Modeling osteoinduction in titanium bone scaffold with a representative channel structure

Impacts of permeability and effective diffusivity of porous scaffolds on bone ingrowth: In silico and in vivo analyses

The permeability and the effective diffusivity of a porous scaffold are critical in the bone-ingrowth process. However, design guidelines for porous structures are still lacking due to inadequate understanding of the complex physiological processes involved. In this study, a model integrating the fundamental biological processes of bone regeneration was constructed to investigate the roles of permeability and effective diffusivity in regulating bone deposition in scaffolds. The in silico analysis results were confirmed in vivo by examining bone depositions in three diamond lattice scaffolds manufactured using selective laser melting. The findings show that the scaffolds with better permeability and effective diffusivity had deeper bone ingrowth and greater bone volume. Compared to permeability, effective diffusivity exhibited greater sensitivity to the orientation of porous structures, and bone ingrowth was deeper in the directions with higher effective diffusivity in spite of identical pore size. A 4.8-fold increase in permeability and a 1.6-fold increase in effective diffusivity by changing the porous structure led to a 1.5-fold increase in newly formed bone. The effective diffusivity of the porous scaffold affects the distribution of osteogenic growth factor, which in turn impacts cell migration and bone deposition through chemotaxis effects. Therefore, effective diffusivity may be a more suitable indicator for porous scaffolds because our study shows changes in this parameter determine changes in bone distribution and bone volume.

Design of a Haversian system-like gradient porous scaffold based on triply periodic minimal surfaces for promoting bone regeneration

INTRODUCTION

The bone ingrowth depth in the porous scaffolds is greatly affected by the structural design, notably the pore size, pore geometry, and the pore distribution. To enhance the bone regeneration capability of scaffolds, the bionic design can be regarded as a potential solution.

OBJECTIVES

We proposed a Haversian system-like gradient structure based on the triply periodic minimal surface architectures with pore size varying from the edge to the center. And its effects in promoting bone regeneration were evaluated in the study.

METHODS

The gradient scaffold was designed using the triply periodic minimal surface architectures. The mechanical properties were analyzed by the finite element simulation and confirmed using the universal machine. The fluid characteristics were calculated by the computational fluid dynamics analysis. The bone regeneration process was simulated using a in silico computational model containing the main biological, physical, and chemical variation during the bone growth process. Finally, the in vitro and in vivo studies were carried out to verify the actual osteogenic effect.

RESULTS

Compared to the uniform scaffold, the biomimetic gradient scaffold demonstrated better performance in stress conduction and reduced stress shielding effects. The fluid features were appropriate for cell migration and flow diffusion, and the permeability was in the same order of magnitude with the natural bone. The bone ingrowth simulation exhibited improved angiogenesis and bone regeneration. Higher expression of the osteogenesis-related genes, higher alkaline phosphatase activity, and increased mineralization could be observed on the gradient scaffold in the in vitro study. The 12-week in vivo study proved that the gradient scaffold had deeper bone inserting depth and a more stable bone-scaffold interface.

CONCLUSION

The Haversian system-like gradient structure can effectively promote the bone regeneration. This structural design can be used as a new solution for the clinical application of prosthesis design.

The combination of a 3D-Printed porous Ti-6Al-4V alloy scaffold and stem cell sheet technology for the construction of biomimetic engineered bone at an ectopic site

Cell sheet technology has been widely used in bone tissue engineering and regenerative medicine. However, controlling the shape and volume of large pieces of engineered bone tissue remains impossible without additional suitable scaffolds. Three-dimensional (3D) printed titanium (Ti) alloy scaffolds are mostly used as implant materials for repairing bone defects, but the unsatisfactory bioactivities of traditional Ti-based scaffolds severely limit their clinical applications. Herein, we hypothesize that the combination of bone marrow mesenchymal stem cell (BMSC) sheet technology and 3D porous Ti–6Al–4V (PT) alloy scaffolds could be used to fabricate biomimetic engineered bone. First, various concentrations of BMSCs were directly cocultured with PT scaffolds to obtain complexes of osteoblastic cell sheets and scaffolds. Then, as an experimental control, an osteoblastic BMSC sheet was prepared by continuous culturing under osteogenic conditions for 2 weeks without passaging and used to wrap the scaffolds. The BMSC sheet was composed of several layers of extracellular matrix (ECM) and a mass of BMSCs. The BMSCs exhibited excellent adherent, proliferative and osteogenic potential when cocultured with PT scaffolds, which may be attributed to the ability of the 3D microstructure of scaffolds to facilitate the biological behaviors of cells, as confirmed by the in vitro results. Moreover, the presence of BMSCs and ECM increased the angiogenic potential of PT scaffolds by the secretion of VEGF. Micro-CT and histological analysis confirmed the in vivo formation of biomimetic engineered bone when the complex of cocultured BMSCs and PT scaffolds and the scaffolds wrapped by prepared BMSC sheets were implanted subcutaneously into nude mice. Therefore, the combination of BMSC sheet technology and 3D-printed PT scaffolds could be used to construct customized biomimetic engineered bone, offering a novel and promising strategy for the precise repair of bone defects.

Three-Dimensionally Printed Ti2448 With Low Stiffness Enhanced Angiogenesis and Osteogenesis by Regulating Macrophage Polarization via Piezo1/YAP Signaling Axis

Previous studies have found that the novel low-elastic-modulus Ti2448 alloy can significantly reduce stress shielding and contribute to better bone repair than the conventional Ti6Al4V alloy. In this study, the promotion of osteogenesis and angiogenesis by three-dimensionally printed Ti2448 were also observed in vivo. However, these were not significant in a series of in vitro tests. The stiffness of materials has been reported to greatly affect the response of macrophages, and the immunological regulation mediated by macrophages directly determines the fate of bone implants. Therefore, we designed more experiments to explore the role of three-dimensionally printed Ti2448 in macrophage activation and related osteogenesis and angiogenesis. As expected, we found a significant increase in the number of M2 macrophages around Ti2448 implants, as well as better osteogenesis and angiogenesis in vivo. In vitro studies also showed that macrophages pre-treated with Ti2448 alloy significantly promoted angiogenesis and osteogenic differentiation through increased PDGF-BB and BMP-2 secretion, and the polarization of M2 macrophages was enhanced. We deduced that Ti2448 promotes angiogenesis and osteogenesis through Piezo1/YAP signaling axis-mediated macrophage polarization and related cytokine secretion. This research might provide insight into the biological properties of Ti2448 and provide a powerful theoretical supplement for the future application of three-dimensionally printed Ti2448 implants in orthopaedic surgery.

In silico and in vivo studies of the effect of surface curvature on the osteoconduction of porous scaffolds

Recent evidence shows that the curvature of porous scaffold plays a significant role in guiding tissue regeneration. However, the underlying mechanism remains controversial to date. In this study, we developed an in silico model to simulate the effect of surface curvature on the osteoconduction of scaffold implants, which comprises the primary aspects of bone regeneration. Selective laser melting was used to manufacture a titanium scaffold with channels representative of different strut curvatures for in vivo assessment. The titanium scaffold was implanted in the femur condyles of rabbits to validate the mathematical model. Simulation results suggest that the curvature affected the distribution of growth factors and subsequently induced the migration of osteoblast lineage cells and bone deposition to the locations with higher curvature. The predictions of the mathematical model are in good agreement with the in vivo assessment results, in which newly formed bone first appeared adjacent to the vertices of the major axes in elliptical channels. The mechanism of curvature-guided osteoconduction may provide a guide for the design optimization of scaffold implants to achieve enhanced bone ingrowth.

Biomimetic Ti-6Al-4V alloy/gelatin methacrylate hybrid scaffold with enhanced osteogenic and angiogenic capabilities for large bone defect restoration

Titanium-based scaffolds are widely used implant materials for bone defect treatment. However, the unmatched biomechanics and poor bioactivities of conventional titanium-based implants usually lead to insufficient bone integration. To tackle these challenges, it is critical to develop novel titanium-based scaffolds that meet the bioadaptive requirements for load-bearing critical bone defects. Herein, inspired by the microstructure and mechanical properties of natural bone tissue, we developed a Ti–6Al–4V alloy (TC4)/gelatin methacrylate (GelMA) hybrid scaffold with dual bionic features (GMPT) for bone defect repair. GMPT is composed of a hard 3D-printed porous TC4 metal scaffold (PT) backbone, which mimics the microstructure and mechanical properties of natural cancellous bone, and a soft GelMA hydrogel matrix infiltrated into the pores of PT that mimics the microenvironment of the extracellular matrix. Ascribed to the unique dual bionic design, the resultant GMPT demonstrates better osteogenic and angiogenic capabilities than PT, as confirmed by the in vitro and rabbit radius bone defect experimental results. Moreover, controlling the concentration of GelMA (10%) in GMPT can further improve the osteogenesis and angiogenesis of GMPT. The fundamental mechanisms were revealed by RNA-Seq analysis, which showed that the concentration of GelMA significantly influenced the expression of osteogenesis- and angiogenesis-related genes via the Pi3K/Akt/mTOR pathway. The results of this work indicate that our dual bionic implant design represents a promising strategy for the restoration of large bone defects.

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A novel TC4/GelMA hybrid scaffold (GMPT) was designed to mimic natural bone microstructure and mechanical property.

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The GMPT with 10 wt% of GelMA showed best capability for promoting osteogenesis and angiogenesis.

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A bioactive soft surface with suitable stiffness can activate focal adhesion pathway and the downstream PI3K/AKT pathway.