**4. Conclusions**

In this study, we extruded β-TCP/PCL filaments of different ratios and sterilized the samples with clinically available E-beam irradiation, and implanted them in subcutaneous sites for 24 weeks. The degradation rates were characterized by micro-CT and live-CT, and biocompatibility of samples was examined by histology analyses. We observed that incorporation of TCP into PCL significantly increased degradation of the composite, but increasing TCP content in the composite did not accelerate degradation. Faster degradation occurred in the first four weeks and gradually slowed down afterward. E-beam sterilization also accelerated degradation, which is due to decreased crystallinity and shorter molecular chains of PCL after the E-beam irradiation. For the TCP/PCL filaments, the chemistry of samples plays a bigger role than the sterilization method in biodegradation. E-beam sterilization did not affect biocompatibility of the implants in the subcutaneous implantation. Our work suggests that creating TCP/PCL composites is a promising method for achieving the degradation properties required to fulfill clinical demands for the use of E-beam sterilization in osteosynthetic applications.

**Author Contributions:** Conceptualization, Y.P.Y., S.-W.P., J.-H.K., and J.K.; methodology, J.-H.K., J.K., J.-G.J., K.S., E.L., and C.K.; software, J.-H.K., J.K., E.L., and C.K.; validation, J.-H.K., J.K., J.-G.J., K.S., E.L., and C.K.; formal analysis, J.K., J.K., E.L., and C.K.; investigation, Y.P.Y., S.-W.P., J.-H.K., J.K., J.-G.J., K.S., E.L., and C.K.; resources, Y.P.Y. and S.-W.P.; data curation, Y.P.Y., S.-W.P., and A.W.; writing—original draft preparation, J.-H.K., J.K., Y.P.Y., and S.-W.P.; writing—review and editing, Y.P.Y., S.-W.P., E.L., K.S., and A.W.; visualization, J.-H.K. and J.K.; supervision, Y.P.Y. and S.-W.P.; project administration, Y.P.Y. and S.-W.P.; funding acquisition, Y.P.Y. and S.-W.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded through financial support from NIH grants R01AR057837, U01AR069395, R01AR072613; R01AR074458 from NIAMS; DoD gran<sup>t</sup> W81XWH18SBAA1 BA180237; and National Research Foundation of Korea (NRF) gran<sup>t</sup> 2019R1A2C1089456.

**Conflicts of Interest:** The authors declare no conflict of interest.
