[Zurück]

J. Van Hoorick, M. Markovic, P. Gruber, L. Tytgat, J Van Erps, H Thienpont, A. Ovsianikov, P. Dubruel, S. Van Vlierberghe:
"Thiolated Crosslinker effect on Physico-Chemical properties and Laser-Based Processing of Gelatin Thiol-ene Hydrogels";
Vortrag: The International Conference on Biofabrication 2018, Würzburg; 28.10.2018 - 31.10.2018; in: "The International Conference on Biofabrication 2018", Abstract book, (2018), S. O14.

Gelatin hydrogels have been frequently applied in the fields of biofabrication and regenerative medicine, due to their close resemblance to the natural extracellular matrix (ECM) since it is derived from collagen, the main constituent of the ECM. As a result, it exhibits favourable cell-interactivity due to the presence of arginylglycyl aspartic acid (RGD) sequences along its backbone. Furthermore, it is biodegradable,low-cost and FDA-approved with a long track record in the food and pharmaceutical industry1,2. Despite all these benefits towards biofabrication, the material also exhibits an upper critical solution temperature (around 30°C) resulting in dissolution at physiological conditions. To overcome this limitation, the material can be modified chemically to introduce photo-crosslinkable functionalities resulting in a covalent network upon UV irradiation in the presence of a photoinitiator.
In this respect, the most frequently reported modification is the introduction of methacrylamides by reaction of the primary amines in gelatin with methacrylic anhydride1,3. These methacrylamides can subsequently be polymerized using UV-irradiaton following a radically induced chain growth polymerization mechanism. Although this material has a proven track record in the field of tissue engineering, throughout the past decade, the interest has shifted more towards thiol-ene photoclick crosslinking chemistry for a number of reasons. First, the crosslinking reaction proceeds via a step growth polymerisation scheme with a high degree of orthogonality. As a consequence, a more homogeneous network is formed. Furthermore, in general, thiol-ene hydrogels are characterised by faster crosslinking kinetics in combination with lower shrinkage during crosslinking, rendering them more suitable candidates towards light-induced additive manufacturing techniques. When aiming at a high degree of orthogonality, preferably an `ene´ functionality is selected which cannot undergo competitive homo-polymerization. However, only vinyl ethers and norbornene functionalities exhibit this behaviour. Of specific interest in this respect is the norbornene functionality due to its "spring-loaded" behaviour, since reaction with the thiol relieves ring strain. Furthermore, norbornene functionalities are also known for their rapid subsequent radical transfer to another thiol. As a result, norbornene thiol-ene reactions typically proceed very fast with a high degree of orthogonaltiy.4
To apply this crosslinking chemistry to gelatin
hydrogels, the primary amines of gelatin functionalized with 5-norbornene-2-carboxylic acid by means of
1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide/N- Hydroxysuccinimide (EDC/NHS) coupling chemistry yielding gel-NB with a degree of substitution of 89%.5 These hydrogel precursors were subsequently photo- crosslinked in an equimolar thiol-ene ratio using a range of multifunctional, thiolated crosslinkers with different molecular weights and thiol functionalities including dithiothreitol (DTT), tetraethylene glycol dithiol (TEG2SH), polyethylene glycol dithiol (Mn 3400 g/mol, PEG2SH 3400), 4-arm polyethylene glycol tetrathiol (Mn 10000 g/mol, PEG4SH 10000), 4-arm polyethylene glycol tetrathiol (Mn 20000 g/mol, PEG4SH 20000) and thiolated gelatin with a degree of substitution of 72% prepared following a previously reported protocol6.
The influence of these different crosslinkers was assessed in terms of mechanical properties, swelling degree, network density and crosslinking kinetics using photorheological measurements. Furthermore, the cytotoxicity of the different crosslinkers was assessed using adipose tissue-derived stem cells, as well as preliminary cell encapsulation experiments were performed.
Finally, the 2PP structuring range and concomitant swelling behaviour of the materials was assessed as a function of required laser power at a constant scanning speed (100 mm/s). The observed swelling degree of these microstructures provides insight with respect to degree of conversion.

https://publik.tuwien.ac.at/files/publik_273798.pdf