The regeneration of critical-size bone defects, especially those with irregular shapes, remains a clinical challenge. Various biomaterials have been developed to enhance bone regeneration, but the limitations on the shape-adaptive capacity, the complexity of clinical operation, and the unsatisfied osteogenic bioactivity have greatly restricted their clinical application. In this work, we construct a mechanically robust, tailorable and water-responsive shape-memory silk fibroin/magnesium (SF/MgO) composite scaffold, which is able to quickly match irregular defects by simple trimming, thus leading to good interface integration. We demonstrate that the SF/MgO scaffold exhibits excellent mechanical stability and structure retention during the degradative process with the potential for supporting ability in defective areas. This scaffold further promotes the proliferation, adhesion and migration of osteoblasts and the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro. With suitable MgO content, the scaffold exhibits good histocompatibility, low foreign-body reactions (FBRs), significant ectopic mineralisation and angiogenesis. Skull defect experiments on male rats demonstrate that the cell-free SF/MgO scaffold markedly enhances bone regeneration of cranial defects. Taken together, the mechanically robust, personalised and bioactive scaffold with water-responsive shape-memory may be a promising biomaterial for clinical-size and irregular bone defect regeneration.

Study Design. In vitro laboratory study. Objective. To measure the effects of transverse partial sacrectomies on the compressive and torsional stiffness of the sacroiliac joints. Summary of Background Data. Surgical treatment for sacral tumor of different location and nature includes partial or complete sacrectomy. Though the biomechanical investigations about the local destructive force of residual sacrum after partial sacrectomy have been reported, biomechanical properties of the residual sacroiliac joints after different transverse partial sacrectomies remain unknown. Methods. Seven fresh human cadaveric L5-pelves with normal bone mineral density were used in this study. Each specimen was tested in intact condition first, followed by a series of segmental transverse partial sacrectomies: under S2 partial sacrectomy (U-S2); U-½S2; U-S1; U-½S1; and right side sacroiliac joint resection (one-side). A material testing machine was used to apply 800 N compression and 7 Nm torsion loads through the L5/S1 joint. The resected dimensional area of sacroiliac joints and structural stiffness of the residual sacroiliac joints were analyzed. Results. Average percentages of the resected area of sacroiliac joints were 8.4% in U-S2, 15.1% in U-½S2, 24.8% in U-S1, and 72.3% in U-½S1, respectively. In compression U-S2 ∼ one-side preserved 98.7%, 97.1%, 94.4%, 82.9%, and 55.2% of the initial stiffness of the sacroiliac joint, respectively. No significant differences were detected among intact, U-S2, U-½S2, and U-S1 (P > 0.05). However, compressive stiffness of U-½S1 and one-side was markedly less than that of intact, U-S2, and U-½S2 (P < 0.05). In Torsion U-S2 ∼ one-side preserved 90.7%, 88.5%, 81.9%, 71.9%, and 44.5% of the initial sacroiliac joint stiffness, respectively. No significant differences were demonstrated among intact, U-S2, and U-½S2 (P > 0.05); However, U-S1, U-½S1 and one-side exhibited significantly less torsional stiffness than intact and U-S2 (P < 0.05). Conclusion. In surgical treatment of distal sacral tumor, transverse partial sacrectomy involving S1 could result in rotational instability, and the resection level beyond ½S1 further led to compressive instability. When the sacrectomy was at or above the S1/2 level, local reconstruction should be considered.

• Several components within the osteosarcoma microenvironment are expressed abnormally. • Osteosarcoma has a markedly different microRNA profile from healthy bone. • microRNAs play roles in the crosstalk between osteosarcoma cells and the tumour microenvironment.

In recent years, mesenchymal stem/stromal cells (MSCs), especially those isolated from bone marrow (BM-MSCs), have been utilized to treat a diverse range of dis