Solid Struts Research Articles

Structure-property relationships of polydisperse open-cell foams: Application to melamine foams

The melamine foam presents a unique microstructure characterized by an interconnected network of solid struts, which form the edges and faces of high porosity open cells. This study investigates the influence of pore size distribution on acoustic properties for three commercially available melamine foams. Based on the measured transport parameters, a top-down approach is employed to determine the equivalent Kelvin-cell size corresponding to each transport parameter. The differences found in these equivalent pore sizes indicate that the mono-size model is not suitable for these materials, a difference from which a quantitative estimate of the level of polydispersity can be deduced (using macro-scale information). The polydispersity was confirmed from experimental evidence at micro-scale from the analysis of SEM images. Moreover, the measurements collected at micro-scale (average pore size and its standard deviation) can be used as input data to determine the transport and sound absorbing behavior of melamine foam samples from structure-property relationships available for open cell microstructures. This work provides evidence that the polydispersity of melamine foams should be taken into account to obtain an accurate and consistent picture of microstructure and transport properties of such open cell high porosity foams.

Characterization of the structural features of Ti-6Al-4V hollow-strut lattices fabricated by laser powder bed fusion

Hollow-strut metal lattices are novel cellular materials. Compared to their solid-strut counterparts, their powder bed fusion additive manufacturing (PBF-AM) features remain largely uninvestigated. This work focuses on characterizing the hollow-strut internal channel and nodal profiles, the defects and microstructures of the hollow-strut thin walls, and the inner surface conditions of the LPBF-manufactured body-centred cubic (BCC) Ti-6Al-4V hollow-strut lattices with different relative densities. BCC lattices are selected because of the low inclination angle (35.26°) of their constituent struts. These low-inclination hollow struts are designed using a recent model developed for PBF of inclined solid struts, together with considerations to prevent powder occlusion and ensure easy removal of powder particles. Detailed characterization indicates that our design considerations resulted in high-quality hollow-strut BCC Ti-6Al-4V lattices, which provide useful design insights for PBF-AM of hollow-strut metal lattices. In terms of microstructure, the Ti-6Al-4V hollow-strut thin walls (≤ 0.5 mm thick) exhibited different microstructures compared with Ti-6Al-4V solid struts, due to the heat accumulation effect in the inner channels. The implications are discussed for in-situ microstructure control.

Superior Lightness-Strength and biocompatibility of bio-inspired heterogeneous glass sponge Ti6Al4V lattice structure fabricated via laser powder bed fusion

Ti6Al4V lattice structures (LSs) have great potentials in medical implants due to their excellent biocompatibility and high strength-to-weight ratio. This paper investigates the manufacturability and performance of unique Ti6Al4V heterogeneous glass sponge (GS) LSs fabricated via laser powder bed fusion (LPBF). Compared with the commonly used LSs, including Cross, body-centered cubic (BCC), Diamond and octet-truss (OCT), Ti6Al4V GS LSs exhibit the strongest compressive strength and energy absorption ability of 58 MPa and 23.84 J/cm3, respectively. Finite element (FE) models are established to evaluate the macroscopic deformation, microscopic stress and strain evolution in the solid struts of five different LSs. Local plastic stresses are found to generate near the nodes of Cross, BCC, Diamond and OCT LSs, thus forming plastic hinges, while the GS LSs can evenly transfer local plastic stresses to the grid-like rods of each layer, eventually showing a uniform stress distribution. Moreover, all the LSs are featured with satisfactory biocompatibility concerning cytotoxicity, cell proliferation, and cell attachment. The results indicate that the Ti6Al4V GS LSs can address the conflict between lightness and strength simultaneously, thus achieving excellent energy absorption performance, compressive properties and great biocompatibility, endowing it with tremendous application potential in the field of medical implants.

Compressive Behavior of Various BCC Lattice Structure

The lattice structures are a particular type of structures made by the multiply of a unit cell. In addition, their structure is close to some physiological tissues and bone structure, which can allow their use to develop prostheses needed to the rehabilitation or replacement of a body part. Lattice structures are widely used in various engineering applications due to their high weight-to-strength ratio and exceptional energy absorbing performance. The feasibility of using different base materials to fabricate these cellular structures with complex geometries has been significantly widen with the development of additive manufacturing (AM) technology. Additive manufacturing in particular metal selective laser melting (SLM) processes are rapidly being industrialized. In this work, samples with different lattice structures were manufactured by SLM technique using CoCr powder alloy. Compression tests were carried out to characterize their mechanical behavior. Starting from a BCC lattice cell measuring 5x5x5mm and 1mm diameter of the strut, were designed using Catia V5 R19 software. The BCC lattice unit cell consists of 4 solid struts with circular cross-section by which they intersected at 45°angle and modify by adding radius at the intersection of all four struts, furthermore the empty space is filled with BCC cell to increase the stiffens of the structure. The BCC cell was duplicate in three directions (X, Y, Z) measuring 20mm in each direction. To obtain the final part the BCC structure ware intersected with a cylindrical part measuring 20mm in Z direction, 15mm diameter and 1mm wall thickness, resulting a cylindrical part with three different BCC lattice structure inside.

Relationship between topological structures and mechanical properties of artificially architected SiC cellular ceramics: Experimental and numerical study

Due to their topological superiority, the architected materials facilitate the improvement of the physical and mechanical properties of cellular materials. With the progress of additive manufacturing technologies, the fabrication of architected silicon carbide (SiC) cellular ceramics has become achievable. This study focuses on the indirect additive manufacturing method of SiC cellular ceramics consisting of 3D printing, replication, and reaction-bonded sintering. To study the impact of the topology on the mechanical performance, three strut-based unit cell structures and stochastic foam with robust solid struts were experimentally and numerically studied. Results showed that the hexahedron structure has the highest compression strength, the tetrakaidecahedron structure has the highest flexural strength, while the regular structures have higher mechanical performance than the stochastic foam. The deformation mechanisms of the topologies under the compression load indicated that the hexahedron, tetrakaidecahedron, and stochastic foam favor the bending-dominated deformation mode, while the octet favors the stretching-dominated deformation mode.

Biological response of 3D-printed β-tricalcium phosphate bioceramic scaffolds with the hollow tube structure

It is a large clinical challenge to repair critical-size bone defects, and vascularization in the early stage is of vital importance in bone regeneration. In recent years, 3D-printed bioceramic is a kind of common bioactive scaffold for repairing bone defects. However, conventional 3D-printed bioceramic scaffolds consist of stacked solid struts with low porosity, which limits the ability of angiogenesis and bone regeneration. The hollow tube structure can induce endothelial cells to build the vascular system. In this study, β-tricalcium phosphate (β-TCP) bioceramic scaffolds containing the hollow tube structure were prepared with digital light processing-based 3D printing strategy. The physicochemical properties and osteogenic activities of prepared scaffolds could be precisely controlled by adjusting the parameters of hollow tubes. Compared with solid bioceramic scaffolds, such scaffolds could significantly improve the proliferation and attachment activity of rabbit bone mesenchymal stem cells in vitro, and facilitate early angiogenesis and subsequent osteogenesis in vivo. Therefore, β-TCP bioceramic scaffolds with the hollow tube structure possess great potential application for the treatment of critical-size bone defects.

Mechanical characterization of additively-manufactured metallic lattice structures with hollow struts under static and dynamic loadings

Inspired by the natural hollow structures, periodic lattice structures composed of hollow struts and spheres were designed and fabricated by selective laser melting (SLM) process with 316L stainless steel. Two architecture configurations with Body-Centered Cubic (BCC) and Face-Centered Cubic (FCC) symmetry were taken into consideration. Finite element (FE) simulations based on representative volume element (RVE) models and cell-assembly models were conducted to investigate the elastic response and large deformation behavior of the hollow lattice materials, respectively. Afterwards, compression experiments were carried out on an electronic universal machine and a drop hammer (DH) system to explore the quasi-static and dynamic mechanical response of the lattice specimens. The complete deformation evolutions of the lattice samples under different loading velocities were captured through high-resolution photography and inspected by the digital imaging correlation (DIC) analysis. Both the experimental research and numerical simulations demonstrated that the hollow beam cross-sections contributed to the stable crushing response of the proposed lattice structures under either quasi-static or dynamic compression. Accordingly, the post-yield behavior of the tested lattice structures was quite smooth without any fluctuations. Meanwhile, the specific strength and energy absorption of the hollow lattice structures were found to be superior to many existed lattice materials with solid struts, and comparable with the reported triply periodic minimal surface (TPMS) lattice structures. Finally, the effect of the geometric characteristic parameters on the specific mechanical properties of the lattice structures was discussed according to the supplemental analysis by numerical simulations.

Additive manufacturing of Ti-6Al-4V horizontal hollow struts with submillimetre wall thickness by laser powder bed fusion

Efficient lattice unit cell topologies often necessitate the manufacture of unsupported horizontal struts. The fabrication of unsupported horizontal struts by laser powder bed fusion (LPBF) is inherently challenging, where the associated research data is limited for solid or dense cross-sections while no data exists for hollow struts. By examining LPBF-fabricated Ti-6Al-4V hollow struts of various diameters and wall thicknesses over increasing span lengths, a robust LPBF additive manufacturability range has been established for Ti-6Al-4V hollow struts. To achieve successful fabrication, three laser scan strategies were explored, proposed, and systematically compared. Horizontal solid struts and vertical hollow struts of equivalent diameters (and wall thickness) were similarly assessed over the same span lengths as comparators to quantify the manufacturability. This research provides previously unavailable design data, required for LPBF additive manufacturing of lattices with horizontal strut elements.

Heat transfer in BCC lattice materials: Conduction, convection, and radiation

Research studies have recently been conducted on heat transfer in architected materials. As a type of rationally-designed lightweight material, lattices have received much attention in the past few years due to their multifunctional properties, mainly realized by the application of 3D printing techniques. In the present research, fluid flow and conduction, convection, and radiation heat transfer in three-dimensional periodic BCC lattices, as a topologically cubic example among a myriad of cellular architectures, are studied for a wide range of porosity (0.7–0.99) and Reynolds numbers (1–150) via a CFD analysis. The steady and incompressible flow of cool fluid with constant thermophysical properties inside a unit cell or an assembly of unit cells is simulated using the Fluent software. First, the hydrodynamic behavior of the fluid flow in the unit cell without a thermal gradient is studied. In the absence of radiation, conduction and convection heat transfer are explored under two different thermal conditions, namely Constant temperature at solid struts and Constant heat release from solid struts. The numerical results show that cell temperature increases for the constant temperature boundary condition and decreases for the constant heat release when the cell porosity decreases at the same Reynolds number. By considering radiation mechanism via the Discrete Ordinates Method, it is observed that radiative thermal conductivity increases by increasing the porosity. The increase, linearly correlated with the cell size, slightly enhances by increasing the solid radiative emission coefficient and the applied temperature difference. At lower porosities, the heat conduction, and at higher porosities, the radiation heat transfer plays a significant role in the effective thermal conductivity. At the average cell temperature of 1800 K, the ratio of radiative thermal conductivity to the effective thermal conductivity is 95% for the porosity of 0.99 and is 12% for the porosity of 0.7. After examining all three modes of heat transfer at the constant heat release thermal condition, it is found that the temperature of solid struts increases by decreasing the Reynolds number, leading to an increase of the ratio of radiation heat transfer to the total heat transfer (the ratio rises six times as the Reynolds number decreases from 150 to 1.5625 for the porosity of 0.99). For the constant heat release thermal condition, radiation heat transfer in BCC lattices can not be ignored when the porosity is high or the thermal conductivity of constitutive solid and the flow Reynolds number are low.

Using a simple rope-pulley system that mechanically couples the arms, legs, and treadmill reduces the metabolic cost of walking

BackgroundEmphasizing the active use of the arms and coordinating them with the stepping motion of the legs may promote walking recovery in patients with impaired lower limb function. Yet, most approaches use seated devices to allow coupled arm and leg movements. To provide an option during treadmill walking, we designed a rope-pulley system that physically links the arms and legs. This arm-leg pulley system was grounded to the floor and made of commercially available slotted square tubing, solid strut channels, and low-friction pulleys that allowed us to use a rope to connect the subject’s wrist to the ipsilateral foot. This set-up was based on our idea that during walking the arm could generate an assistive force during arm swing retraction and, therefore, aid in leg swing.MethodsTo test this idea, we compared the mechanical, muscular, and metabolic effects between normal walking and walking with the arm-leg pulley system. We measured rope and ground reaction forces, electromyographic signals of key arm and leg muscles, and rates of metabolic energy consumption while healthy, young subjects walked at 1.25 m/s on a dual-belt instrumented treadmill (n = 8).ResultsWith our arm-leg pulley system, we found that an assistive force could be generated, reaching peak values of 7% body weight on average. Contrary to our expectation, the force mainly coincided with the propulsive phase of walking and not leg swing. Our findings suggest that subjects actively used their arms to harness the energy from the moving treadmill belt, which helped to propel the whole body via the arm-leg rope linkage. This effectively decreased the muscular and mechanical demands placed on the legs, reducing the propulsive impulse by 43% (p < 0.001), which led to a 17% net reduction in the metabolic power required for walking (p = 0.001).ConclusionsThese findings provide the biomechanical and energetic basis for how we might reimagine the use of the arms in gait rehabilitation, opening the opportunity to explore if such a method could help patients regain their walking ability.Trial registration: Study registered on 09/29/2018 in ClinicalTrials.gov (ID—NCT03689647).

An approach to determine radiative properties of solid struts of open-cell foams by pore scale identification from macro scale measurements

Open-cell foams consisting of interconnected struts are widely used in thermal applications such as volumetric solar receivers. The thermal performance of foams strongly relies on their radiative behaviors which intrinsically depends on the radiative properties of struts. This study proposed a feasible approach to determine the radiative properties of solid struts by a pore scale identification from a macro scale measurement. First, the normal-hemispherical transmittance and reflectance spectra of two nickel foams were measured by an experimental system. Second, a pore scale forward calculation was conducted by a combination of Monte Carlo Ray-tracing method and real foam structures obtained from micro-computed tomography technique. Last, an Adaptive Particle Swarm Optimization algorithm was adopted to retrieve the spectral reflectivity and specularity of nickel struts from the measured spectra. The results show that it is unreasonable to assume the reflection behavior of strut surface simply as either specular or diffused, and also, it is unreliable to assign the reflectivity of strut surface directly by Fresnel's law. Within the investigated wavebands 0.4–2.2 μm, the average reflectivity of nickel struts is 12% lower than that of a nickel mirror. The proportion of specular reflection at nickel strut surface is between 37%–52%, almost increasing with wavelengths.

Designing of Steel CHS Columns Showing Maximum Compression Resistance

The paper deals with a shape optimisation procedure of steel, compressed bars. Circular hollow sections (CHS) of variable cross sections and variable wall thickness are taken into account. The proposed procedure for designing of steel rods exhibiting maximum compression resistance is effective and possible to use in engineering practice. The advantage of the proposed shape of the bar is that it allows to increase the value of its load carrying capacity, i.e. it ensures the transfer of a higher value of compressive force than similar, solid struts of the same mass and length. The extent of the increase in the load capacity relative to the load capacity of the reference solid, cylindrical bar depends on the slenderness of the reference bar and ranges from 60% to 170%. Due to this very beneficial fact, it can be used wherever it is required to maintain a certain stiffness and an increased value of compressive force is desired, as well as in constructions where it is necessary to reduce weight while maintaining the adopted mechanical parameters, e.g. values of load bearing capacity. Final results achieved in the research were presented in the form of the flow chart allowing to design the compressed columns of optimum shape.

Experimental study of internal forces and moments generated by strut injection in a supersonic cross-flow in a C-D nozzle

An experimental investigation was conducted to obtain wall pressure distribution in a convergent divergent nozzle with a strut inserted through the diverging wall and to find out the possible generation of side force. The strut inserted through the nozzle wall represented an active control method for thrust vector control. Laboratory tests were carried out to examine whether this type of strut injection would be effective and serve as an alternative thrust vector control method for the other widely used such as secondary injection thrust vector control. The nozzle model used in the experiments had a design Mach number of 1.84 with a corresponding area ratio of 1.48. The solid strut which was inserted through the diverging wall of the nozzle had a square cross section. Experiments were conducted for identifying three different strut positions from the nozzle throat, i.e. at Ld/3, Ld/2, and 2Ld/3, where Ld was the length of the diverging section of the nozzle. At each strut position, the strut height was varied and the maximum strut height corresponded to the radius of the local cross section where the strut was inserted. The nozzle was operated at overexpansion conditions such as nozzle pressure ratios of 3.4 and 5. The strut side and the opposite side of the nozzle wall had eight wall pressure tappings each and the wall pressure data were obtained using a pressure scanner. The asymmetrical pressure distributions of the strut side and the non-strut side (opposite side) of nozzle wall were used for the calculation of side force and pitching moment in the nominal plane through the wall pressure ports of both sides. The calculated two-dimensional side force, axial force, and pitching moment coefficients were plotted against strut height at each strut position from the nozzle throat. From the experimental data and calculations, it was found that the axial force varied more or less linearly with strut height irrespective of the strut position. However, the side force and pitching moments varied nonlinearly with strut height and the nature of variation of the two was similar. Both the side force and pitching moment exhibited maximum and minimum values at two specific values of the strut height. The change in the strut position did not alter the nature of the above variations and the strut height values for maximum and minimum. The magnitude of the side force was found to be 1–10% of the axial force generated as a fluid dynamic pressure drag. Both positive and negative side force and pitching moments were produced with increase in the strut height.

Mechanical properties and failure behaviour of architected alumina microlattices fabricated by stereolithography 3D printing

Alumina microlattices with solid struts and different topologies were fabricated by the stereolithography 3D printing method. Mechanical analysis shows that specific stiffness and strength were highest for Simple Cubic lattices, followed by Octet Truss, then Kelvin Cell lattices. The mechanical properties followed Ashby's power law well at small relative densities (≤ 0.3), but deviated from it at higher relative densities due to the increased importance of joint deformation. Failure in the Simple Cubic lattices proceeded in a column-by-column manner from the boundaries inwards to the centre, while fracture in Octet Truss and Kelvin Cell lattices took place predominantly along the diagonal (111) and (110) planes respectively. The underlying mechanism controlling these mechanical responses has been thoroughly discussed using finite element simulation analysis. Because lattice strength was limited by the tensile strength of alumina, which was an order of magnitude lower than its compressive strength, the microlattices were weaker than Ashby's predictions. Nevertheless, they were still able to exhibit better specific modulus and strength than many current engineering materials, as well as some degree of ductility in the form of pseudoplastic strains (0.1 % - 0.5 %).

Elastic response of hollow truss lattice micro-architectures

Elastic meta-materials, which we will treat herein as synonymous with elastic micro-architected materials, derive their unique combination of properties from the fine scale geometry of their solid and void regions. Recent advances in additive manufacturing have made the fabrication of such micro-architected materials feasible, and have driven interest in their properties. We consider the class of elastic meta-materials whose micro-architectures are composed of a network of straight struts connected at nodes arranged within a repeating unit cell; the octet truss is one well-known example of such truss lattices. Heretofore, the majority of work characterizing such truss lattices has considered solid struts and has been based on rod theory, a simplification of continuum elasticity which is accurate in the limit of low relative densities. In this paper, we use full continuum theory, solved with finite element analysis on adaptively refined meshes, to characterize the elastic performance of seven truss lattices with cubic geometric symmetry, and whose struts and nodes are hollow; we consider a wide range of strut wall thicknesses and truss relative densities. Varying the wall thickness provides an additional dimension of control, so that stiffness and anisotropy can, to an extent, be decoupled from the relative density of a given truss lattice. We show that a truss’ stiffness can be increased at fixed relative density, with bend-dominated truss lattices showing significantly greater improvement than stretch-dominated designs. Increases in stiffness by a factor of greater than five are observed, and increases by a factor of 100 or more are obtainable. Bend-dominated structures with hollow struts can be found that are stiffer than stretch-dominated ones at nearly all relative densities, contradicting a common rule of thumb. For some trusses, including the octet truss, choosing the wall thickness appropriately allows one to obtain isotropic response over a large range of volume fractions. We use topology optimization to find maximally stiff multiscale structures comprised of micro-architected materials and find that all the trusses we consider perform similarly, with anisotropic trusses resulting in slightly stiffer structures for a given load.

Study on mechanical properties of a hierarchical octet-truss structure

A hierarchical octet-truss lattice material was proposed by replacing the solid strut of the octet-truss structure with a tubular re-entrant structure. The tubular re-entrant structure was constructed via a sheet rolling operation on a planar hexagonal re-entrant structure. Hierarchical octet-truss lattice materials with different relative densities were fabricated via additive manufacturing by adjusting the re-entrant structure rib thickness, and their mechanical properties were studied and compared with the finite element model predictions and shown to be in excellent agreement with each other. The effects of hierarchical ranks on the mechanical properties of structures were also discussed. Results showed that the Poisson’s ratio of the hierarchical octet-truss structure is approximately 0.3 without being affected by the introduction of structural hierarchy. The stress-strain relationships of the hierarchical octet-truss structures exhibit dual-peak characteristic. The lattice stiffness, compressive strength, and energy absorption capacity of the models increased with an increasing rib thickness of the re-entrant structure of the first-order hierarchical octet-truss structure, and the maximum value of specific energy absorption (SEA) was achieved when the relative density is 30.2%. The second-order hierarchical octet-truss structure exhibited lower collapse stress value, and a shorter stress plateau region than those of the zeroth and first-order hierarchical octet-truss structures.

Silver nanoplate-pillared mesoporous nano-clays for surface enhanced raman scattering

Due to characteristic properties of silver (Ag), Ag nanoparticles have attracted unprecedented attention in various scientific fields such as sensors, catalysts, antibacterial materials, and so on. To obtain tailor-made functionalities of Ag nanoparticles with desired physicochemical properties, proper fabrication process is needed to control their sizes, morphologies or arrangements by hybridization with different components, immobilization on solid struts, and etc. Herein, we suggest a facile synthetic route to obtain Ag-pillared mesoporous nanoclays through simultaneous crystal growth and arrangement of Ag nanoplates with the help of a 2-dimensional inorganic template. To obtain Ag-pillars, layered silver-thiolate self-assembly was exfoliated to monolayers (Ag precursor) and then in-situ hybridized with layered double hydroxide in a layer-by-layer manner. Through reductive calcination, silver thiolate transformed to Ag-pillars which grew in nanoplate morphology with well-arrangement in confined space of nanoclays. Crystal structure, morphology, and pore structure of Ag-pillars in nanoclays were systematically characterized. Surface enhanced Raman scattering effect of arranged Ag-pillars on metal oxide substrate obtained upon calcination was also investigated with rhodamine 6G.

Mechanical properties of AlSi10Mg lattice structures fabricated by selective laser melting

Al alloy porous structures have potential application in industries such as light aerospace and some heat exchanger products. A particular advantage of selective laser melting (SLM) over conventional manufacturing processes is its ability to fabricate periodic lattice structures with controllable volume fractions. In this paper, 12 samples of AlSi10Mg periodic diamond lattice structures with interconnected high porosity and volume fractions from 4.5% to 22.5% were fabricated by selective laser melting. At the same time, the optimized radius at the node is introduced to reduce stress concentration. The as-built AlSi10Mg lattice was well formed without large appeared voids and cracks. A full-scale three-dimensional finite element (FE) model was established to evaluate the macroscopic deformation of the lattice structures and the microscopic stress and strain evolution in the solid struts. Local plastic stresses were found to generate near the nodes, thus forming plastic hinges, while most of the struts remain elastic. Evolution under compressive loads determines the mechanical properties of the diamond lattice structures and failure mechanism.

Experimental Study of the Wall Pressure Distribution in a Convergent-Divergent Nozzle with Strut Injection

Wall pressure measurements are made in a convergent-divergent nozzle with strut injection to estimate the internal forces and moments. The strut facing the flow was of rectangular cross section and is placed at two thirds of the diverging length of the nozzle from the throat. The design exit Mach number of the nozzle is 1.84. The strut height varied at constant internal total pressure of 690 kPa. Experiments were conducted to explore the possibility of using a solid strut as an alternative to secondary fluid injection for thrust vector control. The wall pressure distribution of the nozzle is studied to interpret the flow interaction with the strut. The calculations based on the experimental data show that the presence of the strut and a variation in its height produce significant variations in side force and pitching moment which would be useful for thrust vector control.

Three-Dimensional Printing of Scaffolds with Synergistic Effects of Micro–Nano Surfaces and Hollow Channels for Bone Regeneration

The 3D printing technology with unique strategies for accurate fabrication of biomaterials in regenerative medicine has been widely applied in bone regeneration. However, the traditional 3D printing scaffolds are only stacked by solid struts without any hollow channel structures, which limits the new bone tissue formation. In this study, a special 3D scaffold with hollow channels and a micro-nano surface was prepared by a modified 3D printing strategy combined with the hydrothermal treatment approach. By regulating the reaction solution of hydrothermal treatment, the micro-nano structures formed on the surface of scaffolds can be successfully controlled. Moreover, the scaffolds have the ability to facilitate the attachment and proliferation of BMSCs after culturing for 1, 3, and 7 days in vitro. Interestingly, the in vivo results demonstrated that the hollow channels and the micro-nano surface present synergistic effects on bone regeneration. They both boost the new bone formation in femur defects in rabbits for 12 weeks after operation. The study demonstrates a 3D scaffold with special surface microstructures and hollow struts that can overcome the shortages of most traditional scaffolds and meanwhile improve the bioactivity of biomaterials for bone tissue engineering.