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

Abstract

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.

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

“…In order to create thiol-ene photo-crosslinked PCL networks with varying network topologies, alkene-functionalized PCL (E-PCL) precursors were synthesized with different architectures, according to a protocol reported previously. 23 First, linear and star-shaped (bi-, tri-and tetra-functional) PCL precursors were synthesized, using ethylene glycol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (trimethylolpropane) and pentaerythritol as initiator, respectively (Scheme 1). A ring opening polymerization (ROP) approach was chosen, compared to the polycondensation of hydroxycarboxylic acids, since ROP ensures a low polymer dispersity (i.e., 1.1 to 1.6).…”

“…Moreover, their use in several biomedical applications is approved by the Food and Drug Administration. 4 Especially PCL has attracted significant attention as a result of its toughness (tensile strength of [16][17][18][19][20][21][22][23][24] MPa and elongation at break of approximately 1000%, for thermo-plastic PCL) and slow biodegradation rate of 3 to 4 years. Furthermore, due to PCLs excellent visco-elastic properties, it has been frequently applied in injection moulding and extrusion-based 3D-printing.…”

“…The current work builds further on our previous research in which it was demonstrated that the molar mass between crosslinks (M c ) could effectively be used to fine-tune the network's physico-chemical properties. 23 Herein, we further extend the tunability of thiol-ene photo-crosslinked PCL networks by modifying the network topology through both the architecture of the oligomeric precursor (i.e., linear versus starshaped) and the crosslinker (i.e., tri-versus tetrafunctional thiol). The influence of the network topology on the physico-chemical properties of the crosslinked networks is comprehensively evaluated.…”

Digital Light Processing 3D Printing of Soft Semicrystalline Acrylates with Localized Shape Memory and Stiffness Control

“…Axial extension was carried out at 20 mm/min (200%/min) until fracture. Elastic recovery and plastic deformation were extrapolated from straining 5,10,20,30,40,50,75,100,125,150,175,200,250, and 300%. 67 4.11.…”

“…For example, (meso)­phase transitions between crystalline and isotropic (amorphous) states upon heating/cooling have been used extensively for shape-memory applications with 2D liquid crystalline and semicrystalline polymers. − In contrast to T g , a kinetic phenomenon, the melting temperature ( T m ) is associated with a first-order phase transition that results in a sharp, energic change in morphology, exemplified by the large enthalpy of melting (Δ H m ≈ 10–100 J/g). , Thus, actuation through T m can be both rapid and result in a large/reversible deformation with a high output of latent energy that can translate into work. However, only a few examples of semicrystalline shape-memory polymers prepared by vat photopolymerization 3D printing exist. − One such approach by Ge and co-workers involves adding semicrystalline poly­(caprolactone) into a methacrylic resin, where it was demonstrated that between 10 and 50% poly­(caprolactone) provided stiff plastics (tensile moduli, E > 50 MPa) with melting enthalpies ranging from ∼7 to 32 J/g, and shape recovery ratios of 83–95%. , Another example by Furukawa and co-workers describes the incorporation of acrylic monomers containing long, saturated n -alkyl chains into acrylamide-based resins to prepare shape-memory hydrogels, where the monomer ratios were varied to tune the degree of semicrystallinity, water equilibrium swelling between ∼60 and 10% and elastic modulus E between 0.5 and 26.9 MPa . Despite these promising examples, DLP 3D printing of neat semicrystalline resins to access shape-memory materials has yet to be thoroughly examined, with no known cases of multimaterial printing where properties are localized in predefined space (e.g., layers).…”