First report on the effect of topology design on the biodegradation, mechanical properties, and cell responses of additively manufactured Zn.

Bone regeneration is a complex process that is influenced by tissue interactions, inflammatory responses, and progenitor cells. Diseases, lifestyle, or multiple trauma can disturb fracture healing, which might result in prolonged healing duration or even failure. The current gold standard therapy in these cases are bone grafts. However, they are associated with several disadvantages, e.g., donor site morbidity and availability of appropriate material. Bone tissue engineering has been proposed as a promising alternative. The success of bone-tissue engineering depends on the administered cells, osteogenic differentiation, and secretome. Different stem cell types offer advantages and drawbacks in this field, while adipose-derived stem or stromal cells (ASCs) are in particular promising. They show high osteogenic potential, osteoinductive ability, and immunomodulation properties. Furthermore, they can be harvested through a noninvasive process in high numbers. ASCs can be induced into osteogenic lineage through bioactive molecules, i.e., growth factors and cytokines. Moreover, their secretome, in particular extracellular vesicles, has been linked to fracture healing. The aim of this review is a comprehensive overview of ASCs for bone regeneration and bone tissue engineering.

Tenocytes are mechanosensitive cells intimately adapting their expression profile and hence, their phenotype to their respective mechanomilieu. The immunolocalization and expression intensity of tenogenic, anabolic and catabolic markers in tenocytes in response to in vitro mechanical loading have not been monitored by immunohistochemical staining (IHC). Thus, we investigated the association between IHC intensities, different stimulation frequencies, and tenogenic metabolism using a versatile mechanical stretcher. Primary tenocytes obtained from murine Achilles tendons were transferred to poly(dimethylsiloxane) (PDMS) elastomeric chamber. Chambers were cyclically stretched by 5% in uniaxial direction at a variation of tensile frequency (1 or 2 Hz) for 3 h. After stretching, cell physiology, IHC intensities of tendon-related markers, and protein level of the angiogenesis marker vascular endothelial growth factor (VEGF) were evaluated. Cell proliferation in tenocytes stimulated with 1 Hz stretch was significantly higher than with 2 Hz or without stretch, while 2 Hz stretch induced significantly reduced cell viability and proliferation with microscopically detectable apoptotic cell changes. The amount of scleraxis translocated into the nuclei and tenomodulin immunoreactivity of tenocytes treated with stretch were significantly higher than of non-stretched cells. The collagen type-1 expression level in tenocytes stretched at 1 Hz was significantly higher than in those cultivated with 2 Hz or without stretching, whereas the matrix metalloproteinase (MMP)-1 and MMP-13 immunoreactivities of cells stretched at 2 Hz were significantly higher than in those stimulated with 1 Hz or without stretching. The secreted VEGF-protein level of tenocytes stretched at 2 Hz was significantly higher than without stretching. Our IHC findings consistent with cell physiology suggest that appropriate stretching can reproduce in vitro short-term tenogenic anabolic/catabolic conditions and allow us to identify an anabolic stretching profile.

Significance: Osteonecrosis (ON) is characterized by bone tissue death due to disturbance of the nutrient artery. The detailed process leading to the necrotic changes has not been fully elucidated. Clinically, high-dose corticosteroid therapy is one of the main culprits behind osteonecrosis of the femoral head (ONFH). Recent Advances: Numerous studies have proposed that such ischemia concerns various intravascular mechanisms. Of all reported risk factors, the involvement of oxidative stress in the irreversible damage suffered by bone-related and vascular endothelial cells during ischemia simply cannot be overlooked. Several articles also have sought to elucidate oxidative stress in relation to ON using animal models or in vitro cell cultures. Critical Issues: However, as far as we know, antioxidant monotherapy has still not succeeded in preventing ONFH in humans. To provide this desideratum, we herein summarize the current knowledge about the influence of oxidative stress on ON, together with data about the preventive effects of administering antioxidants in corticosteroid-induced ON animal models. Moreover, oxidative stress is counteracted by nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent cytoprotective network through regulating antioxidant expressions. Therefore, we also describe Nrf2 regulation and highlight its role in the pathology of ON. Future Directions: This is a review of all available literature to date aimed at developing a deeper understanding of the pathological mechanism behind ON from the perspective of oxidative stress. It may be hoped that this synthesis will spark the development of a prophylactic strategy to benefit corticosteroid-associated ONFH patients. Antioxid. Redox Signal. 35, 357–376.

Oxidative stress is implicated in osteoarthritis, and nuclear factor erythroid 2–related factor 2 (Nrf2)/antioxidant response element (ARE) pathway maintains redox homeostasis. We investigated whether Nrf2/ARE signaling controls SOX9. SOX9 expression in human C-28/I2 chondrocytes was measured by RT–qPCR after shRNA-mediated knockdown of Nrf2 or its antagonist the Kelch-like erythroid cell-derived protein with cap ‘‘n’’ collar homology-associated protein 1 (Keap1). To verify whether Nrf2 transcriptionally regulates SOX9, putative ARE-binding sites in the proximal SOX9 promoter region were inactivated, cloned into pGL3, and co-transfected with phRL–TK for dual-luciferase assays. SOX9 promoter activities without and with Nrf2-inducer methysticin were compared. Sox9 expression in articular chondrocytes was correlated to cartilage thickness and degeneration in wild-type (WT) and Nrf2-knockout mice. Nrf2-specific RNAi significantly decreased SOX9 expression, whereas Keap1-specific RNAi increased it. Putative ARE sites (ARE₁, ARE₂) were identified in the SOX9 promoter region. ARE₂ mutagenesis significantly reduced SOX9 promoter activity, but ARE₁ excision did not. Functional ARE₂ site was essential for methysticin-mediated induction of SOX9 promoter activity. Young Nrf2-knockout mice revealed significantly lower Sox9-positive chondrocytes, and old Nrf2-knockout animals showed thinner cartilage and more cartilage degeneration. Our results suggest Nrf2 directly regulates SOX9 in articular cartilage, and Nrf2-loss can develop mild osteoarthritis at old age. Pharmacological Nrf2 induction may hold the potential to diminish age-dependent cartilage degeneration through improving SOX9 expression.