Differentiation of physical and chemical cross-linking in gelatin methacryloyl hydrogels

• Published in: Scientific reports 2021-02, Vol.11 (1), p.3256-3256, Article 3256
• Main Authors: Rebers, Lisa, Reichsöllner, Raffael, Regett, Sophia, Tovar, Günter E. M., Borchers, Kirsten, Baudis, Stefan, Southan, Alexander
• Format: Article
• Language: English
• Subjects: 639/301/54/1754; 639/301/54/989; 639/301/923/1027; 639/301/923/1028; 639/301/923/1029; 639/638/298/303; 639/638/298/54; 639/638/298/923/1027; 639/638/298/923/1028; 639/638/298/923/1029; Calorimetry; Circular dichroism; Conformation; Differential scanning calorimetry; Gelatin; Humanities and Social Sciences; Hydrogels; Infrared spectroscopy; Investigations; multidisciplinary; Science; Science (multidisciplinary); Spectrum analysis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-021-82393-z

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.