Highly Elastic, Biodegradable Polyester-Based Citrate Rubber for 3D Printing in Regenerative Engineering

Highly elastic and 3D-printable degradable elastomers are advantageous for many biomedical applications. Herein, we report the synthesis of a biodegradable citrate rubber poly(tetrahydrofuran-<i>co</i>-citrate-<i>co</i>-hydroxyl telechelic natural rubber) (PTCR) using citric acid, poly(tetrahydrofuran), and hydroxyl telechelic natural rubber. The citrate rubber PTCR is methacrylated to synthesize a prepolymer methacrylated-PTCR (mPTCR) that can be used to fabricate bioresorbable scaffolds via 3D printing using micro-continuous liquid interface production. Polymers were chemically characterized via NMR spectroscopy, FTIR spectroscopy, DSC, and TGA and mechanically characterized via tensile testing and crimping. The addition of rubber improved the elasticity of PTCR (658 ± 68% for dry and 415 ± 45% for swollen films) significantly compared with its nonrubber-based citrate copolymer, i.e., poly(tetrahydrofuran-<i>co</i>-citrate) (PTC) (550 ± 51% for dry and 88 ± 10% for swollen films). Also, the mechanical strength of PTCR reached as high as 0.8 ± 0.06 MPa after the successful addition of rubber into PTC, which had a tensile strength of 0.55 ± 0.04 MPa. Notably, the 3D-printed vascular scaffold of mPTCR demonstrated excellent mechanical competence in crimping and expansion, which is necessary for clinical use. The percent diameter recovery of mPTCR vascular scaffolds (89.4 ± 1.1%) was higher than that of its nonrubber version, i.e., methacrylated-poly(tetrahydrofuran-<i>co</i>-citrate) (mPTC) (77.2 ± 6.7%), illustrating the contribution of rubber in mPTCR. In vitro degradation studies showed rapid hydrolytic degradation of the PTCR elastomer in 6 weeks, whereas 3D-printed scaffolds of mPTCR degraded slowly due to its improved stability after methacrylation. The cytocompatibility and cell attachment on the vascular scaffold surfaces were successfully demonstrated by using L929 mouse myoblasts. To conclude, this study reports a citrate-based rubber that should help meet some of the scaffold mechanical requirements for tissue-engineering applications.