Cell-Interactive Gelatin-Based ¹⁹F MRI Tracers: An In Vitro Proof-of-Concept Study

Abstract

Cross-linked gelatin-based hydrogels are highly promising cell-interactive, biocompatible, and biodegradable materials serving tissue engineering. Moreover, gelatins with covalently bound methacrylamide (gel-MA) and 2-aminoethyl methacrylate moieties (gel-AEMA) can be cross-linked through ultraviolet (UV) irradiation, which allows light-based three-dimensional (3D)-printing of such hydrogels. Furthermore, the physicochemical and biological properties of these hydrogels can be broadly tuned by incorporating various comonomers into the polymer chains, which makes these hydrogels a widely applicable platform in tissue engineering and reconstructive surgery. However, monitoring the degradation rate of hydrogel-based implants in vivo is challenging, thereby prohibiting their broad clinical transition and further research. Therefore, herein, we describe the synthesis of 3D-printable gelatin-based hydrogels with N-(2,2-difluoroethyl)acrylamide (DFEA), detectable with the chemical shift of −123 ppm, which enables us to monitor these implants in vivo with 19F magnetic resonance imaging (MRI) and assess their degradation kinetics. Next, we describe the physicochemical and biological properties of these hydrogels. Adding DFEA monomers into the reaction mixture accelerates their cross-linking kinetics. Moreover, increasing the DFEA content within the hydrogels increases their swelling ratio and 19F MRI signal. All hydrogels were detectable at small quantities (<16 mg) using 19F MRI. Moreover, our hydrogels supported the cell proliferation of adipose tissue-derived stem cells (ASCs) and had tunable biodegradation rates. Finally, we present a strategy for increasing the DFEA content without affecting the mechanical properties. Our results may be implemented in the future development of hydrogel implants, whose fate and biodegradation rate can be monitored via 19F MRI.

Photoprintable Radiopaque Hydrogels for Regenerative Medicine

“…Increasing the content of AATIPA in the hydrogels increased their G ′ values and decreased their SRs in water (Table S13), which is in line with what was described earlier for other small-molecular comonomers. , This effect likely arises because increasing the content of a small-molecular comonomer decreases the hydrophilicity of the hydrogels, thereby limiting their ability to swell and thereby increasing their mechanical stiffness. In the context of tissue engineering, the G ′ values of the hydrogels need to match the G ′ values of soft tissues (e.g., adipose tissue, G ′ = 0.3–1.3 kPa; intervertebral disk, G ′ = 8–93 kPa; prostate, G ′ = 6.6–21.9 kPa). , Therefore, the AATIPA content can be adapted to tune the mechanical properties to optimize these materials toward serving tissue engineering purposes for the above-mentioned types of tissue.…”

“…Notwithstanding their properties, these hydrogels are particularly difficult to monitor in vivo . , The inability to do so has markedly hindered their development and transition to clinical practice. Nevertheless, gelatin hydrogels can be modified for fluorescence imaging, optical coherence tomography, ultrasound imaging, X-ray and computed tomography (CT) imaging, − positron emission tomography, and single-photon emission computed tomography, in addition to several 1 H and 19 F magnetic resonance imaging techniques. − …”

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

“…We studied the in vitro degradation of our hydrogels as previously described in literature. 35 As a model enzyme, we used collagenase IV from Clostridium histolyticum metalloproteinase-2 (MMP-2; 0.5 to 5.0 FALGPA units/ mg solid, ≥125 CDU/mg solid), which mimics the in vivo degradation. Briefly, we prepared cylindrical samples of hydrogels (0.8 cm radius, 1.0 mm height) and incubated them in Tris−HCl buffer (0.5 mL, 0.1 M, pH 7.4) in the presence of 0.005% (w/v) NaN 3 and 5 mM CaCl 2 at 37 °C for 30 min.…”

“…27−34 More recently, we incorporated the PDFEA tracer into 2D gelatin-based hydrogel films. 35 We have shown that incorporating PDFEA into hydrogels can fine-tune their mechanical properties and that their in vitro proteolysis can be either sustained or significantly prolonged. In this study, we prepared gelatin-based hydrogels with various levels of crosslinking and DFEA content and studied their physicochemical properties (storage modulus, Young's modulus, swelling ratio, in vitro degradation rate).…”

“…The gel-MA-30, gel-MA-70, and gel-MA-100 were left to dissolve together with or without DFEA monomer in dry DMSO (10 w/v % solutions of the modified gelatin) at 50 °C in a dark glass vial to protect the solution from the light (exact masses and molar amounts are depicted in Table 1). This ratio of DFEA monomer and MA groups has been shown in our previous study to provide the highest fluorine content in final materials, 35 where the ratio resulting in the highest DFEA loading in final hydrogel was selected, ensuring low limits of detection for the 19 F MRI method.…”