Fluid dynamics and oxygen transport in 3D-printed scaffolds within perfusion bioreactors for bone tissue engineering

GENERAL SUMMARY Bone tissue engineering has emerged as a promising approach to overcome the clinical challenges associated with critical-sized bone defects, where bone’s intrinsic regenerative capacity is insufficient. Crucial to the success of engineered bone constructs is the design of three-dimensional (3D)-scaffolds that provide the appropriate structural, biochemical, and biophysical cues to support cell proliferation and osteogenic differentiation. However, a significant limitation of critical-sized scaffolds is insufficient oxygen diffusion to the core of the scaffold, leading to hypoxia-induced cell death and impaired bone regeneration. Furthermore, bone cells, especially osteocytes, are highly mechanosensitive, and fluid-induced mechanical stimulation plays a crucial role in regulating osteogenic activity. This thesis investigated the interplay between fluid dynamics and oxygen transport in functionalized 3D-printed scaffolds cultured in perfusion bioreactors, in order to optimize osteogenic outcomes and address hypoxia-induced challenges for effective bone regeneration in critical-sized bone defects. This thesis offers a solution to the persistent problem of hypoxia-induced cell death in critical-sized scaffolds by unraveling the complex interplay between fluid dynamics and oxygen diffusion in cell-seeded 3D-printed scaffolds in perfusion bioreactors. Innovative surface functionalization approaches of 3D-printed PCL scaffolds, e.g., immobilizing carboxymethyl κ-carrageenan, incorporating a high concentration of carbonated-nanohydroxyapatite and collagen, and employing wet-chemical etching instead of plasma-assisted methods, improved biochemical and mechanical properties of the scaffolds and enhanced osteogenic activity. Furthermore, using experiments and finite element modeling, our studies provide quantitative insight into fluid-induced shear stress and oxygen diffusion in 3D-printed PCL scaffolds within a perfusion bioreactor. The research highlights that perfusion bioreactors are essential tools for preventing hypoxia-induced cell death in critical-sized cell-seeded 3D-printed PCL scaffolds. By elucidating the role of osteocyte mechanosensing and mechanotransduction in bone remodeling and orthodontic movement, this thesis links fluid-derived mechanical cues to cellular signaling pathways that regulate bone regeneration. This thesis not only bridges the gap between fundamental biology and engineering but also paves the way for clinically viable, personalized constructs that could transform the treatment of critical-sized bone defects in oral and maxillofacial surgery and orthopedics, reducing reliance on traditional grafts and promoting bone regeneration.