Three Dimensional Printed Immunomodulatory Scaffolds with Controlled Drug Release for Bone Regeneration

Abstract

Large bone defects pose significant challenges in orthopaedic surgery, necessitating the exploration of innovative repair technologies beyond traditional treatments like autografts, allografts, and synthetic substitutes, each fraught with specific challenges. Tissue engineering and regenerative medicine have emerged as promising fields, employing bioactive materials, growth factors, and cellular components to emulate natural bone properties and functions. Notably, additive manufacturing techniques contribute to these advancements by customising 3D-printed scaffolds enhancing patient-specific treatments. Recent studies underscore the significant influence of immune responses in bone regeneration, an area still in its infancy. Particularly, the modulation of immune reactions through specialised biomaterials and the strategic delivery of anti-inflammatory agents like dexamethasone present a novel approach to support bone healing processes, avoiding the systemic side effects of traditional drug administration. In this thesis, novel inks were developed to sustain the release of dexamethasone from a 3D-printed scaffold to modulate the immune response and osteogenesis. Excipients with surfactant properties, including the poloxamers F127, F68, L31, sorbitan monooleate Span80, and sucrose acetate isobutyrate (SAIB), were added to PCL to test their ability to sustain drug release. All these inks were fabricated into scaffolds by using direct ink writing 3D printing technique. The fabricated scaffolds were then characterised by SEM, DSC, FTIR, and ToF-SIMS. Macrophages and mesenchymal stem cells (MSCs) were cocultured to investigate the effects of the controlled release of dexamethasone on the modulation of macrophage polarisation and osteogenic differentiation of MSCs. Notably, blending PCL with 40% wt/wt (SAIB) has improved dexamethasone-cyclodextrin dispersal and facilitated a sustained 35-day release dominated by first-ordered and Higuchi models. In this modified environment, investigations into macrophage-mesenchymal stem cell (MSC) interactions revealed that controlled dexamethasone release significantly influenced macrophage behaviour and MSC osteogenic differentiation. M1 macrophages boosted early alkaline phosphatase production (ALP) at (7 days), while later stages (21 days) saw dexamethasone's predominance. Bone morphogenic protein-2 (BMP-2) was significantly increased at day 21; meanwhile, interleukin-6 (IL-6) decreased at the same time. Moreover, the released dexamethasone switched the phenotype of macrophages from M1 to M2 at day 21, evidenced by the increased level of mannose receptor and decreased expression of calprotectin receptor. These results offer new insight into macrophage-MSC cross-talk and demonstrate the potential of drug-release scaffolds to modulate inflammation and enhance bone regeneration.