Gyroid Scaffolds Research Articles

Microstructure design and degradation performance in vitro of three-dimensional printed bioscaffold for bone tissue engineering

In bone tissue engineering, three-dimensional printed biological scaffolds play an important role in the development of bone regeneration. The ideal scaffolds should have the ability to match the bone degradation rate and osteogenic ability. This article optimizes the unit cell model of the microstructure including spherical pore, gyroid, and topology to explore degradation performance of scaffolds. Boolean operation of array microstructure unit cells and selected part of a computer-aided design (CAD) femur model are adopted to create a reconstructed scaffold model. Polylactic acid/[Formula: see text]-tricalcium phosphate/hydroxyapatite scaffolds with spherical pore, gyroid, and topology-optimized structures are manufactured by three-dimensional printing utilizing the composition of bio-ink including polylactic acid, [Formula: see text]-tricalcium phosphate, and hydroxyapatite. After degradation of the scaffolds in vitro for several days, the mechanical properties are analyzed to study the effects of different microstructures on the degradation properties. The results show that the gyroid scaffolds with favorable degradability still maintain excellent mechanical properties after degradation. Mechanical properties of the scaffolds with topology-optimized structure and spherical pore microstructure scaffolds have a significant decrease after degradation.

A comparative study on the nanoindentation behavior, wear resistance and in vitro biocompatibility of SLM manufactured CP–Ti and EBM manufactured Ti64 gyroid scaffolds

The present study investigates the nanoindentation behavior, wear resistance and in vitro biocompatibility of SLM manufactured CP–Ti and EBM manufactured Ti64 gyroid scaffolds and the results were compared to those of casting CP–Ti. Both the SLM- and EBM manufactured scaffolds exhibited anisotropic properties with higher reduced modulus (up to 10%) and nanohardness (up to 30%) in the transverse direction than those in building direction. The wear resistance of scaffolds in transverse direction was higher than those of in building direction by up to ∼25% and ∼82% for SLM manufactured CP–Ti and EBM manufactured Ti64 scaffolds, respectively. The SLM manufactured CP–Ti scaffolds displayed significant enhancement in wear resistance over cast dense CP–Ti with 75% lower mean worn height during a nanowear test. The coefficient of friction was varied between 0.11 and 0.24 and exhibited a steady mean value of 0.15–0.18 for CP–Ti and Ti64 scaffolds, respectively. During in vitro cell culture study, CP–Ti scaffolds showed higher cell viability and cell adhesion density in comparison to Ti64 scaffolds for all unit cell sizes. Moreover, cell adhesion density of scaffolds with smaller unit cell sizes (G2) are lower than those of larger unit cells (G3). SEM observations confirmed that both the inner space and surfaces of gyroid scaffolds provided a suitable environment for cell migration, attachment and proliferation after cell culture for 7 d. Statement of significanceIt is essential to evaluate the properties of EBM/SLM manufactured scaffolds and to determine whether they can meet the tough performance requirements of the biomedical industry. In this study, nanoindentation and nanowear properties of SLM manufactured CP–Ti and EBM manufactured Ti64 gyroid scaffolds with different unit cell sizes and sample orientations were evaluated and compared to cast dense CP–Ti samples. Moreover, the in vitro biocompatibility of the scaffolds was assessed and compared to each other. To our best of knowledge, this type of study on EBM/SLM manufactured CP-Ti and Ti64 scaffolds have not been reported, to date.

Fabrication of Graphene-Reinforced Nanocomposites with Improved Fracture Toughness in Net Shape for Complex 3D Structures via Digital Light Processing

A solvent-free method to fabricate graphene-reinforced nanocomposites in net shape via digital light processing (DLP) 3D printing has been developed in this work. The effect of graphene nanofillers on resin viscosity and wettability for various printing parameters has been examined, with a systematic characterization of the mechanical and thermomechanical properties. With the addition of 0.5 wt.% graphene nanoplatelets in the resin, the flexural modulus and fracture toughness have been improved by 14% and 28% from neat resin, respectively. Thermomechanical properties of graphene-reinforced nanocomposites were also enhanced compared with the neat resin, without scarification in their printability. The feasibility of utilizing the DLP method to fabricate a fracture toughness specimen (KIC test) without complex skill-dependent notch preparation steps was explored, with different notch tip angles printed for net-shaped specimens. This provided a simple and versatile way to perform a quick examination of reinforcing efficiency from nanofillers at very low cost with high resolution and reproducibility. To demonstrate the suitability of current resins for complexly shaped structures, a gyroid scaffold for tissue engineering applications based on current graphene nanocomposite resins has been successfully fabricated via DLP, showing the great potential of current photocurable resins for applications in various fields such as tissue engineering or personalized medical devices without the cost barriers of traditional methods.

Permeability versus Design in TPMS Scaffolds.

Scaffolds for bone tissue engineering are porous structures that serve as support for cellular growth and, therefore, new tissue formation. The present work assessed the influence of the porous architecture of triply periodic minimal surface (TPMS) scaffolds on their macroscopic permeability behavior, combining numerical and experimental methods. The TPMS scaffolds considered were Schwartz D, Schwartz P, and Gyroid, which have been previously studied for bone tissue engineering, with 70% porosity. On the experimental side, these scaffolds were produced by MultiJet 3D printing and tested for fluid passage to calculate their permeability through Darcy’s Law. On the numerical side, finite element (FE) models of the scaffolds were simulated on ABAQUS® for fluid passage under compression to assess potential fluid concentration spots. The outcomes revealed that the design of the unit cell had a noticeable effect on both calculated permeability and FE computed fluid flow velocity, regardless of the identical porosity, with the Gyroid scaffold having higher permeability and the Schwartz P a lower probability of fluid trapping. Schwartz D had the worst outcomes in both testing modalities, so these scaffolds would most likely be the last choice for promoting cell differentiation onto bone cells. Gyroid and Schwartz P would be up for selection depending on the application and targeted bone tissue.

Graphene-Reinforced Biodegradable Resin Composites for Stereolithographic 3D Printing of Bone Structure Scaffolds

A biodegradable UV-cured resin has been fabricated via stereolithography apparatus (SLA). The formulation consists of a commercial polyurethane resin as an oligomer, trimethylolpropane trimethacrylate (TEGDMA) as a reactive diluent and phenylbis (2, 4, 6-trimethylbenzoyl)-phosphine oxide (Irgacure 819) as a photoinitiator. The tensile strength of the three-dimensional (3D) printed specimens is 68 MPa, 62% higher than that of the reference specimens (produced by direct casting). The flexural strength and modulus can reach 115 MPa and 5.8 GPa, respectively. A solvent-free method is applied to fabricate graphene-reinforced nanocomposite. Porous bone structures (a jawbone with a square architecture and a sternum with a round architecture) and gyroid scaffold of graphene-reinforced nanocomposite for bone tissue engineering have been 3D printed via SLA. The UV-crosslinkable graphene-reinforced biodegradable nanocomposite using SLA 3D printing technology can potentially remove important cost barriers for personalized biological tissue engineering as compared to the traditional mould-based multistep methods.

Numerical and experimental evaluation of TPMS Gyroid scaffolds for bone tissue engineering

The combination of computational methods with 3D printing allows for the control of scaffolds microstructure. Lately, triply periodic minimal surfaces (TPMS) have been used to design porosity-controlled scaffolds for bone tissue engineering (TE). The goal of this work was to assess the mechanical properties of TPMS Gyroid structures with two porosity levels (50 and 70%). The scaffold stiffness function of porosity was determined by the asymptotic homogenisation method and confirmed by mechanical testing. Additionally, microCT analysis confirmed the quality of the printed parts. Thus, the potential of both design and manufacturing processes for bone TE applications is here demonstrated.

A Comparative Study on the Nanoindentation Behavior, Wear Resistance and <i>in vitro</i> Biocompatibility of SLM Manufactured CP-Ti and EBM Manufactured Ti64 Gyroid Scaffolds

The present study investigates the nanoindentation behavior, wear resistance and in vitro biocompatibility of SLM manufactured CP-Ti and EBM manufactured Ti64 gyroid scaffolds and the results were compared to those of casting CP-Ti. Both the SLM- and EBM manufactured scaffolds exhibited anisotropic properties with higher reduced modulus (up to 10%) and nanohardness (up to 30%) in the transverse direction than those in building direction. The wear resistance of scaffolds in transverse direction was higher than those of in building direction by up to ~25% and ~82% for SLM manufactured CP-Ti and EBM manufactured Ti64 scaffolds, respectively. The SLM manufactured CP-Ti scaffolds displayed significant enhancement in wear resistance over cast dense CP-Ti with 75% lower mean worn height during a nanowear test. The coefficient of friction was varied between 0.11 to 0.24 and exhibited a steady mean value of 0.15 to 0.18 for CP-Ti and Ti64 scaffolds, respectively. During in vitro cell culture study, CP-Ti scaffolds showed higher cell viability and cell adhesion density in comparison to Ti64 scaffolds for all unit cell sizes. Moreover, cell adhesion density of scaffolds with smaller unit cell sizes (G2) are lower than those of larger unit cells (G3). SEM observations confirmed that both the inner space and surfaces of gyroid scaffolds provided a suitable environment for cell migration, attachment and proliferation after cell culture for 7 d.

Ultrasonic characterization of porous gyroid scaffolds for bone tissue engineering: Mechanical modelling and numerical validation

Bone substitutes can be used for pre-implant surgery in presence of volumetric bone defects. In this context, the ultrasound characterization of the bone substitute is a key issue. To this end, we model the implant as a 3D porous structure and we study its ultrasonic behavior. In the framework of artificial bone substitutes, microstructured scaffolds are widely used. In the literature, several geometrical configurations have been tested: among them, the gyroid-shaped scaffolds turn out to be an excellent choice, thanks to its ability to reproduce the behavior and the porous structure of trabecular bone. This study is focused on the mechanical modelling and numerical validation of wave propagation in a porous implant substitute. In particular, 3D finite-difference time-domain (FDTD) simulations were performed on a gyroid-shaped scaffold of saturated with water to validate the continuum mechanical model. Ultrasound excitations at different central frequencies were used in order to investigate the frequency-dependent behavior phase and group velocities.

Ultrahigh-strength titanium gyroid scaffolds manufactured by selective laser melting (SLM) for bone implant applications

Commercially pure titanium (CP–Ti) gyroid scaffolds with interconnected pores and high porosities in the range of 68–73% and three different unit cell sizes of 2, 2.5, and 3 mm were manufactured by selective laser melting (SLM) for bone implant applications. The microstructure and mechanical properties of the scaffolds with different unit cell sizes and sample orientations were evaluated. The microstructure of as-built struts was dominated by massive martensite and the average microhardness of the struts was 2.27 GPa, which is ∼50% higher than that of dense cast CP–Ti. The elastic modulus and yield strength of the as-built scaffolds ranged from 1465 to 2676 MPa and from 44.9 to 56.5 MPa, respectively, values which are close to the elastic modulus of trabecular bone and presumably strong enough to bear the physiological loading of implants. The as-built scaffolds exhibited excellent ductility up to 50% strain and no sign of fracture up to 20–30% strain under compression. The dominant compressive response of the scaffolds was observed by formation of a plastic hinge which led to rotation of the struts about the plastic hinges followed by development of local shear bands in struts in the long plateau region. These SLM-manufactured gyroid CP–Ti scaffolds with significantly enhanced hardness and compressive strength exhibited an elastic modulus close to that of trabecular bone and offer a promising improvement on CP–Ti scaffolds for bone implant applications.

Permeability and fluid flow-induced wall shear stress of bone tissue scaffolds: Computational fluid dynamic analysis using Newtonian and non-Newtonian blood flow models

Among the factors that are important in successful bone tissue regeneration through scaffolds are permeability and fluid flow-induced wall shear stress (WSS) because of the direct contribution of these factors to cell bioactivities. The permeability of scaffolds is usually measured using fluids such as water, which are characterized as Newtonian materials with constant viscosity. However, using the fluid properties of blood as bases in measuring permeability can lead to more realistic results given that scaffolds are implanted in the body, where the only flowing fluid (i.e., blood) is a non-Newtonian fluid. Moreover, the linear relationship of WSS with fluid viscosity challenges the use of Newtonian fluids in determining WSS magnitude. With consideration for these issues, we investigated permeability and WSS through computational fluid dynamics (CFD) analyses of lattice-based and gyroid scaffold architectures with Newtonian and non-Newtonian blood flow properties. With reference to geometrical parameters and the pressure drops derived from the CFD analyses, the permeability levels of the Newtonian and non-Newtonian models were calculated by exploiting the classic and modified Darcy's equations, respectively. Results showed that both scaffold architectures were several times more permeable in the Newtonian blood flow models than in their non-Newtonian counterparts. Within the scaffolds, the non-Newtonian flow of blood caused almost twice the magnitude of WSS originating from Newtonian blood flow. These striking discrepancies in permeability and WSS between the two blood models were due to differences in their viscosity behaviors.

3D-printed biodegradable gyroid scaffolds for tissue engineering applications

Fused deposition modeling (FDM), a low-cost and easy-to-use additive manufacturing technique, was used to produce poly(lactic acid) (PLA) gyroid scaffolds. Such morphology was selected for its spring shape, high porosity leading to good nutrient and waste diffusion, and favorable mechanical properties. Printing parameters were optimized and the need of a support material to improve printing was evidenced. The gyroid was compared to the common strut-based structure. Scaffold porosity was measured by micro-CT, and mechanical properties were determined by compression tests, taking into account the effect of geometry, printing resolution, and PLA crystallinity. The impact of scaffold geometry and crystallinity on its degradation was studied in vitro. Porosity of the gyroid structure was 71%, as expected from the printing model. The compression tests showed an isotropic behavior for the gyroid, in contrast with the strut-based scaffold. Upon aging in physiological conditions, gyroid scaffolds retained their integrity during 64 weeks, while control scaffolds lost struts starting from week 33, in a way that depended on crystallinity and printing resolution. Based on these results, the gyroid design is proposed as a suitable mesh architecture for tissue engineering scaffolds that can be elaborated using FDM techniques, to produce low-cost and personalized implants.

Anisotropic Ti-6Al-4V gyroid scaffolds manufactured by electron beam melting (EBM) for bone implant applications

Ti-6Al-4V gyroid scaffolds with high porosities in the range of 82–85% and three different unit cell sizes 2, 2.5 and 3mm were manufactured by electron beam melting (EBM) for bone implant applications. The microstructure, mechanical properties and failure mode of the scaffolds with different sample orientations were evaluated. The as-built struts showed orthogonally orientated martensite α′ needles in columnar grains along the building direction with an average hardness of 3.89GPa and the elastic modulus and yield strength of scaffolds ranged from 637 to 1084MPa and from 13.1 to 19.2MPa, respectively. The elastic modulus and yield strength along the build direction and perpendicular to building direction varied by ~70% and 49%, respectively, depending on the amount of structural anisotropy and unit cell size. The ratio of elastic modulus anisotropy in orthogonal directions was comparable to those of trabecular bone and could be in favor of bone implant applications. Furthermore, as-built scaffolds showed a mixed mode of ductile and brittle behavior under compression, and the dominant failure mode was by forming orthogonal crush bonds at the peak loads with an angle of ~45° with compression axis.

Finite element analysis of mechanical behavior, permeability and fluid induced wall shear stress of high porosity scaffolds with gyroid and lattice-based architectures

Scaffold design necessitates the consideration of mechanical properties and fluid flow dynamics as the main factors in the development of such materials. The mechanical behavior of bone scaffolds is characterized by properties such as elastic modulus and compressive strength. In terms of fluid flow dynamics, within bone scaffolds, permeability is an important parameter that affects cells' biological activities, and flow-induced shear stress is used as a mechanical stimulant of cell growth. In this study, two scaffold architectures with gyroid and lattice-based rectangular unit cells were designed to analysis the effective elastic moduli, compressive strength, permeability and fluid flow-induced wall shear stress as functions of porosity. Six levels of porosity (65%, 70%, 75%, 80%, 85% and 90%) were assigned to the scaffold architectures, and 12 models were developed. Scaffold deformation under static loading, compressive strength based on von Mises criteria, pressure drop, and fluid flow-induced wall shear stress in the scaffolds were then determined by finite element analysis. In both the scaffold types, models with higher porosity exhibited lower mechanical properties. Under the same porosity, the lattice-based scaffolds exhibited a Young's modulus and a compressive strength higher than those achieved by the gyroid scaffolds. With reference to geometrical parameters and the derived pressure drop from the computational fluid dynamics (CFD) analysis, scaffolds permeability was calculated using Darcy's law. In both the scaffold architectures, high porosity increased permeability and decreased wall shear stress. In the same porosity, the lattice-based models exhibited higher permeability and lower wall shear stress than did the gyroid models. On the basis of the results on elastic modulus and permeability, the models that most effectively mimic the properties of cancellous bones were identified.

A Bioactive Hydrogel and 3D Printed Polycaprolactone System for Bone Tissue Engineering.

In this study, a hybrid system consisting of 3D printed polycaprolactone (PCL) filled with hydrogel was developed as an application for reconstruction of long bone defects, which are innately difficult to repair due to large missing segments of bone. A 3D printed gyroid scaffold of PCL allowed a larger amount of hydrogel to be loaded within the scaffolds as compared to 3D printed mesh and honeycomb scaffolds of similar volumes and strut thicknesses. The hydrogel was a mixture of alginate, gelatin, and nano-hydroxyapatite, infiltrated with human mesenchymal stem cells (hMSC) to enhance the osteoconductivity and biocompatibility of the system. Adhesion and viability of hMSC in the PCL/hydrogel system confirmed its cytocompatibility. Biomineralization tests in simulated body fluid (SBF) showed the nucleation and growth of apatite crystals, which confirmed the bioactivity of the PCL/hydrogel system. Moreover, dissolution studies, in SBF revealed a sustained dissolution of the hydrogel with time. Overall, the present study provides a new approach in bone tissue engineering to repair bone defects with a bioactive hybrid system consisting of a polymeric scaffold, hydrogel, and hMSC.

Bioactive gyroid scaffolds formed by sacrificial templating of nanocellulose and nanochitin hydrogels as instructive platforms for biomimetic tissue engineering.

A sacrificial templating process using lithographically printed minimal surface structures allows complex de novo geo-metries of delicate hydrogel materials. The hydrogel scaffolds based on cellulose and chitin nanofibrils show differences in terms of attachment of human mesenchymal stem cells, and allow their differentiation into osteogenic outcomes. The approach here serves as a first example toward designer hydrogel scaffolds viable for biomimetic tissue engineering.

Design of Porous Three-Dimensional PDLLA/nano-hap Composite Scaffolds Using Stereolithography

The stereolithography process is based on the photopolymerization through a dynamic mask generator of successive layers of photocurable resin, allowing the manufactory of accurate micro objects with high aspect ratio and curved surfaces. In the present work the stereolithography technique is applied to produce nanocomposite bioactive scaffolds from Computer Assisted Design (CAD) files. Porous scaffolds are designed with computer software and built with a composite poly(D,L-lactide)/nano hydroxyapatite based resin. Triply-periodic minimal surfaces are shown to be a more versatile source of biomorphic scaffold designs and scaffolds with Double Gyroid architecture are realized and characterized from morphological, mechanical and biological point of view. The structures show excellent reproduction of the design and good mechanical properties. Human marrow mesenchimal cells (hMSC) are seeded onto porous PDLLA composites for 3 weeks and cultured in osteogenic medium. Presence of nano-hap seems to increase the mechanical properties without affecting the morphology of the structures. The composite Double Gyroid scaffolds exhibit good biocompatibility and confirm that nano-hap enhances the scaffold bioactive and osteoconductive potential. The presented technology and materials enable an accurate preparation of tissue engineering composite scaffolds with a large freedom of design, and really complex internal architectures. Results indicate that the scaffolds fulfill the basic requirements of bone tissue engineering scaffold, and have the potential to be applied in orthopedic surgery.

Effects of the architecture of tissue engineering scaffolds on cell seeding and culturing

The advance of rapid prototyping techniques has significantly improved control over the pore network architecture of tissue engineering scaffolds. In this work, we have assessed the influence of scaffold pore architecture on cell seeding and static culturing, by comparing a computer designed gyroid architecture fabricated by stereolithography with a random pore architecture resulting from salt leaching. The scaffold types showed comparable porosity and pore size values, but the gyroid type showed a more than 10-fold higher permeability due to the absence of size-limiting pore interconnections. The higher permeability significantly improved the wetting properties of the hydrophobic scaffolds and increased the settling speed of cells upon static seeding of immortalised mesenchymal stem cells. After dynamic seeding followed by 5 days of static culture gyroid scaffolds showed large cell populations in the centre of the scaffold, while salt-leached scaffolds were covered with a cell sheet on the outside and no cells were found in the scaffold centre. It was shown that interconnectivity of the pores and permeability of the scaffold prolonged the time of static culture before overgrowth of cells at the scaffold periphery occurred. Furthermore, novel scaffold designs are proposed to further improve the transport of oxygen and nutrients throughout the scaffolds and to create tissue engineering grafts with a designed, pre-fabricated vasculature.