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

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.

Mechano-driven intervertebral bone bridging via oriented mechanical stimulus in a twist metamaterial cage: An in silico study

Stiffer cages provide sufficient mechanical support but fail to promote bone ingrowth due to stress shielding. It remains challenging for fusion cage to satisfy both bone bridging and mechanical stability. Here we designed a fusion cage based on twist metamaterial for improved bone ingrowth, and proved its superiority to the conventional diagonal-based cage in silico. The fusion process was numerically reproduced via an injury-induced osteogenesis model and the mechano-driven bone remodeling algorithm, and the outcomes fusion effects were evaluated by the morphological features of the newly-formed bone and the biomechanical behaviors of the bone-cage composite. The twist-based cages exhibited oriented bone formation in the depth direction, in comparison to the diagonal-based cages. The axial stiffness of the bone-cage composites with twist-based cages was notably higher than that with diagonal-based cages; meanwhile, the ranges of motion of the twist-based fusion segment were lower. It was concluded that the twist metamaterial cages led to oriented bone ingrowth, superior mechanical stability of the bone-cage composite, and less detrimental impacts on the adjacent bones. More generally, metamaterials with a tunable displacement mode of struts might provide more design freedom in implant designs to offer customized mechanical stimulus for osseointegration.

Bamboo-Inspired Porous Scaffolds for Advanced Orthopedic Implants: Design, Mechanical Properties, and Fluid Characteristics

In orthopedic implant development, incorporating a porous structure into implants can reduce the elastic modulus to prevent stress shielding but may compromise yield strength, risking prosthesis fracture. Bamboo's natural structure, with its exceptional strength-to-weight ratio, serves as inspiration. This study explores biomimicry using bamboo-inspired porous scaffolds (BISs) resembling cortical bone, assessing their mechanical properties and fluid characteristics. The BIS consists of two 2D units controlled by structural parameters α and β. The mechanical properties, failure mechanisms, energy absorption, and predictive performance are investigated. BIS exhibits mechanical properties equivalent to those of natural bone. Specifically, α at 4/3 and β at 2/3 yield superior mechanical properties, and the destruction mechanism occurs layer by layer. Besides, the Gibson-Ashby models with different parameters are established to predict mechanical properties. Fluid dynamics analysis reveals two high-flow channels in BISs, enhancing nutrient delivery through high-flow channels and promoting cell adhesion and proliferation in low-flow regions. For wall shear stress below 30 mPa (ideal for cell growth), α at 4/3 achieves the highest percentage (99.04%), and β at 2/3 achieves 98.46%. Permeability in all structural parameters surpasses that of human bone. Enhanced performance of orthopedic implants through a bionic approach that enables the creation of pore structures suitable for implants.

Serial Cultivation of an MSC-Like Cell Line with Enzyme-Free Passaging Using a Microporous Titanium Scaffold

In vitro studies on adherent cells require a process of passage to dissociate the cells from the culture substrate using enzymes or other chemical agents to maintain cellular activity. However, these proteolytic enzymes have a negative influence on the viability and phenotype of cells. The mesenchymal stem cell (MSC)-like cell line, C3H10T1/2, adhered, migrated, and proliferated to the same extent on newly designed microporous titanium (Ti) membrane and conventional culture dish, and spontaneous transfer to another substrate without enzymatic or chemical dissociation was achieved. The present study pierced a 10 μm-thick pure Ti sheet with 25 μm square holes at 75 μm intervals to create a dense porous structure with biomimetic topography. The pathway of machined holes allowed the cells to access both sides of the membrane frequently. In a culture with Ti membranes stacked above- and below-seeded cells, cell migration between the neighboring membranes was confirmed using the through-holes of the membrane and contact between the membranes as migration routes. Furthermore, the cells on each membrane migrated onto the conventional culture vessel. Therefore, a cell culture system with enzyme-free passaging was developed.

Ultraviolet Light Treatment of Titanium Microfiber Scaffolds Enhances Osteoblast Recruitment and Osteoconductivity in a Vertical Bone Augmentation Model: 3D UV Photofunctionalization

Vertical bone augmentation to create host bone prior to implant placement is one of the most challenging regenerative procedures. The objective of this study is to evaluate the capacity of a UV-photofunctionalized titanium microfiber scaffold to recruit osteoblasts, generate intra-scaffold bone, and integrate with host bone in a vertical augmentation model with unidirectional, limited blood supply. Scaffolds were fabricated by molding and sintering grade 1 commercially pure titanium microfibers (20 μm diameter) and treated with UVC light (200-280 nm wavelength) emitted from a low-pressure mercury lamp for 20 min immediately before experiments. The scaffolds had an even and dense fiber network with 87% porosity and 20-50 mm inter-fiber distance. Surface carbon reduced from 30% on untreated scaffold to 10% after UV treatment, which corresponded to hydro-repellent to superhydrophilic conversion. Vertical infiltration testing revealed that UV-treated scaffolds absorbed 4-, 14-, and 15-times more blood, water, and glycerol than untreated scaffolds, respectively. In vitro, four-times more osteoblasts attached to UV-treated scaffolds than untreated scaffolds three hours after seeding. On day 2, there were 70% more osteoblasts on UV-treated scaffolds. Fluorescent microscopy visualized confluent osteoblasts on UV-treated microfibers two days after seeding but sparse and separated cells on untreated microfibers. Alkaline phosphatase activity and osteocalcin gene expression were significantly greater in osteoblasts grown on UV-treated microfiber scaffolds. In an in vivo model of vertical augmentation on rat femoral cortical bone, the interfacial strength between innate cortical bone and UV-treated microfiber scaffold after two weeks of healing was double that observed between bone and untreated scaffold. Morphological and chemical analysis confirmed seamless integration of the innate cortical and regenerated bone within microfiber networks for UV-treated scaffolds. These results indicate synergy between titanium microfiber scaffolds and UV photofunctionalization to provide a novel and effective strategy for vertical bone augmentation.

Sustained Delivery of Methylsulfonylmethane from Biodegradable Scaffolds Enhances Efficient Bone Regeneration

Introduction

As a popular dietary supplement containing sulfur compound, methylsulfonylmethane (MSM) has been widely used as an alternative oral medicine to relieve joint pain, reduce inflammation and promote collagen protein synthesis. However, it is rarely used in developing bioactive scaffolds in bone tissue engineering.

Methods

Three-dimensional (3D) hydroxyapatite/poly (lactide-co-glycolide) (HA/PLGA) porous scaffolds with different doping levels of MSM were prepared using the phase separation method. MSM loading efficiency, in vitro drug release as well as the biological activity of MSM-loaded scaffolds were investigated by incubating mouse pre-osteoblasts (MC3T3-E1) in the uniform and interconnected porous scaffolds.

Results

Sustained release of MSM from the scaffolds was observed, and the total MSM release from 1% and 10% MSM/HA/PLGA scaffolds within 16 days was up to 64.9% and 68.2%, respectively. Cell viability, proliferation, and alkaline phosphatase (ALP) activity were significantly promoted by incorporating 0.1% of MSM in the scaffolds. In vivo bone formation ability was significantly enhanced for 1% MSM/HA/PLGA scaffolds indicated by the repair of rabbit radius defects which might be affected by a stimulated release of MSM by enzyme systems in vivo.

Discussion

Finding from this study revealed that the incorporation of MSM would be effective in improving the osteogenesis activity of the HA/PLGA porous scaffolds.