigation reveals that the critical water fraction for ice formation is about 0.35. Glass transition temperature (Tg) was determined through calorimetry experiments for all the samples studied. Water acts as a strong plasticizer, i.e., decreasing Tg, for water fractions up to about 0.35. A secondary (local) relaxation process is recorded in both dry and hydrated samples, which is sensitive to the presence of water molecules. This fact indicates that this process originates due to the orientation of small polar groups of the side chain, or/and due to the local main chain dynamics. Two types of long-range charge transport processes were resolved. The first is related to the conductive paths being formed via bulk-like ice structures (at high hydration levels), whereas the second can be attributed to proton mobility via the hydrogen bond (HB) network of non-freezing water existing in XG. Interestingly, this process is exactly the same in all the hydrated samples with hw > 0.25. With respect to the sample with hw = 0.27, a Vogel-Tammann-Fulcher (VTF)-like polarization process has also been recorded which seems to be related to long-range charge mobility via interconnected water clusters. As far as we are aware, this is the first time that XG is studied in terms of glass transition and molecular mobility over a wide range of hydration levels combining DSC and BDS techniques.

Primary human hepatocytes-laden scaffolds for the treatment of acute liver failure

Cell-based liver therapies based on retrieving and steadying failed metabolic function(s) for acute and chronic diseases could be a valuable substitute for liver transplants, even though they are limited by the low engraftment capability and reduced functional quality of primary human hepatocytes (PHH). In this paper we propose the use of gelatin-hyaluronic acid (Gel-HA) scaffolds seeded with PHH for the treatment of liver failure. We first optimized the composition using Gel-HA hydrogels, looking for the mechanical properties closer to the human liver and determining HepG2 cells functionality. Gel-HA scaffolds with interconnected porosity (pore size 102 μm) were prepared and used for PHH culture and evaluation of key hepatic functions. PHH cultured in Gel-HA scaffolds exhibited increased albumin and urea secretion and metabolic capacity (CYP and UGT activity levels) compared to standard monolayer cultures. The transplant of the scaffold containing PHH led to an improvement in liver function (transaminase levels, necrosis) and ameliorated damage in a mouse model of acetaminophen (APAP)-induced liver failure. The study provided a mechanistic understanding of APAP-induced liver injury and the impact of transplantation by analyzing cytokine production and oxidative stress induction to find suitable biomarkers of cell therapy effectiveness.

Dielectric relaxation of ice in a partially crystallized poly(N-isopropylacrylamide)microgel suspension compared to other partially crystalized polymer-water mixtures

A broadband dielectric spectroscopy study was conducted on a partially crystallized 10 wt% poly(N-isopropylacrylamide) [PNIPAM] microgel aqueous suspension to investigate the dielectric relaxation of ice in microgel suspensions. The measurements covered a frequency range of 10 mHz to 10 MHz and at temperatures ranging from 123 K to 273 K. Two distinct relaxation processes were observed at specific frequencies below the melting temperature. One is associated with the combination of the local chain motion of PNIPAM and interfacial polarization in the uncrystallized phase, while another is associated with ice. To understand the temperature-dependent behaviour of the ice relaxation process, the relaxation time of ice was compared with those observed in other frozen polymer water mixtures, including gelatin, poly-vinylpyrrolidone (PVP), and bovine serum albumin (BSA). For concentrations ≥ 10 wt%, the temperature dependence of the relaxation time of ice was found to be independent. Therefore, the study primarily focused on the 10 wt% data for easier comprehension of the ice relaxation process. It was found that the microgel and globular protein BSA had no significant effect on ice crystallization, while gelatin slowed down the crystallization process, and PVP accelerated it. To discuss the mechanism of the dielectric relaxation of ice, the trap-controlled proton transport model developed by Khamzin et al. [Chem. Phys., 2021, 541, 111040.] was employed. The model was used to discuss the dynamic heterogeneity of ice observed in this investigation, distinguishing it from the spatial heterogeneity of ice commonly discussed.

Dielectric relaxations of ice and uncrystallized water in partially crystallized bovine serum albumin-water mixtures

To investigate the dielectric relaxations of ice in low-concentration protein-water mixtures, broadband dielectric spectroscopy measurements were performed on partially crystallized bovine serum albumin (BSA)-water mixtures with BSA concentrations of 1-10 wt% at temperatures in the range of 123-298 K. The temperature dependence of the relaxation time of ice observed in all these mixtures changes twice at T_C1 (∼240 K) and T_C2 (200-160 K) (T_C1 > T_C2), i.e., at which the apparent activation energy, E_a, changes. Below 200 K, the relaxation of ice separates as 3-4 relaxations with different T_C2 and E_a values. The presence of the multiple ice relaxations is the same as that observed for the gelatin-water mixtures (T. Yasuda, K. Sasaki, R. Kita, N. Shinyashiki and S. Yagihara, J. Phys. Chem. B, 2017, 121, 2896), but the concentration dependences of T_C1 and T_C2 are different. The relaxation interpreted to be due to uncrystallized water in 20 wt% and 40 wt% BSA-water mixtures reported (N. Shinyashiki, W. Yamamoto, A. Yokoyama, T. Yoshinari, S. Yagihara, R. Kita, K. L. Ngai and S. Capaccioli, J. Phys. Chem. B, 2009, 113, 14448) was re-examined and concluded to be due to one of the multiple relaxations of ice.

Screening of the Chemical Composition and Identification of Hyaluronic Acid in Food Supplements by Fractionation and Fourier-Transform Infrared Spectroscopy

Hyaluronic acid, together with collagen, vitamins or plant extracts, is a part of many cosmetic and food preparations. For example, this polysaccharide is used in formulation of many food supplements due to its protective effects on human health. In this work, the screening of the chemical composition of three chosen dietary supplements (powder, tablets and capsules) containing hyaluronic acid was carried out using Fourier-transform infrared spectroscopy. Because of the low amount of analyte in all these samples, it was isolated or concentrated prior to the analysis using a suitable sequential fractionation protocol. Individual isolation procedures were established for each sample based on their declared composition. Firstly, the major components such as collagen or vitamins were removed to obtain polysaccharide fractions by the enzymatic treatment and/or washing out with the appropriate solvents. In some cases, the water insoluble part was removed from the rest dissolved in water. Then, hyaluronic acid was precipitated with copper(II) cations and thus separated from the other polysaccharides. Finally, the analyte was identified in the enriched fractions by the characteristic vibrational bands. The amount of hyaluronic acid in the purified fractions was determined in three ways: gravimetrically, spectrophotometrically, and using isotachophoresis. The combination of the appropriate preparative and analytical steps led to the successful evaluation of chemical composition, finding and quantification of hyaluronic acid in all the studied samples.

Deciphering the Molecular Mechanism of Water Interaction with Gelatin Methacryloyl Hydrogels: Role of Ionic Strength, pH, Drug Loading and Hydrogel Network Characteristics

Water plays a primary role in the functionality of biomedical polymers such as hydrogels. The state of water, defined as bound, intermediate, or free, and its molecular organization within hydrogels is an important factor governing biocompatibility and hemocompatibility. Here, we present a systematic study of water states in gelatin methacryloyl (GelMA) hydrogels designed for drug delivery and tissue engineering applications. We demonstrate that increasing ionic strength of the swelling media correlated with the proportion of non-freezable bound water. We attribute this to the capability of ions to create ion–dipole bonds with both the polymer and water, thereby reinforcing the first layer of polymer hydration. Both pH and ionic strength impacted the mesh size, having potential implications for drug delivery applications. The mechanical properties of GelMA hydrogels were largely unaffected by variations in ionic strength or pH. Loading of cefazolin, a small polar antibiotic molecule, led to a dose-dependent increase of non-freezable bound water, attributed to the drug’s capacity to form hydrogen bonds with water, which helped recruit water molecules in the hydrogels’ first hydration layer. This work enables a deeper understanding of water states and molecular arrangement at the hydrogel–polymer interface and how environmental cues influence them.