Microstructural design to improve shape memory behavior of 3d-printed poly(L-lactide-co-glycolide-co-e-caprolactone) scaffolds for bone tissue engineering

Abstract

Nowadays, the reconstruction of critical-size bone defects, which occurs in many clinical situations including large open fractures with bone loss, infection requiring debridement of bone, and resection of bone tumors, continues to be challenging. Scaffold-based bone engineering has been provided as an alternative to traditional treatments using autografts and allografts by supporting bone regeneration. However, the classical scaffold remains an obstacle due to the limitations of the irregular shape of the defect. Therefore, this research has studied scaffolds made from biodegradation polymers in combination with shape memory behavior called biodegradable shape-memory polymers (BSMPs) to give the ability to shape recovery and fit the irregular defect and biodegradability simultaneously with new bone formation. BSMPs can be made utilizing traditional biodegradable polyesters by copolymerization, including block copolymerization, or microstructural modification, making them ideally suited for use in biomedical applications. Poly(L-lactide)-based polymers have been commonly studied as shape memory polymers. However, there are certain limitations with the high glass transition temperature of poly(L-lactide), limits in shape memory application, and the low degradation rate of poly(-caprolactone). So, the combination of L-lactide, glycolide, and -caprolactone to form terpolymers can overcome their limitations. In this study, medical-grade poly(L-lactide-co-glycolide-co--caprolactone) (PLGC) terpolymers have been developed to be 3D-printed porous scaffolds with shape memory behavior by copolymerizing block terpolymers for enhancing shape memory behavior and mechanical properties. The porous scaffolds have been designed and fabricated using a 3D printing teวchnique and evaluated for shape memory behavior and mechanical properties. Medical-grade PLGC with a terpolymer composition of LL:GA:CL 65:10:25 mol% was synthesized by both one-pot and two-step ring-opening polymerization methods. The results showed that the synthetic method chosen significantly affected the chain microstructure of the terpolymer obtained. The randomness coefficients calculated from the 13C-NMR spectra of both methods indicated that the two-step method produced a blockier microstructure (R almost 0). In addition, DSC and DMA thermograms showed the effect of chain microstructure on thermal properties, which correspond to mechanical property results from tensile testing. Both 3D-printed scaffolds showed interconnected pores after fabrication, which provide space for the subsequent regeneration of bone tissue for bone defects. However, the 3D-printed scaffolds of two-step PLGC, which have a blocky chain microstructure, have a higher shape recovery ratio and ability to recover shape than one-pot PLGC 3D-printed scaffolds. In addition, two-step PLGC 3D-printed scaffolds have potential mechanical properties equivalent to cancellous bone. In conclusion, PLGC terpolymers obtained from two-step ring-opening copolymerization have a blocky microstructure and inherent viscosity suitable for 3D-printing fabrication. The two-step PLGC 3D-printed scaffold has great shape recovery potential for tissue engineering and will provide a reference for the model 3D design of bone scaffolds.