Chase Nowaczyk

Background: Critical-size bone defects remain a major challenge in orthopedics because successful repair requires more than restoration of structural anatomy alone. Although autografts, allografts, and conventional scaffolds can provide mechanical support or osteogenic material, they frequently fail to reproduce the coordinated biological processes required for durable regeneration, including angiogenesis, immune regulation, and biomineralization. Large defects commonly occur in poorly vascularized, mechanically unstable, or chronically inflamed environments, which further impair healing and contribute to delayed union, nonunion, and repeated surgical intervention. Recent advancements in bone tissue engineering have therefore shifted away from simple passive scaffolds designed primarily to mimic bone architecture and toward multifunctional systems that actively regulate the cellular and molecular events required for repair.

Objective: This narrative review examines the mechanistic progression of bone tissue engineering strategies for critical-size bone defects, with emphasis on how scaffold design has evolved from solely structural biomimicry to multidimensional systems that coordinate vascular, immune, mineralization, and antimicrobial functions.

Search Methods: An online literature search was conducted primarily using Web of Science and publisher-hosted primary research articles published from 2020 to 2025. Search terms included “bone tissue engineering” and the filter “Hot Papers” was utilized to find final primary mechanistic studies that then underwent detailed review.

Results: Early work demonstrated that lamellar intrafibrillar collagen-hydroxyapatite scaffolds improved osteogenic differentiation and in vivo bone formation compared with controls, establishing structural organization as an important component of optimal regenerative.¹ However, this approach did not directly address vascularization or direct stimulation of coordinated signaling axis. Subsequent work showed that biodegradable Mg enhanced bone regeneration through a sensory nerve-mediated CGRP-FAK-VEGF signaling axis, identifying a causal pathway linking biomaterial design to angiogenesis and repair.² Further advances introduced electroactive mineralized scaffolds that increased calcium influx, ATP-dependent purinergic signaling, cytoskeletal remodeling, and BMP2-Smad1/5 osteogenic signaling.³ This same design was shown to simultaneously suppress bacterial burden through silver ion and reactive oxygen species generation.³ Additional study developed biomimetic intrafibrillar mineralized collagen scaffolds containing silver nanowires that showed preserved BMP2-Smad1/5-Runx2 signaling and osteogenesis under inflammatory stress, supporting regeneration in infectious defect models.⁴ The most integrated system, Osteomimix, combined a self-mineralizing magnesium-calcium phosphate/collagen hydrogel with a mechanically supportive scaffold to promote vascularized bone formation, M2-like macrophage polarization, immune modulation, and biomimetic mineralization within a single customizable construct.⁵

Conclusion: Collectively, these studies define a clear mechanistic progression in bone tissue engineering from passive structural scaffolds to active, multidimensional platforms that direct regeneration through coordinated control of not only architecture but angiogenesis, immune signaling, mineralization, and infection resistance. This body of work supports an underlining design principle: the most optimal repair of critical-size bone defects will require scaffold systems that recreate the regenerative cascade of native bone healing rather than addressing any single component in isolation. Future research should focus on improving translational scalability, long-term functional outcomes, and clinical applicability of these integrated biomaterial systems.

Works Cited

1. Yu L, Rowe DW, Perera IP, et al. Intrafibrillar Mineralized Collagen-Hydroxyapatite-Based Scaffolds for Bone Regeneration. ACS Appl Mater Interfaces. 2020;12(16):18235-18249. doi:10.1021/acsami.0c00275
2. Xu J, Mi J, He X, et al. Biodegradable magnesium combined with distraction osteogenesis synergistically stimulates bone tissue regeneration via CGRP-FAK-VEGF signaling axis. Biomaterials. 2021;275:120984. doi:10.1016/j.biomaterials.2021.120984
3. Li Z, He D, Guo B, et al. Self-promoted electroactive biomimetic mineralized scaffolds for bacteria-infected bone regeneration. Nat Commun. 2023;14(1). doi:10.1038/s41467-023-42598-4
4. Zhang Y, Li Z, Guo H, et al. A Biomimetic Multifunctional Scaffold for Infectious Vertical Bone Augmentation. Adv Sci. 2024;11(26). doi:10.1002/advs.202310292
5. Wu X, Yang H, Liu G, et al. Osteomimix: A Multidimensional Biomimetic Cascade Strategy for Bone Defect Repair. Adv Mater. 2025;37(11):e2416715. doi:10.1002/adma.202416715