(Photo-)crosslinkable gelatin derivatives for biofabrication applications

Abstract

Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for biofabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow to tune the material properties of gelatin, making it suitable for a wide range of biofabrication techniques both as a bioink and as a biomaterial ink (component).The present review provides a non-exhaustive overview of the different reported gelatin modification strategies to yield crosslinkable materials that can be used to form hydrogels suitable for 2 biofabrication applications. The different crosslinking chemistries are discussed and classified according to their crosslinking mechanism including chain-growth and step-growth polymerization.The step-growth polymerization mechanisms are further classified based on the specific chemistry including different (photo-)click chemistries and reversible systems. The benefits and drawbacks of each chemistry are also briefly discussed. Furthermore, focus is placed on different biofabrication strategies applying inkjet, deposition and light-based additive manufacturing techniques, and the applications of the obtained 3D constructs.

From Shape to Function: The Next Step in Bioprinting

“…Benefits include its stability and straightforward use as no additional crosslinkers are required ( Figure A). However, the chain growth reaction is prone to oxygen inhibition and leads to a limited control over the number of reacted functionalities resulting in oligo(methacrylamides) and thus also reduced control over mechanical properties and degradation products . In contrast, thiol–ene step growth reactions, like those based on the modification of gelatin with allyl groups (gelAGE) in combination with components containing thiol groups (e.g., dithiothreitol DTT), show faster reaction rates, more homogeneous networks and higher conversion rates.…”

“…In contrast, thiol–ene step growth reactions, like those based on the modification of gelatin with allyl groups (gelAGE) in combination with components containing thiol groups (e.g., dithiothreitol DTT), show faster reaction rates, more homogeneous networks and higher conversion rates. In addition, they are not susceptible to oxygen inhibition . Due to these advantages, step growth reactions are applied more frequently to crosslink functionalized macromers in bioinks and enable printing with high shape fidelity.…”

“…During the last decade the biofabrication window has been extended by improving bioink performance and bioprinting techniques. Many excellent reviews discuss the current status of bioink development [16,[30][31][32][33][34] and this is beyond the scope of the current review; however, several relevant components for bioinks and the respective crosslinking approaches are listed in Table 1.…”

“…However, the chain growth reaction is prone to oxygen inhibition and leads to a limited control over the number of reacted functionalities resulting in oligo(methacrylamides) and thus also reduced control over mechanical properties and degradation products. [33,109,110] In contrast, thiol-ene step growth reactions, like those based on the modification of gelatin with Without functionalization [35][36][37] Blending with stabilizing component (e.g., alginate, fibrin [37] ) Enzymatic crosslinking: transglutaminase [38] tyrosinase [39] Radical (photo-) polymerization Methacrylated [23,[40][41][42][43][44] Radical (photo-) polymerization Allylated [45] Norbornene [46] Thiolated [47,48] Tyramine [49] Furfuryl [50] Collagen type I Most abundant collagen in human body Gly-Pro-X pH-dependent fibrillogenesis and gelation Without functionalization pH-dependent crosslinking [51][52][53] photo-crosslinking (e.g., with riboflavin [54] ) crosslinked with genipin [55] Biodegradable Cell adhesion motifs are present Common sources: Rat tail Bovine skin Rabbit skin Calf skin Fibrinogen/fibrin Fibrous and nonglobular glycoprotein Thrombin (factor IIa) and factor XIIIa can be used to covalently crosslink fibrinogen Without functionalization [18,[35][36][37]43,51] Enzymatic crosslinking (factor IIa, XIIIa and IV) Additionally blended with stabilizing component (e.g., gelatin, hyaluronic acid, and Pluronic F127 [37] )…”

“…In addition, they are not susceptible to oxygen inhibition. [33,45] Due to these advantages, step growth reactions are applied more frequently to crosslink functionalized macromers in bioinks and enable printing with high shape fidelity. Additional examples of gelatin-based step growth systems are norbornene-functionalized (Gel-NB) and thiolated gelatin (Gel-SH), which have been used to create extrudable bioinks as well.…”