Thermogelling and chemoselectively cross-linked hydrogels for 3D bioprinting

Abstract

Event Abstract Back to Event Thermogelling and chemoselectively cross-linked hydrogels for 3D bioprinting Tina Vermonden1, Kristel W. Boere1, Maarten M. Blokzijl1, 2, Jetze Visser2, J Elder A. Linssen2, Jos Malda2, 3 and Wim Hennink1 1 Utrecht Institute for Pharmaceutical Sciences (UIPS), Utrecht University, Department of Pharmaceutics, Netherlands 2 University Medical Center Utrecht, Department of Orthopedics, Netherlands 3 Utrecht University, Department of Equine Sciences, Netherlands Introduction: Chemoselectively cross-linked hydrogels have recently gained increasing attention for the development of novel, injectable biomaterials given their limited side reactions. Recently, oxo-ester mediated native chemical ligation (OMNCL) gained interest as polymer cross-linking mechanism for hydrogels in biomedical applications because of its chemoselective character and rapid reaction kinetics under physiological conditions without the need for catalysts[1]-[3]. The aim of this study was to investigate the properties of novel thermoresponsive, in situ forming hydrogels cross-linked by OMNCL regarding their gelation kinetics, cell viability and suitability as bioinks for 3D-printing. Methods: Polymers solutions were prepared from cysteine functionalized thermo-responsive polymers (PNC) mixed with poly(ethylene)glycol (PEG) or hyaluronic acid (HA), both carrying N-hydroxysuccinimide (NHS) functionalized carboxylic acid moieties with a total polymer concentration of 11.3 and 9.1 wt% respectively. To obtain hydrogels, the solutions were heated to 37 ºC followed by spontaneous crosslinking via the OMNCL mechanism. To monitor gelation kinetics and mechanical properties, rheological experiments were performed using a cone and plate equipped rheometer. Cell viability of chondrocytes encapsulated within the hydrogels was evaluated using live/dead staining. The polymeric solutions were allowed to pre-crosslink for 30 minutes before starting filament deposition using a 3D Discovery bioprinter to obtain porous scaffolds. Results: The storage modulus of OMNCL cross-linked hydrogels reached a value of 26 kPa after 4 hours, which was over a 100 times higher than hydrogels formed by solely thermal physical interactions. The degradation rates of these hydrogels under physiological conditions could be tailored from 12 days up to 6 months by incorporation of hydrolysable dimethyl-γ-butyrolactone acrylate (DBA) monomers in the thermosensitive triblock copolymer. Precisely designed printed 3D constructs were obtained by deposition of partially cross-linked gels on a heated plate of 37°C resulting in stabilization of the construct due to the thermosensitive nature of the hydrogel. Subsequently, further chemical cross-linking of the polymers proceeded after extrusion to form mechanically stable hydrogels that exhibited a storage modulus of 9 kPa after 3 hours with a porosity of 47.9 ± 2.3%. Figure 1: Printed hollow cone shape by thermogelling OMNCL hydrogel Additionally, the hydrogels were covalently grafted to NHS functionalized poly-e-caprolactone printed constructs, which resulted in enhanced mechanical resistance to external forces when compared to an absence of covalent linkages between the two types of materials. Printed thermoplastic constructs infused with hyaluronic acid containing gels showed high cell viability of chondrocytes, showing their potential use as bioink. Conclusions: The favorable and controllable properties of the studied OMNCL cross-linked hydrogels are attractive for further evaluation in biomedical applications. Moreover, 3D-printing of these pre-crosslinked two-component hydrogels allows for the creation of constructs with good shape fidelity. This work was supported by a grant from the Dutch government to the Netherlands Institute for Regenerative Medicine (NIRM, grant No. FES0908).; Part of the research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 309962 (HydroZones).