Microinjection molded PLA/ZnO-TiO2 composites with in situ fibrillation: achieving mechanical matching cortical bone and enhanced osteoinduction

Abstract

Polylactic acid (PLA) has emerged as a cornerstone material in bone tissue engineering due to its biocompatibility and processability. Nevertheless, critical limitations persist, including thermal deformation susceptibility and inadequate osteoinductive capacity, which collectively hinder its clinical translation for load-bearing applications. Herein, we engineer a microinjection molded PLA@ZnO-TiO₂ composite bone fixation plate that simultaneously addresses these challenges through innovative interfacial engineering. The high shear stress during microinjection processing induces in situ fibrillation of ZnO-TiO₂ hybrids, generating a unique oriented structure which promoted the interaction of the interfaces between the PLA and ZnO-TiO₂. All samples demonstrated elastic moduli greater than 1.2 GPa, consistent with the specification of human cortical bone. In addition, a uniform spatial distribution of Zn was also observed. The PLA@6%ZnO-TiO₂ composite maintained a uniform Zn²⁺ release concentration ranging from 0.62 to 1.88 µM under vitro conditions, a bioactive range that effectively supported osteoblast proliferation and differentiation. This unique hierarchical architecture and bioactive Zn²⁺ ions synergistically enhanced the in vitro cell attachment. The PLA@6%ZnO-TiO₂ composite resulted in a 34.5% increase in ALP activity and 200.1% increase in mineralization levels compared to the control group, indicating its strong potential to promote osteogenic differentiation. Our work establishes a paradigm-shifting manufacturing strategy that transcends conventional composite design, offering dual-phase optimization of structural reliability and biological functionality for future resorbable orthopedic implants.