Porous Scaffold Design for Additive Manufacturing in Orthopedics: A Review

Advanced topology of triply periodic minimal surface structure for osteogenic improvement within orthopedic metallic screw

Metallic screws are one of the most common implants in orthopedics. However, the solid design of the screw has often resulted in stress shielding and postoperative loosening, substantially impacting its long-term fixation effect after surgery. Four additive manufacturing porous structures (Fischer-Koch S, Octet, Diamond, and Double Gyroid) are now introduced into the screw to fix those issues. Upon applying the four porous structures, elastic modulus in the screw decreased about 2∼15 times to reduce the occurrence of stress shielding, and bone regeneration effect on the screw surface increased about 1∼50 times to improve bone tissue regrowing. With more bone tissue regrowing on the inner surface of porous screw, a stiffer integration between screw and bone tissue will be achieved, which improves the long-term fixation of the screw tremendously. The biofunctions of the four topologies on osteogenesis have been fully explored, which provides an advanced topology optimization scheme for the screw utilized in orthopedic fixation.

Comparison of stress distribution in fully porous and dense-core porous scaffolds in dental implantation

The aim of this study is to compare the stress distribution in porous scaffolds with different structures with similar geometric parameters to study a new approach in dental implantation. Three-dimensional finite element models of the fully porous and dense-core porous scaffolds with defined porosity parameters including space diameter and thickness with two porosity patterns were embedded in the jaw bone model with cortical and cancellous bone. The cylindrical shape was considered as the main shape of the scaffolds. To evaluate the mechanical performance, the Von Mises stress was compared in the models under static and dynamic masticatory loading. Incidentally, to validate the modeling results, experimental strain gauge tests were performed on four specimens fabricated from Ti6Al4V. Finally, the stress distribution in the models was compared with the results of previous studies on commercial implants. The results of the finite element analysis show that there are considerable differences in the magnitude of the equivalent stress in the models in static and dynamic phases. Also, changes in the defined geometric parameters have significant effects on the stress distribution in terms of Von Mises stress in the overall models. The experimental results indicated good agreement with those of the modeling. It can be concluded that some porous structures with optimal geometries can be proposed as a new structure for dental implants. However, considering the physiology of bone when confronted with porous structures, further studies such as in vivo experiments are needed in this field.

An innovative intramedullary bone graft harvesting concept as a fundamental component of scaffold-guided bone regeneration: A preclinical in vivo validation

Background

The deployment of bone grafts (BGs) is critical to the success of scaffold-guided bone regeneration (SGBR) of large bone defects. It is thus critical to provide harvesting devices that maximize osteogenic capacity of the autograft while also minimizing graft damage during collection. As an alternative to the Reamer-Irrigator-Aspirator 2 (RIA 2) system - the gold standard for large-volume graft harvesting used in orthopaedic clinics today - a novel intramedullary BG harvesting concept has been preclinically introduced and referred to as the ARA (aspirator + reaming-aspiration) concept. The ARA concept uses aspiration of the intramedullary content, followed by medullary reaming-aspiration of the endosteal bone. This concept allows greater customization of BG harvesting conditions vis-à-vis the RIA 2 system. Following its successful in vitro validation, we hypothesized that an ARA concept-collected BG would have comparable in vivo osteogenic capacity compared to the RIA 2 system-collected BG.

Methods

We used 3D-printed, medical-grade polycaprolactone-hydroxyapatite (mPCL-HA, wt 96 %:4 %) scaffolds with a Voronoi design, loaded with or without different sheep-harvested BGs and tested them in an ectopic bone formation rat model for up to 8 weeks.

Results

Active bone regeneration was observed throughout the scaffold-BG constructs, particularly on the surface of the bone chips with endochondral bone formation, and highly vascularized tissue formed within the fully interconnected pore architecture. There were no differences between the BGs derived from the RIA 2 system and the ARA concept in new bone volume formation and in compression tests (Young's modulus, p = 0.74; yield strength, p = 0.50). These results highlight that the osteogenic capacities of the mPCL-HA Voronoi scaffold loaded with BGs from the ARA concept and the RIA 2 system are equivalent.

Conclusion

In conclusion, the ARA concept offers a promising alternative to the RIA 2 system for harvesting BGs to be clinically integrated into SGBR strategies.

The translational potential of this article

Our results show that biodegradable composite scaffolds loaded with BGs from the novel intramedullary harvesting concept and the RIA 2 system have equivalent osteogenic capacity. Thus, the innovative, highly intuitive intramedullary harvesting concept offers a promising alternative to the RIA 2 system for harvesting bone grafts, which are an important component for the routine translation of SGBR concepts into clinical practice.

Surface modification of the laser powder bed-fused Ti-Zr-Nb scaffolds by dynamic chemical etching and Ag nanoparticles decoration

Metallic lattice scaffolds are designed to mimic the architecture and mechanical properties of bone tissue and their surface compatibility is of primary importance. This study presents a novel surface modification protocol for metallic lattice scaffolds printed from a superelastic Ti-Zr-Nb alloy. This protocol consists of dynamic chemical etching (DCE) followed by silver nanoparticles (AgNP) decoration. DCE, using an 1HF + 3HNO3 + 12H2O23% based solution, was used to remove partially-fused particles from the surfaces of different as-built lattice structures (rhombic dodecahedron, sheet gyroid, and Voronoi polyhedra). Subsequently, an antibacterial coating was synthesized on the surface of the scaffolds by a controlled (20 min at a fixed volume flowrate of 500 mL/min) pumping of the functionalization solutions (NaBH4 (2 mg/mL) and AgNO3 (1 mg/mL)) through the porous structures. Following these treatments, the scaffolds' surfaces were found to be densely populated with Ag nanoparticles and their agglomerates, and manifested an excellent antibacterial effect (Ag ion release rate of 4-8 ppm) suppressing the growth of both E. coli and B. subtilis bacteria up to 99 %. The scaffold extracts showed no cytotoxicity and did not affect cell proliferation, indicating their safety for subsequent use as implants. A cytocompatibility assessment using MG-63 spheroids demonstrated good attachment, spreading, and active migration of cells on the scaffold surface (over 96 % of living cells), confirming their biotolerance. These findings suggest the promise of this surface modification approach for developing superelastic Ti-Zr-Nb scaffolds with superior antibacterial properties and biocompatibility, making them highly suitable for bone implant applications.

An explainable machine learning-based probabilistic framework for the design of scaffolds in bone tissue engineering

Recently, 3D-printed biodegradable scaffolds have shown great potential for bone repair in critical-size fractures. The differentiation of the cells on a scaffold is impacted among other factors by the surface deformation of the scaffold due to mechanical loading and the wall shear stresses imposed by the interstitial fluid flow. These factors are in turn significantly affected by the material properties, the geometry of the scaffold, as well as the loading and flow conditions. In this work, a numerical framework is proposed to study the influence of these factors on the expected osteochondral cell differentiation. The considered scaffold is rectangular with a 0/90 lay-down pattern and a four-layered strut made of polylactic acid with a 5% steel particle content. The distribution of the different types of cells on the scaffold surface is estimated through a scalar stimulus, calculated by using a mechanobioregulatory model. To reduce the simulation time for the computation of the stimulus, a probabilistic machine learning (ML)-based reduced-order model (ROM) is proposed. Then, a sensitivity analysis is performed using the Shapley additive explanations to examine the contribution of the various parameters to the framework stimulus predictions. In a final step, a multiobjective optimization procedure is implemented using genetic algorithms and the ROM, aiming to identify the material parameters and loading conditions that maximize the percentage of surface area populated by bone cells while minimizing the area corresponding to the other types of cells and the resorption condition. The results of the performed analysis highlight the potential of using ROMs for the scaffold design, by dramatically reducing the simulation time while enabling the efficient implementation of sensitivity analysis and optimization procedures.

3D printing technology and its combination with nanotechnology in bone tissue engineering

With the graying of the world's population, the morbidity of age-related chronic degenerative bone diseases, such as osteoporosis and osteoarthritis, is increasing yearly, leading to an increased risk of bone defects, while current treatment methods face many problems, such as shortage of grafts and an incomplete repair. Therefore, bone tissue engineering offers an alternative solution for regenerating and repairing bone tissues by constructing bioactive scaffolds with porous structures that provide mechanical support to damaged bone tissue while promoting angiogenesis and cell adhesion, proliferation, and activity. 3D printing technology has become the primary scaffold manufacturing method due to its ability to precisely control the internal pore structure and complex spatial shape of bone scaffolds. In contrast, the fast development of nanotechnology has provided more possibilities for the internal structure and biological function of scaffolds. This review focuses on the application of 3D printing technology in bone tissue engineering and nanotechnology in the field of bone tissue regeneration and repair, and explores the prospects for the integration of the two technologies.

Bamboo-Inspired Porous Scaffolds for Advanced Orthopedic Implants: Design, Mechanical Properties, and Fluid Characteristics

In orthopedic implant development, incorporating a porous structure into implants can reduce the elastic modulus to prevent stress shielding but may compromise yield strength, risking prosthesis fracture. Bamboo's natural structure, with its exceptional strength-to-weight ratio, serves as inspiration. This study explores biomimicry using bamboo-inspired porous scaffolds (BISs) resembling cortical bone, assessing their mechanical properties and fluid characteristics. The BIS consists of two 2D units controlled by structural parameters α and β. The mechanical properties, failure mechanisms, energy absorption, and predictive performance are investigated. BIS exhibits mechanical properties equivalent to those of natural bone. Specifically, α at 4/3 and β at 2/3 yield superior mechanical properties, and the destruction mechanism occurs layer by layer. Besides, the Gibson-Ashby models with different parameters are established to predict mechanical properties. Fluid dynamics analysis reveals two high-flow channels in BISs, enhancing nutrient delivery through high-flow channels and promoting cell adhesion and proliferation in low-flow regions. For wall shear stress below 30 mPa (ideal for cell growth), α at 4/3 achieves the highest percentage (99.04%), and β at 2/3 achieves 98.46%. Permeability in all structural parameters surpasses that of human bone. Enhanced performance of orthopedic implants through a bionic approach that enables the creation of pore structures suitable for implants.

Evaluation of the Morphological Effects of Hydroxyapatite Nanoparticles on the Rheological Properties and Printability of Hydroxyapatite/Polycaprolactone Nanocomposite Inks and Final Scaffold Features

This study is focused on the importance of nanohydroxyapatite (nHA) particle morphology with the same particle size range on the rheological behavior of polycaprolactone (PCL) composite ink with nHA as a promising candidate for additive manufacturing technologies. Two different physiologic-like nHA morphologies, that is, plate and rod shape, with particles size less than 100 nm were used. nHA powders were well characterized and the printing inks were prepared by adding the different ratios of nHA powders to 50% w/v of PCL solution (nHA/PCL: 35/65, 45/55, 55/45, and 65/35 w/w%). Subsequently, the influence of nHA particle morphology and concentration on the printability and rheological properties of composite inks was investigated. HA nanopowder analysis revealed significant differences in their microstructural properties, which affected remarkably the composite ink printability in several ways. For instance, adding up to 65% w/w of plate-like nHA to the PCL solution was possible, while nanorod HA could not be added above 45% w/w. The printed constructs were successfully fabricated using the extrusion-based printing method and had a porous structure with interconnected pores. Total porosity and surface area increased with nHA content due to the improved fiber stability following deposition of material ink. Consequently, degradation rate and bioactivity increased, while compressive properties decreased. While nanorod HA particles had a more significant impact on the mechanical strength than plate-like morphology, the latter showed less crystalline order, which makes them more bioactive than nanorod HA. It is therefore important to note that the nHA microstructure broadly affects the printability of printing ink and should be considered according to the intended biomedical applications.

Computational design and evaluation of the mechanical and electrical behavior of a piezoelectric scaffold: a preclinical study

Piezoelectric scaffolds have been recently developed to explore their potential to enhance the bone regeneration process using the concept of piezoelectricity, which also inherently occurs in bone. In addition to providing mechanical support during bone healing, with a suitable design, they are supposed to produce electrical signals that ought to favor the cell responses. In this study, using finite element analysis (FEA), a piezoelectric scaffold was designed with the aim of providing favorable ranges of mechanical and electrical signals when implanted in a large bone defect in a large animal model, so that it could inform future pre-clinical studies. A parametric analysis was then performed to evaluate the effect of the scaffold design parameters with regard to the piezoelectric behavior of the scaffold. The designed scaffold consisted of a porous strut-like structure with piezoelectric patches covering its free surfaces within the scaffold pores. The results showed that titanium or PCL for the scaffold and barium titanate (BT) for the piezoelectric patches are a promising material combination to generate favorable ranges of voltage, as reported in experimental studies. Furthermore, the analysis of variance showed the thickness of the piezoelectric patches to be the most influential geometrical parameter on the generation of electrical signals in the scaffold. This study shows the potential of computer tools for the optimization of scaffold designs and suggests that patches of piezoelectric material, attached to the scaffold surfaces, can deliver favorable ranges of electrical stimuli to the cells that might promote bone regeneration.

Bone Regeneration Induced by Patient-Adapted Mg Alloy-Based Scaffolds for Bone Defects: Present and Future Perspectives

Treatment of bone defects resulting after tumor surgeries, accidents, or non-unions is an actual problem linked to morbidity and the necessity of a second surgery and often requires a critical healthcare cost. Although the surgical technique has changed in a modern way, the treatment outcome is still influenced by patient age, localization of the bone defect, associated comorbidities, the surgeon approach, and systemic disorders. Three-dimensional magnesium-based scaffolds are considered an important step because they can have precise bone defect geometry, high porosity grade, anatomical pore shape, and mechanical properties close to the human bone. In addition, magnesium has been proven in in vitro and in vivo studies to influence bone regeneration and new blood vessel formation positively. In this review paper, we describe the magnesium alloy's effect on bone regenerative processes, starting with a short description of magnesium's role in the bone healing process, host immune response modulation, and finishing with the primary biological mechanism of magnesium ions in angiogenesis and osteogenesis by presenting a detailed analysis based on a literature review. A strategy that must be followed when a patient-adapted scaffold dedicated to bone tissue engineering is proposed and the main fabrication technologies are combined, in some cases with artificial intelligence for Mg alloy scaffolds, are presented with examples. We emphasized the microstructure, mechanical properties, corrosion behavior, and biocompatibility of each study and made a basis for the researchers who want to start to apply the regenerative potential of magnesium-based scaffolds in clinical practice. Challenges, future directions, and special potential clinical applications such as osteosarcoma and persistent infection treatment are present at the end of our review paper.

Fatigue behaviour of load-bearing polymeric bone scaffolds: A review

Bone scaffolds play a crucial role in bone tissue engineering by providing mechanical support for the growth of new tissue while enduring static and fatigue loads. Although polymers possess favourable characteristics such as adjustable degradation rate, tissue-compatible stiffness, ease of fabrication, and low toxicity, their relatively low mechanical strength has limited their use in load-bearing applications. While numerous studies have focused on assessing the static strength of polymeric scaffolds, little research has been conducted on their fatigue properties. The current review presents a comprehensive study on the fatigue behaviour of polymeric bone scaffolds. The fatigue failure in polymeric scaffolds is discussed and the impact of material properties, topological features, loading conditions, and environmental factors are also examined. The present review also provides insight into the fatigue damage evolution within polymeric scaffolds, drawing comparisons to the behaviour observed in natural bone. Additionally, the effect of polymer microstructure, incorporating reinforcing materials, the introduction of topological features, and hydrodynamic/corrosive impact of body fluids in the fatigue life of scaffolds are discussed. Understanding these parameters is crucial for enhancing the fatigue resistance of polymeric scaffolds and holds promise for expanding their application in clinical settings as structural biomaterials. STATEMENT OF SIGNIFICANCE: Polymers have promising advantages for bone tissue engineering, including adjustable degradation rates, compatibility with native bone stiffness, ease of fabrication, and low toxicity. However, their limited mechanical strength has hindered their use in load-bearing scaffolds for clinical applications. While prior studies have addressed static behaviour of polymeric scaffolds, a comprehensive review of their fatigue performance is lacking. This review explores this gap, addressing fatigue characteristics, failure mechanisms, and the influence of parameters like material properties, topological features, loading conditions, and environmental factors. It also examines microstructure, reinforcement materials, pore architectures, body fluids, and tissue ingrowth effects on fatigue behaviour. A significant emphasis is placed on understanding fatigue damage progression in polymeric scaffolds, comparing it to natural bone behaviour.

The effect of nodal connectivity and strut density within stochastic titanium scaffolds on osteogenesis

Modern orthopaedic implants use lattice structures that act as 3D scaffolds to enhance bone growth into and around implants. Stochastic scaffolds are of particular interest as they mimic the architecture of trabecular bone and can combine isotropic properties and adjustable structure. The existing research mainly concentrates on controlling the mechanical and biological performance of periodic lattices by adjusting pore size and shape. Still, less is known on how we can control the performance of stochastic lattices through their design parameters: nodal connectivity, strut density and strut thickness. To elucidate this, four lattice structures were evaluated with varied strut densities and connectivity, hence different local geometry and mechanical properties: low apparent modulus, high apparent modulus, and two with near-identical modulus. Pre-osteoblast murine cells were seeded on scaffolds and cultured in vitro for 28 days. Cell adhesion, proliferation and differentiation were evaluated. Additionally, the expression levels of key osteogenic biomarkers were used to assess the effect of each design parameter on the quality of newly formed tissue. The main finding was that increasing connectivity increased the rate of osteoblast maturation, tissue formation and mineralisation. In detail, doubling the connectivity, over fixed strut density, increased collagen type-I by 140%, increased osteopontin by 130% and osteocalcin by 110%. This was attributed to the increased number of acute angles formed by the numerous connected struts, which facilitated the organization of cells and accelerated the cell cycle. Overall, increasing connectivity and adjusting strut density is a novel technique to design stochastic structures which combine a broad range of biomimetic properties and rapid ossification.

Role and architectural significance of porous chitosan-based scaffolds in bone tissue engineering

In designing and fabricating scaffolds to fill the bone defects and stimulate new bone formation, the biomimetics of the construct is a crucial factor in invoking the bone microenvironment to promote osteogenic differentiation. Regarding structural traits, changes in porous characteristics of the scaffolds, such as pore size, pore morphology, and percentage porosity, may patronize or jeopardize their other physicochemical and biological properties. Chitosan (CS), a biodegradable naturally occurring polymer, has recently drawn considerable attention as a scaffolding material in tissue engineering and regenerative medicine. CS-based microporous scaffolds have been reported to aid osteogenesis under both in vitro and in vivo conditions by supporting cellular attachment and proliferation of osteoblast cells and the formation of mineralized bone matrix. This related notion may be found in numerous earlier research, even though the precise mechanism of action that encourages the development of new bone still needs to be understood completely. This article presents the potential correlations and the significance of the porous properties of the CS-based scaffolds to influence osteogenesis and angiogenesis during bone regeneration. This review also goes over resolving the mechanical limitations of CS by blending it with other polymers and ceramics.

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

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

In vivo characterization of 3D-printed polycaprolactone-hydroxyapatite scaffolds with Voronoi design to advance the concept of scaffold-guided bone regeneration

Three-dimensional (3D)-printed medical-grade polycaprolactone (mPCL) composite scaffolds have been the first to enable the concept of scaffold-guided bone regeneration (SGBR) from bench to bedside. However, advances in 3D printing technologies now promise next-generation scaffolds such as those with Voronoi tessellation. We hypothesized that the combination of a Voronoi design, applied for the first time to 3D-printed mPCL and ceramic fillers (here hydroxyapatite, HA), would allow slow degradation and high osteogenicity needed to regenerate bone tissue and enhance regenerative properties when mixed with xenograft material. We tested this hypothesis in vitro and in vivo using 3D-printed composite mPCL-HA scaffolds (wt 96%:4%) with the Voronoi design using an ISO 13485 certified additive manufacturing platform. The resulting scaffold porosity was 73% and minimal in vitro degradation (mass loss <1%) was observed over the period of 6 months. After loading the scaffolds with different types of fresh sheep xenograft and ectopic implantation in rats for 8 weeks, highly vascularized tissue without extensive fibrous encapsulation was found in all mPCL-HA Voronoi scaffolds and endochondral bone formation was observed, with no adverse host-tissue reactions. This study supports the use of mPCL-HA Voronoi scaffolds for further testing in future large preclinical animal studies prior to clinical trials to ultimately successfully advance the SGBR concept.

Comparative study in vivo of the osseointegration of 3D-printed and plasma-coated titanium implants

BACKGROUND

Total hip arthroplasty is a common surgical treatment for elderly patients with osteoporosis, particularly in postmenopausal women. In such cases, highly porous acetabular components are a favorable option in achieving osseointegration. However, further discussion is needed if use of such acetabular components is justified under the condition of normal bone mass.

AIM

To determine the features of osseointegration of two different types of titanium implants [3-dimensional (3D)-printed and plasma-coated titanium implants] in bone tissue of a distal metaphysis in a rat femur model.

METHODS

This study was performed on 20 white male laboratory rats weighing 300-350 g aged 6 mo. Rats were divided into two groups of 10 animals, which had two different types of implants were inserted into a hole defect (2 × 3 mm) in the distal metaphysis of the femur: Group I: 3D-printed titanium implant (highly porous); Group II: Plasma-coated titanium implant. After 45 and 90 d following surgery, the rats were sacrificed, and their implanted femurs were extracted for histological examination. The relative perimeter (%) of bone trabeculae [bone-implant contact (BIC%)] and bone marrow surrounding the titanium implants was measured.

RESULTS

Trabecular bone tissue was formed on the 45th day after implantation around the implants regardless of their type. 45 d after surgery, group I (3D-printed titanium implant) and group II (plasma-coated titanium implant) did not differ in BIC% (83.51 ± 8.5 vs 84.12 ± 1 .73; P = 0.838). After 90 d, the BIC% was higher in group I (87.04 ± 6.99 vs 81.24 ± 7.62; P = 0.049), compared to group II. The relative perimeter of the bone marrow after 45 d did not differ between groups and was 16.49% ± 8.58% for group I, and 15.88% ± 1.73% for group II. Futhermore, after 90 d, in group I the relative perimeter of bone marrow was 1.4 times smaller (12.96 ± 6.99 vs 18.76 ± 7.62; P = 0.049) compared to the relative perimeter of bone marrow in group II.

CONCLUSION

The use of a highly porous titanium implant, manufactured with 3D printing, for acetabular components provides increased osseointegration compared to a plasma-coated titanium implant.

Fatigue life of 3D-printed porous titanium dental implants predicted by validated finite element simulations

Introduction: Porous dental implants represent a promising strategy to reduce failure rate by favoring osseointegration or delivering drugs locally. Incorporating porous features weakens the mechanical capacity of an implant, but sufficient fatigue strength must be ensured as regulated in the ISO 14801 standard. Experimental fatigue testing is a costly and time-intensive part of the implant development process that could be accelerated with validated computer simulations. This study aimed at developing, calibrating, and validating a numerical workflow to predict fatigue strength on six porous configurations of a simplified implant geometry. Methods: Mechanical testing was performed on 3D-printed titanium samples to establish a direct link between endurance limit (i.e., infinite fatigue life) and monotonic load to failure, and a finite element model was developed and calibrated to predict the latter. The tool was then validated by predicting the fatigue life of a given porous configuration. Results: The normalized endurance limit (10% of the ultimate load) was the same for all six porous designs, indicating that monotonic testing was a good surrogate for endurance limit. The geometry input of the simulations influenced greatly their accuracy. Utilizing the as-designed model resulted in the highest prediction error (23%) and low correlation between the estimated and experimental loads to failure (R2 = 0.65). The prediction error was smaller when utilizing specimen geometry based on micro computed tomography scans (14%) or design models adjusted to match the printed porosity (8%). Discussion: The validated numerical workflow presented in this study could therefore be used to quantitatively predict the fatigue life of a porous implant, provided that the effect of manufacturing on implant geometry is accounted for.

Hollow channels scaffold in bone regenerative: a review

Bone substitute materials have been extensively used for bone regeneration over the past 50 years. The development of novel materials, fabrication technologies and the incorporation and release of regenerative cytokines, growth factors, cells and antimicrobials has been driven by the rapid development in the field of additive manufacturing technology. There are still however, significant challenges that need addressing, including ways to better mediate the rapid vascularization of bone scaffolds to enhance subsequent regeneration and osteogenesis. Increasing construct porosity can accelerate the development of blood vessels in the scaffold, but doing so also weakens the constructs mechanical properties. A novel design for promoting rapid vascularization is to fabricate custom-made hollow channels as bone scaffolds. Summarized here are the current developments in hollow channels scaffold, including their biological attributes, physio-chemical properties, and effects on regeneration. An overview of recent developments in scaffold fabrication as they relate to hollow channel constructs and their structural features will be introduced with an emphasis on attributes that enhance new bone and vessel formation. Furthermore, the potential to enhance angiogenesis and osteogenesis by replicating the structure of real bone will be highlighted.

Mechanobiology-informed biomaterial and tissue engineering strategies for influencing skeletal stem and progenitor cell fate

Skeletal stem and progenitor cells (SSPCs) are the multi-potent, self-renewing cell lineages that form the hematopoietic environment and adventitial structures of the skeletal tissues. Skeletal tissues are responsible for a diverse range of physiological functions because of the extensive differentiation potential of SSPCs. The differentiation fates of SSPCs are shaped by the physical properties of their surrounding microenvironment and the mechanical loading forces exerted on them within the skeletal system. In this context, the present review first highlights important biomolecules involved with the mechanobiology of how SSPCs sense and transduce these physical signals. The review then shifts focus towards how the static and dynamic physical properties of microenvironments direct the biological fates of SSPCs, specifically within biomaterial and tissue engineering systems. Biomaterial constructs possess designable, quantifiable physical properties that enable the growth of cells in controlled physical environments both in-vitro and in-vivo. The utilization of biomaterials in tissue engineering systems provides a valuable platform for controllably directing the fates of SSPCs with physical signals as a tool for mechanobiology investigations and as a template for guiding skeletal tissue regeneration. It is paramount to study this mechanobiology and account for these mechanics-mediated behaviors to develop next-generation tissue engineering therapies that synergistically combine physical and chemical signals to direct cell fate. Ultimately, taking advantage of the evolved mechanobiology of SSPCs with customizable biomaterial constructs presents a powerful method to predictably guide bone and skeletal organ regeneration.

The Diamond Concept Enigma: Recent Trends of Its Implementation in Cross-linked Chitosan-Based Scaffolds for Bone Tissue Engineering

An increasing number of publications over the past ten years have focused on the development of chitosan-based cross-linked scaffolds to regenerate bone tissue. The design of biomaterials for bone tissue engineering applications relies heavily on the ideals set forth by a polytherapy approach called the "Diamond Concept". This methodology takes into consideration the mechanical environment, scaffold properties, osteogenic and angiogenic potential of cells, and benefits of osteoinductive mediator encapsulation. The following review presents a comprehensive summarization of recent trends in chitosan-based cross-linked scaffold development within the scope of the Diamond Concept, particularly for nonload-bearing bone repair. A standardized methodology for material characterization, along with assessment of in vitro and in vivo potential for bone regeneration, is presented based on approaches in the literature, and future directions of the field are discussed.

Porous metal block based on topology optimization to treat distal femoral bone defect in total knee revision

Metal block augmentations are common solutions in treating bone defects of total knee revision. However, the stress shielding and poor osteointegration resulted from metal block application could not be neglected in bone defects restoration. In this study, a novel porous metal block was designed with topology optimization to improve biomechanical performance. The biomechanical difference of the topologically optimized block, solid Ti6Al4V block, and porous Ti6Al4V block in treating bone defects of total knee revision was compared by finite element analysis. The inhomogeneous femoral model was created according to the computed tomography data. Combined with porous structures, minimum compliance topology optimization subjected to the volume fraction constraint was utilized for the redesign of the metal block. The region of interest was defined as a 10 mm area of the distal femur beneath the contacting surface. The biomechanical performance of daily motions was investigated. The von Mises stress, the strain energy density of the region of interest, and the von Mises stress of metal blocks were recorded. The results were analyzed in SPSS. In terms of the region of interest, the maximum von Mises stress of the topological optimized group increased obviously, and its average stress was significantly higher than that of the other groups (p < 0.05). Moreover, the topologically optimized block group had the highest maximum strain energy density of the three groups, and the lowest maximum stress of block was also found in this group. In this study, the stress shielding reduction and stress transfer capability were found obviously improved through topology optimization. Therefore, the topological optimized porous block is recommended in treating bone defects of total knee revision. Meanwhile, this study also provided a novel approach for mechanical optimization in block designing.

Making In Vitro Tumor Models Whole Again

As a reductionist approach, patient-derived in vitro tumor models are inherently still too simplistic for personalized drug testing as they do not capture many characteristics of the tumor microenvironment (TME), such as tumor architecture and stromal heterogeneity. This is especially problematic for assessing stromal-targeting drugs such as immunotherapies in which the density and distribution of immune and other stromal cells determine drug efficacy. On the other end, in vivo models are typically costly, low-throughput, and time-consuming to establish. Ex vivo patient-derived tumor explant (PDE) cultures involve the culture of resected tumor fragments that potentially retain the intact  TME of the original tumor. Although developed decades ago, PDE cultures have not been widely adopted likely because of their low-throughput and poor long-term viability. However, with growing recognition of the importance of patient-specific TME in mediating drug response, especially in the field of immune-oncology, there is an urgent need to resurrect these holistic cultures. In this Review, the key limitations of patient-derived tumor explant cultures are outlined and technologies that have been developed or could be employed to address these limitations are discussed. Engineered holistic tumor explant cultures may truly realize the concept of personalized medicine for cancer patients.

Biomechanical Effects of the Porous Structure of Gyroid and Voronoi Hip Implants: A Finite Element Analysis Using an Experimentally Validated Model

Total hip arthroplasty (THA) is most likely one of the most successful surgical procedures in medicine. It is estimated that three in four patients live beyond the first post-operative year, so appropriate surgery is needed to alleviate an otherwise long-standing suboptimal functional level. However, research has shown that during a complete THA procedure, a solid hip implant inserted in the femur can damage the main arterial supply of the cortex and damage the medullary space, leading to cortical bone resorption. Therefore, this study aimed to design a porous hip implant with a focus on providing more space for better osteointegration, improving the medullary revascularisation and blood circulation of patients. Based on a review of the literature, a lightweight implant design was developed by applying topology optimisation and changing the materials of the implant. Gyroid and Voronoi lattice structures and a solid hip implant (as a control) were designed. In total, three designs of hip implants were constructed by using SolidWorks and nTopology software version 2.31. Point loads were applied at the x, y and z-axis to imitate the stance phase condition. The forces represented were x = 320 N, y = -170 N, and z = -2850 N. The materials that were used in this study were titanium alloys. All of the designs were then simulated by using Marc Mentat software version 2020 (MSC Software Corporation, Munich, Germany) via a finite element method. Analysis of the study on topology optimisation demonstrated that the Voronoi lattice structure yielded the lowest von Mises stress and displacement values, at 313.96 MPa and 1.50 mm, respectively, with titanium alloys as the materials. The results also indicate that porous hip implants have the potential to be implemented for hip implant replacement, whereby the mechanical integrity is still preserved. This result will not only help orthopaedic surgeons to justify the design choices, but could also provide new insights for future studies in biomechanics.

3D Printing of a Biocompatible Nanoink Derived from Waste Animal Bones

Direct ink writing (DIW) additive manufacturing is a versatile 3D printing technique for a broad range of materials. DIW can print a variety of materials provided that the ink is well-engineered with appropriate rheological properties. DIW could be an ideal technique in tissue engineering to repair and regenerate deformed or missing organs or tissues, for example, bone and tooth fracture that is a common problem that needs surgeon attention. A critical criterion in tissue engineering is that inserts must be compatible with their surrounding environment. Chemically produced calcium-rich materials are dominant in this application, especially for bone-related applications. These materials may be toxic leading to a rejection by the body that may need secondary surgery to repair. On the other hand, there is an abundance of biowaste building blocks that can be used for grafting with little adverse effect on the body. In this work, we report a bioderived ink made entirely of calcium derived from waste animal bones using a benign process. Calcium nanoparticles are extracted from the bones and the ink prepared by mixing with different biocompatible binders. The ink is used to print scaffolds with controlled porosity that allows better growth of cells. DIW printed parts show better mechanical properties and biocompatibility that are important for the grafting application. Degradation tests and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay study were done to examine the biocompatibility of the extracted materials. In addition, discrete element modeling and computational fluid dynamics numerical methods are used in Rocky and Ansys software programs. This work shows that biowaste materials if well-engineered can be a never-ending source of raw materials for advanced application in orthopedic grafting.

Roles of irregularity of pore morphology in osteogenesis of Voronoi scaffolds: From the perspectives of MSC adhesion and mechano-regulated osteoblast differentiation

Bone scaffolds designed based on the Voronoi-tessellation algorithm have been increasingly studied owing to their structural similarity with natural cancellous bone. The irregularity of pore morphology (IPM) influences the osteogenesis efficiency of Voronoi scaffolds since it may alter the static and hydromechanical microenvironments for the initial adhesion and mechano-regulated osteoblast differentiation (MrOD) of mesenchymal stem cells (MSCs). In this work, animal experiments were conducted to explore the relationship between IPM and osteogenesis efficiency in Voronoi scaffolds. A computational fluid dynamics (CFD) analysis based on discrete phase models was performed to predict the efficiency of MSC adhesion in different IPMs. Another combined finite element and CFD analysis based on the mechano-regulation algorithm was performed to predict the influence of IPM on the MrOD of the adhesive MSCs. The results showed that the osteogenesis efficiency of the Voronoi scaffolds increased as the IPM rose from low to moderate and then dropped as the IPM further rose. Same trends were also found in the MSC adhesion and MrOD, which caused by the changes of strain tensors on the strut surface and the tortuosity and fluid velocity of the fluid pathway. Moderate IPM induced the highest osteogenesis efficiency owing to its highest efficiencies of MSC adhesion and MrOD. This work identified the optimal IPM for the osteogenesis of Voronoi scaffolds and clarified its biomechanical mechanisms from the adhesion and mechano-regulated differentiation of MSCs, which is of great importance for guiding Voronoi scaffold design when it is used for bone defect repair.

Numerical analysis of the influence of triply periodic minimal surface structures morphometry on the mechanical response

BACKGROUND AND OBJECTIVE

Design of bone scaffolds requires a combination of material and geometry to fulfil requirements of mechanical properties, porosity and pore size. Triply Periodic Minimal Surface (TPMS) structures have gained attention due to their similarities to cancellous bone. In this work, we aim at exploring relationships between morphometry and mechanical properties for TPMS configurations.

METHODS

Eight TPMS structures are defined considering six porosity levels and their morphometry is characterized. The stiffness matrix of each structure is assessed and related to morphometry through a statistical analysis.

RESULTS

An orthotropic mechanical behavior has been derived from the numerical homogenization. Properties decay exponentially for decreasing volume fraction. Through volume fraction variation, TPMS mechanical properties can be selected to match bone properties in a range of 0.2% to 70% of the bulk material properties.

CONCLUSIONS

The comparison between cancellous bone and TPMS morphometry, considering a unit cell size of 1.5 mm, reveals that the configurations analyzed in this work match the requirements of volume fraction, mean thickness and pore size. However, the TPMS studied in this work differ from cancellous bone anisotropy. The results in this paper provide a framework to select the proper TPMS configuration and its geometry for patient-specific applications.

Controlling Microenvironments with Organs-on-Chips for Osteoarthritis Modelling

Osteoarthritis (OA) remains a prevalent disease affecting more than 20% of the global population, resulting in morbidity and lower quality of life for patients. The study of OA pathophysiology remains predominantly in animal models due to the complexities of mimicking the physiological environment surrounding the joint tissue. Recent development in microfluidic organ-on-chip (OoC) systems have demonstrated various techniques to mimic and modulate tissue physiological environments. Adaptations of these techniques have demonstrated success in capturing a joint tissue's tissue physiology for studying the mechanism of OA. Adapting these techniques and strategies can help create human-specific in vitro models that recapitulate the cellular processes involved in OA. This review aims to comprehensively summarise various demonstrations of microfluidic platforms in mimicking joint microenvironments for future platform design iterations.

A review on design of scaffold for osteoinduction: Toward the unification of independent design variables

Biophysical stimulus quantifies the osteoinductivity of the scaffold concerning the mechanoregulatory mathematical models of scaffold-assisted cellular differentiation. Consider a set of independent structural variables ($) that comprises bulk porosity levels ([Formula: see text]) and a set of morphological features of the micro-structure ([Formula: see text]) associated with scaffolds, i.e., [Formula: see text]. The literature suggests that biophysical stimulus ([Formula: see text]) is a function of independent structural variables ($). Limited understanding of the functional correlation between biophysical stimulus and structural features results in the lack of the desired osteoinductivity in a scaffold. Consequently, it limits their broad applicability to assist bone tissue regeneration for treating critical-sized bone fractures. The literature indicates the existence of multi-dimensional independent design variable space as a probable reason for the general lack of osteoinductivity in scaffolds. For instance, known morphological features are the size, shape, orientation, continuity, and connectivity of the porous regions in the scaffold. It implies that the number of independent variables ([Formula: see text]) is more than two, i.e., [Formula: see text], which interact and influence the magnitude of [Formula: see text] in a unified manner. The efficiency of standard engineering design procedures to analyze the correlation between dependent variable ([Formula: see text]) and independent variables ($) in 3D mutually orthogonal Cartesian coordinate system diminishes proportionally with the increase in the number of independent variables ([Formula: see text]) (Deb in Optimization for engineering design-algorithms and examples, PHI Learning Private Limited, New Delhi, 2012). Therefore, there is an immediate need to devise a framework that has the potential to quantify the micro-structural's morphological features in a unified manner to increase the prospects of scaffold-assisted bone tissue regeneration.

Silk-based hydrogel incorporated with metal-organic framework nanozymes for enhanced osteochondral regeneration

Osteochondral defects (OCD) cannot be efficiently repaired due to the unique physical architecture and the pathological microenvironment including enhanced oxidative stress and inflammation. Conventional strategies, such as the control of implant microstructure or the introduction of growth factors, have limited functions failing to manage these complex environments. Here we developed a multifunctional silk-based hydrogel incorporated with metal-organic framework nanozymes (CuTA@SF) to provide a suitable microenvironment for enhanced OCD regeneration. The incorporation of CuTA nanozymes endowed the SF hydrogel with a uniform microstructure and elevated hydrophilicity. In vitro cultivation of mesenchymal stem cells (MSCs) and chondrocytes showed that CuTA@SF hydrogel accelerated cell proliferation and enhanced cell viability, as well as had antioxidant and antibacterial properties. Under the inflammatory environment with the stimulation of IL-1β, CuTA@SF hydrogel still possessed the potential to promote MSC osteogenesis and deposition of cartilage-specific extracellular matrix (ECM). The proteomics analysis further confirmed that CuTA@SF hydrogel promoted cell proliferation and ECM synthesis. In the full-thickness OCD model of rabbit, CuTA@SF hydrogel displayed successfully in situ OCD regeneration, as evidenced by micro-CT, histology (HE, S/O, and toluidine blue staining) and immunohistochemistry (Col I and aggrecan immunostaining). Therefore, CuTA@SF hydrogel is a promising biomaterial targeted at the regeneration of OCD.

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A multifunctional silk-based hydrogel incorporated with metal-organic framework nanozymes (CuTA@SF) was fabricated.

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CuTA@SF hydrogel has antioxidant, anti-inflammation and antibacterial capacities.

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Proteomics analysis confirmed that CuTA@SF hydrogel promoted cell proliferation and ECM synthesis.

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CuTA@SF hydrogel displayed successful osteochondral regeneration in vivo.

Mechanical performance of porous biomimetic intervertebral body fusion devices: an in vitro biomechanical study

BACKGROUND

Degenerative disc disease is one of the most common ailments severely affecting the quality of life in elderly population. Cervical intervertebral body fusion devices are utilized to provide stability after surgical intervention for cervical pathology. In this study, we design a biomimetic porous spinal cage, and perform mechanical simulations to study its performances following American Society for Testing and Materials International (ASTM) standards before manufacturing to improve design process and decrease cost and consumption of material.

METHODS

The biomimetic porous Ti-6Al-4 V interbody fusion devices were manufactured by selective laser melting (laser powder bed fusion: LPBF in ISO/ASTM 52900 standard) and subsequently post-processed by using hot isostatic pressing (HIP). Chemical composition, microstructure and the surface morphology were studied. Finite element analysis and in vitro biomechanical test were performed.

FINDINGS

The post heat treatment can optimize its mechanical properties, as the stiffness of the cage decreases to reduce the stress shielding effect between two instrumented bodies. After the HIP treatment, the ductility and the fatigue performance are substantially improved. The use of HIP post-processing can be a necessity to improve the physical properties of customized additive manufacturing processed implants.

INTERPRETATION

In conclusion, we have successfully designed a biomimetic porous intervertebral device. HIP post-treatment can improve the bulk material properties, optimize the device with reduced stiffness, decreased stress shielding effect, while still provide appropriate space for bone growth.

CLINICAL SIGNIFICANCE

The biomechanical performance of 3-D printed biomimetic porous intervertebral device can be optimized. The ductility and the fatigue performance were substantially improved, the simultaneously decreased stiffness reduces the stress shielding effect between two instrumented bodies; while the biomimetic porous structures provide appropriate space for bone growth, which is important in the patients with osteoporosis.

Review on Porous Scaffolds Generation Process: A Tissue Engineering Approach

Porous scaffolds have been widely explored for tissue regeneration and engineering in vitro three-dimensional models. In this review, a comprehensive literature analysis is conducted to identify the steps involved in their generation. The advantages and disadvantages of the available techniques are discussed, highlighting the importance of considering pore geometrical parameters such as curvature and size, and summarizing the requirements to generate the porous scaffold according to the desired application. This paper considers the available design tools, mathematical models, materials, fabrication techniques, cell seeding methodologies, assessment methods, and the status of pore scaffolds in clinical applications. This review compiles the relevant research in the field in the past years. The trends, challenges, and future research directions are discussed in the search for the generation of a porous scaffold with improved mechanical and biological properties that can be reproducible, viable for long-term studies, and closer to being used in the clinical field.

Biominerals Added Bioresorbable Calcium Phosphate Loaded Biopolymer Composites

Nanocrystalline calcium phosphate (CP) bioceramic coatings and their combination with biopolymers are innovative types of resorbable coatings for load-bearing implants that can promote the integration of metallic implants into human bodies. The nanocrystalline, amorphous CP particles are an advantageous form of the various calcium phosphate phases since they have a faster dissolution rate than that of crystalline hydroxyapatite. Owing to the biomineral additions (Mg, Zn, Sr) in optimized concentrations, the base CP particles became more similar to the mineral phase in human bones (dCP). The effect of biomineral addition into the CaP phases was thoroughly studied. The results showed that the shape, morphology, and amorphous characteristic slightly changed in the case of biomineral addition in low concentrations. The optimized dCP particles were then incorporated into a chosen polycaprolactone (PCL) biopolymer matrix. Very thin, non-continuous, rough layers were formed on the surface of implant substrates via the spin coating method. The SEM elemental mapping proved the perfect incorporation and distribution of dCP particles into the polymer matrix. The bioresorption rate of thin films was followed by corrosion measurements over a long period of time. The corrosion results indicated a faster dissolution rate for the dCP-PCL composite compared to the dCP and CP powder layers.

Optimisation of the additive manufacturing parameters of polylactic acid (PLA) cellular structures for biomedical applications

Fused deposition modelling (FDM) is an additive manufacturing technology used to create functional and complex geometries directly from computer-generated models. This technique can be utilised to generate cellular structures with controllable pore size, pore shape, and porosity. Cellular structures are fundamental in orthopaedics scaffolds because of its low elastic modulus, high compressive strength, and adequate cell accommodation spaces. This paper aims at investigating and optimising the FDM additive manufacturing process parameters of polylactic Acid (PLA) for two lattice structures namely Schoen Gyroid and Schwarz Primitive. The effect of additive manufacturing critical process parameters including layer height, flow rate, and print speed on the geometrical accuracy and compressive strength of the specimens were analysed. In addition, other parameters that have minimal effect on the geometrical accuracy of the printed parts were discussed. A Full Factorial Analysis (FFA) using Minitab software was undertaken to identify the perfect combination of printing parameters to provide the most geometrically accurate structure. In this study, samples of the Schoen Gyroid and the Schwarz Primitive lattices and a solid control cylinder were 3D printed using the ideal printing combination to assess the manufacturability, the geometrical accuracy, and the mechanical behaviour of both designs. It was found that the optimised FDM process parameters for the studied cellular structures were a layer height of 0.16 mm, a printing speed of 50 mm/s and a flow rate of 90%. As a result of using these parameters, the solid, Schoen Gyroid and Schwarz Primitive specimens demonstrated elastic moduli values of 951 MPa, 264 MPa, and 221 MPa, respectively. In addition, the Schoen Gyroid and the Schwarz Primitive have reached their stress limits at around 8.68 MPa and 7.06 MPa, respectively. It was noticed that the Schoen Gyroid structure exhibited ∼ 18% higher compressive strength and ∼ 16% higher elastic modulus compared to the Schwarz Primitive structure for the same volume fraction of porosity, overall dimensions, and the manufacturing process parameters. Although both structures revealed mechanical properties that fall within the range of the human trabecular bone, but Schoen Gyroid exhibited improved structural integrity performance that is evident by its post-yield behaviour.

Height-to-Diameter Ratio and Porosity Strongly Influence Bulk Compressive Mechanical Properties of 3D-Printed Polymer Scaffolds

Although the architectural design parameters of 3D-printed polymer-based scaffolds-porosity, height-to-diameter (H/D) ratio and pore size-are significant determinants of their mechanical integrity, their impact has not been explicitly discussed when reporting bulk mechanical properties. Controlled architectures were designed by systematically varying porosity (30-75%, H/D ratio (0.5-2.0) and pore size (0.25-1.0 mm) and fabricated using fused filament fabrication technique. The influence of the three parameters on compressive mechanical properties-apparent elastic modulus E_app, bulk yield stress σ_y and yield strain ε_y-were investigated through a multiple linear regression analysis. H/D ratio and porosity exhibited strong influence on the mechanical behavior, resulting in variations in mean E_app of 60% and 95%, respectively. σ_y was comparatively less sensitive to H/D ratio over the range investigated in this study, with 15% variation in mean values. In contrast, porosity resulted in almost 100% variation in mean σ_y values. Pore size was not a significant factor for mechanical behavior, although it is a critical factor in the biological behavior of the scaffolds. Quantifying the influence of porosity, H/D ratio and pore size on bench-top tested bulk mechanical properties can help optimize the development of bone scaffolds from a biomechanical perspective.

Challenges of Periodontal Tissue Engineering: Increasing Biomimicry through 3D Printing and Controlled Dynamic Environment

In recent years, tissue engineering studies have proposed several approaches to regenerate periodontium based on the use of three-dimensional (3D) tissue scaffolds alone or in association with periodontal ligament stem cells (PDLSCs). The rapid evolution of bioprinting has sped up classic regenerative medicine, making the fabrication of multilayered scaffolds-which are essential in targeting the periodontal ligament (PDL)-conceivable. Physiological mechanical loading is fundamental to generate this complex anatomical structure ex vivo. Indeed, loading induces the correct orientation of the fibers forming the PDL and maintains tissue homeostasis, whereas overloading or a failure to adapt to mechanical load can be at least in part responsible for a wrong tissue regeneration using PDLSCs. This review provides a brief overview of the most recent achievements in periodontal tissue engineering, with a particular focus on the use of PDLSCs, which are the best choice for regenerating PDL as well as alveolar bone and cementum. Different scaffolds associated with various manufacturing methods and data derived from the application of different mechanical loading protocols have been analyzed, demonstrating that periodontal tissue engineering represents a proof of concept with high potential for innovative therapies in the near future.

Analysis of the topological motifs of the cellular structure of the tri-spine horseshoe crab (Tachypleus tridentatus) and its associated mechanical properties

Topological motifs in pore architecture can profoundly influence the structural properties of that architecture, such as its mass, porosity, modulus, strength, and surface permeability. Taking the irregular cellular structure of the tri-spine horseshoe crab as a research model, we present a new approach to the quantitative description and analysis of structure-property-function relationships. We employ a robust skeletonization method to construct a curve-skeleton that relies on high-resolution 3D tomographic data. The topological motifs and mechanical properties of the long-range cellular structure were investigated using the Grasshopper plugin and uniaxial compression test to identify the variation gradient. Finite element analysis was conducted for the sub-volumes to obtain the variation in effective modulus along the three principal directions. The results show that the branch length and node distribution density varied from the tip to the base of the sharp corner. These node types formed a low-connectivity network, in which the node types 3-N and 4-N tended to follow the motifs of ideal planar triangle and tetrahedral configurations, respectively, with the highest proportion of inter-branch angles in the angle ranges of 115-120° and 105-110°. In addition, mapping the mechanical gradients to topological properties indicated that narrower profiles with a given branch length gradient, preferred branch orientation, and network connectedness degree are the main factors that affect the mechanical properties. These factors suggest significant potential for designing a controllable, irregularly cellular structure in terms of both morphology and function.

Masquelet technique in military practice: specificities and future directions for combat-related bone defect reconstruction

Because of its simplicity, reliability, and replicability, the Masquelet induced membrane technique (IMT) has become one of the preferred methods for critical bone defect reconstruction in extremities. Although it is now used worldwide, few studies have been published about IMT in military practice. Bone reconstruction is particularly challenging in this context of care due to extensive soft-tissue injury, early wound infection, and even delayed management in austere conditions. Based on our clinical expertise, recent research, and a literature analysis, this narrative review provides an overview of the IMT application to combat-related bone defects. It presents technical specificities and future developments aiming to optimize IMT outcomes, including for the management of massive multi-tissue defects or bone reconstruction performed in the field with limited resources.

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.

Porous construction and surface modification of titanium-based materials for osteogenesis: A review

Titanium and titanium alloy implants are essential for bone tissue regeneration engineering. The current trend is toward the manufacture of implants from materials that mimic the structure, composition and elasticity of bones. Titanium and titanium alloy implants, the most common materials for implants, can be used as a bone conduction material but cannot promote osteogenesis. In clinical practice, there is a high demand for implant surfaces that stimulate bone formation and accelerate bone binding, thus shortening the implantation-to-loading time and enhancing implantation success. To avoid stress shielding, the elastic modulus of porous titanium and titanium alloy implants must match that of bone. Micro-arc oxidation technology has been utilized to increase the surface activity and build a somewhat hard coating on porous titanium and titanium alloy implants. More recently, a growing number of researchers have combined micro-arc oxidation with hydrothermal, ultrasonic, and laser treatments, coatings that inhibit bacterial growth, and acid etching with sand blasting methods to improve bonding to bone. This paper summarizes the reaction at the interface between bone and implant material, the porous design principle of scaffold material, MAO technology and the combination of MAO with other technologies in the field of porous titanium and titanium alloys to encourage their application in the development of medical implants.

Multi-objective Shape Optimization of Bone Scaffolds: Enhancement of Mechanical Properties and Permeability

Porous scaffolds have recently attracted attention in bone tissue engineering. The implanted scaffolds are supposed to satisfy the mechanical and biological requirements. In this study, two porous structures named MFCC-1 (modified face centered cubic-1) and MFCC-2 (modified face centered cubic-2) are introduced. The proposed porous architectures are evaluated, optimized, and tested to enhance mechanical and biological properties. The geometric parameters of the scaffolds with porosities ranging from 70% to 90% are optimized to find a compromise between the effective Young's modulus and permeability, as well as satisfying the pore size and specific surface area requirements. To optimize the effective Young's modulus and permeability, we integrated a mathematical formulation, finite element analysis, and computational fluid dynamics simulations. For validation, the optimized scaffolds were 3D-printed, tested, and compared with two different orthogonal cylindrical struts (OCS) scaffold architectures. The MFCC designs are preferred to the generic OCS scaffolds from various perspectives: a) the MFCC architecture allows scaffold designs with porosities up to 96%; b) the very porous architecture of MFCC scaffolds allows achieving high permeabilities, which could potentially improve the cell diffusion; c) despite having a higher porosity compared to the OCS scaffolds, MFCC scaffolds improve mechanical performance regarding Young's modulus, stress concentration, and apparent yield strength; d) the proposed structures with different porosities are able to cover all the range of permeability for the human trabecular bones. The optimized MFCC designs have simple architectures and can be easily fabricated and used to improve the quality of load-bearing orthopedic scaffolds. STATEMENT OF SIGNIFICANCE: Porous scaffolds are increasingly being studied to repair large bone defects. A scaffold is supposed to withstand mechanical loads and provide an appropriate environment for bone cell growth after implantation. These mechanical and biological requirements are usually contradicting; improving the mechanical performance would require a reduction in porosity and a lower porosity is likely to reduce the biological performance of the scaffold. Various studies have shown that the mechanical and biological performance of bone scaffolds can be improved by internal architecture modification. In this study, we propose two scaffold architectures named MFCC-1 and MFCC-2 and provide an optimization framework to simultaneously optimize their stiffness and permeability to improve their mechanical and biological performances.

Osteoconductive Silk Fibroin Binders for Bone Repair in Alveolar Cleft Palate: Fabrication, Structure, Properties, and In Vitro Testing

Osteoconductive silk fibroin (SF) binders were fabricated for the bone repair of an alveolar cleft defect. Binders were prefigureared by mixing different ratios of a mixture of random coils and SF aggregation with SF fibrils: 100:0 (SFB100), 75:25 (SFB75), 50:50 (SFB50), 25:75 (SFB25), and 0:100 (SFB0). The gelation, molecular organization, structures, topography, and morphology of the binders were characterized and observed. Their physical, mechanical, and biological properties were tested. The SF binders showed gelation via self-assembly of SF aggregation and fibrillation. SFB75, SFB50, and SFB25 had molecular formation via the amide groups and showed more structural stability than SFB100. The morphology of SFB0 demonstrated the largest pore size. SFB0 showed a lowest hydrophilicity. SFB100 showed the highest SF release. SFB25 had the highest maximum load. SFB50 exhibited the lowest elongation at break. Binders with SF fibrils showed more cell viability and higher cell proliferation, ALP activity, calcium deposition, and protein synthesis than without SF fibrils. Finally, the results were deduced: SFB25 demonstrated suitable performance that is promising for the bone repair of an alveolar cleft defect.

Parametric Design of Hip Implant With Gradient Porous Structure

Patients who has been implanted with hip implant usually undergo revision surgery. The reason is that high stiff implants would cause non-physiological distribution loadings, which is also known as stress shielding, and finally lead to bone loss and aseptic loosening. Titanium implants are widely used in human bone tissues; however, the subsequent elastic modulus mismatch problem has become increasingly serious, and can lead to stress-shielding effects. This study aimed to develop a parametric design methodology of porous titanium alloy hip implant with gradient elastic modulus, and mitigate the stress-shielding effect. Four independent adjustable dimensions of the porous structure were parametrically designed, and the Kriging algorithm was used to establish the mapping relationship between the four adjustable dimensions and the porosity, surface-to-volume ratio, and elastic modulus. Moreover, the equivalent stress on the surface of the femur was optimized by response surface methodology, and the optimal gradient elastic modulus of the implant was obtained. Finally, through the Kriging approximation model and optimization results of the finite element method, the dimensions of each segment of the porous structure that could effectively mitigate the stress-shielding effect were determined. Experimental results demonstrated that the parameterized design method of the porous implant with gradient elastic modulus proposed in this study increased the strain value on the femoral surface by 17.1% on average. Consequently, the stress-shielding effect of the femoral tissue induced by the titanium alloy implant was effectively mitigated.

An in silico model predicts the impact of scaffold design in large bone defect regeneration

Large bone defects represent a clinical challenge for which the implantation of scaffolds appears as a promising strategy. However, their use in clinical routine is limited, in part due to a lack of understanding of how scaffolds should be designed to support regeneration. Here, we use the power of computer modeling to investigate mechano-biological principles behind scaffold-guided bone regeneration and the influence of scaffold design on the regeneration process. Computer model predictions are compared to experimental data of large bone defect regeneration in sheep. We identified two main key players in scaffold-guided regeneration: (1) the scaffold surface guidance of cellular migration and tissue formation processes and (2) the stimulation of progenitor cell activity by the scaffold material composition. In addition, lower scaffold surface-area-to-volume ratio was found to be beneficial for bone regeneration due to enhanced cellular migration. To a lesser extent, a reduced scaffold Young's modulus favored bone formation. STATEMENT OF SIGNIFICANCE: 3D-printed scaffolds offer promising treatment strategies for large bone defects but their broader clinical use requires a more thorough understanding of their interaction with the bone regeneration process. The predictions of our in silico model compared to two experimental set-ups highlighted the importance of (1) the scaffold surface guidance of cellular migration and tissue formation processes and (2) the scaffold material stimulation of progenitor cell activity. In addition, the model was used to investigate the effect on the bone regeneration process of (1) the scaffold surface-area-to-volume ratio, with lower ratios favoring more bone growth, and (2) the scaffold material properties, with stiffer scaffold materials yielding a lower bone growth.

Improving the Stability of a Hemipelvic Prosthesis Based on Bone Mineral Density Screw Channel and Prosthesis Optimization Design

In pelvic reconstruction surgery, the hemipelvic prosthesis can cause significant changes in stress distribution due to its high stiffness, and its solid structure is not suitable for osseointegration. The purpose of this study was to identify a novel bone mineral density screw channel and design the structure of the prosthesis so as to improve the distribution of stress, promote bone growth, and enhance the biomechanical properties of the prosthesis. The mechanical characteristics of bone mineral density screw and traditional screw were compared by finite element analysis method, and redesigned by topology optimization. The direction of the newly proposed screw channel was the posterolateral entrance of the auricular surface, ending at the contralateral sacral cape. Compared to the original group, the maximum stress of the optimized prosthesis was decreased by 24.39%, the maximum stress of the sacrum in the optimized group was decreased by 27.23%, and the average strain energy density of the sacrum in the optimized group was increased by 8.43%. On the surface of screw and connecting plate, the area with micromotion more than 28 μm is reduced by 12.17%. On the screw surface, the area with micromotion more than 28 μm is reduced by 22.9%. The newly determined screw channel and optimized prosthesis design can effectively improve the biomechanical properties of a prosthesis and the microenvironment of osseointegration. This method can provide a reference for the fixation of prostheses in clinical pelvic reconstruction.

Selective Laser Melting Fabrication of Porous Ti6Al4V Scaffolds With Triply Periodic Minimal Surface Architectures: Structural Features, Cytocompatibility, and Osteogenesis

The relationship between pore architecture and structure performance needs to be explored, as well as confirm the optimized porous structure. Because of the linear correlation between constant C and pore architecture, triply periodic minimal surface (TPMS) based porous structures could be a controllable model for the investigation of the optimized porous structure. In the present work, three types of TPMS porous scaffolds (S, D and G) combined with four constants (0.0, 0.2, 0.4 and 0.6) were designed, and built successfully via the selective laser melting (SLM) technology. The designed feature and mechanical property of porous scaffolds were investigated through mathematical method and compression test. And the manufactured samples were co-cultured with rMSCs for the compatibility study. The results indicated that the whole manufacturing procedure was good in controllability, repeatability, and accuracy. The linear correlation between the porosity of TPMS porous scaffolds and the constant C in equations was established. The different TPMS porous scaffolds possess the disparate feature in structure, mechanical property and cell compatibility. Comprehensive consideration of the structure features, mechanical property and biology performance, different TPMS structures should be applied in appropriate field. The results could guide the feasibility of apply the different TPMS architectures into the different part of orthopedic implants.

Preparation and Drug Release Profile of Chitosan-Siloxane Hybrid Capsules Coated with Hydroxyapatite

Chitosan is a cationic polymer that forms polymerized membranes upon reaction with anionic polymers. Chitosan−carboxymethyl cellulose (CMC) capsules are drug delivery carrier candidates whose mechanical strength and permeability must be controlled to achieve sustained release. In this study, the capsules were prepared from chitosan−γ-glycidoxypropyltrimethoxysilane (GPTMS)−CMC. The mechanical stability of the capsules was improved by crosslinking the chitosan with GPTMS. The capsules were then coated with hydroxyapatite (HAp) by alternately soaking them in calcium chloride solution and disodium hydrogen phosphate solution to prevent rapid initial drug release. Cytochrome C (CC), as a model drug, was introduced into the capsules via two routes, impregnation and injection, and then the CC released from the capsules was examined. HAp was found to be deposited on the internal and external surfaces of the capsules. The amount of CC introduced, and the release rate were reduced by the HAp coating. The injection method was found to result in the greatest CC loading.

Additively Manufactured Multilevel Voronoi-Lattice Scaffolds with Bonelike Mechanical Properties

Irregular porous scaffold through Voronoi tessellation based on global modeling demonstrated randomness to a certain degree and susceptibility to producing large processing deviations. A modeling method for new types of scaffolds based on periodic arrays of Voronoi unit cell was proposed in this study. These porous scaffolds presented controllable local cells and satisfactory mechanical properties. The topological structure of the Voronoi unit cell was controlled using three independent cell design factors (Voronoi polyhedron volume V, face-centered scaled factor F₁, and body-centered scaled factor F₂), and multilevel Voronoi-lattice scaffolds were constructed on the basis of periodic arrays of the Voronoi unit cell. Compressive test and simulation were combined to quantify the mechanical properties of scaffolds. The regression equations were established using the response surface method (RSM) to determine relationships between Voronoi unit cell design factors and structural characteristic parameters and mechanical properties. The same trends were observed in stress-strain curves of the compressive test and simulation. The mechanical properties of scaffolds can be appropriately quantified via simulation. Regression equations based on RSM can properly predict the structural characteristic parameters and mechanical properties of the scaffold. Compared with V, F₁ and F₂ exerted a stronger influence on the structural characteristic parameters and mechanical properties of the scaffold. The modeling method of the multilevel Voronoi-lattice scaffold based on the Voronoi unit cell was proposed in this study to design the porous scaffold and meet the requirements of human bone morphology, mechanical properties, and actual manufacturing by adjusting factors V, F₁, and F₂. The proposed method can provide a feasible strategy for designing implants with suitable and similar morphologies and mechanical properties to cancellous bone.

3D-Printed Tubular Scaffolds Decorated with Air-Jet-Spun Fibers for Bone Tissue Applications

The fabrication of instructive materials to engineer bone substitute scaffolds is still a relevant challenge. Current advances in additive manufacturing techniques make possible the fabrication of 3D scaffolds with even more controlled architecture at micro- and submicrometric levels, satisfying the relevant biological and mechanical requirements for tissue engineering. In this view, integrated use of additive manufacturing techniques is proposed, by combining 3D printing and air-jet spinning techniques, to optimize the fabrication of PLA tubes with nanostructured fibrous coatings for long bone defects. The physicochemical characterization of the 3D tubular scaffolds was performed by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, profilometry, and mechanical properties. In vitro biocompatibility was evaluated in terms of cell adhesion, proliferation, and cell–material interactions, by using human fetal osteoblasts to validate their use as a bone growth guide. The results showed that 3D-printed scaffolds provide a 3D architecture with highly reproducible properties in terms of mechanical and thermal properties. Moreover, nanofibers are collected onto the surface, which allows forming an intricate and interconnected network that provides microretentive cues able to improve adhesion and cell growth response. Therefore, the proposed approach could be suggested to design innovative scaffolds with improved interface properties to support regeneration mechanisms in long bone treatment.

Evaluation of the Equivalent Mechanical Properties of Lattice Structures Based on the Finite Element Method

Lattice structures have excellent mechanical properties and can be designed by changing the cellular structure. However, the computing scale is extremely large to directly analyze a large-size structure containing a huge number of lattice cells. Evaluating the equivalent mechanical properties instead of the complex geometry of such lattice cells is a feasible way to deal with this problem. This paper aims to propose a series of formulas, including critical structural and material parameters, to fast evaluate the equivalent mechanical properties of lattice structures. A reduced-order model based on the finite element method and beam theory was developed and verified by comparing it with the corresponding full model. This model was then applied to evaluate the equivalent mechanical properties of 25 types of lattice cells. The effects of the material Young's modulus and Poisson's ratio, strut diameter, cell size, and cell number on those equivalent mechanical properties were investigated and discussed, and the linear relationship with the material parameters and the non-linear relationship with the structural parameters were found. Finally, a series of analytical-fitting formulas involving the structural and material parameters were obtained, which allows us to fast predict the equivalent mechanical properties of the lattice cells.