Processing a Tunable Triblock-copolymer Composed of Poly(ε-caprolactone) and Poly(L-lactic acid) by Electrospinning and Melt Electrowriting for Soft-Tissue Biomedical applications

At present, poly(ε-caprolactone) (PCL) is still the gold standard when electrospinning (ES) or melt electrowriting (MEW) are considered for fibrous scaffold design intended for biomedical applications. This can be attributed to its ability to easily form stable jets during ES and its low melting point and melt viscosity required for MEW. However, PCL possesses slow degradation kinetics, making it unsuitable for some soft-tissue biomedical applications such as blood vessels, muscles, tendons or nerves. In particular for MEW, limited success has been achieved when trying to shift away from PCL. To circumvent this limitation, a block-copolymerization of PCL with various poly(L-lactic acid) (PLLA) end-group lengths (PLLA-b-PCL-b-PLLA) is introduced by using a one-pot, two-step ring-opening polymerization (ROP). The first ROP, initiated by diethylene glycol, yields PCL-diol which acts as a high molar mass backbone (>30,000 g mol-1) required for ES. In the second step, different molar ratio's of L-lactide are added to form PLLA-b-PCL-b-PLLA ranging between 32,000 and 52,000 g mol-1. Chromatographic and spectroscopic analysis confirms the polymer molar mass and successful addition of PLLA end-blocks. These polymers display enhanced polymer mobility and degradation kinetics and sufficiently high molar mass without significantly increasing the melting point and melt viscosity compared to commercial PCL. This makes the triblock-copolymer the first tunable copolymer of PCL with PLLA, suitable for both ES and MEW processing of homogeneous fibers at temperatures below 110°C in literature. The fiber quality using ES improves especially for longer PLLA end-group lengths (i.e. 46,000 and 52,000 g mol-1), which additionally shortens degradation time. The two shortest PLLA-b-PCL-b-PLLA polymers (i.e. 32,000 and 38,000 g mol-1) enable MEW processing at 90°C into micro-fibrous grid scaffolds up to 15 layers. Finally, good biocompatibility of PCL and PLLA separately hints to its use as a suitable material for soft-tissue biomedical applications.