A review of shape memory characteristics of 4D printed bone scaffolds based on thermotropic shape memory polymers

Shape Memory Polymers (SMPs), a class of smart materials capable of shape-programed recovery through temperature stimulation, have opened new avenues for personalized preparation and dynamic functional regulation of bone tissue engineering scaffolds when combined with 4D printing technology. This review strictly follows the PRISMA systematic review guidelines, and literature retrieval and screening were independently completed by two researchers. Literature sources included Web of Science, PubMed, and ScienceDirect, with a retrieval time range from January 2018 to May 2025. Excluding review articles, letters, and conference abstracts, 37 original research articles were included. This paper systematically reviews the shape memory mechanisms of thermotropic SMPs and the current status of 4D printing applications in bone scaffold fabrication. Thermotropic SMPs rely on the chemical structure of “fixed phase-reversible phase” dual-network, where the fixed phase maintains the permanent shape, and the reversible phase (e.g. PCL crystalline segments, PLA glassy segments) realizes temporary shape fixation and recovery. Different from existing descriptive reviews, this work critically analyzes the correlation between scaffold shape memory characteristics (recovery rate, response speed, mechanical adaptability) and bone repair performance, deciphers the regulatory mechanisms of material modification and structural design, and summarizes existing performance trade-offs and technical contradictions. This paper also systematically categorizes core challenges in material design, printing processing, biological performance, and clinical translation, and proposes actionable future research directions. This work aims to provide standardized theoretical references and technical guidance for optimizing the design and clinical application of 4D-printed bone scaffolds based on thermotropic SMPs.