Gyroid Scaffolds Research Articles

Development of a 3D-printed bioabsorbable composite scaffold with mechanical properties suitable for treating large, load-bearingarticular cartilage defects.

Extracellular matrix (ECM) biomaterials have shown promise for treating small artucular-joint defetcs. However, ECM-based biomaterials generally lack appropriate mechanical properties to support physiological loads and are prone to delamination in larger cartilage defects. To overcome these common mechanical limitations, a collagen hyaluronic-acid (CHyA) matrix, with proven regenerative potential, was reinforced with a bioabsorbable 3D-printed framework to support physiological loads. Polycaprolactone (PCL) was 3D-printed in two configurations, rectilinear and gyroid designs, that were extensively mechanically characterised. Both scaffold designs increased the compressive modulus of the CHyA matrices by three orders of magnitude, mimicking the physiological range (0.5-2.0 MPa) of healthy cartilage. The gyroid scaffold proved to be more flexible compared to the rectilinear scaffold, thus better contouring to the curvature of a femoral condyle. Additionally, PCL reinforcement of the CHyA matrix increased the tensile modulus and allowed for suture fixation of the scaffold to the subchondral bone, thus addressing the major challenge of biomaterial fixation to articular joint surfaces in shallow defects. In vitro evaluation confirmed successful infiltration of human mesenchymal stromal cells (MSCs) within the PCL-CHyA scaffolds, which resulted in increased production of sulphated glycosaminoglycans (sGAG/DNA; p = 0.0308) compared to non-reinforced CHyA matrices. Histological staining using alcian blue confirmed these results, while also indicating greater spatial distribution of sGAG throughout the PCL-CHyA scaffold. These findings have a great clinical importance as they provide evidence that reinforced PCL-CHyA scaffolds, with their increased chondroinductive potential and compatibility with joint fixation techniques, could be used to repair large-area chondral defects that currently lack effective treatment options.

Determination of Optimum Design Parameters for Gyroid Scaffolds to Mimic a Real Bone-Like Condition In Vitro: A Fluid Structure Interaction Study

Abstract A suitable scaffold architecture is always desirable to get a biomimetic scaffold for bone tissue engineering. In this regard, a fluid structure interaction analysis was carried out on different Micro-CTs (μCTs) and gyroids to observe the in vitro mechanical responses due to fluid flow. Computational fluid dynamics method was used to evaluate the permeability and wall shear stress (WSS), followed by a finite element method to obtain the mechanical stress within scaffolds. Different types of gyroids were designed based on the number of unit cells and porosity, where porosity of gyroids was kept same as μCTs. The main objective of the study is to examine the variations of permeability, WSS and mechanical stress with respect to the number of unit cells and porosity for different gyroids and μCTs. Mechanical responses were also compared between gyroids and μCTs. The results of this study highlighted that permeability and WSS of μCTs came close to the gyroids with eight unit cells but had significant differences in mechanical stress. The permeability of gyroids increased with the increase of porosity but decreased with the increase in number of unit cells. The opposite trend was shown in case of WSS within gyroids. This study will guide us in predicting an ideal scaffold for trabecular bone replacement.

Geometrical features and mechanical properties of the sheet-based gyroid scaffolds with functionally graded porosity manufactured by electron beam melting

Functionally graded porous scaffolds (FGPS) constructed with pores of different size arranged as spatially continuous structure based on sheet-based gyroid with three different scaling factors of 0.05, 0.1 and 0.2 were produced by electron beam powder bed fusion. The pore dimensions of the obtained scaffolds satisfy the values required for optimal bone tissue ingrowth. Agglomerates of residual powder were found inside all structures, which required post-manufacturing treatment. Using X-ray Computed Tomography powder agglomerations were visualized and average wall thickness, wall-to-wall distances, micro- and macro-porosities were evaluated. The initial cleaning by powder recovery system (PRS) was insufficient for complete powder removal. Additional treatment by dry ultrasonic vibration (USV) was applied and was found successful for gyroids with the scaling factors of 0.05 and 0.1. Mechanical properties of the samples, including quasi-elastic gradients and first maximum compressive strengths of the structures before and after USV were evaluated to prove that additional treatment does not produce structural damage. The estimated quasi-elastic gradients for gyroids with different scaling factors lie in a range between 2.5 and 2.9 GPa, while the first maximum compressive strength vary from 52.5 for to 59.8 MPa, compressive offset stress vary from 46.2 for to 53.2 MPa.

Photoinhibiting via simultaneous photoabsorption and free-radical reaction for high-fidelity light-based bioprinting

Light-based 3D bioprinting is now employed widely to fabricate geometrically complex constructs for various biomedical applications. However, the inherent light scattering defect creates significant challenges in patterning dilute hydrogels to form high-fidelity structures with fine-scale features. Herein, we introduce a photoinhibiting approach that can effectively suppress the light scattering effect via a mechanism of simultaneous photoabsorption and free-radical reaction. This biocompatible approach significantly improves the printing resolution (~1.2 - ~2.1 pixels depending on swelling) and shape fidelity (geometric error less than 5%), while minimising the costly trial-and-error procedures. The capability in patterning 3D complex constructs using different hydrogels is demonstrated by manufacturing various scaffolds featuring intricate multi-sized channels and thin-walled networks. Importantly, cellularised gyroid scaffolds (HepG2) are fabricated successfully, exhibiting high cell proliferation and functionality. The strategy established in this study promotes the printability and operability of light-based 3D bioprinting systems, allowing numerous new applications for tissue engineering.

Robocasting of Ceramic Fischer-Koch S Scaffolds for Bone Tissue Engineering.

Triply Periodic Minimal Surfaces (TPMS) are promising structures for bone tissue engineering scaffolds due to their relatively high mechanical energy absorption, smoothly interconnected porous structure, scalable unit cell topology, and relatively high surface area per volume. Calcium phosphate-based materials, such as hydroxyapatite and tricalcium phosphate, are very popular scaffold biomaterials due to their biocompatibility, bioactivity, compositional similarities to bone mineral, non-immunogenicity, and tunable biodegradation. Their brittle nature can be partially mitigated by 3D printing them in TPMS topologies such as gyroids, which are widely studied for bone regeneration, as evidenced by their presence in popular 3D-printing slicers, modeling systems, and topology optimization tools. Although structural and flow simulations have predicted promising properties of other TPMS scaffolds, such as Fischer-Koch S (FKS), to the best of our knowledge, no one has explored these possibilities for bone regeneration in the laboratory. One reason for this is that fabrication of the FKS scaffolds, such as by 3D printing, is challenged by a lack of algorithms to model and slice this topology for use by low-cost biomaterial printers. This paper presents an open-source software algorithm that we developed to create 3D-printable FKS and gyroid scaffold cubes, with a framework that can accept any continuous differentiable implicit function. We also report on our successful 3D printing of hydroxyapatite FKS scaffolds using a low-cost method that combines robocasting with layer-wise photopolymerization. Dimensional accuracy, internal microstructure, and porosity characteristics are also presented, demonstrating promising potential for the 3D printing of TPMS ceramic scaffolds for bone regeneration.

Electrochemical removal of secondary roughness on selective laser melted titanium with an ethylene–glycol-based electrolyte

Partially sintered satellite particles in scaffolds produced via Selective Laser Melting (SLM) create discrepancies between the as-designed and the as-manufactured properties (esp. porosity). These discrepancies impede direct comparison of manufactured parts performance to computer simulations. We propose anodic electrolysis using an electrolyte based on non-aqueous ethlylene-glycol TiCl4 (EthaTi) to remove the secondary roughness on titanium SLM-ed porous scaffolds. Post-processed gyroid scaffolds regained 10% porosity with respect to their as-manufactured value (65.20 ± 0.23%), which was close to the as-designed value (75.12%). Compared to other well-established electrolytes, this method is cost-effective, user-friendly and practical, as it requires shorter processing times, is temperature-stable and of gentler chemistry.

DESIGNING OF DIFFERENT TYPES OF GYROID SCAFFOLD ARCHITECTURE TO ACHIEVE PATIENT-SPECIFIC OSSEOINTEGRATION FRIENDLY MECHANICAL ENVIRONMENT

Porous three-dimensional scaffolds provide a favorable environment for the regeneration of tissues and organs to recover the injured tissue in terms of structure and biological function. Proper design of scaffold architecture is a crucial factor for tissue engineering. The mechanical properties and performance of the scaffold depend on the scaffold architecture, material, and geometry. In this study, numerical analysis is performed on four types of gyroids to see the variation of effective elastic modules in three different directions. The fluid flow induces wall shear stress (WSS), considering the Newtonian fluid is also investigated. Initially, the WSS is evaluated through computational fluid dynamics simulation and compared to previous literature. A good agreement between the results of published literature and those initial works encourages dealing with several cases by varying different parameters. The effect of scaffold architecture, pore size, and flow direction on WSS is studied using 16 different gyroid models. A significant reduction of scaffold stiffness can be achieved with porosity, and WSS increases with a decrease in pore size. Inlet flow direction also has a good influence on WSS. Fluid flow perpendicular to the gyroid cross-sectional area gives maximum WSS and gradually decreases with an increase in direction angle. The present study can be used to reference a specific scaffold design in tissue engineering.

Digital Light Processing 3D Printing of Gyroid Scaffold with Isosorbide-Based Photopolymer for Bone Tissue Engineering.

As one of the most transplanted tissues of the human body, bone has varying architectures, depending on its anatomical location. Therefore, bone defects ideally require bone substitutes with a similar structure and adequate strength comparable to native bones. Light-based three-dimensional (3D) printing methods allow the fabrication of biomimetic scaffolds with high resolution and mechanical properties that exceed the result of commonly used extrusion-based printing. Digital light processing (DLP) is known for its faster and more accurate printing than other 3D printing approaches. However, the development of biocompatible resins for light-based 3D printing is not as rapid as that of bio-inks for extrusion-based printing. In this study, we developed CSMA-2, a photopolymer based on Isosorbide, a renewable sugar derivative monomer. The CSMA-2 showed suitable rheological properties for DLP printing. Gyroid scaffolds with high resolution were successfully printed. The 3D-printed scaffolds also had a compressive modulus within the range of a human cancellous bone modulus. Human adipose-derived stem cells remained viable for up to 21 days of incubation on the scaffolds. A calcium deposition from the cells was also found on the scaffolds. The stem cells expressed osteogenic markers such as RUNX2, OCN, and OPN. These results indicated that the scaffolds supported the osteogenic differentiation of the progenitor cells. In summary, CSMA-2 is a promising material for 3D printing techniques with high resolution that allow the fabrication of complex biomimetic scaffolds for bone regeneration.

Wall Shear Stress Analysis and Optimization in Tissue Engineering TPMS Scaffolds.

When designing scaffolds for bone tissue engineering (BTE), the wall shear stress (WSS), due to the fluid flow inside the scaffold, is an important factor to consider as it influences the cellular process involved in new tissue formation. The present work analyzed the average WSS in Schwartz diamond (SD) and gyroid (SG) scaffolds with different surface topologies and mesh elements using computational fluid dynamics (CFD) analysis. It was found that scaffold meshes with a smooth surface topology with tetrahedral elements had WSS levels 35% higher than the equivalent scaffold with a non-smooth surface topology with hexahedral elements. The present work also investigated the possibility of implementing the optimization algorithm simulated annealing to aid in the design of BTE scaffolds with a specific average WSS, with the outputs showing that the algorithm was able to reach WSS levels in the vicinity of 5 mPa (physiological range) within the established limit of 100 iterations. This proved the efficacy of combining CFD and optimization methods in the design of BTE scaffolds.

Mechanical Characterisation and Numerical Modelling of TPMS-Based Gyroid and Diamond Ti6Al4V Scaffolds for Bone Implants: An Integrated Approach for Translational Consideration.

Additive manufacturing has been used to develop a variety of scaffold designs for clinical and industrial applications. Mechanical properties (i.e., compression, tension, bending, and torsion response) of these scaffolds are significantly important for load-bearing orthopaedic implants. In this study, we designed and additively manufactured porous metallic biomaterials based on two different types of triply periodic minimal surface structures (i.e., gyroid and diamond) that mimic the mechanical properties of bone, such as porosity, stiffness, and strength. Physical and mechanical properties, including compressive, tensile, bending, and torsional stiffness and strength of the developed scaffolds, were then characterised experimentally and numerically using finite element method. Sheet thickness was constant at 300 μm, and the unit cell size was varied to generate different pore sizes and porosities. Gyroid scaffolds had a pore size in the range of 600–1200 μm and a porosity in the range of 54–72%, respectively. Corresponding values for the diamond were 900–1500 μm and 56–70%. Both structure types were validated experimentally, and a wide range of mechanical properties (including stiffness and yield strength) were predicted using the finite element method. The stiffness and strength of both structures are comparable to that of cortical bone, hence reducing the risks of scaffold failure. The results demonstrate that the developed scaffolds mimic the physical and mechanical properties of cortical bone and can be suitable for bone replacement and orthopaedic implants. However, an optimal design should be chosen based on specific performance requirements.

PCL strut-like scaffolds appear superior to gyroid in terms of bone regeneration within a long bone large defect: An in silico study.

The treatment of large bone defects represents a major clinical challenge. 3D printed scaffolds appear as a promising strategy to support bone defect regeneration. The 3D design of such scaffolds impacts the healing path and thus defect regeneration potential. Among others, scaffold architecture has been shown to influence the healing outcome. Gyroid architecture, characterized by a zero mean surface curvature, has been discussed as a promising scaffold design for bone regeneration. However, whether gyroid scaffolds are favourable for bone regeneration in large bone defects over traditional strut-like architecture scaffolds remains unknown. Therefore, the aim of this study was to investigate whether gyroid scaffolds present advantages over more traditional strut-like scaffolds in terms of their bone regeneration potential. Validated bone defect regeneration principles were applied in an in silico modeling approach that allows to predict bone formation in defect regeneration. Towards this aim, the mechano-biological bone regeneration principles were adapted to allow simulating bone regeneration within both gyroid and strut-like scaffolds. We found that the large surface curvatures of the gyroid scaffold led to a slower tissue formation dynamic and conclusively reduced bone regeneration. The initial claim, that an overall reduced zero mean surface curvature would enhance bone formation, could not be confirmed. The here presented approach illustrates the potential of in silico tools to evaluate in pre-clinical studies scaffold designs and eventually lead to optimized architectures of 3D printed implants for bone regeneration.

Corrosion fatigue behavior and anti-fatigue mechanisms of an additively manufactured biodegradable zinc-magnesium gyroid scaffold

Additively manufactured biodegradable zinc (Zn) alloy scaffolds constitute an important branch in orthopedic implants because of their moderate degradation behavior and bone-mimicking mechanical properties. This work investigated the corrosion fatigue response of a zinc-magnesium (Zn-Mg) alloy gyroid scaffold fabricated via laser-powder-bed-fusion additive manufacturing at the first time. The high-cycle compression-compression fatigue testing of the printed Zn-Mg scaffold was conducted in simulated body fluid, showing its favorable fatigue strength, structural reliability, and anti-fatigue capability. The printed Zn-Mg scaffold obtained a 227% higher fatigue strength than that of the printed Zn scaffold but 17% lower strain accumulation at 106 cycles. The accumulative strain of the Zn-Mg scaffold at its fatigue strength was dominant by fatigue ratcheting, since the fatigue damage strain of the scaffold was approximately zero. The corrosion products (ZnO and Zn(OH)2) were conducive to the inhibition of fatigue ratcheting and fatigue damage. Dislocation pile-up and solid solution phases at the grain boundaries of the Zn-Mg scaffold could retard the spreading of the crack tip and impede excessive grain coarsening, improving its fatigue endurance limit. Notably, the printed Zn-Mg scaffold could dissipate the fatigue energy through moderate grain boundary migration, thus reducing its plastic deformation. These findings illuminated the anti-fatigue mechanisms related to microstructural features and corrosive environments and highlighted the promising prospects of additively manufactured Zn-Mg scaffolds in orthopedic applications. Statement of significanceAdditive manufacturing (AM) of biodegradable metals shows unprecedented prospects for bone tissue regeneration medicine. The corrosion fatigue property is one of the key determinants in the performance of AM biodegradable scaffolds. In this study, a Zn-Mg gyroid scaffold was additively manufactured with admirable fatigue endurance limit and anti-fatigue capability. We reported that the corrosion fatigue performance was highly relevant to the microstructural features, validating that the grain boundary engineering strategy improved fatigue strength and inhibited crack penetration. Notably, moderate grain boundary migration could dissipate fatigue energy and reduce plastic deformation. Furthermore, corrosion products were conducive to impeding fatigue ratcheting and fatigue damage, indicating the promising potential of AM Zn-Mg scaffolds in treating load-bearing bone defects.

Comparative evaluation of printability and compression properties of poly-ether-ether-ketone triply periodic minimal surface scaffolds fabricated by laser powder bed fusion

Porous poly-ether-ether-ketone (PEEK) scaffolds have a good application prospect in orthopedics because of their excellent biocompatibility, chemical stability, and permeability. However, the porous PEEK scaffolds fabricated by conventional manufacturing methods are restricted to the uncontrollable and weak mechanical properties. In this work, porous PEEK scaffolds with highly-tunable elastic modulus are designed using typical triply periodic minimal surface (TPMS) structures, Gyroid, Diamond, I-WP, and then printed by laser powder bed fusion (LPBF). The effects of unit cell type and volume fraction on the manufacturing deviation, stress distribution, and mechanical properties of LPBF-printed PEEK scaffolds are investigated. The results illustrate that the Gyroid scaffolds present the lowest volume fraction deviation, followed by the I-WP scaffolds. By adjusting the volume fraction, the elastic modulus of the TPMS scaffolds is in the range of 42.17–512.12 MPa, which is comparable with those of human trabecular bones. Using the finite element (FE) simulation method, the experimental mechanical properties of the TPMS scaffolds can be predicted. In summary, the Gyroid structure is the optimal choice for the design and LPBF fabrication of porous PEEK scaffolds due to the best manufacturing fidelity and relatively good mechanical properties. • PEEK TPMS scaffolds were successfully fabricated by LPBF technology. • A FE method was proposed and it could accurately predict the mechanical responses of the PEEK TPMS scaffolds. • The elastic moduli of PEEK TPMS scaffolds can match those of human trabecular bones.

On the Morphological Deviation in Additive Manufacturing of Porous Ti6Al4V Scaffold: A Design Consideration.

Additively manufactured Ti scaffolds have been used for bone replacement and orthopaedic applications. In these applications, both morphological and mechanical properties are important for their in vivo performance. Additively manufactured Ti6Al4V triply periodic minimal surface (TPMS) scaffolds with diamond and gyroid structures are known to have high stiffness and high osseointegration properties, respectively. However, morphological deviations between the as-designed and as-built types of these scaffolds have not been studied before. In this study, the morphological and mechanical properties of diamond and gyroid scaffolds at macro and microscales were examined. The results demonstrated that the mean printed strut thickness was greater than the designed target value. For diamond scaffolds, the deviation increased from 7.5 μm (2.5% excess) for vertical struts to 105.4 μm (35.1% excess) for horizontal struts. For the gyroid design, the corresponding deviations were larger, ranging from 12.6 μm (4.2% excess) to 198.6 μm (66.2% excess). The mean printed pore size was less than the designed target value. For diamonds, the deviation of the mean pore size from the designed value increased from 33.1 μm (−3.0% excess) for vertical struts to 92.8 μm (−8.4% excess) for horizontal struts. The corresponding deviation for gyroids was larger, ranging from 23.8 μm (−3.0% excess) to 168.7 μm (−21.1% excess). Compressive Young’s modulus of the bulk sample, gyroid and diamond scaffolds was calculated to be 35.8 GPa, 6.81 GPa and 7.59 GPa, respectively, via the global compression method. The corresponding yield strength of the samples was measured to be 1012, 108 and 134 MPa. Average microhardness and Young’s modulus from α and β phases of Ti6Al4V from scaffold struts were calculated to be 4.1 GPa and 131 GPa, respectively. The extracted morphology and mechanical properties in this study could help understand the deviation between the as-design and as-built matrices, which could help develop a design compensation strategy before the fabrication of the scaffolds.

Compensating the anisotropic mechanical properties of electron beam melting-based Gyroid scaffolds using structural design

In recent years, scaffolds based on triply periodic minimal surface (TPMS) have been identified as one of the candidates for bone repair materials because of their excellent mechanical and biological properties. In addition, additive manufacturing (AM) enables the production of porous scaffolds with complex microstructures. However, some AM methods (e.g., electron beam melting, EBM) tend to produce a significant anisotropic discrepancy in the mechanical response of scaffolds, and neither the underlying mechanisms nor the compensation method for this discrepancy is clear so far. The aim of this study was to compensate for this discrepancy using structural design and to reveal the underlying mechanisms of each impact factor. Four types of Gyroid scaffolds ranging from rotational symmetric to obvious anisotropic were produced along the height direction of the scaffold using EBM technique, and the relationship between the degree of structural anisotropy (DA) and compressive modulus was determined. When the value of DA was 1.08, the compressive modulus in the building and non-building directions were equal, which means that the anisotropic mechanical discrepancy generated by EBM process was compensated. On the other hand, the decoupling of factors affecting mechanical properties showed that the effective compressive modulus of the rotational symmetric scaffold in the building direction was 42.6% lower than that of non-building direction in the finite element model with highly reductive geometry, while the discrepancy in experimental method was only 20%. The results suggest that the geometric discrepancy is the main factor of the mechanical discrepancy, and the orientation of columnar grains is inclined to the building direction which helps to alleviate the mechanical anisotropy caused by geometry discrepancy. The findings of this study provide important information for the application of TPMS scaffolds in bone implants.

3D printed magnesium-doped β-TCP gyroid scaffold with osteogenesis, angiogenesis, immunomodulation properties and bone regeneration capability in vivo

Bioceramics have been used in orthopedic surgery for several years. Magnesium (Mg) is an essential element in bone tissue and plays an important role in bone metabolism. Mg-doped bioceramics has attracted the attention of researchers recently. However, the optimal doping amount of Mg in β-TCP and the immunomodulatory property of Mg-doped β-TCP (Mg-TCP) have not been determined yet. In this study, β-TCP scaffolds doped with different contents of magnesium oxide (0wt%, 1wt%, 3wt%, and 5wt%) with gyroid structure were printed by digital light processing (DLP) method, and the physicochemical and biological functions were then investigated. Mg-doping improved the physicochemical properties of the β-TCP scaffolds. In vitro experiments confirmed that the doping of Mg in β-TCP scaffolds promoted the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and angiogenic differentiation of endothelial progenitor cells (EPCs), where the 5Mg-TCP has the optimal properties when using the "one cell type" method. It was also found that all Mg-TCP facilitated the polarization of RAW264.7 cells to the M2 phenotype, especially the 3Mg-TCP. However, 3Mg-TCP displayed the optimal osteogenic and angiogenic potential when using a "multiple cell type" method, which referred to culturing the BMSCs or EPCs in the macrophage-conditioned medium. Finally, the in vivo experiments were conducted and the results confirmed that the 3Mg-TCP scaffolds possessed the satisfying bone defect repair capability both after 6 and 12weeks of implantation. This study suggests that 3Mg-TCP scaffolds provide the optimal biological performance and thus have the potential for clinical translation.

Compressive properties and failure behavior of photocast hydroxyapatite gyroid scaffolds vary with porosity.

Hydroxyapatite is commonly used in tissue engineered scaffolds for bone regeneration due to its excellent bioactivity and slow degradation rate in the human body. A method of layer-wise, photopolymerized viscous extrusion, a type of additive manufacturing, was developed to fabricate hydroxyapatite gyroid scaffolds with 60%, 70%, and 80% porosities. This study uses this method to produce and evaluate calcium phosphate-based scaffolds. Gyroid topology was selected due to its interconnected porosity and superior, isotropic mechanical properties compared to typical rectilinear lattice structures. These 3D printed scaffolds were mechanically tested in compression and examined to determine the relationship between porosity, ultimate compressive strength, and fracture behavior. Compressive strength increased with decreasing porosity. Ultimate compressive strengths of the 60% and 70% porous gyroids are comparable to that of human cancellous bone, and higher than previously reported for hydroxyapatite rectilinear scaffolds. These gyroid scaffolds exhibited ultimate compressive strength increases between 1.5 and 6.5 times greater than expected, based on volume of material, as porosity is decreased. The Weibull moduli, a measure of failure predictability, were predictive of failure mode and found to be in the accepted range for engineering ceramics. The gyroid scaffolds were also found to be self-reinforcing such that initial failures due to minor manufacturing inconsistencies did not appear to be the primary cause of early failure of the scaffold. The porous gyroids exhibited scaffold failure characteristics that varied with porosity, ranging from monolithic failure to layer-by-layer failure, and demonstrated self-reinforcement in each porosity tested.

The design and fabrication of gyroid scaffolds for breast reconstruction by fused deposition modelling

Breast-conserving surgery is widely used for breast cancer treatment. However, the breast morphological and functional deficits after surgery significantly affect the life quality of patients. Biodegradable polyester scaffolds, due to their non-toxic, degradable, good biocompatibility and mechanical properties, can protect tissue and promote tissue regeneration, are suitable for breast reconstruction. Existing biodegradable polyester scaffolds cannot meet the soft and stable requirements of breast reconstruction simultaneously due to lack of structural design and optimization. In this study, a soft and stable gyroid breast scaffold with energy-absorbing ability was designed and manufactured by fused deposition modelling. A compression simulation model was developed to analysis stress distribution and elastic modulus of the scaffolds. Compression testing was carried out to validate the model and evaluate real mechanical properties of the scaffolds. The results show that the model results are consistent with the experimental prediction. The elastic modulus of the designed gyroid scaffolds is in the range of 0.08 MPa to 2 MPa, which is thought to stimulate breast tissue growth. Furthermore, the stress distribution of the scaffolds is uniform and the scaffolds exhibit a wide energy-absorbing window of 10 % to 50 % strain, which can provide a stable and safe environment for breast reconstruction. Future work will focus on the integration of this newly designed scaffold embeded with hydrogels and cells for better breast tissue regeneration.

Mimicking Bone Anisotropic Structure with Modified Gyroid Scaffolds; A Finite Element Analysis

The structure of the bone is very complex and heterogeneous; this causes different mechanical and biological properties in its longitudinal and transverse directions. For example, the modulus of elasticity and the permeability of the trabecular bone in a longitudinal and radial direction can vary up to several times. Therefore, implant design that matches these differences is necessary to maximize compliance with the host bone. Given that, in this study, a gyroid structure that generally is used in bone scaffolds was modified to design anisotropic scaffolds. Therefore, the gyroid triply periodic minimal surface trigonometric function was manipulated, and five different architectures were denoted as G(-50), G(-25), G(0), G(+25), and G(+50) with a constant porosity of 80% were developed. The effective elastic moduli of the models were calculated using finite element analysis. The results showed an anisotropicity rate of 0.21, 0.62, 1.50 and 2.23 in elastic moduli for G(-50), G(-25), G(+25) and G(+50) models respectively. As well, the permeability of the models was calculated using computational fluid dynamics (CFD) analysis. Anisotropic models showed different permeability in longitudinal and transverse directions. Longitudinal permeability to lateral direction rate were 0.67, 0.80, 1.25 and 1.47 for G(-50), G(-25), G(+25) and G(+50) models respectively.

Using a radial point interpolation meshless method and the finite element method for application of a bio-inspired remodelling algorithm in the design of optimized bone scaffold

The design of bone scaffold involves the analysis of stress shielding, which can occur when the Young’s modulus of the implant is higher than the Young’s modulus of the bone it is replacing, leading to bone decay in the surrounding tissue. It is therefore very important that the material is adequately designed to match the properties of the surrounding tissue, allowing an appropriate load transfer. While some approaches exist in the literature exploring functional gradients of material density, there are much less solutions based on biological laws. A homogenized model of gyroid infill obtained with PLA (E = 3145 MPa) was obtained through mechanical tests of 3D printed specimens, namely tensile and compression, and the obtained model was implemented in a bone remodelling algorithm. The homogenized law was compared to the results obtained with a bone tissue law to assess the equivalence of density distribution and mechanical properties. Through a radial point interpolation method, it was found that similar density fields were obtained for the gyroid infill and for bone tissue when subject to the same boundary conditions. The finite element method was also used for comparison and validation. With the density field results, the gyroid mechanical behaviour was extrapolated to other materials, and similar stiffness values were obtained for bone tissue and titanium alloy (E = 110 GPa) scaffold, which justify this proposal of gyroid scaffolds for mimicking bone properties.