Mg and its alloys have been identified as promising bone implant materials owing to their natural degradability, good biocompatibility and favorable mechanical properties. Nevertheless, the too fast ...degradation rate usually results in a premature disintegration of mechanical integrity and local hydrogen accumulation, which limit their clinical bone repair application. In this work, the current research status regarding Mg bone implants was systematically reviewed. The relevant strategies to enhance the corrosion resistance, including purification, alloying treatment, surface coating and Mg-based metal matrix composite, are comprehensively discussed. The fabricating techniques for Mg bone implants are also presented. Particularly, laser additive manufacturing can fabricate customized shape and complex porous structure basing on its unique additive manufacturing concept. More importantly, it can achieve rapid heating and cooling due to the characteristics of high laser energy density and good controllability, thereby regulating the microstructure and performance. Furthermore, the current challenges and future research perspectives are put forward. This work aims to offer some meaningful guidelines for researchers on the future study of Mg bone implants.
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•The advantages and current application of Mg bone implants are described.•The fabrication methods for Mg bone implants are discussed comprehensively.•The strategies to enhance the corrosion resistance of Mg bone implant are evaluated.•The future perspectives are presented to provide some guidelines for researchers.
Polyvinylidene fluoride (PVDF)/barium titanate (BaTiO3) composites are becoming increasingly attractive in bone repair since it combines the advantage of polymer flexibility and ceramic piezoelectric ...constant. Herein, silver (Ag) nanoparticles were decorated on polydopamine functioned BaTiO3 (Ag-pBT) by in situ growth. Then the strawberry-like structured Ag-pBT nanoparticles were introduced into PVDF scaffold fabricated by selective laser sintering. On one hand, Ag nanoparticles would act as a conductive phase to enhance the strength of the polarized electric field on BaTiO3, thereby forcing more domains to be aligned in the direction of the electric field and make piezoelectric effect of BaTiO3 fully play in composite scaffold. On the other hand, Ag nanoparticles would attack multiple targets in bacteria by release of Ag+ and production of reactive oxygen species. In fact, the antibacterial activity is highly desirable for bone repair. Results demonstrated that the PVDF/4Ag-pBT scaffold exhibited enhanced piezoelectric properties with output current and voltage increased by 50% and 40% than that of PVDF/pBT, respectively. In vitro cell culture confirmed that the enhanced electric output further promoted cell proliferation and differentiation. Meanwhile, the scaffold presented robust antibacterial activity against E.coli.
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•A strawberry-like Ag-decorated BaTiO3 nanoparticles were prepared by in situ growth.•A novel three-dimensional porous PVDF/Ag-pBT scaffolds were fabricated by selective laser sintering technique.•The Ag nanoparticles could enhance the electric output performance of the scaffold.•The improved surface electric charges significantly promoted proliferation and differentiation of MG-63 cell.•The scaffold inhibited the growth of Escherichia coli by releasing Ag+.
Zinc (Zn) alloys are promising bone repair materials due to their inherent degradability, favorable mechanical property and biocompatibility. In this investigation, laser powder bed fusion (LPBF) ...known as a representative additive manufacturing technique was applied to fabricate Zn-2Al (wt.%) part for bone repair application. A low energy density (Ev) led to the formation of pores and resultant insufficient densification rate due to the high liquid viscosity within the molten pool. In contrast, a high Ev caused the evaporation of Zn powder and resultant failure of LPBF. With Ev increasing, the obtained grains and the precipitated lamellar eutectic structure contained η-Zn and α-Al phase became coarsened, which could be attributed to the enhanced heat accumulation and consequently decreased cooling rate. At optimized Ev of 114.28 J/mm3, fully dense Zn-2Al part with a densification rate of 98.3 ± 1.4% was achieved, which exhibited an optimal hardness of 64.5 ± 1.8 Hv, tensile strength of 192.2 ± 5.4 MPa and a moderate corrosion rate of 0.14 mm/year. In addition, in vitro cell tests confirmed its good biocompability. This study indicated that LPBF processed Zn-2Al part was a potential material for bone repair.
•Zn-2Al part is successfully built using laser additive manufacturing process.•High densification rate and fine microstructure is achieved at optimized Ev.•It exhibits superior mechanical properties and suitable degradation rate.
Poor mechanical strength and creep resistance limit the orthopedic application of biodegradable Zinc (Zn). In present work, cerium (Ce) was alloyed with Zn using laser additive manufacturing ...technique. As one kind of rare earth element, Ce possessed high surface activity, which effectively interrupted the grain growth and caused the formation of stable intermetallics, thus contributing to grain refinement strengthening and precipitate strengthening. More significantly, Ce alloying activated more pyramidal slip by means of reducing the critical resolved shear stress during plastic deformation, and resultantly formed the sessile dislocations, which caused the accumulated strain hardening and improved the creep resistance. As a result, Zn-Ce alloy exhibited a considerably improved ultimate tensile strength of 247.4 ± 7.2 MPa, and a reduced creep rate of 1.68 × 10−7 s−1. Moreover, it exhibited strong antibacterial activity, as well as favorable cytocompatibility and hemocompatibility. All these results demonstrated the great potential of Zn-Ce alloy as a candidate for bone repair application.
In present study, a strategy is presented to construct a magnetic micro-environment in poly-l-lactide/polyglycolic acid (PLLA/PGA) scaffolds fabricated via selective laser sintering by incorporating ...Fe3O4 magnetic nanoparticles (MNPs), aiming to enhance cell viability and promote bone regeneration. In the micro-environment, each nanoparticle provides a nanoscale magnetic field to activate cellular responses. The results in vitro demonstrated that the magnetic scaffolds not only stimulated cell adhesion and viability, but also enhanced proliferation rate and alkaline phosphatase activity. Meanwhile, the compressive strength and modulus were increased by 81.9% and 71.6%, respectively, which were determined by the rigid enhancement effect of MNPs. Moreover, the magnetic scaffolds were implanted into rabbit radius bone defect in vivo, and the results indicated that the magnetic scaffolds significantly induced substantial blood vessel tissue, fibrous tissue and new bone tissue formation at 2 months post-implantation, revealing the excellent bone regeneration capability. These positive results indicate that the construction of magnetic micro-environment in scaffolds is a working countermeasure to promote bone regeneration.
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•A magnetic micro-environment was constructed in PLLA/PGA scaffolds by incorporating Fe3O4 MNPs.•The magnetic nanoparticle provides a nanoscale magnetic field to activate cellular responses.•Magnetic scaffolds promoted cell adhesion, proliferation and differentiation.•The new bone tissue formation was significantly accelerated.
Polyvinylidene fluoride (PVDF), as a typical piezoelectric polymer, has a great potential in reconstructing the electrical microenvironment of bone tissue. In present study, graphene oxide (GO) was ...introduced into PVDF scaffold manufactured via selective laser sintering, aiming to enhance piezoelectric effect of PVDF by increasing β phase content. In detail, the oxygen-containing functional groups of GO could form strong hydrogen bonding with fluorine groups of PVDF. The interaction would force the fluorine groups to be arranged in parallel and perpendicular to the polymer chain, thereby inducing the transformation from α phase to β phase. Results demonstrated that the PVDF/0.3GO scaffold with improved β phase exhibited the maximal output voltage (~8.2 V) and current (~101.6 nA), which were improved by 82.2% and 68.2%, respectively, in comparison with pure PVDF. In vitro cell culture confirmed that enhanced electrical charges could significantly improve cell behavior. Moreover, the scaffold presented a 97.9% increase in compressive strength and 24.5% increase in tensile strength, which was attributed to GO reinforcements forming strong interaction with PVDF chains. These positive results suggested that the scaffold might have possible application in bone tissue engineering.
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•A novel 3D porous piezoelectric PVDF/GO scaffold was fabricated by SLS.•The scaffold exhibited good piezoelectric and mechanical properties.•The enhanced electrical charges significantly improved the cell behaviors.•The scaffold presented a huge potential in reconstructing the electrical microenvironment of bone tissue.
Polyetheretherketone (PEEK)/β‐tricalcium phosphate (β‐TCP) scaffolds are expected to be able to combine the excellent mechanical strength of PEEK and the good bioactivity and biodegradability of ...β‐TCP. While PEEK acts as a closed membrane in which β‐TCP is completely wrapped after the melting/solidifying processing, the PEEK membrane degrades very little, hence the scaffolds cannot display bioactivity and biodegradability. The strategy reported here is to blend a biodegradable polymer with PEEK and β‐TCP to fabricate multi‐material scaffolds via selective laser sintering (SLS). The biodegradable polymer first degrades and leaves caverns on the closed membrane, and then the wrapped β‐TCP is exposed to body fluid. In this study, poly(l‐lactide) (PLLA) is adopted as the biodegradable polymer. The results show that large numbers of caverns form on the membrane with the degradation of PLLA, enabling direct contact between β‐TCP and body fluid, and allowing for their ion‐exchange. As a consequence, the scaffolds display the bioactivity, biodegradability and cytocompatibility. Moreover, bone defect repair studies reveal that new bone tissues grow from the margin towards the center of the scaffolds from the histological analysis. The bone defect region is completely connected to the host bone end after 8 weeks of implantation.
The biodegradation test of scaffolds reveals that many caverns form on the closed membrane due to poly(l‐lactide) (PLLA) degradation, and the caverns become larger and deeper with increasing PLLA content. As a result, the wrapped β‐tricalcium phosphate (β‐TCP) particles are exposed from the membrane into body fluid environment.
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•The design method based on Voronoi was proposed to mimic the characteristics of cancellous bone in human body.•Ceramic Digital light processing (DLP) method was adopted to satisfy ...the forming requirements of irregular scaffolds.•The compressive strength of scaffolds can be increased by 30% through the regulation of irregularity.•Cell experiments confirmed that structural changes also had influence on the biocompatibility of scaffolds.
Ideal bone scaffolds require good biocompatibility and moderate mechanical properties, so as to promote the proliferation and differentiation of osteoblast cells, and achieve the good bone repair. Inspired by the porous structure of cancellous bone, 15 groups of bone scaffolds with variable irregularity (Ir1-5) and porosity (35.53–61.75%) were designed and fabricated by ceramic digital light processing (DLP) using 20 wt% hydroxyapatite doped zirconia as the matrix material. The effects of structural parameters and material on mechanical properties and biocompatibility were studied. The shrinkage test results showed that the density of scaffolds was mainly affected by the porosity. The mechanical test results showed that Ir2 and Ir3 scaffolds had better compressive behaviors, and the compressive strength could be increased by 30% by regulating the irregularity. All scaffolds showed comparable mechanical properties to that of cancellous bone. Cell experiments showed that the effect of structure on cell proliferation, differentiation, and mineralization was most evident at the early stage of implantation. Meanwhile, the biocompatibility variation with the irregularity was consistent with mechanical properties. This study proved that a bio-inspired bone scaffold with excellent comprehensive properties could be obtained through reasonable design.
Porous metal scaffolds play an important role in the orthopedic field, due to their wide applications in prostheses implantation. Some previous studies showed that the scaffolds with trabecular bone ...structure reconstructed via computed tomography had satisfactory biocompatibility. However, the reverse modeling scaffolds were inflexible for customized design. Therefore, a top-down designing biomimetic bone scaffold with favorable mechanical performances and cytocompatibility is urgently demanded for orthopedic implants. An emerging additive manufacturing technique, selective laser melting, was employed to fabricate the trabecular-like porous Ti-6Al-4 V scaffolds with varying irregularities (0.05-0.5) and porosities (48.83%–74.28%) designed through a novel Voronoi-Tessellation based method. Micro-computed tomography and scanning electron microscopy were used to characterize the scaffolds’ morphology. Quasi-static compression tests were performed to evaluate the scaffolds’ mechanical properties. The MG63 cells culture in vitro experiments, including adhesion, proliferation, and differentiation, were conducted to study the cytocompatibility of scaffolds. Compressive tests of scaffolds revealed an apparent elastic modulus range of 1.93–5.24 GPa and an ultimate strength ranging within 44.9–237.5 MPa, which were influenced by irregularity and porosity, and improved by heat treatment. Furthermore, the in vitro assay suggested that the original surface of the SLM-fabricated scaffolds was favorable for osteoblasts adhesion and migration because of micro scale pores and ravines. The trabecular-like porous scaffolds with full irregularity and higher porosity exhibited enhanced cells proliferation and osteoblast differentiation at earlier time, due to their preferable combination of small and large pores with various shapes. This study suggested that selective laser melting-derived Ti-6Al-4 V scaffold with the trabecular-like porous structure designed through Voronoi-Tessellation method, favorable mechanical performance, and good cytocompatibility was a potential biomaterial for orthopedic implants.
Poly‑l‑lactic acid (PLLA) is a promising bone repair material because of its good biocompatibility and natural degradability. Nevertheless, the poor mechanical properties and local inflammatory ...response limits its further application in bone repair. In this research, nano magnesium oxide (nMgO) was incorporated into PLLA scaffold manufactured by selective laser sintering technique. Results shown that nMgO with good affinity to PLLA could act as nucleating agent during crystallization process and effectively enhance the crystallinity of PLLA, which was proved by the isothermal behavior and non-isothermal behavior analysis. The evolution of crystallization was also achieved by polarized optical microscopy. Mechanical tests confirmed that the tensile strength, young modulus and Vickers hardness of PLLA/3nMgO was enhanced by 38%, 24% and 11%, respectively, as compared with PLLA. On the other hand, the incorporated nMgO neutralized the acid degradation by-products of PLLA, forming a weak alkaline environment which might contribute to avoiding sever local inflammation after implantation. Moreover, in vitro cell culture revealed an improved biocompatibility of PLLA/nMgO scaffolds. All these positive results suggested that PLLA/3nMgO scaffold was a potential material for bone repair application.
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•Porous scaffold is successfully fabricated via selective laser sintering.•The crystallinity of PLLA scaffold is enhanced after the incorporation of nMgO.•The acid degradation by-products of PLLA are neutralized by nMgO.•The mechanical properties and biocompatibility are improved simultaneously.
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