Computational models for the simulation of the elastic and fracture properties of highly porous 3D-printed hydroxyapatite scaffolds

Bone scaffolding is a promising approach for the treatment of critical-size bone defects. Hydroxyapatite can be used to produce highly porous scaffolds as it mimics the mineralized part of bone tissue, but its intrinsic brittleness limits its usage. Among 3D printing techniques, vat photopolymerization allows for the best printing resolution for ceramic materials. In this study, we implemented a Computed micro-Tomography based Finite Element Model of a hydroxyapatite porous scaffold fabricated by vat photopolymerization. We used the model in order to predict the elastic and fracture properties of the scaffold. From the stress–strain diagram of a simulated compression test, we computed the stiffness and the strength of the scaffolds. We found that three morphometric features substantially affect the crack pattern. In particular, the crack propagation is not only dependent on the trabecular thickness but also depends on the slenderness and orientation of the trabeculae with respect to the load. The results found in this study can be used for the design of ceramic scaffolds with heterogeneous pore distribution in order to tailor and predict the compressive strength

Mechanical Properties of Robocast Glass Scaffolds Assessed through Micro-CT-Based Finite Element Models

In this study, the mechanical properties of two classes of robocast glass scaffolds are obtained through Computed micro-Tomography (micro-CT) based Finite Element Modeling (FEM) with the specific purpose to explicitly account for the geometrical defects introduced during manufacturing. Both classes demonstrate a fiber distribution along two perpendicular directions on parallel layers with a (Formula presented.) tilting between two adjacent layers. The crack pattern identified upon compression loading is consistent with that found in experimental studies available in literature. The finite element models have demonstrated that the effect of imperfections on elastic and strength properties may be substantial, depending on the specific type of defect identified in the scaffolds. In particular, micro-porosity, fiber length interruption and fiber detaching were found as key factors. The micro-pores act as stress concentrators promoting fracture initiation and propagation, while fiber detachment reduces the scaffold properties substantially along the direction perpendicular to the fiber plane

Micro-CT imaging and finite element models reveal how sintering temperature affects the microstructure and strength of bioactive glass-derived scaffolds

This study focuses on the finite element simulation and micromechanical characterization of bioactive glass-ceramic scaffolds using Computed micro Tomography (μ CT) imaging. The main purpose of this work is to quantify the effect of sintering temperature on the morphometry and mechanical performance of the scaffolds. In particular, the scaffolds were produced using a novel bioactive glass material (47.5B) through foam replication, applying six different sintering temperatures. Through μ CT imaging, detailed three-dimensional images of the scaffold’s internal structure are obtained, enabling the extraction of important geometric features and how these features change with sintering temperature. A finite element model is then developed based on the μ CT images to simulate the fracture process under uniaxial compression loading. The model incorporates scaffold heterogeneity and material properties—also depending on sintering temperature—to capture the mechanical response, including crack initiation, propagation, and failure. Scaffolds sintered at temperatures equal to or higher than 700 ∘ C exhibit two-scale porosity, with micro and macro pores. Finite element analyses revealed that the dual porosity significantly affects fracture mechanisms, as micro-pores attract cracks and weaken strength. Interestingly, scaffolds sintered at high temperatures, the overall strength of which is higher due to greater intrinsic strength, showed lower normalized strength compared to low-temperature scaffolds. By using a combined strategy of finite element simulation and μ CT-based characterization, bioactive glass-ceramic scaffolds can be optimized for bone tissue engineering applications by learning more about their micromechanical characteristics and fracture response

Micro computed tomography based finite element models for elastic and strength properties of 3D printed glass scaffolds

Abstract: In this study, the mechanical properties of glass scaffolds manufactured by robocasting are investigated through micro computed tomography (μ- CT) based finite element modeling. The scaffolds are obtained by printing fibers along two perpendicular directions on parallel layers with a 90 ∘ tilting between two adjacent layers. A parametric study is first presented with the purpose to assess the effect of the major design parameters on the elastic and strength properties of the scaffold; the mechanical properties of the 3D printed scaffolds are eventually estimated by using the μ- CT data with the aim of assessing the effect of defects on the final geometry which are intrinsic in the manufacturing process. The macroscopic elastic modulus and strength of the scaffold are determined by simulating a uniaxial compressive test along the direction which is perpendicular to the layers of the printed fibers. An iterative approach has been used in order to determine the scaffold strength. A partial validation of the computational model has been obtained through comparison of the computed results with experimental values presented in [10] on a ceramic scaffold having the same geometry. All the results have been presented as non-dimensional values. The finite element analyses have shown which of the selected design parameters have the major effect on the stiffness and strength, being the porosity and fiber shifting between adjacent layers the most important ones. The analyses carried out on the basis of the μ- CT data have shown elastic modulus and strength which are consistent with that found on ideal geometry at similar macroscopic porosity. Graphic Abstract: In this work, elastic and strength properties of glass-ceramic Bone Tissue Engineering scaffolds manufactured by robocasting are investigated through micro-CT based finite element models. An incremental simulation using a multi-grid finite element solver has been implemented to perform a parametric study on the effect of the major geometrical parameters of the scaffold design as well as the effect. Eventually, the effect of the geometrical imperfections deriving from the 3D printing process has been investigated by means of micro-CT image-based models. The porosity and the shifting between adjacent layers play the dominant role in determing elasticity and strength of the scaffolds. The elastic and strength properties of 3D-printed real scaffold were assessed to be consistent those obtained from the idealized geometric models, at least for the subdomain used in this study.[Figure not available: see fulltext.

High-reliability data processing and calculation of microstructural parameters in hydroxyapatite scaffolds produced by vat photopolymerization

The accurate determination of mass transport and microstructural properties within highly-porous trabecular bone specimens and substitutes still represents a challenge due to the complex arrangement in the three-dimensional space, where adjacent pores can be hardly identified due to the open-cell disordered structure resulting from the reciprocal alternation of struts and voids. In the present study, the complete set of mass transport properties of hydroxyapatite (HA) scaffolds produced by digital light processing (DLP)-based vat photopolymerization was determined by applying the recent Ergun-Wu resistance model. Input data include the intrinsic permeability of the scaffolds, obtained by acoustic experimental measurements, and the equivalent pore diameter, calculated as a function of total porosity and average trabecular size from accurate micro-computed tomography (μ-CT) scans. The results, corroborated by an accurate and robust statistical analysis, were compared with previous literature data and confirmed a feasible and concrete application of DLP-derived HA scaffolds in clinical practice

Bioactive glass coatings fabricated by laser cladding on ceramic acetabular cups: a proof-of-concept study

Deposition of bioceramic coatings on medical implants is a valuable strategy to impart key added values, such as bioactivity. While flat coatings can be easily produced by enameling and similar techniques, applying a bioactive glass layer on surfaces with curved geometry is a great challenge from a technological viewpoint. In this work, for the first time we demonstrated the feasibility of bioactive glass coatings produced by laser cladding on alumina/zirconia ceramic acetabular cups for hip joint prosthesis. Laser-cladded glass coatings can be fabricated in a dense (pore-free) or porous form. Morphological analyses by scanning electron microscopy and micro-computed tomography revealed the good quality of joining at the coating/substrate interface and the good interconnectivity of the pores (size within 200-400 lm) in the outer porous layer. Indentation tests at the interface confirmed the excellent joining between glass and ceramic substrate. These coatings also exhibited a good bioactive behavior in vitro, as demonstrated by the formation of a surface apatite layer upon immersion studies in simulated body fluid

High-reliability data processing and calculation of microstructural parameters in hydroxyapatite scaffolds produced by vat photopolymerization

The accurate determination of mass transport and microstructural properties within highly-porous trabecular bone specimens and substitutes still represents a challenge due to the complex arrangement in the three-dimensional space, where adjacent pores can be hardly identified due to the open-cell disordered structure resulting from the reciprocal alternation of struts and voids. In the present study, the complete set of mass transport properties of hydroxyapatite (HA) scaffolds produced by digital light processing (DLP)-based vat photopolymerization was determined by applying the recent Ergun-Wu resistance model. Input data include the intrinsic permeability of the scaffolds, obtained by acoustic experimental measurements, and the equivalent pore diameter, calculated as a function of total porosity and average trabecular size from accurate micro-computed tomography (mu-CT) scans. The results, corroborated by an accurate and robust statistical analysis, were compared with previous literature data and confirmed a feasible and concrete application of DLP-derived HA scaffolds in clinical practice