Online Monitoring Technology of Metal Powder Bed Fusion Processes: A Review.

Metal powder bed fusion (PBF) is an advanced metal additive manufacturing (AM) technology. Compared with traditional manufacturing techniques, PBF has a higher degree of design freedom. Currently, although PBF has received extensive attention in fields with high-quality standards such as aerospace and automotive, there are some disadvantages, namely poor process quality and insufficient stability, which make it difficult to apply the technology to the manufacture of critical components. In order to surmount these limitations, it is necessary to monitor the process. Online monitoring technology can detect defects in time and provide certain feedback control, so it can greatly enhance the stability of the process, thereby ensuring its quality of the process. This paper presents the current status of online monitoring technology of the metal PBF process from the aspects of powder recoating monitoring, powder bed inspection, building process monitoring, and melt layer detection. Some of the current limitations and future trends are then highlighted. The combination of these four-part monitoring methods can make the quality of PBF parts highly assured. We unanimously believe that this article can be helpful for future research on PBF process monitoring.

Bacterial magnetosomes-based nanocarriers for co-delivery of cancer therapeutics in vitro.

In recent times, co-delivery of therapeutics has emerged as a promising strategy for treating dreadful diseases such as cancer. MATERIALS AND METHODS: In this study, we developed a novel nanocarrier based on bacterial magnetosomes (BMs) that co-loaded with siRNA and doxorubicin (DOX) using polyethyleneimine (PEI) as a cross-linker (BMs/DP/siRNA). The delivery efficiency of siRNA as well as the pH-responsive release of DOX, and synergistic efficacy of these therapeutics in vitro were systematically investigated. RESULTS: The structure of DOX-PEI (DP) conjugates that synthesized via hydrazone bond formation was confirmed by 1H nuclear magnetic resonance (NMR). The in vitro release experiments showed that the DP conjugate (DOX-loading efficiency - 5.77%±0.08%) exhibited the long-term release behavior. Furthermore, the optimal BMs/DP/siRNA particle size of 107.2 nm and the zeta potential value of 31.1±1.0 mV facilitated enhanced cellular internalization efficiency. Moreover, the agarose gel electrophoresis showed that the co-delivery system could protect siRNA from degradation in serum and RNase A. In addition, the cytotoxicity assay showed that BMs/DP/siRNA could achieve an excellent synergistic effect compared to that of siRNA delivery alone. The acridine orange (AO)/ethidium bromide (EB) double staining assay also showed that BMs/DP/siRNA complex could induce cells in a stage of late apoptosis and nanocomplex located in the proximity of the nucleus. CONCLUSION: The combination of gene and chemotherapeutic drug using BMs is highly efficient, and the BMs/DP/siRNA would be a promising therapeutic strategy for the future therapeutics.

Codelivery of paclitaxel and small interfering RNA by octadecyl quaternized carboxymethyl chitosan-modified cationic liposome for combined cancer therapy.

Conventional therapeutic approaches for cancer are limited by cancer cell resistance, which has impeded their clinical applications. The main goal of this work was to investigate the combined antitumor effect of paclitaxel with small interfering RNA modified by cationic liposome formed from modified octadecyl quaternized carboxymethyl chitosan. The cationic liposome was composed of 3ß-[N-(N', N'-dimethylaminoethane)-carbamoyl]-cholesterol, dioleoylphosphatidylethanolamine, and octadecyl quaternized carboxymethyl chitosan. The cationic liposome properties were characterized by Fourier transform infrared spectroscopy, dynamic light scattering and zeta potential measurements, transmission electron microscopy, atomic force microscopy, and gel retardation assay. The cationic liposome exhibited good properties, such as a small particle size, a narrow particle size distribution, a good spherical shape, a smooth surface, and a good binding ability with small interfering RNA. Most importantly, when combined with paclitaxel and small interfering RNA, the composite cationic liposome induced a great enhancement in the antitumor activity, which showed a significantly higher in vitro cytotoxicity in Bcap-37 cells than liposomal paclitaxel or small interfering RNA alone. In conclusion, the results indicate that cationic liposome could be further developed as a codelivery system for chemotherapy drugs and therapeutic small interfering RNAs.

Preparation and in vitro antitumor effects of cytosine arabinoside-loaded genipin-poly-l-glutamic acid-modified bacterial magnetosomes.

To solve the problem of synthesized magnetic nanoparticles in cancer therapy, a new drug delivery system synthesized from bacteria was used to load cytosine arabinoside (Ara-C). Genipin (GP) and poly-l-glutamic acid (PLGA) were selected as dual cross-linkers. The preparation and characterization of Ara-C-loaded GP-PLGA-modified bacterial magnetosomes (BMs) (ABMs-P), as well as their in vitro antitumor effects, were all investigated. Transmission electron micrographs (TEM) and Fourier transform infrared (FTIR) spectroscopy suggested that Ara-C could be bound to the membrane of BMs modified by GP-PLGA. The diameters of the BMs and ABMs-P were 42.0±8.6 nm and 74.9±8.2 nm, respectively. The zeta potential revealed that the nanoparticles were stable. Moreover, this system exhibited optimal drug-loading properties and long-term release behavior. The optimal encapsulation efficiency and drug-loading were 64.1%±6.6% and 38.9%±2.4%, respectively, and ABMs-P could effectively release 90% Ara-C within 40 days, without the release of an initial burst. In addition, in vitro antitumor experiments elucidated that ABMs-P is cytotoxic to HL-60 cell lines, with an inhibition rate of 95%. The method of coupling drugs on BMs using dual cross-linkers is effective, and our results reveal that this new system has potential applications for drug delivery in the future.

Preparation of Chitosan-Based Hemostatic Sponges by Supercritical Fluid Technology.

Using ammonium bicarbonate (AB) particles as a porogen, chitosan (CS)-based hemostatic porous sponges were prepared in supercritical carbon dioxide due to its low viscosity, small surface tension, and good compatibility with organic solvent. Fourier transform infrared spectroscopy (FTIR) spectra demonstrated that the chemical compositions of CS and poly-(methyl vinyl ether-co-maleic anhydride) (PVM/MA) were not altered during the phase inversion process. The morphology and structure of the sponge after the supercritical fluid (SCF) process were observed by scanning electron microscopy (SEM). The resulting hemostatic sponges showed a relatively high porosity (about 80%) with a controllable pore size ranging from 0.1 to 200 µm. The concentration of PVM/MA had no significant influence on the porosity of the sponges. Comparative experiments on biological assessment and hemostatic effect between the resulting sponges and Avitene® were also carried out. With the incorporation of PVM/MA into the CS-based sponges, the water absorption rate of the sponges increased significantly, and the CS-PVM/MA sponges showed a similar water absorption rate (about 90%) to that of Avitene®. The results of the whole blood clotting experiment and animal experiment also demonstrated that the clotting ability of the CS-PVM/MA sponges was similar to that of Avitene®. All these results elementarily verified that the sponges prepared in this study were suitable for hemostasis and demonstrated the feasibility of using SCF-assisted phase inversion technology to produce hemostatic porous sponges.

Preparation of methotrexate-loaded, large, highly-porous PLLA microspheres by a high-voltage electrostatic antisolvent process.

A high-voltage (10 kV) electrostatic antisolvent process was used to prepare methotrexate (MTX)-loaded, large, highly-porous poly-L-lactide (PLLA) microspheres. MTX solution in dimethyl sulfoxide (DMSO) and PLLA solution in dichloromethane (DCM) were homogeneously mixed, and then ammonium bicarbonate (AB) aqueous solution was added. The mixed solution was emulsified by ultrasonication with Pluronic F127 (PF127) as an emulsion stabilizer. The emulsion was electrosprayed by the specific high-voltage apparatus and dropped into a 100 mL of ethanol, which acted as an antisolvent for the solute and extracted DMSO and DCM, causing the co-precipitation of PLLA and MTX, thus forming microspheres with AB aqueous micro-droplets uniformly inlaid. The obtained MTX-PLLA microspheres were subsequently lyophilized to obtain large, highly-porous MTX-PLLA microspheres, which exhibited an identifiable spherical shape and a rough surface furnished with open pores, with a mean particle size of 25.0 µm, mass median aerodynamic diameter of 3.1 ± 0.2 µm, fine-particle fraction of 57.1 ± 1.6 %, and porosity of 81.8 %; furthermore, they offered a sustained release of MTX. X-ray diffraction and Fourier transform-infrared spectra revealed that no crystallinity or alteration of chemical structure occurred during the high-voltage electrostatic antisolvent process, which in this study was proved to have great potential for preparing highly-porous drug-loaded polymer microspheres for use in pulmonary drug delivery.

Generation of porous poly-l-lactide microspheres by emulsion-combined precipitation with a compressed CO2 antisolvent process.

An emulsion-combined precipitation of compressed CO2 antisolvent (PCA) process was used to fabricate porous poly-l-lactide (PLLA) microspheres (PLLA PMs). A 24 full factorial experiment was performed to optimize the operating process and analyze the effect of the factors on the size and morphology of the PLLA PMs. An investigation of their in vitro cytotoxicity was also performed. Taking methotrexate (MTX) as a drug model, MTX-loaded PLLA PMs (MTX-PLLA PMs) were fabricated by the optimized process. Drug loading behaviors and in vitro inhibitory activity against A549 lung cancer cells were also evaluated. The resulting PLLA PMs and MTX-PLLA PMs both exhibited a porous and uneven morphology, with a density less than 0.4 g cm-3, a geometric mean diameter (Dg) of 10-25 µm, an aerodynamic diameter (Da) less than 4.7 µm, a fine particle fraction (FPF) of 58-62%, and a porosity of 79-85%, meeting the requirements for pulmonary drug delivery. Various characterizations revealed that no chemical change occurred in the PLLA, while a slight shift in the molecular structure of MTX was observed after the process, as well as a change in its physical state from crystalline to amorphous. No obvious cytotoxicity was detected for the PLLA PMs, and the MTX-PLLA PMs displayed a sustained release profile with an encapsulation efficiency (EE) of 81.6%. The fluorescent MTX-PLLA PMs also revealed that most of the drug was homogeneously distributed inside the matrix. An in vitro antitumor assay indicated that the MTX-PLLA PMs possessed a sustained and improved inhibitory activity compared with the raw MTX. This study demonstrates that the emulsion-combined PCA process has potential for developing a promising inhalable carrier for pulmonary drug delivery.

Study of Lysozyme-Loaded Poly-L-Lactide (PLLA) Porous Microparticles in a Compressed CO2 Antisolvent Process.

Lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) were successfully prepared by a compressed CO2 antisolvent process in combination with a water-in-oil emulsion process using LSZ as a drug model and ammonium bicarbonate as a porogen. The effects of different drug loads (5.0%, 7.5% and 10.0%) on the surface morphology, particle size, porosity, tapped density and drug release profile of the harvested PMs were investigated. The results show that an increase in the amount of LSZ added led to an increase in drug load (DL) but a decrease in encapsulation efficiency. The resulting LSZ-loaded PLLA PMs (LSZ-PLLA PMs) exhibited a porous and uneven morphology, with a density less than 0.1 g·cm-3, a geometric mean diameter of 16.9-18.8 µm, an aerodynamic diameter less than 2.8 µm, a fine particle fraction (FPF) of 59.2%-66.8%, and a porosity of 78.2%-86.3%. According to the results of differential scanning calorimetry, the addition of LSZ improved the thermal stability of PLLA. The Fourier transform infrared spectroscopy analysis and circular dichroism spectroscopy measurement reveal that no significant changes occurred in the molecular structures of LSZ during the fabrication process, which was further confirmed by the evaluation of enzyme activity of LSZ. It is demonstrated that the emulsion-combined precipitation with compressed antisolvent (PCA) process could be a promising technology to develop biomacromolecular drug-loaded inhalable carrier for pulmonary drug delivery.

[Research progress in co-delivery of gene and chemotherapy drugs with cationic liposome carrier for cancer therapy].

Despite recent advances in conventional therapeutic approaches for cancer, the efficacy of chemotherapy for cancer is limited due to the drug resistance and toxic side effects during treatment. To overcome drug resistance, higher doses of the toxic chemotherapy drugs are frequently administered, thus leading to even severe adverse side effects, which have limited their clinical application. Cationic liposome as a novel non-viral carrier for co-delivery of gene and chemotherapy drugs in cancer gene therapy has already attracted more and more attention in recent years. Most importantly, this combined strategy can generate a significant synergistic effect, which can silence the related gene expression and increase the concentration of the intracellular chemotherapy drugs. This approach allows the use of a much lower dose of the chemotherapy drugs to achieve same therapeutic effect, which may have the potential for overcoming some major limitations of the conventional chemotherapy. In conclusion, co-delivery of gene and chemotherapy drugs with cationic liposome delivery system will play a vital role in the future and especially could be a promising clinical treatment for drug-resistant tumors.

Formation of methotrexate-PLLA-PEG-PLLA composite microspheres by microencapsulation through a process of suspension-enhanced dispersion by supercritical CO2.

BACKGROUND: The aim of this study was to improve the drug loading, encapsulation efficiency, and sustained-release properties of supercritical CO(2)-based drug-loaded polymer carriers via a process of suspension-enhanced dispersion by supercritical CO(2) (SpEDS), which is an advanced version of solution-enhanced dispersion by supercritical CO(2) (SEDS). METHODS: Methotrexate nanoparticles were successfully microencapsulated into poly (L-lactide)-poly(ethylene glycol)-poly(L-lactide) (PLLA-PEG-PLLA) by SpEDS. Methotrexate nanoparticles were first prepared by SEDS, then suspended in PLLA-PEG-PLLA solution, and finally microencapsulated into PLLA-PEG-PLLA via SpEDS, where an "injector" was utilized in the suspension delivery system. RESULTS: After microencapsulation, the composite methotrexate (MTX)-PLLA-PEG-PLLA microspheres obtained had a mean particle size of 545 nm, drug loading of 13.7%, and an encapsulation efficiency of 39.2%. After an initial burst release, with around 65% of the total methotrexate being released in the first 3 hours, the MTX-PLLA-PEG-PLLA microspheres released methotrexate in a sustained manner, with 85% of the total methotrexate dose released within 23 hours and nearly 100% within 144 hours. CONCLUSION: Compared with a parallel study of the coprecipitation process, microencapsulation using SpEDS offered greater potential to manufacture drug-loaded polymer microspheres for a drug delivery system.

Biological evaluation of Fe3O4-poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) magnetic microspheres prepared in supercritical CO2.

The biocompatibility of Fe3O4-poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) magnetic microspheres (Fe3O4-PLLA-PEG-PLLA MMPs) prepared in a process of suspension-enhanced dispersion by supercritical CO2 (SpEDS) was evaluated at various levels: cellular, molecular, and integrated. At the cellular level, the investigations of cytotoxicity and intracellular reactive oxygen species (ROS) generation indicate that the polymer-coated MMPs (2.0 mg/mL) had a higher toxicity than uncoated Fe3O4 nanoparticles, which led to about 20% loss of cell viability and an increase (0.2 fold) in ROS generation; the differences were not statistically significant (p > 0.05). However, an opposite phenomenon was observed in tests of hemolysis, which showed that the MMPs displayed the weakest hemolytic activity, namely only about 6% at the highest concentration (20 mg/mL). This phenomenon reveals that polymer-coated MMPs created less toxicity in red blood cells than uncoated Fe3O4 nanoparticles. At the molecular level, the MMPs were shown to be less genotoxic than Fe3O4 nanoparticles by measuring the micronucleus (MN) frequency in CHO-K1 cells. Furthermore, the mRNA expression of pro-inflammatory cytokines demonstrates that polymer-coated MMPs elicited a less intense secretion of pro-inflammatory cytokines than uncoated Fe3O4 nanoparticles. Acute toxicity tests of MMPs show quite a low toxicity, with an LD50 > 1575.00 mg/kg. The evidence of low toxicity presented in the results indicates that the Fe3O4-PLLA-PEG-PLLA MMPs from the SpEDS process have great potential for use in biomedical applications.