Hybrid Modified Cubic-Honeycomb-Plate Structure: A Novel Bone Regeneration Scaffold with Enhanced Mechanical Stiffness Achieved Through High Printing Fidelity

Abstract

Achieving exact printing fidelity in polymer-based bone regeneration scaffolds through additive manufacturing, particularly those of dispensing-type, remains a significant challenge. During fabrication, scaffolds often deviate from the intended design geometry, which can negatively affect their performance. Additionally, achieving mechanical properties similar to natural bone in scaffolds remains challenging. Therefore, this study introduces the Hybrid Modified Cubic-Honeycomb Plate (hybrid MCHP) structure to improve printing fidelity and mechanical properties over previous bone regeneration scaffolds through innovative geometry design. This hybrid MCHP scaffold was inspired by cubic honeycomb and plate-lattice structures due to their excellent mechanical performance and well-optimized geometry, which ensure optimal printability. The effective elastic stiffness of the proposed structure and control group was predicted using a numerical Asymptotic Expansion Homogenization (AEH) model. Bone regeneration scaffolds were fabricated using Polycaprolactone (PCL) and a 3D printer with a Precision Extrusion Deposition (PED) system. Printing fidelity in manufactured scaffolds was then evaluated, resulting in a printing fidelity of 97.93 ± 1.1% for the hybrid MCHP-structure scaffold (compared to 82.31 ± 3.6% and 92.00 ± 2.5% in the case of Kagome-structure and modified honeycomb (MHC)-structure scaffolds, which are the control groups). Mechanical testing of the hybrid MCHP-structure scaffold using a Universal Testing Machine (UTM) depicted similarity with 91.1% of the numerical estimated effective elastic stiffness (compared to 82.8% and 79.0% in the case of Kagome-structure and MHC-structure scaffolds, which serve as the control groups). The biological potential of the scaffolds was evaluated through in vitro studies using MC3T3-E1 pre-osteoblasts. The CCK-8 assay showed significantly enhanced cell viability and proliferation on the hybrid MCHP scaffold at all time points (days 1, 7, and 14), consistently outperforming the Kagome and MHC scaffolds. Additionally, immunofluorescence staining analysis revealed abundant focal adhesions and uniform nuclear distribution, highlighting the superior cytocompatibility and effective support for cellular activity of the hybrid MCHP scaffold.