Chemically cross-linkable gelatin methacryloyl (GM) derivatives are getting increasing attention regarding biomedical applications. Thus, thorough investigations are needed to achieve full understanding and control of the physico-chemical behavior of these promising biomaterials. We previously introduced gelatin methacryloyl acetyl (GMA) derivatives, which can be used to control physical network formation (solution viscosity, sol-gel transition) independently from chemical cross-linking by variation of the methacryloyl-to-acetyl ratio. It is known that temperature dependent physical network formation significantly influences the mechanical properties of chemically cross-linked GM hydrogels. We investigated the temperature sensitivity of GM derivatives with different degrees of modification (GM2, GM10), or similar degrees of modification but different methacryloyl contents (GM10, GM2A8). Rheological analysis showed that the low modified GM2 forms strong physical gels upon cooling while GM10 and GM2A8 form soft or no gels. Yet, compression testing revealed that all photo cross-linked GM(A) hydrogels were stronger if cooling was applied during hydrogel preparation. We suggest that the hydrophobic methacryloyl and acetyl residues disturb triple helix formation with increasing degree of modification, but additionally form hydrophobic structures, which facilitate chemical cross-linking.

In this study, we present a fast and convenient liquid foam templating route to generate gelatin methacryloyl (GM) foams. Microfluidic bubbling was used to generate monodisperse liquid foams with bubble sizes ranging from 220 to 390 μm. The continuous phase contained 20 wt % GM and 0.7 wt % lithium phenyl-2,4,6-trimethylbenzoylphosphinate as photoinitiator. Gelation was achieved via UV-initiated radical cross-linking of GM. After cross-linking, the hydrogel foams were either swollen in water or freeze-dried. The pore sizes of the dry foams were 15−20% smaller than the bubble sizes of the liquid templates, whereas the pore sizes of the swollen porous hydrogels were in the range of the bubble sizes of the liquid templates. Compared to commonly used methods for the fabrication of biopolymer scaffolds, our route neither involves cryogenic treatment nor toxic chemicals or organic solvents and potentially allows for the photoencapsulation of cells.

Gelatin methacryloyl (GM) hydrogels have been investigated for almost 20 years, especially for biomedical applications. Recently, strengthening effects of a sequential cross-linking procedure, whereby GM hydrogel precursor solutions are cooled before chemical cross-linking, were reported. It was hypothesized that physical and enhanced chemical cross-linking of the GM hydrogels contribute to the observed strengthening effects. However, a detailed investigation is missing so far. In this contribution, we aimed to reveal the impact of physical and chemical cross-linking on strengthening of sequentially cross-linked GM and gelatin methacryloyl acetyl (GMA) hydrogels. We investigated physical and chemical cross-linking of three different GM(A) derivatives (GM10, GM2A8 and GM2), which provided systematically varied ratios of side-group modifications. GM10 contained the highest methacryloylation degree (DM), reducing its ability to cross-link physically. GM2 had the lowest DM and showed physical cross-linking. The total modification degree, determining the physical cross-linking ability, of GM2A8 was comparable to that of GM10, but the chemical cross-linking ability was comparable to GM2. At first, we measured the double bond conversion (DBC) kinetics during chemical GM(A) cross-linking quantitatively in real-time via near infrared spectroscopy-photorheology and showed that the DBC decreased due to sequential cross-linking. Furthermore, results of circular dichroism spectroscopy and differential scanning calorimetry indicated gelation and conformation changes, which increased storage moduli of all GM(A) hydrogels due to sequential cross-linking. The data suggested that the total cross-link density determines hydrogel stiffness, regardless of the physical or chemical nature of the cross-links.

Cross‐linkable gelatin methacryloyl (GM) is widely used for the generation of artificial extracellular matrix in tissue engineering. However, so far, isoelectric points (IEPs) of highly methacryloylated GM derivatives are limited to IEPs below 7 due to the consumption of amino groups in the modification reaction. In this contribution, the synthesis of a new GM derivative, gelatin methacryloyl‐aminoethyl (GME), with an IEP above 7 similar to the gelatin type A (GA) starting material is reported, together with a high degree of methacryloylation. GME is obtained by reacting GM with ethylenediamine (EDA). The impact of the EDA functionalization on the properties of GM and GME derivatives is characterized thoroughly via 1H‐NMR, 1H‐13C‐HSQC‐NMR, IEP, solution viscosity, gel point, and physico‐chemical properties of resulting hydrogels. The second functionalization step results in amino group concentrations similar to GA and with that in an IEP of 9.9. The data suggest that amino functionalization with EDA prevents physical cross‐linking in the same way as described before for acetyl functionalization. Therefore, GME hydrogels are less stiff than GM hydrogels from GMs with a comparable amount of methacrylic functions. With GME, a gelatin derivative is available that is positively charged at neutral pH without being limited to low methacryl modifications.

Microwave-assisted extraction (MAE) is recognized as a green method for extraction of natural products. The current research aimed to explore the MAE for fucoidans extraction from different brown seaweeds, including Fucus vesiculosus, F. spiralis, and Laminaria saccharina. Following several solvent-extraction pre-treatment steps and MAE optimization, the algal biomasses were extracted in a ratio of 1:25 in 0.1 M HCl containing 2 M CaCl2 for 1.0 min. The results showed that L. saccharina’s extract was different from the others, regarding the highest sugar content reached 0.47 mg glucose equivalent/mg extract being confirmed by monosaccharide composition analysis and the lowest fucoidan content and sulfation degree at 0.09 mg/mg extract and 0.13, respectively. Moreover, these findings were confirmed by tentative structural elucidation based on Fourier-transform infrared spectrometry which also showed a different spectrum. However, the MAE enhanced melanoidins formation in products, which was confirmed by the intense band at 1420 cm−1. Interestingly, the results of monomeric composition showed that fucoidan extract by MAE from F. vesiculosus belonged to sulfated galactofucans which are known for their potential bioactivities. Furthermore, the cytotoxic activity of the four fucoidans in concentrations ranging from 4.9 µg/mL to 2500 µg/mL was investigated and correlated with the chemical characterization showing that F. vesiculosus_MAE fucoidan was the most potent and safest. The current research revealed the chemical heterogeneity of fucoidans regarding taxonomical class and used greener extraction method of fucoidans toward the achievement of the UN sustainability goals.