¹⁹F MRI In Vivo Monitoring of Gelatin-Based Hydrogels: 3D Scaffolds with Tunable Biodegradation toward Regenerative Medicine

Abstract

Gelatin-based hydrogels emerged as promising biodegradable cell-compatible 3D-printable materials with tunable mechanical properties that serve tissue engineering and applications in regenerative medicine. Nevertheless, these materials are very challenging to monitor in vivo, which has hampered the further development of these materials and their translation into clinical practice. To overcome this limitation, we designed a crosslinked 3D-printable gelatin-based hydrogel endowed with poly[N-(2,2-difluoroethyl)acrylamide] (PDFEA). Such PDFEA-containing hydrogels can be monitored in vivo through fluorine-19 magnetic resonance imaging ( 19 F MRI), which enables to monitor such implants in vivo and to assess their in vivo biodegradation kinetics. Herein, we prepared three different PDFEA-containing hydrogels with varying cross-linking degrees and studied their physicochemical properties (storage modulus, Young's modulus, swelling ratio, in vitro degradation rate). Next, we administered these samples subcutaneously into mice and exploited 19 F MRI to detect the biodegradation kinetics over 370 days. Hydrogels with a high cross-linking degree did not extensively degrade in vitro nor in vivo within the evaluated time frame. In contrast, hydrogels characterized by a low degree of cross-linking extensively degraded in vitro as well as in vivo (half-life of 228 ± 21 days). We demonstrated that endowing hydrogels with PDFEA enables monitoring of these hydrogels in vivo. Our results may become a benchmark in forthcoming studies of biodegradable hydrogels and the development of 19 F MRI detectable gelatin-based hydrogels, paving the way toward their entry in clinical practice.

Digital Light Processing of 19F MRI-Traceable Gelatin-Based Biomaterial Inks towards Bone Tissue Regeneration

“…Szabó et al previously reported on the crosslinking efficiency of gel-MA-AEMA in the context of DLP processing, which resulted in 100% crosslinking efficiency regarding the -MA moieties and 96% for the -AEMA functionalities. Therefore, our findings are in line with previous reports [ 3 , 4 , 48 ].…”

“…The swelling ratio of the gel-MA-AEMA-F hydrogels was 4.8 ± 0.37 for 2D film, which suggests a significant decrease in the swelling capacity of the gel-MA-AEMA component upon supplementing it with a small crosslinker molecule, herein DFEA ( p < 0.0001). The results are in line with our previous study, where the addition of DFEA significantly decreases the swelling ratio of the modified gelatins [ 3 , 4 ]. The reason for this decrease in the SR is due to the hydrophobic nature of the PDFEA linkers and offers the potential to provide superior CAD/CAM mimicry to the hereby developed gel-MA-AEMA-F biomaterial inks.…”

“…Gelatin-based materials are one of the most studied hydrogels in regenerative medicine, since gelatin mimics the extracellular matrix (ECM) and supports cell adhesion and proliferation [ 1 , 2 ]. Additionally, gelatin has the capacity to be chemically modified, thereby allowing for tuning its physico-chemical and biological properties, or for introducing diagnostic modalities for future in vivo tracking capability, among others [ 3 , 4 ]. Moreover, gelatin can be chemically modified to introduce photo-crosslinkable moieties, e.g., methacrylamides (gelatin-methacryloyl, gel-MA) [ 5 , 6 ], to obtain shape fidelity upon applying UV–Vis irradiation in the presence of a suitable photo-initiator, thereby forming crosslinked hydrogel implants to serve regenerative applications [ 7 ].…”

“…Therefore, the current study reports on the optimization of the biomaterial ink composition to obtain mechanically stable (confirmed via oscillatory rheological measurements) porous scaffolds to be applied as cell carriers for osteogenic tissue regeneration. The ink composition is inspired based on our previously reported studies [ 3 , 4 ], yet the ideal composition utilizing gel-MA-AEMA and a specific DFEA content has been carefully selected to obtain scaffolds with ideal properties to support osteogenic differentiation. Subsequently, the scaffolds were combined with adipose tissue-derived stem cells (ASCs) to probe biocompatibility, cell adhesion, and their osteogenic differentiation potential.…”

“…Moreover, 19 F MRI can be executed with common 1 H MRI scanners with only minor hardware adjustments (or can even be acquired simultaneously with 1 H MRI scans) [28]. Previously, we incorporated N-(2,2-difluoroethyl)acrylamide (DFEA) into gelatin-based hydrogels [3,4], which endowed them with high amounts of magnetically equivalent fluorine atoms with optimal 19 F MR properties [29] and thus enabled their 19 F MRI/MRS detection [30][31][32]. Consequently, 19 F MRI (combined with 1 H MRI) scans can be used for anatomical localization of such implants, and 19 F MRS can be used to quantify their biodegradation rates, as demonstrated in our previous research [3].…”