From Chain Growth to Step Growth Polymerization of Photoreactive Poly‐ε‐Caprolactone: The Network Topology of Bioresorbable Networks as Tool in Tissue Engineering

Abstract

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%.

Three dimensional printable multi‐arms poly(CL‐co‐TOSUO) for resilient biodegradable elastomer

“…The minimum cure depth was 85 μm. The resolution was better than previously reported PCL‐based photocurable resins 52–54 …”

“…The resolution was better than previously reported PCL-based photocurable resins. [52][53][54] The ability to print diverse structures with precision was demonstrated by Figure 8B. The grid (6.5 mm  6.5 mm  2 mm, length  width  thickness) and the 'nerve conduit' with four channels (8 mm  2 mm  5 mm, outer diameter  inner diameter  height) were successfully printed by DLP 3D printing.…”

Volumetric Printing of Thiol‐Ene Photo‐Cross‐Linkable Poly(ε‐caprolactone): A Tunable Material Platform Serving Biomedical Applications

“…These results illustrate that the acrylate crosslinked PCLs swell significantly less compared to the thiol-ene crosslinked PCLs, as could be expected given their inhomogeneous network topology. [23] Next, the double bond conversion (DBC) during network formation was investigated via differential photo-calorimetry (DPC) and high-resolution magic-angle spinning (HR-MAS) 1 H-NMR spectroscopy. These techniques were used, instead of more conventional infrared spectroscopy (FTIR), as the relatively low concentration of cross-linkable groups and the presence of noise stemming from the polymeric backbone render FTIR spectroscopy inappropriate.…”

“…[16,22] To overcome this limitation, we have recently introduced thiol-ene cross-linking to photo-cross-link PCL which resulted in a 10-fold improvement of the ultimate strength and elongation at break as compared to the state-ofthe-art. [23,24] This effect was attributed to the homogeneous network topology, stemming from the step-growth polymerization mechanism involved. [25] In an attempt to progress toward the outlined ideal scenario, volumetric 3D-printing of tunable and mechanically robust thiolene cross-linked PCL networks is herein introduced.…”

Exploiting the network architecture of thiol–ene photo-crosslinked poly(ε-caprolactone) towards tailorable materials for light-based 3D-printing

“…The resulting Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) mimicry is significantly improved as compared to deposition-based 3D-printing (e.g., extrusion). 10,19,[40][41][42][43] DLP is of particular interest since each layer is printed simultaneously, thereby strongly reducing the manufacturing time and as a consequence, increasing the cost efficiency of the technique. In DLP, the resolution depends on the material properties such as the cure depth and photo-crosslinking kinetics and can be as low as 25 µm.…”