Poly (l-lactide acid) improves complete nano-hydroxyapatite bone scaffolds through the microstructure rearrangement

Abstract Cracks often occur when nano-hydroxyapatite bone scaffolds are fabricated with selective laser sintering, which affect the performance of scaffolds. In this study, a small amount of poly (l-lactide acid) (PLLA) was added into nano-hydroxyapatite (nano-HAP) powder by mechanical blending in order to improve the sintering properties. The nano-HAP powder combined with 1wt % PLLA was sintered under different laser power (5W, 7.5W, 10W, 12.5W, 15W and 20W). The fabricated scaffolds were characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Micro Hardness Tester. The results showed that nano-HAP particles grew up quickly with the laser power increasing, and there were many strip-like cracks on the surface of sintering zone. The cracks gradually reduced until disappeared when the laser power increased to 15W, together with a great improvement of density. Large pores were observed on the specimen when the laser power further increases, accompanied with the decomposition of HAP into \u3b2-tricalcium phosphate (\u3b2-TCP) and tetracalcium phosphate (TTCP). And the optimum parameters were eventually obtained with laser power of 15W, scanning speed of 1000 mm/min, powder bed temperature of 150\ubaC, laser spot diameter of 2 mm and layer thickness of 0.2 mm. We summarized that the molten PLLA enhanced the particle rearrangement of nano-HAP by capillary force and may absorb thermal stress in laser sintering process, while PLLA would be oxidized gradually until completely excluded from the sintered nano-HAP scaffolds, which was confirmed by FTIR analysis. This study provides a novel method to improve the sintering properties of nano-HAP with no adverse effects which would be used in the application of bone tissue engineering potentially

Formation and characteristic corrosion behavior of alternately lamellar arranged α and β in as-cast AZ91 Mg alloy

Formation and characteristic corrosion resistance of alternately lamellar arranged α and β in as-cast AZ91 Mg alloy were investigated as an independent micro-constituent identity. As-cast AZ91 presented three microstructural entities, i.e. α-Mg grain, (α+β) lamellae and coarse β particle, and each had its own Al content and microstructural morphology. The lamellae occurrence was due to the precipitation of β particle from the divorced eutectic Al-rich-α phase during solidification, because the Al composition can not exceed its maximum solubility. The evidences that were obtained from electrochemical tests, micro-corrosion morphology and hydrogen evolution rate certified that the (α+β) lamellae was beneficial to corrosion resistance, which was different from the reported deleterious influence for its original eutectic Al-rich-α phase. This different corrosion behavior was explained to be ascribed to the changes in fine structure and local composition that resulted in combined electrochemical effects of the changes in α and β phases on the corrosion

Enhanced Stability of Calcium Sulfate Scaffolds with 45S5 Bioglass for Bone Repair

Calcium sulfate (CaSO4), as a promising tissue repair material, has been applied widely due to its outstanding bioabsorbability and osteoconduction. However, fast disintegration, insufficient mechanical strength and poor bioactivity have limited its further application. In the study, CaSO4 scaffolds fabricated by using selective laser sintering were improved by adding 45S5 bioglass. The 45S5 bioglass enhanced stability significantly due to the bond effect of glassy phase between the CaSO4 grains. After immersing for four days in simulated body fluid (SBF), the specimens with 45S5 bioglass could still retain its original shape compared as opposed to specimens without 45S5 bioglass who experienced disintegration. Meanwhile, its compressive strength and fracture toughness increased by 80% and 37%, respectively. Furthermore, the apatite layer was formed on the CaSO4 scaffolds with 45S5 bioglass in SBF, indicating good bioactivity of the scaffolds. In addition, the scaffolds showed good ability to support the osteoblast-like cell adhesion and proliferation

Lanthanum-Containing Magnesium Alloy with Antitumor Function Based on Increased Reactive Oxygen Species

Developing antitumor implants is of great significance to repair tumor-induced bone defects and simultaneously prevent bone tumor recurrence. The tumor cells, compared to normal cells, have a high reactive oxygen species level. They are vulnerable to oxidative insults under increased intrinsic oxidative stress. The lanthanum (La) ion with high phospholipid binding ability can open the mitochondrial permeability transition pore, which blocks the electron transport chain in the mitochondria, and consequently increases reactive oxygen species level. In this study, La was alloyed to Mg-6Zn-0.5Zr (ZK60) through selective laser melting technology. The results indicated that the mitochondrial membrane potential dropped whilst the reactive oxygen species increased as the La content increased. ZK60-1.0La revealed a high cell inhibition rate of 61.9% for bone tumor cell and high cell viability of 91.9% for normal cells, indicating that the alloy could induce bone tumor cell death, as well as exhibit good biocompatibility for normal cell. In addition, its degradation rate 1.23 mm/year was lower than that of ZK60 alloy 2.13 mm/year, which was mainly attributed to the grain refinement

Magnetostrictive alloys: Promising materials for biomedical applications

Magnetostrictive alloys have attracted increasing attention in biomedical applications because of the ability to generate reversible deformation in the presence of external magnetic fields. This review focuses on the advances in magnetostrictive alloys and their biomedical applications. The theories of magnetostriction are systematically summarized. The different types of magnetostrictive alloys and their preparation methods are also reviewed in detail. The magnetostrictive strains and phase compositions of typical magnetostrictive alloys, including iron based, rare-earth based and ferrite materials, are presented. Besides, a variety of approaches to preparing rods, blocks and films of magnetostriction materials, as well as the corresponding methods and setups for magnetostriction measurement, are summarized and discussed. Moreover, the interactions between magnetostrictive alloys and cells are analyzed and emphasis is placed on the transduction and transformation process of mechanochemical signals induced by magnetostriction. The latest applications of magnetostrictive alloys in remote microactuators, magnetic field sensors, wireless implantable devices and biodegradable implants are also reviewed. Furthermore, future research directions of magnetostrictive alloys are prospected with focus on their potential applications in remote cell actuation and bone repair

Heterogeneous grain structure in biodegradable Zn prepared via mechanical alloying and laser powder bed fusion for strength-plasticity synergy

ABSTRACTThis study presented a unique process of mechanical alloying (MA) and laser powder bed fusion (LPBF) to prepare heterogeneous grain structure (HGS) Zn with strength-plasticity synergy. The results showed that the MA-treatment significantly refined the grain sizes of Zn to nano-scale and contributed to the formation of HGS powders. Moreover, the ultra-fast heating and cooling of LPBF process inhibited the grain growth and resulted in a specific core/shell HGS, wherein the cores (micron-grains) were surrounded by interconnected shells (nano-grains). Notably, the prepared HGS Zn demonstrated synergistically improved compressive yield strength (2.1 times) and plasticity (58%) compared with the homogeneous coarse-grained counterparts. This impressive strength-plasticity synergy was primarily attributed to high back stress and dislocation pile-ups generated by the deformation incompatibility between the nano-grained shells and micron-grained cores. These findings open up new fields for MA and LPBF in the preparation of HGS metals and their applications in solving strength-plasticity tradeoff

Characterization of mechanical and biological properties of 3-D scaffolds reinforced with zinc oxide for bone tissue engineering.

A scaffold for bone tissue engineering should have highly interconnected porous structure, appropriate mechanical and biological properties. In this work, we fabricated well-interconnected porous β-tricalcium phosphate (β-TCP) scaffolds via selective laser sintering (SLS). We found that the mechanical and biological properties of the scaffolds were improved by doping of zinc oxide (ZnO). Our data showed that the fracture toughness increased from 1.09 to 1.40 MPam(1/2), and the compressive strength increased from 3.01 to 17.89 MPa when the content of ZnO increased from 0 to 2.5 wt%. It is hypothesized that the increase of ZnO would lead to a reduction in grain size and an increase in density of the strut. However, the fracture toughness and compressive strength decreased with further increasing of ZnO content, which may be due to the sharp increase in grain size. The biocompatibility of the scaffolds was investigated by analyzing the adhesion and the morphology of human osteoblast-like MG-63 cells cultured on the surfaces of the scaffolds. The scaffolds exhibited better and better ability to support cell attachment and proliferation when the content of ZnO increased from 0 to 2.5 wt%. Moreover, a bone like apatite layer formed on the surfaces of the scaffolds after incubation in simulated body fluid (SBF), indicating an ability of osteoinduction and osteoconduction. In summary, interconnected porous β-TCP scaffolds doped with ZnO were successfully fabricated and revealed good mechanical and biological properties, which may be used for bone repair and replacement potentially

Magnetostrictive bulk Fe-Ga alloys prepared by selective laser melting for biodegradable implant applications

Magnetostrictive Fe-Ga alloys have received extensive attention for their good mechanical properties and low saturation magnetization. However, the magnetostriction of bulk polycrystalline Fe-Ga alloys always suffers a major setback due to random grain orientation. In this study, selective laser melting (SLM) was used for the first time to manufacture bulk polycrystalline Fe81Ga19 alloys, and different scanning paths were determined for revealing the influences on grain orientation and magnetostrictive properties. The results showed that elongated columnar grains formed in the building direction due to the epitaxial growth during SLM. For zigzag scanning, grain orientation was parallel to the building direction while tilted by ∼17° for unidirectional scanning. And annular scanning resulted in mixed grain orientations in the alloys. Moreover, Fe81Ga19 alloy with zigzag scanning exhibited 〈100〉 preferred grain orientation. Consequently, the saturated magnetostriction of bulk Fe81Ga19 alloy with zigzag scanning reached ∼77.2 ppm, representing 23.9% and 25.1% increments compared with unidirectional and annular scanning, respectively. The Fe81Ga19 alloy with zigzag scanning also presented an ultimate compressive strength of 448.6 MPa and a degradation rate of 0.09 mm/y, as well as favorable biocompatibility. These results indicated that SLM might be a potential method for manufacturing magnetostrictive bulk Fe-Ga alloys for implant applications

Antibacterial Capability, Physicochemical Properties, and Biocompatibility of nTiO2 Incorporated Polymeric Scaffolds

Postoperative infection is a common risk which brings about failure in bone transplantation. In this study, nano titanium dioxide (nTiO2) was incorporated into Polyetheretherketone/polyglycolicacid (PEEK/PGA) blends to construct antibacterial scaffolds via selective laser sintering. Antibacterial capability was assessed using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The results demonstrated that the scaffolds with nTiO2 presented an effective antibacterial activity, which might be attributed to that nTiO2 would do the mechanical and oxidative damage to bacteria by occurring contact actions and generating reactive oxygen species (ROS), and thus killed bacteria from structure and function. Moreover, nTiO2 could enhance the tensile strength and modulus of scaffolds due to the reinforcing effect and its uniform disperse. And the cell culture experiments showed that nTiO2 stimulated cellular attachment and proliferation. Besides, it also elevated the hydrophily and thermal stability of scaffolds. These results suggested that the polymeric scaffolds incorporated nTiO2 had potential application in bone tissue engineering