Axial-Circular Magnetic Levitation: A Three-Dimensional Density Measurement and Manipulation Approach.

Magnetic levitation (MagLev) is a promising technology for density-based analysis and manipulation of diamagnetic objects of various physical forms. However, one major drawback is that MagLev can be performed only along the central axis (one-dimensional MagLev), thereby leading to (i) no knowledge about the magnetic field in regions other than the axial region, (ii) inability to handle objects of similar densities, because they are aggregated in the axial region, and (iii) objects that can be manipulated (e.g., separated or assembled) in only one single direction, that is, the axial direction. This work explores a novel approach called "axial-circular MagLev" to expand the operational space from one dimension to three dimensions, enabling substances to be stably levitated in both the axial and circular regions. Without noticeably sacrificing the total density measurement range, the highest sensitivity of the axial-circular MagLev device can be adjusted up to 1.5 × 104 mm/(g/cm3), approximately 115× better than that of the standard MagLev of two square magnets. Being able to fully utilize the operational space gives this approach greater maneuverability, as the three-dimensional self-assembly of controllable ring-shaped structures is demonstrated. Full space utilization extends the applicability of MagLev to bioengineering, pharmaceuticals, and advanced manufacturing.

Freeform inkjet printing of cellular structures with bifurcations.

Organ printing offers a great potential for the freeform layer-by-layer fabrication of three-dimensional (3D) living organs using cellular spheroids or bioinks as building blocks. Vascularization is often identified as a main technological barrier for building 3D organs. As such, the fabrication of 3D biological vascular trees is of great importance for the overall feasibility of the envisioned organ printing approach. In this study, vascular-like cellular structures are fabricated using a liquid support-based inkjet printing approach, which utilizes a calcium chloride solution as both a cross-linking agent and support material. This solution enables the freeform printing of spanning and overhang features by providing a buoyant force. A heuristic approach is implemented to compensate for the axially-varying deformation of horizontal tubular structures to achieve a uniform diameter along their axial directions. Vascular-like structures with both horizontal and vertical bifurcations have been successfully printed from sodium alginate only as well as mouse fibroblast-based alginate bioinks. The post-printing fibroblast cell viability of printed cellular tubes was found to be above 90% even after a 24 h incubation, considering the control effect.

In situ 3D bioprinting with bioconcrete bioink.

In-situ bioprinting is attractive for directly depositing the therapy bioink at the defective organs to repair them, especially for occupations such as soldiers, athletes, and drivers who can be injured in emergency. However, traditional bioink displays obvious limitations in its complex operation environments. Here, we design a bioconcrete bioink with electrosprayed cell-laden microgels as the aggregate and gelatin methacryloyl (GelMA) precursor solution as the cement. Promising printability is guaranteed with a wide temperature range benefiting from robust rheological properties of photocrosslinked microgel aggregate and fluidity of GelMA cement. Composite components simultaneously self-adapt to biocompatibility and different tissue mechanical microenvironment. Strong binding on tissue-hydrogel interface is achieved by hydrogen bonds and friction when the cement is photocrosslinked. This bioink owns good portability and can be easily prepared in urgent accidents. Meanwhile, microgels can be cultured to mini tissues and then mixed as bioink aggregates, indicating our bioconcrete can be functionalized faster than normal bioinks. The cranial defects repair results verify the superiority of this bioink and its potential in clinical settings required in in-situ treatment.

Grafting of 3D Bioprinting to In Vitro Drug Screening: A Review.

The inadequacy of conventional cell-monolayer planar cultures and animal experiments in predicting the toxicity and clinical efficacy of drug candidates has led to an imminent need for in vitro methods with the ability to better represent in vivo conditions and facilitate the systematic investigation of drug candidates. Recent advances in 3D bioprinting have prompted the precise manipulation of cells and biomaterials, rendering it a promising technology for the construction of in vitro tissue/organ models and drug screening devices. This review presents state-of-the-art in vitro methods used for preclinical drug screening and discusses the limitations of these methods. In particular, the significance of constructing 3D in vitro tissue/organ models and microfluidic analysis devices for drug screening is emphasized, and a focus is placed on the grafting process of 3D bioprinting technology to the construction of such models and devices. The in vitro methods for drug screening are generalized into three types: mini-tissue, organ-on-a-chip, and tissue/organ construct. The revolutionary process of the in vitro methods is demonstrated in detail, and relevant studies are listed as examples. Specifically, the tumor model is adopted as a precedent to illustrate the possible grafting of 3D bioprinting to antitumor drug screening.

Glucosamine-grafted methacrylated gelatin hydrogels as potential biomaterials for cartilage repair.

Glucosamine (GlcN) has been widely used to reduce joint pain and osteoarthritis progression, but the efficacy of GlcN remains controversial because of the low GlcN concentration reaching the articular cavity. The aim of this study is to provide an effective approach of GlcN delivery to a target site using photocrosslinkable methacrylated gelatin (GelMA)-based hydrogels, where GlcN could be gradually released during the degradation of the GelMA hydrogel. Herein, GlcN was acrylated as the acryloyl glucosamine (AGA) and covalently grafted to GelMA, and more than 87.7% of 15% (w/v) GelMA hydrogel was grafted with AGA. Moreover, in vitro outgrowth and apoptosis assay of bone marrow stem cells (BMSCs) demonstrated that the GelMA-AGA hydrogels had better biocompatibility, larger cell attachment, and higher cell viability than pure GlcN and AGA materials. Also, 15% (w/v) GelMA-AGA hydrogel was injected into the defect site for in vivo rabbit cartilage repair. Compared with oral administration of pure GlcN and injection of pure GelMA, the repaired cartilages using GelMA-AGA hydrogels had the smoothest surface of the defect site, filling more than 95% defect bulk. The similar content of glycosaminoglycans to the native tissue and the maximum amount of type II collagen was found in the repaired cartilage using GelMA-AGA hydrogels, indicating the outgrowth of hyaline cartilage.

A printing-spray-transfer process for attaching biocompatible and antibacterial coatings to the surfaces of patient-specific silicone stents.

An antibacterial coating with stable antibacterial properties and favorable biocompatibility is recognized as an effective method to prevent bacterial adhesion and biofilm formation on biomedical implant surfaces. In this study, a convenient and low-cost printing-spray-transfer process was proposed that enables reliably attaching antibacterial and biocompatible coatings to patient-specific silicone implant surfaces. A desktop three-dimensional printer was used to print the mold of silicone implant molds according to the characteristics of the diseased areas. Multiwalled carbon nanotubes (MWCNTs) uniformly decorated with silver nanoparticles (AgNPs/CNTs) were synthesized as the antibacterial materials for the spray process. The well-distributed AgNPs/CNT coating was anchored to the silicone surface through an in-mold transfer printing process. Stable adhesion of the coatings was assessed via tape testing and UV-vis spectra. Hardly any AgNPs/CNTs peeled off the substrate, and the adhesion was rated at 4B. Antibacterial activity, Ag release, cell viability and morphology were further assessed, revealing high antibacterial activity and great biocompatibility. The process proposed herein has potential applications for fabricating stable antibacterial coatings on silicone implant surfaces, especially for patient-specific silicone implants such as silicone tracheal stents.

3D printed multi-scale scaffolds with ultrafine fibers for providing excellent biocompatibility.

It is a dilemma that both strength and biocompatibility are requirements for an ideal scaffold in tissue engineering. The normal strategy is mixing or coating another material to improve the biocompatibility. Could we solve this dilemma by simply adjusting the scaffold structure? Here, a novel multi-scale scaffold was designed, in which thick fibers provide sufficient strength for mechanical support while the thin fibers provide a cell-favorable microenvironment to facilitate cell adhesion. Moreover, we developed a promising multi-scale direct writing system (MSDWS) for printing the multi-scale scaffolds. By switching the electrostatic field, scaffolds with fiber diameters from 3 µm to 600 µm were fabricated using one nozzle. Using this method, we proved that PCL scaffolds could also have excellent biocompatibility. BMSCs seeded on the scaffolds readily adhered to the thin fibers and maintained a high proliferation rate. Moreover, the cells bridged across the pores to form a cell sheet and gradually migrated to the thick fibers to cover the entire scaffold. We further combined the scaffolds with hydrogel for 3D cell culture and found that the fibers enhanced the strength and induced cell migration. We believe that the multi-scale scaffolds fabricated by an innovative 3D printing system have great potential for tissue engineering.

Cell-modified bioprinted microspheres for vascular regeneration.

Cell therapy is a promising strategy in which living cells or cellular materials are delivered to treat a variety of diseases. Here, we developed an electrospray bioprinting method to rapidly generate cell-laden hydrogel microspheres, which limit the migration of the captured cells and provide an immunologically privileged microenvironment for cell survival in vivo. Currently, therapeutic angiogenesis aims to induce collateral vessel formation after limb ischemia. However, the clinical application of gene and cell therapy has been impeded by concerns regarding its inefficacy, as well as the associated risk of immunogenicity and oncogenicity. In this study, hydrogel microspheres encapsulating VEGF-overexpressing HEK293T cells showed good safety via subcutaneously injecting into male C57BL/6 mice. In addition, these cell-modified microspheres effectively promoted angiogenesis in a mouse hind-limb ischemia model. Therefore, we demonstrated the great therapeutic potential of this approach to induce angiogenesis in limb ischemia, indicating that bioprinting has a bright future in cell therapy.

Magnetic projection: A novel separation method and its first application on separating mixed plastics.

A novel magnetic separation method, denoted as "magnetic projection", was proposed. The method is based on a simple configuration: a container full of paramagnetic medium is placed beside a permanent magnet. Particles of different densities that submerge in the medium are driven by the magnetic force, moving in accordance with different trajectories, and are finally landed in different collection regions. We applied this method to separate mixed plastics, because most of the extant plastic separation processes can only deal with binary mixture. In the experiment, four common plastics such as polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC), and polymethyl methacrylate (PMMA) were used to simulate the plastic mixture. The experimental results showed that the proposed method can effectively separate the plastic mixture, as the purity of each type of recovered plastics was over 95 wt%. This approach demonstrates its tremendous potential in solid waste management and worth further investigation.

Protocols of 3D Bioprinting of Gelatin Methacryloyl Hydrogel Based Bioinks.

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed from mammal collagen. Thus, the arginine-glycine-aspartic acid (RGD) sequences and target motifs of matrix metalloproteinase (MMP) remain on the molecular chains, which help achieve cell attachment and degradation. Furthermore, formation properties of GelMA are versatile. The methacrylamide groups allow a material to become rapidly crosslinked under light irradiation in the presence of a photoinitiator. Therefore, it makes great sense to establish suitable methods for synthesizing three-dimensional (3D) structures with this promising material. However, its low viscosity restricts GelMA's printability. Presented here are methods to carry out 3D bioprinting of GelMA hydrogels, namely the fabrication of GelMA microspheres, GelMA fibers, GelMA complex structures, and GelMA-based microfluidic chips. The resulting structures and biocompatibility of the materials as well as the printing methods are discussed. It is believed that this protocol may serve as a bridge between previously applied biomaterials and GelMA as well as contribute to the establishment of GelMA-based 3D architectures for biomedical applications.

3D printing of complex GelMA-based scaffolds with nanoclay.

Photo-crosslinkable gelatin methacrylate (GelMA) has become an attractive ink in 3D printing due to its excellent biological performance. However, limited by low viscosity and long cross-linking time, it is still a challenge to directly print GelMA by extrusion-based 3D printing. Here, to balance the printability and biocompatibility, biomaterial ink composed of GelMA and nanoclay was specially designed. Using this ink, complex scaffolds with high shape fidelity can be easily printed based on the thixotropic property of nanoclay. In this study, we tried to answer some basic printing-required questions of this ink, including the printability window, general properties (porosity, mechanical strength, et al), and biocompatibility. We found that the GelMA/Nanoclay ink enabled printing complex 3D scaffolds, such as a bionic ear and a branched vessel. Furthermore, the addition of nanoclay improved the porosity, increased the mechanical strength, reduced the degradation ratio, and maintained a good biocompatibility of the printed scaffolds. Therefore, this method offers an easy way to print complex scaffolds with good shape fidelity and biological performance, and it might open up new potential applications for the customized therapy of tissue defects.

Separation of mixed waste plastics via magnetic levitation.

Separation becomes a bottleneck of dealing with the enormous stream of waste plastics, as most of the extant methods can only handle binary mixtures. In this paper, a novel method that based on magnetic levitation was proposed for separating multiple mixed plastics. Six types of plastics, i.e., polypropylene (PP), acrylonitrile butadiene styrene (ABS), polyamide 6 (PA6), polycarbonate (PC), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE), were used to simulate the mixed waste plastics. The samples were mixed and immersed into paramagnetic medium that placed into a magnetic levitation configuration with two identical NdFeB magnets with like-poles facing each other, and Fourier transform infrared (FTIR) spectroscopy was employed to verify the separation outputs. Unlike any conventional separation methods such as froth flotation and hydrocyclone, this method is not limited by particle sizes, as mixtures of different size fractions reached their respective equilibrium positions in the initial tests. The two-stage separation tests demonstrated that the plastics can be completely separated with purities reached 100%. The method has the potential to be industrialised into an economically-viable and environmentally-friendly mass production procedure, since quantitative correlations are determined, and the paramagnetic medium can be reused indefinitely.

Fabrication of cerebral aneurysm simulator with a desktop 3D printer.

Now, more and more patients are suffering cerebral aneurysm. However, long training time limits the rapid growth of cerebrovascular neurosurgeons. Here we developed a novel cerebral aneurysm simulator which can be better represented the dynamic bulging process of cerebral aneurysm The proposed simulator features the integration of a hollow elastic vascular model, a skull model and a brain model, which can be affordably fabricated at the clinic (Fab@Clinic), under $25.00 each with the help of a low-cost desktop 3D printer. Moreover, the clinical blood flow and pulsation pressure similar to the human can be well simulated, which can be used to train the neurosurgical residents how to clip aneurysms more effectively.

Bone regeneration in 3D printing bioactive ceramic scaffolds with improved tissue/material interface pore architecture in thin-wall bone defect.

Three-dimensional (3D) printing bioactive ceramics have demonstrated alternative approaches to bone tissue repair, but an optimized materials system for improving the recruitment of host osteogenic cells into the bone defect and enhancing targeted repair of the thin-wall craniomaxillofacial defects remains elusive. Herein we systematically evaluated the role of side-wall pore architecture in the direct-ink-writing bioceramic scaffolds on mechanical properties and osteogenic capacity in rabbit calvarial defects. The pure calcium silicate (CSi) and dilute Mg-doped CSi (CSi-Mg6) scaffolds with different layer thickness and macropore sizes were prepared by varying the layer deposition mode from single-layer printing (SLP) to double-layer printing (DLP) and then by undergoing one-, or two-step sintering. It was found that the dilute Mg doping and/or two-step sintering schedule was especially beneficial for improving the compressive strength (∼25-104 MPa) and flexural strength (∼6-18 MPa) of the Ca-silicate scaffolds. The histological analysis for the calvarial bone specimens in vivo revealed that the SLP scaffolds had a high osteoconduction at the early stage (4 weeks) but the DLP scaffolds displayed a higher osteogenic capacity for a long time stage (8-12 weeks). Although the DLP CSi scaffolds displayed somewhat higher osteogenic capacity at 8 and 12 weeks, the DLP CSi-Mg6 scaffolds with excellent fracture resistance also showed appreciable new bone tissue ingrowth. These findings demonstrate that the side-wall pore architecture in 3D printed bioceramic scaffolds is required to optimize for bone repair in calvarial bone defects, and especially the Mg doping wollastontie is promising for 3D printing thin-wall porous scaffolds for craniomaxillofacial bone defect treatment.

Bioactive glass-reinforced bioceramic ink writing scaffolds: sintering, microstructure and mechanical behavior.

The densification of pore struts in bioceramic scaffolds is important for structure stability and strength reliability. An advantage of ceramic ink writing is the precise control over the microstructure and macroarchitecture. However, the use of organic binder in such ink writing process would heavily affect the densification of ceramic struts and sacrifice the mechanical strength of porous scaffolds after sintering. This study presents a low-melt-point bioactive glass (BG)-assisted sintering strategy to overcome the main limitations of direct ink writing (extrusion-based three-dimensional printing) and to produce high-strength calcium silicate (CSi) bioceramic scaffolds. The 1% BG-added CSi (CSi-BG1) scaffolds with rectangular pore morphology sintered at 1080 °C have a very small BG content, readily induce apatite formation, and show appreciable linear shrinkage (∼21%), which is consistent with the composite scaffolds with less or more BG contents sintered at either the same or a higher temperature. These CSi-BG1 scaffolds also possess a high elastic modulus (∼350 MPa) and appreciable compressive strength (∼48 MPa), and show significant strength enhancement after exposure to simulated body fluid-a performance markedly superior to those of pure CSi scaffolds. Particularly, the honeycomb-pore CSi-BG1 scaffolds show markedly higher compressive strength (∼88 MPa) than the scaffolds with rectangular, parallelogram, and Archimedean chord pore structures. It is suggested that this approach can potentially facilitate the translation of ceramic ink writing and BG-assisted sintering of bioceramic scaffold technologies to the in situ bone repair.