Application of Three-Dimension Printing Nano-Carbonated-Hydroxylapatite to the Repair of Defects in Rabbit Bone.

Introduction: Hydroxylapatite (HAp) is a biodegradable bone graft material with high biocompatibility. However, the clinical application of HAp has been limited due to the poor absorption rate in vivo. Methods: In this study, carbonated hydroxylapatite (CHAp) with a chemical composition similar to natural bone was synthesized. HAp and CHAp scaffolds were fabricated by 3D printing. Each material was designed by two types of scaffold model with a maximum width of 8 mm and a thickness of 2 mm, ie, structure I (round shape) and structure II (grid shape). Then, the HAp scaffolds were loaded with lutein. These scaffolds were implanted into the 8 mm bone defect on the top of the rabbit skull within 3 hours in the morning. The curative effects of the scaffolds were assessed two months after implantation. Results: The 3D printed scaffolds did not cause severe inflammation or rejection after implantation. It showed that the porous structures allow bone cells to enter into the scaffolds. Furthermore, CHAp scaffolds were more biocompatible than HAp scaffolds, and showed a higher level of degradation and new bone formation after implantation. Structure II scaffolds with a smaller mineral content degraded faster than structure I, while structure I had better osteoconductive properties than structure II. Besides, the addition of lutein significantly enhanced the rate of new bone formation. Discussion: The uniqueness of this study lies in the synthesis of 3D printed CHAp scaffolds and the implantation of CHAp in rabbit bone defects. The incorporation of suitable carbonate and lutein into HAp can enhance the osteoinductivity of the graft, and CHAp has a faster degradation rate in vivo, all of which provide a new reference for the research and application of apatite-based composites.

3D printed barium titanate/calcium silicate composite biological scaffold combined with structural and material properties.

In the case of a large bone defect, the human endogenous electrical field is no longer sufficient. Therefore, it is necessary to support structural electrical bone scaffolds. Barium titanate (BT) has received much attention in bone tissue engineering applications due to its biocompatibility and ability to maintain charged surfaces. However, its processability is poor and it does not have the biological activity to promote mineralization, which limits its use in bone repair. In this paper, a composite bone scaffold with excellent piezoelectric properties was prepared by combining 20 wt% calcium silicate. The influence of the light curing process on the properties of the piezoelectric biological scaffold was investigated by comparing it with the traditional piezoelectric ceramic molding method (dry pressing). Despite the structural features of 3D printing (layered structure, pore features), the piezoelectric and mechanical properties of the scaffold are weakened. However, 3D-printed scaffolds can combine structural and piezoelectric properties, which makes the 3D-printed scaffold more effective in terms of degradation and antibacterial performance. In terms of cell activity, piezoelectric properties attract proteins and nutrients into the scaffold, promoting cell growth and differentiation. Besides, it is undeniable that the pore structure of the scaffolds plays an important role in the biological properties. Finally, the 3D printed scaffolds have excellent antimicrobial properties due to the redox reaction under piezoelectric effect as well as structural characterization.

An Aerial-Wall Robotic Insect That Can Land, Climb, and Take Off from Vertical Surfaces.

Insects that can perform flapping-wing flight, climb on a wall, and switch smoothly between the 2 locomotion regimes provide us with excellent biomimetic models. However, very few biomimetic robots can perform complex locomotion tasks that combine the 2 abilities of climbing and flying. Here, we describe an aerial-wall amphibious robot that is self-contained for flying and climbing, and that can seamlessly move between the air and wall. It adopts a flapping/rotor hybrid power layout, which realizes not only efficient and controllable flight in the air but also attachment to, and climbing on, the vertical wall through a synergistic combination of the aerodynamic negative pressure adsorption of the rotor power and a climbing mechanism with bionic adhesion performance. On the basis of the attachment mechanism of insect foot pads, the prepared biomimetic adhesive materials of the robot can be applied to various types of wall surfaces to achieve stable climbing. The longitudinal axis layout design of the rotor dynamics and control strategy realize a unique cross-domain movement during the flying-climbing transition, which has important implications in understanding the takeoff and landing of insects. Moreover, it enables the robot to cross the air-wall boundary in 0.4 s (landing), and cross the wall-air boundary in 0.7 s (taking off). The aerial-wall amphibious robot expands the working space of traditional flying and climbing robots, which can pave the way for future robots that can perform autonomous visual monitoring, human search and rescue, and tracking tasks in complex air-wall environments.

Zn-doped chitosan/alginate multilayer coatings on porous hydroxyapatite scaffold with osteogenic and antibacterial properties.

Porous hydroxyapatite (HA) scaffolds prepared by three-dimensional (3D) printing have wide application prospects owing to personalized structural design and excellent biocompatibility. However, the lack of antimicrobial properties limits its widespread use. In this study, a porous ceramic scaffold was fabricated by digital light processing (DLP) method. The multilayer chitosan/alginate composite coatings prepared by layer-by-layer method were applied to scaffolds and Zn2+ was doped into coatings in the form of ion crosslinking. The chemical composition and morphology of coatings were characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Energy dispersive spectroscopy (EDS) analysis demonstrated that Zn2+ was uniformly distributed in the coating. Besides, the compressive strength of coated scaffolds (11.52 ± 0.3 MPa) was slightly improved compared with that of bare scaffolds (10.42 ± 0.56 MPa). The result of soaking experiment indicated that coated scaffolds exhibited delayed degradation. In vitro experiments demonstrated that within the limits of concentration, a higher Zn content in the coating has a stronger capacity to promote cell adhesion, proliferation and differentiation. Although excessive release of Zn2+ led to cytotoxicity, it presented a stronger antibacterial effect against Escherichia coli (99.4%) and Staphylococcus aureus (93%).

Intelligent geometry compensation for additive manufactured oral maxillary stent by genetic algorithm and backpropagation network.

Recently, laser powder bed fusion (LPBF) has shown great potential in advanced manufacturing. However, the rapid melting and re-solidification of the molten pool in LPBF leads to the distortion of parts, especially thin-walled parts. The traditional geometric compensation method, which is used to overcome this problem, is simply based on mapping compensation, with the general effect of distortion reduction. In this study, we used a genetic algorithm (GA) and backpropagation (BP) network to optimize the geometric compensation of Ti6Al4V thin-walled parts fabricated by LPBF. The GA-BP network method can generate free-form thin-walled structures with enhanced geometric freedom for compensation. For the GA-BP network training, an arc thin-walled structure was designed and printed by LBPF and measured via optical scanning measurements. The final distortion of the compensated arc thin-walled part based on GA-BP was reduced by 87.9% compared with PSO-BP and mapping method. The effectiveness of this GA-BP compensation method is further evaluated in an application case using new data points, and the result shows that the final distortion of the oral maxillary stent was reduced by 71%. In summary, the GA-BP-based geometric compensation proposed in this study can better reduce the distortion of thin-walled parts with higher time and cost efficiencies.

Evaluation of Compressive and Permeability Behaviors of Trabecular-Like Porous Structure with Mixed Porosity Based on Mechanical Topology.

The mechanical properties and permeability properties of artificial bone implants have high-level requirements. A method for the design of trabecular-like porous structure (TLPS) with mixed porosity is proposed based on the study of the mechanical and permeability characteristics of natural bone. With this technique, the morphology and density of internal porous structures can be adjusted, depending on the implantation requirements, to meet the mechanical and permeability requirements of natural bone. The design parameters mainly include the seed points, topology optimization coefficient, load value, irregularity, and scaling factor. Characteristic parameters primarily include porosity and pore size distribution. Statistical methods are used to analyze the relationship between design parameters and characteristic parameters for precise TLPS design and thereby provide a theoretical basis and guidance. TLPS scaffolds were prepared by selective laser melting technology. First, TLPS under different design parameters were analyzed using the finite element method and permeability simulation. The results were then verified by quasistatic compression and cell experiments. The scaling factor and topology optimization coefficient were found to largely affect the mechanical and permeability properties of the TLPS. The corresponding compressive strength reached 270-580 MPa; the elastic modulus ranged between 6.43 and 9.716 GPa, and permeability was 0.6 × 10-9-21 × 10-9; these results were better than the mechanical properties and permeability of natural bone. Thus, TLPS can effectively improve the success rate of bone implantation, which provides an effective theory and application basis for bone implantation.

3D printing of flexible strain sensor based on MWCNTs/flexible resin composite.

The flexible strain sensor is an indispensable part in flexible integrated electronic systems and an important intermediate in external mechanical signal acquisition. The 3D printing technology provides a fast and cheap way to manufacture flexible strain sensors. In this paper, a MWCNTs/flexible resin composite for photocuring 3D printing was prepared using mechanical mixing method. The composite has a low percolation threshold (1.2%ωt). Based on the composite material, a flexible strain sensor with high performance was fabricated using digital light processing technology. The sensor has a GF of 8.98 under strain conditions ranging between 0% and 40% and a high elongation at break (48%). The sensor presents mechanical hysteresis under cyclic loading. With the increase of the strain amplitude, the mechanical hysteresis becomes more obvious. At the same time, the resistance response signal of the sensor shows double peaks during the unloading process, which is caused by the competition of disconnection and reconstruction of conductive network in the composite material. The test results show that the sensor has different response signals to different types of loads. Finally, its practicability is verified by applying it to balloon pressure detection.

Comparison of efficacy and safety of ripertamab (SCT400) versus rituximab (Mabthera® ) in combination with CHOP in patients with previously untreated CD20-positive diffuse large B-cell lymphoma: A randomized, single-blind, phase III clinical trial.

This study compared the efficacy, safety and immunogenicity of ripertamab (SCT400) and rituximab (Mabthera® ) combined with CHOP as the first-line treatment for Chinese patients with CD20-positive diffuse large B cell lymphoma (DLBCL). This is a randomized, patient-blind, multicenter, active-control, non-inferiority study with parallel design. Patients were randomly (2:1) to receive ripertamab combined with CHOP (S-CHOP) or rituximab (Mabthera® ) combined with CHOP (R-CHOP) for up to 6 cycles. The primary endpoint was the Independent Review Committee (IRC) assessed objective response rate (ORR) in full analysis set (FAS) and the per protocol set (PPS). A total of 364 patients (243 in the S-CHOP and 121 in the R-CHOP groups) were enrolled in this study. In FAS, IRC-assessed ORRs were 93.8% (95% confidence interval (CI) 90.0%, 96.5%) and 94.2% (95% CI: 88.4%, 97.6%) in the S-CHOP and R-CHOP groups (p = 0.9633), respectively. The ORR difference between the two groups -0.4% (95% CI: -5.5%, 4.8%) met the pre-specified non-inferiority margin of -12%. There were no significant differences between the S-CHOP and R-CHOP groups in 1-year progression-free survival rates (81.1% vs. 83.2%, p = 0.8283), 1 year event-free survival rates (56.2% vs. 58.1%, p = 0.8005), and 3-year overall survival rates (81.0% vs. 82.8%, p = 0.7183). The results in PPS were consistent with those in FAS. The rates of treatment-emergent adverse events (TEAEs) and ≥ grade 3 TEAEs were 97.9% and 99.2%, 85.2% and 86.0% in the S-CHOP and R-CHOP groups, respectively in safety set. The percentage of anti-drug antibodies positive patients in the S-CHOP group was numerically lower than the R-CHOP group (10.9% vs. 16.0%). This study demonstrated that S-CHOP was not inferior to R-CHOP in the first-line treatment of Chinese patients with CD20-positive DLBCL in efficacy, safety and immunogenecity. S-CHOP could be an alternative first-line standard treatment regimen for this patient population.

Microstructure and Corrosion Behavior of Iron Based Biocomposites Prepared by Laser Additive Manufacturing.

Iron (Fe) has attracted great attention as bone repair material owing to its favorable biocompatibility and mechanical properties. However, it degrades too slowly since the corrosion product layer prohibits the contact between the Fe matrix and body fluid. In this work, zinc sulfide (ZnS) was introduced into Fe bone implant manufactured using laser additive manufacturing technique. The incorporated ZnS underwent a disproportionation reaction and formed S-containing species, which was able to change the film properties including the semiconductivity, doping concentration, and film dissolution. As a result, it promoted the collapse of the passive film and accelerated the degradation rate of Fe matrix. Immersion tests proved that the Fe matrix experienced severe pitting corrosion with heavy corrosion product. Besides, the in vitro cell testing showed that Fe/ZnS possessed acceptable cell viabilities. This work indicated that Fe/ZnS biocomposite acted as a promising candidate for bone repair material.

Preparation of Graphene Oxide-loaded Nickel with Excellent Antibacterial Property by Magnetic Field-Assisted Scanning Jet Electrodeposition.

Graphene oxide (GO) is recognized as a promising antibacterial material that is expected to be used to prepare a new generation of high-efficiency antibacterial coatings. The propensity of GO to agglomeration makes it difficult to apply it effectively. A new method of preparing GO-loaded nickel (GNC) with excellent antibacterial property is proposed in this paper. In this work, GNC was prepared on a titanium sheet by magnetic field-assisted scanning jet electrodeposition. The massive introduction of GO on the coating was proven by energy disperse spectroscopy and Raman spectroscopy. The antibacterial performance of GNC was proven by agar plate assessment and cell living/dead staining. The detection of intracellular reactive oxygen species (ROS) and the concentration of nickel ions, indicate that the antibacterial property of GNC are not entirely derived from the nickel ions released by the coating and the intracellular ROS induced by nickel ions, but rather are due to the synergistic effect of nickel ions and GO.

Laser Additive Manufacturing of Zinc Targeting for Biomedical Application.

Biodegradable zinc (Zn) is expected to be used in clinical application like bone tissue engineering scaffolds, since it possesses favorable biocompatibility and suitable degradation rate. Laser powder bed fusion (LPBF), which is a typical additive manufacturing technique, offers tremendous advantages in fabricating medical devices with personalized geometric shape and complex porous structure. Therefore, the combination of LPBF and biodegradable Zn has gained intensive attention and also achieved rapid development in recent years. However, it severely challenges the formation quality and resultant performance of LPBF-processed Zn-based materials, due to the evaporation and element loss during laser processing. In this study, the current research status and future research trends for LPBF of Zn-based implants are reviewed from comprehensive viewpoints including formation quality, microstructure feature, and performance. The influences of powder characteristics and process parameters on formation quality are described systematically. The microstructure evolution, mechanical properties, as well as the degradation behavior are also discussed. Finally, the research perspectives for LPBF of Zn are summarized, aiming to provide guideline for future study.

3D-printed composite, calcium silicate ceramic doped with CaSO4·2H2O: Degradation performance and biocompatibility.

Calcium silicate is a common implant material with excellent mechanical strength and good biological activity. In recent years, the addition of strengthening materials to calcium silicate has been proven to promote bone tissue regeneration, but its degradation properties require further improvements. In this paper, calcium silicate was used as the matrix, and 10 wt% hydroxyapatite and 10 wt% strontium phosphate were added to im prove the biological activity of the scaffold. The effect of adding different amounts of calcium sulfate dihydrate (CaSO4·2H2O) on the degradation of the scaffold was explored. A porous ceramic scaffold was prepared by digital light processing (DLP) technology, and its performance was evaluated. Cell experiments showed that the addition of calcium sulfate improved cell proliferation and differentiation. Simulated body fluid (SBF) immersion tests showed that small amounts of apatite deposits appeared on the fourth day, larger deposits appeared on the 14th day, and degradation occurred on the surface after 28 days of immersion. Mechanical tests showed that the addition of 5 wt% CaSO4·2H2O improved the compressibility of the composite. After soaking in SBF for 14 days, it retained its compressive strength (11.8 MPa), which meets the requirements of cancellous bone, demonstrating its potential application value for bone repair.

Design and Compressive Fatigue Properties of Irregular Porous Scaffolds for Orthopedics Fabricated Using Selective Laser Melting.

An irregular porous structure plays a major role in bone tissue engineering, and it is more suitable for bone tissue growth than a regular porous structure. The response surface method was used to establish a relationship between the average pore size and the design parameters. The technology of selective laser melting was utilized to fabricate the porous Ti-6Al-4V scaffolds with an irregularity of (0.4) and porosities of (70, 80, and 90%) designed using the Voronoi-tessellation method. Compression tests of porous scaffolds showed an elastic modulus range of 0.84-1.97 GPa and an ultimate strength ranging within 21.0-99.1 MPa. The elastic modulus was mainly influenced by the porosity and heat-treatment process. Furthermore, the fatigue test results suggested that the number of cycles (9 × 104 to 1.8 × 106) was greatly influenced by the porosity and heat-treatment process. The heat treatment of annealing greatly improved the fatigue performance of porous scaffolds. The irregular porous scaffolds with lower porosity and after full annealing exhibited the best fatigue behavior.

Analysis of Mechanical Properties and Permeability of Trabecular-Like Porous Scaffold by Additive Manufacturing.

Human bone cells live in a complex environment, and the biomimetic design of porous structures attached to implants is in high demand. Porous structures based on Voronoi tessellation with biomimetic potential are gradually used in bone repair scaffolds. In this study, the mechanical properties and permeability of trabecular-like porous scaffolds with different porosity levels and average apertures were analyzed. The mechanical properties of bone-implant scaffolds were evaluated using finite element analysis and a mechanical compression experiment, and the permeability was studied by computational fluid dynamics. Finally, the attachment of cells was observed by confocal fluorescence microscope. The results show that the performance of porous structures can be controlled by the initial design of the microstructure and tissue morphology. A good structural design can accurately match the performance of the natural bone. The study of mechanical properties and permeability of the porous structure can help address several problems, including stress shielding and bone ingrowth in existing biomimetic bone structures, and will also promotes cell adhesion, migration, and eventual new bone attachment.

Numerical Simulation and Experimental Investigation of Laser Ablation of Al2O3 Ceramic Coating.

This paper presents an evaluation of the molten pool laser damage done to an Al2O3 ceramic coating. Mechanism analysis of the laser damage allowed for a 2D finite element model of laser ablation of the Al2O3 ceramic coating to be built. It consisted of heat transfer, laminar flow, and a solid mechanics module with the level set method. Results showed that the laser damage mechanisms through laser ablation were melting, gasification, spattering, and micro-cracking. The ablation depth and diameter increased with the increasing laser ablation time under continuous irradiation. The simulation profile was consistent with the experimental one. Additionally, the stress produced by the laser ablation was 3500-9000 MPa, which exceeded the tensile stress (350-500 MPa), and fracturing and micro-cracks occurred. Laser damage analysis was performed via COMSOL Multiphysics to predict laser damage morphology, and validate the 3D surface profiler and scanning electron microscope results.

Surface modification enhances interfacial bonding in PLLA/MgO bone scaffold.

The poor interfacial bonding and resultant agglomeration of nanoparticles in polymer-based composite severely deteriorated their reinforcement effect. In this work, MgO nanoparticles (MgO-NPs) were surface modified with Poly (L-lactic acid-co-malic acid) (PLMA) to improve the interfacial compatibility in Poly-l-lactic acid (PLLA) scaffold manufactured by selective laser sintering. PLMA possess a hydrophilic end with carboxyl group (comes from the malic acid) and an l-lactic acid chain. On one hand, the carboxyl group was able to form hydrogen bonding with the hydroxyl groups of MgO-NPs. On the other hand, the l-lactic acid chain containing the hydroxyl groups could react with the carboxyl group of PLLA. Results revealed that the scaffold exhibited significantly enhanced compressive strength and modulus by 47.1% and 237.7%, respectively, which could be ascribed to the enhanced interfacial bonding between PLLA and MgO-NPs, as well as the rigid particle reinforcement. In addition, the scaffold was favorable for cell adhesion, proliferation and differentiation, owing to the improved hydrophilic and suitable pH environment. It was suggested the scaffold was a promising material for bone repair application.

Research on laser-assisted selective metallization of a 3D printed ceramic surface.

In recent years, the question of how to fabricate conductive patterns on complex ceramic surfaces in a high-definition and low-cost manner has been an increasing challenge. This paper presents a complete process chain for the selective metallization of Al2O3 ceramic surfaces based on 3D printing. Laser pre-activation (LPA) is used to "activate" the surface of the ceramic substrate, and then, combined with the electroless copper plating (ECP) process, the Al2O3 substrates can be metalized with preset patterns at room temperature, and a densely packed copper layer with high accuracy and good reproducibility can be obtained. The obtained coating has satisfactory roughness, excellent stability and bonding force, and good solderability. The resistivity of the copper layer measured using a four-probe resistance meter is about 3.1 mΩ cm. The limit line width of the metal circuit is about 33.2 µm. Finally, application cases of precision devices such as antennas with ceramic substrates are prepared. This study opens up a broader space for the design and manufacture of 3D microwave devices.

Additive manufacturing of bone scaffolds.

Additive manufacturing (AM) can obtain not only customized external shape but also porous internal structure for scaffolds, both of which are of great importance for repairing large segmental bone defects. The scaffold fabrication process generally involves scaffold design, AM, and post-treatments. Thus, this article firstly reviews the state-of-the-art of scaffold design, including computer-aided design, reverse modeling, topology optimization, and mathematical modeling. In addition, the current characteristics of several typical AM techniques, including selective laser sintering, fused deposition modeling (FDM), and electron beam melting (EBM), especially their advantages and limitations are presented. In particular, selective laser sintering is able to obtain scaffolds with nanoscale grains, due to its high heating rate and a short holding time. However, this character usually results in insufficient densification. FDM can fabricate scaffolds with a relative high accuracy of pore structure but with a relative low mechanical strength. EBM with a high beam-material coupling efficiency can process high melting point metals, but it exhibits a low-resolution and poor surface quality. Furthermore, the common post-treatments, with main focus on heat and surface treatments, which are applied to improve the comprehensive performance are also discussed. Finally, this review also discusses the future directions for AM scaffolds for bone tissue engineering.

Cause of Angular Distortion in Fusion Welding: Asymmetric Cross-Sectional Profile along Thickness.

Angular distortion is a common problem in fusion welding, especially when it comes to thick plates. Despite the fact that various processes and influencing factors have been discussed, the cause of the angular distortion has not been clearly revealed. In this research, the asymmetry of cross-sectional profile along thickness is considered of great importance to the angular distortion. A theoretical model concerning the melting-solidification process in fusion welding was established. An expression of the angular distortion was formulated and then validated by experiments of laser welding 316L stainless steel. The results show that the asymmetric cross-sectional profile is a major contributory factor towards the angular distortion mechanism. The asymmetry of cross-section profile along thickness causes the difference between two bending moments in the lower and upper parts of the joint. This is the difference that drives the angular distortion of the welded part. Besides, the asymmetry of cross-section profile is likely to be influenced by various processes and parameters, thereby changing the angular distortion.

Assumption of Constraining Force to Explain Distortion in Laser Additive Manufacturing.

Distortion is a common but unrevealed problem in metal additive manufacturing, due to the rapid melting in metallurgy and the intricate thermal-mechanical processes involved. We explain the distortion mechanism and major influencing factors by assumption of constraining force, which is assumed between the added layer and substrate. The constraining force was set to act on the substrate in a static structural finite element analysis (FEA) model. The results were compared with those of a thermal-mechanical FEA model and experiments. The constraining force and the associated static structural FEA showed trends in distortion and stress distribution similar to those shown by thermal-mechanical FEA and experiments. It can be concluded that the constraining force acting on the substrate is a major contributory factor towards the distortion mechanism. The constraining force seems to be primarily related to the material properties, temperature, and cross-sectional area of the added layer.