Control of the network topology by selection of an appropriate cross‐linking chemistry is introduced as a new strategy to improve the elasticity and toughness of bioresorbable networks. The development of novel photocross‐linkable and bioresorbable oligomers is essential for the application of light‐based 3D‐printing techniques in the context of tissue engineering. Although light‐based 3D‐printing techniques are characterized by an increased resolution and manufacturing speed as compared to extrusion‐based 3D‐printing, their application remains limited. Via chemical modification, poly‐ε‐caprolactone (PCL) is functionalized with photoreactive end groups such as acrylates, alkenes, and alkynes. Based on these precursors, networks with different topologies are designed via chain growth polymerization, step growth polymerization, or a combination thereof. The influence of the network topology and the concomitant cross‐linking chemistry on the thermal, mechanical, and biological properties are elucidated together with their applicability in digital light processing (DLP). Photocross‐linkable PCL with an elongation at break of 736.3 ± 47% and an ultimate strength of 21.3 ± 0.8 MPa is realized, which is approximately tenfold higher compared to the current state‐of‐the‐art. Finally, extremely elastic DLP‐printed dog bones are developed which can fully retrieve their initial length upon stress relieve at an elongation of 1000%.

Current thoroughly described biodegradable and cross‐linkable polymers mainly rely on acrylate cross‐linking. However, despite the swift cross‐linking kinetics of acrylates, the concomitant brittleness of the resulting materials limits their applicability. Here, photo‐cross‐linkable poly(ε‐caprolactone) networks through orthogonal thiol‐ene chemistry are introduced. The step‐growth polymerized networks are tunable, predictable by means of the rubber elasticity theory and it is shown that their mechanical properties are significantly improved over their acrylate cross‐linked counterparts. Tunability is introduced to the materials, by altering Mc (or the molar mass between cross‐links), and its effect on the thermal properties, mechanical strength and degradability of the materials is evaluated. Moreover, excellent volumetric printability is illustrated and the smallest features obtained via volumetric 3D‐printing to date are reported, for thiol‐ene systems. Finally, by means of in vitro and in vivo characterization of 3D‐printed constructs, it is illustrated that the volumetrically 3D‐printed materials are biocompatible. This combination of mechanical stability, tunability, biocompatibility, and rapid fabrication by volumetric 3D‐printing charts a new path toward bedside manufacturing of biodegradable patient‐specific implants.

Acrylate-based photo-cross-linked poly­(ε-caprolactone) (PCL) tends to show low elongation and strength. Incorporation of osteo-inductive hydroxyapatite (HAp) further enhances this effect, which limits its applicability in bone tissue engineering. To overcome this, the thiol–ene click reaction is introduced for the first time in order to photo-cross-link PCL composites with 0, 10, 20, and 30 wt % HAp nanoparticles. It is demonstrated that the elongation at break and ultimate strength increase 10- and 2-fold, respectively, when the photopolymerization mechanism is shifted from a radical chain-growth (i.e., acrylate cross-linking) toward a radical step-growth polymerization (i.e., thiol–ene cross-linking). Additionally, it is illustrated that osteoblasts can attach to and proliferate on the surface of the photo-cross-linked PCL-HAp composites. Finally, the incorporation of HAp nanoparticles is shown to reduce the ALP activity of osteoblasts. Overall, thiol–ene cross-linked PCL-HAp composites can be considered as promising potential materials for bone tissue engineering.

Thiol–ene photo-crosslinked poly-ε-caprolactone networks, exhibiting varying network architectures, were employed to fine-tune physico-chemical characteristics, while simultaneously exploring their potential application in digital light processing.

In an attempt to mimic nature's ability to adhere cells, PCL is often coated with nature-derived polymers or its surface is functionalized with a cell-binding motif. However, said surface modifications are limited to the material's surface, include multiple steps, and are mediated by harsh conditions. Here, we introduce a single-step strategy toward cell-adhesive polymer networks where thiol-ene chemistry serves a dual purpose. First, alkene-functionalized PCL is crosslinked by means of a multifunctional thiol. Second, by means of a cysteine coupling site, the cell-binding motif C(-linker-)RGD is covalently bound throughout the PCL networks during crosslinking. Moreover, the influence of various linkers (type and length), between the cysteine coupling site and the cell-binding motif RGD, is investigated and the functionalization is assessed by means of static contact angle measurements and X-ray photoelectron spectroscopy. Finally, successful introduction of cell adhesiveness is illustrated for the networks by seeding fibroblasts onto the functionalized PCL networks.