Effects of design, porosity and biodegradation on mechanical and morphological properties of additive-manufactured triply periodic minimal surface scaffolds

Design of 3D printing osteotomy block for foot based on triply periodic minimal surface

The ankle joint, which connects the lower limbs and the sole of the foot, is prone to sprain during walking and sports, which leads to ankle arthritis. Supratroleolar osteotomy is an ankle preserving operation for the treatment of ankle arthritis, in which the osteotomy is an important fixing and supporting part. In order to avoid stress shielding effect as much as possible, the osteotomy block is designed as a porous structure. In this study, the osteotomy block was designed based on three-period minimal surface, and the designed structure was manufactured by 3D printing. The mechanical properties of different structures were studied by mechanical test and finite element simulation. In mechanical tests, the Gyroid structure showed a progressive failure mechanism from bottom to bottom, while the Diamond structure showed a shear failure zone at 45° Angle, which was not conducive to energy absorption and was more prone to brittle fracture than the Gyroid structure. Therefore, the Gyroid structure is valuable for further research in the development of porous osteotomy.

Mechanical Behaviour of Photopolymer Cell-Size Graded Triply Periodic Minimal Surface Structures at Different Deformation Rates

This study investigates how varying cell size affects the mechanical behaviour of photopolymer Triply Periodic Minimal Surfaces (TPMS) under different deformation rates. Diamond, Gyroid, and Primitive TPMS structures with spatially graded cell sizes were tested. Quasi-static experiments measured boundary forces, representing material behaviour, inertia, and deformation mechanisms. Separate studies explored the base material's behaviour and its response to strain rate, revealing a strength increase with rising strain rate. Ten compression tests identified a critical strain rate of 0.7 s-1 for "Grey Pro" material, indicating a shift in failure susceptibility. X-ray tomography, camera recording, and image correlation techniques observed cell connectivity and non-uniform deformation in TPMS structures. Regions exceeding the critical rate fractured earlier. In Primitive structures, stiffness differences caused collapse after densification of smaller cells at lower rates. The study found increasing collapse initiation stress, plateau stress, densification strain, and specific energy absorption with higher deformation rates below the critical rate for all TPMS structures. However, cell-size graded Primitive structures showed a significant reduction in plateau and specific energy absorption at a 500 mm/min rate.

Novel 3D printed TPMS scaffolds: microstructure, characteristics and applications in bone regeneration

Bone defect disease seriously endangers human health and affects beauty and function. In the past five years, the three dimension (3D) printed radially graded triply periodic minimal surface (TPMS) porous scaffold has become a new solution for repairing bone defects. This review discusses 3D printing technologies and applications for TPMS scaffolds. To this end, the microstructural effects of 3D printed TPMS scaffolds on bone regeneration were reviewed and the structural characteristics of TPMS, which can promote bone regeneration, were introduced. Finally, the challenges and prospects of using TPMS scaffolds to treat bone defects were presented. This review is expected to stimulate the interest of bone tissue engineers in radially graded TPMS scaffolds and provide a reliable solution for the clinical treatment of personalised bone defects.

Effect of Porosity and Pore Shape on the Mechanical and Biological Properties of Additively Manufactured Bone Scaffolds

This study investigates the effect of porosity and pore shape on the biological and mechanical behavior of additively manufactured scaffolds for bone tissue engineering (BTE). Polylactic acid scaffolds with varying porosity levels (15-78%) and pore shapes, including regular (rectangular pores), gyroid, and diamond (triply periodic minimal surfaces) structures, are fabricated by fused filament fabrication. Murine-derived macrophages and human bone marrow-derived mesenchymal stromal cells (hBMSCs) are seeded onto the scaffolds. The compressive behavior and surface morphology of the scaffolds are characterized. The results show that scaffolds with 15%, 30%, and 45% porosity display the highest rate of macrophage and hBMSC growth. Gyroid and diamond scaffolds exhibit a higher rate of macrophage proliferation, while diamond scaffolds exhibit a higher rate of hBMSC proliferation. Additionally, gyroid and diamond scaffolds exhibit better compressive behavior compared to regular scaffolds. Of particular note, diamond scaffolds have the highest compressive modulus and strength. Surface morphology characterization indicates that the surface roughness of diamond and gyroid scaffolds is greater than that of regular scaffolds at the same porosity level, which is beneficial for cell attachment and proliferation. This study provides valuable insights into porosity and pore shape selection for additively manufactured scaffolds in BTE.

Understanding of trabecular-cortical transition zone: Numerical and experimental assessment of multi-morphology scaffolds

Applications of additive manufacturing (AM) in tissue engineering develop rapidly. AM offers layer-by-layer creation of complex objects, developed to restore functionality of, or replace, damaged tissues. Porous 3D-printed functional gradient structures are of particular interest: their special architecture makes it possible to simulate the heterogeneity of the replaced tissue and, by continuously changing the mechanical properties, to avoid the concentration of stresses that can be caused by abrupt geometric changes. Such structures also allow combinations of different types of unit cells and a smooth transition between them, making design of personalised scaffolds with optimal parameters for the replacement of damaged host tissue at the interface between tissues possible. This paper presents the results of development of scaffold structures with gradients of porosity and multi-morphology using unit cells based on triply periodic minimal surfaces (TPMS). The mechanical behaviour of additively manufactured scaffold prototypes made of polylactide acid (PLA) was studied under compressive loading. Strain fields on their surface were captured using the Vic-3d Micro-DIC digital image correlation system and compared with those obtained with detailed numerical simulations, employing elastic-plastic properties of PLA, obtained in experiments. The effect of gradient parameters and unit-cell morphology on the stress distribution in scaffolds was analysed. A smooth gradient transition between cells with different morphologies was found to reduce the probability of structural failure under intense compressive loading. A good agreement between numerical results and experimental data was achieved, which justifies application of the developed approach to design of personalised bone scaffolds.

Design and manufacturing of biomimetic scaffolds for bone repair inspired by bone trabeculae

Porous scaffold (PorS) implants, particularly those that mimic the structural features of natural cancellous bone (NCanB), are increasingly essential for the treatment of large-area bone defects. However, the mechanical properties of NCanB-based bionic bone scaffold (BioS) and its performance as a bone repair material have not been fully explored. This study investigates the effect of bionic structure parameters on the mechanical properties and bone reconstruction performance of BioS. Using laser powder bed fusion (L-PBF) technology, different BioS with various structural parameters were created and evaluated using Micro-CT, compression testing, Finite Element (FE) Simulation, and computational fluid dynamics (CFD), and compared to commonly used clinical PorS. Assess the capacity of the BioS scaffold to support and enhance bone reconstruction following implantation through the evaluation of its mechanical properties, permeability, and fluid shear stress (FSS). BioS-85-90 and BioS-80-50 showed suitable mechanical properties, performed well in FE simulation of implantation, demonstrated outstanding abilities for osteoinductive ingrowth and bone tissue differentiation, and proved to be reliable materials for the reconstruction of bone defects. Therefore, BioS shows significant potential for clinical application as a bone reconstruction material, providing a solid foundation for the integration of tissue engineering and bionic design.

Mechanical Properties Directionality and Permeability of Fused Triply Periodic Minimal Surface Porous Scaffolds Fabricated by Selective Laser Melting

Titanium alloy porous scaffolds possess excellent mechanical properties and biocompatibility, making them promising for applications in bone tissue engineering. The integration of triply periodic minimal surface (TPMS) with porous scaffolds provides a structural resemblance to the trabecular and cortical bone structures of natural bone tissue, effectively reducing stress-shielding effects, enabling the scaffold to withstand complex stress environments, and facilitating nutrient transport. In this study, we designed fused porous scaffolds based on the Gyroid and Diamond units within TPMS and fabricated samples using selective laser melting technology. The effects of the rotation direction and angle of the inner-layer G unit on the elastic modulus of the fused TPMS porous scaffold were investigated through quasi-static compression experiments. Furthermore, the influence of the rotation direction and angle of the inner-layer G unit on the permeability, pressure, and flow velocity of the fused TPMS porous scaffold structure was studied using computational fluid dynamics (CFD) based on the Navier-Stokes model. The quasi-static compression experiment results demonstrated that the yield strength of the fused TPMS porous scaffold ranged from 367.741 to 419.354 MPa, and the elastic modulus ranged from 10.617 to 11.252 GPa, exhibiting stable mechanical performance in different loading directions. The CFD simulation results indicated that the permeability of the fused TPMS porous scaffold model ranged from 5.70015 × 10-8 to 6.33725 × 10-8 m2. It can be observed that the fused porous scaffold meets the requirements of the complex stress-bearing demands of skeletal structures and complies with the permeability requirements of human bone tissue.

3D printed TPMS structural PLA/GO scaffold: Process parameter optimization, porous structure, mechanical and biological properties

Bone scaffolds should have good biocompatibility and mechanical and biological properties, which are primarily by the material design, porous structure, and preparation process. In this study, we proposed polylactic acid (PLA) as the base material, graphene oxide (GO) as an enhancing filler, triply periodic minimal surface (TPMS) as a porous structure, and fused deposition modeling (FDM) 3D printing as a preparation technology to develop a TPMS structural PLA/GO scaffold and evaluate their porous structures, mechanical properties, and biological properties towards bone tissue engineering. Firstly, the influence of the FDM 3D printing process parameters on the forming quality and mechanical properties of PLA was studied by orthogonal experimental design, based on which the process parameters were optimized. Then, GO was composited with PLA, and PLA/GO nanocomposites were prepared by FDM. The mechanical tests showed that GO can effectively improve the tensile and compression strength of PLA; only by adding 0.1% GO the tensile and compression modulus was increased by 35.6% and 35.8%, respectively. Then, TPMS structural (Schwarz-P, Gyroid) scaffold models were designed and TPMS structural PLA/0.1%GO nanocomposite scaffolds were prepared by FDM. The compression test showed that the TPMS structural scaffolds had higher compression strength than the Grid structure; This was owing to the fact that the continuous curved structure of TMPS alleviated stress concentration and had a more uniform stress bearing. Moreover, cell culture indicated bone marrow stromal cells (BMSCs) showed better adhesion, proliferation, and osteogenic differentiation behaviors on the TPMS structural scaffolds as the continuous surface structure of TPMS had better connectivity and larger specific surface area. These results suggest that the TPMS structural PLA/GO scaffold has potential application in bone repair. This article suggests the feasibility of co-designing the material, structure, and technology for achieving the good comprehensive performance of polymer bone scaffolds.

The effects of nano-hydroxyapatite/polyamide 66 scaffold on dog femoral head osteonecrosis model: a preclinical study

The lack of mechanical support in the bone tunnel formed after CD often results in a poor therapeutic effect in ONFH. The n-HA/P66 has excellent biocompatibility and mechanical properties and has been widely used in bone regeneration. The present study aimed to evaluate the effects of n-HA/P66 scaffold treatment in a dog model of ONFH. A FEA was performed to analyze the mechanical changes in the femoral head after CD and n-HA/P66 scaffold or tantalum rod implantation. Fifteen male beagles were selected to establish the model of ONFH by liquid nitrogen freezing method, and the models were identified by x-ray and MRI 4 weeks after modeling and randomly divided into three groups. Nine weeks later, femoral head samples were taken for morphology, micro-CT, and histological examination. The FEA showed that the n-HA/P66 scaffold proved the structural support in the bone tunnel, similar to the tantalum rod. The morphology showed that the femoral head with n-HA/P66 implantation is intact, while the femoral heads in the model group and CD group are collapsing. Moreover, the micro-CT results of the n-HA/P66 scaffold group were better than the model group and the CD group, and the interface between the n-HA/P66 scaffold and bone tissue is blurred. Furthermore, the histological result also verifies the alterations in micro-CT, and bone tissue grows in the bone tunnel with n-HA/P66 scaffold implanted while few in the CD group. The CD results in a lack of mechanical support in the femoral head subchondral bone and bone tunnel high stress. The n-HA/P66 scaffold implantation can provide mechanical support and relieve high stress induced by CD. The n-HA/P66 scaffold can treat femoral head necrosis and provide the bone tissue growth scaffold for the femoral head after CD to promote bone tissue regeneration.

Biomechanical behavior of PMMA 3D printed biomimetic scaffolds: Effects of physiologically relevant environment

Functional cellular structures with controllable mechanical and morphological properties are of great interest for applications including tissue engineering, energy storage, and aerospace. Additive manufacturing (AM), also referred to as 3D printing, has enabled the potential for fabrication of functional porous scaffolds (i.e., meta-biomaterials) with controlled geometrical, morphological, and mechanical properties. Understanding the biomechanical behavior of 3D printed porous scaffolds under physiologically relevant loading and environmental conditions is crucial in accurately predicting the in vivo performance. This study was aimed to investigate the environmental dependency of the mechanical responses of 3D printed porous scaffolds of poly(methyl methacrylate) (PMMA) Class IIa biomaterial that was based on triply periodic minimal surfaces - TPMS (i.e., Primitive and Schoen-IWP). The 3D printed scaffolds (n = 5/study group) were tested under compressive loading in both ambient and fluidic (distilled water with pH = 7.4) environments according to ASTM D1621 standards. Outcomes of this study showed that compressive properties of the developed scaffolds are significantly lower in the fluidic condition than the ambient environment for the same topological and morphological group (p≤0.023). Additionally, compressive properties and flexural stiffness of the studied scaffolds were within the range of trabecular bone's properties, for both topological classes. Relationships between predicted mechanical responses and morphological properties (i.e., porosity) were evaluated for each topological class. Quantitative correlation analysis indicated that mechanical behavior of the developed 3D printed scaffolds can be controlled based on both topology and morphology.

Effect of Heat Treatment on Elastic Properties and Fracture Toughness of Fused Filament Fabricated PEEK for Biomedical Applications

This work presents the results of an experimental investigation of the mechanical properties of polyetheretherketone (PEEK) specimens additively manufactured (AM) by using fused filament fabrication with different printing parameters and subjected to postprocessing heat treatment. Standard and compact tension samples were manufactured with a different infill angle using 0.4 mm and 0.6 mm nozzle diameters. Some of the samples were subjected to heat treatment at 220 °C after manufacturing. Tensile tests were conducted to determine the values of elastic modulus, tensile strength, as well as mode-I fracture toughness and critical strain energy release rate. Tensile properties of single-thread and as-delivered filaments were also studied. It was concluded that heat treatment significantly improved the elastic properties, tensile strength and fracture toughness of the AM PEEK samples: the fracture resistance increased by 33 to 45% depending on the stacking order, while the tensile strength increased by some 45-65%, with the elasticity modulus grown by up to 20%. Strain fields induced in specimens by crack propagation were captured with a digital image correlation technique and compared with results of numerical simulations implemented with the extended finite-element method (XFEM). Conclusions on the optimal parameters of 3D printing of PEEK were made.

Aspects of In Vitro Biodegradation of Hybrid Fibrin-Collagen Scaffolds

The success of the regenerative process resulting from the implantation of a scaffold or a tissue-engineered structure into damaged tissues depends on a series of factors, including, crucially, the biodegradability of the implanted materials. The selection of a scaffold with appropriate biodegradation characteristics allows for synchronization of the degradation of the construct with the processes involved in new tissue formation. Thus, it is extremely important to characterize the biodegradation properties of potential scaffold materials at the stage of in vitro studies. We have analyzed the biodegradation of hybrid fibrin–collagen scaffolds in both PBS solution and in trypsin solution and this has enabled us to describe the processes of both their passive and enzymatic degradation. It was found that the specific origin of the collagen used to form part of the hybrid scaffolds could have a significant effect on the nature of the biodegradation process. It was also established, during comparative studies of acellular scaffolds and scaffolds containing stem cells, that the cells, too, make a significant contribution to changes in the biodegradation and structural properties of such scaffolds. The study results also provided evidence indicating the dependency between the pre-cultivation period for the cellular scaffolds and the speed and extent of their subsequent biodegradation. Our discussion of results includes an attempt to explain the mechanisms of the changes found. We hope that the said results will make a significant contribution to the understanding of the processes affecting the differences in the biodegradation properties of hybrid, biopolymer, and hydrogel scaffolds.

Simulation of the Mechanical Behaviour of Metal Gyroids for Bone Tissue Application

Additive manufacturing is a valid solution to build complex geometries, including lightweight structures. Among these, gyroids offer a viable concept for bone tissue application, although many preliminary trials would be required to validate the design before actual implantation. In this frame, this study is aimed at presenting the background and the steps to build a numerical simulation to extract the mechanical behaviour of the structure, thus reducing the experimental effort. The results of the simulation are compared to the actual outcome resulting from quasi-static compressive tests and the effectiveness of the model is measured with reference to similar studies presented in the literature about other lightweight structures.

Development, processing and characterization of Polycaprolactone/Nano-Hydroxyapatite/Chitin-Nano-Whisker nanocomposite filaments for additive manufacturing of bone tissue scaffolds

This paper focuses on utilizing the Fused Deposition Modeling (FDM) to manufacture Polycaprolactone/Nano-Hydroxyapatite/Chitin-Nano-Whisker nanocomposite scaffolds and their subsequent characterization for biomedical applications. FDM nanocomposite filaments were manufactured in multiple nanocomposite formulations of Polycaprolactone/Nano-Hydroxyapatite (nHA), Polycaprolactone/Chitin-Nano-Whisker (CNW), and Polycaprolactone/nHA/CNW using a green method. The FDM processing conditions were optimized using Taguchi orthogonal array method. The mechanical, biodegradation, and biocompatibility properties of the bone tissue scaffolds were assessed. A preosteoblast mouse bone cell line was used for cell proliferation and attachment assays. The results indicated that CNW content in the filaments slightly increases the mechanical properties of the 3D printed parts, and the nanocomposite with 3% CNW content exhibited significant improvement in the cell proliferation and attachment properties of the scaffolds. The nHA content considerably improved the mechanical properties of the scaffolds. The nHA and CNW nanofillers increased the biodegradation rate of PCL. In general, considering all types of responses, a green manufactured nanocomposite of PCL/nHA/CNW can significantly increase the biological and mechanical properties of the 3D printed products for bone tissue scaffolds.

Structural and Material Determinants Influencing the Behavior of Porous Ti and Its Alloys Made by Additive Manufacturing Techniques for Biomedical Applications

One of the biggest challenges in tissue engineering is the manufacturing of porous structures that are customized in size and shape and that mimic natural bone structure. Additive manufacturing is known as a sufficient method to produce 3D porous structures used as bone substitutes in large segmental bone defects. The literature indicates that the mechanical and biological properties of scaffolds highly depend on geometrical features of structure (pore size, pore shape, porosity), surface morphology, and chemistry. The objective of this review is to present the latest advances and trends in the development of titanium scaffolds concerning the relationships between applied materials, manufacturing methods, and interior architecture determined by porosity, pore shape, and size, and the mechanical, biological, chemical, and physical properties. Such a review is assumed to show the real achievements and, on the other side, shortages in so far research.