Inferior Mechanical Properties Research Articles

Applied Compressive Strain Governs Hyaline-like Cartilage versus Fibrocartilage-like ECM Produced within Hydrogel Constructs.

The goal of cartilage tissue engineering (CTE) is to regenerate new hyaline cartilage in joints and treat osteoarthritis (OA) using cell-impregnated hydrogel constructs. However, the production of an extracellular matrix (ECM) made of fibrocartilage is a potential outcome within hydrogel constructs when in vivo. Unfortunately, this fibrocartilage ECM has inferior biological and mechanical properties when compared to native hyaline cartilage. It was hypothesized that compressive forces stimulate fibrocartilage development by increasing production of collagen type 1 (Col1), an ECM protein found in fibrocartilage. To test the hypothesis, 3-dimensional (3D)-bioprinted hydrogel constructs were fabricated from alginate hydrogel impregnated with ATDC5 cells (a chondrogenic cell line). A bioreactor was used to simulate different in vivo joint movements by varying the magnitude of compressive strains and compare them with a control group that was not loaded. Chondrogenic differentiation of the cells in loaded and unloaded conditions was confirmed by deposition of cartilage specific molecules including glycosaminoglycans (GAGs) and collagen type 2 (Col2). By performing biochemical assays, the production of GAGs and total collagen was also confirmed, and their contents were quantitated in unloaded and loaded conditions. Furthermore, Col1 vs. Col2 depositions were assessed at different compressive strains, and hyaline-like cartilage vs. fibrocartilage-like ECM production was analyzed to investigate how applied compressive strain affects the type of cartilage formed. These assessments showed that fibrocartilage-like ECM production tended to reduce with increasing compressive strain, though its production peaked at a higher compressive strain. According to these results, the magnitude of applied compressive strain governs the production of hyaline-like cartilage vs. fibrocartilage-like ECM and a high compressive strain stimulates fibrocartilage-like ECM formation rather than hyaline cartilage, which needs to be addressed by CTE approaches.

Performance enhancement of adhesive joints of additive manufactured parts by using different types of fibre reinforcements

The main objective of this study was to investigate experimentally the mechanical performance of adhesive joints made of additive manufactured (AM) polymeric parts reinforced with different types of fibres. PLA (PolyLactic Acid) and ABS (acrylonitrile butadiene styrene) AM adherends were fabricated by fused deposition modelling (FDM). Further, natural (jute and curauá) and synthetic (glass) fibre reinforcement fabrics were laminated on the outer sides of the AM parts using an epoxy resin via compression moulding. The type of reinforcement (natural or synthetic) and the effect of the number of the layers (1 and 2 layers) on the performance of the bonded joints was studied by testing single lap joints (SLJs) bonded with an epoxy structural adhesive. It was found that the mechanical performance of adhesively bonded SLJs is improved by using different types of fibre reinforcements to the 3D printed core adherends. The failure load varied as a function of fibre type and number of layers used as reinforcement, as well as the material used for the core of the adherends. The ABS SLJs presented lower strength compared to PLA SLJs, mainly due to the ABS adherend inferior mechanical properties. In addition, the PLA core specimens presented a better interface adhesion with the epoxy resin used in this study to laminate the reinforcements, when compared to the ABS core reinforced specimens. The best results in terms of improvement in failure load were obtained for the curauá fibre reinforced PLA 3D printed SLJ specimens (the average joint strength was more than 1.5 times higher than the neat-PLA SLJ specimens).

High-strength and functional nanocellulose filaments made by direct wet spinning from low concentration suspensions

Continuous filaments obtained through the wet spinning of nanocellulose have promising mechanical properties with sustainable features. To guarantee proper spinnability for wet spinning, freshly made cellulose nanofibril (CNF) suspension needs to be concentrated to have a concentration above 1 wt%, resulting in energy- and time-consuming, and inferior mechanical properties of the final filaments owing to decreasing the CNF alignment against shear flows. In this study, a CNF spinning suspension at a low concentration (0.4 wt%) can be used right after the fibrillation process without further treatments. The effects of the concentration and re-concentrating process are studied by carefully characterizing the rheological behavior and filament solidification processes, which provides more fundamental understandings on the spinnability and CNF network formation of such colloidal CNF suspensions. Combined with a post stretching process, the final dried CNF filaments have superior mechanical properties with Young's modulus and tensile strength of 35 GPa and 567 MPa, surpassing most literature data. Moreover, different functional particles can be easily incorporated to prepare functional filaments. With facile preparation and superior properties, these CNF filaments may be suitable for advanced composite filler and special textile applications.

Effect of TiO2 on mechanical and thermal properties of Al2O3-based coating via atmospheric plasma spraying

ABSTRACT In this study, Al2O3-based coatings with varying TiO2 contents (0, 3, 13, and 40%) were fabricated using atmospheric plasma spraying technique. To compare the superiority of the samples, their mechanical (Vickers hardness and adhesion strength) and thermal properties (thermal conductivity and thermal shock resistance) were characterized. As observed, Al2O3-40%TiO2 (A-40T) coating exhibited relatively inferior mechanical properties but superior thermal insulation and thermal shock resistance at 600°C. According to the microstructure and phase analysis, this finding is attributed to the special phase, Al2TiO5, and preexisting microcracks inside the coating. Thus, A-40T manifested excellent characteristics for thermal insulation application compared with pure Al2O3 and low-TiO2 content coatings.

Evaluating the grafting of Maleic anhydride with Poly(lactic acid) (PLA) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) via batch compounding

Maleic anhydride (MA) was grafted to Poly(lactic acid) (PLA) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) at twelve different content ratios by batch compounding method. The rheology, morphology and grafting possibilities of blend components were analysed. It was found that excessive peroxide content can cause chain scission and chain shortening in the blend which produces a porous structure with inferior mechanical properties. The addition of MA increases the degradation rate of the blend. MA increased the dispersity and interfacial adhesion of PHBV phase within PLA phase.

Effect of friction stir processing on microstructural evolution and mechanical properties of nanosized SiC reinforced AA5083 nanocomposites developed by stir casting

AA5xxx alloys are widely used for different parts of marine appliances of low to moderate level of strength. However, these alloys are not suitable for high-strength marine parts because of its low mechanical strength, elastic modulus, and weld yield strength. Hence, with an aim to improve performance of these alloys for various high-strength marine components, the present study efforts to develop fine grained AA5083 alloy-based nanocomposites with uniform dispersion of nanosize SiC particles through stir casting followed by microstructural modification using friction stir processing (FSP). AA5083-SiC nanocomposites (1, 2 & 3 wt%) were produced by an indigenously designed bottom pouring stir casting setup reinforced with nanosize SiC (n-SiC, ∼80 nm) particles. Then, FSP was performed with the optimized parameters (1216 rpm rotational speed and 41 mm/min traverse speed) to modify as-cast interdendritic structures of the nanocomposites. Microstructural investigation through optical and electron microscopy (SEM-EBSD, TEM-EDS) confirmed the evolution of fine recrystallized grains with a uniform distribution of n-SiC within the matrix after the FSP. The FSP is found more advantageous to attain better grain refinement (∼50 % more) for the n-SiC reinforced composites as compared to that of the FSPed pure AA5083 alloy. The mechanical properties were found to improve up to 2 wt% reinforcement significantly as compared to the as-cast counterparts. However, because of huge agglomeration of n-SiC particles in the 3 % reinforced composite, it showed inferior mechanical properties. Tensile yield strength (YS) and average hardness were recorded to be 224 MPa and 84 HV, respectively, for the FSPed AA5083–2 wt% n-SiC nanocomposite as compared to the YS-152 MPa, hardness-75 HV for the FSPed AA5083 alloy without any reinforcement. The enhancement in the mechanical performance is attributed to the breakdown of interdendritic microstructure to evolve dynamically recrystallized fine grains (grain boundary strengthening) with uniform distribution of n-SiC particles (dispersion strengthening) and other secondary precipitate phases. Analysis of strengthening mechanisms’ contribution found to be in good agreement with the experimental YS up to 2 % reinforced nanocomposites. Fractography analysis of the tensile samples is found to correlate well in accordance with the tensile properties.

Improving the mechanical properties of mussel shell aggregate concrete by aggregate modification and mixture design

Utilization of mussel shell as a construction material has a promising application potential to meet the challenges of mussel shell wastes treatment in coastal cities. However, the inferior mechanical properties of mussel shell aggregate concrete (MSAC) has restricted its wider promotion in high performance applications due to the inferior properties of mussel shell aggregate (MSA) and the poor interface bonding behavior between MSA and mortar. To improve the mechanical properties of MSAC with a MSA replacement ratio of 30%, this study focused on the mixture proportions design of MSAC by particle size optimization of MSA and compact packing of raw materials, and the MSA modification by polymer-cement paste composite and microbial induced carbonate precipitation. Microstructure tests were conducted to provide an insight into the mechanism behind the improved mechanical properties of MSAC. The results exhibit that, both of mixture design and aggregate modification, have beneficial effects on improving the compressive strength and splitting tensile strength of MSAC. The enhancement mechanism of MSAC mechanical properties can be explained by the enhancement in the microstructure of MSAC, i.e. the increased compactness of MSA-mortar interface and the refined pore structure of mortar.

The impact of mild hypercholesterolemia on injury repair in the rat patellar tendon.

Hypercholesterolemia is associated with tendon pathology and injury prevalence. Lipids can accumulate in the tendon's extracellular spaces, which may disrupt its hierarchical structure and the tenocytes physicochemical environment. We hypothesized that the tendon's ability to repair after injury would be attenuated with elevated cholesterol levels, leading to inferior mechanical properties. Fifty wild-type (sSD) and 50 apolipoprotein E knock-out rats (ApoE-/ - ) were given a unilateral patellar tendon (PT) injury at 12 weeks old; the uninjured limb served as a control. Animals were euthanized at 3-, 14,- or 42-days postinjury and PT healing was investigated. ApoE-/ - serum cholesterol was double that of SD rats (mean: 2.12 vs. 0.99 mg/mL, p < 0.001) and cholesterol level was related to the expression of several genes after injury; notably rats with higher cholesterol demonstrated a blunted inflammatory response. There was little physical evidence of tendon lipid content or differences in injury repair between groups, therefore we were not surprised that tendon mechanical or material properties did not differ between strains. The young age and the mild phenotype of our ApoE-/ - rats might explain these findings. Hydroxyproline content was positively related to total blood cholesterol, but this result did not translate to observable biomechanical differences, perhaps due to the narrow range of cholesterol levels observed. Tendon inflammatory and healing activity is modulated at the mRNA level even with a mild hypercholesterolemia. These important initial impacts need to be investigated as they may contribute to the known consequences of cholesterol on tendons in humans.

Thermal insulation of 3D printed complex and miniaturized SiO2 aerogels at medium-high temperatures

Due to aerogel's network structure, specific surface area, and high porosity, SiO2 aerogel has excellent thermal insulation and inferior mechanical properties. It is challenging to produce micro-objects and complex-shaped objects accurately by traditional manufacturing method because of the fragile mechanical properties. Here, we use 3D printing to fabricate SiO2 aerogels. At the same time, we add opacifiers to reduce the aerogel's medium-high temperature thermal conductivity. The thermal conductivity of the SiO2 aerogel printed in the experiment is as low as 0.028 W/(m·K) at room temperature. The aerogel doped with 10 wt% SiC has the best thermal insulation at medium-high temperatures. And the 3D printed aerogel doped with 10 wt% SiC has a compression performance of 1.19 MPa, which is more than 10 times better than the usual aerogel. This paper provides a method for creating micro-objects and complex-shaped objects with excellent medium-high temperature thermal insulation using Direct Ink Writing (DIW).

Comparison of NIH 3T3 Cellular Adhesion on Fibrous Scaffolds Constructed from Natural and Synthetic Polymers.

Polymer scaffolds are increasingly ubiquitous in the field of tissue engineering in improving the repair and regeneration of damaged tissue. Natural polymers exhibit better cellular adhesion and proliferation than biodegradable synthetics but exhibit inferior mechanical properties, among other disadvantages. Synthetic polymers are highly tunable but lack key binding motifs that are present in natural polymers. Using collagen and poly(lactic acid) (PLA) as models for natural and synthetic polymers, respectively, an evaluation of the cellular response of embryonic mouse fibroblasts (NIH 3T3 line) to the different polymer types was conducted. The samples were analyzed using LIVE/DEAD™, alamarBlue™, and phalloidin staining to compare cell proliferation on, interaction with, and adhesion to the scaffolds. The results indicated that NIH3T3 cells prefer collagen-based scaffolds. PLA samples had adhesion at the initial seeding but failed to sustain long-term adhesion, indicating an unsuitable microenvironment. Structural differences between collagen and PLA are responsible for this difference. Incorporating cellular binding mechanisms (i.e., peptide motifs) utilized by natural polymers into biodegradable synthetics offers a promising direction for biomaterials to become biomimetic by combining the advantages of synthetic and natural polymers while minimizing their disadvantages.

Segmental defect healing in the presence or absence of recombinant human BMP2: Novel insights from a rat model.

This study defined and compared the course of native, impaired and growth factor-stimulated bone regeneration in a rat femoral defect model. A mid-diaphyseal defect with rigid internal fixation was surgically created in the right femur of male Fischer rats and serially analyzed over 36 weeks. Native bone regeneration was modeled using a sub-critical, 1 mm size defect, which healed uneventfully. Critical size defects of 5 mm were used to analyze impaired bone regeneration. In a third group, the 5 mm defects were filled with 11 µg of recombinant human bone morphogenetic protein 2 (rhBMP2) impregnated onto an absorbable collagen sponge, modeling its clinical use. Native bone regeneration was characterized by endochondral ossification with progressive remodeling to ultimately resemble intact femora. An endochondral response was also observed under conditions of impaired bone regeneration, but by week 8 medullary capping occurred with fibrofatty consolidation of the tissue within the defect, resembling an atrophic non-union. rhBMP2 treatment was associated with prolonged inflammatory cytokine expression and rapid intramembranous bone formation occurring with reduced expression of cartilage-associated collagens. Between weeks 4 and 36, rhBMP2-treated bones demonstrated decreased trabecular number and increased trabecular separation, which resulted in inferior mechanical properties compared with bones that healed naturally. Clinical Significance: Recombinant human bone morphogenetic protein 2 (rhBMP2) is used clinically to promote healing of long bones. Our data suggest that it drives intramembraneous ossification producing an inferior regenerate that deteriorates with time. Clinical outcomes would be improved by technologies favoring endochondral regenerative ossification.

Mechanically Strong and Thermally Insulating Polyimide Aerogel Fibers Reinforced by Prefabricated Long Polyimide Fibers.

Aerogel fibers inherit the merits of aerogel and fibrous materials, such as high porosity and satisfactory knittability, demonstrating great potential as thermal protective materials applied in harsh environments. Nevertheless, the inferior mechanical property resulting from the porous structure immensely hampers the practical application of aerogel fibers. Herein, we develop robust and thermally insulating long polyimide fiber-reinforced polyimide composite aerogel fibers (LPF-PAFs). The porous crosslinked polyimide aerogel as the sheath endows LPF-PAFs with good thermal insulation performance, while the long polyimide fibers as the core provide LPF-PAFs with superior mechanical strength. Due to the introduction of the high-strength long polyimide fibers to undertake significant stress, LPF-PAFs display outstanding strength surpassing 150 MPa without obvious mechanical performance degeneration in a wide range of temperatures from -100 to 300 °C. Moreover, the textile woven by LPF-PAFs exhibits a superior thermal insulation ability and stability to cotton textile at 200 and -100 °C, indicating its potential application in thermal protective clothing under extreme environments.

Portable solar interfacial evaporator based on polyimide nanofiber aerogel for efficient desalination

Solar vapor generation is a friendly water purification technology via efficiently utilization of natural sunlight. However, the present solar evaporation devices are impeded by high cost, inferior mechanical property, low efficiency and poor durability. Here, inspired by plant transpiration, we designed and fabricated a scalable and portable polypyrrole-modified polyimide nanofiber aerogel (PPy-PI NAG) for efficient and durable solar vapor generation. During the evaporation process, the bottom hydrophilic PI NAG with hierarchical cellular fibrous structure acts as the roots for fast water transportation, while the upper PPy layer with porous and rough surface plays as the leaves for evaporation. More importantly, the highly porous PPy-PI NAG possesses a low thermal conductivity (0.05 W m−1 K−1), which can confine the heat energy on the air–water interface, exhibiting superior heat localization effect. Under one sun illumination, the PPy-PI NAG exhibits a high average evaporation rate of 1.42 kg m−2 h−1 and achieved 99.7 % ion removal efficiency for seawater. Moreover, the PPy-PI NAG exhibits stable evaporation efficiency with continuous desalination for 15 days and compressing/folding for 1000 cycles, and can be compressed or folded into small size to the benefit of carriage or transportation, demonstrating great potential as portable solar evaporation device for personal and household evaporation systems.

Improvement of Mechanical Properties and Solvent Resistance of Polyurethane Coating by Chemical Grafting of Graphene Oxide.

Waterborne polyurethane coatings (WPU) are widely used in various types of coatings due to their environmental friendliness, rich gloss, and strong adhesion. However, their inferior mechanical properties and solvent resistance limit their application on the surface of wood products. In this study, graphene oxide (GO) with nanoscale size, large surface area, and abundant functional groups was incorporated into WPU by chemical grafting to improve the dispersion of GO in WPU, resulting in excellent mechanical properties and solvent resistance of WPU coatings. GO with abundant oxygen-containing functional groups and nanoscale size was prepared, and maintained good compatibility with WPU. When the GO concentration was 0.7 wt%, the tensile strength of GO-modified WPU coating film increased by 64.89%, and the abrasion resistance and pendulum hardness increased by 28.19% and 15.87%, respectively. In addition, GO also improved the solvent resistance of WPU coatings. The chemical grafting strategy employed in this study provides a feasible way to improve the dispersion of GO in WPU and provides a useful reference for the modification of waterborne wood coatings.

In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review.

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics.

The effects of microstructures on the mechanical performances and fracture mechanisms of boron-alloyed ferritic and martensitic stainless steels fabricated by powder metallurgy

Porosity is generally the major cause of the inferior mechanical properties of powder metallurgy (PM) steels. Boron (B) is an effective element for improving the sintering densification of PM steel via liquid phase sintering (LPS). To date, the microstructure and mechanical properties of B-alloyed PM stainless steels remain to be determined. The objective of this research was to study the influences of B on the LPS, microstructures, mechanical performances, and fracture mechanisms of PM 410L ferritic and 410 martensitic stainless steels. The roles of the Fe-based matrix, eutectic areas, and pores in the fracture behavior and mechanical properties were examined.The results showed that after 1250 °C sintering, the 0.6 wt% B additive in 410L and 410 obviously induced LPS and decreased the porosity from 8.9 vol% to less than 4 vol%. In both 410L+0.6B and 410+0.6B, the B-containing compounds were identified by electron backscatter diffraction as M2B boride with a tetragonal structure. The 0.13 wt% C additive in 410L+0.6B increased the ultimate tensile strength from 420 MPa to 843 MPa but decreased the elongation from 10.4% to 2.7% and the impact energy from 21 J to 6 J due to the transformation of the Fe-based matrix from ferrite to martensite. In the combination of fracture analyses and strain distribution as a function of tensile stress, the results indicated that in 410L+0.6B and 410+0.6B, the predominant sites for strain localization and fracture were respectively the ferritic grains and intergranular eutectic areas. Furthermore, the pores played different roles in the deformation and fracture of the two B-alloyed PM stainless steels.

Uncovering the Early Stages of Magnesium Silicate Hydrate Formation: A Nonclassical Multistep Pathway

Understanding the fundamental physicochemical processes that occur during the hydration of cementitious materials is essential for developing alternative binders that enable the partial substitution of Portland cement (PC), lowering the carbon footprint associated with the cement industry. Magnesium-silicate-hydrate (M-S-H) stands as a potential alternative binder; however, its inferior mechanical properties attributed to its nanostructure, and the high-water demand for curing, hinder the application of MgO-based cement as PC surrogate. A potential strategy to tackle these major drawbacks is based on controlling M-S-H formation from the early stages, building the properties and nanostructure of this binding phase from its basic building units. The present work provides insights into M-S-H nucleation and early growth gathered by combining titration experiments with electrospray ionization mass spectrometry, analytical ultracentrifugation, and transmission electron microscopy. We evidenced a nonclassical multistep pathway where a highly complex mixture of defined hydrated magnesium (sodium)-silicate oligomeric species exists in solution prior nucleation. Our results suggest that these entities aggregate, yielding an ill-defined M-S-H precursor phase (depleted in Mg compared to the final product) which later transforms into a denser M-S-H interconnected network (Mg:Si ratio ca. 1) with a more defined sheet-like structure that still retains its poorly crystalline character. The identification of oligomeric silicates species prior nucleation is of great importance for developing means to regulate M-S-H (and potentially other hydrous silicates) formation by using a bottom-up approach. This work reveals that, during the hydration process of cementitious materials, the stages prior to the formation of hydrated solids cannot be disregarded, as they could open new avenues for engineering the properties of the final materials.

Redox cationic frontal polymerization: a new strategy towards fast and efficient curing of defect-free fiber reinforced polymer composites.

Frontal polymerization of epoxy-based thermosets is a promising curing technique for the production of carbon fiber reinforced composites (CFRCs). It exploits the exothermicity of polymerization reactions to convert liquid monomers to a solid 3D network. A self-sustaining curing reaction is triggered by heat or UV-radiation, resulting in a localized thermal reaction zone that propagates through the resin formulation. To date, frontal polymerization is limited to CFRCs with a low fiber volume percent as heat losses compromise on the propagation of the heat front, which is crucial for this autocatalytic curing mechanism. In addition, the choice of suitable epoxy monomers and thermal radical initiators is limited, as highly reactive cycloaliphatic epoxies as well as peroxides decarboxylate during radical induced cationic frontal polymerization. The resulting networks suffer from high defect rates and inferior mechanical properties. Herein, we overcome these shortcomings by introducing redox cationic frontal polymerization (RCFP) as a new frontal curing concept. In the first part of this study, the influence of stannous octoate (reducing agent) was studied on a frontally cured bisphenol A diglycidyl ether resin and mechanical and thermal properties were compared to a conventional anhydride cured counterpart. In a subsequent step, a quasi-isotropic CFRC with a fiber volume of >50 vol%, was successfully cured via RCFP. The composite exhibited a glass transition temperature > 100 °C and a low number of defects. Finally, it was demonstrated that the redox agent effectively prevents decarboxylation during frontal polymerization of a cycloaliphatic epoxy, demonstrating the versatility of RCFP in future applications.

The Influence of Elimination of Roving Frame on Ring Spun Cotton Yarn Characteristics

Generally, ring spun yarns are manufactured from roving which is produced by roving frame. In this paper, an experiment has been done producing ring spun cotton yarn directly from finisher drawn sliver eliminating the roving frame. Total 3 types of yarn with the various linear density of 8 Ne, 10 Ne & 12 Ne were produced using a roving frame and without using a roving frame. In the next step, physical and mechanical properties of those yarns including unevenness, imperfections, hairiness & tenacity were investigated. The result showed that ring spun cotton yarns produced from sliver exhibited inferior physical and mechanical properties compared with samples from the conventional ring spinning system.

Printability enhancement and mechanical property improvement via in situ synthesis of carbon nanotubes on aluminium powder

A strategy of powder surface functional modification involving in situ synthesis of carbon nanotubes (CNTs) on Al powder is described to address the poor forming ability and inferior mechanical properties of Al parts produced by laser powder bed fusion. The obtained CNTs-Al composite powder exhibited a combination of high sphericity and flowability of powder, as well as good dispersion uniformity, bonding force and structural integrity of CNTs. The presence of CNTs significantly reduced the laser reflectivity and enhanced the printability of Al powder. The in situ synthesized CNTs contributed to reinforcement after printing and enhanced the tensile properties of printed sample. The printing behavior of powder, the distribution of reinforcement, and the tensile properties of printed sample were optimized by tuning the content of CNTs. The CNT-content in the composite powder was optimized at 0.96 wt% to achieve the synergy of high forming quality, densification and good tensile properties. • High-quality carbon nanotubes (CNTs) were in situ synthesized on Al powder. • Coating CNTs effectively increased the laser absorptivity of Al powder. • The incompatible issue of Al powder with laser additive manufacturing was addressed. • High forming quality and good properties of were obtained in the printed composite.