Advancing synthetic bone tissue engineering materials: Nano-scale investigation into transitional Interface in carbon dots/ polymer composites

Identifying suitable biocompatible and processable materials that mimic the properties of native bone tissue remains a significant challenge in bone tissue engineering (BTE). Polymerized Trimethylolpropane Triacrylate (PTMPTA), a rapid photocurable, stiff, bioinert thermoset polymer, has previously suggested as matrix of BTE composites, but still lacks mechanical properties, biocompatibility, and printing accuracy, which need to be improved to meet BTE requirements. In this study, citric acid carbon dots (CA CDs) synthesized via microwave pyrolysis were blended into the PTMPTA matrix. Nano-scale spectroscopy and atomic force microscopy (AFM) techniques for the first time revealed the transitional interface layers with different chemical structures between CA CDs and PTMPTA. Those transitional interface layers facilitate uniform stress distribution, enhance load transfer, prevent debonding caused by CDs agglomeration, reduce over-curing and thermal stress and improving surface cell adhesion and proliferation, together with CA CDs enhancing mechanical strength, biocompatibility, and processability of the resulting composite. Ultimately, composite incorporating 8 wt% CA CDs was determined to the highest mechanical properties, biocompatibility, and 3D printing accuracy, achieving a 3.5-fold increase in compressive Young's modulus and load-bearing capacity, a 1.5-fold increase in tensile Young's modulus, and a 2-fold cell surface proliferation compared to pure PTMPTA, and has successfully approached the target 3D printing accuracy. This work opens the door to the vast compositional space of different carbon dot/polymer composites targeting the demanding requirements of BTE and lays the foundation for future BTE materials.