Computationally designed lattices with tuned properties for tissue engineering using 3D printing

Computational methods for biofabrication in tissue engineering and regenerative medicine - a literature review

This literature review rigorously examines the growing scientific interest in computational methods for Tissue Engineering and Regenerative Medicine biofabrication, a leading-edge area in biomedical innovation, emphasizing the need for accurate, multi-stage, and multi-component biofabrication process models. The paper presents a comprehensive bibliometric and contextual analysis, followed by a literature review, to shed light on the vast potential of computational methods in this domain. It reveals that most existing methods focus on single biofabrication process stages and components, and there is a significant gap in approaches that utilize accurate models encompassing both biological and technological aspects. This analysis underscores the indispensable role of these methods in understanding and effectively manipulating complex biological systems and the necessity for developing computational methods that span multiple stages and components. The review concludes that such comprehensive computational methods are essential for developing innovative and efficient Tissue Engineering and Regenerative Medicine biofabrication solutions, driving forward advancements in this dynamic and evolving field.

Structural tuning of anisotropic mechanical properties in 3D-Printed hydrogel lattices

We investigated the ability to tune the anisotropic mechanical properties of 3D-printed hydrogel lattices by modifying their geometry (lattice strut diameter, unit cell size, and unit cell scaling factor). Many soft tissues are anisotropic and the ability to mimic natural anisotropy would be valuable for developing tissue-surrogate "phantoms" for elasticity imaging (shear wave elastography or magnetic resonance elastography). Vintile lattices were 3D-printed in polyethylene glycol di-acrylate (PEGDA) using digital light projection printing. Two mechanical benchtop tests, dynamic shear testing and unconfined compression, were used to measure the apparent shear storage moduli (G') and apparent Young's moduli (E) of lattice samples. Increasing the unit cell size from 1.25 mm to 2.00 mm reduced the Young's and shear moduli of the lattices by 91% and 85%, respectively. Decreasing the strut diameter from 300 μm to 200 μm reduced the apparent shear moduli of the lattices by 95%. Increasing the geometric scaling ratio of the lattice unit cells from 1.00 × to 2.00 × increased mechanical anisotropy in shear (by a factor of 3.1) and in compression (by a factor of 2.9). Both simulations and experiments show that the effects of unit cell size and strut diameter are consistent with power law relationships between volume fraction and apparent elastic moduli. In particular, experimental measurements of apparent Young's moduli agree well with predictions of the theoretical Gibson-Ashby model. Thus, the anisotropic mechanical properties of a lattice can be tuned by the unit cell size, the strut diameter, and scaling factors. This approach will be valuable in designing tissue-mimicking hydrogel lattice-based composite materials for elastography phantoms and tissue engineered scaffolds.

Reasoning on Pore Terminology in 3D Bioprinting

Terminology is pivotal for facilitating clear communication and minimizing ambiguity, especially in specialized fields such as chemistry. In materials science, a subset of chemistry, the term "pore" is traditionally linked to the International Union of Pure and Applied Chemistry (IUPAC) nomenclature, which categorizes pores into "micro", "meso", and "macro" based on size. However, applying this terminology in closely-related areas, such as 3D bioprinting, often leads to confusion owing to the lack of consensus on specific definitions and classifications tailored to each field. This review article critically examines the current use of pore terminology in the context of 3D bioprinting, highlighting the need for reassessment to avoid potential misunderstandings. We propose an alternative classification that aligns more closely with the specific requirements of bioprinting, suggesting a tentative size-based division of interconnected pores into 'parvo'-(d < 25 µm), 'medio'-(25 < d < 100 µm), and 'magno'-(d > 100 µm) pores, relying on the current understanding of the pore size role in tissue formation. The introduction of field-specific terminology for pore sizes in 3D bioprinting is essential to enhance the clarity and precision of research communication. This represents a step toward a more cohesive and specialized lexicon that aligns with the unique aspects of bioprinting and tissue engineering.

3D-Printed Osteoinductive Polymeric Scaffolds with Optimized Architecture to Repair a Sheep Metatarsal Critical-Size Bone Defect

The reconstruction of critical-size bone defects in long bones remains a challenge for clinicians. A new osteoinductive medical device is developed here for long bone repair by combining a 3D-printed architectured cylindrical scaffold made of clinical-grade polylactic acid (PLA) with a polyelectrolyte film coating delivering the osteogenic bone morphogenetic protein 2 (BMP-2). This film-coated scaffold is used to repair a sheep metatarsal 25-mm long critical-size bone defect. In vitro and in vivo biocompatibility of the film-coated PLA material is proved according to ISO standards. Scaffold geometry is found to influence BMP-2 incorporation. Bone regeneration is followed using X-ray scans, µCT scans, and histology. It is shown that scaffold internal geometry, notably pore shape, influenced bone regeneration, which is homogenous longitudinally. Scaffolds with cubic pores of ≈870 µm and a low BMP-2 dose of ≈120 µg cm-3 induce the best bone regeneration without any adverse effects. The visual score given by clinicians during animal follow-up is found to be an easy way to predict bone regeneration. This work opens perspectives for a clinical application in personalized bone regeneration.

Polyhedron-Like Biomaterials for Innervated and Vascularized Bone Regeneration

Neural-vascular networks are densely distributed through periosteum, cortical bone, and cancellous bone, which is of great significance for bone regeneration and remodeling. Although significant progress has been made in bone tissue engineering, ineffective bone regeneration, and delayed osteointegration still remains an issue due to the ignorance of intrabony nerves and blood vessels. Herein, inspired by space-filling polyhedra with open architectures, polyhedron-like scaffolds with spatial topologies are prepared via 3D-printing technology to mimic the meshwork structure of cancellous bone. Benefiting from its spatial topologies, polyhedron-like scaffolds greatly promoted the osteogenic differentiation of bone mesenchymal stem cells (BMSCs) via activating PI3K-Akt signals, and exhibiting satisfactory performance on angiogenesis and neurogenesis. Computational fluid dynamic (CFD) simulation elucidates that polyhedron-like scaffolds have a relatively lower area-weighted average static pressure, which is beneficial to osteogenesis. Furthermore, in vivo experiments further demonstrate that polyhedron-like scaffolds obviously promote bone formation and osteointegration, as well as inducing vascularization and ingrowth of nerves, leading to innervated and vascularized bone regeneration. Taken together, this work offers a promising approach for fabricating multifunctional scaffolds without additional exogenous seeding cells and growth factors, which holds great potential for functional tissue regeneration and further clinical translation.

The Innovation Press: A Primer on the Anatomy of Digital Design in Plastic Surgery

ABSTRACT

Three-dimensional (3D) printing continues to revolutionize the field of plastic surgery, allowing surgeons to adapt to the needs of individual patients and innovate, plan, or refine operative techniques. The utility of this manufacturing modality spans from surgical planning, medical education, and effective patient communication to tissue engineering and device prototyping and has valuable implications in every facet of plastic surgery. Three-dimensional printing is more accessible than ever to the surgical community, regardless of previous background in engineering or biotechnology. As such, the onus falls on the surgeon-innovator to have a functional understanding of the fundamental pipeline and processes in actualizing such innovation. We review the broad range of reported uses for 3D printing in plastic surgery, the process from conceptualization to production, and the considerations a physician must make when using 3D printing for clinical applications. We additionally discuss the role of computer-assisted design and manufacturing and virtual and augmented reality, as well as the ability to digitally modify devices using this software. Finally, a discussion of 3D printing logistics, printer types, and materials is included. With innovation and problem solving comprising key tenets of plastic surgery, 3D printing can be a vital tool in the surgeon's intellectual and digital arsenal to span the gap between concept and reality.

Conceptual design of compliant bone scaffolds by full-scale topology optimization

A promising new treatment for large and complex bone defects is to implant specifically designed and additively manufactured synthetic bone scaffolds. Optimizing the scaffold design can potentially improve bone in-growth and prevent under- and over-loading of the adjacent tissue. This study aims to optimize synthetic bone scaffolds over multiple-length scales using the full-scale topology optimization approach, and to assess the effectiveness of this approach as an alternative to the currently used mono- and multi-scale optimization approaches for orthopaedic applications. We present a topology optimization formulation, which is matching the scaffold's mechanical properties to the surrounding tissue in compression. The scaffold's porous structure is tuneable to achieve the desired morphological properties to enhance bone in-growth. The proposed approach is demonstrated in-silico, using PEEK, cortical bone and titanium material properties in a 2D parameter study and on 3D designs. Full-scale topology optimization indicates a design improvement of 81% compared to the multi-scale approach. Furthermore, 3D designs for PEEK and titanium are additively manufactured to test the applicability of the method. With further development, the full-scale topology optimization approach is anticipated to offer a more effective alternative for optimizing orthopaedic structures compared to the currently used multi-scale methods.

Design and Manufacturing of a Novel Trabecular Tibial Implant

The elastic modulus of traditional solid titanium alloy tibial implants is much higher than that of human bones, which can cause stress shielding. Designing them as a porous structure to form a bone-like trabecular structure effectively reduces stress shielding. However, the actual loading conditions of bones in different parts of the human body have not been considered for some trabecular structures, and their mechanical properties have not been considered concerning the personalized differences of other patients. Therefore, based on the elastic modulus of the tibial stem obtained from Quantitative Computed Tomography (QCT) imaging between 3.031 and10.528 GPa, and the load-bearing state of the tibia at the knee joint, a porous structure was designed under compressive and shear loading modes using topology optimization. Through comprehensive analysis of the mechanical and permeability properties of the porous structure, the results show that the Topology Optimization-Shear-2 (TO-S2) structure has the best compressive, shear mechanical properties and permeability and is suitable as a trabecular structure for tibial implants. The Gibson-Ashby model was established to control the mechanical properties of porous titanium alloy. A gradient filling of porous titanium alloy with a strut diameter of 0.106-0.202 mm was performed on the tibial stem based on the elastic modulus range, achieving precise matching of the mechanical properties of tibial implants and closer to the natural structure than uniformly distributed porous structures in human bones. Finally, the new tibial implant was printed by selective laser melting (SLM), and the molding effect was excellent.

Metal and Polymer Based Composites Manufactured Using Additive Manufacturing-A Brief Review

This review examines the mechanical performance of metal- and polymer-based composites fabricated using additive manufacturing (AM) techniques. Composite materials have significantly influenced various industries due to their exceptional reliability and effectiveness. As technology advances, new types of composite reinforcements, such as novel chemical-based and bio-based, and new fabrication techniques are utilized to develop high-performance composite materials. AM, a widely popular concept poised to shape the development of Industry 4.0, is also being utilized in the production of composite materials. Comparing AM-based manufacturing processes to traditional methods reveals significant variations in the performance of the resulting composites. The primary objective of this review is to offer a comprehensive understanding of metal- and polymer-based composites and their applications in diverse fields. Further on this review delves into the intricate details of metal- and polymer-based composites, shedding light on their mechanical performance and exploring the various industries and sectors where they find utility.

Deep Learning Accelerated Design of Mechanically Efficient Architected Materials

Lattice structures are known to have high performance-to-weight ratios because of their highly efficient material distribution in a given volume. However, their inherently large void fraction leads to low mechanical properties compared to the base material, high anisotropy, and brittleness. Most works to date have focused on modifying the spatial arrangement of beam elements to overcome these limitations, but only simple beam geometries are adopted due to the infinitely large design space associated with probing and varying beam shapes. Herein, we present an approach to enhance the elastic modulus, strength, and toughness of lattice structures with minimal tradeoffs by optimizing the shape of beam elements for a suite of lattice structures. A generative deep learning-based approach is employed, which leverages the fast inference of neural networks to accelerate the optimization process. Our optimized lattice structures possess superior stiffness (+59%), strength (+49%), toughness (+106%), and isotropy (+645%) compared to benchmark lattices consisting of cylindrical beams. We fabricate our lattice designs using additive manufacturing to validate the optimization approach; experimental and simulation results show good agreement. Remarkable improvement in mechanical properties is shown to be the effect of distributed stress fields and deformation modes subject to beam shape and lattice type.

Recent advancement in finite element analysis of spinal interbody cages: A review

Finite element analysis (FEA) is a widely used tool in a variety of industries and research endeavors. With its application to spine biomechanics, FEA has contributed to a better understanding of the spine, its components, and its behavior in physiological and pathological conditions, as well as assisting in the design and application of spinal instrumentation, particularly spinal interbody cages (ICs). IC is a highly effective instrumentation for achieving spinal fusion that has been used to treat a variety of spinal disorders, including degenerative disc disease, trauma, tumor reconstruction, and scoliosis. The application of FEA lets new designs be thoroughly "tested" before a cage is even manufactured, allowing bio-mechanical responses and spinal fusion processes that cannot easily be experimented upon in vivo to be examined and "diagnosis" to be performed, which is an important addition to clinical and in vitro experimental studies. This paper reviews the recent progress of FEA in spinal ICs over the last six years. It demonstrates how modeling can aid in evaluating the biomechanical response of cage materials, cage design, and fixation devices, understanding bone formation mechanisms, comparing the benefits of various fusion techniques, and investigating the impact of pathological structures. It also summarizes the various limitations brought about by modeling simplification and looks forward to the significant advancement of spine FEA research as computing efficiency and software capabilities increase. In conclusion, in such a fast-paced field, the FEA is critical for spinal IC studies. It helps in quantitatively and visually demonstrating the cage characteristics after implanting, lowering surgeons' learning costs for new cage products, and probably assisting them in determining the best IC for patients.

Mechanics of 3D-Printed Polymer Lattices with Varied Design and Processing Strategies

Emerging polymer 3D-printing technologies are enabling the design and fabrication of mechanically efficient lattice structures with intricate microscale structures. During fabrication, manufacturing inconsistencies can affect mechanical efficiency, thereby driving a need to investigate how design and processing strategies influence outcomes. Here, mechanical testing is conducted for 3D-printed lattice structures while altering topology, relative density, and exposure time per layer using digital light processing (DLP). Experiments compared a Cube topology with 800 µm beams and Body-Centered Cube (BCC) topologies with 500 or 800 µm beams, all designed with 40% relative density. Cube lattices had the lowest mean measured relative density of ~42%, while the 500 µm BCC lattice had the highest relative density of ~55%. Elastic modulus, yield strength, and ultimate strength had a positive correlation with measured relative density when considering measurement distributions for thirty samples of each design. BCC lattices designed with 50%, 40%, and 30% relative densities were then fabricated with exposure-per-layer times of 1500 and 1750 ms. Increasing exposure time per layer resulted in higher scaling of mechanical properties to relative density compared to design alteration strategies. These results reveal how design and fabrication strategies affect mechanical performance of lattices suitable for diverse engineering applications.

Wall Shear Stress Analysis and Optimization in Tissue Engineering TPMS Scaffolds

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

Additively manufactured metallic biomaterials

Metal additive manufacturing (AM) has led to an evolution in the design and fabrication of hard tissue substitutes, enabling personalized implants to address each patient's specific needs. In addition, internal pore architectures integrated within additively manufactured scaffolds, have provided an opportunity to further develop and engineer functional implants for better tissue integration, and long-term durability. In this review, the latest advances in different aspects of the design and manufacturing of additively manufactured metallic biomaterials are highlighted. After introducing metal AM processes, biocompatible metals adapted for integration with AM machines are presented. Then, we elaborate on the tools and approaches undertaken for the design of porous scaffold with engineered internal architecture including, topology optimization techniques, as well as unit cell patterns based on lattice networks, and triply periodic minimal surface. Here, the new possibilities brought by the functionally gradient porous structures to meet the conflicting scaffold design requirements are thoroughly discussed. Subsequently, the design constraints and physical characteristics of the additively manufactured constructs are reviewed in terms of input parameters such as design features and AM processing parameters. We assess the proposed applications of additively manufactured implants for regeneration of different tissue types and the efforts made towards their clinical translation. Finally, we conclude the review with the emerging directions and perspectives for further development of AM in the medical industry.

3D Printing Silk-Based Bioresorbable Piezoelectric Self-Adhesive Holey Structures for In Vivo Monitoring on Soft Tissues

Flexible and biocompatible adhesives with sensing capabilities can be integrated onto human body and organ surfaces, characterized by complex geometries, thus having the potential to sense their physiological stimuli offering monitoring and diagnosis of a wide spectrum of diseases. The challenges in this innovative field are the following: (i) the coupling method between the smart adhesive and the soft human substrates, (ii) the bioresorbable behavior of the material, and (iii) the electrical exchange with the substrate. Here, we introduce a multifunctional composite by mixing silk fibroin, featuring piezoelectric properties, with a soluble plant-derived polyphenol (i.e., chestnut tannin) modified with graphene nanoplatelets. This material behaves as a glue on different substrates and gives rise to high elongation at break, conformability, and adhesive performances to gastrointestinal tissues in a rat model and favors the printability via extrusion-based 3D printing. Exploiting these properties, we designed a bioresorbable 3D printed flexible and self-adhesive piezoelectric device that senses the motility once applied onto a phantom intestine and the hand gesture by signal translation. Experimental results also include the biocompatibility study using gastrointestinal cells. These findings could have applicability in animal model studies, and, thanks to the bioresorbable behavior of the materials, such an adhesive device could be used for monitoring the motility of the gastrointestinal tract and for the diagnosis of motility disorders.

Generative machine learning algorithm for lattice structures with superior mechanical properties

Lattice structures are typically made up of a crisscross pattern of beam elements, allowing engineers to distribute material in a more structurally effective way. However, a main challenge in the design of lattice structures is a trade-off between the density and mechanical properties. Current studies have often assumed the cross-sectional area of the beam elements to be uniform for reducing the design complexity. This simplified approach limits the possibility of finding superior designs with optimized weight-to-performance ratios. Here, the optimized shape of the beam elements is investigated using a deep learning approach with high-order Bézier curves to explore the augmented design space. This is then combined with a hybrid neural network and genetic optimization (NN-GO) adaptive method for the generation of superior lattice structures. In our optimized design, the distribution of material is smartly shifted more towards the joint region, the weakest location of lattice structures, to achieve the highest modulus and strength. This design strikes to balance between two modes of deformation: axial and bending. Thus, the optimized design is efficient for load bearing and energy absorption. To validate our simulations, the optimized design is then fabricated by additive manufacturing and its mechanical properties are evaluated through compression testing. A good correlation between experiments and simulations is observed and the optimized design has outperformed benchmark ones in terms of modulus and strength. We show that the extra design flexibility from high-order Bézier curves allows for a smoother transition between the beam elements which reduces the overall stress concentration profile.

Restoration and Possible Upgrade of a Historical Motorcycle Part Using Powder Bed Fusion

Reverse engineering is the process of creating a digital version of an existing part without any knowledge in advance about the design intent. Due to 3D printing, the reconstructed part can be rapidly fabricated for prototyping or even for practical usage. To showcase this combination, this study presents a workflow on how to restore a motorcycle braking pedal from material SS316L with the Powder Bed Fusion (PBF) technology. Firstly, the CAD model of the original braking pedal was created. Before the actual PBF printing, the braking pedal printing process was simulated to identify the possible imperfections. The printed braking pedal was then subjected to quality control in terms of the shape distortion from its CAD counterpart and strength assessments, conducted both numerically and physically. As a result, the exterior shape of the braking pedal was restored. Additionally, by means of material assessments and physical tests, it was able to prove that the restored pedal was fully functional. Finally, an approach was proposed to optimize the braking pedal with a lattice structure to utilize the advantages the PBF technology offers.

Challenges in computational fluid dynamics applications for bone tissue engineering

Bone injuries or defects that require invasive surgical treatment are a serious clinical issue, particularly when it comes to treatment success and effectiveness. Accordingly, bone tissue engineering (BTE) has been researching the use of computational fluid dynamics (CFD) analysis tools to assist in designing optimal scaffolds that better promote bone growth and repair. This paper aims to offer a comprehensive review of recent studies that use CFD analysis in BTE. The mechanical and fluidic properties of a given scaffold are coupled to each other via the scaffold architecture, meaning an optimization of one may negatively affect the other. For example, designs that improve scaffold permeability normally result in a decreased average wall shear stress. Linked with these findings, it appears there are very few studies in this area that state a specific application for their scaffolds and those that do are focused on in vitro bioreactor environments. Finally, this review also demonstrates a scarcity of studies that combine CFD with optimization methods to improve scaffold design. This highlights an important direction of research for the development of the next generation of BTE scaffolds.

Design Optimization of Lattice Structures under Compression: Study of Unit Cell Types and Cell Arrangements

Additive manufacturing enables innovative structural design for industrial applications, which allows the fabrication of lattice structures with enhanced mechanical properties, including a high strength-to-relative-density ratio. However, to commercialize lattice structures, it is necessary to define the designability of lattice geometries and characterize the associated mechanical responses, including the compressive strength. The objective of this study was to provide an optimized design process for lattice structures and develop a lattice structure characterization database that can be used to differentiate unit cell topologies and guide the unit cell selection for compression-dominated structures. Linear static finite element analysis (FEA), nonlinear FEA, and experimental tests were performed on 11 types of unit cell-based lattice structures with dimensions of 20 mm × 20 mm × 20 mm. Consequently, under the same relative density conditions, simple cubic, octahedron, truncated cube, and truncated octahedron-based lattice structures with a 3 × 3 × 3 array pattern showed the best axial compressive strength properties. Correlations among the unit cell types, lattice structure topologies, relative densities, unit cell array patterns, and mechanical properties were identified, indicating their influence in describing and predicting the behaviors of lattice structures.

Design and properties of graded polyamide12/hydroxyapatite scaffolds based on primitive lattices using selective laser sintering

Scaffolds with favorable biological characteristics and controlled functional gradient architectures are preferable for the repair of damaged tissues in bone tissue engineering. In this study, the triply periodic minimal surfaces (TPMS) were introduced to design functional gradient porous scaffolds based on Primitive lattices which were then manufactured by selective laser sintering (SLS) using pure polyamide12 (PA12) material and PA12/hydroxyapatite (HA) composite material. The mechanical properties and permeability of the scaffolds were then evaluated by mechanical compression experiments and computational fluid dynamics (CFD) analysis. The radial-graded scaffold was found to have superior good mechanical properties and permeability and be favorable for the subsequent growth of bone tissue. Further, the optimal PA12/HA composition was determined by analyzing the effect of the addition of HA particles on the hydrophilicity and mechanical properties of the composite scaffold. Additionally, the cytotoxicity tests were performed to evaluate the effects of PA12/HA gradient scaffold on cell growth. The obtained results demonstrate that the radial gradient scaffold with 15% HA addition exhibits a feasible combination of comprehensive performance and biological activity, indicating a great application potential in the field of bone tissue engineering.

Femoral Stems With Porous Lattice Structures: A Review

Cementless femoral stems are prone to stress shielding of the femoral bone, which is caused by a mismatch in stiffness between the femoral stem and femur. This can cause bone resorption and resultant loosening of the implant. It is possible to reduce the stress shielding by using a femoral stem with porous structures and lower stiffness. A porous structure also provides a secondary function of allowing bone ingrowth, thus improving the long-term stability of the prosthesis. Furthermore, due to the advent of additive manufacturing (AM) technology, it is possible to fabricate femoral stems with internal porous lattices. Several review articles have discussed porous structures, mainly focusing on the geometric design, mechanical properties and influence on bone ingrowth. However, the safety and effectiveness of porous femoral stems depend not only on the characteristic of porous structure but also on the macro design of the femoral stem; for example, the distribution of the porous structure, the stem geometric shape, the material, and the manufacturing process. This review focuses on porous femoral stems, including the porous structure, macro geometric design of the stem, performance evaluation, research methods used for designing and evaluating the femoral stems, materials and manufacturing techniques. In addition, this review will evaluate whether porous femoral stems can reduce stress shielding and increase bone ingrowth, in addition to analyzing their shortcomings and related risks and providing ideas for potential design improvements.

Understanding and utilizing textile-based electrostatic flocking for biomedical applications

Electrostatic flocking immobilizes electrical charges to the surface of microfibers from a high voltage-connected electrode and utilizes Coulombic forces to propel microfibers toward an adhesive-coated substrate, leaving a forest of aligned fibers. This traditional textile engineering technique has been used to modify surfaces or to create standalone anisotropic structures. Notably, a small body of evidence validating the use of electrostatic flocking for biomedical applications has emerged over the past several years. Noting the growing interest in utilizing electrostatic flocking in biomedical research, we aim to provide an overview of electrostatic flocking, including the principle, setups, and general and biomedical considerations, and propose a variety of biomedical applications. We begin with an introduction to the development and general applications of electrostatic flocking. Additionally, we introduce and review some of the flocking physics and mathematical considerations. We then discuss how to select, synthesize, and tune the main components (flocking fibers, adhesives, substrates) of electrostatic flocking for biomedical applications. After reviewing the considerations necessary for applying flocking toward biomedical research, we introduce a variety of proposed use cases including bone and skin tissue engineering, wound healing and wound management, and specimen swabbing. Finally, we presented the industrial comments followed by conclusions and future directions. We hope this review article inspires a broad audience of biomedical, material, and physics researchers to apply electrostatic flocking technology to solve a variety of biomedical and materials science problems.

Simulated tissue growth in tetragonal lattices with mechanical stiffness tuned for bone tissue engineering

Bone tissue engineering approaches have recently begun considering 3D printed lattices as viable scaffold solutions due to their highly tunable geometries and mechanical efficiency. However, scaffold design remains challenging due to the numerous biological and mechanical trade-offs related to lattice geometry. Here, we investigate novel tetragonal unit cell designs by independently adjusting unit cell height and width to find scaffolds with improved tissue growth while maintaining suitable scaffold mechanical properties for bone tissue engineering. Lattice tissue growth behavior is evaluated using a curvature-based growth model while elastic modulus is evaluated with finite element analysis. Computationally efficient modeling approaches are implemented to facilitate bulk analysis of lattice design trade-offs using design maps for biological and mechanical functionalities in relation to unit cell height and width for two contrasting unit cell topologies. Newly designed tetragonal lattices demonstrate higher tissue growth per unit volume and advantageous stiffness in preferred directions compared to cubically symmetric unit cells. When lattice beam diameter is fixed to 200 μm, Tetra and BC-Tetra lattices with elastic moduli of 200 MPa-400 MPa are compared for squashed, cubic, and stretched topologies. Squashed Tetra lattices demonstrated higher growth rates and growth densities compared to symmetrically cubic lattices. BC-Tetra lattices with the same range of elastic moduli show squashed lattices tend to achieve higher growth rates, whereas stretched lattices promote higher growth density. The results suggest tetragonal unit cells provide favorable properties for biological and mechanical tailoring, therefore enabling new strategies for diverse patient needs and applications in regenerative medicine.

Augmented Design with Additive Manufacturing Methodology: Tangible Object-Based Method to Enhance Creativity in Design for Additive Manufacturing

Additive manufacturing (AM) brings new design potential compared with traditional manufacturing. Nevertheless, traditional manufacturing knowledge remains embedded in the minds of designers and is a real cognitive barrier to design in AM. Design for Additive Manufacturing (DfAM) provides tools, techniques, and guidelines to optimize design with the specifics of AM. These methods are usable at different moments of the design process. Only few DfAMs focus on the early stages of design, the ideation phase, which allows for the most innovation. The literature highlights the effectiveness of methodologies based on tangible tools, such as cards or objects, to generate creativity. The difficulty with such tools is to be inspirational as well as formative. Therefore, this article presents a method to help designers capture the design potential of AM to design creative solutions at the early stages of product design, named the Augmented Design with AM Methodology (ADAM²). This methodology relies on the potential of AM, defined in 14 opportunities and a set of 14 inspirational objects, each representing an opportunity. Dedicated to creativity sessions, this methodology allows forcing the association between knowledge of a company's sector and the design potential of AM. To validate the effectiveness of the ADAM² methodology, we use it for an industrial application in a jewelry and watchmaking company. The results showed that ADAM² promote the generation of creative solutions and the exploitation of the design potential of AM during the early design stages.

Artificial Intelligence Aided Design of Tissue Engineering Scaffolds Employing Virtual Tomography and 3D Convolutional Neural Networks

Design requirements for different mechanical metamaterials, porous constructions and lattice structures, employed as tissue engineering scaffolds, lead to multi-objective optimizations, due to the complex mechanical features of the biological tissues and structures they should mimic. In some cases, the use of conventional design and simulation methods for designing such tissue engineering scaffolds cannot be applied because of geometrical complexity, manufacturing defects or large aspect ratios leading to numerical mismatches. Artificial intelligence (AI) in general, and machine learning (ML) methods in particular, are already finding applications in tissue engineering and they can prove transformative resources for supporting designers in the field of regenerative medicine. In this study, the use of 3D convolutional neural networks (3D CNNs), trained using digital tomographies obtained from the CAD models, is validated as a powerful resource for predicting the mechanical properties of innovative scaffolds. The presented AI-aided or ML-aided design strategy is believed as an innovative approach in area of tissue engineering scaffolds, and of mechanical metamaterials in general. This strategy may lead to several applications beyond the tissue engineering field, as we analyze in the discussion and future proposals sections of the research study.

Polymer 3D Printing Review: Materials, Process, and Design Strategies for Medical Applications

Polymer 3D printing is an emerging technology with recent research translating towards increased use in industry, particularly in medical fields. Polymer printing is advantageous because it enables printing low-cost functional parts with diverse properties and capabilities. Here, we provide a review of recent research advances for polymer 3D printing by investigating research related to materials, processes, and design strategies for medical applications. Research in materials has led to the development of polymers with advantageous characteristics for mechanics and biocompatibility, with tuning of mechanical properties achieved by altering printing process parameters. Suitable polymer printing processes include extrusion, resin, and powder 3D printing, which enable directed material deposition for the design of advantageous and customized architectures. Design strategies, such as hierarchical distribution of materials, enable balancing of conflicting properties, such as mechanical and biological needs for tissue scaffolds. Further medical applications reviewed include safety equipment, dental implants, and drug delivery systems, with findings suggesting a need for improved design methods to navigate the complex decision space enabled by 3D printing. Further research across these areas will lead to continued improvement of 3D-printed design performance that is essential for advancing frontiers across engineering and medicine.

Numerical-experimental analysis of the permeability-porosity relationship in triply periodic minimal surfaces scaffolds

Bone Tissue Engineering has been focusing on improving the current methods for bone repair, being the use of scaffolds presented as an upgrade to traditional surgery techniques. Scaffolds are artificially porous matrices, meant to promote cell seeding and proliferation, being these properties influenced by the permeability of the structure. This work employed experimental pressure drop tests and Computational Fluid Dynamics models to assess permeability (and fluid streamlines) within different triply periodic minimal surfaces scaffold geometries (Schwarz D, Gyroid and Schwarz P). The pressure outputs from the computational analysis presented a good correlation with the experimental results, with R² equal to 0.903; they have also shown that a lower porosity may not mean a lower permeability if the geometry is altered, such as the difference between 60% porous Gyroid scaffolds (8.1*10^-9 mm²) and 70% porous Schwarz D scaffolds (7.1*10^-9 mm²). Fluid streamlines revealed how the Gyroid geometries are the most appropriate design for most bone tissue engineering applications, due to their consistent fluid permeation, followed by Schwarz D. The Schwarz P geometries have shown flat streamlines and significant variation of the permeability with the porosity (an increase of 10% in their porosity lead to an increase in the permeability from 5.1*10^-9 mm² to 11.7*10^-9 mm²), which would imply a poor environment for cell seeding and proliferation.

On the mechanical behaviour of additively manufactured metamaterials under dynamic conditions

High-energy absorption and light-weightiness are two critical properties for impact protection in the aerospace sector. In the past, the use of periodic honeycomb structures or random porous metallic foams were the preferred route to obtain a good specific-energy absorption performance. In recent years, the use of additive manufacturing has increased the design freedom creating a new generation of reticulated and porous materials: the metamaterials or lattice materials. The internal geometries of these lattice structures can be tuned for superior optimal properties, e.g., energyabsorption and density. However, the mechanics of these materials under impact need to be understood with the purpose of mechanical optimisation, and the computational models validated. In this work, we present the experimental compressive behaviour, at room temperature, of two Ti6Al4V lattice structures under static and dynamic conditions. The quasi-static tests were performed by using a universal testing machine while the dynamic tests were conducted at 480s-1 with a split-Hopkinson bar. In all cases, the deformation process was filmed to analyse the failure. Finally, finiteelement simulations were done, employing the Johnson-Cook model, to describe the response of the alloy. The simulations were able to reflect the failure characteristics of each metamaterial but were not able to describe the macroscopic response due to the differences between the experimental and computational volume fraction.

Guidelines for establishing a 3-D printing biofabrication laboratory

Advanced manufacturing and 3D printing are transformative technologies currently undergoing rapid adoption in healthcare, a traditionally non-manufacturing sector. Recent development in this field, largely enabled by merging different disciplines, has led to important clinical applications from anatomical models to regenerative bioscaffolding and devices. Although much research to-date has focussed on materials, designs, processes, and products, little attention has been given to the design and requirements of facilities for enabling clinically relevant biofabrication solutions. These facilities are critical to overcoming the major hurdles to clinical translation, including solving important issues such as reproducibility, quality control, regulations, and commercialization. To improve process uniformity and ensure consistent development and production, large-scale manufacturing of engineered tissues and organs will require standardized facilities, equipment, qualification processes, automation, and information systems. This review presents current and forward-thinking guidelines to help design biofabrication laboratories engaged in engineering model and tissue constructs for therapeutic and non-therapeutic applications.

Relationship between the morphological, mechanical and permeability properties of porous bone scaffolds and the underlying microstructure

Bone scaffolds are widely used as one of the main bone substitute materials. However, many bone scaffold microstructure topologies exist and it is still unclear which topology to use when designing scaffold for a specific application. The aim of the present study was to reveal the mechanism of the microstructure-driven performance of bone scaffold and thus to provide guideline on scaffold design. Finite element (FE) models of five TPMS (Diamond, Gyroid, Schwarz P, Fischer-Koch S and F-RD) and three traditional (Cube, FD-Cube and Octa) scaffolds were generated. The effective compressive and shear moduli of scaffolds were calculated from the mechanical analysis using the FE unit cell models with the periodic boundary condition. The scaffold permeability was calculated from the computational fluid dynamics (CFD) analysis using the 4×4×4 FE models. It is revealed that the surface-to-volume ratio of the Fischer-Koch S-based scaffold is the highest among the scaffolds investigated. The mechanical analysis revealed that the bending deformation dominated structures (e.g., the Diamond, the Gyroid, the Schwarz P) have higher effective shear moduli. The stretching deformation dominated structures (e.g., the Schwarz P, the Cube) have higher effective compressive moduli. For all the scaffolds, when the same amount of change in scaffold porosity is made, the corresponding change in the scaffold relative shear modulus is larger than that in the relative compressive modulus. The CFD analysis revealed that the structures with the simple and straight pores (e.g., Cube) have higher permeability than the structures with the complex pores (e.g., Fischer-Koch S). The main contribution of the present study is that the relationship between scaffold properties and the underlying microstructure is systematically investigated and thus some guidelines on the design of bone scaffolds are provided, for example, in the scenario where a high surface-to-volume ratio is required, it is suggested to use the Fischer-Koch S based scaffold.

Design framework for mechanically tunable soft biomaterial composites enhanced by modified horseshoe lattice structures

Soft biomaterials have a wide range of applications in many areas. However, one material can only cover a specific range of mechanical performance such as the elastic modulus and stretchability. In order to improve the mechanical performance of soft biomaterials, lattice structures are embedded to reinforce the biomaterials. In this paper, rectangular and triangular lattice structures formed by modified horseshoe microstructures are used because their mechanical properties are tunable and can be tailored precisely to match the desired properties by adjusting four geometrical parameters, the length L, radius R, width w and arc angle θ0. A theoretical design framework for the modified horseshoe lattice structures is developed to predict the dependence of the mechanical behaviors on geometrical parameters. Both experiments and finite element simulations on lattice structures are conducted to validate the theoretical models. Results show that a wide range of design space for the elastic modulus (a few kPa to hundreds of MPa), stretchability (strain up to 180%) and Poisson ratio (ranging from -0.5 to 1.2) can be achieved. Experiments on lattice-hydrogel composites are also conducted to verify the reinforcement effect of lattice structures on the hydrogel. This work provides a theoretical method to predict the mechanical behaviors of the lattice structures and aid the rational design of reinforced biomaterials, which has applications in tissue engineering, drug delivery and intraocular lenses.

Mechanical performance of highly permeable laser melted Ti6Al4V bone scaffolds

Critically engineered stiffness and strength of a scaffold are crucial for managing maladapted stress concentration and reducing stress shielding. At the same time, suitable porosity and permeability are key to facilitate biological activities associated with bone growth and nutrient delivery. A systematic balance of all these parameters are required for the development of an effective bone scaffold. Traditionally, the approach has been to study each of these parameters in isolation without considering their interdependence to achieve specific properties at a certain porosity. The purpose of this study is to undertake a holistic investigation considering the stiffness, strength, permeability, and stress concentration of six scaffold architectures featuring a 68.46-90.98% porosity. With an initial target of a tibial host segment, the permeability was characterised using Computational Fluid Dynamics (CFD) in conjunction with Darcy's law. Following this, Ashby's criterion, experimental tests, and Finite Element Method (FEM) were employed to study the mechanical behaviour and their interdependencies under uniaxial compression. The FE model was validated and further extended to study the influence of stress concentration on both the stiffness and strength of the scaffolds. The results showed that the pore shape can influence permeability, stiffness, strength, and the stress concentration factor of Ti6Al4V bone scaffolds. Furthermore, the numerical results demonstrate the effect to which structural performance of highly porous scaffolds deviate, as a result of the Selective Laser Melting (SLM) process. In addition, the study demonstrates that stiffness and strength of bone scaffold at a targeted porosity is linked to the pore shape and the associated stress concentration allowing to exploit the design freedom associated with SLM.

Synthetic bone: Design by additive manufacturing

A broad range of synthetic trabecular-like metallic lattices are 3D printed, to study the extra design freedom conferred by this new manufacturing process. The aim is to propose new conceptual types of implant structures for superior bio-mechanical matching and osseo-integration: synthetic bone. The target designs are 3D printed in Ti-6Al-4V alloy using a laser-bed process. Systematic evaluation is then carried out: (i) their accuracy is characterised at high spatial resolution using computed X-ray tomography, to assess manufacturing robustness with respect to the original geometrical design intent and (ii) the mechanical properties - stiffness and strength - are experimentally measured, evaluated, and compared. Finally, this new knowledge is synthesised in a conceptual framework to allow the construction of so-called implant design maps, to define the processing conditions of bone tailored substitutes, with focus on spine fusion devices. The design criteria emphasise the bone stiffness-matching, preferred range of pore structure for bone in-growth, manufacturability of the device and choice of inherent materials properties which are needed for durable implants. Examples of the use of such maps are given with focus on spine fusion devices, emphasising the stiffness-matching, osseo-integration properties and choice of inherent materials properties which are needed for durable implants. STATEMENT OF SIGNIFICANCE: We present a conceptual bio-engineering design methodology for new biomedical lattices produced by additive manufacturing, which addresses some of the critical points in currently existing porous implant materials. Amongst others: (i) feasibility and accuracy of manufacturing, (ii) design to the elastic properties of bone, and (iii) sensible pores sizes for osseointegration. This has inspired new and novel geometrical latticed designs which aim at improving the properties of intervertebral fusion devices. In their fundamental form, these structures are here fabricated and tested. When integrated into medical devices, these concepts could offer superior medical outcomes.

Continuum Modeling and Simulation in Bone Tissue Engineering

Bone tissue engineering is currently a mature methodology from a research perspective. Moreover, modeling and simulation of involved processes and phenomena in BTE have been proved in a number of papers to be an excellent assessment tool in the stages of design and proof of concept through in-vivo or in-vitro experimentation. In this paper, a review of the most relevant contributions in modeling and simulation, in silico, in BTE applications is conducted. The most popular in silico simulations in BTE are classified into: (i) Mechanics modeling and scaffold design, (ii) transport and flow modeling, and (iii) modeling of physical phenomena. The paper is restricted to the review of the numerical implementation and simulation of continuum theories applied to different processes in BTE, such that molecular dynamics or discrete approaches are out of the scope of the paper. Two main conclusions are drawn at the end of the paper: First, the great potential and advantages that in silico simulation offers in BTE, and second, the need for interdisciplinary collaboration to further validate numerical models developed in BTE.

Reconsidering Osteoconduction in the Era of Additive Manufacturing

Bone regeneration procedures in clinics and bone tissue engineering stand on three pillars: osteoconduction, osteoinduction, and stem cells. In the last two decades, the focus in this field has been on osteoinduction, which is realized by the use of bone morphogenetic proteins and the application of mesenchymal stem cells to treat bone defects. However, osteoconduction was reduced to a surface phenomenon because the supposedly ideal pore size of osteoconductive scaffolds was identified in the 1990s as 0.3-0.5 mm in diameter, forcing bone formation to occur predominantly on the surface. Meanwhile, additive manufacturing has evolved as a new tool to realize designed microarchitectures in bone substitutes, thereby enabling us to study osteoconduction as a true three-dimensional phenomenon. Moreover, by additive manufacturing, wide-open porous scaffolds can be produced in which bone formation occurs distant to the surface at a superior bony defect-bridging rate enabled by highly osteoconductive pores 1.2 mm in diameter. This review provides a historical overview and an updated definition of osteoconduction and related terms. In addition, it shows how additive manufacturing can be instrumental in studying and optimizing osteoconduction of bone substitutes, and provides novel optimized features and boundaries of osteoconductive microarchitectures. Impact Statement This review updates the definition of osteoconduction and draws clear lines to discriminate between osteoconduction, osseointegration, and osteoinduction. Moreover, additively manufactured libraries of scaffolds revealed that: osteoconduction is more a three-dimensional than a surface phenomenon; microarchitecture dictates defect bridging, which is the measure for osteoconduction; pore diameter or the diagonal of lattice microarchitectures of osteoconductive bone substitutes should be ∼1.2 mm.

Integrated Design Approaches for 3D Printed Tissue Scaffolds: Review and Outlook

Emerging 3D printing technologies are enabling the fabrication of complex scaffold structures for diverse medical applications. 3D printing allows controlled material placement for configuring porous tissue scaffolds with tailored properties for desired mechanical stiffness, nutrient transport, and biological growth. However, tuning tissue scaffold functionality requires navigation of a complex design space with numerous trade-offs that require multidisciplinary assessment. Integrated design approaches that encourage iteration and consideration of diverse processes including design configuration, material selection, and simulation models provide a basis for improving design performance. In this review, recent advances in design, fabrication, and assessment of 3D printed tissue scaffolds are investigated with a focus on bone tissue engineering. Bone healing and fusion are examples that demonstrate the needs of integrated design approaches in leveraging new materials and 3D printing processes for specified clinical applications. Current challenges for integrated design are outlined and emphasize directions where new research may lead to significant improvements in personalized medicine and emerging areas in healthcare.

Computational Design and Optimization of Nerve Guidance Conduits for Improved Mechanical Properties and Permeability

Nerve guidance conduits (NGCs) are tubular tissue engineering scaffolds used for nerve regeneration. The poor mechanical properties and porosity have always compromised their performances for guiding and supporting axonal growth. Therefore, in order to improve the properties of NGCs, the computational design approach was adopted to investigate the effects of different NGC structural features on their various properties, and finally design an ideal NGC with mechanical properties matching human nerves and high porosity and permeability. Three common NGC designs, namely hollow luminal, multichannel, and microgrooved, were chosen in this study. Simulations were conducted to study the mechanical properties and permeability. The results show that pore size is the most influential structural feature for NGC tensile modulus. Multichannel NGCs have higher mechanical strength but lower permeability compared to other designs. Square pores lead to higher permeability but lower mechanical strength than circular pores. The study finally selected an optimized hollow luminal NGC with a porosity of 71% and tensile modulus of 8 MPa to achieve multiple design requirements. The use of computational design and optimization was shown to be promising in future NGC design and nerve tissue engineering research.

3D Printing of Porous Scaffolds with Controlled Porosity and Pore Size Values

3D printed scaffolds can be used, for example, in medical applications for simulating body tissues or for manufacturing prostheses. However, it is difficult to print porous structures of specific porosity and pore size values with fused deposition modelling (FDM) technology. The present paper provides a methodology to design porous structures to be printed. First, a model is defined with some theoretical parallel planes, which are bounded within a geometrical figure, for example a disk. Each plane has randomly distributed points on it. Then, the points are joined with lines. Finally, the lines are given a certain volume and the structure is obtained. The porosity of the structure depends on three geometrical variables: the distance between parallel layers, the number of columns on each layer and the radius of the columns. In order to obtain mathematical models to relate the variables with three responses, the porosity, the mean of pore diameter and the variance of pore diameter of the structures, design of experiments with three-level factorial analysis was used. Finally, multiobjective optimization was carried out by means of the desirability function method. In order to favour fixation of the structures by osseointegration, porosity range between 0.5 and 0.75, mean of pore size between 0.1 and 0.3 mm, and variance of pore size between 0.000 and 0.010 mm² were selected. Results showed that the optimal solution consists of a structure with a height between layers of 0.72 mm, 3.65 points per mm² and a radius of 0.15 mm. It was observed that, given fixed height and radius values, the three responses decrease with the number of points per surface unit. The increase of the radius of the columns implies the decrease of the porosity and of the mean of pore size. The decrease of the height between layers leads to a sharper decrease of both the porosity and the mean of pore size. In order to compare calculated and experimental values, scaffolds were printed in polylactic acid (PLA) with FDM technology. Porosity and pore size were measured with X-ray tomography. Average value of measured porosity was 0.594, while calculated porosity was 0.537. Average value of measured mean of pore size was 0.372 mm, while calculated value was 0.434 mm. Average value of variance of pore size was 0.048 mm², higher than the calculated one of 0.008 mm². In addition, both round and elongated pores were observed in the printed structures. The current methodology allows designing structures with different requirements for porosity and pore size. In addition, it can be applied to other responses. It will be very useful in medical applications such as the simulation of body tissues or the manufacture of prostheses.

Additive manufacturing technique-designed metallic porous implants for clinical application in orthopedics

Traditional metallic scaffold prostheses, as vastly applied implants in clinical orthopedic operations, have achieved great success in rebuilding limb function. However, mismatch of bone defects and additional coating requirements limit the long-term survival of traditional prostheses. Recently, additive manufacturing (AM) has opened up unprecedented possibilities for producing complicated structures in prosthesis shapes and microporous surface designs of customized prostheses, which can solve the drawback of traditional prostheses mentioned above. This review presents the most commonly used metallic additive manufacturing techniques, the microporous structure design of metallic scaffolds, and novel applications of customized prostheses in the orthopedic field. Challenges and future perspectives on AM fabricated scaffolds are also summarized.

Mechanical Properties of Optimized Diamond Lattice Structure for Bone Scaffolds Fabricated via Selective Laser Melting

Developments in selective laser melting (SLM) have enabled the fabrication of periodic cellular lattice structures characterized by suitable properties matching the bone tissue well and by fluid permeability from interconnected structures. These multifunctional performances are significantly affected by cell topology and constitutive properties of applied materials. In this respect, a diamond unit cell was designed in particular volume fractions corresponding to the host bone tissue and optimized with a smooth surface at nodes leading to fewer stress concentrations. There were 33 porous titanium samples with different volume fractions, from 1.28 to 18.6%, manufactured using SLM. All of them were performed under compressive load to determine the deformation and failure mechanisms, accompanied by an in-situ approach using digital image correlation (DIC) to reveal stress–strain evolution. The results showed that lattice structures manufactured by SLM exhibited comparable properties to those of trabecular bone, avoiding the effects of stress-shielding and increasing longevity of implants. The curvature of optimized surface can play a role in regulating the relationship between density and mechanical properties. Owing to the release of stress concentration from optimized surface, the failure mechanism of porous titanium has been changed from the pattern of bottom-up collapse by layer (or cell row) to that of the diagonal (45°) shear band, resulting in the significant enhancement of the structural strength.

Influence of crosslinking on the mechanical behavior of 3D printed alginate scaffolds: Experimental and numerical approaches

Tissue scaffolds fabricated by three-dimensional (3D) bioprinting are attracting considerable attention for tissue engineering applications. Because the mechanical properties of hydrogel scaffolds should match the damaged tissue, changing various parameters during 3D bioprinting has been studied to manipulate the mechanical behavior of the resulting scaffolds. Crosslinking scaffolds using a cation solution (such as CaCl₂) is also important for regulating the mechanical properties, but has not been well documented in the literature. Here, the effect of varied crosslinking agent volume and crosslinking time on the mechanical behavior of 3D bioplotted alginate scaffolds was evaluated using both experimental and numerical methods. Compression tests were used to measure the elastic modulus of each scaffold, then a finite element model was developed and a power model used to predict scaffold mechanical behavior. Results showed that crosslinking time and volume of crosslinker both play a decisive role in modulating the mechanical properties of 3D bioplotted scaffolds. Because mechanical properties of scaffolds can affect cell response, the findings of this study can be implemented to modulate the elastic modulus of scaffolds according to the intended application.

Integration of High-Resolution Laser Displacement Sensors and 3D Printing for Structural Health Monitoring

This paper presents a novel experimental design for complex structural health monitoring (SHM) studies achieved by integrating 3D printing technologies, high-resolution laser displacement sensors, and multiscale entropy SHM theory. A seven-story structure with a variety of composite bracing systems was constructed using a dual-material 3D printer. A wireless Bluetooth vibration speaker was used to excite the ground floor of the structure, and high-resolution laser displacement sensors (1-μm resolution) were used to monitor the displacement history on different floors. Our results showed that the multiscale entropy SHM method could detect damage on the 3D-printed structures. The results of this study demonstrate that integrating 3D printing technologies and high-resolution laser displacement sensors enables the design of cheap, fast processing, complex, small-scale civil structures for future SHM studies. The novel experimental design proposed in this study provides a suitable platform for investigating the validity and sensitivity of SHM in different composite structures and damage conditions for real life applications in the future.