Development of photocurable resins for the fabrication of self-healing hydrogels via Digital Light Processing 3D printing

Hydrogels represent a versatile class of biomaterials with unique properties that have sparked significant interest across various fields. In particular, they have emerged as promising candidates for numerous biomedical applications thanks to their biocompatibility, tunable mechanical properties and ability to mimic biological tissues. Self-healing hydrogels are biomaterials that can repair structural damage and recover their properties, similarly to human tissues. This characteristic makes these kinds of materials able to restore the morphology and mechanical properties after being damaged, thereby extending their lifespan and maintaining their structural integrity and functionality over time. The aim of the work is to investigate a self-healing hydrogel based on a resin which can be 3D printed via Digital Light Processing (DLP). DLP consists in a layer-by-layer 3D printing technology based on the photopolymerization of liquid polymer, that allows rapid and precise fabrication of objects. The network of the above-mentioned hydrogel is composed of polyethylene glycol diacrylate (PEGDA), hydroxyethyl methacrylate (HEMA), dithiothreitol (DTT), and borax. The self-healing chemistry is mainly based on boronic ester bonds, a class of dynamic covalent bonds. The experimental part consisted of studying the properties, including self-healing behaviour, of different formulations varying DTT-borax ratio and DTT-acrylates ratio, in order to select the optimal one in terms of mechanical properties recovery and 3D printing requirements. To do so, rheological and mechanical tests were performed. The results indicated that the printed hydrogel is able to recover its mechanical features even after multiple cycles of self-healing. Furthermore, the printing process was optimized, selecting parameters (such as time of exposure, light intensity, layer thickness) that best suited for a fast and controlled printing.