Numerical investigation of the mechanical properties of the additive manufactured bone scaffolds fabricated by FDM: The effect of layer penetration and post-heating

Application of additively manufactured bone scaffold: a systematic review

The application of additive manufacturing (AM) technology plays a significant role in various fields, incorporating a wide range of cutting-edge technologies such as aerospace, medical treatment, electronic information, and materials. It is currently widely adopted for medical services, national defense, and industrial manufacturing. In recent years, AM has also been extensively employed to produce bone scaffolds and implant materials. Through AM, products can be manufactured without being constrained by complex internal structures. AM is particularly advantageous in the production of macroscopically irregular and microscopically porous biomimetic bone scaffolds, with short production cycles required. In this paper, AM commonly used to produce bone scaffolds and orthopedic implants is overviewed to analyze the different materials and structures adopted for AM. The applications of antibacterial bone scaffolds and bone scaffolds in biologically relevant animal models are discussed. Also, the influence on the comprehensive performance of product mechanics, mass transfer, and biology is explored. By identifying the reasons for the limited application of existing AM in the biomedical field, the solutions are proposed. This study provides an important reference for the future development of AM in the field of orthopedic healthcare. In conclusion, various AM technologies, the requirements of bone scaffolds and the important role of AM in building bridges between biomaterials, additives, and bone tissue engineering scaffolds are described and highlighted. Nevertheless, more caution should be exercised when designing bone scaffolds and conducting in vivo trials, due to the lack of standardized processes, which prevents the accuracy of results and reduces the reliability of information.

Tensile Properties of Four Types of ABS Lattice Structures-A Comparative Study

This article aims to compare the behaviour of four types of lattice structures named Cartesian, Rhomboid, Octagonal, and Starlit under tensile stress loading. The structures were made of Acrylonitrile Butadiene Styrene (ABS) material using the Fused Filament Fabrication (FFF) technique with three different specific volumes (24, 42, and 60%). Five samples of each type were produced, and a total of 60 samples were tested. Experimental testing was performed according to EN ISO 527-1:2012 and EN ISO 527-2:2012. The obtained data were statistically processed, while no outliers were identified. The experimental results pointed out that the specimens' topology, together with the specific volume, very significantly affected the resultant ABS properties of the tested samples made of the same material. The comparative study showed that in terms of ultimate strength, yield strength, and Young's modulus, the Cartesian structure appeared to be the most suitable for tensile stress, and the least suitable structure was the Rhomboid structure. On the other hand, the Rhomboid-type of the structure showed not only the highest amount of absorbed energy but also the highest toughness among the investigated lattice structures, so in the near future, its behaviour under an impact test should be studied.

Multilayer 3D bioprinting and complex mechanical properties of alginate-gelatin mesostructures

In the biomedical field, extrusion-based 3D bioprinting has emerged as a promising technique to fabricate tissue replacements. However, a main challenge is to find suitable bioinks and reproducible procedures that ensure good printability and generate final printed constructs with high shape fidelity, similarity to the designed model, and controllable mechanical properties. In this study, our main goal is to 3D print multilayered structures from alginate-gelatin (AG) hydrogels and to quantify their complex mechanical properties with particular focus on the effects of the extrusion process and geometrical parameters, i.e. different mesostructures and macroporosities. We first introduce a procedure including a pre-cooling step and optimized printing parameters to control and improve the printability of AG hydrogels based on rheological tests and printability studies. Through this procedure, we significantly improve the printability and flow stability of AG hydrogels and successfully fabricate well-defined constructs similar to our design models. Our subsequent complex mechanical analyses highlight that the extrusion process and the mesostructure, characterized by pore size, layer height and filament diameter, significantly change the complex mechanical response of printed constructs. The presented approach and the corresponding results have important implications for future 3D bioprinting applications when aiming to produce replacements with good structural integrity and defined mechanical properties similar to the native tissue, especially in soft tissue engineering. The approach is also applicable to the printing of gelatin-based hydrogels with different accompanying materials, concentrations, or cells.

3D-Printed PLA Scaffold with Fibronectin Enhances In Vitro Osteogenesis

BACKGROUND

Tricalcium phosphate (TCP, Molecular formula: Ca₃(PO₄)₂) is a hydrophilic bone graft biomaterial extensively used for guided bone regeneration (GBR). However, few studies have investigated 3D-printed polylactic acid (PLA) combined with the osteo-inductive molecule fibronectin (FN) for enhanced osteoblast performance in vitro, and specialized bone defect treatments.

AIM

This study evaluated PLA properties and efficacy following glow discharge plasma (GDP) treatment and FN sputtering for fused deposition modeling (FDM) 3D printed PLA alloplastic bone grafts.

METHODS

3D trabecular bone scaffolds (8 × 1 mm) were printed by the 3D printer (XYZ printing, Inc. 3D printer da Vinci Jr. 1.0 3-in-1). After printing PLA scaffolds, additional groups for FN grafting were continually prepared with GDP treatment. Material characterization and biocompatibility evaluations were investigated at 1, 3 and 5 days.

RESULTS

SEM images showed the human bone mimicking patterns, and EDS illustrated the increased C and O after fibronectin grafting, XPS and FTIR results together confirmed the presence of FN within PLA material. Degradation increased after 150 days due to FN presence. 3D immunofluorescence at 24 h demonstrated better cell spreading, and MTT assay results showed the highest proliferation with PLA and FN (p < 0.001). Cells cultured on the materials exhibited similar alkaline phosphatase (ALP) production. Relative quantitative polymerase chain reaction (qPCR) at 1 and 5 days revealed a mixed osteoblast gene expression pattern.

CONCLUSION

In vitro observations over a period of five days, it was clear that PLA/FN 3D-printed alloplastic bone graft was more favorable for osteogenesis than PLA alone, thereby demonstrating great potential for applications in customized bone regeneration.

Advances in Computational Techniques for Bio-Inspired Cellular Materials in the Field of Biomechanics: Current Trends and Prospects

Cellular materials have a wide range of applications, including structural optimization and biomedical applications. Due to their porous topology, which promotes cell adhesion and proliferation, cellular materials are particularly suited for tissue engineering and the development of new structural solutions for biomechanical applications. Furthermore, cellular materials can be effective in adjusting mechanical properties, which is especially important in the design of implants where low stiffness and high strength are required to avoid stress shielding and promote bone growth. The mechanical response of such scaffolds can be improved further by employing functional gradients of the scaffold's porosity and other approaches, including traditional structural optimization frameworks; modified algorithms; bio-inspired phenomena; and artificial intelligence via machine learning (or deep learning). Multiscale tools are also useful in the topological design of said materials. This paper provides a state-of-the-art review of the aforementioned techniques, aiming to identify current and future trends in orthopedic biomechanics research, specifically implant and scaffold design.

Prediction of the mechanical response of a 3D (bio)printed hybrid scaffold for improving bone tissue regeneration by structural finite element analysis

Scaffolds for bone tissue engineering should be osteoinductive, osteoconductive, biocompatible, biodegradable, and, at the same time, exhibit proper mechanical properties. The present study investigated the mechanical properties of a coprinted hybrid scaffold made of polycaprolactone (PCL) and an alginate-based hydrogel, which was conceived to possess a double function of in vivo bio-integration (due to the ability of the hydrogel to release lyosecretome, a freeze-dried formulation of mesenchymal stem cell secretome with osteoinductive and osteoconductive properties) and withstanding loads (due to the presence of polycaprolactone, which provides mechanical resistance). To this end, an in-silico study was conducted to predict mechanical properties. Structural finite element analysis (FEA) of the hybrid scaffold under compression was performed to compare the numerical results with the corresponding experimental data. The impact of alginate inclusion and infill patterns on scaffold stiffness was investigated. Results show an increase in mechanical properties by changing the scaffold infill pattern (linear: 145.38±28.90 vs. honeycomb: 278.96±50.19, mean and standard deviation, n = 8), while alginate inclusion does not always impact the mechanical performance of the hybrid scaffold (stiffness: 145.38±28.90 vs. 195.42±38.68 N/mm, with vs without hydrogel inclusion, respectively). This is confirmed by FEA analysis, in which a good correspondence between experimental and numerical stiffness is shown (142±28.94 vs. 117.18, respectively, linear scaffold with hydrogel inclusion). In conclusion, the computational framework is a valid tool for predicting the mechanical performance of scaffolds and is promising for future clinical applications in the maxillofacial field.

Nondeterministic multiobjective optimization of 3D printed ceramic tissue scaffolds

Despite significant advances in the design optimization of bone scaffolds for enhancing their biomechanical properties, the functionality of these synthetic constructs remains suboptimal. One of the main challenges in the structural optimization of bone scaffolds is associated with the large uncertainties caused by the manufacturing process, such as variations in scaffolds' geometric features and constitutive material properties after fabrication. Unfortunately, such non-deterministic issues have not been considered in the existing optimization frameworks, thereby limiting their reliability. To address this challenge, a novel multiobjective robust optimization approach is proposed here such that the effects of uncertainties on the optimized design can be minimized. This study first conducted computational analyses of a parameterized ceramic scaffold model to determine its effective modulus, structural strength, and permeability. Then, surrogate models were constructed to formulate explicit mathematical relationships between the geometrical parameters (design variables) and mechanical and fluidic properties. The Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was adopted to generate the robust Pareto solutions for an optimal set of trade-offs between the competing objective functions while ensuring the effects of the noise parameters to be minimal. Note that the nondeterministic optimization of tissue scaffold presented here is the first of its kind in open literature, which is expected to shed some light on this significant topic of scaffold design and additive manufacturing in a more realistic way.

Photothermal Sensitive 3D Printed Biodegradable Polyester Scaffolds with Polydopamine Coating for Bone Tissue Engineering

Biodegradable scaffolds with photothermal effects and customizable pore structures are a hot topic of research in the field of bone repair. In this study, we prepared porous scaffolds using poly(lactic acid) (PLA) as the raw material and customized the pore structure with 3D printing technology. First, we investigated the effect of pore structure on the mechanical properties of this 3D PLA scaffold. Subsequently, the optimally designed PLA scaffolds were coated with PDA to enhance their hydrophilicity and bioactivity. XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy) and EDS (Energy dispersive spectroscopy) results indicated that PDA was successfully coated on the surface of PLA scaffolds. SEM (Scanning electron microscopy) micrographs showed that the surface of the PDA/PLA scaffolds became rough. WCA (water contact angle) confirmed that the material has enhanced hydrophilic properties. PDA/PLA scaffolds exhibit a tunable photothermal effect under NIR (near infrared) irradiation. The 3D-printed PLA/PDA scaffolds have remarkable potential as an alternative material for repairing bone defects.

Advances in additive manufacturing processes and their use for the fabrication of lower limb prosthetic devices

INTRODUCTION

Traditional methods of prosthesis fabrication are not efficient and user centric and are made for common purposes without focusing on individual demands of user which leads to rejection of prosthesis for long-term use. Utilizing advanced additive manufacturing techniques for fabrication of prosthesis makes the development process user centric and covers all the user demands thus providing better fit, comfort, and more stable gait rehabilitation for the user.

AREAS COVERED

The articles reporting fabrication of lower limb prosthesis and its socket are included in the study. Standard fabrication and additive manufacturing method are both systematically assessed by the reviewers. The review also covers the advanced methods of additive manufacturing that are presently being used for fabrication of rehabilitation devices.

EXPERT OPINION

Additive manufacturing method of fabrication of prosthesis provides more flexibility for manufacturing prosthesis parts as per demand of the user. The fabrication method takes into account the residual limb and thus makes the prosthesis user-specific providing better comfort and fit.

Effect of cellulose nanofibers on polyhydroxybutyrate electrospun scaffold for bone tissue engineering applications

The choice of materials and preparation methods are the most important factors affecting the final characteristics of the scaffolds. In this study, cellulose nanofibers (CNFs) as a nano-additive reinforcer were selected to prepare a polyhydroxybutyrate (PHB) based nanocomposite mat. The PHB/CNF (PC) scaffold properties, created via the electrospinning method, were investigated and compared with pure PHB. The obtained results, in addition to a slight increment of crystallinity (from ≃46 to 53 %), showed better water contact angle (from ≃120 to 96°), appropriate degradation rate (up to ≃25 % weight loss in two months), prominent biomineralization (Ca/P ratio about 1.50), and ≃89 % increment in toughness factor of PC compare to the neat PHB. Moreover, the surface roughness as an affecting parameter on cell behavior was also increased up to ≃43 % in the presence of CNFs. Eventually, not only the MTT assay revealed better human osteoblast MG63 cell viability on PC samples, but also DAPI staining and SEM results confirmed the more plausible cell spreading in the presence of cellulose nano-additive. These improvements, along with the appropriate results of ALP and Alizarin red, authenticate that the newly PC nanocomposite composition has the required efficiency in the field of bone tissue engineering.

Biomechanical behavior of diamond lattice scaffolds obtained by two different design approaches with similar porosity; a numerical investigation with FEM and CFD analysis

Scaffolds provide a suitable environment for the bone tissue to maintain its self-healing ability and help new bone-cell formation by creating structures with similar mechanical properties to the surrounding tissue. In the modeling of the scaffolds, an optimum environment is tried to be provided by changing the geometrical properties of the cell architecture such as porosity, pore size, and specific surface area. For this purpose, different design approaches have been used in studies to change these properties. This study aims to determine whether scaffolds with similar porosities modeled by different design approaches exhibit distinct biomechanical behaviors or not. By using the Diamond lattice architecture, two different design approaches were constituted. The first approach has constant wall thickness and variable cell size, whereas the second approach contains variable wall thickness and constant cell size. The usage of different design approaches affected the amount of specific surface area in models with similar porosity. Mechanical compression tests were conducted via finite element analysis, while the permeability performance of configurations with similar porosities (50%, 60%, 70%, 80%, and 90%) was evaluated by using computational fluid dynamics. The mechanical results revealed that the structural strength decreased with increasing porosity. Since their higher specific surface area causes lower pressure drops, the second group exhibits better permeability. In addition, it was found that to evaluate the wall shear stresses occurring on the scaffold surfaces properly, it is essential to consider the stress distributions within the scaffold rather than the maximum values.

Lattice implants that generate homeostatic and remodeling strains in bone

Bone remodeling is mediated by several factors including strain. An increase in strain between 1% and 10% compared to homeostasis can trigger bone formation. We aim to create an orthopedic implant using clinically established imaging and manufacturing methods that induces this strain control in human bone. Titanium scaffolds were manufactured with multiaxial apparent modulus tailored to the mechanical properties of bone defined from computed tomography scans of cadaver human tibiae. Five bone cubes were tested with corresponding titanium scaffolds by loading under compression, which is similar to the implanted tibia loading condition. Bone strain was precisely controlled by varying the scaffold modulus, from 0% to 15% bone strain increase. This strain increase is the magnitude reported to invoke bone's positive remodeling. Axial modulus was closely matched between titanium scaffolds and bone, ranging from 48-728 and 81-800 MPa, respectively, whereby scaffold axial modulus was within 2% of nominal target values. Fine control of multiaxial moduli resulted in transverse modulus that matched bone well; ranging from 42-648 and 47-585 MPa in scaffolds and bone respectively. The scaffold manufacturing material and method are already used in the orthopedic industry. This study has significant clinical implications as it enables the design of implants which positively harness bone's natural mechanoresponse and respect bone's mechanical anisotropy and heterogeneity.

Three-dimensional printing of polycaprolactone/hydroxyapatite bone tissue engineering scaffolds mechanical properties and biological behavior

Controlled pore size and desirable internal architecture of bone scaffolds play a significant role in bone regeneration efficiency. In addition to choosing appropriate materials, the manufacturing method is another significant factor in fabricating the ideal scaffold. In this study, scaffolds were designed and fabricated by the fused filament fabrication (FFF) technique. Polycaprolactone (PCL) and composites films with various percentages of hydroxyapatite (HA) (up to 20%wt) were used to fabricate filaments. The influence of (HA) addition on the mechanical properties of filaments and scaffolds was investigated. in vitro biological evaluation was examined as well as the apatite formation in simulated body fluid (SBF). The addition of HA particles increased the compressive strength and Young's modulus of filaments and consequently the scaffolds. Compared to PCL, Young's modulus of PCL/HA20% filament and three-dimensional (3D) printed scaffold has increased by 30% and 50%, respectively. Also, Young's modulus for all scaffolds was in the range of 30-70 MPa, which is appropriate to use in spongy bone. Besides, the MTT assay was utilized to evaluate cell viability on the scaffolds. All the samples had qualified cytocompatibility, and it would be anticipated that addition of HA particles raise the biocompatibility in vivo. Alkaline phosphatase (ALP) evaluation shows that the addition of HA caused higher ALP activity in the PCL/HA scaffolds than PCL. Furthermore, calcium deposition in the PCL/HA specimens is higher than control. In conclusion, the addition of HA particles into the PCL matrix, as well as utilizing an inexpensive commercial FFF device, lead to the fabrication of scaffolds with proper mechanical and biological properties for bone tissue engineering applications. Graphical abstract.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering

The most common three-dimensional (3D) printing method is material extrusion, where a pre-made filament is deposited layer-by-layer. In recent years, low-cost polycaprolactone (PCL) material has increasingly been used in 3D printing, exhibiting a sufficiently high quality for consideration in cranio-maxillofacial reconstructions. To increase osteoconductivity, prefabricated filaments for bone repair based on PCL can be supplemented with hydroxyapatite (HA). However, few reports on PCL/HA composite filaments for material extrusion applications have been documented. In this study, solvent-free fabrication for PCL/HA composite filaments (HA 0%, 5%, 10%, 15%, 20%, and 25% weight/weight PCL) was addressed, and parameters for scaffold fabrication in a desktop 3D printer were confirmed. Filaments and scaffold fabrication temperatures rose with increased HA content. The pore size and porosity of the six groups’ scaffolds were similar to each other, and all had highly interconnected structures. Six groups’ scaffolds were evaluated by measuring the compressive strength, elastic modulus, water contact angle, and morphology. A higher amount of HA increased surface roughness and hydrophilicity compared to PCL scaffolds. The increase in HA content improved the compressive strength and elastic modulus. The obtained data provide the basis for the biological evaluation and future clinical applications of PCL/HA material.

Fabrication of chitosan/alginate/hydroxyapatite hybrid scaffolds using 3D printing and impregnating techniques for potential cartilage regeneration

Three-dimensional (3D) printed hydrogel scaffolds enhanced with ceramics have shown potential applications for cartilage regeneration, but leaving biological and mechanical properties to be desired. This paper presents our study on the development of chitosan /alginate scaffolds with nano hydroxyapatite (nHA) by combining 3D printing and impregnating techniques, forming a hybrid, yet novel, structure of scaffolds for potential cartilage regeneration. First, we incorporated nHA into chitosan scaffold printing and studied the printability by examining the difference between the printed scaffolds and their designs. Then, we impregnated alginate with nHA into the printed chitosan scaffolds to forming a hybrid structure of scaffolds; and then characterized the scaffolds mechanically and biologically, with a focus on identifying the influence of nHA and alginate for potential cartilage regeneration. The results of compression tests on the scaffolds showed that the inclusion of nHA increased the elastic moduli of scaffolds; while the live/dead assay illustrated that nHA had a great effect on improving attachment and viability of ATCD5 cells on the scaffolds. Also, our results illustrated scaffolds with nHA impregnated in alginate hydrogel enhanced the cell viability and attachment. Furthermore, antibacterial activity of hybrid scaffolds was characterized with results indicating that the chitosan scaffolds had favourable antibacterial ability, which was further enhanced with the impregnated nHA. Taken together, our study has illustrated that chitosan/HA/alginate hybrid scaffolds are promising for cartilage regeneration and the methods developed to create hybrid scaffolds based on 3D printing and impregnating techniques, which can also be extended to fabricating scaffolds for other tissue engineering applications.

Total and partial knee arthroplasty implants that maintain native load transfer in the tibia

AIMS

Unicompartmental and total knee arthroplasty (UKA and TKA) are successful treatments for osteoarthritis, but the solid metal implants disrupt the natural distribution of stress and strain which can lead to bone loss over time. This generates problems if the implant needs to be revised. This study investigates whether titanium lattice UKA and TKA implants can maintain natural load transfer in the proximal tibia.

METHODS

In a cadaveric model, UKA and TKA procedures were performed on eight fresh-frozen knee specimens, using conventional (solid) and titanium lattice tibial implants. Stress at the bone-implant interfaces were measured and compared to the native knee.

RESULTS

Titanium lattice implants were able to restore the mechanical environment of the native tibia for both UKA and TKA designs. Maximum stress at the bone-implant interface ranged from 1.2 MPa to 3.3 MPa compared with 1.3 MPa to 2.7 MPa for the native tibia. The conventional solid UKA and TKA implants reduced the maximum stress in the bone by a factor of 10 and caused > 70% of bone surface area to be underloaded compared to the native tibia.

CONCLUSION

Titanium lattice implants maintained the natural mechanical loading in the proximal tibia after UKA and TKA, but conventional solid implants did not. This is an exciting first step towards implants that maintain bone health, but such implants also have to meet fatigue and micromotion criteria to be clinically viable. Cite this article: Bone Joint Res 2022;11(2):91-101.

Effect of 3D-Printed PLA Structure on Sound Reflection Properties

3D printing technique is currently one of the promising emerging technologies. It is used in many areas of human activity, including acoustic applications. This paper focuses on studying the sound reflection behavior of four different types of 3D-printed open-porous polylactic acid (PLA) material structures, namely cartesian, octagonal, rhomboid and starlit structures. Sound reflection properties were evaluated by means of the normal incidence sound reflection coefficient based on the transfer function method using an acoustic impedance tube. In this study, various factors affecting the sound reflection performance of the investigated PLA samples were evaluated. It can be concluded that the sound reflection behavior of the tested PLA specimens was strongly affected by different factors. It was influenced, not only by the type of 3D-printed open-porous material structure, but also by the excitation frequency, the total volume porosity, the specimen thickness, and the air gap size behind the tested specimen inside the acoustic impedance tube.

From 3D printing to 3D bioprinting: the material properties of polymeric material and its derived bioink for achieving tissue specific architectures

The application of 3D printing technologies fields for biological tissues, organs, and cells in the context of medical and biotechnology applications requires a significant amount of innovation in a narrow printability range. 3D bioprinting is one such way of addressing critical design challenges in tissue engineering. In a more general sense, 3D printing has become essential in customized implant designing, faithful reproduction of microenvironmental niches, sustainable development of implants, in the capacity to address issues of effective cellular integration, and long-term stability of the cellular constructs in tissue engineering. This review covers various aspects of 3D bioprinting, describes the current state-of-the-art solutions for all aforementioned critical issues, and includes various illustrative representations of technologies supporting the development of phases of 3D bioprinting. It also demonstrates several bio-inks and their properties crucial for being used for 3D printing applications. The review focus on bringing together different examples and current trends in tissue engineering applications, including bone, cartilage, muscles, neuron, skin, esophagus, trachea, tympanic membrane, cornea, blood vessel, immune system, and tumor models utilizing 3D printing technology and to provide an outlook of the future potentials and barriers.

3D printing of poly(butylene adipate-co-terephthalate) (PBAT)/niobium containing bioactive glasses (BAGNb) scaffolds: Characterization of composites, in vitro bioactivity, and in vivo bone repair

This study aimed to produce poly(butylene adipate-co-terephthalate) (PBAT)/niobium containing bioactive glasses (BAGNb) composites scaffolds produced by fused deposition modeling (FDM) printing and evaluate their physicochemical and biological properties in vitro and in vivo. The composite filaments were produced by melt-extrusion with the addition of 10 wt% of BAGNb (PBAT/BAGNb). Filaments without BAGNb were produced as the control group (PBAT). The filaments were characterized and were used to produce 3D-printed scaffolds using FDM. The scaffolds' structure and surface properties were assessed. In vitro cell, proliferation, and cell mineralization analysis were performed. In vivo data was obtained in the rat femur model (n = 10), and the bone repair was assessed after 15, 30, and 60 postoperative days. The printed structures presented 69.81% porosity for the PBAT/BAGNb group and 74.54% for the PBAT group. Higher cell mineralization was observed for the PBAT/BAGNb group. The in vivo data showed that the PBAT/BAGNb presented new bone formation comparable to positive controls. The combination of PBAT and BAGNb in 3D-printed scaffolds may be an alternative to produce bioactive materials with controllable shapes and properties for bone regeneration treatments.

Design procedure for triply periodic minimal surface based biomimetic scaffolds

Cellular additively manufactured metallic structures for load-bearing scaffolds in the context of bone tissue engineering (BTE) have emerged as promising candidates. Due to many advantages in terms of morphology, stiffness, strength and permeability compared to conventional truss structures, lattices based on triply periodic minimal surfaces (TPMS) have recently attracted increasing interest for this purpose. In addition, the finite element method (FEM) has been proven to be suitable for accurately predicting the deformation behavior as well as the mechanical properties of geometric structures after appropriate parameter validation based on experimental data. Numerous publications have examined many individual aspects, but conceptual design procedures that consider at least the essential requirements for cortical and trabecular bone simultaneously are still rare. Therefore, this paper presents a numerical approach to first determine the actual admissible design spaces for a choice of TPMS based lattices with respect to key parameters and then weight them with respect to further benefit parameters. The admissible design spaces are limited by pore size, strut size and volume fraction, and the subsequent weighting is based on Young's modulus, cell size and surface area. Additively manufactured beta-Ti-42Nb with a strain stiffness of 60.5GPa is assumed as material. In total, the procedure considers twelve lattice types, consisting of six different TPMS, each as network solid and as sheet solid. The method is used for concrete prediction of suitable TPMS based lattices for cortical bone and trabecular bone. For cortical bone a lattice based on the Schwarz Primitive sheet solid with 67.572μm pore size, 0.5445 volume fraction and 18.758GPa Young's modulus shows to be the best choice. For trabecular bone a lattice based on the Schoen Gyroid network solid with 401.39μm pore size, 0.3 volume fraction and 4.6835GPa Young's modulus is the identified lattice. Finally, a model for a long bone scaffold is generated from these two lattices using functional grading methods in terms of volume fraction, cell size and TPMS type. In particular, the presented procedure allows an efficient estimation for a likely suitable biometric TPMS-based scaffolds. In addition to medical applications, however, the method can also be transferred to numerous other applications in mechanical, civil and electrical engineering.

Comparison of CAD and Voxel-Based Modelling Methodologies for the Mechanical Simulation of Extrusion-Based 3D Printed Scaffolds

Porous structures are of great importance in tissue engineering. Most scaffolds are 3D printed, but there is no single methodology to model these printed parts and to apply finite element analysis to estimate their mechanical behaviour. In this work, voxel-based and geometry-based modelling methodologies are defined and compared in terms of computational efficiency, dimensional accuracy, and mechanical behaviour prediction of printed parts. After comparing the volumes and dimensions of the models with the theoretical and experimental ones, they are more similar to the theoretical values because they do not take into account dimensional variations due to the printing temperature. This also affects the prediction of the mechanical behaviour, which is not accurate compared to reality, but it makes it possible to determine which geometry is stiffer. In terms of comparison of modelling methodologies, based on process efficiency, geometry-based modelling performs better for simple or larger parts, while voxel-based modelling is more advantageous for small and complex geometries.

Production and Characterization of Poly (Lactic Acid)/Nanostructured Carboapatite for 3D Printing of Bioactive Scaffolds for Bone Tissue Engineering

Biocompatible scaffolds are porous matrices that are bone substitutes with great potential in tissue regeneration. For this, these scaffolds need to have bioactivity and biodegradability. From this perspective, 3D printing presents itself as one of the techniques with the greatest potential for scaffold manufacturing with porosity and established structure, based on 3D digital modeling. Thus, the objective of the present work was to produce 3D scaffolds from the poly (lactic acid) (PLA) and the nanostructured hydroxyapatite doped with carbonate ions (CHA). For this purpose, filaments were produced via fusion for the fused-filament 3D printing and used to produce scaffolds with 50% porosity in the cubic shape and 0/90°configuration. The dispersive energy spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis demonstrated the presence of CHA in the polymeric matrix, confirming the presence and incorporation into the composite. The thermogravimetric analysis made it possible to determine that the filler concentration incorporated in the matrix was very similar to the proposed percentage, indicating that there were no major losses in the process of obtaining the filaments. It can be assumed that the influence of CHA as a filler presents better mechanical properties up to a certain amount. The biological results point to a great potential for the application of PLA/CHA scaffolds in bone tissue engineering with effective cell adhesion, proliferation, biocompatibility, and no cytotoxicity effects.

The State of Starch/Hydroxyapatite Composite Scaffold in Bone Tissue Engineering with Consideration for Dielectric Measurement as an Alternative Characterization Technique

Hydroxyapatite (HA) has been widely used as a scaffold in tissue engineering. HA possesses high mechanical stress and exhibits particularly excellent biocompatibility owing to its similarity to natural bone. Nonetheless, this ceramic scaffold has limited applications due to its apparent brittleness. Therefore, this had presented some difficulties when shaping implants out of HA and for sustaining a high mechanical load. Fortunately, these drawbacks can be improved by combining HA with other biomaterials. Starch was heavily considered for biomedical device applications in favor of its low cost, wide availability, and biocompatibility properties that complement HA. This review provides an insight into starch/HA composites used in the fabrication of bone tissue scaffolds and numerous factors that influence the scaffold properties. Moreover, an alternative characterization of scaffolds via dielectric and free space measurement as a potential contactless and nondestructive measurement method is also highlighted.

Porosity and pore design influence on fatigue behavior of 3D printed scaffolds for trabecular bone replacement

Polymeric scaffolds provide several advantages when compared with other bone replacement and regenerating techniques. Namely, when compared with the current gold standard, bone autografts, there is no shortage of supply nor donor site morbidity. Contrarily to metallic implants, their mechanical properties are similar to those of cortical bone and they are biodegradable, therefore stress shielding is not expected to occur, and they will be gradually replaced by new bone tissue. Yet, there are still several challenges to overcome. After implantation scaffolds are subjected to dynamic loads, thus understanding polymeric scaffolds' fatigue behavior plays a major role on the design of better products. In this work PLA scaffolds were manufactured using 3D printing with optimized parameters. A total of six configurations were tested under static and dynamic load conditions. Static compression testing and numerical simulation showed good correlation. Numerical simulation provided a viable resource for scaffold design and innovation. Four different low-cycle fatigue loads were applied, during 3600 cycles with a frequency of 0.25 Hz. While under dynamic conditions, with a maximum stress of 24 MPa and R = 0.1, the apparent compressive modulus reached 973 MPa, due to pore collapse. Even after 3600 cycles no significant fatigue damage mechanisms were found on low porosity scaffolds, rendering them useful for trabecular bone replacement under dynamic conditions.

Photopolymerized poly(l-lactide-b-N-vinyl-2-pyrrolidone) network resists cell adhesion in situ

A three-armed star-shaped poly(l-lactide) (PLLA) oligomer was synthesized using glycerol to ring-opening and polymerize l-lactide. The resultant oligomer introduced photoreactive groups at the terminal of PLLA chains by a coupling reaction with monoethyl fumarate (FAME). Photopolymerizable resin has been prepared by mixing PLLA 3-FAME, N-vinyl-2-pyrrolidone (NVP) as a reactive diluent and Irgacure 2959 as a photoinitiator. The PLLA 3-FAME/NVP cross-linked network could be formed by UV curing and was characterized through mechanical property tests, cytotoxicity experiments and cell adhesion experiments. In the dry state, Young's modulus and tensile strength of the network were significantly higher than those of pure PLLA formed by fused deposition modeling (FDM) printing, due to the formation of the cross-linked net. In the wet state, however, Young's modulus and tensile strength of the network were reduced by less than those of PLLA since the water-absorbed NVP content was easy to stretch. Moreover, the resultant network not only exhibited no obvious cytotoxicity but also resisted the adhesion of L929 fibroblasts. Combined with Digital Light Processing (DLP) technology, the poly(l-lactide-b-N-vinyl-2-pyrrolidone) network may be widely used in the field of anti-adhesion barrier materials and/or biological anti-fouling materials with customization requirements.

The poly(l-lactide-b-N-vinyl-2-pyrrolidone) network could be formed by UV curing, and resist the adhesion of L929 fibroblasts. It could be used in the field of biological anti-fouling material with customization requirements.

Determination of the Elasticity Modulus of Additively Manufactured Wrist Hand Orthoses

The article describes the experimental and simulation research on the material properties of the individualized wrist orthoses produced in the additive manufacturing (AM) process by the fused filament fabrication (FFF) method. The authors produced a series of standard (normalized) samples for three-point bending from acrylonitrile butadiene styrene (ABS) filament on a low-budget 3D printer and a series of samples in the shape of a fragment of the orthosis and the entire orthosis. All types of samples were subjected to experimental tests on a universal testing machine, which allowed us to determine the modulus of elasticity of the produced materials by comparing it with finite element method (FEM) simulation models in the ABAQUS environment. The adopted research methodology allowed us to compare the material properties of the material of the entire product-wrist hand orthosis (WHO)-with the material properties of standard bending samples. The obtained values of Young's modulus are characterized by a large discrepancy between the standard samples and the entire orthosis. On the other hand, the samples with the shape of the middle part of the orthosis were similar in the value of Young's modulus to the results obtained during the examination of the complete orthosis.

Morphological and mechanical characterization of 3D printed PLA scaffolds with controlled porosity for trabecular bone tissue replacement

Bone transplant is still the gold standard approach when dealing with orthopedic trauma or disease. When this solution is not possible, scaffolding is a possibility provided by bone tissue engineering. To support the regeneration process, damaged bone tissue is removed and replaced by porous scaffold structures. In recent years, additive manufacturing has shown huge potential to produce scaffold structures with the required performance. In the current work, PLA scaffolds with different designs were 3D printed, using optimal manufacturing parameters. Scaffolds with three different porosity values were obtained by changing the filament offset from 571 to 1333 μm. A total of twelve designs were tested under monotonic and dynamic compression conditions. Numerical analysis showed good correlation with experimental results, allowing for a better assessment of scaffold mechanical behavior. Stress relaxation was measured on four different strain levels, assessing scaffold's behavior after implantation and consequent static response over time. Overall, orthogonal design provided better performance, due to improved material deposition. With lower porosity scaffolds equilibrium stress reached 24 MPa after 300 s relaxation time under 4% deformation, and the obtained equilibrium modulus was 428 MPa. Overall, attained results show that 3D printing with PLA can be applied in the manufacture of scaffolds for trabecular bone replacement.

Integrating finite element modelling and 3D printing to engineer biomimetic polymeric scaffolds for tissue engineering

The suitability of a scaffold for tissue engineering is determined by a number of interrelated factors. The biomaterial should be biocompatible and cell instructive, with a porosity and pore interconnectivity that facilitates cellular migration and the transport of nutrients and waste products into and out of the scaffolds. For the engineering of load bearing tissues, the scaffold may also be required to possess specific mechanical properties and/or ensure the transfer of mechanical stimuli to cells to direct their differentiation. Achieving these design goals is challenging, but could potentially be realised by integrating computational tools such as finite element (FE) modelling with three-dimensional (3D) printing techniques to assess how scaffold architecture and material properties influence the performance of the implant. In this study we first use Fused Deposition Modelling (FDM) to modulate the architecture of polycaprolactone (PCL) scaffolds, exploring the influence of varying fibre diameter, spacing and laydown pattern on the structural and mechanical properties of such scaffolds. We next demonstrate that a simple FE modelling strategy, which captures key aspects of the printed scaffold's actual geometry and material behaviour, can be used to accurately model the mechanical characteristics of such scaffolds. We then show the utility of this strategy by using FE modelling to help design 3D printed scaffolds with mechanical properties mimicking that of articular cartilage. In conclusion, this study demonstrates that a relatively simple FE modelling approach can be used to inform the design of 3D printed scaffolds to ensure their bulk mechanical properties mimic specific target tissues.

Effect of the nano/microscale structure of biomaterial scaffolds on bone regeneration

Natural bone is a mineralized biological material, which serves a supportive and protective framework for the body, stores minerals for metabolism, and produces blood cells nourishing the body. Normally, bone has an innate capacity to heal from damage. However, massive bone defects due to traumatic injury, tumor resection, or congenital diseases pose a great challenge to reconstructive surgery. Scaffold-based tissue engineering (TE) is a promising strategy for bone regenerative medicine, because biomaterial scaffolds show advanced mechanical properties and a good degradation profile, as well as the feasibility of controlled release of growth and differentiation factors or immobilizing them on the material surface. Additionally, the defined structure of biomaterial scaffolds, as a kind of mechanical cue, can influence cell behaviors, modulate local microenvironment and control key features at the molecular and cellular levels. Recently, nano/micro-assisted regenerative medicine becomes a promising application of TE for the reconstruction of bone defects. For this reason, it is necessary for us to have in-depth knowledge of the development of novel nano/micro-based biomaterial scaffolds. Thus, we herein review the hierarchical structure of bone, and the potential application of nano/micro technologies to guide the design of novel biomaterial structures for bone repair and regeneration.

Bioprinting of Vascularized Tissue Scaffolds: Influence of Biopolymer, Cells, Growth Factors, and Gene Delivery

Over the past decades, tissue regeneration with scaffolds has achieved significant progress that would eventually be able to solve the worldwide crisis of tissue and organ regeneration. While the recent advancement in additive manufacturing technique has facilitated the biofabrication of scaffolds mimicking the host tissue, thick tissue regeneration remains challenging to date due to the growing complexity of interconnected, stable, and functional vascular network within the scaffold. Since the biological performance of scaffolds affects the blood vessel regeneration process, perfect selection and manipulation of biological factors (i.e., biopolymers, cells, growth factors, and gene delivery) are required to grow capillary and macro blood vessels. Therefore, in this study, a brief review has been presented regarding the recent progress in vasculature formation using single, dual, or multiple biological factors. Besides, a number of ways have been presented to incorporate these factors into scaffolds. The merits and shortcomings associated with the application of each factor have been highlighted, and future research direction has been suggested.

Studies on the Stress-Strain Relationship Bovine Cortical Bone Based on Ramberg–Osgood Equation

Bone is a complex material that exhibits an amount of plasticity before bone fracture takes place, where the nonlinear relationship between stress and strain is of importance to understand the mechanism behind the fracture. This brief presents our study on the examination of the stress–strain relationship of bovine femoral cortical bone and the relationship representation by employing the Ramberg–Osgood (R–O) equation. Samples were taken and prepared from different locations (upper, middle, and lower) of bone diaphysis and were then subjected to the uniaxial tensile tests under longitudinal and transverse loading conditions, respectively. The stress–strain curves obtained from tests were analyzed via linear regression analysis based on the R–O equation. Our results illustrated that the R–O equation is appropriate to describe the nonlinear stress–strain behavior of cortical bone, while the values of equation parameters vary with the sample locations (upper, middle, and lower) and loading conditions (longitudinal and transverse).

Characterization of the Mechanical Properties of FFF Structures and Materials: A Review on the Experimental, Computational and Theoretical Approaches

The increase in accessibility of fused filament fabrication (FFF) machines has inspired the scientific community to work towards the understanding of the structural performance of components fabricated with this technology. Numerous attempts to characterize and to estimate the mechanical properties of structures fabricated with FFF have been reported in the literature. Experimental characterization of printed components has been reported extensively. However, few attempts have been made to predict properties of printed structures with computational models, and a lot less work with analytical approximations. As a result, a thorough review of reported experimental characterization and predictive models is presented with the aim of summarizing applicability and limitations of those approaches. Finally, recommendations on practices for characterizing printed materials are given and areas that deserve further research are proposed.

Three-dimensional (3D) printed scaffold and material selection for bone repair

Critical-sized bone defect repair remains a substantial challenge in clinical settings and requires bone grafts or bone substitute materials. However, existing biomaterials often do not meet the clinical requirements of structural support, osteoinductive property, and controllable biodegradability. To treat large-scale bone defects, the development of three-dimensional (3D) porous scaffolds has received considerable focus within bone engineering. A variety of biomaterials and manufacturing methods, including 3D printing, have emerged to fabricate patient-specific bioactive scaffolds that possess controlled micro-architectures for bridging bone defects in complex configurations. During the last decade, with the development of the 3D printing industry, a large number of tissue-engineered scaffolds have been created for preclinical and clinical applications using novel materials and innovative technologies. Thus, this review provides a brief overview of current progress in existing biomaterials and tissue engineering scaffolds prepared by 3D printing technologies, with an emphasis on the material selection, scaffold design optimization, and their preclinical and clinical applications in the repair of critical-sized bone defects. Furthermore, it will elaborate on the current limitations and potential future prospects of 3D printing technology. STATEMENT OF SIGNIFICANCE: 3D printing has emerged as a critical fabrication process for bone engineering due to its ability to control bulk geometry and internal structure of tissue scaffolds. The advancement of bioprinting methods and compatible ink materials for bone engineering have been a major focus to develop optimal 3D scaffolds for bone defect repair. Achieving a successful balance of cellular function, cellular viability, and mechanical integrity under load-bearing conditions is critical. Hybridization of natural and synthetic polymer-based materials is a promising approach to create novel tissue engineered scaffolds that combines the advantages of both materials and meets various requirements, including biological activity, mechanical strength, easy fabrication and controllable degradation. 3D printing is linked to the future of bone grafts to create on-demand patient-specific scaffolds.

Current state of fabrication technologies and materials for bone tissue engineering

A range of traditional and free-form fabrication technologies have been investigated and, in numerous occasions, commercialized for use in the field of regenerative tissue engineering (TE). The demand for technologies capable of treating bone defects inherently difficult to repair has been on the rise. This quest, accompanied by the advent of functionally tailored, biocompatible, and biodegradable materials, has garnered an enormous research interest in bone TE. As a result, different materials and fabrication methods have been investigated towards this end, leading to a deeper understanding of the geometrical, mechanical and biological requirements associated with bone scaffolds. As our understanding of the scaffold requirements expands, so do the capability requirements of the fabrication processes. The goal of this review is to provide a broad examination of existing scaffold fabrication processes and highlight future trends in their development. To appreciate the clinical requirements of bone scaffolds, a brief review of the biological process by which bone regenerates itself is presented first. This is followed by a summary and comparisons of commonly used implant techniques to highlight the advantages of TE-based approaches over traditional grafting methods. A detailed discussion on the clinical and mechanical requirements of bone scaffolds then follows. The remainder of the manuscript is dedicated to current scaffold fabrication methods, their unique capabilities and perceived shortcomings. The range of biomaterials employed in each fabrication method is summarized. Selected traditional and non-traditional fabrication methods are discussed with a highlight on their future potential from the authors' perspective. This study is motivated by the rapidly growing demand for effective scaffold fabrication processes capable of economically producing constructs with intricate and precisely controlled internal and external architectures. STATEMENT OF SIGNIFICANCE: The manuscript summarizes the current state of fabrication technologies and materials used for creating scaffolds in bone tissue engineering applications. A comprehensive analysis of different fabrication methods (traditional and free-form) were summarized in this review paper, with emphasis on recent developments in the field. The fabrication techniques suitable for creating scaffolds for tissue engineering was particularly targeted and their use in bone tissue engineering were articulated. Along with the fabrication techniques, we emphasized the choice of materials in these processes. Considering the limitations of each process, we highlighted the materials and the material properties critical in that particular process and provided a brief rational for the choice of the materials. The functional performance for bone tissue engineering are summarized for different fabrication processes and the choice of biomaterials. Finally, we provide a perspective on the future of the field, highlighting the knowledge gaps and promising avenues in pursuit of effective scaffolds for bone tissue engineering. This extensive review of the field will provide research community with a reference source for current approaches to scaffold preparation. We hope to encourage the researchers to generate next generation biomaterials to be used in these fabrication processes. By providing both advantages and disadvantage of each fabrication method in detail, new fabrication techniques might be devised that will overcome the limitations of the current approaches. These studies should facilitate the efforts of researchers interested in generating ideal scaffolds, and should have applications beyond the repair of bone tissue.

3D biofabrication of vascular networks for tissue regeneration: A report on recent advances

Rapid progress in tissue engineering research in past decades has opened up vast possibilities to tackle the challenges of generating tissues or organs that mimic native structures. The success of tissue engineered constructs largely depends on the incorporation of a stable vascular network that eventually anastomoses with the host vasculature to support the various biological functions of embedded cells. In recent years, significant progress has been achieved with respect to extrusion, laser, micro-molding, and electrospinning-based techniques that allow the fabrication of any geometry in a layer-by-layer fashion. Moreover, decellularized matrix, self-assembled structures, and cell sheets have been explored to replace the biopolymers needed for scaffold fabrication. While the techniques have evolved to create specific tissues or organs with outstanding geometric precision, formation of interconnected, functional, and perfused vascular networks remains a challenge. This article briefly reviews recent progress in 3D fabrication approaches used to fabricate vascular networks with incorporated cells, angiogenic factors, proteins, and/or peptides. The influence of the fabricated network on blood vessel formation, and the various features, merits, and shortcomings of the various fabrication techniques are discussed and summarized.

Modeling of the Mechanical Behavior of 3D Bioplotted Scaffolds Considering the Penetration in Interlocked Strands

Three-dimensional (3D) bioplotting has been widely used to print hydrogel scaffolds for tissue engineering applications. One issue involved in 3D bioplotting is to achieve the scaffold structure with the desired mechanical properties. To overcome this issue, various numerical methods have been developed to predict the mechanical properties of scaffolds, but limited by the imperfect representation of one key feature of scaffolds fabricated by 3D bioplotting, i.e., the penetration or fusion of strands in one layer into the previous layer. This paper presents our study on the development of a novel numerical model to predict the elastic modulus (one important index of mechanical properties) of 3D bioplotted scaffolds considering the aforementioned strand penetration. For this, the finite element method was used for the model development, while medium-viscosity alginate was selected for scaffold fabrication by the 3D bioplotting technique. The elastic modulus of the bioplotted scaffolds was characterized using mechanical testing and results were compared with those predicted from the developed model, demonstrating a strong congruity between them. Once validated, the developed model was also used to investigate the effect of other geometrical features on the mechanical behavior of bioplotted scaffolds. Our results show that the penetration, pore size, and number of printed layers have significant effects on the elastic modulus of bioplotted scaffolds; and also suggest that the developed model can be used as a powerful tool to modulate the mechanical behavior of bioplotted scaffolds.

Strategic Design and Fabrication of Nerve Guidance Conduits for Peripheral Nerve Regeneration

Nerve guidance conduits (NGCs) have been drawing considerable attention as an aid to promote regeneration of injured axons across damaged peripheral nerves. Ideally, NGCs should include physical and topographic axon guidance cues embedded as part of their composition. Over the past decades, much progress has been made in the development of NGCs that promote directional axonal regrowth so as to repair severed nerves. This paper briefly reviews the recent designs and fabrication techniques of NGCs for peripheral nerve regeneration. Studies associated with versatile design and preparation of NGCs fabricated with either conventional or rapid prototyping (RP) techniques have been examined and reviewed. The effect of topographic features of the filler material as well as porous structure of NGCs on axonal regeneration has also been examined from the previous studies. While such strategies as macroscale channels, lumen size, groove geometry, use of hydrogel/matrix, and unidirectional freeze-dried surface are seen to promote nerve regeneration, shortcomings such as axonal dispersion and wrong target reinnervation still remain unsolved. On this basis, future research directions are identified and discussed.