4D Printing of Biocompatible Scaffolds via In Situ Photo-crosslinking from Shape Memory Copolyesters.

The complexity of surgical treatments for large-area soft tissue injuries makes placing large implants into injury sites challenging. Aliphatic polyesters are often used for scaffold preparation in tissue engineering owing to their excellent biodegradability and biocompatibility. Scaffolds with shape-memory effect (SME) can also avoid large-volume trauma during the implantation. However, the complexity and diversity of diseases require more adaptable and precise processing methods. Four-dimensional (4D) printing, a booming smart material additive manufacturing technology, provides a new opportunity for developing shape memory scaffolds. With the aim of personalized or patient-adaptable soft tissues such as blood vessels, we developed a feasible strategy for fabricating scaffolds with fine architectures using 4D printing crosslinkable shape memory linear copolyesters using fused deposition modeling (FDM). To overcome the weak bonding strength of each printed layer during FDM, a catalyst-free photo-crosslinkable functional group derived from biocompatible cinnamic acid was embedded into the linear copolyesters as in situ crosslinking points during FDM printing. Under ultraviolet-assisted irradiation, the resulting 4D scaffold models demonstrated excellent SME, desirable mechanical performance, and good stability in a water environment owing to the chemical bonding between each layer. Moreover, the excellent biocompatibility of the scaffold was evaluated in vitro and in vivo. The developed composite scaffolds could be used for minimally invasive soft tissue repair.

Shape Memory Polyester Scaffold Promotes Bone Defect Repair through Enhanced Osteogenic Ability and Mechanical Stability.

Bone tissue engineering involving scaffolds is recognized as the ideal approach for bone defect repair. However, scaffold materials exhibit several limitations, such as low bioactivity, less osseointegration, and poor processability, for developing bone tissue engineering. Herein, a bioactive and shape memory bone scaffold was fabricated using the biodegradable polyester copolymer's four-dimensional fused deposition modeling. The poly(ε-caprolactone) segment with a transition temperature near body temperature was selected as the molecular switch to realize the shape memory effect. Another copolymer segment, i.e., poly(propylene fumarate), was introduced for post-cross-linking and improving the regulation effect of the resulting bioadaptable scaffold on osteogenesis. To mimic the porous structures and mechanical properties of the native spongy bone, the pore size of the printed scaffold was set as ∼300 µm, and a comparable compression modulus was achieved after photo-cross-linking. Compared with the pristine poly(ε-caprolactone), the scaffold made from fumarate-functionalized copolymer considerably enhanced the adhesion and osteogenic differentiation of MC3T3-E1 cells in vitro. In vivo experiments indicated that the bioactive shape memory scaffold could quickly adapt to the defect geometry during implantation via shape change, and bone regeneration at the defect site was remarkably promoted, providing a promising strategy to treat bone defects in the clinic, substantial bone defects with irregular geometry.